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 369/98 Input Shaft Coupling - Inspection 5/99 Applicability: All McDonnell Douglas Helicopter System (MDHS) model 369D, 369E, 369FF, 369H, MD500N and MD600N helicopters, with input shaft coupling assemblies part number (P/N) 369F5133-1, serial number (S/N) 030829-0126 through 030829-0207, installed on main transmission, P/N 369F5100-503, and on overrunning clutch P/N 369F5450. Requirement: 1. Visually inspect the coupling assemblies P/N 369F5133-1, installed on main transmission P/N 369F5100-503, and on overrunning clutch P/N 369F5450, for pitting under the solid film lubricant in the spline area of the coupling. Boeing Service Bulletins SB369H-240, SB369E-085, SB500N-013, SB369D-192, SB369F-072 and SB600N-003 dated 26 September 1997 refer. 2. Replace the coupling assembly with an airworthy coupling assembly P/N 369F5133-1 that has been inspected as required by paragraph (1) above. Note: US FAA 99-04-12 Amendment 39-11036 refers. Compliance: 1. Within 100 hrs time in service of the effective date of this Directive. 2. Before next flight if pitting is detected at the inspection at requirement 1 above. This Airworthiness Directive becomes effective on 20 May 1999. Background: Three operators reports of pitting on the internal spline teeth of the input shaft coupling led to the issue of a US FAA AD to inspect the shaft coupling. Existence of the pitting could lead to failure of the spline teeth in the input shaft coupling assembly, loss of drive to the main rotor system and subsequent loss of control of the helicopter.