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 369/88 Tailrotor Swashplate Locknut Lock Washer 1/95 DM Applicability: Models 369D, 369E and 369F/FF Series. Requirement: Action in accordance with MDHC SINs DN-185, EN-78 or FN-64 as applicable. Compliance: Within 25 hours time in service after 9 November 1994, thereafter inspect at intervals not exceeding 100 hours time in service. Background: There have been reports of the MS172209 lockwashers failing due to a flaw in the tang. Failure of the tang could allow the locknut to lose torque, and thereby causing eventual disengagement of the assembly resulting in loss of tail rotor control.