Incident Details
On 7 May 1999 at 1200 UTC, a Boeing 777-222, registered N768UA, was parked at Stand J15 at London Heathrow Airport. The area had a slope of approximately 0.6%. Rain had fallen most of the day, leaving the pavement surface wet, though rain had stopped by the time of the incident.
During pushback, clearance was given to start engines. An incoming aircraft was holding for Stand J15, necessitating towing the aircraft forward to allow passage. As the tug driver began to straighten the tug and tow the aircraft forward, he felt the tug being pushed forward and accelerating, despite his foot not being on the accelerator. The thrust from the aircraft caused the tug to skid, shearing the head off the towbar.
The driver requested the flight crew to set brakes and cut engines, but there was no response as the communication cable had become disconnected. As the aircraft continued forward, the driver jumped out of the tug and, along with two wingwalkers, signalled for the flight crew to set brakes. The aircraft passed over the tug, with the starboard main gear wheels coming to rest against the side of the tug.
The aircraft required a wheel change. No injuries were reported among the 8 crew and 147 passengers.
Operator Response
The operator planned to publicise the incident in company safety and training publications and use it in tug driver training to emphasise early detection and appropriate actions in loss of control. Additionally, they were revising their maintenance manual to prohibit towing the Boeing 777 with both engines running and modifying pushback procedures to delay engine start until brakes are set.