COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES McDonnell Douglas (Hughes) and Kawasaki 369 Series Helicopters AD/HU 369/51 Amdt 3 Rotor Brake and Tail Rotor Drive Shaft Coupling 1/87 Applicability: 1. Model 369D Series Helicopters equipped with a rotor brake system P/N 369H90123, not modified in accordance with S.I.N. DN-95 (installation of fail- safe coupling); 2. All model 369 Helicopters not modified in accordance with Service Information Notice DN-95, HN-173, DN-143, HN-206 or EN-31 as applicable. Requirement: 1. De-activate the rotor brake system in accordance with Part I of Hughes S.I.N. DN-94. Note: FAA AD 81-17-02 refers. 2. Inspect the forward and rear flexible couplings (P/Nos. 369H92564 and/or 369A5501) in accordance with Part II of S.I.N. DN-94. Compliance: 1. Within 25 hours time in service after 26 October 1981. 2. Inspect within 100 hours time in service after 31 August 1986 and thereafter at each issue of a new Maintenance Release. Note: Rotor brake may be re-activated after installation of coupling fail safe device in accordance with S.I.N. DN-95. Background: In the past, there have been reports of several fatigue failures of forward flexible couplings on helicopters equipped with a rotor brake system. A recent investigation after an accident has revealed the possibility of either forward or rear couplings failing. Amdt 2 was issued to include both couplings, on all model 369 helicopters, for inspection. This amendment excludes helicopters amended to the requirement of AD/HU 369/68.