91-21-12 BOEING: Amendment 39-8059. Docket No. 91-NM-86-AD. \n\n\tApplicability: Model 737, 757, and 747-400 series airplanes, equipped with Boeing part number (P/N) 285U0037-104, -105, -201, -202, or -203 series radio control panels, certificated in any category. \n\n\tCompliance: Required within 12 months of the effective date of this AD unless previously accomplished. \n\n\tTo prevent uncommanded frequency changes of the high frequency (HF) and very high frequency (VHF) radios, accomplish the following: \n\n\t(a)\tRemove the P/N 285U0037-104, -105, -201, -202, or -203 series radio control panels and replace them with panels approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. \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.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. \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\tThis amendment (39-8059, AD 91-21-12) becomes effective on November 12, 1991.