COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 737 Series Aeroplanes AD/B737/107 Aileron and Elevator Power Control Unit Replacement 7/97 Applicability: Model 737 series airplanes equipped with aileron or elevator power control unit (PCU) having part number (P/N) 65-45180-29, serial numbers 182 through 1297 inclusive. Note: PCUs part number 65-45180-29 may also be identified by the serial numbers of the PCU sub-assembly part number 65-44761-21. These serial numbers are listed in the FAA AD 97-05-09 Amendment 39-9953. Requirement: Replace the flow restrictors P/N JETA 1875500D on the subject PCUs in accordance with Boeing Service Letter 737-SL-27-71-A dated June 19 1992, including Attachment 1. Note: FAA AD 97-05-09, Amendment 39-9953 refers. Compliance: Within 5 years of the effective date of this directive. This Airworthiness Directive becomes effective on 19 June 1997. Background: As part of the recent Design Review of the Boeing 737 flight control system, it was decided that the filter screens in the flow restrictors in the aileron and elevator PCUs could, under certain extreme conditions, break up and cause a blockage. Due to the extreme conditions necessary to cause this possible defect, the FAA agreed to extend the period of compliance from 18 months to five years. No in-service failure of these screens has ever been recorded.