What happened
Following a normal preflight and engine run-up, the pilot of a Cessna (type not specified in source) was cleared for takeoff. After advancing the throttle to 1,270 pounds of torque and releasing the brakes, the aircraft reached 85 knots, rotated, and achieved a positive rate of climb. The pilot then retracted the landing gear.
Immediately after the wheels were up, the engine experienced a substantial loss of power, described by the pilot as feeling like an engine running on half its cylinders. The pilot reduced power to idle and focused on returning the aircraft to the runway. The aircraft performed a gear-up forced landing. After touching down, the pilot activated the emergency fuel cutoff, traveled across a taxiway, and came to rest approximately 100 yards past said taxiway. The pilot then shut off the battery and exited through the rear door. The aircraft sustained substantial damage.
The investigation
The engine had 183 hours since new. Although the pilot reported a propeller overspeed warning during a flight prior to the accident, the tach generator was replaced following this incident; subsequent testing of the removed tach generator showed no discrepancies. A teardown inspection of the engine failed to identify any malfunctions or failures capable of causing the power loss.
Investigators examined both the primary and overspeed propeller governors. The primary governor's airbleed system reset-eccentric screw featured non-standard lockwire and the torque sealant had been removed. On the overspeed governor, the inside of the speed setting hex screw lacked torque sealant, and the external sealant was cracked. Bench testing revealed that the overspeed governor was set to a lower RPM than the primary governor, meaning it was controlling the system. Flight tests using these specific settings indicated propeller RPM was limited between 96-97% and stabilized quickly.