87-12-04 BOEING: Amendment 39-5635. Applies to Model 747 series airplanes, listed in Boeing Service Bulletin 747-29-2063, dated December 23, 1986, certificated in any category. Compliance required as indicated, unless previously accomplished. \n\n\tTo prevent the loss of all four hydraulic systems in the event of severe damage to or loss of the vertical stabilizer, accomplish the following: \n\n\tA.\tWithin the next 24 months after the effective date of this AD, modify the number 4 hydraulic system by installing a hydraulic fuse in accordance with Boeing Service Bulletin 747- 29-2063, dated December 23, 1986, or later FAA-approved revision. \n\n\tB.\tAn 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, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region. \n\n\tC.\tSpecial flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to abase for accomplishment of the modification required by 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 the Boeing Commercial Airplane Company, P.O. Box 3707, Seattle, Washington 98124-2207. These documents may be examined at FAA, Northwest Mountain Region, 17900 Pacific Highway South, Seattle, Washington, or the Seattle Aircraft Certification Office, 9010 East Marginal Way South, Seattle, Washington. \n\n\tThis amendment becomes effective July 13, 1987.