Piper PA-24-250 N6430P accident near Alturas, California

Probable cause

A loss of engine power due to the failure of the right magneto distributor gear and the pilot’s decision to conduct a test flight with known mechanical issues.

NTSB analysis

The pilot reported that, shortly after takeoff, the airplane’s engine began to run rough, so he returned to the airport, landed uneventfully, parked the airplane, and deplaned his passengers to conduct another preflight inspection. The pilot sampled the fuel, checked for loose spark plugs, and checked the magnetos. The pilot then decided to do an engine run-up and test flight before departing the area with the passengers. After takeoff, about 100 ft above ground level (agl), the engine began to shake violently, and he initiated a turn back to the airport. The engine lost total power, and the airplane landed hard and came to rest upright in the grass adjacent to the runway, resulting in substantial damage to fuselage, both wings, and the right horizontal stabilizer.

Postaccident examination of the engine established mechanical and valvetrain continuity. When the propeller was rotated, the No. 5 ignition harness top lead did not spark. The right magneto was removed and functionally tested with an intermittent spark. The left magneto was also removed, and spark was obtained on all posts during the functional check. Further testing revealed that the intermittent spark from the right magneto could not be duplicated. Disassembly of right magneto revealed about 1/4 of the teeth were separated from the distributor gear, which would likely result in a partial loss of engine power and a rough running engine. No additional evidence of any preexisting mechanical malfunctions that would have precluded normal operation were observed with either magneto.

Text from the NTSB. Open the NTSB docket for WPR23LA239 for the full record.