[Federal Register: March 12, 2007 (Volume 72, Number 47)]
[Proposed Rules]
[Page 10941-10947]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr12mr07-17]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM362 Special Conditions No. 25-06-15-SC]
Special Conditions: Boeing Model 787-8 Airplane; Interaction of
Systems And Structures, Electronic Flight Control System--Control
Surface Awareness, High Intensity Radiated Fields (HIRF) Protection,
Limit Engine Torque Loads for Sudden Engine Stoppage, and Design Roll
Maneuver Requirement
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed special conditions.
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SUMMARY: This notice proposes special conditions for the Boeing Model
787-8 airplane. This airplane will have novel or unusual design
features when compared to the state of technology envisioned in the
airworthiness standards for transport category airplanes. These design
features include electronic flight control systems and high bypass
engines. These special conditions also pertain to the effects of such
novel or unusual design features, such as effects on the structural
performance of the airplane. Finally, these special conditions pertain
to effects of certain conditions on these novel or unusual design
features, such as the effects of high intensity radiated fields (HIRF).
Additional special conditions will be issued for other novel or unusual
design features of the Boeing Model 787-8 airplanes.
DATES: Comments must be received on or before April 26, 2007.
ADDRESSES: Comments on this proposal may be mailed in duplicate to:
Federal Aviation Administration, Transport Airplane Directorate,
Attention: Rules Docket (ANM-113), Docket No. NM362, 1601 Lind Avenue,
SW., Renton, Washington 98057-3356; or delivered in duplicate to the
Transport Airplane Directorate at the above address. All comments must
be marked Docket No. NM362. Comments may be inspected in the Rules
Docket weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.
FOR FURTHER INFORMATION CONTACT: Meghan Gordon, FAA, Standardization
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification
Service, 1601 Lind Avenue, SW., Renton, Washington 98057-3356;
telephone (425) 227-2138; facsimile (425) 227-1149.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites interested persons to participate in this
rulemaking by submitting written comments, data, or views. The most
helpful comments reference a specific portion of the special
conditions, explain the reason for any recommended change, and include
supporting data. We ask that you send us two copies of written
comments.
We will file in the docket all comments we receive as well as a
report summarizing each substantive public contact with FAA personnel
concerning these proposed special conditions. The docket is available
for public inspection before and after the comment closing date. If you
wish to review the docket in person, go to the address in the ADDRESSES
section of this notice between 7:30 a.m. and 4 p.m., Monday through
Friday, except Federal holidays.
We will consider all comments we receive on or before the closing
date for comments. We will consider comments filed late if it is
possible to do so without incurring expense or delay. We may change the
proposed special conditions based on comments we receive.
If you want the FAA to acknowledge receipt of your comments on this
proposal, include with your comments a pre-addressed, stamped postcard
on which the docket number appears. We will stamp the date on the
postcard and mail it back to you.
Background
On March 28, 2003, Boeing applied for an FAA type certificate for
its new Boeing Model 787-8 passenger airplane. The Boeing Model 787-8
airplane will be an all-new, two-engine jet transport airplane with a
two-aisle cabin. The maximum takeoff weight will be 476,000 pounds,
with a maximum passenger count of 381 passengers.
Type Certification Basis
Under provisions of 14 CFR 21.17, Boeing must show that Boeing
Model 787-8 airplanes (hereafter referred to as ``the 787'') meet the
applicable provisions of 14 CFR part 25, as amended by Amendments 25-1
through 25-117, except Sec. Sec. 25.809(a) and 25.812, which will
remain at Amendment 25-115. If the Administrator finds that the
applicable airworthiness regulations do not contain adequate or
appropriate safety standards for the 787 because of a novel or unusual
design feature, special conditions are prescribed under provisions of
14 CFR 21.16.
In addition to the applicable airworthiness regulations and special
conditions, the 787 must comply with the fuel vent and exhaust emission
requirements of 14 CFR part 34 and the noise certification requirements
of part 36. In addition, the FAA must issue a finding of regulatory
adequacy pursuant to section 611 of Public Law 92-574, the ``Noise
Control Act of 1972.''
Special conditions, as defined in Sec. 11.19, are issued in
accordance with Sec. 11.38 and become part of the type certification
basis in accordance with Sec. 21.17(a)(2).
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same or similar
novel or unusual design feature, the special conditions would also
apply to the other model under the provisions of Sec. 21.101.
[[Page 10942]]
Discussion of Novel or Unusual Design Features
The 787 will incorporate a number of novel or unusual design
features. Because of rapid improvements in airplane technology, the
applicable airworthiness regulations do not contain adequate or
appropriate safety standards for these design features. These proposed
special conditions for the 787 contain the additional safety standards
that the Administrator considers necessary to establish a level of
safety equivalent to that established by the existing airworthiness
standards.
Most of these proposed special conditions are identical or nearly
identical to those previously required for type certification of the
Model 777 series airplanes.
Most of these proposed special conditions were derived initially
from standardized requirements developed by the Aviation Rulemaking
Advisory Committee (ARAC), comprised of representatives of the FAA,
Europe's Joint Aviation Authorities (now replaced by the European
Aviation Safety Agency), and industry. In the case of some of these
requirements, a draft notice of proposed rulemaking has been prepared
but no final rule has yet been promulgated.
Additional special conditions will be issued for other novel or
unusual design features of the 787 in the near future.
1. Interaction of Systems and Structures
The 787 is equipped with systems that affect the airplane's
structural performance, either directly or as a result of failure or
malfunction. That is, the airplane's systems affect how it responds in
maneuver and gust conditions, and thereby affect its structural
capability. These systems may also affect the aeroelastic stability of
the airplane. Such systems represent a novel and unusual feature when
compared to the technology envisioned in the current airworthiness
standards. A special condition is needed to require consideration of
the effects of systems on the structural capability and aeroelastic
stability of the airplane, both in the normal and in the failed state.
This special condition requires that the airplane meet the
structural requirements of subparts C and D of 14 CFR part 25 when the
airplane systems are fully operative. The special condition also
requires that the airplane meet these requirements considering failure
conditions. In some cases, reduced margins are allowed for failure
conditions based on system reliability.
2. Electronic Flight Control System: Control Surface Awareness
With a response-command type of flight control system and no direct
coupling from cockpit controller to control surface, such as on the
787, the pilot is not aware of the actual surface deflection position
during flight maneuvers. These features are novel and unusual when
compared to the state of technology envisioned in the airworthiness
standards for transport category airplanes. These special conditions
are meant to contain the additional safety standards that the
Administrator considers necessary to establish a level of safety
equivalent to that established by the existing airworthiness standards.
Some unusual flight conditions, arising from atmospheric conditions or
airplane or engine failures or both, may result in full or nearly full
surface deflection. Unless the flightcrew is made aware of excessive
deflection or impending control surface deflection limiting, piloted or
auto-flight system control of the airplane might be inadvertently
continued in a way that would cause loss of control or other unsafe
handling or performance characteristics.
These proposed special conditions require that suitable
annunciation be provided to the flightcrew when a flight condition
exists in which nearly full control surface deflection occurs.
Suitability of such an annunciation must take into account that some
pilot-demanded maneuvers, such as a rapid roll, are necessarily
associated with intended full or nearly full control surface
deflection. Simple alerting systems which would function in both
intended or unexpected control-limiting situations must be properly
balanced between providing needed crew awareness and avoiding nuisance
warnings.
3. High Intensity Radiated Fields (HIRF) Protection
The 787 will use electrical and electronic systems which perform
critical functions. These systems may be vulnerable to high-intensity
radiated fields (HIRF) external to the airplane. There is no specific
regulation that addresses requirements for protection of electrical and
electronic systems from HIRF. Increased power levels from radio
frequency transmitters and use of sensitive avionics /electronics and
electrical systems to command and control the airplane have made it
necessary to provide adequate protection.
To ensure that a level of safety is achieved that is equivalent to
that intended by the regulations incorporated by reference, the
proposed special conditions are needed for the 787. These proposed
special conditions require that avionics/electronics and electrical
systems that perform critical functions be designed and installed to
preclude component damage and interruption of function because of HIRF.
High-power radio frequency transmitters for radio, radar,
television, and satellite communications can adversely affect
operations of airplane electrical and electronic systems. Therefore,
immunity of critical avionics/electronics and electrical systems to
HIRF must be established. Based on surveys and analysis of existing
HIRF emitters, adequate protection from HIRF exists if airplane system
immunity is demonstrated when exposed to the HIRF environments in
either paragraph (a) OR (b) below:
(a) A minimum environment of 100 volts rms (root-mean-square) per
meter electric field strength from 10 KHz to 18 GHz.
(1) System elements and their associated wiring harnesses must be
exposed to the environment without benefit of airframe shielding.
(2) Demonstration of this level of protection is established
through system tests and analysis.
(b) An environment external to the airframe of the field strengths
shown in the table below for the frequency ranges indicated. Immunity
to both peak and average field strength components from the table must
be demonstrated.
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Field strength
(volts per meter)
Frequency ---------------------
Peak Average
------------------------------------------------------------------------
10 kHz-100 kHz.................................... 50 50
100 kHz-500 kHz................................... 50 50
500 kHz-2 MHz..................................... 50 50
2 MHz-30 MHz...................................... 100 100
30 MHz-70 MHz..................................... 50 50
70 MHz-100 MHz.................................... 50 50
100 MHz-200 MHz................................... 100 100
200 MHz-400 MHz................................... 100 100
400 MHz-700 MHz................................... 700 50
700 MHz-1 GHz..................................... 700 100
1 GHz-2 GHz....................................... 2000 200
2 GHz-4 GHz....................................... 3000 200
4 GHz-6 GHz....................................... 3000 200
6 GHz-8 GHz....................................... 1000 200
8 GHz-12 GHz...................................... 3000 300
12 GHz-18 GHz..................................... 2000 200
18 GHz-40 GHz..................................... 600 200
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Field strengths are expressed in terms of peak root-mean-square (rms)
values over the complete modulation period.
The environment levels identified above are the result of an FAA
review of existing studies on the subject of HIRF and of the work of
the
[[Page 10943]]
Electromagnetic Effects Harmonization Working Group of ARAC.
4. Limit Engine Torque Loads for Sudden Engine Stoppage
The 787 will have high-bypass engines with a chord-swept fan 112
inches in diameter. Engines of this size were not envisioned when Sec.
25.361, pertaining to loads imposed by engine seizure, was adopted in
1965. Worst case engine seizure events become increasingly more severe
with increasing engine size because of the higher inertia of the
rotating components.
Section 25.361(b)(1) requires that for turbine engine
installations, the engine mounts and the supporting structures must be
designed to withstand a ``limit engine torque load imposed by sudden
engine stoppage due to malfunction or structural failure.'' Limit loads
are expected to occur about once in the lifetime of any airplane.
Section 25.305 requires that supporting structures be able to support
limit loads without detrimental permanent deformation, meaning that
supporting structures should remain serviceable after a limit load
event.
Since adoption of Sec. 25.361(b)(1), the size, configuration, and
failure modes of jet engines have changed considerably. Current engines
are much larger and are designed with large bypass fans. In the event
of a structural failure, these engines are capable of producing much
higher transient loads on the engine mounts and supporting structures.
As a result, modern high bypass engines are subject to certain
rare-but-severe engine seizure events. Service history shows that such
events occur far less frequently than limit load events. Although it is
important for the airplane to be able to support such rare loads safely
without failure, it is unrealistic to expect that no permanent
deformation will occur.
Given this situation, ARAC has proposed a design standard for
today's large engines. For the commonly-occurring deceleration events,
the proposed standard requires engine mounts and structures to support
maximum torques without detrimental permanent deformation. For the
rare-but-severe engine seizure events such as loss of any fan,
compressor, or turbine blade, the proposed standard requires engine
mounts and structures to support maximum torques without failure, but
allows for some deformation in the structure.
The FAA concludes that modern large engines, including those on the
787, are novel and unusual compared to those envisioned when Sec.
25.361(b)(1) was adopted and thus warrant a special condition. The
proposed special condition contains design criteria recommended by
ARAC. The ARAC proposal would revise the wording of Sec. 25.361(b),
including Sec. Sec. 25.361(b)(1) and (b)(2), removing language
pertaining to structural failures and moving it to a separate
requirement that discusses the reduced factors of safety that apply to
these failures.
5. Design Roll Maneuver Requirement
The 787 is equipped with an electronic flight control system that
provides control of the aircraft through pilot inputs to the flight
computer. Current part 25 airworthiness regulations account for
``control laws,'' for which aileron deflection is proportional to
control stick deflection. They do not address any nonlinearities \1\ or
other effects on aileron actuation that may be caused by electronic
flight controls. Therefore, the FAA considers the flight control system
to be a novel and unusual feature compared to those envisioned when
current regulations were adopted. Since this type of system may affect
flight loads, and therefore the structural capability of the airplane,
special conditions are needed to address these effects.
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\1\ A nonlinearity is a situation where output does not change
in the same proportion as input.
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This proposed special condition differs from current requirements
in that it requires that the roll maneuver result from defined
movements of the cockpit roll control as opposed to defined aileron
deflections. Also, the proposed special condition requires an
additional load condition at design maneuvering speed (VA),
in which the cockpit roll control is returned to neutral following the
initial roll input.
This proposed special condition differs from similar special
conditions applied to previous designs. This special condition is
limited to the roll axis only, whereas previous special conditions also
included pitch and yaw axes. A special condition is no longer needed
for the yaw axis because Sec. 25.351 was revised at Amendment 25-91 to
take into account effects of an electronic flight control system. No
special condition is needed for the pitch axis because the applicant's
proposed methodology for the pitch maneuver takes into account effects
of an electronic flight control system.
Applicability
As discussed above, these proposed special conditions are
applicable to the 787. Should Boeing apply at a later date for a change
to the type certificate to include another model incorporating the same
novel or unusual design features, these proposed special conditions
would apply to that model as well under the provisions of Sec. 21.101.
Conclusion
This action affects only certain novel or unusual design features
of the 787. It is not a rule of general applicability, and it affects
only the applicant that applied to the FAA for approval of these
features on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
The authority citation for these Special Conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Proposed Special Conditions
Accordingly, the Administrator of the Federal Aviation
Administration (FAA) proposes the following special conditions as part
of the type certification basis for the Boeing Model 787-8 airplane.
1. Interaction of Systems and Structures
The Boeing Model 787-8 airplane is equipped with systems which
affect the airplane's structural performance either directly or as a
result of failure or malfunction. The influence of these systems and
their failure conditions must be taken into account when showing
compliance with requirements of subparts C and D of part 25 of Title 14
of the Code of Federal Regulations. The following criteria must be used
for showing compliance with this proposed special condition for
airplanes equipped with flight control systems, autopilots, stability
augmentation systems, load alleviation systems, flutter control
systems, fuel management systems, and other systems that either
directly or as a result of failure or malfunction affect structural
performance. If this proposed special condition is used for other
systems, it may be necessary to adapt the criteria to the specific
system.
(a) The criteria defined here address only direct structural
consequences of system responses and performances. They cannot be
considered in isolation but should be included in the overall safety
evaluation of the airplane. They may in some instances duplicate
standards already established for this evaluation. These criteria are
only applicable to structures whose failure could prevent continued
safe flight and landing. Specific criteria defining acceptable limits
on handling characteristics or stability requirements when operating in
the system degraded
[[Page 10944]]
or inoperative mode are not provided in this special condition.
(b) Depending on the specific characteristics of the airplane,
additional studies may be required that go beyond the criteria provided
in this special condition in order to demonstrate capability of the
airplane to meet other realistic conditions such as alternative gust
conditions or maneuvers for an airplane equipped with a load
alleviation system.
(c) The following definitions are applicable to this special
condition.
(1) Structural performance: Capability of the airplane to meet the
structural requirements of part 25.
(2) Flight limitations: Limitations that can be applied to the
airplane flight conditions following an in-flight failure occurrence
and that are included in the flight manual (speed limitations or
avoidance of severe weather conditions, for example).
(3) Operational limitations: Limitations, including flight
limitations, that can be applied to the airplane operating conditions
before dispatch (fuel, payload, and master minimum equipment list
limitations, for example).
(4) Probabilistic terms: Terms (probable, improbable, extremely
improbable) used in this special condition which are the same as those
probabilistic terms used in Sec. 25.1309.
(5) Failure condition: Term that is the same as that used in Sec.
25.1309. The term failure condition in this proposed special condition,
however, applies only to system failure conditions that affect
structural performance of the airplane. Examples are system failure
conditions that induce loads, change the response of the airplane to
inputs such as gusts or pilot actions, or lower flutter margins.
Note: Although failure annunciation system reliability must be
included in probability calculations for paragraph (f) of the
proposed special condition, there is no specific reliability
requirement for the annunciation system required in paragraph (g) of
the proposed special condition.
(d) General. The following criteria will be used in determining the
influence of a system and its failure conditions on the airplane
structure.
(e) System fully operative. With the system fully operative, the
following apply:
(1) Limit loads must be derived in all normal operating
configurations of the system from all the limit conditions specified in
subpart C of 14 CFR part 25 (or used in lieu of those specified in
subpart C), taking into account any special behavior of such a system
or associated functions or any effect on the structural performance of
the airplane that may occur up to the limit loads. In particular, any
significant degree of nonlinearity in rate of displacement of control
surface or thresholds, or any other system nonlinearities, must be
accounted for in a realistic or conservative way when deriving limit
loads from limit conditions.
(2) The airplane must meet the strength requirements of part 25 for
static strength and residual strength, using the specified factors to
derive ultimate loads from the limit loads defined above. The effect of
nonlinearities must be investigated beyond limit conditions to ensure
the behavior of the system presents no anomaly compared to the behavior
below limit conditions. However, conditions beyond limit conditions
need not be considered if the applicant demonstrates that the airplane
has design features that will not allow it to exceed those limit
conditions.
(3) The airplane must meet the aeroelastic stability requirements
of Sec. 25.629.
(f) System in the failure condition. For any system failure
condition not shown to be extremely improbable, the following apply:
(1) Establishing loads at the time of failure. Starting from 1-g
level flight conditions, a realistic scenario, including pilot
corrective actions, must be established to determine loads occurring at
the time of failure and immediately after failure.
(i) For static strength substantiation, these loads, multiplied by
an appropriate factor of safety related to probability of occurrence of
the failure, are ultimate loads to be considered for design. The factor
of safety (FS) is defined in Figure 1.
[GRAPHIC] [TIFF OMITTED] TP12MR07.000
(ii) For residual strength substantiation, the airplane must be
able to withstand two thirds of the ultimate loads defined in
subparagraph (f)(1)(i) of these special conditions. For pressurized
cabins, these loads must be combined with the normal operating
differential pressure.
(iii) Freedom from aeroelastic instability must be shown up to the
speeds defined in Sec. 25.629(b)(2). For failure conditions that
result in speeds beyond design cruise speed or design cruise mach
number (VC/MC), freedom from aeroelastic
instability must be shown to increased speeds, so that the margins
intended by Sec. 25.629(b)(2) are maintained.
(iv) Failures of the system that result in forced structural
vibrations (oscillatory failures) must not produce loads that could
result in detrimental deformation of primary structure.
(2) Establishing loads in the system failed state for the
continuation of the flight. For the continuation of flight of the
airplane in the system failed state and considering any appropriate
reconfiguration and flight limitations, the following apply:
(i) Loads derived from the following conditions (or used in lieu of
the following conditions) at speeds up to VC/MC,
or the speed limitation
[[Page 10945]]
prescribed for the remainder of the flight, must be determined:
(A) The limit symmetrical maneuvering conditions specified in Sec.
25.331 and Sec. 25.345.
(B) The limit gust and turbulence conditions specified in Sec.
25.341 and Sec. 25.345.
(C) The limit rolling conditions specified in Sec. 25.349 and the
limit unsymmetrical conditions specified in Sec. 25.367 and Sec.
25.427(b) and (c).
(D) The limit yaw maneuvering conditions specified in Sec. 25.351.
(E) The limit ground loading conditions specified in Sec. 25.473
and Sec. 25.491.
(ii) For static strength substantiation, each part of the structure
must be able to withstand the loads in paragraph (f)(2)(i) of the
special condition multiplied by a factor of safety depending on the
probability of being in this failure state. The factor of safety is
defined in Figure 2.
[GRAPHIC] [TIFF OMITTED] TP12MR07.001
Qj = (Tj)(Pj)
Where:
Tj = Average time spent in failure condition j (in hours)
Pj = Probability of occurrence of failure mode j (per hour)
Note: If Pj is greater than 10-3 per flight hour then
a 1.5 factor of safety must be applied to all limit load conditions
specified in subpart C-Structure, of 14 CFR part 25.
(iii) For residual strength substantiation, the airplane must be
able to withstand two-thirds of the ultimate loads defined in paragraph
(f)(2)(ii) of the special condition. For pressurized cabins, these
loads must be combined with the normal operating differential pressure.
(iv) If the loads induced by the failure condition have a
significant effect on fatigue or damage tolerance then the effects of
these loads must be taken into account.
(v) Freedom from aeroelastic instability must be shown up to a
speed determined from Figure 3. Flutter clearance speeds V' and V'' may
be based on the speed limitation specified for the remainder of the
flight using the margins defined by Sec. 25.629(b).
[GRAPHIC] [TIFF OMITTED] TP12MR07.002
V' = Clearance speed as defined by Sec. 25.629(b)(2).
V'' = Clearance speed as defined by Sec. 25.629(b)(1).
Qj = (Tj)(Pj)
Where:
Tj = Average time spent in failure condition j (in hours)
Pj = Probability of occurrence of failure mode j (per hour)
Note: If Pj is greater than 10-3 per flight hour, then the
flutter clearance speed must not be less than V''.
(vi) Freedom from aeroelastic instability must also be shown up to
V' in Figure 3 above, for any probable system failure condition
combined with any damage required or selected for investigation by
Sec. 25.571(b).
(3) Consideration of certain failure conditions may be required by
other sections of 14 CFR part 25 regardless of calculated system
reliability. Where
[[Page 10946]]
analysis shows the probability of these failure conditions to be less
than 10-9, criteria other than those specified in this paragraph may be
used for structural substantiation to show continued safe flight and
landing.
(g) Failure indications. For system failure detection and
indication, the following apply.
(1) The system must be checked for failure conditions, not
extremely improbable, that degrade the structural capability of the
airplane below the level required by part 25 or significantly reduce
the reliability of the remaining system. As far as reasonably
practicable, the flightcrew must be made aware of these failures before
flight. Certain elements of the control system, such as mechanical and
hydraulic components, may use special periodic inspections, and
electronic components may use daily checks, instead of detection and
indication systems to achieve the objective of this requirement. Such
certification maintenance inspections or daily checks must be limited
to components on which faults are not readily detectable by normal
detection and indication systems and where service history shows that
inspections will provide an adequate level of safety.
(2) The existence of any failure condition, not extremely
improbable, during flight that could significantly affect the
structural capability of the airplane and for which the associated
reduction in airworthiness can be minimized by suitable flight
limitations, must be signaled to the flightcrew. For example, failure
conditions that result in a factor of safety between the airplane
strength and the loads of subpart C below 1.25, or flutter margins
below V'', must be signaled to the crew during flight.
(h) Dispatch with known failure conditions. If the airplane is to
be dispatched in a known system failure condition that affects
structural performance, or affects the reliability of the remaining
system to maintain structural performance, then the provisions of this
special condition must be met, including the provisions of paragraph
(e) for the dispatched condition, and paragraph (f) for subsequent
failures. Expected operational limitations may be taken into account in
establishing Pj as the probability of failure occurrence for
determining the safety margin in Figure 1. Flight limitations and
expected operational limitations may be taken into account in
establishing Qj as the combined probability of being in the dispatched
failure condition and the subsequent failure condition for the safety
margins in Figures 2 and 3. These limitations must be such that the
probability of being in this combined failure state and then
subsequently encountering limit load conditions is extremely
improbable. No reduction in these safety margins is allowed if the
subsequent system failure rate is greater than 10-3 per
hour.
2. Electronic Flight Control System: Control Surface Awareness
In addition to compliance with Sec. Sec. 25.143, 25.671, and
25.672, the following special condition applies:
(a) The system design must ensure that the flightcrew is made
suitably aware whenever the primary control means nears the limit of
control authority. This indication should direct the pilot to take
appropriate action to avoid the unsafe condition in accordance with
appropriate airplane flight manual (AFM) instructions. Depending on the
application, suitable annunciations may include cockpit control
position, annunciator light, or surface position indicators.
Furthermore, this requirement applies at limits of control authority,
not necessarily at limits of any individual surface travel.
(b) Suitability of such a display or alerting must take into
account that some pilot-demanded maneuvers are necessarily associated
with intended full performance, which may require full surface
deflection. Therefore, simple alerting systems, which would function in
both intended or unexpected control-limiting situations, must be
properly balanced between needed crew awareness and nuisance factors. A
monitoring system which might compare airplane motion, surface
deflection, and pilot demand could be useful for eliminating nuisance
alerting.
3. High Intensity Radiated Fields (HIRF) Protection
(a) Protection from Unwanted Effects of High-intensity Radiated
Fields. Each electrical and electronic system which performs critical
functions must be designed and installed to ensure that the operation
and operational capabilities of these systems to perform critical
functions are not adversely affected when the airplane is exposed to
high intensity radiated fields external to the airplane.
(b) For the purposes of these Special Conditions, the following
definition applies: Critical Functions: Functions whose failure would
contribute to or cause a failure condition that would prevent continued
safe flight and landing of the airplane.
4. Limit Engine Torque Loads for Sudden Engine Stoppage
In lieu of Sec. 25.361(b) the following special condition is
proposed:
(a) For turbine engine installations, the engine mounts, pylons,
and adjacent supporting airframe structure must be designed to
withstand 1g level flight loads acting simultaneously with the maximum
limit torque loads imposed by each of the following:
(1) Sudden engine deceleration due to a malfunction which could
result in a temporary loss of power or thrust.
(2) The maximum acceleration of the engine.
(b) For auxiliary power unit installations, the power unit mounts
and adjacent supporting airframe structure must be designed to
withstand 1g level flight loads acting simultaneously with the maximum
limit torque loads imposed by each of the following:
(1) Sudden auxiliary power unit deceleration due to malfunction or
structural failure.
(2) The maximum acceleration of the power unit.
(c) For engine supporting structure, an ultimate loading condition
must be considered that combines 1g flight loads with the transient
dynamic loads resulting from each of the following:
(1) Loss of any fan, compressor, or turbine blade.
(2) Where applicable to a specific engine design, any other engine
structural failure that results in higher loads.
(d) The ultimate loads developed from the conditions specified in
paragraphs (c)(1) and (c)(2) are to be multiplied by a factor of 1.0
when applied to engine mounts and pylons and multiplied by a factor of
1.25 when applied to adjacent supporting airframe structure.
5. Design Roll Maneuver Requirement
In lieu of compliance to Sec. 25.349(a), the following special
conditions are proposed.
The following conditions, speeds, and cockpit roll control motions
(except as the motions may be limited by pilot effort) must be
considered in combination with an airplane load factor of zero and of
two-thirds of the positive maneuvering factor used in design. In
determining the resulting control surface deflections, the torsional
flexibility of the wing must be considered in accordance with Sec.
25.301(b):
(a) Conditions corresponding to steady rolling velocities must be
investigated. In addition, conditions corresponding to maximum angular
[[Page 10947]]
acceleration must be investigated for airplanes with engines or other
weight concentrations outboard of the fuselage. For the angular
acceleration conditions, zero rolling velocity may be assumed in the
absence of a rational time history investigation of the maneuver.
(b) At VA, sudden movement of the cockpit roll control
up to the limit is assumed. The position of the cockpit roll control
must be maintained until a steady roll rate is achieved and then must
be returned suddenly to the neutral position.
(c) At VC, the cockpit roll control must be moved
suddenly and maintained so as to achieve a roll rate not less than that
obtained in paragraph (2).
(d) At VD, the cockpit roll control must be moved
suddenly and maintained so as to achieve a roll rate not less than one-
third of that obtained in paragraph (2).
Issued in Renton, Washington, on March 1, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. E7-4306 Filed 3-9-07; 8:45 am]
BILLING CODE 4910-13-P