What happened
On 16 January 2003, an Embraer EMB-145EP, registration G-RJXA, was parked at Manchester Airport preparing for a passenger flight. Because the aircraft's Auxiliary Power Unit was unserviceable, the crew attempted to start the engines using an external ground air supply. Following difficulties with the initial start sequence and low pressure from the aircart, the crew decided to perform a cross-bleed start using the No 2 engine to start the No 1 engine.
To avoid further delays, the crew elected to initiate the No 1 engine start while the aircraft was being pushed back onto the taxiway centerline. As the tug began moving the aircraft forward, the ground crew cleared the flight crew to proceed. The commander disengaged the elevator gust lock and increased the thrust on the No 2 engine to 81% N2. This surge in power caused the tug to rapidly jack-knife to the right. Although the pilot immediately reduced thrust and applied the brakes, the towbar snapped, and the right nose gear door struck the tug. There were no injuries to the 4 crew members or 47 passengers on board.
The investigation
The investigation focused on the procedures used during the engine start and the mechanical failure of the towbar. It was established that the aircraft's operations manual lacked a specific procedure for an engine start assisted by the opposite engine (cross-start). While the commander recalled performing this maneuver during training, it was not formally documented in the operator's manual at the time of the event.
Findings
- The primary cause of the incident was the advancement of thrust beyond ground idle during pushback, which led to the sudden jack-knifing of the tug.
- The operator's manual did not contain a formal procedure for a cross-bleed engine start.
- The manufacturer's manual did include the procedure, which the operator has since implemented.
- The operator has since updated its manual to include specific warnings, stating that thrust must never be advanced beyond ground idle during pushback and that cross-starts should only be performed with the park brake applied or after the tug has been disconnected.