Airworthiness Directives; Boeing Model 737-300, -400, -500, -600, -700, and -800 Series Airplanes Equipped with Vickers Combined Stabilizer Trim Motors

[Federal Register Volume 64, Number 91 (Wednesday, May 12, 1999)]
[Rules and Regulations]
[Pages 25426-25428]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-11783]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-97-AD; Amendment 39-11166; AD 99-10-13]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-300, -400, -500, -600, 
-700, and -800 Series Airplanes Equipped with Vickers Combined 
Stabilizer Trim Motors

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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SUMMARY: This amendment adopts a new airworthiness directive (AD) that 
is applicable to certain Boeing Model 737 series airplanes. This action 
requires repetitive inspections and functional tests of a trailing edge 
flap limit switch to verify proper operation, and replacement of the 
existing limit switch with a new limit switch, if necessary. This AD 
also requires modification of the stabilizer control system, which 
constitutes terminating action for the repetitive inspections and 
tests. This amendment is prompted by reports of uncommanded stabilizer 
trim motion due to failure of the trailing edge flap limit switch. The 
actions specified in this AD are intended to prevent such failure, 
which could result in uncommanded (nose down) stabilizer trim motion 
and consequent reduced controllability of the airplane.

DATES: Effective May 27, 1999.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of May 27, 1999.
    Comments for inclusion in the Rules Docket must be received on or 
before July 12, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-97-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056.

[[Page 25427]]

    The service information referenced in this AD 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; or at 
the Office of the Federal Register, 800 North Capitol Street, NW., 
suite 700, Washington, DC.

FOR FURTHER INFORMATION CONTACT: R.C. Jones, 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) 227-1118; fax (425) 
227-1181.

SUPPLEMENTARY INFORMATION: The FAA has received reports of several 
incidents of uncommanded nose down stabilizer trim motion on certain 
Boeing Model 737 series airplanes having Vickers type combined manual-
autopilot stabilizer trim motors (STM). Investigation revealed the 
cause as a single point failure in the stabilizer control system, in 
conjunction with a design deficiency in the STM. Analysis of the S245 
trailing edge flap limit switch of the stabilizer control system 
revealed that the switch had failed due to moisture penetration into 
the switch contacts, resulting in corrosion and an electrical short 
circuit. This short circuit caused an erroneously energized STM and 
subsequent uncommanded stabilizer trim motion in the airplane nose down 
direction. This condition, if not corrected, could result in reduced 
controllability of the airplane.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletins 
737-27A1227 (for Model 737-300, -400, and -500 series airplanes) and 
737-27A1228 (for Model 737-600, -700, and -800 series airplanes), both 
dated April 8, 1999, which describe procedures for repetitive 
inspections and functional tests of the S245 trailing edge flap limit 
switch to verify proper operation, and replacement of any 
malfunctioning limit switch with a new limit switch.

Explanation of the Requirements of the Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other airplanes of the same type design, this AD is 
being issued to prevent failure of the S245 trailing edge flap limit 
switch, and subsequent uncommanded (nose down) stabilizer trim motion, 
which could result in reduced controllability of the airplane. This AD 
requires accomplishment of the actions specified in the alert service 
bulletins described previously. This AD also requires that operators 
submit a report of findings of malfunctioning to the FAA.
    Additionally, this AD requires modification of the stabilizer 
control system, which constitutes terminating action for the repetitive 
inspections and tests required by this AD.

Interim Action

    This is considered to be interim action until final action is 
identified, at which time the FAA may consider further rulemaking.

Differences Between This AD and Alert Service Bulletins

    Operators should note that, although the alert service bulletins do 
not specify procedures for terminating action for the repetitive 
inspections and tests, this AD mandates, within 3 months, incorporation 
of an improved design of the stabilizer control system as terminating 
action for the repetitive inspections and tests.
    The FAA has determined that long-term continued operational safety 
will be better assured by design changes to remove the source of the 
problem, rather than by repetitive inspections and tests. Long-term 
inspections and tests may not be providing the degree of safety 
assurance necessary for the transport airplane fleet. This, coupled 
with a better understanding of the human factors associated with 
numerous continual inspections, has led the FAA to consider placing 
less emphasis on inspections and more emphasis on design improvements. 
Incorporation of an improved design of the stabilizer control system 
requirement is in consonance with these conditions.

Determination of Rule's Effective Date

    Since a situation exists that requires the immediate adoption of 
this regulation, it is found that notice and opportunity for prior 
public comment hereon are impracticable, and that good cause exists for 
making this amendment effective in less than 30 days.

Comments Invited

    Although this action is in the form of a final rule that involves 
requirements affecting flight safety and, thus, was not preceded by 
notice and an opportunity for public comment, comments are invited on 
this rule. Interested persons are invited to comment on this 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 under the caption ADDRESSES. All 
communications received on or before the closing date for comments will 
be considered, and this rule may be amended in light of the comments 
received. Factual information that supports the commenter's ideas and 
suggestions is extremely helpful in evaluating the effectiveness of the 
AD action and determining whether additional rulemaking action would be 
needed.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the rule that might 
suggest a need to modify the 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 that 
summarizes each FAA-public contact concerned with the substance of this 
AD will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this rule must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-97-AD.'' The postcard will be date stamped and 
returned to the commenter.

Regulatory Impact

    The regulations adopted herein will 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 final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    The FAA has determined that this regulation is an emergency 
regulation that must be issued immediately to correct an unsafe 
condition in aircraft, and that it is not a ``significant regulatory 
action'' under Executive Order 12866. It has been determined further 
that this action involves an emergency regulation under DOT Regulatory 
Policies and Procedures (44 FR 11034, February 26, 1979). If it is 
determined that this emergency regulation otherwise would be 
significant under DOT Regulatory Policies and Procedures, a final 
regulatory evaluation will be prepared and placed in the Rules Docket. 
A copy of it, if filed, may be obtained from the Rules Docket at the 
location provided under the caption ADDRESSES.

[[Page 25428]]

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

Adoption of the Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration amends 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:

99-10-13  Boeing: Amendment 39-11166. Docket 99-NM-97-AD.

    Applicability: Model 737-300, -400, -500, -600, -700, and -800 
series airplanes, certificated in any category; equipped with 
Vickers combined stabilizer trim motors.

    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 (e) 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 failure of the trailing edge flap limit switch, which 
could result in uncommanded (nose down) stabilizer trim motion and 
reduced controllability of the airplane, accomplish the following:

Inspections and Tests

    (a) Perform a special detailed inspection and functional test to 
verify proper operation of the S245 trailing edge flap limit switch, 
in accordance with the applicable Boeing Alert Service Bulletin 737-
27A1227 (for Model 737-300, -400, and -500 series airplanes) or 737-
27A1228 (for Model 737-600, -700, and -800 series airplanes), both 
dated April 8, 1999; as applicable; at the time specified in 
paragraph (a)(1) or (a)(2) of this AD, as applicable.
    (1) For airplanes that have accumulated less than 1,000 total 
flight hours as of the effective date of this AD: Inspect and test 
prior to the accumulation of 1,000 total flight hours, or within 10 
days after the effective date of this AD, whichever occurs later. 
Repeat the inspection and test thereafter at intervals not to exceed 
300 flight hours, until accomplishment of paragraph (c) of this AD.
    (2) For airplanes that have accumulated 1,000 or more total 
flight hours as of the effective date of this AD: Inspect and test 
within 5 days after the effective date of this AD. Repeat the 
inspection and test thereafter at intervals not to exceed 300 flight 
hours, until accomplishment of paragraph (c) of this AD.

    Note 2: Any inspection and test of the S245 trailing edge flap 
limit switch accomplished prior to the effective date of this AD in 
accordance with the Accomplishment Instructions of either Boeing 
Alert Service Bulletin 737-27A1227 (for Model 737-300, -400, and -
500 series airplanes) or 737-27A1228 (for Model 737-600, -700, and -
800 series airplanes), both dated April 8, 1999, as applicable, is 
considered acceptable for compliance with the initial inspection and 
test specified in paragraph (a) of this AD.

Corrective Action

    (b) If any malfunction is detected during any inspection and 
test required by paragraph (a) of this AD, prior to further flight, 
replace the existing limit switch with a new limit switch in 
accordance with the Boeing Alert Service Bulletin 737-27A1227 (for 
Model 737-300, -400, and -500 series airplanes) or 737-27A1228 (for 
Model 737-600, -700, and -800 series airplanes), both dated April 8, 
1999, as applicable. Repeat the inspection and test thereafter at 
intervals not to exceed 300 flight hours, until accomplishment of 
paragraph (c) of this AD.
    (c) Within 3 months after the effective date of this AD: 
Incorporate an improved design of the stabilizer control system in 
accordance with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA, Transport Airplane Directorate. 
Incorporation of an improved design, as required by this paragraph, 
constitutes terminating action for the repetitive inspection and 
test requirements of this AD.

Reporting Requirement

    (d) Within 10 days after accomplishing the inspection and test 
required by paragraph (a) of this AD, submit a report of the 
inspection and test results (positive findings of malfunctioning 
only) to the Manager, Seattle ACO, FAA, Transport Airplane 
Directorate, 1601 Lind Avenue SW., Renton, Washington, 98055-4056. 
The report must include the inspection results, the airplane serial 
number, and the total number of landings and flight hours on the 
airplane. Information collection requirements contained in this 
regulation have been approved by the Office of Management and Budget 
(OMB) under the provisions of the Paperwork Reduction Act of 1980 
(44 U.S.C. 3501 et seq.) and have been assigned OMB Control Number 
2120-0056.

Alternative Methods of Compliance

    (e) 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 ACO. 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 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (f) 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.

Incorporation by Reference

    (g) Except as provided by paragraph (c) of this AD, the actions 
shall be done in accordance with Boeing Alert Service Bulletin 737-
27A1227, dated April 8, 1999; or Boeing Alert Service Bulletin 737-
27A1228, dated April 8, 1999; as applicable. This incorporation by 
reference was approved by the Director of the Federal Register in 
accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, 
Seattle, Washington 98124-2207. Copies may be inspected at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington; or at the Office of the Federal Register, 800 North 
Capitol Street, NW., suite 700, Washington, DC.
    (h) This amendment becomes effective on May 27, 1999.

    Issued in Renton, Washington, on May 4, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-11783 Filed 5-11-99; 8:45 am]
BILLING CODE 4910-13-P