[Federal Register Volume 61, Number 179 (Friday, September 13, 1996)]
[Proposed Rules]
[Pages 48435-48437]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-23444]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-156-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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[[Page 48436]]

SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-300, -
400, and -500 series airplanes. This proposal would require 
modification of the system that detects a loss of tension in the cable 
controlling the flaps by removing the shim from behind the bracket for 
the proximity switch; and by trimming this bracket. This proposal is 
prompted by reports that the bracket could impair the movement of a 
pulley arm mechanism, ultimately preventing the detection system from 
operating. The actions specified by the proposed AD are intended to 
prevent such impairment, which could result in movement of the flaps 
without action by the pilot, and ultimately cause reduced 
controllability of the airplane.

DATES: Comments must be received by October 24, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-156-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: Kristin Larson, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington; 
telephone (206) 227-1760; fax (206) 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 96-NM-156-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-103, Attention: Rules 
Docket No. 96-NM-156-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports of a discrepancy identified in the 
system that detects a loss of tension in the cable controlling the 
flaps (hereinafter called ``the detection system''), which is installed 
on certain Boeing Model 737-300, -400 and -500 series airplanes. Should 
an uncontained engine failure result in severing of the cable, this 
system detects the resultant loss of tension in the cable and turns off 
the hydraulic power that operates the flaps. Consequently, the flaps 
remain in the position in which they had been set prior to engine 
failure.
    A loss of tension in the cable causes a pulley arm mechanism in the 
detection system to move a magnet away from the proximity switch. This 
enables the switch to provide a ground to the relay that supplies 
electrical power for closing a bypass valve. When this valve is closed, 
hydraulic power to the flap power unit is turned off.
    An analysis of the detection system, performed by the manufacturer, 
showed that the pulley arm mechanism may not have sufficient clearance 
to move the magnet far enough from the proximity switch to activate the 
system. This condition, if not corrected, could cause movement of the 
flaps without action by the pilot, and ultimately could reduce the 
pilot's ability to control the airplane.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
737-27A1199, dated June 20, 1996, which describes procedures for 
removing a shim, if installed, from behind the proximity switch; and 
trimming the bracket for the proximity switch. These modifications will 
enable the pulley arm mechanism to move the magnet the distance 
necessary for activating the detection system.

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 removal of the shim behind the proximity 
switch, if installed; and trimming of the bracket for the proximity 
switch. The actions would be required to be accomplished in accordance 
with the service bulletin described previously.

Cost Impact

    There are approximately 1,619 Model 737-300, -400, and -500 series 
airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 685 airplanes of U.S. registry would be affected by this 
proposed AD, that it would take approximately 7 work hours per airplane 
to accomplish the proposed actions, and that the average labor rate is 
$60 per work hour. Based on these figures, the cost impact of the 
proposed AD on U.S. operators is estimated to be $287,700, or $420 per 
airplane.
    The cost impact figure discussed above is 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 substantial direct 
effects 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, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    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 under 
the criteria of the Regulatory

[[Page 48437]]

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 96-NM-156-AD.

    Applicability: Model 737-300, -400 and -500 series airplanes 
having line production numbers 1001 through 2765, inclusive; 
certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise 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 (b) 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 movement of the flaps from their last set position 
without action by the pilot, which could reduce controllability of 
the airplane, accomplish the following:
    (a) Within 18 months or 3,200 hours time-in-service after the 
effective date of this AD, whichever occurs first, remove the shim, 
if installed, from behind the bracket of the proximity switch in the 
system which detects a loss of tension in the cable controlling the 
flaps; and trim this bracket; in accordance with Boeing Alert 
Service Bulletin 737-27A1199, dated June 20, 1996.
    (b) 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.

    (c) Special flight permits may be issued in accordance with 
sections 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 September 6, 1996.
James V. Devany,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-23444 Filed 9-12-96; 8:45 am]
BILLING CODE 4910-13-U