# AD 91-15-24: Auxiliary Power Unit Pneumatic Ducts Inspection - Type: Airworthiness directive - Status: Current - Products: Boeing 747-100 Series, 747-100B Series, 747-100B SUD Series, 747-200B Series, 747-200C Series, 747-200F Series, 747-300 Series, 747-400 Series, 747-400D Series, 747-400F Series, 747SP Series and 747SR Series - Effective: September 9, 1991 - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Large airplane - Amendment: 39-7089 - Docket: 91-NM-14-AD - Registered aircraft: 63 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/893A5C400DFC658C862569610072D6AF.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/91-15-24 ## The airworthiness directive 91-15-24 BOEING: Amendment 39-7089. Docket No. 91-NM-14-AD. Applicability: Model 747 series airplanes, line positions 2 through 720 for Auxiliary Power Unit (APU) pneumatic ducts in body sections 44, 46, and 48; and line positions 721 through 734 for APU pneumatic ducts in body sections 44 and 48; certificated in any category. Compliance: Required as indicated, unless previously accomplished. To prevent damage to adjacent structure, pneumatic ducts, hydraulic lines, and/or electrical wiring as a result of failure of Auxiliary Power Unit (APU) pneumatic ducts, accomplish the following: A. Prior to the accumulation of 7,000 flight cycles, or within the next 3,000 flight cycles after the effective date of this AD, whichever occurs later, conduct a penetrant inspection, proof pressure test, and penetrant inspection again to detect cracks or ruptures in the APU pneumatic ducts in accordance with the Accomplishment Instructions, Items A. through G., K., O., and P.of Boeing Service Bulletin 747-36-2081, dated November 29, 1990. If cracks or ruptures are detected, prior to further flight, repair or replace in accordance with the service bulletin. The stress relieving procedure specified in Accomplishment Instructions, Items H., I., and J. of the service bulletin may be accomplished in conjunction with the penetrant inspection and proof pressure test required by this paragraph, and constitutes terminating action for the requirements of paragraph B. of this AD for all APU pneumatic ducts. B. Prior to the accumulation of 7,000 flight cycles after the accomplishment of the initial inspection required by paragraph A. of this AD, conduct an additional penetrant inspection, proof pressure test, and penetrant inspection of the APU pneumatic ducts, and stress relieve the APU pneumatic duct assemblies, in accordance with the Accomplishment Instructions, Items A. through K., O., and P. of Boeing Service Bulletin 747-36-2081, dated November 29, 1990.If cracks or ruptures are detected, prior to further flight, repair or replace in accordance with the service bulletin. C. Replacement of all APU pneumatic ducts in accordance with Accomplishment Instructions A., B., L. through O., and P. of Boeing Service Bulletin 747-36-2081, dated November 29, 1990; or in accordance with Boeing Service Bulletin 747-36-2092, dated June 28, 1990; constitutes terminating action for the requirements of this AD. 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 tocomply with the requirements of this AD. F. The penetrant inspections, proof pressure testing, and stress relieving shall be done in accordance with Boeing Service Bulletin 747-36-2081, dated November 29, 1990. APU pneumatic duct replacement shall be done in accordance with either Boeing Service Bulletin 747- 36-2081, dated November 29, 1990, or Boeing Service Bulletin 747-36-2092, dated June 28, 1990. 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, Northwest Mountain Region, 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. This amendment (39-7089, AD 91-15-24) becomes effective on September 9, 1991. ## Affected data sheets (1) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS A20WE](https://openairdocs.org/tcds/A20WE): The Boeing Company; names 12 of 14 models: 747-100B Series, 747SP Series, 747-400D Series, 747-400F Series, 747-200B Series, 747-200F Series, 747-300 Series, 747-200C Series… ## Registered aircraft it may apply to (OpenAirDocs) Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment. - Aircraft: 63 (63 by airframe model, 0 by engine model) - Makers: Boeing 63 Models with the most aircraft: - [Boeing 747-446](https://openairdocs.org/model/boeing-747-446): 10 aircraft (airframe model) - [Boeing 747-422](https://openairdocs.org/model/boeing-747-422): 8 aircraft (airframe model) - [Boeing 747-412](https://openairdocs.org/model/boeing-747-412): 5 aircraft (airframe model) - [Boeing 747-400F](https://openairdocs.org/model/boeing-747-400f): 4 aircraft (airframe model) - [Boeing 747-409](https://openairdocs.org/model/boeing-747-409): 4 aircraft (airframe model) - [Boeing 747-481F](https://openairdocs.org/model/boeing-747-481f): 3 aircraft (airframe model) - [Boeing 747-409F](https://openairdocs.org/model/boeing-747-409f): 3 aircraft (airframe model) - [Boeing 747-481](https://openairdocs.org/model/boeing-747-481): 3 aircraft (airframe model) - [Boeing 747-428F](https://openairdocs.org/model/boeing-747-428f): 3 aircraft (airframe model) - [Boeing 747-123](https://openairdocs.org/model/boeing-747-123): 2 aircraft (airframe model) - [Boeing 747-251F](https://openairdocs.org/model/boeing-747-251f): 2 aircraft (airframe model) - [Boeing 747-443](https://openairdocs.org/model/boeing-747-443): 2 aircraft (airframe model) - [Boeing 747-438](https://openairdocs.org/model/boeing-747-438): 2 aircraft (airframe model) - [Boeing 747-428](https://openairdocs.org/model/boeing-747-428): 2 aircraft (airframe model) - [Boeing 747-257B](https://openairdocs.org/model/boeing-747-257b): 1 aircraft (airframe model) - [Boeing 747-283B](https://openairdocs.org/model/boeing-747-283b): 1 aircraft (airframe model) - [Boeing 747-121](https://openairdocs.org/model/boeing-747-121): 1 aircraft (airframe model) - [Boeing 747-131](https://openairdocs.org/model/boeing-747-131): 1 aircraft (airframe model) - [Boeing 747-128](https://openairdocs.org/model/boeing-747-128): 1 aircraft (airframe model) - [Boeing 747-273C](https://openairdocs.org/model/boeing-747-273c): 1 aircraft (airframe model) All 24 models: https://openairdocs.org/ad/91-15-24/models.md Every aircraft: https://openairdocs.org/ad/91-15-24/aircraft.md Its text cites no advisory circulars or STCs. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.