[Federal Register: November 26, 2008 (Volume 73, Number 229)]
[Rules and Regulations]
[Page 71913-71917]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr26no08-2]
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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