Description

On 13 November 2008, a Boeing 737-800 with an unserviceable APU was being operated by Ryanair on a passenger flight at night was in collision with a tug after a cross-bleed engine start procedure was initiated prior to the completion of a complex aircraft pushback in rain. As the power was increased on the No 1 engine in preparation for the No 2 engine start, the resulting increase in thrust was greater than the counter-force provided by the tug and the aircraft started to move forwards. The towbar attachment failed and subsequently the aircraft’s No 1 engine impacted the side of the tug, prior to the aircraft brakes being applied.

The Investigation

An Investigation was carried out by the UK AAIB who found that there was no prohibition or specific caution concerning cross bleed starts during pushback in the Aircraft Operator’s Operations Manual but that the procedures of the Handling Agent involved did not permit cross-bleed starts during pushback under any circumstances and that their personnel, including the headset operator during the event, had been so trained.

The commander advised the Investigation that “he would not normally have intended to carry out a cross-bleed start while the aircraft was still being pushed back. However, when the headset operator said “CLEAR TO START”, (contrary to his employers’ procedures and his own training), it had triggered the start process in his mind and he had automatically begun”.