What happened
The captain overflew the airfield to assess wind conditions prior to arrival. At the time, the windsock indicated a quartering headwind for runway 12. During the landing rollout, as the power levers were moved into the beta range, the aircraft immediately veered to the right. Although the captain attempted to maintain directional control using rudder and braking, the aircraft ran off the right side of the runway and collided with a ditch and an embankment. Following the event, the crew determined that the actual wind conditions were a 60-degree tailwind on runway 12; the windsock had failed to rotate correctly because its pivot point was rusted.
The investigation
Investigators discovered that the beta pin had backed out of position on the left engine's beta control linkage. The beta pin, along with the washer and cotter pin, were found in the bottom of the engine cowling. The left engine had been replaced two days before the accident.
During the initial engine installation, an inspector had verified that the beta pin was in place and properly safety wired. However, after this signoff, mechanics found that a teleflex cable was too short for the beta valve to be properly flushed, necessitating an adjustment. The director of maintenance performed this adjustment, which required disturbing the existing safety wire on the beta pin. While two mechanics were instructed to re-safety the connections following this work, one mechanic believed the rear portion had already been secured and did not recheck the area. The inspector also failed to re-examine the beta pin, believing the area had already been inspected.