HUGHES 369A (OH-6A)

Full Narrative

On September 28, 2009, about 1700 Alaska daylight time, a Hughes 369A [OH-6A] helicopter, N501SU, sustained substantial damage following a loss of engine power and subsequent emergency landing after takeoff from the Wolf Lake Airport, Wasilla, Alaska. The helicopter was being operated as a visual flight rules (VFR) personal flight, under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91, when the accident occurred. The private pilot and one passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The accident flight originated at the Wolf Lake Airport.

During a telephone conversation with the National Transportation Safety Board investigator-in-charge on September 29, the pilot reported that during takeoff, as the helicopter climbed to about 35 feet agl, it suddenly yawed to the right, the red engine out annunciator light illuminated, and the low rotor warning horn sounded. The pilot entered an emergency autorotation and attempted to cushion the landing, but the helicopter landed hard and the main rotor blades struck the tail boom, severing it from the helicopter. The pilot noted that after the accident the engine continued to run, but at a low power setting, requiring him to close the engine throttle and shutdown the engine. The helicopter sustained substantial damage to the tail boom, fuselage, and main rotor system.

A witness to the accident reported seeing a puff of white smoke and sparks coming from the helicopter’s engine exhaust just before the helicopter landed.

The helicopter was equipped with an Allison [Rolls-Royce] 250-C10D turbine engine.

A Federal Aviation Administration (FAA) airworthiness inspector from the Anchorage Flight Standards District Office (FSDO), traveled to the accident airport on October 1, and examined the helicopter at the owner’s hangar. He reported that no preaccident mechanical anomalies were discovered during his examination. The engine was removed from the helicopter and shipped to a Rolls-Royce service center in Oakland, California for examination.

On January 12, 2010, under the supervision of an airworthiness inspector from the Oakland FSDO, the engine was examined externally, which revealed no preaccident mechanical anomalies. The engine was then placed in an engine test cell, started, and it produced its full range of rated rpm. An air safety investigator from Rolls-Royce reported that the engine operated at a slightly lower power setting, but still within acceptable Rolls-Royce performance standards.