SEA03LA086 · Grumman G-164B

The pilot had just executed a reversal turn in order to start another spraying swath when the turbine engine suddenly stopped and the propeller feathered. He attempted to land on a road near the edge of the field he was spraying, but a tractor was on the road so he had to land in a crop of tall wheat. Just before touchdown, one of the aircraft's wings impacted the terrain, and during the landing roll on the soft terrain, the aircraft nosed over. During a post-accident teardown inspection it was determined that the torque sensor idler gear duplex bearing (part number 3103035-1) had failed, which is a condition that would normally result in an uncommanded in-flight shutdown of the engine. Further inspection of the bearing revealed only minimal heat stress discoloration and no clear lack of lubrication, but the bearing balls had been worn undersize, and the bearing cage had fractured into pieces. Further inspection of the bearing by Honeywell Mechanical Systems, revealed that the bearing condition was consistent with advanced rolling contact fatigue failure. As part of the investigation, an FAA Airworthiness Inspector determined that, "The installation of the subject matched bearing set was performed properly by the last overhaul shop in accordance with the Allied-Signal (Honeywell) Overhaul Specification No. 72-00-17, revised July 20, 1992." Although the reason for the unexpected failure of this bearing after approximately 100 hours of operation could not be determined, it was noted that at the last overhaul, the Torque Sensor was not upgraded to the available -3 bearing, which uses a larger bearing assembly and a different gear set.

Verbatim NTSB analysis and probable cause from the NTSB dataset