COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Enstrom F-28 Series Helicopters AD/ENST 28/35 Inadvertent Trim Motor Operation 2/94 TX Applicability: All F-28C, F-28C-2, F-28F, 280C, 280F and 280FX series helicopters equipped with a 24 volt DC electrical system. Requirement: 1. Inspect and modify the trim system in accordance with Enstrom Helicopter Corporation Service Directive Bulletin 0082 Revision A dated 18 March 1993. 2. Inspect the trim system in accordance with Enstrom Helicopter Corporation Service Directive Bulletin 0082 Revision A dated 18 March 1993. Note: FAA Priority Letter AD 93-12-14 issued 6 December 1993. Compliance: 1. Within five hours time in service from 13 December 1993. 2. At intervals not to exceed 100 hours time in service or at each annual inspection, whichever occurs first. Background: There have been three reports of inadvertent trim motor operation as a result of sticking relays. A stuck relay causes the trim motor to rapidly deploy to the full trim position, resulting in high cyclic control forces that significantly reduce the controllability of the helicopter and possibly lead to total loss of control.