[Federal Register Volume 65, Number 179 (Thursday, September 14, 2000)]
[Rules and Regulations]
[Pages 55443-55448]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-23174]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM174; Special Conditions No. 25-164-SC]


Special Conditions: Boeing Model 737-700 IGW; 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 737-700IGW 
airplane as modified by Aviation Partners Supplemental Type Certificate 
(STC). The modified airplane will have a novel or unusual design 
feature involving installation of winglets on the wing tips of the 
airplane which require the use of an existing system to limit yawing 
maneuvers at higher speeds thereby reducing the design loads for the 
winglets. The applicable airworthiness regulations for the Boeing 737-
700IGW 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 August 30, 
2000. Comments must be received on or before October 30, 2000.

ADDRESSES: Comments on these special conditions may be mailed in 
duplicate to: Federal Aviation Administration, Transport Airplane 
Directorate, Aircraft Certification Service, Attention: Rules Docket 
(ANM-114), Docket No. NM174, 1601 Lind Avenue SW., Renton, Washington 
98055-4056; or delivered in duplicate to the Transport Airplane 
Directorate at the above address. Comments must be marked: Docket No. 
NM174. Comments may be inspected in the Rules Docket weekdays, except 
Federal holidays, between 7:30 a.m. and 4:00 p.m.

FOR FURTHER INFORMATION CONTACT: James Haynes, FAA, Transport Airplane 
Directorate, Aircraft Certification Service, Airframe/Cabin Safety 
Branch, ANM-115, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; 
telephone (425) 227-2131; facsimile (425) 227-1320.

SUPPLEMENTARY INFORMATION: The FAA has determined that notice and 
opportunity for prior public comment hereon are impracticable because 
these procedures would significantly delay issuance of the approval 
design 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.

Comments Invited

    Interested persons are invited to submit such written data, views, 
or arguments, as they may desire. Communications should identify the 
regulatory docket or notice number and be submitted in duplicate to the 
address specified above. All communications received on or before the 
closing date for comments will be considered by the Administrator. The 
special conditions may be changed in light of the comments received. 
All comments received will be available in the Rules Docket for 
examination by interested persons, both before and after the closing 
date for comments. A report summarizing each substantive public contact 
with FAA personnel concerning this rulemaking will be filed in the 
docket. Commenters wishing the FAA to acknowledge receipt of their 
comments submitted in response to this request must include a self-
addressed, stamped postcard on which the following statement is made: 
``Comments to Docket No. NM174.'' The postcard will be date stamped and 
returned to the commenter.

Background

    On January 15, 1998, Aviation Partners applied for an STC to 
install winglets on the wingtips of the Boeing Model 737-700IGW 
airplane listed in Type Certificate No. A16WE. These winglets must be 
designed to aerodynamic loads associated with the yawing maneuver 
conditions of 14 CFR 25.351. Aviation Partners will make use of the 
load relief during yawing maneuvers provided by an existing system on 
the airplane that limits rudder authority thereby reducing the design 
loads for the winglets.
    The Boeing Model 737-700IGW is an increased gross weight version of 
the Boeing Model 737-700 airplane commonly known as the Boeing Business 
Jet (BBJ). The Model 737-700IGW is a hybrid model which combines the 
Model 737-700 fuselage with the Model 737-800 wing and landing gear. 
The airplane is intended for private use such as the business or

[[Page 55444]]

VIP markets. The airplane uses a crew of two and the passenger capacity 
depends on the interior design which will vary by customer. Aviation 
Partners is further modifying the Boeing 737-700IGW by installing 
blended winglets to improve performance.
    The Boeing 737-700IGW airplane, has an existing rudder pressure 
limiter (RPL) system that limits the rudder authority at high speeds 
when full authority is not needed. This system is part of the Boeing 
type design for all the 737NG (new generation) airplanes and is not 
changed by the Aviation Partners modifications, which mainly installs 
blended winglets. At low airspeeds where full rudder authority is 
needed to provide directional control with an engine failed, full 
hydraulic pressure is available to both actuator pistons within the 
main rudder power control unit (PCU). However, above 137 knots 
calibrated airspeed (KCAS), the RPL system reduces the rudder authority 
by limiting pressure to one of the systems that control the rudder. 
When functioning properly, this effectively reduces the design loads on 
the winglets when applying the yawing maneuvers prescribed by 
Sec. 25.351. The existing rules adequately cover the design for the 
case with the RPL system functioning properly and the safety factor of 
1.5 as prescribed by Sec. 25.303, is applied to these design loads. 
However, when the system is failed, the airplane can be subjected to 
higher rudder displacements, greater yawing conditions, and larger 
loads on the winglets. Since the regulations do not provide specific 
safety factors to use for design in this system failure state, these 
special conditions are necessary.
    The RPL system for the modified Boeing Model 737-700IGW airplane, 
although not specifically designed for this purpose, will alleviate the 
design loads for the winglets when it functions properly. Special 
conditions which provide factors of safety for system failure cases 
have been previously issued for many airplane models that have load 
alleviation systems (i.e. systems specifically designed to alleviate 
loads) and these same special conditions are issued for use on the 
Aviation Partners modified Boeing Model 737-700IGW airplane.

Type Certification Basis

    Under the provisions of Sec. 21.101, Aviation Partners must show 
that the Boeing Model 737-700IGW, as changed, continues to meet the 
applicable provisions of the regulations incorporated by reference in 
Type Certificate No. A16WE, 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 regulations incorporated by 
reference in Type Certificate No. A16WE are as follows:
    Part 25, as amended by Amendments 25-1 through 25-77. In addition, 
the certification basis includes certain special conditions unrelated 
to these special conditions, later elected amendments for certain 
sections, and reversions to earlier amendments for certain sections. 
Sections 25.351 ``Yawing conditions'' and 25.303 ``Factor of safety,'' 
which are relevant to these special conditions, are elected at 
amendment level 25-86 and 25-77 respectively.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25, as amended) do not contain adequate or 
appropriate safety standards for the Boeing Model 737-700IGW because of 
a novel or unusual design feature, special conditions are prescribed 
under the provisions of Sec. 21.16 to establish a level of safety 
equivalent to that established in the regulations.
    In addition to the applicable airworthiness regulations and special 
conditions, the Boeing Model 737-700IGW 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; and the FAA must issue a 
finding of regulatory adequacy pursuant to Sec. 611 of Public Law 92-
574, the ``Noise Control Act of 1972.''
    Special conditions, as appropriate, are issued in accordance with 
Sec. 11.49, as required by Secs. 11.28 and 11.29(b), and become part of 
the type certification basis in accordance with Sec. 21.101(b)(2).

Novel or Unusual Design Features

    The Boeing Model 737-700IGW as modified by Aviation Partners will 
incorporate the following novel or unusual design features:
    Winglets will be installed on the wing tips which must be designed 
for the yaw maneuver conditions of Sec. 25.351. Aviation Partners will 
take advantage of an existing rudder limiting system on the airplane 
that will limit the required design loads to reduced levels. The 
regulations do not provide adequate criteria governing the safety 
margins required for systems that affect design loads when they fail. 
Previously, special conditions have been issued for new model airplanes 
which have systems which are specifically designed for the purpose of 
alleviating design loads. In the case of the Aviation Partners winglet 
installation, the existing rudder limiting system on the Boeing Model 
737-700IGW was not specifically designed for the purpose of alleviating 
the design loads, but it will provide such relief and Aviation Partners 
will take advantage of it in the structural design of the winglets. 
These special conditions prescribe structural design factors of safety 
for the winglets to be applied to loads produced at the time of failure 
of the rudder limiting system and for loads occurring during continued 
operation with the system failed.

Conclusion

    This action affects only certain novel or unusual design features 
on one model airplane. 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 period in several prior instances and has been 
derived without substantive change from those previously issued. It is 
unlikely that prior public comment would result in a significant change 
from the substance contained herein. For this reason, and because a 
delay would significantly affect the certification of the Aviation 
Partners modified Boeing Model 737-700IWG 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. Under standard practice, the effective date of final special 
conditions is 30 days after the date of publication in the Federal 
Register; however, because of the above reasons, the FAA finds that 
good cause exists to make these special conditions effective upon 
issuance.

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

    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 Model

[[Page 55445]]

737-700IGW airplanes modified by Aviation Partners.
    I. Interaction of Systems and Structures. The following criteria 
must be used for showing compliance for the Aviation Partners winglet 
modification to the Boeing Model 737-700IGW airplane. The criteria 
apply to the structural design of the winglets under the conditions of 
normal operation and failures of the rudder pressure limiter system 
that affects the yawing maneuver conditions.
    (a) 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. 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.
    (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 special 
condition.
    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, avoidance of severe weather conditions, etc.).
    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, 
extremely improbable) used in this special condition 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 induce loads, change the 
response of the airplane to inputs such as gusts or pilot actions, or 
lower flutter margins).
    II. Effects of Systems on Structures. The following criteria will 
be used in determining the influence of a system and its failure 
conditions on the airplane structure.
    (a) System fully operative. With the system fully operative, the 
following apply:
    (1) Limit loads must be derived in all normal operating 
configurations of the system from all the limit conditions specified in 
Subpart C of part 25, 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.
    (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 
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) 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 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 (F.S.) is defined in Figure 1.

[[Page 55446]]

[GRAPHIC] [TIFF OMITTED] TR14SE00.008

    (ii) For residual strength substantiation, the airplane must be 
able to withstand two thirds of the ultimate loads defined in 
subparagraph (b)(1)(i).
    (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 increased speeds, so that the 
margins intended by Sec. 25.629(b)(2) are maintained.
    (iv) 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 at speeds up to 
Vc, or the speed limitation prescribed for the remainder of 
the flight must be determined:
    (A) The limit symmetrical maneuvering conditions specified in 
Sec. 25.331 and in Sec. 25.345.
    (B) The limit gust and turbulence conditions specified in 
Sec. 25.341 and in Sec. 25.345.
    (C) The limit rolling conditions specified in Sec. 25.349 and the 
limit unsymmetrical conditions specified in Sec. 25.367 and 
Sec. 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. 25.473 
and Sec. 25.491.
    (ii) For static strength substantiation, each part of the structure 
must be able to withstand the loads in subparagraph (2)(i) of this 
paragraph 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 55447]]

[GRAPHIC] [TIFF OMITTED] TR14SE00.010

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 
subparagraph (b)(2)(ii).
    (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 55448]]

[GRAPHIC] [TIFF OMITTED] TR14SE00.012

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 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) Warning considerations. For system failure detection and 
warning, the following apply:
    (1) 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. 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 
that 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 Subpart C of part 25 below 1.25, or flutter 
margins below V", must be signaled to the crew during flight.
    (d) 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 for the dispatched condition and for 
subsequent failures. 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 August 30, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 00-23174 Filed 9-13-00; 8:45 am]
BILLING CODE 4910-13-P