Airworthiness Directive 99-17-18
one-timeAirworthiness Directives; MD Helicopters, Inc. Model 600N Helicopters
What this AD requires
This amendment adopts a new airworthiness directive (AD), applicable to MD Helicopters, Inc. (MDHI) Model 600N helicopters, that requires applying serial numbers to several life-limited components related to pitch control and removing and replacing the components according to new life-limits. This amendment is prompted by fatigue tests that indicate a need for shorter service lives for these components. The actions specified by this AD are intended to prevent failure of the collective pitch control tubes, collective stick housings, and collective pitch tube assemblies, which can cause loss of collective pitch control, and subsequent loss of control of the helicopter.
Which aircraft AD 99-17-18 applies to
Life-limited flight-control components per McDonnell Douglas Helicopter Systems Mandatory Service Bulletin No. 600N-009, dated February 24, 1998: collective stick housing P/N 369A7347/369A7820/369H7837 (450 hr TIS); pilot collective pitch control tube P/N 369A7348 (400 hr TIS) and tube assembly P/N 369H7354-3 (600 hr TIS); co-pilot collective pitch control tube P/N 369A7809 (1,800 hr TIS) and tube assembly P/N 369H7838-3 (1,000 hr TIS). Applicable S/N must also be applied to housings/tubes by 400 hr TIS. Model designation '600N' inferred from the referenced Service Bulletin number prefix (600N-009); not stated verbatim as 'Model 600N' in the captured applicability text.
Whether AD 99-17-18 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.