Mechanical failure for Glasair

Aircraft: Glasair III. Injuries: 1 Fatal. Location: Falls of Rough, Kentucky Aircraft damage: Substantial.

What reportedly happened: According to witnesses on the ground, the airplane took off and then circled back to make a fly-by over the runway. The witnesses said the engine sounded like it “over revved” and they saw what appeared to be a puff of smoke emitting from the nose of the airplane.

The Glasair entered a left downwind for the runway. The engine power seemed to surge, then went silent. The airplane turned toward the runway but lacked the altitude to glide to the runway. The pilot appeared to level the wings, and the landing gear was lowered as the airplane descended into the trees, collided with a building, and exploded.

The post-accident 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. Investigators determined it is likely that the airplane lost airspeed and altitude due to this condition.

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

NTSB Identification: ERA11FA512

This September 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.


  1. says

    I never liked, or trust the idea of non purpose built engines being used in aircraft. The reduction unit is a weak link. The idea of aircraft engines is simplicity. By adding more mechanical items that can fail you are stacking the deck against yourself.

    • Dietrich Fecht says

      Ray, what about the cylinder head separations due to cracks at the “simple aircraft engines”, we just heard about in he last weeks? As more parts you have so more can fail. That is true. When the propeller drive shaft from a reduction gear fractured as a result of fatigue, it is not an issue of the engine. An improper reduction gear, may be not tested enough for this usage, perhaps was used. The best solution is no reduction gear and motors with a bigger engine displacement. So you have the HP you need at lower engine rpm. You save a reduction gear.

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