[Federal Register Volume 65, Number 113 (Monday, June 12, 2000)]
[Proposed Rules]
[Pages 36803-36805]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-14793]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2000-NM-107-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-300, -400, and -500 
Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to all Boeing Model 737-300, -400, 
and -500 series airplanes. This proposal would require replacement of 
the existing autothrottle computer with a new, improved autothrottle 
computer. This proposal is prompted by reports of asymmetric thrust 
conditions during flight caused by irregular autothrottle operation in 
which the thrust levers slowly move apart causing the airplane

[[Page 36804]]

to bank excessively and go into a roll. The actions specified by the 
proposed AD are intended to prevent such conditions, which could result 
in loss of control of the airplane.

DATES: Comments must be received by July 27, 2000.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 2000-NM-107-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except 
Federal holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Thanh Truong, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane 
Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, 
SW., Renton, Washington 98055-4056; telephone (425) 227-2552; fax (425) 
227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 2000-NM-107-AD.'' The postcard will be date stamped 
and returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 2000-NM-107-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports on certain Boeing Model 737-300, -400, 
and -500 series airplanes indicating an asymmetric thrust condition 
caused by irregular autothrottle operation, in which the thrust levers 
slowly move apart causing the airplane to bank and roll. This thrust 
condition exceeds the autopilot roll authority and results in a bank 
angle of more than 30 degrees. In one incident, the airplane rolled 
more than 46 degrees without crew recognition. Without pilot 
intervention, an airplane that has asymmetric thrust can bank 
excessively and go into a roll. Such conditions, if not corrected, 
could result in loss of control of the airplane.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
737-22A1130, dated September 24, 1998, which describes procedures for 
replacement of the existing autothrottle computer with a new, improved 
autothrottle computer. The improved autothrottle computer disengages 
the autothrottle if an asymmetric thrust condition is detected, and 
prevents the airplane from rolling to an excessive bank angle.
    Accomplishment of the actions specified in the alert service 
bulletin is intended to adequately address the unsafe condition.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require accomplishment of the actions specified in 
the alert service bulletin described previously, except as discussed 
below.

Differences Between Proposed Rule and Alert Service Bulletin

    Operators should note that this proposed AD would require 
replacement of the autothrottle computer to be accomplished within one 
year after the effective date of this AD. The alert service bulletin 
recommends that this replacement should be accomplished ``as soon as 
manpower and materials are available.'' However, in developing an 
appropriate compliance time for the proposed replacement, the FAA 
considered not only the degree of urgency associated with addressing 
the subject unsafe condition, but also the number of proposed 
requirements and the availability of required parts. The FAA has 
determined that one year represents an appropriate interval of time 
allowable wherein all of these actions can be accomplished during 
scheduled airplane maintenance and an ample number of required parts 
will be available for modification of the U.S. fleet within the 
proposed compliance period. The FAA also finds that such a compliance 
time will not adversely affect the safety of the affected airplanes.

Cost Impact

    There are approximately 1,974 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 799 airplanes of U.S. 
registry would be affected by this proposed AD, that it would take 
approximately 1 work hour per airplane to accomplish the proposed 
replacement, and that the average labor rate is $60 per work hour. 
Required parts would cost between $1,400 and $4,200 per airplane. Based 
on these figures, the cost impact of the proposed AD on U.S. operators 
is estimated to be between $1,460 and $4,260 per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would not have a substantial direct 
effect on the States, on the relationship between the national 
Government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, it 
is determined that this proposal would not have federalism implications 
under Executive Order 13132.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities

[[Page 36805]]

under the criteria of the Regulatory Flexibility Act. A copy of the 
draft regulatory evaluation prepared for this action is contained in 
the Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: Docket 2000-NM-107-AD.

    Applicability: All Model 737-300, -400, and -500 series 
airplanes; certificated in any category.


    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (c) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent a severe asymmetric thrust condition during flight 
which could result in loss of control of the airplane, accomplish 
the following:

Replacement

    (a) Within 1 year after the effective date of this AD: Replace 
the existing autothrottle computer with a new, improved autothrottle 
computer in accordance with Boeing Alert Service Bulletin 737-
22A1130, dated September 24, 1998.

Spares

    (b) As of the effective date of this AD, no person shall install 
on any airplane, an autothrottle computer having part number 10-
62017-1, -2, -3, -4, -5, -11, -21, -23, -25, or -27.

Alternative Methods of Compliance

    (c) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle Aircraft Certification 
Office (ACO), FAA, Transport Airplane Directorate. Operators shall 
submit their requests through an appropriate FAA Principal 
Maintenance Inspector, who may add comments and then send it to the 
Manager, Seattle ACO.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permit

    (d) Special flight permits may be issued in accordance with 
Secs. 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 
21.197 and 21.199) to operate the airplane to a location where the 
requirements of this AD can be accomplished.

    Issued in Renton, Washington, on June 6, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 00-14793 Filed 6-9-00; 8:45 am]
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