Amateur-built Saberwing N120SW accident near Valdosta, Georgia

Probable cause

The total loss of engine power due to the shearing of the woodruff key that indexed the crankshaft gear and hub assembly to the crankshaft, which resulted in the gear and hub rotating from their indexed position and caused the crankshaft-to-camshaft timing to become misaligned.

NTSB analysis

The pilot departed the airport on a local flight to perform system checks of the experimental amateur-built airplane. During a functional check of the ignition system, while the pilot was selecting between the points and electronic ignition at a high engine power setting, the engine lost all power about 8 miles away from the airport. After multiple unsuccessful attempts to restart the engine, the pilot declared an emergency and executed a forced landing to a field. The airplane subsequently impacted a utility line and came to rest inverted in a field about 2 miles from the airport. The right wing, fuselage, and empennage sustained substantial damage.

Postaccident examination of the automotive conversion engine revealed that the woodruff key that indexed the crankshaft gear and hub assembly to the crankshaft was sheared. The gear and hub assembly had rotated about 30° from its indexed position, resulting in the crankshaft-to-camshaft timing being out of alignment and a subsequent total loss of engine power. According to the pilot, who had built the engine about 17 years and 20 flight hours before the accident, when switching from points to electronic ignition sources, there was a small interval for the electronics to power up, resulting in a jolt across the engine when power was restored. The jolt, at a high power setting, was likely enough to rotate the gear and shear the woodruff key.

Text from the NTSB. Open the NTSB docket for ERA24LA258 for the full record.