91-12-15 BOEING: Amendment 39-7027. Docket No. 90-NM-36-AD. \n\n\tApplicability: Model 757 series airplanes, line numbers 001 through 199, on which Production Revision Release (PRR) 53736 has not been incorporated, certificated in any category. \n\n\tCompliance: Required within the next 3,600 hours time-in-service or 24 calendar months after the effective date of this AD, whichever occurs later, unless previously accomplished. \n\n\tTo prevent loss of fluid from all three hydraulic systems, accomplish the following: \n\n\tA.\tModify the center hydraulic system in accordance with the instructions contained in Boeing Alert Service Bulletin 757-29A0030, Revision 3, dated February 7, 1991. \n\n\tB.\tAn 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. \n\n\tNOTE: The request should be forwarded throughan FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Seattle ACO. \n\n\tC.\tSpecial 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. \n\n\tAll persons affected by this directive who have not already received the appropriate service documents from the manufacturer may obtain copies upon request to Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124. These documents may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington. \n\n\tThis amendment (39-7027, AD 91-12-15) becomes effective on July 15, 1991.