[Federal Register Volume 67, Number 67 (Monday, April 8, 2002)]
[Proposed Rules]
[Pages 16656-16664]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-7963]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM213; Notice No. 25-02-05-SC]


Special Conditions: Airbus Industrie, Model A340-500 and -600 
Series Airplanes; Interaction of Systems and Structure; Electronic 
Flight Control System, Longitudinal Stability and Low Energy Awareness; 
and Use of High Incidence Protection and Alpha-floor Systems

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.

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SUMMARY: This action proposes special conditions for the Airbus 
Industrie Model A340-500 and -600 series airplanes. These airplanes 
will have novel or unusual design features when compared to the state 
of technology envisioned in the airworthiness standards for transport 
category airplanes associated with the systems that affect the 
structural performance of the airplane; the electronic flight control 
system (EFCS); and the use of high incidence protection and alpha-floor 
systems. The applicable airworthiness regulations do not contain 
adequate or appropriate safety standards for these design features. 
These proposed 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.

DATES: Comments must be received on or before May 8, 2002.

ADDRESSES: Comments on this proposal may be mailed in duplicate to: 
Federal Aviation Administration, Transport Airplane Directorate, Attn: 
Rules Docket (ANM-113), Docket No. NM213, 1601 Lind Avenue SW., Renton, 
Washington, 98055-4056; or delivered in duplicate to the Transport 
Airplane Directorate at the above address. All comments must be marked: 
Docket No. NM213. Comments may be inspected in the Rules Docket 
weekdays, except Federal holidays, between 7:30 a.m. and 4:00 p.m.

FOR FURTHER INFORMATION CONTACT: Tim Backman, FAA, ANM-116, Transport 
Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue 
SW., Renton, Washington, 98055-4056; telephone (425) 227-2797; 
facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION:

[[Page 16657]]

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 proposal, 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 preamble between 7:30 a.m. and 4:00 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 
this proposal for special conditions in light of the 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 November 14, 1996, Airbus Industrie applied for an amendment to 
U.S. type certificate (TC) A43NM to include the new Models A340-500 and 
-600. These models are derivatives of the A340-300 airplane that is 
approved under the same TC.
    The Model A340-500 fuselage is a 6-frame stretch of the Model A340-
300 and is powered by 4 Rolls Royce Trent 553 engines, each rated at 
53,000 pounds of thrust. The airplane has interior seating arrangements 
for up to 375 passengers, with a maximum takeoff weight (MTOW) of 
820,000 pounds. The Model A340-500 is intended for long-range 
operations and has additional fuel capacity over that of the Model 
A340-600.
    The Model A340-600 fuselage is a 20-frame stretch of the Model 
A340-300 and is powered by 4 Rolls Royce Trent 556 engines, each rated 
at 56,000 pounds of thrust. The airplane has interior seating 
arrangements for up to 440 passengers, with a MTOW of 804,500 pounds.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Airbus Industrie must show 
that the Model A340-500 and -600 airplanes meet the applicable 
provisions of the regulations incorporated by reference in TC A43NM or 
the applicable regulations in effect on the date of application for the 
change to the type certificate. The regulations incorporated by 
reference in the type certificate are commonly referred to as the 
``original type certification basis.'' The regulations incorporated by 
reference in TC A43NM are 14 CFR part 25, effective February 1, 1965, 
including Amendments 25-1 through 25-63, and Amendments 25-64, 25-65, 
25-66, and 25-77, with certain exceptions that are not relevant to 
these proposed special conditions.
    In addition, if the regulations incorporated by reference do not 
provide adequate standards with respect to the change, the applicant 
must comply with certain regulations in effect on the date of 
application for the change. The FAA has determined that the Model A340-
500 and -600 airplanes must be shown to comply with Amendments 25-1 
through 25-91, and with certain FAA-allowed reversions for specific 
part 25 regulations to the part 25 amendment levels of the original 
type certification basis.
    Airbus has also chosen to comply with part 25 as amended by 
Amendments 25-92, -93, -94, -95, -97, -98, and -104. In addition, 
Airbus has elected to redefine the reference stall speed as the 1-g 
stall speed as proposed in Notice No. 95-17 (61 FR 1260, January 18, 
1996).
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25 as amended) do not contain adequate or 
appropriate safety standards for the Airbus Industrie Model A340-500 
and -600 because of a novel or unusual design feature, special 
conditions are prescribed under the provisions of Sec. 21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the Airbus Industrie Model A340-500 and -600 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.
    Special conditions, as defined in 14 CFR 11.19, are issued in 
accordance with Sec. 11.38 and become part of the type certification 
basis in accordance with Sec. 21.101(b)(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 feature, or should any other model already included on 
the same type certificate be modified to incorporate the same novel or 
unusual design feature, the special conditions would also apply to the 
other model under the provisions of Sec. 21.101(a)(1).

Novel or Unusual Design Features

    The Airbus Model A340-500 and A340-600 airplanes will incorporate 
the following novel or unusual design features.

1. Interaction of Systems and Structure

    The Model A340-500 and -600 airplanes will have systems that affect 
the structural performance of the airplane, either directly or as a 
result of a failure or malfunction. These novel or unusual design 
features are systems that can serve to alleviate loads in the airframe 
and, when in a failure state, can create loads in the airframe. The 
current regulations do not adequately account for the effects of these 
systems and their failures on structural performance. The proposed 
special conditions provide the criteria to be used in assessing the 
effects of these systems on structures.

2. Electronic Flight Control System: Longitudinal Stability and Low 
Energy Awareness

    The EFCS of the Model A340-500 and -600, as with its predecessors, 
will result in the airplanes having neutral static longitudinal 
stability. This condition, when combined with the 3 automatic trim 
feature of the EFCS, could result in insufficient feedback cues to the 
pilot of speed excursions below normal operating speeds. The 
longitudinal flight control laws provide neutral static stability 
within the normal flight envelope; therefore, the proposed novel or 
unusual design features for these new airplane model designs will make 
them unable to show compliance with the static longitudinal stability 
requirements of Secs. 25.171, 25.173, and 25.175.
    The unique features of the Model A340-500 and -600 airplanes could 
cause an unsafe condition if the airspeed becomes too slow near the 
ground and results in the airplane stalling. The flightcrew would be 
unaware of the flight condition and would not be able to intervene and 
recover before stall. The French Direction Generale De L'Aviation 
Civile (DGAC) took action for this condition by introducing a special 
condition for predecessor airplanes with the same design features that 
required adequate

[[Page 16658]]

awareness of the flightcrew to unsafe low speed conditions. This 
awareness may be provided by an appropriate warning in the cockpit to 
allow for recovery. There was no corresponding special condition 
developed by the FAA. This proposed special condition will provide for 
an appropriate warning in the cockpit of the A340-500 and -600 
airplanes to allow for recovery.
    Subsequent to certification of the predecessor Model A330 and A340 
airplanes and in establishing the certification requirements for the 
A340-500 and -600, the French DGAC decided to combine two special 
conditions from the A330 into a new special condition titled ``Static 
Longitudinal Stability and Low Energy Awareness.'' Since the FAA did 
not take action on the introduction of the low energy awareness 
requirement during the A330 and A340 certification, this proposed 
special condition for the Model A340-500 and -600 airplane 
certification will harmonize to the French DGAC special condition for 
static longitudinal stability and low energy awareness. The purpose of 
the new proposed low energy awareness special condition item 2(a)(2) is 
to provide awareness to the pilot of a low speed (or low energy state) 
of flight when the flight control laws provide neutral static 
longitudinal stability significantly below the normal operating speeds, 
and offer no cues to the pilot through the side stick controller. The 
proposed special condition item 2(a)(1) addresses the fact that the 
airplane has neutral stability and does not meet regulatory 
requirements for positive dynamic and static longitudinal stability 
(Secs. 25.171, 25.173, and 25.175, and 25.181(a)).

3. High Incidence Protection and Alpha-floor Systems

    The Model A340-500 and -600 airplanes will have a novel or unusual 
feature to accommodate the unique features of the high incidence 
protection and the alpha-floor systems. The high incidence protection 
system replaces the stall warning system during normal operating 
conditions by prohibiting the airplane from stalling. The high 
incidence protection system limits the angle of attack at which the 
airplane can be flown during normal low speed operation, impacts the 
longitudinal airplane handling characteristics, and can not be over-
ridden by the crew. The existing regulations do not provide adequate 
criteria to address this proposed system.
    The function of the alpha-floor system is to automatically increase 
the thrust on the operating engines under unusual circumstances where 
the airplane pitches to a predetermined high angle of attack or bank 
angle. The regulations do not provide adequate criteria to address this 
proposed system.

Discussion

1. Interaction of Systems and Structure

    The Model A340-500 and -600 will have systems that affect the 
structural performance of the airplane, either directly or as a result 
of failure or malfunction. These proposed special conditions provide 
the criteria to be used in assessing the effects of these systems on 
structures. The applicant, Airbus Industrie, acknowledges that 
advancements in technology led to the development of these novel and 
unusual design features. These criteria are now in the regulatory 
process and will become a new regulation, Sec. 25.302, ``Interaction of 
systems and structures,'' and a new appendix to part 25. Until the rule 
is adopted, it is necessary to apply these proposed special conditions. 
Airbus accepts and embraces these special conditions and has every 
intent of complying with them as they are presented here.
    The criteria defined herein are similar to those previously applied 
by special conditions to other fly-by-wire airplanes, including the 
Airbus A340, in Special Conditions No. 25-ANM-69, Docket No. NM-75, 
published in the Federal Register on April 15, 1993, (58 FR 19553), 
item 4. Since the issuance of the Airbus A340 special condition item 4, 
advancements in technology have occurred leading to the proposed 
Sec. 25.302, which will address the interaction of systems and 
structures, and to a revised version of the original special condition 
item 4. The FAA proposes that this new special condition apply to the 
Airbus A340-500 and -600 airplanes, in lieu of the original special 
condition.

2. Electronic Flight Control System: Longitudinal Stability and Low 
Energy Awareness

    The following special conditions are proposed in lieu of compliance 
with Secs. 25.171, 25.173, 25.175, and 25.181(a), and in lieu of the 
previously issued Special Conditions No. 25-ANM-69, Docket No. NM-75, 
published in the Federal Register on April 15, 1993 (58 FR 19553), item 
11(b), ``Flight Characteristics--Longitudinal Stability.''
    Static longitudinal stability on conventional airplanes means that 
a pull force on the controller in the pitch axis (airplane nose up) 
will result in a reduction in speed relative to the trim speed for 
straight flight, and a push force (airplane nose down) will result in 
higher than trim speed. This required characteristic of the flight 
control system, as specified in Secs. 25.171, 25.173, and 25.175, is 
intended to provide the pilot with a predictable, tactile feeling for 
increased pitch forces on the controller and to maintain trim speed 
during straight flight.
    The Model A340-500 and -600 EFCS with fly-by-wire technology has 
unique and novel design features, relative to those envisioned by 
current regulations, for controlling the airplane pitch attitude and 
flight path. Movement of the elevator surfaces in conjunction with 
movement of the cockpit controllers, is accomplished by ``electrical 
flight control laws'' contained in the flight control computer. The 
pitch control law (C*) utilizes feedback from normal load factor and 
pitch rate to provide a load factor (g) demand such that displacement 
of the controller results in a constant g maneuver where a pull force 
(nose up) is positive g, and a push force (nose down) is negative g. 
The net result of the C* law, with the integration of the automatic 
pitch trim function on the horizontal stabilizer, is that the pilot can 
command a rate of climb or descent with displacement of the controller 
and release the controller to its neutral position. The airplane rate 
of climb or descent will remain until a new command to the controller 
is given by the pilot. Furthermore, a stick-free (controller remains in 
the neutral position) deceleration/acceleration away from ``trim'' will 
result in constant 1 g straight flight with no stick forces (neutral 
static stability). As a result of this neutral stability, the Model 
A340-500 and -600 does not meet the part 25 requirements for static 
longitudinal stability as described above.
    In addition, past experience on airplanes with EFCS providing 
neutral longitudinal stability shows that there is insufficient 
feedback cue of excursion below operational speeds. Pitch limit 
protection systems of this design protect the airplane against stall 
but are not sufficient to prevent potentially hazardous low speed 
excursions because they intervene far below normal operational speeds. 
Until intervention, there are no stability cues since the airplane 
remains trimmed. Additionally, 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 situation is 
associated with a low altitude and with the engines at idle. These low 
energy situations (low speed and low engine thrust) must be

[[Page 16659]]

avoided and therefore, the pilots must be given adequate cues when 
approaching such situations. An acceptable method of compliance to this 
requirement may be provided by an appropriate warning with the 
following characteristics:
    (a) Warning must be unique, unambiguous and unmistakable.
    (b) Warning must be active at appropriate altitudes and in 
appropriate configurations.
    (c) Warning must be sufficiently timely to allow pilot 
intervention, without recourse to any aircraft automatic protection 
system.
    (d) Warning must not be triggered during normal operations, 
including operation in moderate turbulence for recommended maneuvers at 
recommended speeds.
    (e) Warning must not be cancelable by the pilot other than by 
achieving a higher energy state.
    (f) Various warnings must have an adequate hierarchy so that the 
pilot will not be confused and lead to take inappropriate recovery 
action in the event that multiple warnings occur.

3. High Incidence Protection and Alpha-floor Systems

    An initial review of the Airbus Model A330 and A340 special 
condition item 12(b), issued in Special Conditions No. 25-ANM-69, 
Docket No. NM-75, published in the Federal Register on April 15, 1993 
(58 FR 19553), compared with the corresponding French DGAC special 
condition finds that the FAA special condition item 12(b) did not 
adequately address the high incidence protection and alpha-floor 
systems, and the automatic trim feature on the A330 and A340 and on the 
Model A340-500 and -600 airplanes. Furthermore, the requirements for 
the 1-g stall speeds, which are now an equivalent safety finding (ESF), 
were embedded in the same special conditions (No. 25-ANM-69), item 
12(b), addressing high incidence protection limits. Current FAA 
procedures do not allow combining a special conditions and an ESF in 
the manner previously done for the Model A330 and A340 series 
airplanes. Therefore, this special condition addresses the high 
incidence protection and alpha-floor systems, while the requirements 
for the 1-g stall will be addressed separately as an ESF. The Model 
A330 and A340 airplanes, special condition item 12(b), therefore does 
not apply to the Model A340-500 and -600 certification program.
    The proposed special condition parallels that of the French DGAC 
for the A340-500 and -600 in presenting amendments to the appropriate 
regulations to accommodate the unique features of the high incidence 
protection systems and the alpha-floor system. The high incidence 
protection systems replaces the stall warning system during normal 
operating conditions by prohibiting the airplane from stalling.

Applicability

    As discussed above, these special conditions are applicable to the 
Model A340-500 and -600 airplanes. Should Airbus Industrie apply at a 
later date for a change to the type certificate to include another 
model incorporating the same novel or unusual design feature, the 
special conditions would apply to that model as well under the 
provisions of Sec. 21.101(a)(1).

Conclusion

    This action affects only certain novel or unusual design features 
on the Model A340-500 and -600 airplanes. It is not a rule of general 
applicability, and it affects only the applicant who 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 FAA proposes the following special conditions as 
part of the type certification basis for Airbus Industrie Model A340-
500 and -600 series airplanes.

1. Interaction of System and Structures

    The following special conditions are proposed in lieu of the 
compliance with previously issued Special Conditions No. 25-ANM-69 
(Docket No. NM-75), published in the Federal Register on April 15, 1993 
(58 FR 19553) item 4, ``Interaction of Systems and Structure.''
    (a) General. For airplanes equipped with systems that affect 
structural performance, either directly or as a result of a failure or 
malfunction, the influence of these systems and their failure 
conditions must be taken into account when showing compliance with the 
requirements of subparts C and D of part 25. The following criteria 
must be used for showing compliance with these special conditions for 
airplanes equipped with flight control systems, autopilots, stability 
augmentation systems, load alleviation systems, flutter control 
systems, and fuel management systems. If these special conditions are 
used for other systems, it may be necessary to adapt the criteria to 
the specific system.
    (1) The criteria defined herein only address the direct structural 
consequences of the system responses and performances and cannot be 
considered in isolation but should be included in the overall safety 
evaluation of the airplane. These criteria 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 that define 
acceptable limits on handling characteristics or stability requirements 
when operating in the system degraded or inoperative mode are not 
provided in these special conditions.
    (2) Depending upon the specific characteristics of the airplane, 
additional studies that go beyond the criteria provided in these 
special conditions may be required in order to demonstrate the 
capability of the airplane to meet other realistic conditions such as 
alternative gust or maneuver descriptions for an airplane equipped with 
a load alleviation system.
    (3) The following definitions are applicable to these special 
conditions.
    Structural performance: Capability of the airplane to meet the 
structural requirements of part 25.
    Flight limitations: Limitations that can be applied to the airplane 
flight conditions following an in-flight occurrence and that are 
included in the flight manual (e.g., speed limitations, avoidance of 
severe weather conditions, etc.).
    Operational limitations: Limitations, including flight limitations 
that can be applied to the airplane operating conditions before 
dispatch (e.g., fuel, payload, and Master Minimum Equipment List 
limitations).
    Probabilistic terms: The probabilistic terms (probable, improbable, 
extremely improbable) used in these special conditions are the same as 
those used in Sec. 25.1309.
    Failure condition: The term failure condition is the same as that 
used in Sec. 25.1309; however, these special conditions apply only to 
system failure conditions that affect the structural performance of the 
airplane (e.g., system failure conditions that induce loads, lower 
flutter margins, or change the response of the airplane to inputs such 
as gusts or pilot actions).
    (b) Effects of Systems on Structures. The following criteria will 
be used in determining the influence of a system and its failure 
conditions on the airplane structure.

[[Page 16660]]

    (1) System fully operative. With the system fully operative, the 
following apply:
    (i) Limit loads must be derived in all normal operating 
configurations of the system from all the limit conditions 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 nonlinearity (rate of displacement of control surface, 
thresholds or any other system nonlinearities) must be accounted for in 
a realistic or conservative way when deriving limit loads from limit 
conditions.
    (ii) The airplane must meet the strength requirements of part 25 
(static strength, 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 when it can be shown that the airplane has 
design features that will not allow it to exceed those limit 
conditions.
    (iii) The airplane must meet the aeroelastic stability requirements 
of Sec. 25.629.
    (2) System in the failure condition. For any system failure 
condition not shown to be extremely improbable, the following apply:
    (i) At the time of occurrence. Starting from 1-g level flight 
conditions, a realistic scenario, including pilot corrective actions, 
must be established to determine the loads occurring at the time of 
failure and immediately after failure.
    (A) For static strength substantiation, these loads multiplied by 
an appropriate factor of safety that is related to the 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] TP08AP02.000

    (B) For residual strength substantiation, the airplane must be able 
to withstand two thirds of the ultimate loads defined in subparagraph 
(b)(1)(i).
    (C) Freedom from aeroelastic instability must be shown up to the 
speeds defined in Sec. 25.629(b)(2). For failure conditions that result 
in speed increases beyond 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.
    (D) 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.
    (ii) For the continuation of the flight. For the airplane in the 
system failed state and considering any appropriate reconfiguration and 
flight limitations, the following apply:
    (A) The loads derived from the following conditions at speeds up to 
Vc, or the speed limitation prescribed for the remainder of the flight, 
must be determined:
    (1) The limit symmetrical maneuvering conditions specified in 
Sec. 25.331 and in Sec. 25.345.
    (2) The limit gust and turbulence conditions specified in 
Sec. 25.341 and in Sec. 25.345.
    (3) 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).
    (4) The limit yaw maneuvering conditions specified in Sec. 25.351.
    (5) The limit ground loading conditions specified in Sec. 25.473 
and Sec. 25.491.
    (B) For static strength substantiation, each part of the structure 
must be able to withstand the loads defined in subparagraph (ii)(A), 
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.

[[Page 16661]]

[GRAPHIC] [TIFF OMITTED] TP08AP02.001

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 to paragraph (B): 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.

    (C) For residual strength substantiation, the airplane must be able 
to withstand two thirds of the ultimate loads defined in subparagraph 
(2)(ii)(B).
    (D) If the loads induced by the failure condition have a 
significant effect on fatigue or damage tolerance, then their effects 
must be taken into account.
    (E) Freedom from aeroelastic instability must be shown up to a 
speed determined from Figure 3. Flutter clearance speeds VI 
and VII 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] TP08AP02.002

VI = Clearance speed as defined by Sec. 25.629(b)(2).
VII = 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 to paragraph (E): If Pj is greater than 
10-3 per flight hour, then the flutter clearance speed 
must not be less than VII.

    (F) Freedom from aeroelastic instability must also be shown up to 
V\I\ in Figure 3 above for any probable system failure condition 
combined with any damage required or selected for investigation by 
Sec. 25.571(b).
    (iii) Consideration of certain failure conditions may be required 
by other sections of part 25, regardless of calculated system 
reliability. Where 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.
    (3) Warning considerations. For system failure detection and 
warning, the following apply:
    (i) The system must be checked for failure conditions, not 
extremely improbable, that degrade the structural capability below the 
level required by part 25 or significantly reduce the reliability of 
the remaining system. 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, in lieu of 
warning systems, to achieve the objective of this requirement. These 
certification maintenance requirements must be limited to components 
that are not readily detectable by normal warning systems and where 
service history shows that inspections will provide an adequate level 
of safety.
    (ii) 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\II\, must be signaled to the crew during flight.
    (4) 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 these 
special conditions must be met for the dispatched

[[Page 16662]]

condition and for subsequent failures. 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: Longitudinal Stability and Low 
Energy Awareness

    (a) The following special conditions are proposed in lieu of 
compliance with 14 CFR Secs. 25.171, 25.173, 25.175, and 25.181(a), and 
in lieu of the previously issued Special Conditions No. 25-ANM-69 
(Docket No. NM-75), published in the Federal Register on April 15, 1993 
(58 FR 19553) item 11(b) ``Flight Characteristics--Longitudinal 
Stability.''
    (1) The airplane must be shown to have suitable dynamic and static 
longitudinal stability in any condition normally encountered in 
service, including the effects of atmospheric disturbance.
    (2) The airplane must provide adequate awareness to the pilot of a 
low energy state when flight control laws provide neutral longitudinal 
stability significantly below the normal operating speeds.

3. High Incidence Protection and Alpha-floor Systems

    (a) The following special conditions are proposed in lieu of 
compliance with certain 14 CFR sections (listed below), and in lieu of 
compliance with previously issued Special Conditions No. 25-ANM-69 
(Docket No. NM-75) published in the Federal Register on April 15, 1993 
(58 FR 19553) item 12(b), ``Flight Envelope Protection, Angle-of-Attack 
Limiting.''
    (1) The following definitions are applicable to these special 
conditions.
    High Incidence Protection System. A system that operates directly 
and automatically on the airplane's flying controls to limit the 
maximum incidence that can be attained to a value below that at which 
an aerodynamic stall would occur.
    Alpha-floor System. A system that automatically increases thrust on 
the operating engines when incidence increases through a particular 
value.
    Alpha-limit. The maximum steady incidence at which the airplane 
stabilizes with the High Incidence Protection System operating and the 
longitudinal control held on its aft stop.
    Vmin. The minimum steady flight speed, for the airplane 
configuration under consideration and with the High Incidence 
Protection System 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 controller is 
on its stop.
    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.
    (2) Capability and Reliability of the High Incidence Protection 
System: In lieu of compliance with previously issued Special Conditions 
No. 25-ANM-69, this special condition requires that acceptable 
capability and reliability of the High Incidence Protection System must 
be established by flight test, simulation, and analysis as appropriate. 
The capability and reliability required are as follows:
    (i) It shall not be possible during pilot induced maneuvers to 
encounter a stall and handling characteristics shall be acceptable, as 
required by Section 5 of this special condition.
    (ii) The airplane shall be protected against stalling due to the 
effects of windshears and gusts at low speeds as required by Section 6 
of this special condition.
    (iii) The ability of the High Incidence Protection System to 
accommodate any reduction in stalling incidence resulting from residual 
ice must be verified.
    (iv) The reliability of the system and the effects of failures must 
be acceptable in accordance with Sec. 25.1309, and the associated 
policy.
    (3) Minimum Steady Flight Speed and Reference Stall Speed. In lieu 
of Sec. 25.103 the following special conditions is proposed:
    (i) Vmin. The minimum steady flight speed, for the 
airplane configuration under consideration and with the High Incidence 
Protection System 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 control is on its 
stop.
    (ii) The Minimum Steady Flight Speed, Vmin, must be 
determined with:
    (A) The High Incidence Protection System operating normally.
    (B) Idle thrust and Alpha-floor System inhibited.
    (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.
    (iii) Vmin1 g. Vmin corrected to 1 g 
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. Vmin1g is defined as follows:
[GRAPHIC] [TIFF OMITTED] TP08AP02.003

Where:

nZW = load factor normal to the flight path at 
Vmin

    (iv) The Reference Stall Speed, VSR, is a calibrated 
airspeed defined by the applicant. VSR may not be less than 
a 1-g stall speed. VSR is expressed as:
[GRAPHIC] [TIFF OMITTED] TP08AP02.004

Where:

V CLMAX = Calibrated airspeed obtained when the load factor-
corrected lift coefficient
[GRAPHIC] [TIFF OMITTED] TP08AP02.005

is first a maximum during the maneuver prescribed in paragraph (v)(H) 
of this section.
nZW = Load factor normal to the flight path at 
VCLMAX
W = Airplane gross weight;
S = Aerodynamic reference wing area; and
q = Dynamic pressure.

    Note: Unless Angle of Attack (AOA) protection system (stall 
warning and stall identification) production tolerances are 
acceptably small, so as to produce insignificant changes in 
performance determinations, the flight test settings for stall 
warning and stall identification should be set at the low AOA 
tolerance limit; high AOA tolerance limits should be used for 
characteristics evaluations.

    (v) VSR 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.

[[Page 16663]]

    (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) The Alpha-floor system inhibited.
    (G) The High Incidence Protection System 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.
    (vi) The flight characteristics at the AOA for CLMAX 
must be suitable in the traditional sense at FWD and AFT CG in straight 
and turning flight at IDLE power. Although for a normal production EFCS 
and steady full aft stick this AOA for CLMAX cannot be 
achieved, the AOA can be obtained momentarily under dynamic 
circumstances and deliberately in a steady state sense with some EFCS 
failure conditions.

(4) Stall Warning

    (i) Normal Operation. If the conditions of Paragraph 2 are 
satisfied, equivalent safety to the intent of Sec. 25.207, Stall 
Warning, shall be considered to have been met without provision of an 
additional, unique warning device.
    (ii) Failure Cases. Following failures of the High Incidence 
Protection System, not shown to be extremely improbable, such that the 
capability of the system no longer satisfies items (i), (ii), and (iii) 
of Paragraph 2, stall warning must be provided in accordance with 
Secs. 25.207(a), (b) and (f).

(5) Handling Characteristics at High Incidence

    (i) High Incidence Handling Demonstrations. Replace the existing 
Sec. 25.201 with the following:
    (A) 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 with:
    (1) The high incidence protection system operating normally.
    (2) Initial power condition of:
    (i) Power off
    (ii) The power necessary to maintain level flight at 1.5 
VSR1, where VSR1 is the 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 percent of the stall speed, 
VSR0, with the flaps in the most extended landing position.
    (3) Alpha-floor system operating normally unless more severe 
conditions are achieved with alpha-floor inhibited.
    (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.
    (B) The following procedures must be used to show compliance with 
Sec. 25.203 as amended by this item (5)(ii) of this special condition.
    (1) 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.
    (2) 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.
    (3) 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.
    (ii) Characteristics in High Incidence Maneuvers. Replace the 
existing Sec. 25.203 with the following:
    (A) 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 shall be as follows:
    (1) There shall not be any abnormal airplane nose-up pitching.
    (2) There shall not be any uncommanded nose-down pitching, which 
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.
    (3) There shall 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.
    (4) The airplane must not exhibit severe buffeting of a magnitude 
and severity that would act as a deterrent to completing the maneuver 
specified in Sec. 25.201(a), as amended by this special condition.
    (B) 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 period of time appropriate to the maneuvers.
    (C) It must always be possible to reduce incidence by conventional 
use of the controller.
    (D) 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 shall not be unduly damped or 
significantly slower than can be achieved on conventionally controlled 
transport airplanes.

(6) Atmospheric Disturbances

    Operation of the High Incidence Protection System and the Alpha-
floor System must not adversely effect aircraft control during expected 
levels of atmospheric disturbances, nor 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.

(7) Alpha Floor

    The Alpha-floor setting must be such that the aircraft can be flown 
at normal landing operational speed and maneuvered up to bank angles 
consistent with the flight phase (including the maneuver capabilities 
specified in Sec. 25.143(g)) of the 1-g stall Equivalent Safety Finding 
without triggering Alpha-floor. In addition, there must be no Alpha-
floor triggering unless appropriate when the airplane is flown in usual 
operational maneuvers and in turbulence.

(8) Change Sec. 25.145 as follows:

    (i) It must be possible, at any point between the trim speed 
prescribed in item 3(ii)(F) of this special condition and 
Vmin, to pitch the nose downward so

[[Page 16664]]

that the acceleration to this selected trim speed is prompt with:
    (ii) The airplane trimmed at the trim speed prescribed in item 
3(ii)(F) of this special condition.
    (A) The landing gear extended;
    (B) The wing flaps retracted and extended; and
    (C) Power off and at maximum continuous power on the engines.

(9) Change Sec. 25.145(b)(6), as follows:

    With power off, flaps extended and the airplane trimmed at 1.3 
VSR1, obtain and maintain airspeeds between Vmin 
and either 1.6VSR1 or VFE, whichever is lower.

(10) Change Sec. 25.1323(c), as follows:

    (A) VMO to Vmin with the flaps retracted; and
    (B) Vmin to VFE with flaps in the landing 
position.

    Issued in Renton, Washington, on March 21, 2002.
Kalene C. Yanamura,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 02-7963 Filed 4-5-02; 8:45 am]
BILLING CODE 4910-13-U