What happened
On August 1, 2000, at 03:55 local time, a Fairchild SA-227-AC Metro III, registration EC-FSV, was performing a scheduled cargo flight from Madrid-Barajas to Barcelona. During the initial takeoff roll at Madrid, the crew noted an unusually long takeoff run, which extended past the runway intersection and prompted the crew to consider aborting the departure. The initial climb rate was also lower than normal, staying below 60 and 600 feet per minute until reaching 1,500 feet.
Upon arrival at Barcelona Airport, the aircraft followed a stabilized approach and touched down at the reference speed. Immediately after touchdown, the crew observed the aircraft veering toward the left side of the runway. Despite attempts to correct the deviation using rudder input and differential engine power, the aircraft continued toward the runway edge. In an effort to stop the aircraft, the crew applied heavy braking, which resulted in the aircraft exiting the runway and coming to a stop a few meters off the side.
Following the incident, a visual inspection revealed that three of the four main landing gear tyres (numbers 1, 2, and 3) had burst. Marks on the runway pavement indicated that the tyres had been sliding across the surface from the moment of touchdown.
The investigation
The investigation examined the aircraft's braking system and maintenance history. While a post-incident inspection of the EC-FSV found no mechanical anomalies in the brakes, investigators noted that the tyre marks on the pavement proved the wheels were locked at the moment of contact. This locking caused the tyres to slide and eventually burst due to friction-induced wear.
Investigators also reviewed the aircraft's performance during the preceding takeoff in Madrid. Although no brake malfunction was found during the inspection, the crew had experienced an abnormally long takeoff roll. Furthermore, a subsequent flight twelve days later showed that the aircraft required significantly more power to begin taxiing, though the takeoff distance was normal and no directional oscillations occurred.
Findings
- The primary cause of the incident was a malfunction in the braking system that left residual pressure in the lines.
- This residual pressure caused the brakes to overheat during the taxi and takeoff phases in Madrid, leading to wheel seizure.
- Because the wheels were locked upon touchdown in Barcelona, the tyres slid along the pavement, resulting in the burst of three main gear tyres.
- At the time of the accident, the aircraft had only implemented one of several relevant Airworthiness Directives (AD-92-01-02) regarding the parking brake assembly; newer directives aimed at replacing brake master cylinders and shuttle valves to prevent residual pressure had not yet been applied to this aircraft.