Special Conditions: Boeing Model 747-8/-8F Airplanes; Interaction of Systems and Structures, 40479-40482 [E9-19246]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 74, Number 154 (Wednesday, August 12, 2009)]
[Rules and Regulations]
[Pages 40479-40482]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E9-19246]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM400; Special Conditions No. 25-388-SC]


Special Conditions: Boeing Model 747-8/-8F Airplanes; Interaction 
of Systems and Structures

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Boeing Model 747-
8/-8F airplanes. These airplanes will have a novel or unusual design 
feature(s) that will affect structural performance. The applicable 
airworthiness regulations do not contain adequate or appropriate safety 
standards for this design feature. 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.

DATES: Effective Date: September 11, 2009.

FOR FURTHER INFORMATION CONTACT: Mark Freisthler, FAA, Airframe & Cabin 
Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue, SW., Renton, Washington 98057-
3356; telephone (425) 227-1119; facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION:

Background

    On November 4, 2005, The Boeing Company, PO Box 3707, Seattle, WA 
98124, applied for an amendment to Type Certificate Number A20WE to 
include the new Model 747-8 passenger airplane and the new Model 747-8F 
freighter airplane. The Model 747-8 and the Model 747-8F are 
derivatives of the 747-400 and the 747-400F, respectively. Both the 
Model 747-8 and the Model 747-8F are four-engine jet transport 
airplanes that will have a maximum takeoff weight of 970,000 pounds and 
new General Electric GEnx-2B67 engines. The Model 747-8 will have two 
flight crew and the capacity to carry 660 passengers. The Model 747-8F 
will have two flight crew and a zero passenger capacity, although 
Boeing has submitted a petition for exemption to allow the carriage of 
supernumeraries.

Type Certification Basis

    Under the provisions of Title 14 Code of Federal Regulations (14 
CFR) 21.101, Boeing must show that the Model 747-8 and 747-8F airplanes 
(hereafter referred to as the 747-8/-8F) as changed, continue to meet 
the applicable provisions of 14 CFR part 25, as amended by Amendments 
25-1 through 25-117, except for earlier amendments as agreed upon by 
the FAA. These regulations will be incorporated into Type Certificate 
No. A20WE after type certification approval of the 747-8/-8F.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25) do not contain adequate or appropriate 
safety standards for the 747-8/-8F 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 747-8/-8F 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 Sec.  11.19, are issued under 
Sec.  11.38, and become part of the type certification basis under 
Sec.  21.101.
    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 Sec.  21.101.

Novel or Unusual Design Features

    The Boeing Model 747-8/-8F is equipped with systems that affect the 
airplane's structural performance, either directly or as a result of 
failure or malfunction. That is, the airplane's systems affect how it 
responds in maneuver and gust conditions, and thereby affect its 
structural capability. These systems may also affect the aeroelastic 
stability of the airplane. Such systems represent a novel and unusual 
feature when compared to the technology envisioned in the current 
airworthiness standards. A special condition is needed to require 
consideration of the effects of systems on the structural capability 
and aeroelastic stability of the airplane, both in the normal and in 
the failed state.
    These special conditions require that the airplane meet the 
structural requirements of subparts C and D of 14 CFR part 25 when the 
airplane systems are fully operative. These special conditions also 
require that the airplane meet these requirements considering failure 
conditions. In some cases, reduced margins are allowed for failure 
conditions based on system reliability.

Discussion of Comments

    Notice of proposed special conditions No. 25-09-03-SC for the 
Boeing Model 747-8 and 747-8F airplanes was published in the Federal 
Register on April 8, 2009 (74 FR 15888). No comments were received and 
the special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to 
Boeing Model 747-8/-8F airplanes. Should Boeing apply at a later date 
for a change to the type certificate to include another model 
incorporating the same novel or unusual design features, the special 
conditions would apply to that model as well.

Conclusion

    This action affects only certain novel or unusual design features 
of the Boeing Model 747-8/-8F 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.

[[Page 40480]]

The Special Conditions

A. General

    The Boeing Model 747-8/8F airplane is equipped with automatic 
control systems that affect the airplane's 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, fuel management 
systems, and other systems that either directly or as a result of 
failure or malfunction affect structural performance. 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 here 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 structural elements 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 this special condition.
    2. Depending on the specific characteristics of the airplane, 
additional studies may be required that go beyond the criteria provided 
in these special conditions 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.
    (a) Structural performance: Capability of the airplane to meet the 
structural requirements of part 25.
    (b) Flight limitations: Limitations that can be applied to the 
airplane flight conditions following an in-flight occurrence and that 
are included in the Airplane Flight Manual (AFM) (e.g., speed 
limitations, avoidance of severe weather conditions).
    (c) 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 
(MMEL) limitations).
    (d) Probabilistic terms: The probabilistic terms (probable, 
improbable, extremely improbable) used in these special conditions are 
the same as those used in Sec.  25.1309.
    (e) 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, change 
the response of the airplane to inputs such as gusts or pilot actions, 
or lower flutter margins). The system failure condition includes 
consequential or cascading effects resulting from the first failure.

B. Effects of Systems on Structures

    1. General. The following criteria will be used in determining the 
influence of a system and its failure conditions on the airplane 
structural elements.
    2. System fully operative. With the system fully operative, the 
following apply:
    (a) Limit loads must be derived in all normal operating 
configurations of the system from all the limit conditions specified in 
subpart C (or used in lieu of those specified in subpart C), taking 
into account any special behavior of such a system or associated 
functions or any effect on the structural performance of the airplane 
that may occur up to the limit loads. In particular, any significant 
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.
    (b) The airplane must meet the strength requirements of part 25 
(i.e., 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.
    (c) The airplane must meet the aeroelastic stability requirements 
of Sec.  25.629.
    3. System in the failure condition. For any system failure 
condition not shown to be extremely improbable, the following apply:
    (a) At the time of occurrence, starting from 1g 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.
    (1) 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 (F.S.) is defined in Figure 1.

[[Page 40481]]

[GRAPHIC] [TIFF OMITTED] TR12AU09.000

    (2) For residual strength substantiation, the airplane must be able 
to withstand two thirds of the ultimate loads defined in subparagraph 
3(a)(1). For pressurized cabins, these loads must be combined with the 
normal operating differential pressure.
    (3) Freedom from aeroelastic instability must be shown up to the 
speeds defined in Sec.  25.629(b)(2). For failure conditions that 
result in speeds beyond 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.
    (4) Failures of the system that result in forced structural 
vibrations (oscillatory failures) must not produce loads that could 
result in detrimental deformation of the affected structural elements.
    (b) For continuation of flight, for an airplane in the system 
failed state and considering any appropriate reconfiguration and flight 
limitations, the following apply:
    (1) The loads derived from the following conditions (or used in 
lieu of the following conditions) at speeds up to VC/
MC, or the speed limitation prescribed for the remainder of 
the flight, must be determined:
    (i) The limit symmetrical maneuvering conditions specified in Sec.  
25.331 and in Sec.  25.345.
    (ii) The limit gust and turbulence conditions specified in Sec.  
25.341 and in Sec.  25.345.
    (iii) The limit rolling conditions specified in Sec.  25.349 and 
the limit asymmetrical conditions specified in Sec. Sec.  25.367 and 
25.427(b) and (c).
    (iv) The limit yaw maneuvering conditions specified in Sec.  
25.351.
    (v) The limit ground loading conditions specified in Sec. Sec.  
25.473, 25.491 and 25.493.
    (2) For static strength substantiation, each part of the structure 
must be able to withstand the loads in paragraph (3)(b)(1) of this 
special condition multiplied by a factor of safety depending on the 
probability of being in this failure state. The factor of safety is 
defined in Figure 2.
[GRAPHIC] [TIFF OMITTED] TR12AU09.001

Qj = (Tj)(Pj) where:
Tj = Average time spent in failure condition j (in hours)
Pj = Probability of occurrence of failure mode j (per 
hour)

    Note: If Pj is greater than 10-3 per 
flight hour then a 1.5 factor of safety must be applied to all limit 
load conditions specified in Subpart C.

    (3) For residual strength substantiation, the airplane must be able 
to withstand two thirds of the ultimate loads defined in paragraph 
(3)(b)(1) of this special condition. For pressurized cabins, these 
loads must be combined with the normal operating differential pressure.
    (4) 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.
    (5) Freedom from aeroelastic instability must be shown up to a 
speed determined from Figure 3. Flutter clearance speeds V' and V'' may 
be based on the speed limitation specified for the remainder of the 
flight using the margins defined by Sec.  25.629(b).

[[Page 40482]]

[GRAPHIC] [TIFF OMITTED] TR12AU09.002

V' = Clearance speed as defined by Sec.  25.629(b)(2).
V'' = Clearance speed as defined by Sec.  25.629(b)(1).
Qj = (Tj)(Pj) where:
Tj = Average time spent in failure condition j (in hours)
Pj = Probability of occurrence of failure mode j (per 
hour)

    Note: If Pj is greater than 10-3 per 
flight hour, then the flutter clearance speed must not be less than 
V''.

    (6) Freedom from aeroelastic instability must also be shown up to 
V' in Figure 3 above, for any probable system failure condition 
combined with any damage required or selected for investigation by 
Sec.  25.571(b). 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.
    4. Failure indications. For system failure detection and 
indication, the following apply:
    (a) 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. As far as reasonably practicable, the flight crew 
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 detection and indication systems to achieve 
the objective of this requirement. These Certification Maintenance 
Requirements (CMRs) must be limited to components that are not readily 
detectable by normal detection and indication systems and where service 
history shows that inspections will provide an adequate level of 
safety.
    (b) 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 flight crew. For example, failure 
conditions that result in a factor of safety between the airplane 
strength and the loads of subpart C below 1.25, or flutter margins 
below V'', must be signaled to the crew during flight.
    5. Dispatch with known failure conditions. If the airplane is to be 
dispatched in a known system failure condition that affects structural 
performance, or affects the reliability of the remaining system to 
maintain structural performance, then the provisions of this special 
condition must be met, including the provisions of paragraph 2 for the 
dispatched condition, and paragraph 3 for subsequent failures. Expected 
operational limitations may be taken into account in establishing Pj as 
the probability of failure occurrence for determining the safety margin 
in Figure 1. Flight limitations and expected operational limitations 
may be taken into account in establishing Qj as the combined 
probability of being in the dispatched failure condition and the 
subsequent failure condition for the safety margins in Figures 2 and 3. 
These limitations must be such that the probability of being in this 
combined failure state and then subsequently encountering limit load 
conditions is extremely improbable. No reduction in these safety 
margins is allowed if the subsequent system failure rate is greater 
than 10-3 per hour.

    Issued in Renton, Washington, on July 29, 2009.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E9-19246 Filed 8-11-09; 8:45 am]
BILLING CODE 4910-13-P