[Federal Register: November 26, 2002 (Volume 67, Number 228)]
[Rules and Regulations]
[Page 70811-70828]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr26no02-21]
[[Page 70811]]
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Part II
Department of Transportation
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Federal Aviation Administration
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14 CFR Parts 1, 25, and 97
1-g Stall Speed as the Basis for Compliance With Part 25 of the Federal
Aviation Regulations; Final Rule
[[Page 70812]]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Parts 1, 25, and 97
[Docket No. 28404; Amendment Nos. 1-49, 25-108, 97-1333]
RIN 2120-AD40
1-g Stall Speed as the Basis for Compliance With Part 25 of the
Federal Aviation Regulations
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final rule.
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SUMMARY: This action amends the airworthiness standards for transport
category airplanes to redefine the reference stall speed for transport
category airplanes as a speed not less than the 1-g stall speed instead
of the minimum speed obtained in a stalling maneuver. The FAA is taking
this action to provide for a consistent, repeatable reference stall
speed; ensure consistent and dependable maneuvering margins; provide
for adjusted multiplying factors to maintain approximately the current
requirements in areas where use of the minimum speed in the stalling
maneuver has proven adequate; and harmonize the applicable regulations
with those currently adopted in Change 15 to the European Joint
Aviation Requirements-25 (JAR-25). These changes will provide a higher
level of safety for those cases in which the current methods result in
artificially low operating speeds.
EFFECTIVE DATE: December 26, 2002.
FOR FURTHER INFORMATION CONTACT: Don Stimson, Airplane and Flightcrew
Interface Branch, ANM-111, Transport Airplane Directorate, Aircraft
Certification Service, FAA, 1601 Lind Avenue SW., Renton, WA 98055-
4056; telephone (425) 227-1129; facsimile (425) 227-1320, e-mail
Don.Stimson@faa.gov.
SUPPLEMENTARY INFORMATION:
Availability of Rulemaking Documents
You can get an electronic copy using the Internet by taking the
following steps:
(1) Go to the search function of the Department of Transportation's
electronic Docket Management System (DMS) web page (http://dms.dot.gov/search
).
(2) On the search page type in the last four digits of the Docket
number shown at the beginning of this notice. Click on ``search.''
(3) On the next page, which contains the Docket summary information
for the Docket you selected, click on the document number for the item
you wish to view.
You can also get an electronic copy using the Internet through the
Office of Rulemaking's Web page at http://www.faa.gov/avr/armhome.htm
or the Federal Register's Web page at http://www.access.gpo.gov/su_docs/aces/aces140.html
.
You can also get a copy by submitting a request to the Federal
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence
Avenue SW., Washington, DC, 20591, or by calling (202) 257-9680. Make
sure to identify the amendment number or docket number of this
rulemaking.
Small Business Regulatory Enforcement Fairness Act
The Small Business Regulatory Enforcement Fairness Act (SBREFA) of
1996 requires FAA to comply with small entity requests for information
or advice about compliance with statutes and regulations within its
jurisdiction. Therefore, any small entity that has a question regarding
this document may contact their local FAA official, or the person
listed under FOR FURTHER INFORMATION CONTACT. You can find out more
about SBREFA on the Internet at our site, http://www.faa.gov/avr/arm/sbrefa.htm.
For more information on SBREFA, e-mail us at 9-AWA-
SBREFA@faa.gov.
Background
These amendments are based on notice of proposed rulemaking (NPRM)
Notice No. 95-17, which was published in the Federal Register on
January 18, 1996 (61 FR 1260). In that notice, the FAA proposed
amendments to 14 CFR parts 1, 25, 36, and 97 to redefine the reference
stall speed (VSR) for transport category airplanes as the 1-
g stall speed instead of the minimum speed obtained in the stalling
maneuver. The FAA received nearly 40 comments from 12 different
commenters on the proposals contained in Notice No. 95-17. As a result
of these comments, this final rule differs in some aspects from the
original proposals.
As explained in Notice No. 95-17, the stalling speed
(VS) is defined as the minimum speed demonstrated in the
performance stall maneuver described in Sec. 25.103 of 14 CFR part 25
(part 25). VS has historically served as a reference speed
for determining the minimum operating speeds required under part 25 for
transport category airplanes. Examples of minimum operating speeds that
are based on VS include the takeoff safety speed
(V2), the final takeoff climb speed, and the landing
approach speed. For example, under part 25, V2 must be at
least 1.2 times VS, the final takeoff climb speed must be at
least 1.25 times VS, and the landing approach speed must be
at least 1.3 times VS.
The speed margin, or difference in speed, between VS and
each minimum operating speed provides a safety ``cushion'' to ensure
that normal operating speeds are sufficiently higher than the speed at
which the airplane stalls. Using multiplying factors applied to
VS to provide this speed margin, however, assumes that
VS provides a proper reference stall speed. Since
VS is the minimum speed obtained in the stalling maneuver,
it can be less than the lowest speed at which the airplane's weight is
still supported entirely by aerodynamic lift. If VS is
significantly less than this speed, applying multiplying factors to
VS to determine the minimum operating speeds may not provide
as large a speed margin as intended.
A proper reference stall speed should provide a reasonably
consistent approximation of the wing's maximum usable lift. Maximum
usable lift occurs at the minimum speed for which the lift provided by
the wing is capable of supporting the weight of the airplane. This
speed is known as the 1-g stall speed because the load factor (the
ratio of airplane lift to weight) at this speed is equal to 1.0 ``g''
(where ``g'' is the acceleration caused by the force of gravity) in the
direction perpendicular to the flight path of the airplane. Speeds
lower than the 1-g stall speed during the stalling maneuver represent a
transient flight condition that, if used as a reference for the
deriving minimum operating speeds, may not provide the desired speed
margin to protect against inadvertently stalling the airplane.
For transport category airplanes, the minimum speed obtained in the
stall maneuver of Sec. 25.103 usually occurs near the point in the
maneuver where the airplane spontaneously pitches nose-down or where
the pilot initiates recovery after reaching a deterrent level of
buffet, i.e., a vibration of a magnitude and severity that is a strong
and effective deterrent to further speed reduction. Early generation
transport category airplanes, which had fairly straight wings and non-
advanced airfoils, typically pitched nose-down near the 1-g stall
speed. The minimum speed in the maneuver was easy to note and record,
and served as an adequate approximation of the speed for maximum lift.
For the recent generation of high speed transport category
airplanes with swept wings and highly advanced airfoils, however, the
minimum speed
[[Page 70813]]
obtained in the stalling maneuver can be substantially lower than the
speed for maximum lift. Furthermore, the point at which the airplane
pitches nose down or exhibits a deterrent level of buffet is more
difficult to distinguish and can vary with piloting technique. As a
result, the minimum speed in the stalling maneuver has become an
inappropriate reference for most modern high speed transport category
airplanes for establishing minimum operating speeds since it may: (1)
Be inconsistently determined, and (2) represent a flight condition in
which the load factor perpendicular to the flight path is substantially
less than 1.0 g.
In recent years, advanced technology transport category airplanes
have been developed that employ novel flight control systems. These
flight control systems incorporate unique protection features that are
intended to prevent the airplane from stalling. They also prevent the
airplane from maintaining speeds that are slower than a small
percentage above the 1-g stall speed. Because of their unique design
features, the traditional method of establishing VS as the
minimum speed obtained in the stalling maneuver was inappropriate for
these airplanes. The FAA issued special conditions for these airplanes
to define the reference stall speed as not less than the 1-g stall
speed for the flight requirements contained in subpart B of part 25.
In these special conditions, the multiplying factors used to
determine the minimum operating speeds were reduced in order to
maintain equivalency with acceptable operating speeds used by previous
transport category airplanes. Since the 1-g stall speed is generally
higher than the minimum speed obtained in the stalling maneuver,
retaining the current multiplying factors would have resulted in higher
minimum operating speeds for airplanes using the 1-g stall speed as a
basis for the reference stall speed. However, increasing the minimum
operating speeds could impose costs on operators because payloads might
have to be reduced to comply with the regulations at the higher
operating speeds under some performance-limited conditions. Based on
the service experience of the current fleet of transport category
airplanes, the costs imposed would not be offset by a commensurate
increase in safety.
Several airplane types with conventional flight control systems
have also been certificated using the 1-g stall speed as a lower limit
to the reference stall speed. Because of the potential deficiencies in
using the minimum speed demonstrated in the stalling maneuver, the FAA
has been encouraging applicants to use the 1-g stall speed methodology
in lieu of the minimum speed obtained in the stalling maneuver.
Applicants generally desire to use 1-g stall speeds because the 1-g
stall speeds are less dependent on pilot technique and other subjective
evaluations. Hence, 1-g stall speeds are easier to predict and provide
a higher level of confidence for developing predictions of overall
airplane performance. Again, reduced multiplying factors are applied to
the 1-g stall speeds to obtain minimum operating speeds equivalent to
the speeds that have been found acceptable in operational service.
Using 1-g stall speeds ensures that the airplane's minimum operating
speeds will not be unreasonably low.
Discussion of the Proposals
In Notice No. 95-17, the FAA proposed to define the reference stall
speed in Sec. 25.103 as a speed not less than the 1-g stall speed,
rather than the minimum speed obtained in the stalling maneuver. This
proposal was made to provide a consistent basis for use in all type
design certification requirements for transport category airplanes. The
FAA proposed to introduce the symbol VSR to represent this
speed and to indicate that it is different than the minimum speed
obtained in the stalling maneuver, VS.
In addition, the FAA proposed to reduce the multiplying factors
that are used in combination with the reference stall speed to
determine the minimum operating speeds by approximately 6 percent. This
change would result in minimum operating speeds equivalent to those for
most current transport category airplanes since the 1-g stall speed for
these airplanes is approximately 6 percent higher than the minimum
speed obtained in the stalling maneuver. Demonstrating a minimum
stalling speed more than 6 percent slower than the 1-g stall speed,
which is possible under the current standards, would provide an
unacceptable basis for determining the minimum operating speeds. The
proposed standards would prevent this situation from occurring. In this
respect, the proposed standards would provide a higher level of safety
than the existing standards.
However, the proposed reduced factors would allow lower minimum
operating speeds to be established for those airplanes that have a
minimum speed in the stalling maneuver approximately equal to the 1-g
stall speed. One particular class of airplanes for which this applies
is airplanes equipped with devices that abruptly push the nose down
(e.g., stick pushers) near the angle of attack for maximum lift. These
devices are typically installed on airplanes with unacceptable natural
stalling characteristics. The abrupt nose down push provides an
artificial stall indication and acceptable stall characteristics, and
prevents the airplane from reaching a potentially hazardous natural
aerodynamic stall. Typically, the minimum speed obtained in this
maneuver is approximately equal to the 1-g stall speed.
Traditionally, the existing multiplying factors have been applied
to these airplanes. The proposal to define the reference stall speed as
the 1-g stall speed would generally have no impact for these airplanes,
but reducing the multiplying factors would allow lower minimum
operating speeds to be established. Therefore, this proposal would
allow these airplanes to be operated at speeds and angles of attack
closer to the pusher activation point than has been experienced in
operational service.
The FAA considered this reduction in operating speeds for pusher-
equipped airplanes to be acceptable, provided the pusher reliably
performs its intended function and that unwanted operation is
minimized. The FAA has addressed the majority of these concerns in a
revision to Advisory Circular (AC) 25-7, the ``Flight Test Guide for
Certification of Transport Category Airplanes.'' This revision, AC 25-
7A, dated March 31, 1998, provides criteria for the design and function
of stall indication systems, including arming and disarming, indicating
and warning devices, system reliability and safety, and system
functional requirements. The FAA plans to address other concerns, such
as system design and manufacturing tolerances, and system design
features like filtering and phase advancing, in a future revision to AC
25-7A.
In addition to proposing to define the reference stall speed as a
speed not less than the 1-g stall speed and to reduce the multiplying
factors for establishing the minimum operating speeds, the FAA also
proposed to require applicants to demonstrate adequate maneuvering
capability during the takeoff climb, en route climb, and landing
approach phases of flight. During a banked turn, a portion of the lift
generated by the wing provides a force to help turn the airplane. To
remain at the same altitude, the airplane must produce additional lift.
Therefore, banking the airplane (at a constant speed and altitude)
reduces the stall margin, which is the difference between the lift
required for the maneuver and the maximum lift capability of the wing.
As the bank
[[Page 70814]]
angle increases, the stall margin is reduced proportionately. This bank
angle effect on the stall margin can be determined analytically, and
the multiplying factors applied to VSR to determine the
minimum operating speeds are intended to ensure that an adequate stall
margin is maintained.
In addition to the basic effect of bank angle, however, modern wing
designs also typically exhibit a significant reduction in maximum lift
capability with increasing Mach number. The magnitude of this Mach
number effect depends on the design characteristics of the particular
wing. For wing designs with a large Mach number effect, the maximum
bank angle that can be achieved while retaining an acceptable stall
margin can be significantly reduced. Because the effect of Mach number
can be significant, and because it can also vary greatly for different
wing designs, the multiplying factors applied toVSR are
insufficient to ensure that adequate maneuvering capability exists at
the minimum operating speeds.
To address this issue, the FAA proposed to require a minimum bank
angle capability in a coordinated turn without encountering stall
warning or any other characteristic that might interfere with normal
maneuvering. This requirement would be added to Sec. 25.143 as a new
paragraph (g). The proposed minimum bank angles were derived by adding
a 15 degree allowance for wind gusts and inadvertent overshoot to a
maneuvering capability the FAA considers necessary for the specific
cases identified in the proposed new paragraph. These proposed maneuver
margin requirements would increase the level of safety in maneuvering
flight.
Consistent with the proposed maneuver margin requirements, the FAA
proposed adding Sec. Sec. 25.107(c)(3), 25.107(g)(2), and
25.125(a)(2)(iii) to reference Sec. 25.143(g) in the list of
constraints applicants must consider when selecting the minimum takeoff
safety speed, final takeoff speed, and reference landing speeds,
respectively. The normal all-engines-operating takeoff climb speed
selected by the applicant would also have to provide the minimum bank
angle capability specified in the proposed Sec. 25.143(g).
Section 25.145(a) requires that there be adequate longitudinal
control available to promptly pitch the airplane's nose down from at or
near the stall in order to return to the original trim speed. The
intent of this requirement is to ensure sufficient pitch control for a
prompt recovery if the airplane is inadvertently slowed to the point of
stall. The FAA proposed to change the wording of this requirement to
replace ``VS'' with ``the stall,'' ``Sec. 25.103(b)(1)''
with ``Sec. 25.103(a)(6),'' and ``at any speed'' with ``at any
point.'' These changes would be consistent with the proposed change to
the definition of the reference stall speed and the proposed
reformatting of Sec. 25.103.
Although compliance with Sec. 25.145(a) must be demonstrated both
with power off and with maximum continuous power, there is no intention
to require flight test demonstrations of full stalls at engine powers
above that specified in Sec. 25.201(a)(2). Instead of performing a
full stall at maximum continuous power, compliance will be assessed by
demonstrating sufficient static longitudinal stability and nose down
control margin when the deceleration is ended at least one second past
stall warning during a one knot per second deceleration. The static
longitudinal stability during the maneuver and the nose down control
power remaining at the end of the maneuver must be sufficient to assure
compliance with the requirement.
Section 25.207 requires that a warning of an impending stall must
be provided in order to prevent the pilot from inadvertently stalling
the airplane. The warning must occur at a speed sufficiently higher
than the stall speed to allow the pilot time to take action to avoid a
stall. The speed difference between the stall speed and the speed at
which the stall warning occurs is known as the stall warning margin.
The FAA proposed amending the size of the stall warning margin required
by Sec. 25.207(c) because of the change in definition of the reference
stall speed.
Currently, the stall warning must begin at a speed exceeding
VS by seven knots, or a lesser margin if the stall warning
has enough clarity, duration, distinctiveness, or other similar
properties. Requiring the same seven knot warning margin to be provided
relative to VSR would result in an increase to the minimum
operating speeds. This increase in the minimum operating speeds would
be necessary to meet the maneuvering margin requirements proposed in
Sec. 25.143(g), which are defined relative to the stall warning speed.
However, as discussed previously, requiring an increase to the minimum
operating speeds would impose costs to airplane operators that cannot
be justified by service experience.
On the other hand, if the stall warning margin were reduced to
retain approximately the same stall warning speed, the warning would
occur only one or two knots prior to reaching the 1-g stall speed.
Although reaching the 1-g stall speed is not likely to be a
catastrophic occurrence, the FAA considers such a small stall warning
margin to be unacceptable. The FAA proposed requiring a stall warning
margin of at least 3 knots or 3 percent, whichever is greater, relative
to VSR. The FAA's proposal was made on the basis that this
margin represents a reasonable balance between providing the pilot with
enough warning to avert an impending stall, and providing adequate
maneuvering capability at the minimum operating speeds. This proposal
would retain the existing level of safety.
The FAA proposed to require a larger stall warning margin for
airplanes equipped with devices that abruptly push the nose down at a
selected angle of attack (e.g., stick pushers). Inadvertent operation
of such a device, especially close to the ground, can have more serious
consequences than a comparable situation in which the pilot of an
airplane without the device inadvertently slows to VSR.
Therefore, the FAA proposed adding Sec. 25.207(d) to require the stall
warning, for airplanes equipped with one of these devices, to occur at
least 5 knots or 5 percent, whichever is greater, above the speed at
which the device activates. This proposal was made on the basis of
retaining the existing level of safety for airplanes equipped with such
devices.
The FAA proposed to add a new paragraph, Sec. 25.207(e), to
require that, in a slow-down turn with load factors up to 1.5 g and
deceleration rates up to 3 knots per second, sufficient stall warning
must exist to prevent stalling when recovery is initiated not less than
one second after stall warning occurs. The FAA considered this proposed
requirement necessary to provide adequate stall warning during a
dynamic maneuver, such as a collision avoidance maneuver. In addition,
this new paragraph would provide a quantitative requirement with which
to assess whether ``sufficient margin to prevent inadvertent stalling *
* * in turning flight'' has been provided as required by Sec.
25.207(a). This proposal would increase the level of safety during
maneuvering flight.
The FAA proposed to add a new paragraph, Sec. 25.207(f), to
require that stall warning be provided for abnormal airplane
configurations likely to be used following system failures. This
proposal would add a requirement currently contained in JAR-25 and is
consistent with current transport category airplane designs. There
would be no impact on the existing level of safety.
On modern transport category airplanes, the natural buffet or
vibration
[[Page 70815]]
caused by the airflow separating and reattaching itself to the wing as
the airplane approaches the stall speed is usually not strong enough by
itself to provide an effective stall warning. Therefore, stall warning
on modern transport category airplanes is usually provided through an
artificial means, such as a stick shaker that shakes the pilot's
control column. Production tolerances associated with these systems can
result in variations in the size of the stall warning margin for
different airplanes manufactured under the same approved type design.
The FAA considers the stall warning margins proposed in Sec. Sec.
25.207(c) and (d) to be the minimum acceptable warning margins, and
that these margins should not be reduced by production tolerances
associated with a system added to the airplane to provide an artificial
stall warning. The FAA intends for the proposed stall warning margins
to be available at the most critical tolerance expected in production.
Applicants would be expected to demonstrate compliance with the
proposed stall warning margin either by flight testing with the stall
warning system set to its critical tolerance setting, or by adjusting
flight test data obtained at some other setting.
The tolerances associated with the stall warning system must also
be considered in relation to the proposed minimum maneuvering
requirements of Sec. 25.143(g). As proposed, Sec. 25.143(g) would
require that the airplane be capable of reaching a minimum bank angle
during a coordinated turn without encountering stall warning. Because
the proposed requirements already provide the capability to overshoot
the intended bank angle by 15 degrees, the small differences in the
speed at which the stall warning system operates due to system
tolerances are not as critical. Therefore, the FAA intends for the
minimum bank angles in the proposed Sec. 25.143(g) to apply at the
designed nominal setting of the stall warning system. To ensure that
large production tolerances do not adversely impact the airplane's
maneuvering capability free of stall warning, the bank angle capability
specified in the proposed Sec. 25.143(g) should not be reduced by more
than two degrees with the stall warning system operating at its most
critical tolerance. Applicants would be expected to demonstrate this
capability either by flight test with the system set to its critical
tolerance, or by analytically adjusting flight test data obtained at
some other setting.
To be consistent with the proposed revision of the definition of
the reference stall speed, the FAA proposed to incorporate reduced
multiplying factors throughout part 25, where appropriate, in
requirements that use speeds based on a multiple of the reference stall
speed. The FAA also proposed numerous minor wording and structural
changes to various sections to improve editorial clarity and to
harmonize with the wording and structure proposed for JAR-25. Note that
the proposed change to the term ``1.3 VS0'' in Sec.
25.175(d) reflects not only the change in multiplying factor, but also
corrects a typographical error. (``1.3 VS0'' should have
been ``1.8 VS0.'')
The FAA proposed to add the nomenclature ``final takeoff speed''
and ``reference landing speed'' and the abbreviations
``VFTO'' and ``VREF'' to denote these speeds,
respectively, to part 1 of the FAR. These terms and abbreviations,
which are commonly used in the aviation industry, would be referenced
throughout the proposed amendments to part 25. The reference landing
speed would be defined as the speed of the airplane, in a specified
landing configuration, at the point where it descends through the
landing screen height in the determination of the landing distance for
manual landings. The term ``landing screen height'' refers to the
height of the airplane at the beginning of the defined landing
distance. This height is normally 50 feet above the landing surface
(see Sec. 25.125(a)), but approvals have been granted for steep
approaches that use a landing screen height of 35 feet. The final
takeoff speed would be defined as the speed of the airplane that exists
at the end of the takeoff path in the en route configuration with one
engine inoperative.
The FAA also proposed to add the abbreviations VSR,
VSR0, and VSRI to part 1, and use them in part 25
to denote the reference stall speed corresponding to different airplane
configurations. In addition, the FAA proposed adding the abbreviation
VSW to part 1 to refer to the speed at which the onset of
stall warning occurs.
The FAA proposed to amend Sec. C36.9(e)(1) of Appendix C to part
36 by replacing ``1.3 VS + 10 knots'' with ``VREF
+ 10 knots'' and by removing the words ``or the speed used in
establishing the approved landing distance under the airworthiness
regulations constituting the type certification basis of the airplane,
whichever speed is greatest.'' The words proposed for deletion would no
longer be necessary because VREF would denote the speed used
in establishing the approved landing distance under the airworthiness
regulations constituting the type certification basis of the airplane.
Also, VREF would refer to the speed at the landing screen
height, regardless of whether that speed for a particular airplane is
1.3 VS, 1.23 VSR, or some higher speed.
In the same manner, the FAA proposed to amend Sec. 97.3(b) by
replacing ``1.3 VS0'' with ``VREF.'' As noted
above, VREF would refer to the speed at the landing screen
height used in establishing the approved landing distance under the
airworthiness regulations constituting the type certification basis of
the airplane, regardless of whether that speed for a particular
airplane is 1.3 VS, 1.23 VSR, or some higher
speed.
These proposals were discussed extensively with the European Joint
Aviation Authorities (JAA) with the intent of harmonizing the
certification requirements related to stall speed for transport
category airplanes. The Joint Aviation Requirements (JAR) 25 prescribes
the airworthiness standards for transport category airplanes that are
accepted by the aviation regulatory authorities of a number of European
states. The JAA introduced an equivalent proposal to the FAA's NPRM 95-
17, called Notice of Proposed Amendment (NPA) 25B-215, to amend JAR-25
accordingly. The JAA's final 1-g stall requirements, which are
equivalent to those adopted by the FAA in this rulemaking, were adopted
by the JAA as part of Change 15 to JAR-25, dated October 1, 2000.
Discussion of the Comments
The FAA received nearly 40 comments from 12 different commenters on
the proposals contained in Notice No. 95-17. The commenters include
airplane pilots, manufacturers, operators, and the associations
representing them, foreign airworthiness authorities, an organization
specializing in flight testing, and private citizens. In general, the
proposal to redefine the reference stall speed for transport category
airplanes as the 1-g stall speed instead of the minimum speed obtained
in a stalling maneuver was supported, although there were comments
critical of specific details, and some commenters were supportive only
if the current minimum speed method would be retained as an option that
would be available for the certification of small transport category
airplanes.
Those commenters who recommend retaining the minimum stall speed
methodology for small transport category airplanes--small airplane
manufacturers and the association representing them--believe that the
proposed changes introduce additional cost and complexity into
applicants'
[[Page 70816]]
type certification programs with no increase in safety for this class
of airplanes.
One manufacturer of small transport category airplanes notes that
when 1-g stall speeds were determined for one of their airplanes, the
resulting operating speeds were virtually the same as those determined
using the current requirements. This commenter also states that
variation in piloting technique remains an issue even if the stall
speeds are defined as a 1-g condition, and a more expensive flight test
data system is needed to determine where the 1-g stall break occurs.
The commenter points out that straight (i.e., non-swept) winged
airplanes, for which the discussion in Notice No. 95-17 implied the
current minimum speed method is adequate, will continue to be designed
and produced in the future. On airplanes with swept wings, due to
different stiffness characteristics between large and small airplanes,
which result in different responses to aerodynamic influences, the
minimum speed in the stalling maneuver is not difficult to obtain on
small transport category airplanes. The commenter concludes that the
current methods should be retained for airplanes weighing less than
75,000 pounds because of the costs involved in changing to the 1-g
stall speed methodology for no apparent increase in safety. (100,000
pounds is suggested as an appropriate cutoff by another commenter.)
The FAA disagrees that the proposed rule changes significantly
increases cost and does not increase safety. Cost data supplied by one
commenter substantially overstates the incremental cost of the test
instrumentation and other items needed to support a 1-g stall speed
evaluation. This commenter allocates the entire cost of a new data
collection system, including purchase, installation, and calibration,
to the proposed rule change, stating that this new system would be
needed to determine the ``g-break'' denoting the 1-g stall speed.
The only additional instrumentation the FAA considers necessary to
determine the 1-g stall speed instead of the minimum speed in the
stalling maneuver would be accelerometers capable of resolving the load
factor normal to the flight path. At the minimum, one accelerometer
aligned along the expected 1-g stall pitch angle may provide acceptable
data. Determining the point at which the 1-g stall condition is reached
is most readily accomplished by a continuous calculation of the load
factor-corrected lift coefficient and noting the point at which this
parameter is first a maximum. Experience to date with applicants
voluntarily complying with the proposed requirements has not
highlighted any significant difficulties in determining the 1-g stall
speed using typically existing data recording equipment. These
applicants have included manufacturers of both large and small
transport category airplanes.
The FAA is not surprised that for one of the commenter's airplane
types, the current requirements and the 1-g stall proposal yielded
virtually the same minimum operating speeds. As noted in Notice No. 95-
17 and repeated in the background discussion above, the proposed change
to the multiplying factors that are applied to the reference stall
speed to obtain the minimum operating speeds was intentionally chosen
to yield equivalent operating speeds, on average, for current transport
category airplanes. However, the proposed standards would prevent the
reference stall speed from being more than six percent slower than the
1-g stall speed, which the current standards do not prohibit. In this
respect, the proposed standards would provide a higher level of safety
than the existing standards by ensuring that unreasonably low minimum
operating speeds will not be obtained.
The FAA agrees that the use of a 1-g stall speed may not entirely
remove the effect of pilot technique from being a factor during the
flight tests to determine the reference stall speed. However, the use
of a 1-g stall speed would significantly mitigate this effect.
Subjective assessments of airplane behavior for identifying the stalled
condition (using the criteria specified in Sec. 25.201(d)) would no
longer be used to determine the reference stall speed. (These criteria
will continue to be used, however, for evaluating the airplane handling
characteristics during the stalling maneuver.) Test pilot techniques
that take advantage of these subjective assessments and allow
unreasonably low load factors, and hence unreasonably low stall speeds,
to be achieved would no longer be permitted.
In addition, it is usually much easier to measure airspeed
accurately at the 1-g stall condition than at the minimum speed reached
in the stalling maneuver. Based on the experience gained from the many
type certification programs that have already used the 1-g stall speed
methodology, the FAA has determined that this methodology provides a
more consistent, repeatable reference stall speed than the existing
method.
One commenter notes that the International Civil Aviation
Organization's (ICAO) Airworthiness Technical Manual (Document 9051,
1987) uses the abbreviation VS1g to denote the 1-g stall
speed, which is the reference speed for determining the minimum
operating speeds for transport category airplanes with a certified
takeoff mass of over 5,700 kg. The commenter suggests that the FAA
could further international standardization by adopting ICAO's
VS1g abbreviation to denote the reference stall speed as a
part of the rulemaking to redefine the reference stall speed as a 1-g
stall speed.
The FAA actively promotes international standardization and has
been working closely with the regulatory authorities of Europe and
Canada during this rulemaking. The FAA considered using the
abbreviation VS1g to denote the reference stall speed;
however, the reference stall speed may not always be equal to the 1-g
stall speed. It is only required to be no less than the 1-g stall
speed. Other design constraints may dictate using a reference stall
speed that is higher than the 1-g stall speed. Since the reference
stall speed may be different than the 1-g stall speed, the abbreviation
VSR was proposed and has been adopted in Sec. 1.2 to denote
the reference stall speed. This abbreviation has also been adopted by
the JAA of Europe and is expected to be adopted by the Canadian
regulatory authority. There were no comments on the other proposed
abbreviations nor on the proposed definitions for final takeoff speed
and reference landing speed. Therefore, these abbreviations and
definitions are adopted as proposed.
One commenter questions the reason for the new wording in Sec.
25.103(a)(1) to describe the option of idle or zero thrust. The
commenter does not see the new wording as an improvement in clarity.
The current rule states that zero thrust must be used in determining
the stalling speed, except that idle thrust may be used when it does
not appreciably affect the stalling speed. Stated in this manner, the
rule permits the use of zero thrust when idle thrust causes an increase
in the stalling speed. On some turboprop airplanes, where flight idle
thrust may be negative, a lower stall speed may be demonstrated using
zero thrust than would occur with idle thrust.
The FAA considers such a loss of stall speed margin in a normal
flight condition to be unacceptable. In Notice No. 95-17, the FAA
proposed a change such that the reference stall speed must be
determined with idle thrust, except in cases where that thrust level
causes an appreciable decrease in the stall speed. For such cases, not
more than zero thrust must be used. There were no
[[Page 70817]]
comments regarding the substance of the proposed change; therefore,
this section is adopted as proposed.
One commenter notes that while the proposal to the reference stall
speed in terms of a 1-g stall speed would reduce the amount of scatter
in the flight test data used to determine the stall speed, a
significant amount of scatter would remain. To further limit the amount
of experimental error inherent in the data analysis process, the
commenter suggests defining the reference stall speed in terms of the
maximum normal force coefficient instead of the maximum lift
coefficient. Using the normal force coefficient would yield slightly
higher reference stall speeds, which could penalize an airplane's load
carrying capability due to the resulting increase in minimum takeoff
and landing speeds, but certification costs might be reduced because
the data reduction process would be simplified.
The FAA agrees that defining the reference stall speed in terms of
the maximum normal force coefficient instead of the maximum lift
coefficient may further reduce flight test data scatter and simplify
data acquisition and analysis. However, these slight benefits are
outweighed by the potentially significant economic penalties associated
with the resulting higher reference stall speed. Many recent airplane
types have been certified using 1-g stall criteria similar to those
contained in Notice No. 95-17 and this experience does not indicate any
significant problems in data quality or in the acquisition and analysis
process. Data scatter using the proposed 1-g stall criteria is
inconsequential compared to the data uncertainty inherent in the
current stall speed definition. Therefore, the commenter's suggested
change is not being adopted. However, the FAA would find it acceptable
if an applicant proposed using the higher reference stall speeds
derived from the maximum normal coefficient in order to simplify the
data acquisition and analysis process. The proposed amendment need not
be changed to allow this option.
A commenter suggests that it is technically more accurate in Sec.
25.103(c) to refer to the lift coefficient in the definition of
VCLMAX as the load factor-corrected lift coefficient. The
commenter also considers the proposed definition of VCLMAX
to be ambiguous and lacking in guidance material that would provide
clarification. Other commenters made various editorial and formatting
suggestions to further improve the clarity of Sec. 25.103. The FAA
agrees with these suggestions and has modified the proposal
accordingly. In addition, the FAA proposes to revise Advisory Circular
(AC) 25-7A, ``Flight Test Guide for Certification of Transport Category
Airplanes,'' to add clarifying guidance material. A notice of proposed
advisory circular revisions was published in the Federal Register on
November 21, 2002.
Detailed comments were received from one commenter regarding the
effect of the proposed rules on airplanes equipped with devices that
abruptly push the nose down (e.g., stick pushers) to define the point
of stall. As noted in Notice No. 95-17, this proposal would allow
airplanes equipped with such devices that have a trigger point set
close to or before CLMAX to achieve lower minimum operating
speeds than under the existing requirements, and hence, operate at
speeds and angles-of-attack closer to the device activation point than
has been experienced in operational service. The FAA considered this
aspect of the proposal to be acceptable provided the device performs
its intended function and unwanted operation is minimized.
The commenter points out that ensuring operation when desired and
preventing unwanted operation are contradictory goals that result in
design tradeoffs. Regardless of the design choice, however, allowing
operation closer to the device activation point increases both the
probability of reaching the activation point, where the device may fail
to operate, and the probability of unwanted operation. Considering
these aspects, the commenter contends that the proposed standards would
reduce the level of safety relative to the current standards.
The commenter suggests adding the stipulation, for airplanes
equipped with a device that abruptly pushes the nose down at a selected
angle-of-attack, that VSR must not be less than the greater
of 2 knots or 2 percent above the speed at which the device activates.
The commenter further suggests that this additional requirement need
not apply to turbopropeller powered airplanes that demonstrate a
significant reduction in stall speed in the one-engine-inoperative
power-on condition. The commenter points out that this additional
requirement is very similar in scope and intent to the Notice No. 95-17
proposed requirements for stall warning, where, in addition to the
requirement applying to all transport category airplanes that stall
warning be 3 knots or 3 percent above VSR, the stall warning
for airplanes equipped with devices that abruptly push the nose down at
a selected angle-of-attack would be 5 knots or 5 percent above the
speed at which the device operates. The commenter believes that the
proposed stall warning requirements represent an acknowledgment that
the class of airplanes cannot be treated the same as conventionally
stalling airplanes with respect to minimum operating speeds and
associated margins.
The FAA agrees with the commenter's analysis and fundamental
principle that in terms of the protection from stall provided by such a
device, the characteristics resulting from its operation, and its
reliability and safety, there are significant differences from a
conventionally stalling airplane. Also, the difference between the 1-g
stall speed and the minimum speed obtained in the stalling maneuver for
this class of airplanes is closer to 0 to 3 percent, rather than the 6
percent average for conventionally stalling airplanes upon which the
reduction in operating speed factors was based. Permitting a reduction
in the operating speeds for this class of airplanes could potentially
result in a reduction in safety that is not justified by existing
operational experience.
The commenter's suggested additional constraint on VSR
represents a reasonable means to retain approximately equivalent safety
without penalizing airplanes for which the device trigger point is at
an angle-of-attack well beyond CLMAX. Therefore, Sec.
25.103(d) is revised accordingly to require, for airplanes equipped
with a device that abruptly pushes the nose down at a selected angle-
of-attack, that VSR not be less than 2 percent or 2 knots,
whichever is greater, above the speed at which the device operates. The
suggested exception for turbopropeller powered airplanes that
demonstrate a significant reduction in stall speed in the one-engine-
inoperative power-on condition is not included, however, because the
applicable minimum operating speeds already allow for a significant
effect of power on stall speeds.
The effect of this provision is to increase the minimum operating
speeds, relative to the Notice No. 95-17 proposals, for airplanes
equipped with devices that abruptly push the nose down at a selected
angle-of-attack, but only if the device activates at a speed higher
than VCLMAX (at a load factor of one) minus 2 knots or 2
percent. This requirement for a supplementary speed margin, in
combination with criteria added to AC 25-7A, dated March 31, 1998, for
system arming and disarming, indicating and warning devices, system
reliability and safety, and system functional requirements are intended
to provide an equivalent level of safety to the requirements existing
prior to the adoption of this amendment. Other
[[Page 70818]]
considerations, such as the effect of system design and manufacturing
tolerances, and system design features like filtering and phase
advancing are also relevant, and should be considered when showing
compliance with the applicable requirements. The FAA is currently
trying to harmonize its policy in these areas with those of Transport
Canada and the JAA, and intends to add guidance in these areas in a
future revision to AC 25-7A.
The FAA received several comments regarding the proposed addition
of specific maneuvering requirements as a new Sec. 25.143(g). One
commenter suggests that the FAA should perform a rigorous study before
including a specific gust margin in airplane maneuvering requirements.
The commenter points out that the same atmospheric gust would have
different effects at different airspeeds, and that using the same gust
margin throughout causes the proposed after takeoff maneuvering
requirement at V2 speed to be unduly restrictive. Similarly,
another commenter states that the need for a 15-degree overshoot
capability should first be justified by the FAA. This commenter
suggests that a 5-degree overshoot, as specified as an objective for
accomplishing steep turns in the ``Airplane Transport Pilot and Type
Rating Practical Test Standards,'' would be more reasonable.
Several commenters claim that the proposed maneuvering
requirements, particularly the one associated with the final takeoff
speed (VFTO), are excessive and would be difficult to meet
without increasing the operating speeds. One commenter notes that for
an airplane equipped with a stick pusher that activates near
CLMAX, due to design tolerances for the stick pusher and
stall warning systems, V2 and VFTO would most
likely be set by the proposed maneuvering requirements rather than the
1.13 and 1.18 factors applied to VSR, respectively. Another
commenter notes that the maneuvering requirement associated with
VFTO relates to a one-engine-inoperative condition of short
duration, after which the airplane is accelerated to the en route climb
speed. This commenter suggests that a maneuvering bank angle of 30
degrees, the same as specified for the takeoff safety speed
(V2) one-engine-inoperative condition, would be more
appropriate for this condition.
This commenter further states that for many existing large
transport category airplanes, an early onset of natural stall warning
results in a larger stall warning margin than the minimum margin
required by the regulations. At VFTO, these airplanes would
have a maneuvering capability to stall warning of less than the
proposed 40 degrees of bank, possibly as low as 27 degrees. Requiring
40 degrees of bank capability would necessitate an increase in
VFTO, which could affect the net takeoff flight path used
for clearance of distant obstacles. Either a different departure path
may be necessary in the event of an engine failure, or takeoff weight
may have to be reduced. The commenter considers the existing rule to be
adequate, and the potential penalties associated with the FAA's
proposal to be unjustifiable.
This commenter also questions whether the proposed 40 degree bank
angle requirement at VFTO was based on a 25 degree bank
angle limit used by many current flight guidance systems. If so, this
commenter considers such reasoning to be flawed in that not all flight
guidance systems use 25 degrees as their bank angle limit. In some
cases, flight guidance systems are limited to a 15 degree bank angle at
the final takeoff speed.
As a final comment on this section, this commenter suggests that if
the FAA believes that increased bank angles are appropriate for the en
route flight paths, which are of longer time duration, this need should
be addressed separately from the takeoff flight path requirements.
However, the commenter does not consider it necessary to do so as this
commenter is unaware of any associated safety issues.
The FAA disagrees that the maneuvering requirements specified in
the proposed Sec. 25.143(g) are excessive, including the proposed 40
degree bank angle requirement at VFTO. These maneuvering
requirements are comparable to the maneuvering capability implied by
the current regulations assuming the stall warning margin is near the
regulatory minimum. Safety records and operating practices indicate
that low speed maneuvering capability is a genuine concern. Some
airports necessitate close-in maneuvering on a regular or contingency
basis. Accidents and incidents have occurred due to windshear, icing,
and high-lift device anomalies. The ability to tolerate such
operational conditions can depend on the maneuvering capability at the
designated minimum operating speeds.
The proposed maneuvering requirements consist of the minimum bank
angle capability the FAA deems adequate for the specified regimes of
flight combined with a further 15 degrees of bank angle to provide a
safety margin for various operational factors. These operational
factors include both potential environmental conditions (e.g.,
turbulence, wind gusts) and an allowance for piloting imprecision
(e.g., inadvertent overshoots). Because this safety margin does not
represent either a specific gust margin or expected piloting precision
alone, the FAA does not consider it necessary to either perform a
rigorous study of the effect of atmospheric gusts nor to restrict the
size of the margin to a piloting test standards objective as suggested
by the commenters. The allowance and magnitude of the proposed bank
angle margin is also consistent with typical industry practice.
The maneuvering requirement at V2 speed with one engine
inoperative is derived from the 15 degree bank angle allowed under
Sec. 121.189(f) after takeoff plus the specified 15 degree safety
margin. At the higher speed of VFTO, after the airplane has
transitioned to the en route configuration and is farther along in the
flight path, it is reasonable to require additional maneuvering
capability appropriate to that phase of flight. The FAA considers an
additional 10 degrees of maneuvering capability to be a reasonable
expectation for a minimum capability after transitioning to the en
route configuration and accelerating to the final takeoff climb speed.
This same level of maneuvering capability exists on most transport
category airplanes currently in service, and the FAA has determined
that there is not a compelling reason to set a lower minimum standard.
The FAA considers this same maneuvering capability (25 degrees of bank
plus a 15 degree safety margin) to also be appropriate for the normal
all-engines-operating takeoff case as well as for the landing approach.
For those airplane types for which the proposed maneuvering
requirements would lead to an increase in VFTO, any
resulting penalty is expected to be small. An increase in
VFTO would only cause a penalty (in terms of a reduced
payload capability) when the takeoff weight is restricted due to an
obstacle that must be cleared in the final takeoff climb segment and
cannot be avoided by turning or using an alternative flight path
procedure (e.g., retracting the flaps at the maximum level-off height
or extending the second segment to the takeoff thrust time limit).
Recent FAA acceptance of proposals to increase the time limit for using
takeoff thrust from five minutes to ten minutes should further reduce
the potential for economic penalties resulting from an increase in
VFTO.
In addition to receiving comments on the minimum bank angles
proposed for the new Sec. 25.143(g), the FAA received comments on the
footnotes accompanying the table of conditions to
[[Page 70819]]
be demonstrated. A commenter notes that because the trigger point of an
artificial stall warning device may vary with thrust or power setting,
the proposed wording of footnote 1 may not cover the most critical
condition for determining the airplane's maneuver margin. This
commenter suggests adding the phrase ``or any greater thrust or power
if more critical'' to the thrust/ power setting references in footnotes
1 and 3 to the table in Sec. 25.143(g).
Although the FAA agrees with the intent of this comment, the FAA
believes that the comment may stem from a misinterpretation of the
proposed requirement. The condition specified in the proposed footnote
1 to Sec. 25.143(g) represents the highest thrust or power setting for
the applicable conditions of weight, altitude, and temperature. If
system design features or other relevant characteristics result in any
condition of weight, altitude, or temperature being more critical than
another, compliance with this requirement must be demonstrated for the
most critical condition of weight, altitude, and temperature. This
point is addressed further in guidance material being proposed for
inclusion into AC 25-7A (a notice of proposed advisory circular
revisions will be published in the Federal Register shortly after
publication of this final rule).
The commenter further suggests simplifying the text of footnote 3
by replacing the FAA proposed text with, ``The critical thrust or power
for all engines operating should be that which in the event of an
engine failure would result in the minimum climb gradient specified in
Sec. 25.121, or any greater thrust or power if more critical.''
Although the FAA agrees with the intent of simplifying this footnote,
the wording proposed in Notice No. 95-17 is needed to address all-
engines-operating climb procedures, such as those used for noise
abatement, that may use a thrust or power setting less than that used
during the takeoff. Therefore, the FAA does not concur with the
commenter's suggestion.
Section 25.143(g) is adopted as proposed.
One commenter suggests that the Notice No. 95-17 proposal to
replace ``VS'' with ``the stall'' in Sec. 25.145(a) is
misleading and inaccurate relative to the Notice No. 95-17 supporting
discussion. The commenter believes that changing ``VS'' to
``the stall'' is unsatisfactory for two reasons: (1) ``The stall'' is a
vague terminology that might generally be defined by Sec. 25.201(d),
but without defining the configuration (i.e., flaps, center-of-gravity
position, power, etc.); and (2) The Notice No. 95-17 preamble
discussion states that the demonstration should only have to be
conducted down to stall warning speed plus one second, which is less
demanding than the proposed new Sec. 25.145(a). Therefore, the
commenter suggests adding the words ``In a deceleration'' at the
beginning of Sec. 25.145(a) and replacing the proposed reference to
``the stall'' with ``one second after stall warning.'' Guidance could
then be provided in AC 25-7 to clarify that there must be sufficient
longitudinal control in this maneuver to provide confidence that
pushout from an actual stall could still be accomplished.
The FAA does not intend for the change in the reference stall speed
to alter the basic requirement of Sec. 25.145(a), namely that the
capability exists on transport category airplanes, at the specified
configurations and power settings, to pitch the nose down from any
point in the stalling maneuver and regain the trim speed. The
commenter's suggested change would reduce the stringency of the
regulatory requirement, while depending on non-regulatory guidance
material to provided assurances that equivalent capability is retained.
Because the FAA cannot rely on non-regulatory material to establish
a capability required of the airplane, the FAA has not adopted the
commenter's suggested change. However, to improve clarity, the words
``the stall,'' proposed in Notice No. 95-17, have been replaced by
``stall identification (as defined in Sec. 25.201(d))'' in the adopted
Sec. 25.145(a). In addition, techniques to show compliance with this
requirement without performing a stall at maximum continuous power/
thrust were included in the recent issuance of AC 25-7A. Consistent
with the preamble discussion of Notice No. 95-17, compliance at maximum
continuous power may be assessed by demonstrating sufficient static
longitudinal stability and nose down control margin when the
deceleration is ended at least one second past stall warning during a
one knot per second deceleration. The static longitudinal stability
during the maneuver and the nose down control power remaining at the
end of the maneuver must be sufficient to assure compliance with the
requirement.
Two comments were received regarding the flight test demonstrations
to show compliance with Sec. 25.177. Both comments were relative to
the safety aspects of conducting full rudder sideslips at low
airspeeds, as required by the current rule, although both commenters
also noted that this situation may be exacerbated by the lower speeds
that can result from the proposed change. The proposed changes were not
intended to result in overall lower speeds. Because these comments
raise issues with not only speed, but also rudder deflection, they are
considered beyond the scope of the Notice No. 95-17 proposals, and
Sec. 25.177 has been adopted as proposed. These comments will be
retained for consideration of potential future rulemaking to address
the concerns expressed by the commenters.
There were many comments on the proposed changes to the stall
warning requirements of Sec. 25.207. One commenter requests explicit
criteria to address whether or not a stick shaker is required to
provide stall warning, or if a visual or aural warning is sufficient.
This same commenter also asked whether production tolerances affecting
the stall warning margin will be addressed in AC 25-7.
The issue of what constitutes an acceptable artificial stall
warning is beyond the scope of this rulemaking. However, as stated in
the current Sec. 25.207(b) (and unchanged by this rulemaking), ``a
visual stall warning device that requires the attention of the crew
within the cockpit is not acceptable by itself.'' The FAA is
considering future rulemaking to further address the issue of what
constitutes an acceptable stall warning. Regarding stall warning
tolerances, the FAA has proposed the inclusion of material addressing
stall warning system tolerances into a proposed revision to AC 25-7A (a
notice of proposed advisory circular revisions will be published in the
Federal Register shortly after publication of this final rule). This
material is consistent with the FAA positions expressed in the preamble
of Notice No. 95-17.
Several commenters took issue with the proposed three percent or
three knots stall warning margin of Sec. 25.207(c). One commenter
believes that the proposal represents an unjustified increase in the
severity of this requirement relative to the current rules. This
commenter notes that a requirement for stall warning to begin one
percent above the 1-g stall speed would be equivalent to the current
requirement of a seven percent margin from the minimum speed obtained
in the stalling maneuver. As a compromise, this commenter suggests a
two percent or two knot stall warning margin relative to the redefined
reference stall speed. Another commenter has a concern over possible
difficulties in showing compliance with the proposed arbitrary
numerical margin for airplanes with a gradual loss of lift
[[Page 70820]]
as the angle-of-attack for maximum lift is exceeded. Both of these
commenters request that any increase in the severity of this
requirement: (1) Be tempered such that inappropriate design changes are
not imposed for small shortfalls in meeting the strict numerical
criteria; and (2) be taken into account in the Aviation Rulemaking
Advisory Committee (ARAC) discussions of stall warning margin when
operating in icing conditions.
Another commenter has concerns that the change in stall warning
margin requirements will reduce the margin that is currently required
and therefore would not retain the existing level of safety. This
commenter believes that the proposed margin would not represent a
reasonable balance between providing the pilot with enough warning to
avert an impending stall and providing adequate maneuvering capability
at the minimum operating speeds. This commenter suggests retaining the
current seven knot stall warning margin from the reference stall speed,
even though the reference stall speed would be redefined as the 1-g
stall speed, in order to retain the existing level of safety.
Another commenter considers the proposed Sec. 25.207(c) to
represent an unjustified increase in the currently required minimum
stall warning margin that would inhibit use of part of the airplane
flight envelope within which the airplane is controllable without risk
of structural damage. The commenter remarks that in windshear avoidance
maneuvers, the likelihood of escape is maximized by flying at the
minimum controllable airspeed. The commenter also disagrees with the
statement made in Notice No. 95-17 that a speed lower than the 1-g
stall speed represents a transient flight condition. The commenter
notes that in steady climbing flight, the lift force needed to sustain
steady flight is less than the airplane weight, and for larger climb
angles, steady flight is sustainable at speeds lower than the 1-g stall
speed. This commenter suggests revising the proposed Sec. 25.207(c) to
require the stall warning to begin at the greater of: (1) A speed
higher than either one knot or one percent higher than the reference
stall speed; or (2) seven knots or seven percent higher than the speed
at the occurrence of a stall (as defined in Sec. 25.201(d)).
Other comments were received on the proposed Sec. 25.207(c)
relative to the engine thrust or power setting associated with the
proposed three percent or three knot stall warning margin. Two
commenters support removing the reference to ``engines idling and
throttles closed'' so that the same stall warning margin would apply to
all power and thrust settings. One commenter suggests that to be
consistent with the proposed Sec. 25.103(a)(1) it is unnecessary to
refer to throttles. This commenter also questions why the proposal
states that ``Sec. 25.103(a)(5) does not apply'' when defining the
reference stall speed to be used in connection with this requirement.
In combination with adopting the 1-g stall speed as the appropriate
benchmark for the low speed end of an airplane's limit flight envelope,
the FAA considers a warning three knots or three percent prior to
reaching this speed to be the minimum margin needed to prevent the crew
from inadvertently slowing beyond this speed. A categorical statement
regarding the severity of this requirement relative to the current
requirement cannot be made since the effect of the change in the
reference stall speed will vary with airplane type (and with the high
lift device configuration on a given type). It would, however, be
inappropriate to couple the existing seven percent margin requirement
relative to the minimum speed reached in the stalling maneuver with the
redefined reference stall speed as one commenter suggests.
The FAA does not consider the proposed stall warning margin to
unduly restrict access to useable parts of the airplane flight
envelope. Relative to windshear escape, the dynamic nature of windshear
warrants, if anything, a larger speed margin to the stalled condition.
Using current windshear escape procedures, frequent and irregular
penetrations of the stall warning margin are more likely to occur. This
type of trained maneuver was not envisioned when the current stall
warning requirements were promulgated. Regarding the comment that for
climbing flight the lift force will be less than the airplane's weight,
this condition is irrelevant for establishing the reference stall speed
or defining a reasonable stall warning margin. The FAA has determined
that the intent of the proposal is sufficiently clear in this respect.
The FAA agrees that the stall warning margin for other than idle
thrust or power settings should be addressed. The FAA did not intend to
restrict consideration of the adequacy of the stall warning margin to
only the idle thrust or power condition. The general requirement for a
stall warning with sufficient margin to prevent inadvertently stalling
prescribed by Sec. 25.207(a) applies to all normal configurations and
flight conditions. The three knot or three percent warning margin
reference in the proposed Sec. 25.207(c) would specifically quantify
this requirement for the conditions under which VSR is
determined. At other conditions, the FAA would have expected an
equivalent margin to that prescribed by Sec. 25.207(c). However, there
is an inherent difficulty in either specifying an appropriate warning
margin or determining an equivalent warning margin to that specified in
the proposed Sec. 25.207(c) for conditions other than idle thrust or
power, straight flight, and the center-of-gravity position defined in
the proposed Sec. 25.103(a)(5), because VSR is undefined for those
other conditions.
In response to the comments, and to clarify the situation regarding
the acceptable stall warning margin for conditions other than those
under which VSR is defined, the FAA has revised the proposed Sec.
25.207(c) by specifying that stall warning must begin at least five
knots or five percent, whichever is greater, prior to the speed at
which the airplane is considered stalled (as defined in Sec.
25.201(d)). This is also the stall warning margin required by JAR-25
prior to the adoption of Change 15, and is considered to neither
increase nor decrease the current level of safety. By referencing the
speed at which the stall is identified for determining the adequacy of
the stall warning margin, and not limiting this requirement to specific
conditions of thrust or power, bank angle, or center-of-gravity
position, the adopted rule requires that the five knot or five percent
margin must be available at all thrust/power settings, bank angles, and
center-of-gravity positions.
The FAA expects this stall warning margin to be demonstrated for
the conditions of bank angle, power, and center-of-gravity position
prescribed for the stall demonstration tests by Sec. 25.201(a). If,
however, the stall warning margin may be affected by the system design
(e.g., a stall warning or stall identification system that modifies the
stall warning or stall identification system as a function of thrust,
bank angle, angle-of-attack rate, etc.), compliance with the adopted
Sec. 25.207(c) should be demonstrated at the most critical conditions
in terms of stall warning margin.
The proposed three knot or three percent (whichever is greater)
stall warning margin requirement relative to VSR is retained
in Sec. 25.207(d) as an additional criterion applicable to that
specific flight condition. The reference to throttles has been removed,
as has the statement that the proposed Sec. 25.103(a)(5) should not
apply when
[[Page 70821]]
defining the reference stall speed to be used in connection with this
requirement. In response to the commenter's question, the reference to
Sec. 25.103(a)(5) had been proposed because the proposed definition of
the reference stall speed would have required that the center-of-
gravity position for determining the reference stall speed would be
that which results in the highest value of the reference stall speed.
Since the center-of-gravity position at which the proposed three knot
or three percent stall warning requirement would apply was not
specified, it presumably would apply to all center-of-gravity
positions. Therefore, without the proposed statement, a literal
interpretation of the proposed requirement would have required the
stall warning speed at any center-of-gravity position to be three knots
or three percent above the stall speed evaluated at the most adverse
center-of-gravity position. This was not the intention. Any evaluation
of the effect of center-of-gravity position on the stall warning margin
should be based on the same center-of-gravity position for both the
stall speed and the stall warning speed.
The proposed wording, along with additional explanatory material
that would have been proposed for addition to AC 25-7A, was intended to
clarify that for center-of-gravity positions other than that specified
in the proposed Sec. 25.103(a)(5), the same center-of-gravity position
should be used for both the stall speed and the stall warning speed.
However, due to the potential for confusion over the proposed wording,
and because the explicit stall warning speed margin prescribed by the
proposed Sec. 25.207(c) only applies to the conditions under which VSR
is determined, the proposed wording regarding center-of-gravity
position has been removed. Instead, the center-of-gravity position
specified in Sec. 25.103(b)(5) (re-numbered from the proposed Sec.
25.103(a)(5)) has been included in the list of conditions for which the
specific three knot or three percent stall warning margin of the
adopted Sec. 25.207(d) applies. For other center-of-gravity positions,
the acceptable stall warning margin is now addressed in the adopted
Sec. 25.207(c).
Because of the differences between naturally stalling airplanes and
those that employ a device to abruptly push the nose down at a selected
angle of attack to identify the stall, the FAA proposed that the stall
warning margin for airplanes that employ these devices would be
required to be five knots or five percent prior to the speed at which
the device activates. The application of Sec. 25.207(d), as adopted,
in combination with the adopted new requirement of Sec. 25.103(d) will
ensure that there must be a 5 knot or 5 percent stall warning margin
relative to VSR for these airplanes. Therefore, the proposed Sec.
25.207(d) is removed.
The stall speed margins required by the adopted Sec. Sec.
25.207(c) and (d) must be available in terms of calibrated airspeed.
Normally, test demonstrations at the conditions specified in Sec.
25.201 (Stall demonstration) will be sufficient to show compliance with
these requirements. However, if the stall warning margin for a
particular airplane type varies significantly with power or thrust,
center-of-gravity position, bank angle, of some other characteristic,
additional test conditions may be necessary.
As with other part 25 requirements, shortfalls in demonstrating
compliance with the literal terms of the stall warning margin
requirements would necessitate either a design change, an exemption
(per Sec. 11.25), or features that would provide equivalent safety
using an alternate means of compliance (per Sec. 21.21(b)(1)). Other
rulemaking projects in which the stall warning margin is an issue
(e.g., discussions of flight in icing conditions by the ARAC) will be
considered on their own merits.
Several commenters object to the accelerated stall warning margin
requirement proposed as a new Sec. 25.207(e). Some of the commenters
claim that, in some cases, attempts to demonstrate compliance with this
proposed requirement during flight testing resulted in maneuvers that
the commenters consider inappropriate for a transport category
airplane. These commenters provide several examples of the maneuvers
they described as inappropriate. Other commenters note that the phrase
``to prevent stalling'' needs further clarification. One commenter
questions the lack of a bank angle stipulation in the proposed
requirement and provided an analysis indicating that bank angles of
about 45 degrees have the greatest effect on aerodynamics. This
commenter also claims that a prescribed load factor and deceleration
rate are not simultaneously achievable at CLMAX. The
commenter suggests revising the proposed Sec. 25.207(e) to specify 30
degree banked turns (for consistency with the turning flight stall
characteristics demonstration required by Sec. 25.201(a)) with
accelerated rates of entry into the stall, up to the greater of 1.5g
load factor and 3 knots per second speed reduction. This suggestion was
made by other commenters as well.
The FAA concurs that detailed guidance material may be helpful to
ensure an appropriate and consistent demonstration of compliance with
the proposed accelerated stall warning requirement. This material will
be presented in the proposed revisions to AC 25-7A, which will be
published in the Federal Register shortly after publication of this
final rule.
The purpose of the proposed requirement is to ensure that adequate
stall warning exists to prevent an inadvertent stall under the most
demanding conditions likely to occur in normal flight. The proposed
conditions of 1.5g and a three knots per second entry rate (i.e.,
airspeed deceleration rate) correspond to the steep turn maneuver
prescribed in part 121, Appendices E and F for pilot initial and
proficiency training, respectively, plus some margin for error (three
degrees more bank and a decreasing airspeed). The elevated load factor
will emphasize any adverse stall characteristics, such as wing drop or
asymmetric wing flow breakdown, while also investigating Mach and
potential aeroelastic effects on available lift. The proposed three
knots per second deceleration rate is intended to result in a
reasonable penetration beyond the onset of stall warning. A 30-degree
banked turn maneuver, as proposed by several of the commenters,
produces a load factor of only 1.15g, which the FAA does not consider
high enough to evaluate the effect of elevated load factor on the
capability to prevent an inadvertent stall.
As noted by one of the commenters, the bank angle used during the
maneuver to demonstrate compliance with this proposed requirement may
affect the airplane's stall characteristics. However, this aspect is
considered secondary to the primary effect of an elevated load factor
on the stall warning margin. For this reason, Sec. 25.207(e) is
revised from the version published in the NPRM to prescribe a load
factor rather than a bank angle. An acceptable means of producing this
load factor would be a 48-degree banked turn in level flight.
As adopted, Sec. 25.207(e) requires an airspeed deceleration rate
of greater than two knots per second instead of rates up to three knots
per second. This change clarifies the intent of achieving a reasonable
deceleration rate rather than one specific value, and will result in
the intended penetration beyond the onset of stall warning. The FAA
anticipates that with typical test techniques, requiring a deceleration
rate of greater than two knots per second will result in deceleration
rates close to
[[Page 70822]]
three knots per second. The power and trim conditions are now specified
in the rule in order to ensure consistent application of this
requirement.
To clarify the meaning of the phrase ``to prevent stalling,'' the
parenthetical expression, ``(as defined in Sec. 25.201(d)),'' has been
added in the adopted Sec. 25.207(e). Therefore, any of the acceptable
indications of a stall applicable to stall demonstration testing is
also considered an indication that the airplane has stalled during the
accelerated stall warning demonstration. If any of these indications of
a stall occur during the accelerated stall warning demonstration,
compliance with Sec. 25.207(e) will not have been demonstrated.
Two commenters offered comments relative to subpart C (Structure)
of part 25. One of these commenters suggests that the interpretation of
the stall speed used in subpart C be undertaken urgently as part of the
Harmonization Work Program. The other commenter suggests that either
subpart C should be reworked to reflect the introduction of
VSR or Sec. 25.103 should introduce definitions of
VS0 and VS1 in terms of VSR.
These comments regarding subpart C of part 25 are beyond the scope
of this rulemaking, which is confined to the definition of the stall
speed used for airplane performance determination and handling
characteristics. This amendment does not affect the stall speeds used
in subpart C for structural analysis.
Further consideration by the FAA regarding the proposed revisions
to Sec. Sec. 1.1 (Definition of reference landing speed) and 97.3(b)
(Definition of aircraft approach category) has resulted in minor
changes in the adopted rule relative to the original proposals. The
proposed definition of reference landing speed had used the term
``landing screen height'' to identify the point in the approach at
which the reference landing speed is determined. Although this term is
defined in the preamble discussion of the rule proposal, it is not
defined or used elsewhere within the regulations. The landing distance
requirements of Sec. 25.125 specify this height as the 50 foot height,
and the adopted definition of reference landing speed in Sec. 1.1 has
been changed to be consistent with this requirement.
The preamble discussion references approvals of steep approach
operations that use a ``landing screen height'' of less than the 50
foot height prescribed by the Sec. 25.125 landing distance
requirements. These types of approvals are not the norm, however, and
should be processed as equivalent safety findings, special conditions,
or exemptions, whichever is appropriate for the specific case.
In addition to replacing ``landing screen height'' with ``50 foot
height,'' the words ``for manual landings'' have been removed from the
definition of ``reference landing speed'' since the applicable Sec.
25.125 landing distance requirements make no such distinction. Approval
of automatic landing systems, including consideration of associated
landing speeds and distances, is addressed in FAA ACs 20-57A, 120-28D,
and 120-29.
Further review of the proposed change to Sec. 97.3(b) indicated a
potential for confusion with respect to its application to aircraft
certificated using VS, the minimum speed in the stalling
maneuver, rather than VSR. There is some concern that the
proposed replacement of 1.3 VS0 with VREF may
introduce terminology which is not well understood by all potential
users of the airspace system, and that information provided in some
Airplane Flight Manuals may not be consistent with the new terminology.
Therefore, as adopted, Sec. 97.3(b) will continue to reference 1.3
VS0 for use in those cases where VREF is not
specified.
One adverse comment was received on the proposed change to Sec.
C36.9(e)(1) of Appendix C to part 36. The commenter notes that the
proposed change could result in increasing the speed used to show
compliance with the approach noise requirements for those cases where
VREF is greater than 1.23 VSR0 (or 1.3
VS for airplanes certificated under the existing stall speed
requirements). The commenter states that this increased speed can
result in higher certificated noise levels. The commenter objects to
the increased stringency and believes it to be an inappropriate
consequence of changing to the 1-g stall speed reference. The commenter
also notes the importance of arriving at harmonized criteria with the
JAA for the approach speed used for noise certifications.
The FAA disagrees with the commenter. The proposed amendment would
have replaced the words ``1.3 VS + 10 knots'' with
``VREF + 10 knots'' and removed the words ``or the speed
used in establishing the approved landing distance under the
airworthiness regulations constituting the type certification basis of
the airplane, whichever speed is greatest.'' The effect of the proposal
would have been to require a steady approach speed of VREF +
10 knots over the approach noise measuring point during the flight test
measurement of approach noise levels.
The reference to 1.3 VS in the current Sec. C36.9(e)(1)
had been derived from the Sec. 25.125 landing requirements, i.e., 1.3
VS was interpreted to be the speed at the 50 foot height.
Further away from the runway, at the point at which the approach noise
is measured (6,562 feet from the runway threshold), the airplane is
likely to be at a somewhat higher speed. Higher speeds are used during
the approach to provide greater stall and controllability margins,
especially in the presence of winds and gusts, with the additional
speed being bled off by the time the airplane is at the 50 foot height.
As stated in the preamble to the amendment that added part 36 to the
FAR, ``The intent of this proposal was to require an airspeed that is
highly typical of normal approach airspeeds, so that a realistic
approach speed is generated. The speed 1.3 VS + 10 knots is
such an airspeed and is therefore specified * * *'' The ten knot
increment applied to 1.3 VS represents the typical approach
speed at the approach noise measuring point.
In a later amendment to part 36 (Amendment 36-5), the FAA
recognized that, for various reasons, a speed higher than 1.3
VS may be used in establishing the landing distance under
Sec. 25.125. Amendment 36-5 added the words ``or the speed used in
establishing the approved landing distance under the airworthiness
regulations constituting the type certification basis of the airplane,
whichever speed is greatest'' to the ``1.3 VS + 10 knots''
speed requirement over the approach noise measuring point.
The additional 10 knot speed increment added to 1.3 VS
was not added to ``the speed used in establishing the approved landing
distance under the airworthiness regulations constituting the type
certification basis of the airplane.'' The FAA has since determined,
however, that the ten knot speed increment should be applied to the
speed used to determine the landing distance under Sec. 25.125,
regardless of whether that speed is 1.3 VS or some higher
speed. The flightcrew does not know whether the approach speed provided
in their manuals is based on 1.3 VS or some higher speed and
will use the same procedures and speed increments in either case.
The FAA's proposal would have set the speed over the approach noise
measuring point at VREF +10 knots. Since VREF is
the speed used to determine the landing distance, a consistent speed
increment would be applied to the speed applicable to the 50 foot
height, regardless of whether VREF is determined by stall
speed,
[[Page 70823]]
controllability requirements, or some other parameter.
Subsequent to the publication of Notice 95-17, Working Group 1
(WG1) of the International Civil Aviation Organization (ICAO) Committee
on Aviation Environmental Protection (CAEP) recommended to the ICAO
CAEP that the noise certification approach reference speed contained in
Volume I of Annex 16 to the Convention on International Civil Aviation
(the ICAO International Standard and Recommended Practice for Aircraft
Noise Certification) be changed to VREF + 10 knots. The WG1
was established by the CAEP to provide technical guidance regarding
revisions to Annex 16, Volume 1. The United States is a member of both
the ICAO CAEP and WG1. The WG1 did not view the adoption of
VREF + 10 knots as having a significant effect on
stringency. At its 5th meeting, which was held in January 2001, the
ICAO CAEP accepted the WG1 recommendation regarding adoption of
VREF + 10 knots. This recommendation was subsequently
included in Amendment 7 of Annex 16, Volume 1, which was adopted by the
ICAO Council on June 29, 2001.
As a member of the ICAO Council, CAEP and WG1, the FAA supported
the conclusion to use VREF + 10 knots. The commenter has
provided no support for the expressed effect on stringency. The concern
expressed by the commenter regarding the use of harmonized criteria
between the FAA and JAA would be eliminated by FAA adoption of the
Annex 16, Amendment 7 requirement, considering that Annex 16 is the
basis for the JAA noise certification requirements. Accordingly, the
FAA adopted the Annex 16, Amendment 7 requirement as part of Amendment
24 to part 36, which was published in the Federal Register on July 8,
2002 (67 FR 45193).
Other than the changes noted above, the proposed changes to part 25
are adopted as proposed in Notice No. 95-17.
Paperwork Reduction Act
In accordance with the Paperwork Reduction Act of 1995 (44 U.S.C.
3507(d)), there are no requirements for information collection
associated with this amendment.
International Compatibility
In keeping with U.S. obligations under the Convention on
International Civil Aviation, it is FAA policy to comply with
International Civil Aviation Organization (ICAO) Standards and
Recommended Practices to the maximum extent practical. The FAA has
reviewed the corresponding ICAO Standards and Recommended Practices and
the Joint Aviation Authorities regulations, where they exist, and has
identified no differences in these amendments and the foreign
regulations.
Regulatory Evaluation Summary
Economic Evaluation, Regulatory Flexibility Determination,
International Trade Impact Assessment, and Unfunded Mandates Assessment
Changes to Federal regulations must undergo several economic
analyses. First, Executive Order 12866 directs each Federal agency to
propose or adopt a regulation only if the agency makes a reasoned
determination that the benefits of the intended regulation justify its
costs. Second, the Regulatory Flexibility Act of 1980 requires agencies
to analyze the economic impact of regulatory changes on small entities.
Third, the Trade Agreements Act (19 U.S.C. section 2531-2533) prohibits
agencies from setting standards that create unnecessary obstacles to
the foreign commerce of the United States. In developing U.S.
standards, this Trade Act requires agencies to consider international
standards. Where appropriate, agencies are directed to use those
international standards as the basis of U.S. standards. And fourth, the
Unfunded Mandates Reform Act of 1995 requires agencies to prepare a
written assessment of the costs, benefits and other effects of proposed
or final rules. This requirement applies only to rules that include a
Federal mandate on State, local or tribal governments or the private
sector, likely to result in a total expenditure of $100 million or more
in any one year (adjusted for inflation.)
In conducting these analyses, the FAA has determined that this
final rule: (1) Has benefits that do justify its costs; (2) is not a
``significant rulemaking'' either as defined in the Executive Order or
in DOT's Regulatory Policies and Procedures; (3) will not have a
significant impact on a substantial number of small entities; (4) will
lessen restraints on international trade; and (5) will not contain a
significant intergovernmental or private sector mandate.
These analyses, available in the docket, are summarized as follows.
Economic Evaluation
The Benefits Estimate
This rule supports the existing level of safety because type
certification for part 25 airplanes based on 1-g criteria is common
practice, the FAA having accepted 1-g stall criteria since the mid-80s
for most part 25 type certifications, in many cases through the Issue
Paper process. This rule establishes the codification of this practice,
and thus adds the safety benefit of preventing deviation from this
practice. The FAA has not attempted to quantify this benefit.
The FAA also expects this rule will result in added benefits in the
form of cost savings to those affected manufacturers that carry out
type certification to both FAR and JAR requirements. Historically, U.S.
manufacturers that certificate part 25 airplanes to both FAA and JAA
requirements using 1-g stall speed criteria have done so by working out
separate arrangements with both authorities. The FAA expects compliance
with a single harmonized FAA/JAA regulatory standard will be simpler
and more direct than compliance through separate arrangements, and that
cost savings will result. The FAA has not attempted to quantify this
benefit.
The Estimate of Costs and Its Evolution
As noted, the FAA has accepted 1-g stall speed criteria for most
part 25 type certification projects since the mid-1980s. The FAA
expects this rule will not change the substance of accepted
certification practices. Thus, no more than minimal additional
certification costs will be associated with this new rule.
However, as certification practices and aviation technology have
evolved since the mid-1980s, the costs of certification at 1-g have
changed. As these costs have changed, manufacturers' estimates of
comparative certification costs have changed; and FAA's estimates of
the costs associated with this rule have changed.
This final rule evaluation was begun in 1999. It completes the
regulatory evaluation process that began with research pursuant to a
1996 NPRM. Comments to the docket in response to that NPRM were
received in 1996. Pursuant to this final rule evaluation, providers of
previously received information were asked to review, clarify and
update their information as necessary. Their clarifications and
updates, together with the previous research and analysis are the basis
for the conclusions developed in this final rule evaluation.
While the costs provided in the 1996 comments were much higher than
those of the 1996 NPRM, the 1999 clarifications and updates brought the
costs developed in this final rule evaluation more into line with those
of the NPRM. Cost estimates for typical
[[Page 70824]]
type certification projects that use 1-g stall speed as the reference
datum have evolved as follow:
[sbull] In 1996, the NPRM concluded that the costs of 1-g
compliance differed depending upon the size of the airplane certified.
In then-current dollars, the NPRM estimated compliance costs of
$195,000 for a type certification for large part 25 airplanes. For
small part 25 airplanes, the NPRM estimate included a one-time cost of
$70,000 for each manufacturer and subsequent type certification costs
of $250,000. This final rule evaluation concludes that neither
regulatory nor practical distinctions between small and large airplanes
allow the unambiguous grouping by size category needed to support the
level of economic analysis characteristic of final rules.
[sbull] In 1996, comments received in response to the NPRM gave
additional compliance costs per type certification in then-current
dollars that ranged from $331,412 for instrumentation costs plus
$35,029 for testing and analysis, to an undifferentiated $1,000,000 per
type certification project.
[sbull] For this final rule evaluation, the baseline for cost
comparisons is the estimate of the current cost of type certification
using minimum stall speed as the reference datum for a typical part 25
airplane. Building on the NPRM, the comments to the Docket, and the
clarifications and updates, this final rule evaluation estimates
typical additional compliance costs of about $130,000 for a type
certification program conducted at 1-g for a part 25 airplane,
expressed in 1999 dollars.
[sbull] During the time the FAA has been accepting certification at
1-g, additional costs of instrumentation have become small to
negligible. Falling instrumentation costs and rising instrumentation
capability have resulted in acceptable test data being achieved by
adding as little additional instrumentation as one accelerometer to the
test equipment required for certification at minimum stall speed. (The
estimated uninstalled cost of an accelerometer appropriate to this use
is the minimal cost of $500 to $2,000, in 1999 dollars. Further,
accelerometer and gyroscopic components already present in the inertial
navigation systems incorporated on modern transport category airplanes
are the fundamental starting point for instrumentation sufficient to
measure a 1-g stall speed.)
In summary, for a typical part 25 airplane, the current industry
practice of type certification using 1-g stall as the reference datum
adds a minor cost ($130,000) for flight-testing and analysis to the
costs of the baseline alternative of type certification using minimum
speed stall. This practice also is expected to add very minor or no
cost for additional instrumentation beyond that required for the type
certification baseline.
This final evaluation notes the possibility, also raised in the
NPRM and in the 1999 clarifications and updates, that codification of
this ongoing practice, and its consequent extension to all U.S.
manufacturers and to all part 25 airplanes they will certificate in the
future, could have an adverse impact on marketing efforts by
manufacturers. (In general, this rule reduces the multiplying factors
used to convert reference speed to minimum operational speeds by about
6 percent. When the reduced multiplying factors are applied to the 1-g
stall speed, which is generally about 6 percent higher than minimum
speed stall, the resulting minimum operating speeds generally will
result in the same values produced by using minimum stall speed as the
reference datum. However, variation is possible. This possible
variation is at the heart of assertions of marketing impact. No such
impact is considered in this evaluation, for the reasons that follow:
--The possible differences in operational speeds between type
certification using 1-g stall speed and type certification using
minimum stall speed are in the low single digits when expressed as
speeds
--The very large number of possible combinations of airplane types,
operational conditions, operators' services and airport characteristics
forestalls practical quantitative consideration of the possible small
consequences noted above
--Any operational consequence of certification at 1-g already results
from ongoing industry practice and cannot also be considered to result
from this rule
--The possible differences in operational speeds between type
certification using 1-g stall speed and type certification using
minimum stall speed are in the low single digits when expressed as
speeds
Benefits/Costs Comparison
The FAA finds that this rule improves the codification of current
industry practices that have evolved over a period of about 15 years.
These practices already result in the benefits of the current level of
safety. With one exception, this rule will add little or nothing to
these benefits. The exception is the elimination of the possibility
that a future part 25 airplane might not be certificated based on 1-g
stall speed criteria. Removing this possibility ensures that the
benefits being received cannot be reduced, thus diminishing the current
level of safety. The agency has not attempted to quantify either this
added benefit or the benefits already being received.
Another additional benefit of improved codification is that type
certification to both FAR and JAR requirements will be simpler, more
direct and consequently less costly. The agency has not attempted to
quantify this harmonization benefit.
Because it is an improvement of the codification of voluntary
industry practices, the FAA concludes that this rule will add little or
no cost to the industry. The agency estimates that affected
manufacturers already voluntarily incur costs of about $130,000 (in
1999 dollars) for each type certification project they base on 1-g
stall speed criteria, beyond the costs they would incur in type
certification based on minimum stall speed criteria.
The FAA concludes that while this final rule will add little or
nothing to the safety benefits and the certification costs that already
result from voluntary industry practices, it does add safety and
harmonization benefits. Thus, the FAA believes this rule is cost
effective.
Regulatory Flexibility Determination
The Regulatory Flexibility Act of 1980 (RFA) establishes ``as a
principle of regulatory issuance that agencies shall endeavor,
consistent with the objective of the rule and of applicable statutes,
to fit regulatory and informational requirements to the scale of the
business, organizations, and governmental jurisdictions subject to
regulation.'' To achieve that principle, the Act requires agencies to
solicit and consider flexible regulatory proposals and to explain the
rationale for their actions. The Act covers a wide-range of small
entities, including small businesses, not-for-profit organizations and
small governmental jurisdictions.
Agencies must perform a review to determine whether a proposed or
final rule will have a significant economic impact on a substantial
number of small entities. If the determination is that it will, the
agency must prepare a regulatory flexibility analysis as described in
the Act.
However, if an agency determines that a proposed or final rule is
not expected to have a significant economic impact on a substantial
number of small entities, section 605(b) of the 1980 act provides that
the head of the agency may so certify and a regulatory flexibility
analysis is not required. The certification must include a statement
providing the factual basis for this determination, and the reasoning
should
[[Page 70825]]
be clear. For aircraft manufacturers, a small entity is one with 1,500
or fewer employees.
Evaluation of this final rule in terms of this standard shows that
no current manufacturer of transport category airplanes is a small
manufacturer. Although the future entry of a small manufacturer into
the business of manufacturing transport category airplanes is possible,
such an unusual single entrant could not be construed to equate to a
``substantial number.''
Finally, no regulatory flexibility analysis is required for this
rule because it adds little or nothing to the costs that otherwise
would be required for type certification of a transport category
airplane by a manufacturer of any size. Therefore the impact of this
rule would not be significant whether it fell on a large or on a small
manufacturer.
In light of these arguments, the FAA certifies that the rule change
will not have a significant economic impact on a substantial number of
small entities, and a regulatory flexibility analysis is not required.
International Trade Impact Analysis
The Trade Agreement Act of 1979 prohibits Federal agencies from
engaging in any standards or related activities that create unnecessary
obstacles to the foreign commerce of the United States. Legitimate
domestic objectives, such as safety, are not considered unnecessary
obstacles. The statute also requires consideration of international
standards and where appropriate, that they be the basis for U.S.
standards.
Because this rule is a part of a harmonization process that will
result in a single FAA/JAA regulatory standard, it reduces a barrier to
international trade. Thus, in accordance with the above statute, the
FAA has assessed the potential effect of this final rule and has
determined that it will support the Act.
Unfunded Mandates Reform Act
The Unfunded Mandates Reform Act of 1995 (the Act), enacted as
Public Law 104-4 on March 22, 1995 is intended, among other things, to
curb the practice of imposing unfunded Federal mandates on State,
local, and tribal governments.
Title II of the Act requires each Federal agency to prepare a
written statement assessing the effects of any Federal mandate in a
proposed or final agency rule that may result in a $100 million or more
expenditure (adjusted annually for inflation) in any one year by State,
local, and tribal governments, in the aggregate, or by the private
sector; such a mandate is deemed to be a ``significant regulatory
action.'' This final rule does not contain such a mandate. Therefore,
the assessment requirements of Title II of the Unfunded Mandates Reform
Act of 1995 do not apply.
Executive Order 3132, Federalism
The FAA has analyzed this final rule under the principles and
criteria of Executive Order 13132, Federalism. We determined that this
action will not have a substantial direct effect on the State, or the
relationship between the national Government and the States, or on the
distribution of power and responsibilities among the various levels of
government. Therefore, we determined that this final rule does not have
federalism implications.
Regulations Affecting Interstate Aviation in Alaska
Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat.
3213) requires the Administrator, when modifying regulations in Title
14 of the CFR in a manner affecting interstate aviation in Alaska, to
consider the extent to which Alaska is not served by transportation
modes other than aviation, and to establish such regulatory
distinctions as he or she considers appropriate. Because this rule
would apply to the certification of future designs of transport
category airplanes and their subsequent operation, it could, if
adopted, affect interstate aviation in Alaska.
Environmental Analysis
FAA Order 1050.1D defines FAA actions that may be categorically
excluded from presentation of a National Environmental Policy Act
(NEPA) environmental impact statement. In accordance with FAA Order
1050.1D, appendix 4, paragraph 4(j), this rulemaking action qualifies
for a categorical exclusion.
Energy Impact
The energy impact of this amendment has been assessed in accordance
with the Energy Policy and Conservation Act (EPCA) Public Law 94-163,
as amended (42 U.S.C. 6362) and FAA Order 1053.1. It has been
determined that the final rule is not a major regulatory action under
the provisions of the EPCA.
List of Subjects
14 CFR Part 1
Air transportation.
14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
14 CFR Part 97
Air traffic control, Airports, Navigation (air), Weather.
The Amendments
In consideration of the foregoing, the Federal Aviation
Administration (FAA) amends Chapter I of Title 14 Code of Federal
Regulations (CFR) parts 1, 25, and 97 as follows:
PART 1--DEFINITIONS AND ABBREVIATIONS
1. The authority citation for part 1 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
2. Section 1.1 is amended by adding new definitions in alphabetical
order to read as follows:
Sec. 1.1 General definitions.
* * * * *
Final takeoff speed means the speed of the airplane that exists at
the end of the takeoff path in the en route configuration with one
engine inoperative.
* * * * *
Reference landing speed means the speed of the airplane, in a
specified landing configuration, at the point where it descends through
the 50 foot height in the determination of the landing distance.
* * * * *
3. Section 1.2 is amended by adding new abbreviations in
alphabetical order to read as follows:
Sec. 1.2 Abbreviations and symbols.
* * * * *
VFTO means final takeoff speed.
* * * * *
VREF means reference landing speed.
* * * * *
VSR means reference stall speed.
VSR0 means reference stall speed in the landing
configuration.
VSR1 means reference stall speed in a specific
configuration.
VSW means speed at which onset of natural or artificial
stall warning occurs.
* * * * *
PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
4. The authority citation for part 25 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
5. Section 25.103 is revised to read as follows:
Sec. 25.103 Stall speed.
(a) The reference stall speed, VSR, is a calibrated
airspeed defined by the
[[Page 70826]]
applicant. VSR may not be less than a 1-g stall speed.
VSR is expressed as:
[GRAPHIC] [TIFF OMITTED] TR26NO02.001
where:
VCLMAX = Calibrated airspeed obtained when the load factor-
corrected lift coefficient
[GRAPHIC] [TIFF OMITTED] TR26NO02.002
is first a maximum during the maneuver prescribed in paragraph (c) of
this section. In addition, when the maneuver is limited by a device
that abruptly pushes the nose down at a selected angle of attack (e.g.,
a stick pusher), VCLMAX may not be less than the speed
existing at the instant the device operates;
nZW = Load factor normal to the flight path at
VCLMAX
W = Airplane gross weight;
S = Aerodynamic reference wing area; and
q = Dynamic pressure.
(b) VCLMAX is determined with:
(1) Engines idling, or, if that resultant thrust causes an
appreciable decrease in stall speed, not more than zero thrust at the
stall speed;
(2) Propeller pitch controls (if applicable) in the takeoff
position;
(3) The airplane in other respects (such as flaps and landing gear)
in the condition existing in the test or performance standard in which
VSR is being used;
(4) The weight used when VSR is being used as a factor
to determine compliance with a required performance standard;
(5) The center of gravity position that results in the highest
value of reference stall speed; and
(6) The airplane trimmed for straight flight at a speed selected by
the applicant, but not less than 1.13VSR and not greater
than 1.3VSR.
(c) Starting from the stabilized trim condition, apply the
longitudinal control to decelerate the airplane so that the speed
reduction does not exceed one knot per second.
(d) In addition to the requirements of paragraph (a) of this
section, when a device that abruptly pushes the nose down at a selected
angle of attack (e.g., a stick pusher) is installed, the reference
stall speed, VSR, may not be less than 2 knots or 2 percent,
whichever is greater, above the speed at which the device operates.
6. Section 25.107 is amended by revising paragraphs (b)(1)
introductory text, b(1)(ii), (b)(2) introductory text, b(2)(ii), (c)(1)
and (c)(2), and by adding new paragraphs (c)(3) and (g) to read as
follows:
Sec. 25.107 Takeoff speeds.
* * * * *
(b) * * *
(1) 1.13VSR for--
* * * * *
(ii) Turbojet powered airplanes without provisions for obtaining a
significant reduction in the one-engine-inoperative power-on stall
speed;
(2) 1.08VSR for--
* * * * *
(ii) Turbojet powered airplanes with provisions for obtaining a
significant reduction in the one-engine-inoperative power-on stall
speed; and
* * * * *
(c)* * *
(1) V2MIN;
(2) VR plus the speed increment attained (in accordance
with Sec. 25.111(c)(2)) before reaching a height of 35 feet above the
takeoff surface; and
(3) A speed that provides the maneuvering capability specified in
Sec. 25.143(g).
* * * * *
(g) VFTO, in terms of calibrated airspeed, must be
selected by the applicant to provide at least the gradient of climb
required by Sec. 25.121(c), but may not be less than--
(1) 1.18 VSR; and
(2) A speed that provides the maneuvering capability specified in
Sec. 25.143(g).
7. Section 25.111 is amended by revising paragraph (a) introductory
text to read as follows:
Sec. 25.111 Takeoff path.
(a) The takeoff path extends from a standing start to a point in
the takeoff at which the airplane is 1,500 feet above the takeoff
surface, or at which the transition from the takeoff to the en route
configuration is completed and VFTO is reached, whichever
point is higher. In addition--
* * * * *
8. Section 25.119 is amended by revising paragraph (b) to read as
follows:
Sec. 25.119 Landing climb: All-engines-operating.
* * * * *
(b) A climb speed of not more than VREF.
9. Section 25.121 is amended by revising paragraphs (c)
introductory text, (d) introductory text, (d)(2) and (d)(3), and by
adding paragraph (d)(4) to read as follows:
Sec. 25.121 Climb: One-engine-inoperative.
* * * * *
(c) Final takeoff. In the en route configuration at the end of the
takeoff path determined in accordance with Sec. 25.111, the steady
gradient of climb may not be less than 1.2 percent for two-engine
airplanes, 1.5 percent for three-engine airplanes and 1.7 percent for
four-engine airplanes, at VFTO and with
* * * * *
(d) Approach. In a configuration corresponding to the normal all-
engines-operating procedure in which VSR for this
configuration does not exceed 110 percent of the VSR for the
related all-engines-operating landing configuration, the steady
gradient of climb may not be less than 2.1 percent for two-engine
airplanes, 2.4 percent for three-engine airplanes, and 2.7 percent for
four engine airplanes, with
* * * * *
(2) The maximum landing weight;
(3) A climb speed established in connection with normal landing
procedures, but not more than 1.4 VSR; and
(4) Landing gear retracted.
10. Section 25.125 is amended by revising paragraph (a)(2) to read
as follows:
Sec. 25.125 Landing.
(a) * * *
(2) A stabilized approach, with a calibrated airspeed of
VREF, must be maintained down to the 50 foot height.
VREF may not be less than
(i) 1.23 VSR0;
(ii) VMCL established under Sec. 25.149(f); and
(iii) A speed that provides the maneuvering capability specified in
Sec. 25.143(g).
* * * * *
11. Section 25.143 is amended by adding a new paragraph (g) to read
as follows:
Sec. 25.143 General.
* * * * *
(g) The maneuvering capabilities in a constant speed coordinated
turn at forward center of gravity, as specified in the following table,
must be free of stall warning or other characteristics that might
interfere with normal maneuvering:
[[Page 70827]]
--------------------------------------------------------------------------------------------------------------------------------------------------------
Maneuvering bank
Configuration Speed angle in a Thrust power setting
coordinated turn
--------------------------------------------------------------------------------------------------------------------------------------------------------
Takeoff............................ V2 30[deg] Asymmetric WAT-Limited.\1\
Takeoff............................ \2\V2 + XX 40[deg] All-engines-operating climb.\3\
En route........................... VFTO 40[deg] Asymmetric WAT-Limited.\1\
Landing............................ VREF 40[deg] Symmetric for -3[deg] flight path angle.
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ A combination of weight, altitude, and temperature (WAT) such that the thrust or power setting produces the minimum climb gradient specified in Sec.
25.121 for the flight condition.
\2\ Airspeed approved for all-engines-operating initial climb.
\3\ That thrust or power setting which, in the event of failure of the critical engine and without any crew action to adjust the thrust or power of the
remaining engines, would result in the thrust or power specified for the takeoff condition at V2, or any lesser thrust or power setting that is used
for all-engines-operating initial climb procedures.
12. Section 25.145 is amended by revising paragraphs (a)
introductory text, (a)(1), (b)(1), (b)(4), (b)(6), and (c) introductory
text to read as follows:
Sec. 25.145 Longitudinal control.
(a) It must be possible, at any point between the trim speed
prescribed in Sec. 25.103(b)(6) and stall identification (as defined
in Sec. 25.201(d)), to pitch the nose downward so that the
acceleration to this selected trim speed is prompt with
(1) The airplane trimmed at the trim speed prescribed in Sec.
25.103(b)(6);
* * * * *
(b) * * *
(1) With power off, flaps retracted, and the airplane trimmed at
1.3 VSR1, extend the flaps as rapidly as possible while
maintaining the airspeed at approximately 30 percent above the
reference stall speed existing at each instant throughout the maneuver.
* * * * *
(4) With power off, flaps retracted, and the airplane trimmed at
1.3 VSR1, rapidly set go-around power or thrust while
maintaining the same airspeed.
* * * * *
(6) With power off, flaps extended, and the airplane trimmed at 1.3
VSR1, obtain and maintain airspeeds between VSW
and either 1.6 VSR1 or VFE, whichever is lower.
(c) It must be possible, without exceptional piloting skill, to
prevent loss of altitude when complete retraction of the high lift
devices from any position is begun during steady, straight, level
flight at 1.08 VSR1 for propeller powered airplanes, or 1.13
VSR1 for turbojet powered airplanes, with--
* * * * *
Sec. 25.147 [Amended]
13. Section 25.147 is amended in paragraphs (a) introductory text,
(a)(2), (c) introductory text, and (d) by revising the expression ``1.4
VS1'' to read ``1.3 VSR1.''
Sec. 25.149 [Amended]
14. Section 25.149 is amended in paragraph (c) introductory text by
revising the expression ``1.2 VS'' to read ``1.13
VSR.''
Sec. 25.161 [Amended]
15. Section 25.161 is amended in paragraphs (b), (c)(1), (c)(2),
(c)(3) and (d) introductory text by revising the expression ``1.4
VS1'' to read ``1.3 VSR1''; and in paragraph
(e)(3) by revising the expression ``0.013 VS02''
to read ``0.013 VSR02.''
Sec. 25.175 [Amended]
16. Section 25.175 is amended: a. In paragraphs (a)(2), (b)(1)
introductory text, (b)(2) introductory text, (b)(3) introductory text
and (c)(4) by revising the expression ``1.4 VS1'' to read
``1.3 VSR1'';
b. In paragraph (b)(2)(ii) by revising the expression
``VMO + 1.4 VS1/2'' to read ``(VMO +
1.3 VSR1)/2'';
c. In paragraph (c) introductory text by revising the expressions
``1.1 VS1'' to read ``VSW'' and ``1.8
VS1'' to read ``1.7 VSR1'';
d. In paragraph (d) introductory text by revising the expressions
``1.1 VSO'' to read ``VSW'' and ``1.3
VS0'' to read ``1.7 VSR0''; and
e. In paragraph (d)(5) by revising the expression ``1.4
VS0'' to read ``1.3 VSR0.''
Sec. 25.177 [Amended]
17. Section 25.177 is amended in paragraph (c) by revising the
expression ``1.2 VS1'' to read ``1.13 VSR1.''
Sec. 25.181 [Amended]
18. Section 25.181 is amended in paragraphs (a) introductory text
and (b) by revising the reference to ``1.2 VS'' to read
``1.13 VSR.''
19. Section 25.201 is amended by revising paragraphs (a)(2) and
(b)(4) to read as follows:
Sec. 25.201 Stall demonstration.
(a) * * *
(2) The power necessary to maintain level flight at 1.5
VSR1 (where VSR1 corresponds to the reference
stall speed at maximum landing weight with flaps in the approach
position and the landing gear retracted).
(b) * * *
(4) The airplane trimmed for straight flight at the speed
prescribed in Sec. 25.103(b)(6).
* * * * *
20. Section 25.207 is amended by revising paragraphs (b) and (c),
and by adding new paragraphs (d), (e), and (f) to read as follows:
Sec. 25.207 Stall warning.
* * * * *
(b) The warning must be furnished either through the inherent
aerodynamic qualities of the airplane or by a device that will give
clearly distinguishable indications under expected conditions of
flight. However, a visual stall warning device that requires the
attention of the crew within the cockpit is not acceptable by itself.
If a warning device is used, it must provide a warning in each of the
airplane configurations prescribed in paragraph (a) of this section at
the speed prescribed in paragraphs (c) and (d) of this section.
(c) When the speed is reduced at rates not exceeding one knot per
second, stall warning must begin, in each normal configuration, at a
speed, VSW, exceeding the speed at which the stall is
identified in accordance with Sec. 25.201(d) by not less than five
knots or five percent CAS, whichever is greater. Once initiated, stall
warning must continue until the angle of attack is reduced to
approximately that at which stall warning began.
(d) In addition to the requirement of paragraph (c) of this
section, when the speed is reduced at rates not exceeding one knot per
second, in straight flight with engines idling and at the center-of-
gravity position specified in Sec. 25.103(b)(5), VSW, in
each normal configuration, must exceed VSR by not less than
three knots or three percent CAS, whichever is greater.
(e) The stall warning margin must be sufficient to allow the pilot
to prevent
[[Page 70828]]
stalling (as defined in Sec. 25.201(d)) when recovery is initiated not
less than one second after the onset of stall warning in slow-down
turns with at least 1.5g load factor normal to the flight path and
airspeed deceleration rates of at least 2 knots per second, with the
flaps and landing gear in any normal position, with the airplane
trimmed for straight flight at a speed of 1.3 VSR, and with
the power or thrust necessary to maintain level flight at 1.3
VSR.
(f) Stall warning must also be provided in each abnormal
configuration of the high lift devices that is likely to be used in
flight following system failures (including all configurations covered
by Airplane Flight Manual procedures).
Sec. 25.231 [Amended]
21. Section 25.231 is amended in paragraph (a)(2) by revising the
word ``altitude'' to read ``attitude'' and by revising the expression
``80 percent of VS1'' to read ``75 percent of
VSR1.''
Sec. 25.233 [Amended]
22. Section 25.233 is amended in paragraph (a) by revising the
reference ``0.2 VS0'' to read ``0.2 VSR0.''
Sec. 25.237 [Amended]
23. Section 25.237 is amended in paragraphs (a), (b)(1), and (b)(2)
by revising the reference ``0.2 VS0'' to read ``0.2
VSR0.''
24. Section 25.735 is amended by revising paragraphs (f)(2) and (g)
to read as follows:
Sec. 25.735 Brakes and braking systems.
* * * * *
(f) * * *
(2) Instead of a rational analysis, the kinetic energy absorption
requirements for each main wheel-brake assembly may be derived from the
following formula, which must be modified in cases of designed unequal
braking distributions.
[GRAPHIC] [TIFF OMITTED] TR26NO02.000
where--
KE = Kinetic energy per wheel (ft.-lb.);
W = Design landing weight (lb.);
V = VREF/1.3
VREF = Airplane steady landing approach speed, in knots, at the maximum
design landing weight and in the landing configuration at sea level;
and
N = Number of main wheels with brakes.
* * * * *
(g) In the landing case, the minimum speed rating of each main
wheel-brake assembly (that is, the initial speed used in the
dynamometer tests) may not be more than the V used in the determination
of kinetic energy in accordance with paragraph (f) of this section,
assuming that the test procedures for wheel-brake assemblies involve a
specified rate of deceleration, and, therefore, for the same amount of
kinetic energy, the rate of energy absorption (the power absorbing
ability of the brake) varies inversely with the initial speed.
* * * * *
Sec. 25.773 [Amended]
25. Section 25.773 is amended in paragraph (b)(1)(i) by revising
the expression ``1.6 VS1'' to read ``1.5 VSR1.''
Sec. 25.1001 [Amended]
26. Section 25.1001 is amended in paragraphs (c)(1) and (c)(3) by
revising the expression ``1.4 VS1'' to read ``1.3
VSR1.''
Sec. 25.1323 [Amended]
27. Section 25.1323 is amended in paragraph (c)(1) by revising the
expression ``1.3 VS1'' to read ``1.23 VSR1'' and
in paragraph (c)(2) by revising the expression ``1.3 VS0''
to read ``1.23 VSR0.''
Sec. 25.1325 [Amended]
28. Section 25.1325 is amended in paragraph (e) by revising the
expressions ``1.3 VS0'' and ``1.8 VS1'' to read
``1.23 VSR0'' and ``1.7 VSR1,'' respectively.
Sec. 25.1587 [Amended]
29. Section 25.1587 is amended by in paragraph (b)(2) by revising
the expression ``VS'' to read ``VSR.''
PART 97--STANDARD INSTRUMENT APPROACH PROCEDURES
30. The authority citation for part 97 is revised to read as
follows:
Authority: 49 U.S.C. 106(g), 40103, 40106, 40113, 40114, 40120,
44502, 44514, 44701, 44719, 44721-44722.
31. Section 97.3 is amended by revising the first two sentences of
paragraph (b) introductory text to read as follows:
Sec. 97.3 Symbols and terms used in procedures.
* * * * *
(b) Aircraft approach category means a grouping of aircraft based
on a speed of VREF, if specified, or if VREF is
not specified, 1.3 VS0 at the maximum certificated landing
weight. VREF, VS0, and the maximum certificated
landing weight are those values as established for the aircraft by the
certification authority of the country of registry. * * *
* * * * *
Issued in Washington, DC on November 14, 2002.
Marion C. Blakey,
Administrator.
[FR Doc. 02-29667 Filed 11-25-02; 8:45 am]
BILLING CODE 4910-13-U