Aircraft Accident/Incident Report

Newark, New Jersey 07104
Thursday, December 3, 1998 17:42 EST

The pilot flew the helicopter below and behind the flight path of an airliner, and encountered wake turbulence. He inadvertently rolled the throttles to manual, and never restabilized the engines or main rotor rpm. In addition, he did not understand the reset procedures for the engine controls (FADEC), and never returned the engines to FADEC control. After about 2 minutes of flight with several power changes, and a climb of 700 feet, rotor RPM had decreased to 73%. The pilot declared an emergency, reported a double power loss, and ditched the helicopter in a river. A video of the last several seconds of the flight revealed periodic bursts of flames, and bright objects emitted from the rear of the helicopter before it contacted the water. Although the left engine had been overtempted, and experienced turbine failure, the right engine was capable of producing power at water impact. A failed hydraulic line was found in-line with a failed coupling on the tail rotor drive shaft, in an area where a fire had burned. The mfg reported the tail rotor drive shaft could become unstable above 168% Nr, or lower if the mounts were loose or rubber grommets deteriorated. A sound analysis recorded the main rotor momentarily at 125% Nr during the autorotation. A fault code from the right engine FADEC indicated the power turbine had reached 127% Nr. The hanger bearings for the long tail rotor drive shaft had not been retorqued as required after being replaced. Non-mechanic rated pilots had signed off 100-hour inspections, and required inspections from airworthiness directives.

the pilot's failure to maintain proper rotor rpm and his improper in flight decision to enter autorotation due to his lack of knowledge of the power plant controls. Factors in the accident were the night conditions and the pilot's improper decision to fly through wake turbulence.