What happened
On 18 May 2005, an Airbus A320-211, registration JY-JAR, operated by Jordan Aviation, was landing on Runway 14 at Leeds Bradford International Airport. The aircraft touched down approximately 400 m beyond the touchdown zone and 700 m beyond the displaced threshold. Following touchdown, the crew applied manual braking; however, once the aircraft reached a groundspeed of roughly 70 kt, the brakes ceased to function for approximately 17 seconds.
As the aircraft continued down the runway, the commander realized the end of the paved surface was approaching. To avoid a high-speed excursion into a steep downslope, the commander chose not to engage alternate braking—fearing the loss of nosewheel steering would compromise directional control—and instead used the nosewheel steering to steer the aircraft sharply to the right. This maneuver caused the aircraft to skid sideways off the runway, eventually coming to a halt on the grassed area with the nosewheels off the pavement.
The investigation
The investigation focused on the sudden loss of braking and the lack of cockpit warnings. Investigators found that the crew, while properly licensed and rested, were unfamiliar with the specific line-of-sight characteristics of Runway 14. A significant dip in the runway surface also obscured the view of the runway end from the flight deck until late in the ground roll.
Technical examination of the braking system revealed that two mainwheel tachometer driveshafts were bent. This physical defect created excessive electrical noise in the signals used to sense groundspeed. The investigation established that this signal noise caused the aircraft's computerised brake control system to erroneously calculate the aircraft's speed, triggering the anti-skid system to release the brakes. Furthermore, the investigation found that the aircraft's monitoring systems were unable to detect the signal noise because it occurred at a speed outside the monitored range, leaving the crew without any flight deck indication of the malfunction.
Findings
- The primary cause of the braking failure was excessive wheel tachometer signal noise resulting from bent driveshafts on each main landing gear assembly.
- Inadequate fault tolerance within the brake control system prevented the system from managing the loss of Normal braking.
- The crew did not receive a flight deck warning regarding the brake malfunction, which delayed their recognition of the issue.
- The selection of a low autobrake setting was inappropriate for the landing conditions.
- The aircraft manufacturer and authorities had previously identified similar anomalies, but updated components and software had not yet been implemented on JY-JAR.