Amateur-built SWEARINGEN SX300 N5SX accident near Buckeye, Arizona

Probable cause

The total loss of engine power due to the failure of the left magneto.

NTSB analysis

The pilot departed uneventfully, leveled the airplane at 1,000 ft above ground level, and set the engine power to 2,500 rpm. He then initiated a climb, during which the engine power increased to 3,200 rpm and the engine became “unresponsive to input” just before it lost power. The pilot initiated a forced landing, during which the pilot sustained minor injuries and the airplane sustained substantial damage.

A postaccident examination of the engine revealed the left magneto flange was securely clamped at the mounting pad; however, the flange was detached from the magneto. The three screw holes where the flange and magneto should have attached exhibited severe elongation and deformation, which was indicative of a loss of torque and subsequent prolonged inability to maintain proper mating of the magneto flange and housing. The three attachment screws were not recovered.

The condition observed during postaccident examination likely existed for an extended time as evidenced by fretting and wear signatures of the housing components. Internally, the magneto components become misaligned to such a degree that proper magneto internal timing and the ability to operate within the manufacturer’s specification were affected, resulting in the total loss of engine power.

Text from the NTSB. Open the NTSB docket for WPR21LA357 for the full record.