On September 18, 1985, a Grumman 164A (registration N48405) operated by Randy Lahren was involved in an aviation accident near Becker, MN. Investigators recorded the probable cause as: Failure of one propeller blade counterweight, allowing one blade to travel to a high-pitch (low RPM) setting while the other remained in a low-pitch (high RPM) setting. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During an aerial application flight, engine power dropped from 2000 to 1550 RPM. Increasing throttle and propeller control had no effect. The aircraft settled to the ground, nosed over. Post-accident inspection revealed a failed propeller blade counterweight caused asymmetric blade pitch.
Incident Overview
A pilot reported a loss of engine power during an aerial application flight. The engine RPM decreased from 2000 to 1550. The pilot attempted to increase power by advancing the throttle and propeller control, but no increase in power was observed. The aircraft subsequently settled to the ground, impacting the terrain and nosing over.
Post-Accident Findings
Inspection after the accident disclosed that one of the propeller blade counterweights had failed. This failure allowed one propeller blade to move to a high-pitch (low RPM) setting while the other blade remained in a low-pitch (high RPM) setting. The asymmetric propeller blade pitch resulted in a loss of available power, contributing to the aircraft's inability to maintain flight.
Probable Cause
The stated probable cause is the failure of one propeller blade counterweight, which allowed one blade to travel to a high-pitch (low RPM) setting while the other blade remained in a low-pitch (high RPM) setting.
What happened in the 18 Sept 1985 Grumman 164A accident near Becker, MN?
During an aerial application flight, engine power dropped from 2000 to 1550 RPM. Increasing throttle and propeller control had no effect. The aircraft settled to the ground, nosed over. Post-accident inspection revealed a failed propeller blade counterweight caused asymmetric blade pitch.
What aircraft was involved and where did it happen?
The accident on 18 Sept 1985 involved a Grumman 164A, registration N48405, operated by Randy Lahren, at Becker, MN.
What was the probable cause of the accident?
Failure of one propeller blade counterweight, allowing one blade to travel to a high-pitch (low RPM) setting while the other remained in a low-pitch (high RPM) setting.
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