Incident Overview
On July 11, 2009, at approximately 1300 Alaska daylight time, a Noordyun UC-64A (Norseman) airplane, registration N225BL, operated by Renfro's Alaska Adventures, sustained substantial damage during an emergency landing. The aircraft came to rest about 300 feet short of runway 1 at Akiachak Airport, Akiachak, Alaska. The flight was conducted under Title 14, CFR Part 135 as a visual flight rules (VFR) passenger flight from Bethel to Tuluksak, Alaska. Visual meteorological conditions prevailed, and company flight following procedures were in effect.
Pilot Report
During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on July 12, the pilot stated that he was en route from Bethel to Tuluksak when the engine began to run rough. He diverted to Akiachak, which was near the airplane's position. The engine then quit completely, and the pilot was unable to reach the runway. The airplane collided with terrain short of the runway. The pilot noted that the engine had been rebuilt about 100 flight hours before the accident, after experiencing problems following a previous rebuild. The airplane sustained substantial damage to both wings and the fuselage. The pilot and sole passenger were not injured.
Engine Examination Findings
An internal examination of the engine was conducted by the NTSB IIC on November 6. The examination revealed that a locking screw had backed out of one of the two anti-vibration counterweights on the crankshaft. This screw scored the interior back surface of the engine case. The locking screw itself was not located. The engine case and oil passages contained fractured metal pieces, including fragments from piston skirts, piston rings, and ground pieces of connecting rods. A large part of the crankshaft counterweight and half of the bolt that normally secures the counterweight halves were found in a piston cylinder. The other half of the counterweight was located in the crankcase, fractured into three large pieces and many smaller fragments. The second counterweight remained bolted in its proper position. Piston heads were found in the crankcase, and the engine's master rod was bent.