COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 737 Series Aeroplanes AD/B737/55 APU Power Feeder Cable Bundle Chafing 4/91 Applicability: All model Boeing 737 series aeroplanes listed in Boeing SB 737-35-1033 dated 15 March 1990. Requirement: Action in accordance with the technical requirements of FAA AD 90-25-12. Note: Boeing SB 737-35-1033 also refers. Compliance: As specified in the Requirement Document but with a revised effectivity date of 18 April 1991 for Australian registered aircraft. Background: Boeing have advised that insufficient clearance may exist between the APU power feeder cable, the crew oxygen system tubing, and the horizontal stabiliser trim control cables in the area below the control cabin floor. This condition, if not corrected, could result in an oxygen fed fire caused by chafing and subsequent electrical arcing between the power feeder bundle and the crew oxygen system tubing.