On May 11, 1997, a Hughes 369D (registration N5105N) operated by Kaohukaukuahiwi K. Sproat was involved in an aviation accident near Puako, HI. Investigators recorded the probable cause as: erosion of second stage stator vanes, inadequate maintenance inspection for the erosion, and subsequent fatigue failure of a stator vane, which resulted in loss of engine power and a forced landing on mountainous/hilly terrain. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced engine failure during low-level cruise. Autorotation with tailwind led to ground impact on upslope. Investigation found forward CG limit exceeded and stator vane fatigue failure.
Sequence of Events
The helicopter was cruising at low level when the engine failed. The pilot turned toward a landing area and entered an autorotation with a quartering tailwind. During the autorotation, the helicopter continued to descend while maintaining a nose low attitude, until it struck the ground. Impact occurred on upsloping terrain, resulting in damage to the helicopter.
Weight and Balance Examination
A computation of the weight and balance revealed that the helicopter's moment arm exceeded the forward center of gravity (CG) limit by approximately one inch. This condition limited the availability of aft cyclic control.
Engine Examination
An examination of the engine determined that a stator vane had failed due to excessive erosion and fatigue cracking. This condition had not been detected during a compressor case erosion inspection conducted 60 flight hours before the accident.