What happened
On April 9, 2007, an Airbus A321, registration I-BIXK, was performing a scheduled flight to Naples Capodichino. During the approach, the crew observed several warnings on the ECAM, including a brake system fault and a steering failure. In an attempt to clear the warnings, the crew performed a system reset while the landing gear was already extended.
Upon landing on runway 24, the aircraft experienced a sudden loss of braking capability. Despite the pilot applying maximum manual braking and using maximum reverse thrust, the aircraft failed to decelerate significantly. The pilot notified Air Traffic Control of a Mayday emergency, stating they could not brake. To avoid obstacles, the pilot steered the aircraft off the left side of the runway onto a grassy area, eventually re-entering the runway via taxiway A and traveling in the opposite direction. The aircraft finally came to a stop after the parking brake was applied. There were no injuries to the 182 passengers or the crew, though the engine ingested debris during the excursion.
The investigation
The ANSV investigation focused on the sequence of technical failures and the crew's response. Investigators examined the Brake and Steering Control Unit (BSCU) and performed X-ray analysis on the internal components. The investigation also reviewed the crew's use of the 'BSCU RESET' and 'LOSS OF BRAKING' procedures, as well as the aircraft's maintenance logs, which showed a series of intermittent faults in the BSCU channels during previous flight legs.
Findings
- The primary cause was a malfunction of the BSCU caused by a faulty solder joint in a connection between the CTP and PSM components.
- The crew performed the BSCU reset procedure from memory rather than consulting the operational manual.
- The reset procedure was ambiguous, as it did not explicitly state that the system test only occurs during gear extension, nor did it specify that resetting with the gear extended might only clear warnings without actually testing the system.
- The crew did not implement the 'LOSS OF BRAKING' procedure, partly because the pilot prioritized maintaining directional control via the nose wheel steering over activating the alternate braking system.
- A misleading pressure indication on the triple indicator led the crew to believe the alternate braking system was already functional.