ANC21LA094

The pilot reported that, while on the base leg approach, he heard a “loud bang,” and the engine lost total power. The pilot determined that the airplane would not be able to reach its intended destination, so he turned the airplane into the wind and made a forced landing on tundra-covered terrain, which resulted in substantial damage to the fuselage. The airplane’s maintenance records were unremarkable. Postaccident examination of the engine revealed that it had seized and sheared the propeller spline into two pieces. The accessory wall could not be removed because of the extensive internal damage to the engine. As a result, the investigation was unable to determine the reason that the engine seized during the flight.

On August 21, 2021, about 1325 Alaska daylight time, a float-equipped de Havilland DHC-3 Otter airplane, N560TR, sustained substantial damage when it was involved in an accident near Bettles, Alaska. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 commercial flight. The pilot reported that, while on the base leg approach for a landing at a remote lake, he heard a “loud bang,” and the engine lost total power. The pilot determined that the airplane would not be able to reach its intended destination, so he turned the airplane into the wind and made a forced landing onto an area with tundra-covered terrain, which resulted in substantial damage to the fuselage. A review of the airplane’s maintenance records was unremarkable, and no evidence of regulatory noncompliance was found. Postaccident disassembly and examination of the engine found that it had seized and that the propeller spline had fractured into two pieces. A substantial amount of metal fragmentation was found in the oil screen. The engine was subsequently examined using a lighted borescope, and fragments of broken internal engine pieces were visible, preventing the removal of the aft accessory wall.