Summary
We propose to adopt a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-61A, D, E, L, N, NM, R, and V helicopters to require replacing each forward and aft fuel system 40 micron fuel filter element with a 10 micron fuel filter element. This proposed AD is prompted by a National Transportation Safety Board (NTSB) review of in-service events where engine performance degradation occurred and the review determined that some of these events were caused by contaminants larger than 10 microns present in the engine fuel control units (FCUs). The proposed actions are intended to prevent particulate contamination in the FCU, which could lead to malfunction of an internal valve(s), power loss at a critical phase of flight, and loss of control of the helicopter.