What happened
On 17 July 1997, an Airbus A3/B4, registration EI-TLL, was operating a passenger flight from Faro, Portugal, to Manchester International Airport. Approximately 90 minutes into the flight, the crew was notified that a brake unit anti-rotation bar had been found on the runway at the departure airport in Faro. During the approach to Manchester, the crew observed a loss of hydraulic fluid from the yellow system and noted that the No 6 brake anti-skid release light had failed to illuminate upon gear extension.
Upon landing, the aircraft experienced a burst on the No 6 tyre, which led to a further loss of the remaining yellow system hydraulic fluid. The aircraft vacated the runway and came to a halt, prompting the shutdown of the left engine as a precaution. While no fire was observed, significant smoke emerged from the left main landing gear. Passengers were evacuated via stairs and a bus. Subsequent inspections revealed that the No 1 brake anti-rotation bar was missing, and the resulting movement of the brake housing had damaged various hydraulic lines and electrical wiring.
The investigation
The investigation focused on the mechanical failure of the anti-rotation bar and its retaining hardware. The recovered bar and bolts were examined, revealing that the retaining collars had been distorted by excessive compressive loads. Analysis of the bolts showed clear evidence of shear failure caused by a small number of high-load reversals.
Investigators also examined the aircraft's maintenance history and the functionality of the Brake and Steering Control Unit (BSCU). The BSCU was found to have defective cards that could potentially cause uneven braking efficiency or locked-wheel conditions. Furthermore, the aircraft's records showed a persistent history of braking issues on the left main landing gear, including instances of overheating, tyre bursts, and seized brakes.
Findings
- The primary cause of the hardware failure was asymmetric braking forces causing structural distortion of the bogie.
- The aircraft was equipped with the 'La Guardia bogie' configuration, which features a wider track; this specific geometry likely amplified the torsional effects during braking.
- The presence of a faulty anti-skid system or malfunctioning brakes likely contributed to the uneven application of braking force.
- The aircraft was operating with the No 5 brake de-activated at the time of the incident, which may have exacerbated the imbalance in braking torque.
- The failure of the retaining bolts was consistent with high-magnitude, transient lateral loads applied to the anti-rotation bar.