Incident Overview
An aircraft on a radar tracking mission departed Den Helder-De Kooy Airport and flew over the North Sea. After an uneventful flight, the crew returned to De Kooy Airport for landing. Following touchdown on runway 03, the pilots activated the thrust reverser systems, at which point the aircraft became uncontrollable.
Pilot Actions
The pilot attempted to regain control by moving the left throttle from reverse back to forward thrust to turn the aircraft to the right. He then feathered the right propeller and cut off the fuel supply, causing the right engine to stop. Despite these efforts, the aircraft veered off the left side of the runway and came to rest in a ditch.
Outcome
Both pilots escaped uninjured. The aircraft sustained damage beyond economic repair.
Probable Cause
According to the official investigation, the landing speed, touchdown point, runway length, and runway condition were all considered satisfactory. The problem was attributed to an expired adjustment screw on the speed controller (prop governor) of the right engine. This prevented the propeller from achieving reverse pitch, instead continuing to provide forward thrust, which resulted in an asymmetric aerodynamic braking effect. Additionally, the Beta light indicator had burned out and could not illuminate, depriving the pilot of a potential warning about the reverse thrust system malfunction.