Amateur-built CH701 N3784A accident near Pima, Arizona

Probable cause

A total loss of engine power while maneuvering due to a spark plug failure.

NTSB analysis

The pilot reported that the purpose of the local flight was to practice maneuvers. After departure, the airplane climbed to 2,000 feet above ground level (agl). The pilot stated that the engine was running smoothly, producing full power, and he noted no anomalies. He then descended to 1,000 feet agl under cruise power, and after completing a turn, the engine had an immediate loss of power. It began to vibrate significantly and subsequently lost total power. The airplane collided with a tree during a forced landing on a road. Postaccident examination of the engine revealed that the spark plug in the right rear cylinder was fractured and separated in the porcelain area of the plug. The spark plug base remained screwed into the cylinder, and it was more than finger tight. The remainder of the plug was in the ignition harness’s rubber boot. There was no indication that the spark plug fractured due to impact damage. The spark plug was then replaced and the engine started with no anomalies noted. The engine had accumulated 4 hours since being installed on the airplane.

Text from the NTSB. Open the NTSB docket for WPR10LA341 for the full record.