Background
A post-maintenance test flight was conducted after an overhauled engine had been installed on the right side of the airplane. Both propeller assemblies had been subsequently re-rigged. Ground checks were satisfactory, though the right engine propeller idled 90-100 rpm higher than the left.
Accident
Test flight engine start and run-up were performed per the checklist with no anomalies noted. The takeoff ground roll and initial climb were normal. However, when the airplane reached approximately 100 feet, it stopped climbing and lost airspeed. The pilot could not identify the malfunction and executed a forced landing to rough, hilly terrain. Upon landing, the landing gear collapsed and the engine nacelles were compromised. The airplane subsequently burned.
Investigation
Post-accident examination revealed that the propeller beta valves of both engines were improperly rigged. Activation of the landing gear squat switch at takeoff resulted in both propellers going into feather. The maintenance personnel did not have rigging experience in that airplane make and model.
Probable Cause
The official probable cause states: Improper rigging of both propeller assemblies by maintenance personnel, which resulted in the inadvertent feathering of both propellers after takeoff. Factors included a lack of rigging experience in airplane make and model by maintenance personnel, unclear maintenance manual information, and unsuitable terrain for the forced landing.
As a result of the investigation, the manufacturer clarified maintenance manual and pilot handbook procedures.