Universal Stinson 108 N9063K accident near Big Lake, Alaska

Probable cause

A total loss of engine power during cruise flight for reasons that could not be determined because postaccident examination of the airframe and engine revealed no mechanical malfunctions or failures that would have precluded normal operation.

NTSB analysis

The private pilot stated that, about 35 minutes into the personal, local flight and while circling a friend's cabin about 550 ft above ground level, the engine began to "sputter," followed by a total loss of engine power. He subsequently made a forced landing in an area of densely populated trees, during which the airplane sustained substantial damage to the wings and fuselage.

A postaccident examination of the airframe and engine revealed no mechanical malfunctions or anomalies that would have precluded normal operation. Although the wing fuel tanks had been modified and no Federal Aviation Administration major repair and alteration form nor entry in the airplane's maintenance records were found regarding the modification, no evidence was found indicating that the modification led to the loss of engine power. The reason for the loss of engine power could not be determined.

Text from the NTSB. Open the NTSB docket for ANC16LA035 for the full record.