[Federal Register: October 31, 2006 (Volume 71, Number 210)]
[Proposed Rules]
[Page 63718-63722]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr31oc06-19]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM357; Notice No. 25-06-11-SC]
Special Conditions: Boeing Model 737-900ER Series Airplanes;
Interaction of Systems and Structures
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed special conditions.
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SUMMARY: This action proposes a special condition for the Boeing Model
737-900ER airplane. This airplane will have a novel or unusual design
feature(s) when compared to the state of technology envisioned in the
airworthiness standards for transport category airplanes. These design
features include interaction of systems and structures. The applicable
airworthiness regulations do not contain adequate or appropriate safety
standards for this design feature. The proposed special condition
contains 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: We must receive your comments by November 20, 2006.
ADDRESSES: You must mail two copies of your comments to: Federal
Aviation Administration, Transport Airplane Directorate, Attn: Rules
Docket (ANM-113), Docket No. NM357, 1601 Lind Avenue, SW., Renton,
Washington, 98057-3356. You may deliver two copies to the Transport
Airplane Directorate at the above address. You must mark your comments:
Docket No. NM357. You can inspect comments in the Rules Docket
weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.
FOR FURTHER INFORMATION CONTACT: Todd Martin, Aerospace Engineer,
Airframe/Cabin Safety Branch, ANM-115, Transport Airplane Directorate,
Aircraft Certification Service, 1601 Lind Avenue, SW., Renton,
Washington 98057-3356; telephone (425) 227-1178; facsimile (425) 227-
1323; electronic mail Todd.Martin@faa.gov.
SUPPLEMENTARY INFORMATION:
Comments Invited
We invite interested people to take part in this rulemaking by
sending written comments, data, or views. The most helpful comments
reference a specific portion of the special condition, 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 this special condition. You can inspect the docket 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 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 special condition based on 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 June 5, 2002, The Boeing Company, P.O. Box 3707, Seattle,
Washington 98124, applied for an amendment to Type Certificate No.
A16WE to include the new Model 737-900ER. The Model 737-900ER, which is
a derivative of the Model 737-900 currently approved under A16WE, is a
large transport airplane with two flight crew and the capacity to carry
215 passengers. The airplane is powered by two CFM 56-7B or CFM-567B/2
series turbofan engines.
Type Certification Basis
Under the provisions of Sec. 21.101, Boeing must show that the
Model 737-900ER meets the applicable provisions of 14 CFR part 25, as
amended by Amendments 25-1 through 25-108, except for earlier
amendments as agreed upon by the FAA. These regulations will be
incorporated into the Type Certificate No. A16WE after type
certification approval of the 737-900ER.
In addition, the certification basis includes other regulations,
special conditions and exemptions that are not relevant to this
proposed special condition. Refer to Type Certificate No. A16WE for a
complete description of the certification basis for this model
airplane.
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 737-900ER 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 Model 737-900ER 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 Sec. 11.19, under
Sec. 11.38, and they 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 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.
Novel or Unusual Design Features
Model 737-900ER airplane will incorporate novel or unusual design
features. This proposed special condition addresses equipment which may
affect the airplane's structural performance, either directly or as a
result of failure or malfunction.
This proposed special condition is identical or nearly identical to
those previously required for type certification of other Boeing
airplane models. The proposed special condition was derived initially
from standardized requirements developed by the Aviation Rulemaking
Advisory Committee (ARAC), comprised of representatives of the FAA,
Europe's Joint Aviation Authorities (now replaced by the European
Aviation Safety Agency), and industry.
Discussion
In addition to the requirements of part 25, subparts C and D, the
following special condition applies.
Interaction of Systems and Structures
The Boeing Model 737-900ER is equipped with systems that may affect
the airplane's structural performance either directly or as a result of
failure or malfunction. The effects of these systems on structural
performance must be considered in the certification analysis. This
analysis must include consideration of normal operation and of failure
conditions with required
[[Page 63719]]
structural strength levels related to the probability of occurrence.
Applicability
As discussed above, this special condition is applicable to the
Boeing Model 737-900ER. 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 feature, this special condition would
apply to that model as well.
Certification of the Model 737-900ER is currently scheduled for
February 2007. Because a delay would significantly affect the
applicant's installation of the systems and certification of the
airplane we are shortening the public comment period to 20 days.
Conclusion
This action affects only certain novel or unusual design features
on one model of airplane. 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.
The Proposed Special Condition
Accordingly, the Federal Aviation Administration (FAA) proposes the
following special condition as part of the type certification basis for
Boeing Model 737-900ER airplanes.
Interaction of Systems and Structures
In addition to the requirements of part 25, subparts C and D, the
following proposed special condition would apply:
a. 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 part 25, subparts C and D. Paragraph b, below, must be
used to evaluate the structural performance of airplanes equipped with
these systems.
b. Interaction of Systems and Structures.
(1) General: The following criteria must be used for showing
compliance with this special condition for interaction of systems and
structures and with Sec. 25.629 for airplanes equipped with flight
control systems, autopilots, stability augmentation systems, load
alleviation systems, flutter control systems, and fuel management
systems.
(a) The criteria defined herein address only the direct structural
consequences of the system responses and performances. They 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 applicable only 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 modes are not
provided in this special condition.
(b) Depending upon the specific characteristics of the airplane,
additional studies may be required that go beyond the criteria provided
in this special condition 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.
(c) The following definitions are applicable to this paragraph.
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 and avoidance of
severe weather conditions).
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,
and extremely improbable) used in this 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, this special condition applies only to
system failure conditions that affect the structural performance of the
airplane (e.g., system failure conditions that include loads, change
the response of the airplane to inputs as gusts or pilot actions, or
lower flutter margins).
(2) Effects of Systems on Structures.
(a) General. The following criteria will be used in determining the
influence of a system and its failure conditions on the airplane
structure.
(b) System fully operative. With the system fully operative, the
following apply:
(1) Limit loads must be derived in all normal operating
configurations of 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
non-linearity (rate of displacement of control surface, thresholds or
any other system non-linearities) 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
(static strength, residual strength), using the specified factors to
derive ultimate loads from the limit loads defined above. The effect of
non-linearities 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 will not allow it to exceed those
limit conditions.
(3) The airplane must meet the aeroelastic stability requirements
of Sec. 25.629.
(c) System in the failure condition. For any system failure
condition not shown to be extremely improbable, the following apply:
(1) 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.
(i) For static strength substantiation, those 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.
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[GRAPHIC] [TIFF OMITTED] TP31OC06.033
(ii) For residential strength substantiation, the airplane must be
able to withstand two thirds of the ultimate loads defined in paragraph
(c)(1)(i) of this section. 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 speed increases beyond Vc/Mc, freedom
from aeroelastic instability must be shown to those increased speeds,
so that the margins intended by Sec. 25.629(b)(2) are maintained.
(vi) 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.
(2) 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:
(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 in 25.345.
(C) The limit rolling conditions specified in Sec. 25.349 and
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 and 25.491.
(ii) For static strength substantiation, each part of the structure
must be able to withstand the loads in paragraph (c)(2)(i) 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.
[[Page 63721]]
[GRAPHIC] [TIFF OMITTED] TP31OC06.034
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.
(iii) For residual strength substantiation, the airplane must be
able to withstand two thirds of the ultimate loads defined in paragraph
(c)(2)(ii). For pressurized cabins, these loads must be defined
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 for the remainder of the
flight, using the margins defined by Sec. 25.629(b).
[[Page 63722]]
[GRAPHIC] [TIFF OMITTED] TP31OC06.035
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''.
(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 this Part, 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.
(d) Warning considerations. For system failure detection and
warning, the following apply:
(1) The system must be checked for failure conditions, not
extremely improbably, 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 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 the failures of which are not readily detectable
by normal warning 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 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 part 25, subpart C, below 1.25 or flutter
margins below V'' must be signaled to the crew during flight.
(e) 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
(b), for the dispatched condition and paragraph (c) for subsequent
failures. Expected operational limitations may be taken into account in
establishing P)j 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 flight hour.
Issued in Renton, Washington, on October 19, 2006.
Jeffrey E. Duven,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 06-8974 Filed 10-30-06; 8:45 am]
BILLING CODE 4910-13-M