What happened
On 3 January 2013, an Airbus A321-211, registration EC-HUI, was undergoing pushback from Stand 522 at London Heathrow Airport. The aircraft was prepared for a commercial passenger flight to Madrid. During the initial stages of the maneuver, the pushback ground crew provided clearance to the flight crew to begin engine start-up.
As the right-hand engine was being started, a 'NW STRG DISC' message appeared on the flight crew's display. The ground crew halted the pushback procedure immediately following this alert.
The investigation
The investigation established that the aircraft's nosewheel steering mechanism, which relies on hydraulic power, is designed to be inhibited during pushback. This inhibition is managed via a towing control lever located on the nose landing gear, allowing the pushback vehicle to maneuver the aircraft without causing damage to the steering system.
In this instance, the commander reported that the towing control lever was not correctly set to the towing position. Consequently, as the engine was started, the nosewheel steering system became pressurized. This unexpected pressure resulted in damage to the nose landing gear assembly.
Following the incident, the aircraft was towed back to its stand. It was subsequently inspected and taken out of service to undergo necessary maintenance.