92-04-03 BOEING: Amendment 39-8172. Docket 91-NM-176-AD. \n\n\tApplicability: Model 747 series airplanes, as listed in Boeing Service Bulletin 747-35- 2074, dated June 27, 1991, certificated in any category. \n\n\tCompliance: Required within the next 4,000 flight hours after the effective date of this AD, unless accomplished previously. \n\n\tTo ensure that the passenger oxygen system activates at the proper altitude, accomplish the following: \n\n\t(a)\tInspect the flow control units to determine the serial numbers, in accordance with Boeing Service Bulletin 747-35-2074, Revision 1, dated December 12, 1991. \n\n\t\t(1)\tIf the flow control unit serial number is listed in Table 1 of the service bulletin and the unit has not been reworked, prior to further flight, replace the unit and perform a low pressure leak check and a simulated automatic actuation test, in accordance with paragraph III.C. of the Accomplishment Instructions of the service bulletin. \n\n\t\t(2)\tIf the flow control unit serial number is not listed in Table 1 of the service bulletin, or if the unit has been reworked in accordance with paragraph III.C. of the Accomplishment Instructions of the service bulletin, no further action is necessary. \n\n\t(b)\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 through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Seattle ACO. \n\n\t(c)\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\t(d)\tThe inspection, replacement, check, and test required by this AD shall be done in accordance with Boeing Service Bulletin 747-35-2074, Revision 1, dated December 12, 1991. Thisincorporation 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 SW., Renton, Washington; or at the Office of the Federal Register, 1100 L Street NW., Room 8401, Washington, DC. \n\n\t(e)\tThis amendment (39-8172, AD 92-04-03) becomes effective on March 16, 1992.