What happened
On 19 January 2021, an Avro 146-RJ85, registration G-JOTR, was being moved across the apron at London Biggin Hill Airport during a positioning flight. Due to local airfield restrictions, the aircraft had to be towed from its parking position on a taxiway to a specific area of the apron to allow for engine start-up. The towing route required the tug to navigate a downhill, damp path that included a 90-degree left turn.
During the maneuver, the tug driver, who was navigating the route in reverse and facing unfamiliarity with the operating base, struggled to clearly identify the taxiway markings. This led to the driver initiating the left turn later than necessary. Because the turn was entered too late, the angle became excessively sharp. On the slippery surface, the tug lost traction and jackknifed. The momentum of the aircraft moving downhill, combined with the acute angle of the towbar, caused the shear pin to break. Although the pilot applied the brakes immediately upon hearing the metal snap, the aircraft continued to roll forward and struck the tug, resulting in a puncture to the front left fuselage. There were no injuries to the five crew members on board.
The investigation
The AAIB examined the circumstances surrounding the towing maneuver, focusing on the environmental conditions and the driver's navigation of the airfield. The investigation established that the combination of the damp, downhill gradient and the difficulty in interpreting indistinct taxiway markings contributed to the late turn. The investigators also looked into the mechanical failure of the towbar shear pin and the subsequent impact between the aircraft and the towing vehicle.
Findings
- The primary cause of the accident was the tug jackknifing due to a late entry into a sharp turn.
- The driver's difficulty in interpreting indistinct taxiway markings and the lack of familiarity with the airfield contributed to the error.
- The damp, downhill surface reduced traction for the tug.
- The breaking of the towbar shear pin was caused by the extreme angle of the turn and the aircraft's downhill momentum.
Safety action
Following an internal review, the operator implemented several safety improvements, including:
- A revision of towing procedures and enhanced training for drivers.
- The implementation of radio communication for towing teams.
- Improvements to the clarity of taxiway markings.
- The inclusion of towing operations within the company's regular audit plan and a review of apron risk assessments.