Airworthiness Directive 99-3591
one-timeAirworthiness Directives; McDonnell Douglas Helicopter Systems Model 369D, 369E, 369FF, 369H, MD500N, and MD600N Helicopters
What this AD requires
This amendment adopts a new airworthiness directive (AD), applicable to McDonnell Douglas Helicopter Systems (MDHS) Model 369D, 369E, 369FF, 369H, MD500N, and MD600N helicopters, that requires a one- time visual inspection of certain input shaft coupling assemblies for pitting. This amendment is prompted by three operators' reports of discovering pitting on the internal spline teeth. The actions specified by this AD are intended to prevent 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.
Which aircraft AD 99-3591 applies to
Within 100 hours TIS, visually inspect the input shaft coupling assembly, P/N 369F5133-1 (installed on main transmission P/N 369F5100-503 and on overrunning clutch P/N 369F5450), for spline pitting under the solid film lubricant; replace if pitted. References Boeing SBs SB369H-240, SB369E-085, SB500N-013, SB369D-192, SB369F-072, and SB600N-003 -- the SB numbering suggests coverage of the 369/500N/600N model line, but no literal 'Model' designation appears in the extracted applicability text.
Whether AD 99-3591 actually applies to your aircraft (by serial and installed parts) and whether it’s already complied with comes from that aircraft’s records.
How AD compliance is recorded
A valid compliance record (14 CFR 43.9) states:
Tailplate reads a tail number’s logbooks and matches every applicable AD — including this one — to its compliance evidence, with recurring next-due dates computed.
Look up a tail number →Read the full directive (Federal Register)Applicability is derived from the FAA directive corpus and is advisory, not a legal airworthiness determination. Compliance is established only from an aircraft’s actual records.