Special Conditions: Boeing Commercial Airplanes, Model 767-2C Airplane; Interaction of Fuel Systems and Structures, 63302-63305 [2014-25242]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 79, Number 205 (Thursday, October 23, 2014)]
[Rules and Regulations]
[Pages 63302-63305]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2014-25242]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2014-0421; Special Conditions No. 25-571-SC]


Special Conditions: Boeing Commercial Airplanes, Model 767-2C 
Airplane; Interaction of Fuel 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 767-
2C 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 the addition of four body fuel tanks and a modified 
fuel management system that, directly or as a result of failure or 
malfunction, could affect the airplane's structural performance. 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.

DATES: Effective Date: This action is effective on November 24, 2014.

FOR FURTHER INFORMATION CONTACT: Mark Freisthler, FAA, Airframe and 
Cabin Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-
3356; telephone 425-227-1119; facsimile 425-227-1232.

SUPPLEMENTARY INFORMATION: 

Background

    On January 18, 2010, Boeing Commercial Airplanes applied for an 
amendment to Type Certificate No. A1NM to include the new Model 767-2C. 
The Boeing Model 767-2C, which is a derivative of the Model 767-200 
currently approved under Type Certificate No. A1NM, is a transport 
category airplane, intended for use as a freighter, powered by two 
PW4062 engines with a maximum takeoff weight of 415,000 pounds.
    The Boeing Model 767-2C will have more fuel capacity than a 
traditional freighter through the addition of four body fuel tanks. The 
Model 767-2C contains fuel systems that could, directly or as a result 
of failure or malfunction, affect the aircraft's structural 
performance. Current regulations do not take into account loads for the 
airplane due to the effects of fuel system failures on structural 
performance; therefore, special conditions are needed.

Type Certification Basis

    Under the provisions of Title 14, Code of Federal Regulations (14 
CFR) 21.101, Boeing must show that the Model 767-2C meets the 
applicable provisions of 14 CFR part 25, as amended by Amendments 25-0 
through 25-130, except for earlier amendments as agreed upon by the 
FAA. These regulations will be incorporated into Type Certificate No. 
A1NM after type certification approval of the Model 767-2C.
    In addition, the certification basis includes other regulations, 
special conditions, and exemptions that are not relevant to these 
special conditions. Type Certificate No. A1NM will be updated to 
include a complete description of the certification basis for these 
model airplanes.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for the Model 767-2C because of a novel or 
unusual design feature, special conditions are prescribed under the 
provisions of Sec.  21.16.
    Special conditions are initially applicable to the model for which 
they are issued. Should the type certificate for that model be amended 
later to include any other model that incorporates the same or similar 
novel or unusual design feature, or should any other model already 
included on the same type certificate be modified to incorporate the 
same or similar novel or unusual design feature, the special conditions 
would also apply to the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the Model 767-2C 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 14 CFR 11.19, in 
accordance with Sec.  11.38, and they become part of the type-
certification basis under Sec.  21.101.

Novel or Unusual Design Features

    The Boeing Model 767-2C will incorporate the following novel or 
unusual design features: Fuel system changes including the addition of 
forward and aft body fuel tanks, a main-to-center-tank gravity transfer 
system, hydraulically-powered-pumps for jettison, a nitrogen generation 
system for inerting of all fuel tanks, and a pressure-regulating closed 
fuel tank vent system. Digital electronic controls (i.e., fuel 
management systems) are added for control and monitoring of these 
systems.

Discussion

    The fuel management system is designed to keep the fuel distributed 
in accordance with fuel usage requirements. System failures of these 
new and modified systems may result in adverse fuel distributions or 
center-of-gravity excursions that increase the airplane loads. For 
example, a failure of the main tank gravity drain valve may result in 
less wing main tank fuel than normal management; or failure of the body 
auxiliary tank transfer systems may result in excessive body fuel at 
landing. Additionally, failures of the nitrogen generation system, fuel 
transfer system, or vent/pressure regulating system may result in 
excessive fuel tank pressures. These types of failures are addressed by 
these special conditions.
    Special conditions have been applied on past airplane programs in 
order to require consideration of the effects of systems on structures. 
These special conditions are similar to those previously applied except 
that the scope is limited to new fuel system features unique to the 
Model 767-2C. These

[[Page 63303]]

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.

Discussion of Comments

    Notice of proposed special conditions No. 25-14-07-SC for the 
Boeing Model 767-2C airplane was published in the Federal Register on 
July 2, 2014 (79 FR 37670). No comments were received, and the special 
conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
Boeing Model 767-2C airplane. Should Boeing Commercial Airplanes 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.

Conclusion

    This action affects only certain novel or unusual design features 
on one model of airplanes. It is not a rule of general applicability.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.


0
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 Boeing Commercial Airplanes Model 767-
2C airplane.
    1. Interactions of fuel systems and structures. General.
    a. For airplanes equipped with fuel 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 14 CFR part 25 subparts C and D.
    b. The criteria in Section 2 below must be used for showing 
compliance with these special conditions for airplanes equipped with 
fuel systems that either directly or as a result of failure or 
malfunction affect structural performance.
    c. The criteria 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 these special conditions.
    d. Depending on the specific characteristics of the airplane, 
additional studies may be required that 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.
    e. The following definitions are applicable to these special 
conditions:
    (1) Structural performance: Capability of the airplane to meet the 
structural requirements of part 25.
    (2) Flight limitations: Limitations that can be applied to the 
airplane flight conditions following an in-flight occurrence and that 
are included in the airplane flight manual (e.g., speed limitations, 
avoidance of severe weather conditions, etc.).
    (3) 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).
    (4) Probabilistic terms: The probabilistic terms (probable, 
improbable, extremely improbable) used in these special conditions are 
the same as those used in Sec.  25.1309.
    (5) 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 
conditions include consequential or cascading effects resulting from 
the first failure.
    2. Effects of Fuel System Failure on Structures. The following 
criteria will be used in determining the influence of the fuel system 
and its failure conditions on the airplane structural elements.
    a. Fuel system fully operative. With the fuel system fully 
operative, the following apply:
    (1) Limit loads must be derived in all normal operating 
configurations of the fuel 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 fuel transfer, thresholds or any 
other system nonlinearities) must be accounted for in a realistic or 
conservative way when deriving limit loads from limit conditions.
    (2) The airplane must meet the strength requirements of part 25 
(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.
    (3) The airplane must meet the aeroelastic stability requirements 
of Sec.  25.629.
    b. Fuel system in the failure condition. For any fuel system 
failure condition not shown to be extremely improbable, the following 
apply:
    (1) 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.
    (i) 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 is defined in Figure 1.

[[Page 63304]]

[GRAPHIC] [TIFF OMITTED] TR23OC14.000

    (ii) For residual strength substantiation, the airplane must be 
able to withstand two thirds of the ultimate loads defined in 
subparagraph 2b(1)(i). For pressurized cabins, these loads must be 
combined with the normal operating differential pressure.
    (iii) Freedom from aeroelastic instability must be shown up to the 
speeds defined in Sec.  25.629(b)(2). For failure conditions that 
result in speeds beyond VC/MC, freedom from 
aeroelastic instability must be shown to increased speeds, so that the 
margins intended by Sec.  25.629(b)(2) are maintained.
    (iv) Failures of the fuel system that result in forced structural 
vibrations (oscillatory failures) must not produce loads that could 
result in detrimental deformation of the affected structural elements.
    (2) For continuation of flight, for an airplane in the system 
failed state and considering any appropriate reconfiguration and flight 
limitations, the following apply:
    (i) 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:
    (A) The limit symmetrical maneuvering conditions specified in 
Sec. Sec.  25.331 and 25.345.
    (B) The limit gust and turbulence conditions specified in 
Sec. Sec.  25.341 and 25.345.
    (C) The limit rolling conditions specified in Sec.  25.349 and the 
limit unsymmetrical conditions specified in Sec. Sec.  25.367 and 
25.427(b) and (c).
    (D) The limit yaw maneuvering conditions specified in Sec.  25.351.
    (E) The limit ground loading conditions specified in Sec. Sec.  
25.473, 25.491, and 25.493.
    (ii) For static strength substantiation, each part of the structure 
must be able to withstand the loads in paragraph 2b(2)(i) of these 
special conditions 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] TR23OC14.001

    (iii) For residual strength substantiation, the airplane must be 
able to withstand two thirds of the ultimate loads defined in paragraph 
2b(2)(ii) of these special conditions. For pressurized cabins, these 
loads must be combined with the normal operating differential pressure.
    (iv) If the loads induced by the failure condition have a 
significant effect on fatigue or damage tolerance, then their effects 
must be taken into account.
    (v) Freedom from aeroelastic instability must be shown up to a 
speed determined from Figure 3. Flutter clearance speeds V' and V'' may 
be based on the speed limitation specified

[[Page 63305]]

for the remainder of the flight using the margins defined by Sec.  
25.629(b).
[GRAPHIC] [TIFF OMITTED] TR23OC14.002

    (vi) Freedom from aeroelastic instability must also be shown up to 
V' in Figure 3 above, for any probable system failure condition 
combined with any damage required or selected for investigation by 
Sec.  25.571(b).
    (3) Consideration of certain failure conditions may be required by 
other sections of 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.
    c. Failure indications. For fuel system failure detection and 
indication, the following apply:
    (1) The fuel 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 fuel 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 identified inspections 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.
    (2) The existence of any failure condition, not extremely 
improbable, during flight that could significantly affect the 
structural capability of the airplane and for which the associated 
reduction in airworthiness can be minimized by suitable flight 
limitations, requires a caution level alert for immediate flightcrew 
awareness and a warning level alert for immediate flightcrew awareness 
and corrective action. For example, a flightcrew alert during flight is 
required for 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'', because it could significantly affect the 
structural capability of the airplane.
    d. Dispatch with known failure conditions. If the airplane is to be 
dispatched in a known fuel 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, including the provisions of paragraph 
2a for the dispatched condition, and paragraph 2b 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 October 16, 2014.
Michael Kaszycki,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2014-25242 Filed 10-22-14; 8:45 am]
BILLING CODE 4910-13-P