Airworthiness Directive · Amendment 39-18379 · Rotorcraft tail boom
MD Helicopters Inc.
This AD applies to MD Helicopters Inc. (MDHI) Model 500N with a rotating cone assembly part number (P/N) 500N3740-81 installed, and Model 600N helicopters with a rotating cone assembly P/N 500N3740-71 installed, certificated in any category.
We are adopting a new airworthiness directive (AD) for MD Helicopters Inc. (MDHI) Model 500N and 600N helicopters with certain rotating cone assemblies installed. This AD requires establishing a life limit of 10,000 hours time-in-service (TIS) on these rotating cone assemblies. This AD was prompted by the determination that MDHI created rotating cone assemblies with new dash numbers but incorrectly failed to identify them as life-limited parts. The actions are intended to prevent operation of rotating cone assemblies past their life limits, failure of the rotating cone assemblies, loss of directional control, and subsequent loss of control of the helicopter.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
(1) Within 1 year or at the next annual inspection, whichever comes later:
(i) Create a component history card or equivalent record for each rotating cone assembly, P/N 500N3740-81 and P/N 500N3740-71, and record a life limit of 10,000 hours time-in-service (TIS).
(ii) Revise the Airworthiness Limitations Section of the applicable maintenance manual or Instructions for Continued Airworthiness by establishing a new retirement life of 10,000 hours TIS for each rotating cone assembly, P/N 500N3740-81 and P/N 500N3740-71, by making pen-and-ink changes or by inserting a copy of this AD into the Airworthiness Limitations Section of the maintenance manual or the Instructions for Continued Airworthiness.
(iii) Remove from service any rotating cone assembly, P/N 500N3740-81 and P/N 500N3740-71, that has 10,000 or more hours TIS.
(2) Do not install a rotating cone assembly, P/N 500N3740-81 or P/N 500N3740-71, on any helicopter unless you have complied with the requirements of this AD.
