AD 92-03-07

92-03-07 BOEING: Amendment 39-8162. Docket No. 91-NM-160-AD. Supersedes AD 89-08-11, Amendment 39-6190 and AD 90-05-02, Amendment 39-6518.

Applicability: Model 737 series airplanes, line number 0001 through 2060 equipped with Garrett GTCP 85-129 series auxiliary power units (APU), certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent an uncontained APU tailpipe fire due to clogged shroud and fuel drains, accomplish the following:

(a) Prior to the accumulation of 150 flight hours after April 25, 1989 (the effective date of Amendment 39-6190, AD 89-08-11), perform a one-time inspection of the exhaust flange and the exhaust muffler heat shield skin joint and remove any excess or loose sealant, and perform an inspection and cleaning of the APU shroud, plenum and combustor drain lines, in accordance with Boeing Service Letter 737-SL-49-14, Revision A, dated March 29, 1989, or Boeing Service Letter 737-SL-49-14, Revision B, dated April 20, 1989. Thereafter, at intervals not to exceed 500 hours, or immediately following maintenance involving the drain system (e.g., APU change, etc.), perform an inspection and cleaning of the APU shroud drains and plenum fuel drain in accordance with the service letters.

(b) Within 10 days after March 12, 1990 (the effective date of Amendment 39-6518, AD 90-05- 02), revise the Limitations section of the FAA-approved Airplane Flight Manual (AFM) by adding the following instructions. This may be accomplished by inserting a copy of this AD into the AFM.

"AUXILIARY POWER UNIT LIMITATION: After any unsuccessful APU ground start, either placard the APU "NO GROUND STARTING" or accomplish the following during the subsequent ground start attempt(s):

(1) Following an unsuccessful APU ground start attempt, the subsequent APU ground start attempt(s) must be monitored by a qualified ground observer to assure proper APU starting. The FAA Principal Maintenance Inspector (PMI) must approve the qualified ground observer, the monitoring procedures, and the method of documentation for compliance with these procedures. If APU tail pipe torching is observed, prior to flight, inspect the affected airplane surface(s) for fire damage and/or paint blistering. Repair or replace fire-damaged area(s) in a manner approved by the Manager, Seattle Aircraft Certification Office, prior to further flight.

(2) Following successful APU operation, if subsequent unsuccessful APU ground starts are again experienced, the ground start monitoring requirements required by paragraph (b)(1) of this AD must be repeated.

(3) The placard may be removed and normal APU ground starting procedures resumed following appropriate maintenance action to determine and resolve the cause of the unsuccessful ground start, or successful ground start has been accomplished in accordance with paragraph (b)(1) of this AD, or in-flight starting and operation is accomplished.

NOTE: In-flight starting and operating of the APU is not impacted by this action."

(c) Within 36 months after the effective date of this AD, modify the APU drain assembly in accordance with Boeing Service Bulletin 737-49-1073, dated July 25, 1991. This modification constitutes terminating action for the repetitive inspections and cleaning requirement required by paragraph (a) of this AD. The AFM limitation required by paragraph (b) of this AD may be removed following completion of the modification.

(d) An alternative method of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate.

NOTE: The request should be forwarded through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Seattle ACO.

(e) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base in order to comply with the requirements of this AD.

(f) The inspection required by this AD shall be done in accordance with Boeing Service Letter 737-SL-49-14, Revision A, dated March 29, 1989; or Boeing Service Letter 737-SL-49-14, Revision B, dated April 20, 1989. The modifications required by this AD shall be done in accordance with Boeing Service Bulletin 737-49-1073, dated July 25, 1991. 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. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue S.W., Renton, Washington; or at the Office of the Federal Register, 1100 L Street N.W., Room 8401, Washington, D.C.

(g) This amendment (39-8162, AD 92-03-07) becomes effective on March 16, 1992.