[Federal Register: April 12, 2007 (Volume 72, Number 70)]
[Rules and Regulations]
[Page 18365-18372]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr12ap07-4]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM370; Special Conditions No. 25-349-SC]
Special Conditions: Dassault Aviation Model Falcon 7X Airplane;
Side Stick Controllers, Electronic Flight Control System: Lateral-
Directional and Longitudinal Stability, Low Energy Awareness, Flight
Control Surface Position Awareness, and Flight Characteristics
Compliance Via the Handling Qualities Rating Method; Flight Envelope
Protection: General Limiting Requirements, High Incidence Protection
Function, Normal Load Factor (g) Limiting, and Pitch, Roll, and High
Speed Limiting Functions
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for the Dassault Aviation
Model Falcon 7X 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 side stick controllers, electronic flight
control systems, and flight envelope protections. These special
conditions pertain to control and handling qualities of the airplane
and protection limits within the normal flight envelope. The applicable
airworthiness regulations do not contain adequate or appropriate safety
standards for these design features. These special conditions 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.
EFFECTIVE DATE: April 4, 2007.
FOR FURTHER INFORMATION CONTACT: Joe Jacobsen, FAA, Airplane and Flight
Crew Interface Branch, ANM-111, Transport Airplane Directorate,
Aircraft Certification Service, 1601 Lind Avenue SW., Renton,
Washington 98057-3356; telephone (425) 227-2011; facsimile (425) 227-
1149.
SUPPLEMENTARY INFORMATION:
Background
On June 4, 2002, Dassault Aviation, 9 rond Point des Champs
Elysees, 75008, Paris, France, applied for FAA type certificate for its
new Model Falcon 7X airplane. The Dassault Model Falcon 7X airplane is
a 19 passenger transport
[[Page 18366]]
category airplane powered by three aft mounted Pratt & Whitney PW307A
high bypass ratio turbofan engines. Maximum takeoff weight will be
63,700 pounds, and maximum certified altitude will be 51,000 feet with
a range of 5,700 nautical miles. The airplane is operated using a fly-
by-wire (FBW) primary flight control system. This will be the first
application of a FBW primary flight control system in an airplane
primarily intended for private/corporate use.
The Dassault Aviation Model Falcon 7X design incorporates equipment
that was not envisioned when part 25 was created. This equipment
includes side stick controllers, and an electronic flight control
system that provides flight envelope protection. Therefore, special
conditions are required that provide the level of safety equivalent to
that established by the regulations.
Type Certification Basis
Under the provisions of 14 CFR 21.17, Dassault Aviation must show
that the Model Falcon 7X airplane meets the applicable provisions of 14
CFR part 25, as amended by Amendments 25-1 through 25-108.
If the Administrator finds that the applicable airworthiness
regulations do not contain adequate or appropriate safety standards for
the Model Falcon 7X airplane because of novel or unusual design
features, special conditions are prescribed under the provisions of
Sec. 21.16.
In addition to the applicable airworthiness regulations and special
conditions, the Dassault Model Falcon 7X airplane must comply with the
fuel vent and exhaust emission requirements of 14 CFR part 34 and the
noise certification requirements of 14 CFR part 36.
The FAA issues special conditions, as defined in Sec. 11.19, under
Sec. 11.38, and they become part of the type certification basis under
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 novel or
unusual design features, these special conditions would also apply to
the other model under Sec. 21.101.
Novel or Unusual Design Features
The Dassault Falcon 7X airplane will incorporate the following
novel or unusual design features:
Side stick controllers;
Electronic flight control system: lateral-directional and
longitudinal stability, low energy awareness,
Electronic flight control system: flight control surface
position awareness,
Electronic flight control system: flight characteristics
compliance via the handling qualities rating method (HQRM);
Flight envelope protection: general limiting requirements,
Flight envelope protection: high incidence protection
function,
Flight envelope protection: normal load factor (g)
limiting,
Flight envelope protection: pitch, roll, and high speed
limiting functions.
Because of these rapid improvements in airplane technology, the
applicable airworthiness regulations do not contain adequate or
appropriate safety standards for these design features. These special
conditions address equipment which may affect the airplane's structural
performance, either directly or as a result of failure or malfunction.
These special conditions are identical or nearly identical to those
previously required for type certification of other airplane models.
Discussion
Because of these rapid improvements in airplane technology, the
applicable airworthiness regulations do not contain adequate or
appropriate safety standards for these design features. Therefore, in
addition to the requirements of part 25, subparts C and D, the
following special conditions apply.
Special Condition No. 1. Side Stick Controllers
The Falcon 7X will use side stick controllers for pitch and roll
control. Regulatory requirements for conventional wheel and column
controllers, such as requirements pertaining to pilot strength and
controllability, are not directly applicable to side stick controllers.
Certain ergonomic considerations such as armrest support, freedom of
arm movement, controller displacement, handgrip size and accommodations
for a range of pilot sizes are not addressed in the regulations. In
addition, pilot control authority may be uncertain, because the side
sticks are not mechanically interconnected as with conventional wheel
and column controls. Pitch and roll control force and displacement
sensitivity must be compatible, so that normal inputs on one control
axis will not cause significant unintentional inputs on the other.
These special conditions require that the unique features of the
side stick must be demonstrated through flight and simulator tests to
have suitable handling and control characteristics.
Special Condition No. 2. Electronic Flight Control System: Lateral-
Directional Stability, Longitudinal Stability, and Low Energy Awareness
In lieu of compliance with the regulations pertaining to lateral-
directional and longitudinal stability, these special conditions ensure
that the Model Falcon 7X will have suitable airplane handling qualities
throughout the normal flight envelope.
The unique features of the Model Falcon 7X flight control system
and side stick controllers, when compared with conventional airplanes
with wheel and column controllers, do not provide conventional
awareness to the flightcrew of a change in speed or a change in the
direction of flight. These special conditions require that adequate
awareness be provided to the pilot of a low energy state (low speed,
low thrust, and low altitude) below normal operating speeds.
a. Lateral-Directional Static Stability: The electronic flight
control system (EFCS) on the Falcon 7X contains fly-by-wire control
laws that result in neutral lateral-directional static stability.
Therefore, the conventional requirements of the regulations are not
met.
The Model Falcon 7X airplane has a flight control design feature
within the normal operational envelope in which side stick deflection
in the roll axis commands roll rate. As a result, the stick force in
the roll axis will be zero (neutral stability) during the straight,
steady sideslip flight maneuver of Sec. 25.177(c) and will not be
``substantially proportional to the angle of sideslip,'' as required by
the regulation.
With conventional control system requirements, positive static
directional stability is defined as the tendency to recover from a skid
with the rudder free. Positive static lateral stability is defined as
the tendency to raise the low wing in a sideslip with the aileron
controls free. These special conditions are intended to accomplish the
following:
Provide additional cues of inadvertent sideslips and skids
through control force changes.
Ensure that short periods of unattended operation do not
result in any significant changes in yaw or bank angle.
Provide predictable roll and yaw response.
Provide acceptable level of pilot attention (i.e.,
workload) to attain and maintain a coordinated turn.
[[Page 18367]]
b. Longitudinal Static Stability: The longitudinal flight control
laws for the Falcon 7X provide neutral static stability within the
normal operational envelope. Therefore, it is inappropriate to require
the airplane design to comply with the static longitudinal stability
requirements of Sec. Sec. 25.171, 25.173, and 25.175.
Static longitudinal stability on conventional airplanes with
mechanical links to the pitch control surface means that a pull force
on the controller will result in a reduction in speed relative to the
trim speed, and a push force will result in higher than trim speed.
Longitudinal stability is required by the regulations for the following
reasons:
Speed change cues are provided to the pilot through
increased and decreased forces on the controller.
Short periods of unattended control of the airplane do not
result in significant changes in attitude, airspeed, or load factor.
A predictable pitch response is provided to the pilot.
An acceptable level of pilot attention (i.e., workload) to
attain and maintain trim speed and altitude is provided to the pilot.
Longitudinal stability provides gust stability.
The pitch control movement of the side stick is a normal load
factor or ``g'' command which results in an initial movement of the
elevator surface to attain the commanded load factor. That movement is
followed by integrated movement of the stabilizer and elevator to
automatically trim the airplane to a neutral (1g) stick-free stability.
The flight path commanded by the initial side stick input will remain
stick-free until the pilot gives another command. This control function
is applied during ``normal'' control law within the speed range from
the speed at the angle of attack protection limit to initiation of the
angle of attack protection limit. Once outside this speed range, the
control laws introduce the conventional longitudinal static stability
as described above.
As a result of neutral static stability, the Falcon 7X does not
meet the part 25 requirements for static longitudinal stability. It
would not be appropriate to apply the conventional part 25 requirements
for static longitudinal stability to the unconventional control systems
of the Falcon 7X. These special conditions require that the airplane be
shown to have suitable static longitudinal stability in any condition
normally encountered in service.
c. Low Energy Awareness: Static longitudinal stability provides an
awareness to the flightcrew of a low energy state (low speed and thrust
at low altitude). Past experience on airplanes fitted with a flight
control system which provides neutral longitudinal stability shows
there are insufficient feedback cues to the pilot of excursion below
normal operational speeds. The maximum angle of attack protection
system limits the airplane angle of attack and prevents stall during
normal operating speeds, but this system is not sufficient to prevent
stall at low speed excursions below normal operational speeds. Until
intervention, there are no stability cues because the airplane remains
trimmed. Additionally, feedback from the pitching moment due to thrust
variation is reduced by the flight control laws. Recovery from a low
speed excursion may become hazardous when the low speed is associated
with low altitude and the engines are operating at low thrust or with
other performance limiting conditions.
Because Sec. 25.173 requires that the pilot receive speed change
cues through increased or decreased forces on the controller, it would
be inappropriate to apply those requirements for feedback cues to the
Falcon Model 7X systems. These special conditions require that the
airplane provide adequate awareness of a low energy state to the pilot.
Special Condition No. 3. Electronic Flight Control System: Flight
Control Surface Position Awareness
With a response-command type of flight control system and no direct
mechanical coupling from cockpit controller to control surface, the
controller does not provide the Falcon 7X pilot with an awareness of
the actual surface deflection position during flight maneuvers. 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, the pilot
or auto-flight system may encounter situations where loss of control or
other unsafe handling or performance characteristics occur.
These 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 a
display must take into account that some pilot-demanded maneuvers
(e.g., rapid roll) are necessarily associated with intended full or
nearly full control surface deflection. Therefore, simple alerting
systems which function in both intended or unexpected control-limiting
situations must be properly balanced between needed crew awareness and
nuisance warnings.
Special Condition No. 4. Electronic Flight Control System: Flight
Characteristics Compliance Via the Handling Qualities Rating Method
(HQRM)
The Model Falcon 7X airplane will have an electronic flight control
system (EFCS). This system provides an electronic interface between the
pilot's flight controls and the flight control surfaces (for both
normal and failure states). The system also generates the actual
surface commands that provide for stability augmentation and control
about all three airplane axes. Because EFCS technology has outpaced
existing regulations-written essentially for unaugmented airplanes with
provision for limited ON/OFF augmentation-suitable special conditions
and a method of compliance are required to aid in the certification of
flight characteristics.
These special conditions and the method of compliance presented in
Appendix 7, FAA Handling Qualities Rating Method, of AC 25-7A, Flight
Test Guide Certification of Transport Category Airplanes, provide a
means to evaluate flight characteristics--for example,
``satisfactory,'' ``adequate,'' or ``controllable''--to determine
compliance with the regulations. The HQRM in Appendix 7 was developed
for airplanes with control systems having similar functions and is
employed to aid in the evaluation of the following:
All EFCS/airplane failure states not shown to be extremely
improbable and where the envelope (task) and atmospheric disturbance
probabilities are each 1.
All combinations of failures, atmospheric disturbance
level, and flight envelope not shown to be extremely improbable.
Any other flight condition or characteristic where 14 CFR
part 25 proves to be inadequate for proper assessment of unique Falcon
Model 7X flight characteristics.
The Handling Qualities Rating Method provides a systematic approach
to the assessment of handling qualities. It is not intended to dictate
program size or need for a fixed number of pilots to achieve multiple
opinions. The airplane design itself and success in defining critical
failure combinations from the many reviewed in Systems Safety
Assessments dictate the scope of any HQRM application.
Handling qualities terms, principles, and relationships familiar to
the aviation community have been used to
[[Page 18368]]
formulate the HQRM. For example, we have established that the well-
known COOPER-HARPER rating scale and the FAA three-part rating system
are similar. This approach on the flying qualities of highly augmented/
relaxed static stability airplanes in relation to regulatory and flight
test guide requirements is reported in DOT/FAA/CT-82/130, Flying
Qualities of Relaxed Static Stability Aircraft, Volumes I and II.
Special Condition No. 5. Flight Envelope Protection: General Limiting
Requirements
These special conditions and the following ones-pertaining to
flight envelope protection-present general limiting requirements for
all the unique flight envelope protection features of the basic Model
Falcon 7X Electronic Flight Control System (EFCS) design. Current
regulations do not address these types of protection features. The
general limiting requirements are necessary to ensure a smooth
transition from normal flight to the protection mode and adequate
maneuver capability. The general limiting requirements also ensure that
the structural limits of the airplane are not exceeded. Furthermore,
failure of the protection feature must not create hazardous flight
conditions. Envelope protection parameters include angle of attack,
normal load factor, pitch angle, and speed. To accomplish these
envelope protections, one or more significant changes occur in the EFCS
control laws as the normal flight envelope limit is approached or
exceeded.
Each specific type of envelope protection is addressed individually
in the special conditions that follow.
Special Condition No. 6. Flight Envelope Protection-High Incidence
Protection Function
The Falcon 7X is equipped with a high incidence protection function
that limits the angle of attack at which the airplane can be flown
during normal low speed operation and that cannot be overridden by the
flightcrew. This function prevents the airplane from stalling and
therefore, the stall warning system is not needed during normal flight
conditions. If there is a failure of the high incidence protection
function that is not shown to be extremely improbable, the flight
characteristics at the angle of attack for CLMAX must be
suitable in the traditional sense, and stall warning must be provided
in a conventional manner. These special conditions address these and
other unique features of this function on the Model Falcon 7X.
These special conditions define a minimum steady flight speed,
VMIN, to be demonstrated during flight test, at which the
airplane can develop lift normal to the flight path and equal to its
weight at the angle of attack limit of the protection function. It
further defines procedures for establishing the reference stall speed,
VSR, to be used for defining reference speeds during takeoff
and landing.
In the absence of specific regulations in 14 CFR part 25, these
special conditions present High Incidence Protection Function
requirements for the capability and reliability of the function, stall
warning with a failure condition, handling qualities and
characteristics at high incidence or angle of attack flight maneuvers,
and specific applications of the newly defined VMIN in lieu
of current regulations.
Special Condition No. 7. Flight Envelope Protection: Normal Load Factor
(G) Limiting
The Falcon 7X flight control system design incorporates a normal
load factor limiting function on a full time basis that will prevent
the pilot from inadvertently or intentionally exceeding the positive or
negative airplane limit load factor. This limiting feature is active in
the normal flight control mode and cannot be overridden by the pilot.
There is no requirement in the regulations for this limiting feature.
This normal load factor limit is unique in that traditional
airplanes with conventional flight control systems (mechanical
linkages) are limited in the pitch axis only by the elevator surface
area and deflection limit. The elevator control power is normally
derived for adequate controllability and maneuverability at the most
critical longitudinal pitching moment. The result is that traditional
airplanes have a significant portion of the flight envelope in which
maneuverability in excess of limit structural design values is
possible.
Part 25 does not require a demonstration of maneuver control or
handling qualities beyond the design limit structural loads.
Nevertheless, some pilots have become accustomed to the availability of
this excess maneuver capacity in case of extreme emergency, such as
upset recoveries or collision avoidance.
Because Dassault has chosen to include this optional design feature
on the Falcon 7X, for which part 25 does not contain adequate or
appropriate safety standards, special conditions pertaining to this
feature are included. These special conditions establish minimum load
factor requirements to ensure adequate maneuver capability during
normal flight. Other limiting features of the normal load factor
limiting function, as discussed above, that affect the upper load
limits are not addressed in these special conditions. The phrase ``in
the absence of other limiting factors'' has been added relative to past
similar special conditions to clarify that while the main focus is on
the lower load factor limits, there are other limiting factors that
must be considered in the load limiting function.
Special Condition No. 8. Flight Envelope Protection: Pitch, Roll, and
High Speed Limiting Functions
The Model Falcon 7X will incorporate pitch attitude and high speed
limiting functions via the Electronic Flight Control System (EFCS)
normal operating mode. In addition, positive spiral stability and
partial pitch compensation will be introduced in the lateral and pitch
axes through the control laws for bank angles greater than 35 degrees.
The purpose of the pitch attitude limiting function, in conjunction
with the high incidence protection function, is to prevent airplane
stall during low speed, high angle of attack excursions.
The high speed limiting protection function prevents the pilot from
inadvertently or intentionally exceeding the airplane maximum design
speeds, VD/MD. Part 25 does not address such a
function that would limit or modify flying qualities in the high speed
region.
There are no specific hard limits on the Falcon 7X for bank angle.
At bank angles up to 35 degrees, side movement of the controller
commands roll rate depending on the amount of deflection. Bank angle is
immediately accomplished by the control law function and deflection of
the control surfaces. With the stick released to its neutral point, the
airplane will maintain the commanded bank angle (neutral spiral
stability). Positive spiral stability is introduced at and above 35
degrees band angle such that a stick force is required to maintain bank
angle, and releasing the stick will return the airplane to 35 degrees.
In addition to the requirements of Sec. 25.143, this special
condition establishes requirements to ensure that pitch and high speed
limiting functions do not impede normal maneuvering and that pitch and
roll limiting functions do not restrict or prevent attaining bank
angles necessary for emergency maneuvering.
Discussion of Comments
Notice of proposed special conditions No. 25-07-06-SC for the
Dassault
[[Page 18369]]
Aviation Model Falcon 7X airplanes was published in the Federal
Register on February 26, 2007 (72 FR 8296). No comments were received,
and the special conditions are adopted as proposed.
Applicability
As discussed above, these special conditions are applicable to the
Dassault Aviation Model Falcon 7X airplanes. Should Dassault Aviation
apply at a later date for a change to the type certificate to include
another model on the same type certificate incorporating the same novel
or unusual design features, these special conditions would apply to
that model as well.
For Final Special Conditions Effective Upon Issuance
Under standard practice, the effective date of final special
conditions would be 30 days after the date of publication in the
Federal Register; however, as the certification date for the Dassault
Aviation Model Falcon 7X airplanes is imminent, the FAA finds that good
cause exists to make these special conditions effective upon issuance.
Conclusion
This action affects only certain novel or unusual design features
on model Falcon 7X airplanes. It is not a rule of general
applicability.
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 Special Conditions
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special conditions are issued as part of
the type certification basis for Dassault Aviation Model Falcon 7X
airplanes.
1. Side Stick Controllers
In the absence of specific requirements for side stick controllers,
the following special conditions apply:
a. Pilot strength: In lieu of the ``strength of pilots'' limits
shown in Sec. 25.143(c) for pitch and roll, and in lieu of the
specific pitch force requirements of Sec. Sec. 25.145(b) and
25.175(d), it must be shown that the temporary and maximum prolonged
force levels for the side stick controllers are suitable for all
expected operating conditions and configurations, whether normal or
non-normal.
b. Pilot control authority: The electronic side stick controller
coupling design must provide for corrective and/or overriding control
inputs by either pilot with no unsafe characteristics. Annunciation of
the controller status must be provided, and must not be confusing to
the flightcrew.
c. Pilot control: It must be shown by flight tests that the use of
side stick controllers does not produce unsuitable pilot-in-the-loop
control characteristics when considering precision path control/tasks
and turbulence. In addition, pitch and roll control force and
displacement sensitivity must be compatible, so that normal inputs on
one control axis will not cause significant unintentional inputs on the
other.
d. Autopilot quick-release control location: In lieu of compliance
with Sec. 25.1329(d), autopilot quick release (emergency) controls
must be on both side stick controllers. The quick release means must be
located so that it can readily and easily be used by the flightcrew.
2. Electronic Flight Control System: Lateral-Directional and
Longitudinal Stability, and Low Energy Awareness
In lieu of the requirements of Sec. Sec. 25.171, 25.173, 25.175,
and 25.177(c), the following special conditions apply:
a. The airplane must be shown to have suitable static lateral,
directional, and longitudinal stability in any condition normally
encountered in service, including the effects of atmospheric
disturbance. The showing of suitable static lateral, directional and
longitudinal stability must be based on the airplane handling
qualities, including pilot workload and pilot compensation, for
specific test procedures during the flight test evaluations.
b. The airplane must provide adequate awareness to the pilot of a
low energy (low speed/low thrust/low height) state when fitted with
flight control laws presenting neutral longitudinal stability
significantly below the normal operating speeds. ``Adequate awareness''
means warning information must be provided to alert the crew of unsafe
operating conditions and to enable them to take appropriate corrective
action.
c. The static directional stability--as shown by the tendency to
recover from a skid with the rudder free--must be positive for any
landing gear and flap position and symmetrical power condition, at
speeds from 1.13 VSR1 up to VFE, VLE,
or VFC/MFC (as appropriate).
d. In straight, steady sideslips (unaccelerated forward slips), the
rudder control movements and forces must be substantially proportional
to the angle of sideslip, and the factor of proportionality must be
between limits found necessary for safe operation throughout the range
of sideslip angles appropriate to the operation of the airplane. At
greater angles--up to the angle at which full rudder control is used or
a rudder pedal force of 180 pounds (81.72 kg) is obtained--the rudder
pedal forces may not reverse, and increased rudder deflection must
produce increased angles of sideslip. Unless the airplane has a
suitable sideslip indication, there must be enough bank and lateral
control deflection and force accompanying sideslipping to clearly
indicate any departure from steady, unyawed flight.
3. Electronic Flight Control System: Flight Control Surface Position
Awareness
In addition to the requirements of Sec. Sec. 25.143, 25.671 and
25.672, the following special conditions apply:
a. A suitable flight control position annunciation must be provided
to the crew in the following situation:
A flight condition exists in which--without being commanded by the
crew--control surfaces are coming so close to their limits that return
to normal flight and (or) continuation of safe flight requires a
specific crew action.
b. In lieu of control position annunciation, existing indications
to the crew may be used to prompt crew action, if they are found to be
adequate.
Note: The term ``suitable'' also indicates an appropriate
balance between nuisance and necessary operation.
4. Electronic Flight Control System: Flight Characteristics Compliance
Via the Handling Quantities Rating Method (HQRM)
a. Flight characteristics compliance determination for electronic
flight control system (EFCS) Failure Cases:
In lieu of compliance with Sec. 25.672(c), the HQRM contained in
Appendix 7, FAA Handling Qualities Rating Method, of the Flight Test
Guide for Certification of Transport Category Airplanes, AC 25-7A (or
an equivalent method of compliance found acceptable to the FAA), must
be used for evaluation of EFCS configurations resulting from single and
multiple failures not shown to be extremely improbable.
The handling qualities ratings are:
(1) Satisfactory: Full performance criteria can be met with routine
pilot effort and attention.
(2) Adequate: Adequate for continued safe flight and landing; full
or specified
[[Page 18370]]
reduced performance can be met, but with heightened pilot effort and
attention.
(3) Controllable: Inadequate for continued safe flight and landing,
but controllable for return to a safe flight condition, safe flight
envelope and/or reconfiguration, so that the handling qualities are at
least Adequate.
b. Handling qualities will be allowed to progressively degrade with
failure state, atmospheric disturbance level, and flight envelope, as
shown in Figure 12, ``Minimum HQ Requirements,'' of Appendix 7.
Specifically, for probable failure conditions within the normal flight
envelope, the pilot-rated handling qualities must be satisfactory in
light atmospheric disturbance and adequate in moderate atmospheric
disturbance. The handling qualities rating must not be less than
adequate in light atmospheric disturbance for improbable failures.
Note: AC 25-7A, Appendix 7 presents a method of compliance and
provides guidance for the following:
Minimum handling qualities rating requirements in
conjunction with atmospheric disturbance levels, flight envelopes,
and failure conditions (Figure 12),
Flight Envelope definition (Figures 5A, 6 and 7),
Atmospheric Disturbance Levels (Figure 5B),
Flight Control System Failure State (Figure 5C),
Combination Guidelines (Figures 5D, 9 and 10), and
General flight task list, from which appropriate
specific tasks can be selected or developed (Figure 11).
5. Flight Envelope Protection: General Limiting Requirements
a. General Requirements.
(1) Onset characteristics of each envelope protection function must
be smooth, appropriate to the phase of flight and type of maneuver, and
not in conflict with the ability of the pilot to satisfactorily change
the airplane flight path, speed, or attitude, as needed.
(2) Limit values of protected flight parameters (and if applicable,
associated warning thresholds) must be compatible with the following:
(a) Airplane structural limits,
(b) Required safe and controllable maneuvering of the airplane, and
(c) Margins to critical conditions. Dynamic maneuvering, airframe
and system tolerances (both manufacturing and in-service), and non-
steady atmospheric conditions--in any appropriate combination and phase
of flight--must not result in a limited flight parameter beyond the
nominal design limit value that would cause unsafe flight
characteristics.
(3) The airplane must be responsive to intentional dynamic
maneuvering to within a suitable range of the parameter limit. Dynamic
characteristics, such as damping and overshoot, must also be
appropriate for the flight maneuver and limit parameter in question.
(4) When simultaneous envelope limiting is engaged, adverse
coupling or adverse priority must not result.
b. Failure States: EFCS failures, including sensor failures, must
not result in a condition where a parameter is limited to such a
reduced value that safe and controllable maneuvering is no longer
available. The crew must be alerted by suitable means, if any change in
envelope limiting or maneuverability is produced by single or multiple
failures of the EFCS not shown to be extremely improbable.
6. Flight Envelope Protection: High Incidence Protection Function
a. Definitions. For the purpose of this special condition, the
following definitions apply:
Electronic Flight Control System (EFCS): The electronic and
software command and control elements of the flight control system.
High Incidence Protection Function: An airplane level function that
automatically limits the maximum angle of attack that can be attained
to a value below that at which an aerodynamic stall would occur.
Alpha Limit: The maximum angle of attack at which the airplane
stabilizes with the high incidence protection function operating and
the longitudinal control held on its aft stop.
VMIN: The minimum steady flight speed is the stabilized, calibrated
airspeed obtained when the airplane is decelerated at an entry rate not
exceeding 1 knot per second, until the longitudinal pilot control is on
its stop with the high incidence protection function operating.
VMIN1g: VMIN corrected to 1g conditions. It is the
minimum calibrated airspeed at which the airplane can develop a lift
force normal to the flight path and equal to its weight when at an
angle of attack not greater than that determined for VMIN.
b. Capability and Reliability of the High Incidence Protection
Function
(1) It must not be possible to encounter a stall during pilot
induced maneuvers, and handling characteristics must be acceptable, as
required by paragraphs e and f below, titled High Incidence Handling
Demonstrations and High Incidence Handling Characteristics
respectively.
(2) The airplane must be protected against stalling due to the
effects of environmental conditions such as windshears and gusts at low
speeds, as required by paragraph g, Atmospheric Disturbances, below.
(3) The ability of the high incidence protection function to
accommodate any reduction in stalling incidence resulting from residual
ice must be verified.
(4) The reliability of the function and the effects of failures
must be acceptable, in accordance with Sec. 25.1309 and Advisory
Circular 25.1309-1A, System Design and Analysis.
(5) The high incidence protection function must not impede normal
maneuvering for pitch angles up to the maximum required for normal
maneuvering, including a normal all-engines operating takeoff plus a
suitable margin to allow for satisfactory speed control.
c. Minimum Steady Flight Speed and Reference Stall Speed. In lieu
of the requirements of Sec. 25.103, the following special conditions
apply:
(1) VMIN: The minimum steady flight speed, for the
airplane configuration under consideration and with the high incidence
protection function operating, is the final stabilized calibrated
airspeed obtained when the airplane is decelerated at an entry rate not
exceeding 1 knot per second until the longitudinal pilot control is on
its stop.
(2) The minimum steady flight speed, VMIN, must be
determined with:
(a) The high incidence protection function operating normally.
(b) Idle thrust.
(c) All combinations of flap settings and landing gear positions.
(d) The weight used when VSR is being used as a factor
to determine compliance with a required performance standard.
(e) The most unfavorable center of gravity allowable, and
(f) The airplane trimmed for straight flight at a speed achievable
by the automatic trim system.
(3) VMIN1g is VMIN corrected to 1g
conditions. VMIN1g is the minimum calibrated airspeed at
which the airplane can develop a lift force normal to the flight path
and equal to its weight when at an angle of attack not greater than
that determined for VMIN. VMIN1g is defined as
follows:
[GRAPHIC] [TIFF OMITTED] TR12AP07.007
Where--
nzw = load factor normal to the flight path at
VMIN
(4) The Reference Stall Speed, VSR, is a calibrated
airspeed selected by the
[[Page 18371]]
applicant. VSR may not be less than the 1g stall speed.
VSR is expressed as:
[GRAPHIC] [TIFF OMITTED] TR12AP07.008
Where--
VCLMAX = Calibrated airspeed obtained when the load
factor-corrected lift coefficient
[GRAPHIC] [TIFF OMITTED] TR12AP07.009
is first a maximum during the maneuver prescribed in paragraph
(5)(h) of this special condition.
nzw = Load factor normal to the flight path at
VCLMAX
W = Airplane gross weight
S = Aerodynamic reference wing area, and
q = Dynamic pressure.
(5) VCLMAX must be determined with the following
conditions:
(a) Engines idling or--if that resultant thrust causes an
appreciable decrease in stall speed--not more than zero thrust at the
stall speed
(b) 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.
(c) The weight used when VSR is being used as a factor
to determine compliance with a required performance standard.
(d) The center of gravity position that results in the highest
value of reference stall speed.
(e) The airplane trimmed for straight flight at a speed achievable
by the automatic trim system, but not less than 1.13 VSR and
not greater than 1.3 VSR.
(f) [Reserved]
(g) The high incidence protection function adjusted to a high
enough incidence to allow full development of the 1g stall.
(h) 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.
(6) The flight characteristics at the angle of attack for
CLMAX must be suitable in the traditional sense at FWD and
AFT center of gravity in straight and turning flight at IDLE power.
Although for a normal production EFCS and steady full aft stick this
angle of attack for CLMAX cannot be achieved, the angle of
attack can be obtained momentarily under dynamic circumstances and
deliberately in a steady state sense with some EFCS failure conditions.
(7) The reference stall speed, VSR, is a calibrated
airspeed defined by the applicant. If VSR is chosen equal to
VMIN1g, an equivalent safety finding to the intent of Sec.
25.103 may be considered to have been met. The applicant may choose
VSR to be less than VMIN1g but not less than
VS1g if compensating factors are provided to ensure safe
characteristics.
d. Stall Warning.
(1) Normal Operation. If the conditions of paragraph b, Capability
and Reliability of the High Incidence Protection Function, of this
special conditions are satisfied, a level of safety equivalent to that
intended by Sec. 25.207, Stall Warning, must be considered to have
been met without provision of an additional, unique warning device.
(2) Failure Cases. Following failures of the high incidence
protection function not shown to be extremely improbable, if the
function no longer satisfies paragraph b, Capability and Reliability of
the High Incidence Protection Function, paragraphs b(1), (2), and (3)
of this special condition, stall warning must be provided in accordance
with Sec. 25.207. The stall warning should prevent inadvertent stall
under the following conditions:
(a) Power off straight stall approaches to a speed 5 percent below
the warning onset.
(b) Turning flight stall approaches with at least 1.5g load factor
normal to the flight path at entry rate of at least 2 knots per second
when recovery is initiated not less than one second after warning
onset.
e. High Incidence Handling Demonstrations. In lieu of the
requirements of Sec. 25.201, the following special conditions apply:
Maneuvers to the limit of the longitudinal control in the nose up
direction must be demonstrated in straight flight and in 30 degree
banked turns under the following conditions:
(1) The high incidence protection function operating normally.
(2) Initial power condition of:
(a) Power off.
(b) The power necessary to maintain level flight at 1.5
VSR1, where VSR1 is the reference stall speed
with the flaps in the approach position, the landing gear retracted,
and the maximum landing weight. The flap position to be used to
determine this power setting is that position in which the stall speed,
VSR1, does not exceed 110% of the stall speed,
VSR0, with the flaps in the most extended landing position.
(3) [Reserved]
(4) Flaps, landing gear and deceleration devices in any likely
combination of positions.
(5) Representative weights within the range for which certification
is requested, and
(6) The airplane trimmed for straight flight at a speed achievable
by the automatic trim system.
f. High Incidence Handling Characteristics. In lieu of the
requirements of Sec. 25.203, the following special conditions apply:
(1) In demonstrating the handling characteristics specified in
paragraphs (2), (3), (4), and (5) below, the following procedures must
be used:
(a) Starting at a speed sufficiently above the minimum steady
flight speed to ensure that a steady rate of speed reduction can be
established, apply the longitudinal control so that the speed reduction
does not exceed one knot per second until the control reaches the stop.
(b) The longitudinal control must be maintained at the stop until
the airplane has reached a stabilized flight condition and must then be
recovered by normal recovery techniques.
(c) The requirements for turning flight maneuver demonstrations
must also be met with accelerated rates of entry to the incidence
limit, up to the maximum rate achievable.
(2) Throughout maneuvers with a rate of deceleration of not more
than 1 knot per second, both in straight flight and in 30 degree banked
turns, the airplane's characteristics must be as follows:
(a) There must not be any abnormal airplane nose-up pitching.
(b) There must not be any uncommanded nose-down pitching that would
be indicative of stall. However, reasonable attitude changes associated
with stabilizing the incidence at alpha limit as the longitudinal
control reaches the stop would be acceptable. Any reduction of pitch
attitude associated with stabilizing the incidence at the alpha limit
should be achieved smoothly and at a low pitch rate, such that it is
not likely to be mistaken for natural stall identification.
(c) There must not be any uncommanded lateral or directional
motion, and the pilot must retain good lateral and directional control
by conventional use of the cockpit controllers throughout the maneuver.
(d) The airplane must not exhibit buffeting of a magnitude and
severity that would act as a deterrent to completing the maneuver.
(3) In maneuvers with increased rates of deceleration, some
degradation of characteristics is acceptable, associated with a
transient excursion beyond the stabilized alpha-limit. However, the
airplane must not exhibit dangerous characteristics or characteristics
that would deter the pilot from holding the longitudinal controller on
the stop for a
[[Page 18372]]
period of time appropriate to the maneuvers.
(4) It must always be possible to reduce incidence by conventional
use of the controller.
(5) The rate at which the airplane can be maneuvered from trim
speeds associated with scheduled operating speeds, such as
V2 and VREF, up to alpha-limit must not be unduly
damped or significantly slower than can be achieved on conventionally
controlled transport airplanes.
g. Atmospheric Disturbances. Operation of the high incidence
protection function must not adversely affect aircraft control during
expected levels of atmospheric disturbances or impede the application
of recovery procedures in case of windshear. Simulator tests and
analysis may be used to evaluate such conditions but must be validated
by limited flight testing to confirm handling qualities at critical
loading conditions.
h. [Reserved]
i. Proof of Compliance. In addition to the requirements of Sec.
25.21, the following special conditions apply:
The flying qualities must be evaluated at the most unfavorable
center of gravity position.
j. Longitudinal Control:
(1) In lieu of the requirements of Sec. 25.145(a) and (a)(1), the
following special conditions apply:
It must be possible--at any point between the trim speed for
straight flight and Vmin--to pitch the nose downward, so
that the acceleration to this selected trim speed is prompt, with:
The airplane trimmed for straight flight at the speed achievable by
the automatic trim system and at the most unfavorable center of
gravity;
(2) In lieu of the requirements of Sec. 25.145(b)(6), the
following special conditions apply:
With power off, flaps extended and the airplane trimmed at 1.3
VSR1, obtain and maintain airspeeds between Vmin
and either 1.6 VSR1 or VFE, whichever is lower.
k. Airspeed Indicating System. (1) In lieu of the requirements of
Sec. 25.1323(c)(1), the following special conditions apply:
VMO to Vmin with the flaps retracted.
(2) In lieu of the requirements of Sec. 25.1323(c)(2), the
following special conditions apply: Vmin to VFE
with flaps in the landing position.
7. Flight Envelope Protection: Normal Load Factor (g) Limiting
In addition to the requirements of Sec. 25.143(a)--and in the
absence of other limiting factors--the following special conditions
apply:
a. The positive limiting load factor must not be less than:
(1) 2.5g for the Electronic Flight Control System (EFCS) normal
state.
(2) 2.0g for the EFCS normal state with the high lift devices
extended.
b. The negative limiting load factor must be equal to or more
negative than:
(1) Minus 1.0g for the EFCS normal state.
(2) 0.0g for the EFCS normal state with high lift devices extended.
Note: This special condition does not impose an upper bound for
the normal load factor limit, nor does it require that the limit
exist. If the limit is set at a value beyond the structural design
limit maneuvering load factor ``n,'' indicated in Sec. Sec.
25.333(b) and 25.337(b) and (c), there should be a very positive
tactile feel built into the controller and obvious to the pilot that
serves as a deterrent to inadvertently exceeding the structural
limit.
8. Flight Envelope Protection: Pitch, Roll, and High Speed Limiting
Functions
In addition to Sec. 25.143, the following special conditions
apply:
a. Operation of the high speed limiter during all routine and
descent procedure flight must not impede normal attainment of speeds up
to the overspeed warning.
b. The pitch limiting function must not impede airplane
maneuvering, including an all-engines operating takeoff, for pitch
angles up to the maximum required for normal operations plus a suitable
margin in the pitch axis to allow for satisfactory speed control.
c. The high speed limiting function must not impede normal
attainment of speeds up to VMO/MMO during all
routine and descent procedure flight conditions.
d. The pitch and roll limiting functions must not restrict nor
prevent attaining bank angles up to 65 degrees and pitch attitudes
necessary for emergency maneuvering. Positive spiral stability, which
is introduced above 35 degrees bank angle, must not require excessive
pilot strength on the side stick controller to achieve bank angles up
to 65 degrees. Stick force at bank angles greater than 35 degrees must
not be so light that over-control would lead to pilot-induced
oscillations.
Issued in Renton, Washington, on April 4, 2007.
Stephen P. Boyd,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. E7-6888 Filed 4-11-07; 8:45 am]
BILLING CODE 4910-13-P