Overview
During a takeoff, the aircraft collided with a dirt bank after a left engine overspeed and loss of directional control.
Background
Approximately one month prior, the pilot had aborted a takeoff due to an overboost condition and a sticking wastegate. A mechanic performed work and lubrication on the affected components, after which the system operated satisfactorily for about a month.
Event
During the subsequent takeoff, the overboost condition recurred, causing a loss of directional control. The aircraft departed the runway, and the pilot attempted to return to the runway by maneuvering back. During this attempt, the aircraft's wing struck a dirt pile.
Investigation Findings
Post-accident investigation revealed that a sticking valve in the turbocharger wastegate of the left engine and a stuck pressure relief valve caused the overboost condition.