Incident
On 12 May 2011 at 0815 UTC, a Boeing 737-800 (registration EI-DYM) operating a scheduled passenger service to Alicante was involved in an accident during pushback from Stand 8 at Liverpool John Lennon Airport. The aircraft, powered by two CFM 56-7B26 turbofan engines and manufactured in 2008, had 169 passengers and 6 crew on board. Weather was fine and daylight. Pushback commenced at 0812 using a tug and towbar arrangement, conducted by two ground crew personnel: a tug driver and a headset operative who also acted as dispatch officer. After a normal pushback with standard exchanges between the headset operative and the commander, the commander received confirmation that the steering bypass pin had been removed and the towbar disconnected. The headset operative disconnected his headset, waited on the left of the aircraft, gave a 'thumbs up' showing the bypass pin, and the commander waved him off. The headset operative boarded the tug and rode back to the parking area. The tug driver reported connecting the towbar to the back of the tug and driving back after clearance. He looked back and saw the towbar still on the apron in front of the aircraft. He alerted the headset operator, who attempted to attract the crew's attention but could not. The ground crew then rushed to their office to alert Air Traffic Control. The flight crew requested taxi clearance and taxied for Runway 27. After traveling approximately 400 m, ATC called stating the aircraft may have struck a towbar and to hold position. Inspection revealed the towbar had become lodged against the left main landing gear, causing damage to the nosewheel tyre and left main undercarriage assembly, and substantial damage to ground towing equipment. The flight crew reported feeling or hearing nothing untoward. Passengers were disembarked, and the aircraft was towed to stand. A sweep of the taxiways was carried out, and they were returned to service.
Investigation
The accident was investigated by the airport authority and the ground handling company; findings were made available to the AAIB upon request.
Ground Crew Actions
The headset operative reported disconnecting the towbar and removing the steering bypass pin as usual. He walked to the left side of the aircraft and saw the tug driver connect the towbar to the rear of the tug. As the tug moved away, he showed the pin to the commander and was waved off. He boarded the tug and rode back. The tug driver stated he connected the towbar, received clearance, and drove back. Upon looking back, he saw the towbar still on the apron. He alerted the headset operator, who unsuccessfully tried to attract the crew's attention.
Equipment
The pushback tug was not fitted with a radio, but the tug driver had a hand-held radio. There had been a failure of the airport's radio communications system shortly before pushback, but this reportedly would not have affected vehicle radios or hand-held sets. The tug driver reported his handset showed very low signal strength at the time and he did not attempt to use it. The pushback tug had a towbar locking pin that was not fitted to the vehicle and was apparently not the original pin. The history of the pin was not established, but it was confirmed the tug driver had used it on two previous occasions. Photographs showed the locking pin was fitted with a square flange at one end, with remnants of a handle that had broken off some time beforehand. The flange rested on top of a locking mechanism intended to prevent a correctly fitted pin from jumping out while the tug was in motion. In the photographed position, the pin would only partially engage the towbar eye-end fitting if inserted into the lower of three available positions, and would not mechanically prevent lifting enough to release the towbar.
Procedures
The ground handling company's investigation established that procedures intended to prevent such an occurrence had not been fully complied with. Once pushback was complete and the towbar attached to the tug, the driver was required to position the vehicle forward of the aircraft, in view of the flight crew but blocking its taxi path, to prevent premature movement. Then, upon clearance from the headset operator, the tug should have positioned to a point beyond the aircraft's wing tip, where the driver should make a visual check for obstacles. The headset operator was required to show the bypass pin and give the 'thumbs up' once he established that the tug, towbar, and all people were clear of the aircraft's taxi route, from a position level with the wing tip in view of the flight crew. The procedures stressed that this action confirmed the route was clear.
Safety Actions
Disciplinary actions were taken against the two ground crewmen. The tug concerned was removed from service pending installation of a radio. All tugs were inspected to ensure correct towbar locking pins were fitted. A programme of daily ramp inspections was initiated to ensure correct pushback procedures were being followed.