What happened
During passenger boarding, a DC-9 was parked and being prepared for departure. While a tug driver was maneuvering the vehicle into position to connect the tow bar for pushback, the tug suddenly lurched forward into the parked aircraft. The impact was severe enough that pieces of the aircraft protruded through the tug's windshield, pinning the driver in his seat.
The driver reported being unable to shift the vehicle into reverse and noted that his leg remained pinned against the accelerator pedal. Nearby ground workers attempted to shut off the engine, but the vehicle continued to move forward until the engine was successfully stopped. During the collision, the pilot applied the aircraft brakes upon noticing the unplanned movement. The impact pushed the aircraft backward approximately 30 feet, resulting in substantial damage to the nose section of the fuselage.
The investigation
Following the accident, the tug was placed on jacks for a mechanical inspection. Investigators discovered that the engine shutoff switch failed to stop the engine when it was operated at high throttle settings. Additionally, testing revealed that the braking system was unable to stop the rotation of the drive wheels when the engine was at high throttle.
While these mechanical failures were identified, no anomalies were found during the inspection that could specifically explain the initial lurching described by the driver. Records indicated that this specific tug had been involved in a previous incident involving aircraft damage, where it also reportedly lurched while positioning for a tow bar connection. The manufacturer stated they had no records of operational problems or a known history of lurching issues associated with this model of tug.