What happened
On 27 June 2017, an Airbus A330-243, registration G-VYGL, operated by AirTanker Ltd, was performing a scheduled international passenger flight from Manchester to Tenerife South. The flight, carrying 332 people (321 passengers and 11 crew), proceeded normally through the descent and approach phases. The crew had configured the aircraft for landing and set the autobrake system to the LOW setting.
Upon touchdown on runway 07 at 12:40 UTC, the aircraft experienced a sudden and simultaneous locking of the four rear main landing gear wheels. This occurred without any input from the pilot. The intense friction caused the tires on these wheels to blow out and left significant marks on the runway pavement for approximately 1,000 meters. The aircraft continued traveling down the runway until it reached a complete stop.
While there were no fatalities, 3 passengers sustained minor injuries. Following the incident, airport firefighters inspected the aircraft and confirmed there was no fire. Passengers were eventually disembarked via stairs. The incident caused significant damage to the aircraft's rear tires, rims, and main gear, as well as damage to the runway pavement. The runway remained closed for approximately 5.5 hours.
The investigation
The investigation focused on the sudden activation of the braking system. Investigators analyzed flight data from the flight recorders, which showed that while the approach was stable and within parameters, the brake pressure in the affected wheels (5, 6, 7, and 8) surged to approximately 2,500 psi immediately upon contact with the ground.
Technical examinations were conducted by the manufacturers of the landing gear (Safran) and the braking and steering control unit (Thales). These included:
- Analysis of the tachometers, servo valves, and the Braking and Steering Control Unit (BSCU).
- Temperature cycle tests ranging from -40°C to 70°C.
- Vibration tests spanning 10 to 2000 Hz.
- Visual inspections and X-ray examinations of the internal circuits of the BSCU.
Despite these extensive efforts, the manufacturers were unable to reproduce the incident or identify a specific hardware or software fault during testing.
Findings
- The abnormal behavior of the anti-skid system was the likely cause of the incident.
- The BSCU generated a command that applied maximum braking power to the rear wheels immediately after landing, despite the autobrake being set to LOW.
- The manufacturer noted that the incident might have been caused by a fault in the BSCU operating algorithm, potentially leading to a temporary corruption of variables used by the unit.