Bethel, AK, USA
N6439H
Cessna 207A
The commercial certificated pilot was conducting a non-scheduled domestic cargo flight carrying mail, and the airplane was in cruise flight about 1,000 feet agl when the engine lost all power. The pilot performed a forced landing in rough, tundra covered terrain. During the landing, the airplane nosed over. The engine was overhauled 1090.9 hours before the accident. During the overhaul process, the engine case was sent to a vendor to be welded and rebored to match original engine case specifications. A postaccident examination of the engine revealed that the number 1 main bearing was deformed in its bearing saddle, and portions of the number 2 main bearing were flattened, fractured and fragmented, and were found in the engine case. The number 2 bearing saddle was extensively distorted and gouged. The engine crankshaft was fractured at the radius of the number 2 main bearing and the number 3 crankshaft cheek, adjacent to the main bearing surface. The fracture surface had discoloration consistent with high heat, and beach marks consistent with fatigue. The area of the number 2 engine bearing saddle, under the bearing insert, had several areas of cracking and exfoliation of the case material along the edges of the oil supply channel. No evidence of engine case fretting was observed during the examination. The engine case was examined by the manufacturer's metallurgical personnel. The report of examination stated that the case contained no signs of lubrication distress on the journals. The manufacturer's metallurgist stated that a determination of a weld repair at the number 2 main bearing support could not be made with a high degree of certainty, although there were several work order stamps on the crankcase indicating that it had been reworked.
On August 8, 2003, about 1253 Alaska daylight time, a wheel-equipped Cessna 207A airplane, N6439H, sustained substantial damage when it nosed over during a forced landing following a loss of engine power about 8 miles northwest of Bethel, Alaska. The airplane was being operated as a visual flight rules (VFR) non-scheduled domestic cargo flight under Title 14, CFR Part 135, when the accident occurred. The airplane was operated as Flight 10-1 by Hageland Aviation Inc., Anchorage, Alaska. The commercial certificated pilot, and the sole passenger, who is the director of training for the operator, were not injured. Visual meteorological conditions prevailed, and VFR company flight following procedures were in effect. The flight originated at the Tuluksak Airport, Tuluksak, Alaska, about 1245, with a planned destination of Atmautluak, Alaska. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on August 8, the director of operations for the operator reported the airplane was carrying mail, and was in cruise flight about 1,000 feet agl. He said the pilot reported a complete loss of engine power, and made a forced landing in rough, tundra-covered terrain. During the landing, the airplane nosed over. At 1253, an Aviation Routine Weather Report (METAR) at Bethel was reporting, in part: Wind, light and variable; visibility, 10 statute miles; clouds and sky condition, few at 6,000 feet, 20,000 feet scattered; temperature, 70 degrees F; dew point, 59 degrees F; altimeter, 30.27 inHg. Examination of the engine maintenance records revealed that the engine was overhauled on July 18, 2002, by Aero Recip, Anchorage, Alaska. During the overhaul process, the engine case was reportedly welded by Divco Inc., Tulsa, Oklahoma, on March 28, 2002. The engine case was rebored to match original engine case specifications, and released as serviceable. The engine was then installed by the operator in the accident airplane. At the time of the accident, the engine had accrued 4557.3 total service hours, 1090.9 hours since the overhaul, and 1 hour since its most recent approved airworthiness inspection program (AAIP) inspection. The engine also received a top overhaul in May, 2003, during which all 6 engine cylinders were replaced. The engine then accrued 279.9 hours before the accident. On September 9, a postaccident examination of the engine revealed that the engine case was fractured under the left magneto. A portion of the number 2 piston connecting rod was visible, protruding through the case. Removal of the engine cylinders and separation of the engine case halves revealed that the lower half of the number 2 connecting rod cap and bearing had separated from the upper half. The connecting rod cap bolts were stretched and broken. The number 1 main bearing was deformed in its bearing saddle. Portions of the number 2 main bearing were deformed, flattened, fractured and fragmented, and were found in the engine case. The number 2 bearing saddle was extensively distorted and gouged. The engine crankshaft had a transverse shear fracture at the aft fillet radius of the number 2 main bearing, and the number 3 crankshaft cheek, adjacent to the main bearing surface. The fracture surface had areas of deep blue discoloration, and beach marks radiating inward from the outer edge of the crankshaft surface. The area of the number 2 engine bearing saddle, under the bearing insert, had several areas of cracking and exfoliation of the case material along the edges of the oil supply channel. No evidence of engine case fretting was observed during the examination. The oil filter contained numerous metal fragments. On December 8, 2003, the engine case was examined by the manufacturer's metallurgical personnel at Teledyne Continental Motors, Mobile, Alabama. The report of examination stated that the case contained no signs of lubrication distress on the journals. The metallurgist stated that a determination of a weld repair at the number 2 main bearing support could not be made with a high degree of certainty, although there were several work order stamps on the crankcase indicating that it had been reworked. Following the examination at Teledyne Continental Motors, the engine case was released to the owner's representatives on January 22, 2004.
A complete loss of engine power during cruise flight due to the shifting of a main crankshaft bearing that produced a fatigue failure of the crankshaft. A factor contributing to the accident was unsuitable terrain for a forced landing, which resulted in a nose over .
Source: NTSB Aviation Accident Database
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