What happened
On 15 August 2001, a Boeing 737-204 Advanced, registration EI-CJH, was operating a scheduled passenger flight from Dublin to Manchester. The flight was being conducted with a training captain in the right seat and a trainee pilot in the left seat. The aircraft had departed Dublin with the outboard anti-skid system inoperative, a condition permitted under the Minimum Equipment List.
As the aircraft approached Runway 2D, the crew attempted to arm the speedbrakes. However, a warning light indicated the speedbrakes could not be armed, prompting the crew to prepare for manual spoiler deployment upon landing. Following a smooth touchdown, the handling pilot applied reverse thrust and braking. Immediately after the deployment of the speedbrakes, the inboard tyre on the left main landing gear burst, causing the aircraft to swing slightly to the left.
As the aircraft continued toward the runway turn-off, the outboard tyre on the left main gear also burst. This second failure caused a more significant veer to the left. The trainee pilot, who had control of the nose gear steering, struggled to steer the aircraft toward the "BD" turn-off. The aircraft eventually came to a halt on the taxiway. There were no fatalities and no injuries among the 5 crew members or 33 passengers on board.
The investigation
The investigation focused on the mechanical failures following the incident. The operating company performed extensive checks on the aircraft, including inspections for brake seizure and high-energy stops. During the maintenance process, several components were replaced, including the No 1 and No 2 wheels, brake units, the left brake metering valve, and the left inboard anti-skid control valve.
Testing of the anti-skid control valve by its manufacturer revealed a defect. Additionally, the aircraft manufacturer noted that a malfunction in the left inboard anti-skid circuit could have prevented the release of hydraulic pressure to the brake during a skid event.
Findings
- The investigation established that a defective anti-skid control valve likely caused the left inboard wheel to lock.
- The failure of the left outboard tyre was attributed to it supporting double its intended load after the inner tyre had already failed.
- The outboard anti-skid system was already inoperative at the time of the incident, which contributed to the severity of the tyre failure.