What happened
On 25 February 2009, a BAe 146-200, registration G-ZAPO, was undergoing pushback from Stand 1L on the Alpha Apron at London Stansted Airport. The aircraft was operating a routine cargo flight. During the maneuver, the tug was pushing the aircraft backwards and to the left before transitioning to pulling it forwards and to the right to align it with the taxiway centerline.
As the aircraft reached the point where the tug began pulling forward, a loud bang was heard on the flightdeck. While the crew was occupied with the 'after start' checklist, the headset operator observed the towbar disconnect and urgently called for the aircraft brakes to be applied. Despite the crew's response, the aircraft could not be halted in time to avoid the stationary tug. The nose of the aircraft struck the tug, resulting in a dent to the aircraft radome and damage to the tug's windscreen. No injuries were reported.
The investigation
The investigation examined the towbar assembly and the sequence of the pushback. It was established that the towbar had detached from the tug end because a shear pin failed. Upon inspection, the commander noted that the pin was heavily corroded and had partially sheared prior to the final failure. The ground handling company's investigation could not provide the specific pin for further analysis, but they confirmed the equipment was subject to regular maintenance.
Findings
- The primary cause of the collision was the failure of a heavily corroated shear pin within the towbar.
- The physical dimensions of the aircraft and the towbar provided very little clearance between the aircraft nose and the tug windscreen, leaving minimal reaction time once the towbar disconnected.
- The crew's attention was diverted by the 'after start' checklist at the moment the failure occurred.