On June 7, 2004, a Schweizer Aircraft Corp. G-164B (registration N3626T) operated by AV Ag, Inc. was involved in an aviation accident near Richvale, CA. Investigators recorded the probable cause as: the loss of engine power during takeoff due to the engine's deteriorated fuel control unit's inner drive shaft bearing. The reason for the bearing's deteriorated condition could not be determined. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An agricultural airplane experienced engine power loss after takeoff from a dirt strip, leading to impact with an embankment. Post-accident examination revealed a deteriorated FCU bearing.
Accident Overview
An agricultural airplane was conducting an aerial application flight. Shortly after lifting off from a dirt airstrip, the engine experienced a slow and subtle loss of power. The pilot responded by placing the fuel lever to flight idle and ensuring the power lever was full forward. However, the pilot was unable to dump the application load before the airplane struck a dirt embankment.
Post-Accident Examination
Examination of the engine after the accident revealed that it was rotating at the time of impact, but the power output may have been lower than required to sustain flight. The only anomaly identified with the engine and its components that could have resulted in the loss of engine power was a spalled and deteriorated inner drive bearing of the fuel control unit (FCU). This condition could result in fluctuations in torque. The bearing grease had deteriorated to the point that only residue remained. The reason for the deterioration of the bearing grease and the bearing itself is unknown.
Maintenance History
At the time of the accident, the FCU was 53 hours short of its recommended inspection period.