Date & Time: Jul 11, 2009 at 1300 LT
Type of aircraft:
Noorduyn Norseman
Operator:
Registration:
N225BL
Survivors:
Yes
Schedule:
Bethel-Tuluksak
MSN:
542
Crew on board:
1
Crew fatalities:
0
Pax on board:
1
Pax fatalities:
0
Other fatalities:
0
Total fatalities:
0
Captain / Total flying hours:
8500
Captain / Total hours on type:
100
Aircraft flight hours:
15729
Circumstances:
While on a flight from Bethel to Tuluksak, engine started to run rough. The pilot decided to divert to Akiachak Airport but on final approach, aircraft stalled and crashed 300 feet short of runway 01. Both occupants were slightly injured while the aircraft was damaged beyond repair.
Probable cause:
The pilot said the engine had been rebuilt about 100 flight hours prior to the accident, after developing problems following a previous rebuild. He said that the airplane sustained substantial damage to both wings and the fuselage during the accident.
An internal examination of the engine by the NTSB IIC on November 6, showed that a locking screw had backed out of one of the two anti-vibration counterweights on the crankshaft, and scored the interior back surface of the engine case. The locking screw was not located. The engine case and oil passages had fractured metal pieces from piston skirts, piston rings, and ground pieces of connecting rods. A large part of the crankshaft counterweight and half of bolt that normally secures the counterweight halves were found in a piston cylinder. The other half of the counterweight was found in the crankcase; it was fractured into three large and many smaller pieces. The second counterweight was still bolted in its proper place. Piston heads were found in the crankcase, and the engine's master rod was bent.