Special Conditions: Boeing Model 767-300 and -300F Series Airplanes; Interaction of Systems and Structures, 71913-71917 [E8-28024]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 73, Number 229 (Wednesday, November 26, 2008)]
[Rules and Regulations]
[Pages 71913-71917]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-28024]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM396 Special Conditions No. 25-376-SC]


Special Conditions: Boeing Model 767-300 and -300F Series 
Airplanes; Interaction of Systems and Structures

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions; request for comments.

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SUMMARY: These special conditions are issued for the Boeing Model 767-
300 and -300F airplane as modified by Aviation Partners Boeing 
Supplemental Type Certificate (STC). The modified airplane has novel or 
unusual design features involving installation of blended winglets and 
a speedbrake wing-load-alleviation system. This system reduces loading 
on the wing. The applicable airworthiness regulations for the Boeing 
Model 767-300 and -300F do not contain adequate or appropriate safety 
standards for systems which alleviate loads on structures. 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 applicable airworthiness 
standards.

DATES: The effective date of these special conditions is November 14, 
2008. We must receive your comments by January 12, 2009.

ADDRESSES: Comments on this proposal may be mailed in duplicate to: 
Federal Aviation Administration, Transport Airplane Directorate, 
Attention: Rules Docket (ANM-113), Docket No. NM396, 1601 Lind Avenue, 
SW., Renton, Washington 98057-3356; or delivered in duplicate to the 
Transport Airplane Directorate at the above address. All comments must 
be marked Docket No. NM396. Comments may be inspected in the Rules 
Docket weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.

FOR FURTHER INFORMATION CONTACT: Ian Won, FAA, Airframe & Cabin Safety 
Branch, ANM-115, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; 
telephone (425) 227-2145; facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION: 

Comments Invited

    The FAA has determined that notice and opportunity for prior public 
comment is impracticable because these procedures would significantly 
delay certification of the airplane and thus delivery of the affected 
aircraft. In addition, the substance of these special conditions has 
been subject to the public-comment process in several prior instances 
with no substantive comments received. The FAA therefore finds that 
good cause exists for making these special conditions effective upon 
issuance; however, the FAA invites interested persons to participate in 
this rulemaking by submitting written comments, data, or views. The 
most helpful comments reference a specific portion of the special 
conditions, explain the reason for any recommended change, and include 
supporting data. We ask that you send us two copies of written 
comments.
    We will file in the docket all comments we receive, as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning these 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 p.m., Monday through Friday, 
except Federal holidays.
    We consider all comments we receive on or before the closing date 
for comments. We consider comments filed late if it is possible to do 
so without incurring expense or delay. We may change these special 
conditions based on the comments we receive.
    If you want the FAA to acknowledge receipt of your comments on 
these special conditions, include with your comments a self-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 February 21, 2007, Aviation Partners Boeing, Seattle, WA, 
applied for an STC to modify Boeing Model 767-300 and -300F series 
airplanes. These models are currently approved under Type Certificate 
No. A1NM. The Boeing Model 767-300 and 767-300F series airplanes are 
large transport-category airplanes. The Model 767-300 airplane is 
powered by either two Pratt

[[Page 71914]]

& Whitney or two General Electric engines. The Model 767-300F airplane 
is powered by two General Electric engines. The Boeing Model 767-300 
airplane carries a maximum of 351 passengers. The Boeing Model 767-300F 
airplane is a freighter configuration.
    The Boeing Model 767-300 and -300F airplanes, as modified by 
Aviation Partners Boeing, feature a wing-load-alleviation system which 
precludes full deployment of the speedbrakes given certain aircraft 
weights and airspeeds, thereby reducing wing loading. Special 
conditions have been applied on past airplane programs to require 
consideration of the effects of systems on structures. Current 
regulations do not take into account the effects of system failures on 
aircraft loads. A special condition is needed to account for these 
effects. These special conditions define the necessary requirements for 
assessing the effects of the speedbrake wing-load alleviation system on 
structures.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Aviation Partners Boeing 
must show that the Boeing Model 767-300 and -300F series airplanes, as 
changed, continue to meet the applicable provisions of the regulations 
incorporated by reference in Type Certificate No. A1NM, or the 
applicable regulations in effect on the date of application for the 
change. The regulations incorporated by reference in the type 
certificate are commonly referred to as the ``original type 
certification basis.'' The certification basis for Boeing Model 767-300 
and -300F series airplanes includes applicable sections of 14 CFR part 
25, as amended by Amendments 25-1 through 25-37, with some later 
amendments as noted in Type Certificate No. AINM. In addition, the 
certification basis includes certain special conditions, exemptions, 
equivalent levels of safety, or later amended sections of the 
applicable part 25 that are not relevant to these special conditions.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25, as amended) do not contain adequate or 
appropriate safety standards for Boeing Model 767-300 and -300F series 
airplanes 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 Boeing Model 767-300 and -300F series airplanes 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.
    Special conditions are initially applicable to the model for which 
they are issued. Should Aviation Partners Boeing apply at a later date 
for an STC to modify any other model included on Type Certificate No. 
A1NM to incorporate the same or similar novel or unusual design 
feature, these special conditions would also apply to the other model 
under the provisions of Sec. 21.101.

Novel or Unusual Design Features

    The Boeing Model 767-300 and -300F, as modified by Aviation 
Partners Boeing, incorporates the following novel or unusual design 
features:
    Blended winglets are installed on the wing tips. To reduce the 
structural loading of the 767-300 and 767-300F with Aviation Partners 
Boeing blended winglets, a wing-load-alleviation system will be used 
that limits the speedbrake deflection under certain conditions. The 
regulations do not provide adequate criteria governing the safety 
margins required for systems that affect design loads when they fail.
    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 14 CFR part 25 Subparts C and D.
    The following criteria must be used for showing compliance with 
this special condition for airplanes equipped with flight-control 
systems, autopilots, stability-augmentation systems, load-alleviation 
systems, flutter-control systems, fuel-management systems, and other 
systems that either directly, or as a result of failure or malfunction, 
affect structural performance. If this special condition is used for 
other systems, it may be necessary to adapt the criteria to the 
specific system.
    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 this special condition.
    Depending upon the specific characteristics of the airplane, 
additional studies may be required that go beyond the criteria provided 
in this special condition 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 wing-load-alleviation 
system.
    The following definitions are applicable to this special condition.
    1. Structural performance: Capability of the airplane to meet the 
structural requirements of 14 CFR 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 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 this special condition 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, this special condition applies 
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).

Applicability

    As discussed above, these special conditions are applicable to 
Boeing Model 767-300 and -300F airplanes modified by Aviation Partners 
Boeing. Should Aviation Partners Boeing apply at a later date for an 
STC to modify any other model included on Type Certificate No. A1NM, to 
incorporate the same or similar novel or unusual design feature, these 
special conditions would apply to that model as well under the 
provisions of Sec. 21.101.

Conclusion

    This action affects only certain novel or unusual design features 
on Boeing Model 767-300 and -300F series

[[Page 71915]]

airplanes modified by Aviation Partners Boeing. It is not a rule of 
general applicability and affects only the applicant who applied to the 
FAA for approval of these features on the airplane.
    The substance of these special conditions has been subjected to the 
notice and comment procedure in several prior instances and has been 
derived without substantive change from those previously issued. 
Because a delay would significantly affect the certification of the 
airplane, which is imminent, the FAA has determined that prior public 
notice and comment are unnecessary and impracticable, and good cause 
exists for adopting these special conditions upon issuance. The FAA is 
requesting comments to allow interested persons to submit views that 
may not have been submitted in response to the prior opportunities for 
comment described above.

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

0
Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special conditions are issued as part of 
the STC basis for the Boeing Model 767-300 and -300F series airplanes 
modified by Aviation Partners Boeing.
    1. General. The following criteria will be used in determining the 
influence of a system and its failure conditions on the airplane 
structure.
    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 defined by special condition or equivalent level of 
safety 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 
(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 
that 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 do 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 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.
    (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 (FS) is defined in Figure 1.
[GRAPHIC] [TIFF OMITTED] TR26NO08.005

    Factor of safety at the time of occurrence(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 increase 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 primary structure.
    (b) 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:
    (1) The loads derived from the following conditions (or defined by 
special condition or equivalent level of safety in lieu of the 
following conditions) at speeds up to VC/MC, or 
the speed limitation prescribed for the

[[Page 71916]]

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
    (iv) The limit-unsymmetrical conditions specified in Sec.  25.367 
and Sec.  25.427(b) and (c).
    (v) The limit-yaw-maneuvering conditions specified in Sec.  25.351.
    (vi) The limit-ground-loading conditions specified in Sec. Sec.  
25.473 and 25.491.
    (2) For static-strength substantiation, each part of the structure 
must be able to withstand the loads in paragraph 3(b)(1) of the special 
condition multiplied by a factor of safety depending on the probability 
of being in this failure state. The factor of safety is defined in 
Figure 2.
[GRAPHIC] [TIFF OMITTED] TR26NO08.006

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)(2) of the 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).
[GRAPHIC] [TIFF OMITTED] TR26NO08.007

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).

[[Page 71917]]

    (c) Consideration of certain failure conditions may be required by 
other sections of 14 CFR 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 must be limited to components that are not readily 
detectable by normal detection-and-indication systems and where service 
history shows that inspections 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 1E-3 per hour.

    Issued in Renton, Washington, on November 14, 2008.
Stephen P. Boyd,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. E8-28024 Filed 11-25-08; 8:45 am]
BILLING CODE 4910-13-P