Airworthiness Directive · Amendment 39-18300 · Flight control system
Sikorsky Aircraft Corporation Helicopters
This AD applies to Model S-76A, S-76B, S-76C, and S-76D helicopters with main rotor (M/R) servo input control pushrod (pushrod) assembly part number (P/N) 76400-00034-059 or tail rotor (T/R) pushrod assembly P/N 76400-00014-071 installed, certificated in any category.
We are publishing a new airworthiness directive (AD) for Sikorsky Aircraft Corporation Model S-76A, S-76B, S-76C, and S-76D helicopters, which was sent previously to all known U.S. owners and operators of these helicopters. This AD requires inspecting the main rotor (M/R) and tail rotor (T/R) pushrod assemblies and the jamnuts, and applying slippage marks across the pushrod tubes and jamnuts. This AD is prompted by an accident of a Sikorsky Aircraft Corporation Model S-76C helicopter. During preliminary investigation, a failed pushrod assembly was identified. These actions are intended to prevent loss of M/R or T/R flight 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.
Within five hours time-in-service:
(1) Inspect each pushrod end to determine whether a 0.020 inch diameter lockwire can pass through the inspection hole.
(i) If the lockwire passes through the inspection hole, replace the pushrod assembly.
(ii) If the lockwire does not pass through the inspection hole, inspect the jamnut to determine whether it is seated against the pushrod and whether it can be turned with finger pressure. If the jamnut is not seated against the pushrod or can be turned with finger pressure, replace the pushrod assembly.
(2) Apply two slippage marks across each pushrod tube and jamnut as follows:
(i) Clean the area where a slippage mark is to be applied.
(ii) Apply two slippage marks across the pushrod tube and jamnut, parallel and on opposite sides of each other. Each slippage mark must extend at least 0.5 inch onto the pushrod tube and must not cover the inspection hole. Figures 2 and 4 of Sikorsky Alert Service Bulletin No. 76-67-57, Basic Issue, dated September 10, 2015, illustrate slippage marks across a pushrod tube and jamnut.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
