COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Bombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes AD/DHC-8/29 Anti-Collision Strobe Light Power Supplies 11/93 DM Applicability: DHC-8 Series 100 and 300 aircraft with serial numbers 3 through 214 inclusive, which do not have Modification 8/1273 incorporated. Requirement: 1. Action in accordance with Part B of the Accomplishment Instructions Bombardier Regional Aircraft Division de Havilland Dash 8 Alert Service Bulletin A8-33-33 dated 31 May 1993. 2. Incorporate Modification 8/1273 in accordance with Bombardier Regional Aircraft Division de Havilland Dash 8 Service Bulletin 8-33-19 Revision A dated 31 May 1993. Note: Transport Canada AD CF-93-20 dated 3 August 1993 refers. Compliance: 1. Prior to further flight after 6 September 1993 if any of the following faults have been experienced: 1. With landing gear up and locked, one or more of the landing gear green locked down advisory lights illuminate continuously or intermittently. b. With landing gear down and locked prior to or after landing, one or more of the green locked down advisory lights illuminate intermittently. c. The above indications may also be accompanied by one or more of the following: (i) Continuous or intermittent illumination of the gear selector lever advisory light. (ii) Continuous or intermittent illumination of one or more of the red gear unsafe advisory lights. (iii) Fluctuation of the cabin pressurisation rate needle. 2. Prior to 31 March 1994. Note: Incorporation of Modification 8/1273 is considered termination for the maintenance actions specified by Requirement 1. Background: The aircraft manufacturer has received reports indicating that the white anti-collision light power supply units (pre-modification 8/1273) may develop a fault which produces a strong parasitic electromagnetic emission. This emission, when coupled into the wiring of the proximity switch electronics unit (PSEU), can adversely affect operation of associated systems as follows: 1. flashing of the landing gear locked down advisory lights during cruise, b. fluctuation of cabin pressurisation rate needle during cruise, COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES c. retraction and extension of roll and ground spoilers during ground operation, d. nose gear steering inoperative after landing, and e. normal wheel brakes not available below 35-40 knots. Compliance with this Directive will alleviate the possibility of electromagnetic interference causing incorrect operation of the PSEU.