90-23-17: Rear Pressure Bulkhead

90-23-17 BRITISH AEROSPACE: Amendment 39-6800. Docket No. 90-NM-122-AD. Applicability: Model DH.125-1A series airplanes, equipped with Hawker Siddeley Dynamics Air Conditioning System and Rolls Royce Viper Engines, certified in any category. Compliance: Required as indicated, unless previously accomplished. To prevent chafing between the air conditioning duct and the rear pressure bulkhead, and subsequent rapid decompression of the airplane, accomplish the following: A. Within 30 days after the effective date of this AD, perform a detailed visual inspection for chafing on the aft face of the rear pressure bulkhead, in accordance with the Accomplishment Instructions of British Aerospace Service Bulletin 53-71, dated November 1, 1989. B. If defects are found, prior to further flight, perform a dye penetrant inspection to detect cracks in the vicinity of the affected area; and perform a dial test indicator measurement to determine the depth of damage in therear pressure bulkhead, in accordance with British Aerospace Service Bulletin 53-71, dated November 1,1989. 1. If the damage to the rear pressure bulkhead is less than 0.003 inch deep, prior to further flight, carefully blend out, polish, and then restore protective treatment in accordance with the service bulletin. 2. If the damage to the rear pressure bulkhead is greater than 0.003 but less than 0.010 inch deep, within 100 landings, repair in accordance with Appendix B of the Service Bulletin. 3. If the damage to the rear pressure bulkhead is greater than 0.010 inch deep, prior to further flight, repair in accordance with Appendix B of the Service Bulletin. C. Within 30 days after the effective date of this AD, adjust the clearance between the air conditioning duct clamp and the rear pressure bulkhead so there is at least a 3/4-inch clearance. This can be accomplished by rotating and adjusting the duct position. D. An alternate means of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate. NOTE: The request should be submitted directly to the Manager, Standardization Branch, ANM-113, and a copy sent to the cognizant Principal Inspector (PI). The PI will then forward comments or concurrence to the Manager, Standardization Branch, ANM-113. 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. All persons affected by this directive who have not already received the appropriate service documents from the manufacturer may obtain copies upon request to British Aerospace, PLC, Librarian for Service Bulletins, P.O. Box 17414, Dulles International Airport, Washington, D.C. 20041-0414. These documents may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue, S.W., Renton, Washington. This amendment (39-6800, AD 90-23-17) becomes effective on December 11, 1990.