[Federal Register Volume 71, Number 210 (Tuesday, October 31, 2006)]
[Proposed Rules]
[Pages 63718-63722]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 06-8974]



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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 [email protected].

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.

[[Page 63720]]

[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.

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[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