What happened
During normal cruise flight, the right engine began emitting visible sparks from the cowling area. The pilot observed a corresponding drop in manifold pressure on that engine. In response, the pilot reduced power on the affected engine, which caused the sparking to cease. The aircraft was subsequently landed at Bethel without further incident.
The investigation
Upon landing, the fire department applied a fire extinguishing agent to the right engine as a precaution. A subsequent inspection of the right engine revealed that a bolt securing the exhaust clamp had broken. This clamp is part number MVT 68637-375M and is responsible for securing the exhaust pipe to the turbocharger.
Further examination showed that the clamp securing the pipe to the engine nacelle had slipped off its bracket. This displacement allowed the exhaust pipe to slip downward, releasing hot exhaust gases directly into the engine nacelle. The resulting excessive heat removed the waste gate from the operational system of the engine.
Findings
The primary mechanical failure was a broken bolt on the exhaust clamp. This failure allowed hot gases to escape into the nacelle, causing minor damage and affecting engine operation. No injuries were reported among the occupants.