What happened
On July 20, 2000, a Mitsubishi Mu-2B-35 turboprop, registration N848/4T, was performing a radar tracking flight over the North Sea. Upon completing the mission, the pilot attempted to land at Marinevliegkamp De Kooy. Immediately following touchdown, the pilot engaged the reverse pitch setting. This action caused the aircraft to veer uncontrollably toward the left side of the runway.
In an attempt to correct the deviation, the pilot applied full right rudder and utilized intermittent braking on the right side. The pilot then transitioned the left engine out of reverse pitch to induce a rightward turn, but the aircraft continued its leftward trajectory. To regain control, the pilot eventually feathered the propeller blades on the right engine, which simultaneously cut the fuel supply and caused the engine to shut down. Although this reduced the leftward pull, the aircraft could not be recovered and exited the runway to the left, eventually coming to a stop in a ditch. Both occupants escaped the substantial damage to the aircraft uninjured.
The investigation
The investigation focused on the mechanical state of the engines and the pilot's cockpit procedures. Investigators confirmed that the landing speed, touchdown point, runway length, and runway surface conditions were all within safe parameters. The inquiry examined the propeller governor of the right engine and the functionality of the cockpit warning systems.
Findings
- The primary cause of the excursion was a displaced adjustment screw on the right engine's propeller governor. This malfunction prevented the engine from entering reverse pitch, causing it to continue providing forward thrust and creating asymmetric aerodynamic braking.
- The locking lacquer intended to secure the adjustment screw in place was missing, allowing the screw to move.
- The pilot failed to notice that the right BETA control light was not illuminated. These lights are critical indicators that signal whether the engines are in the proper operating state to safely select reverse pitch.
- According to the flight manual, the pilot should have refrained from using reverse pitch because the non-functioning warning light indicated that the engines were not in the correct configuration.