COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES De Havilland DHC-1 (Chipmunk) Series Aeroplanes AD/DHC-1/37 Engine Start Isolation Switch 7/97 Applicability: All DHC-1 Chipmunk Aircraft fitted with Mod H85 or similar Electric Start installation. Requirement: Unless previously incorporated, install an isolation switch in accordance with British Aerospace Aerostructures Ltd Technical News Sheet (TNS) CT (C1) No. 201 Issue 1, dated 1 March 1997. Note: This TNS is classified Mandatory by UK CAA. Compliance: Prior to 19 June 1998. This Airworthiness Directive becomes effective on 19 June 1997. Background: The manufacturer has determined that there is a possibility that a safety hazard could arise with ground power applied to the aeroplane. With the aeroplane electrically safe, an undetected fault in the starter switch, or inadvertent operation of the starter switch could render the engine start system live. The subsequent connection to ground power would cause an uncommanded rotation of the propeller and possibly endanger maintenance personnel.