Amateur-built GLASAIR III N43KH accident near Falls Of Rough, Kentucky

Probable cause

The failure of the propeller power speed reduction unit, which resulted in a loss of engine power at low altitude.

NTSB analysis

According to witnesses, the airplane departed the airport and circled back to make a fly-by over the runway. As the airplane flew over the runway, a witness reported that the engine sounded like it “over revved.” Witnesses also stated that they saw what appeared to be a puff of smoke emitting from the nose of the airplane. The pilot made a left banking turn, and then entered a left downwind for the runway. The engine power seemed to surge as the airplane descended. Then the engine went silent and the airplane turned toward the airport but did not have enough altitude to reach the runway. The pilot appeared to level the wings, and the landing gear was lowered as the airplane descended into the trees, struck a building, and exploded.

A postaccident examination of the airplane revealed that it was equipped an automotive Chevrolet LS1 engine. The airplane’s propeller was attached to a propeller speed reduction unit (PSRU). The system was designed with an automatic clutch and was tuned to remain disengaged at idle and engage with an increase in power. An examination of the PSRU revealed that the propeller drive shaft fractured as a result of fatigue. This fracture separated the propeller drive gears from the clutch, which resulted in the loss of power to the propeller. Given the witness accounts of the loss of engine power, it is likely that the airplane lost airspeed and altitude due to this condition.

Text from the NTSB. Open the NTSB docket for ERA11FA512 for the full record.