What happened
On April 6, 2019, a Finnair Airbus A319, registration OH-LVA, was operating flight AY322 from Vaasa to Helsinki with 86 occupants. During the initial taxi from the apron, the captain experienced a sudden jerk and a distinct noise as the brakes engaged sharply. While the crew initially attributed this to cold brakes, a second similar jerk occurred during taxiing toward runway 16. To prevent further jolts during a turn, the captain applied light braking pressure.
During the takeoff roll, the crew noted a slight vibration that subsided before reaching 10/0 knots. After takeoff, a passenger—a Finnair ferry captain—notified the crew via the interphone that they had observed a burst or puff of debris near the left main landing gear. Following a runway inspection by airport personnel, which revealed black rubber streaks and tire fragments on the pavement, the pilots proceeded to Helsinki.
Upon landing at Helsinki-Vantaa on runway 04R, the crew utilized engine thrust for deceleration and manually applied the brake on the intact right gear. Once stopped, the aircraft's hydraulic pressure began to drop, requiring the use of the electric hydraulic pump to maintain brake pressure until a tug could be attached. During the subsequent tow, personnel observed fragments of the failed tire striking the landing gear strut and noted a hydraulic fluid leak.
The investigation
The OTKES investigation examined the aircraft at the Finnair maintenance hangar in Helsinki. Investigators discovered that a hydraulic line in one of the landing gear circuits had fractured due to being struck by fragments from the burst tire. This fracture caused the drop in hydraulic pressure observed after the parking brake was engaged. The left main landing gear sustained extensive surface damage, and three of the four fasteners on the gear door were broken.
Analysis of video footage from Vaasa Airport confirmed that the brake had locked twice during taxiing: first when turning onto taxiway A, and a second time as the aircraft moved toward the end of the runway. The tire eventually burst just before the aircraft turned for takeoff. The investigation also confirmed that the tire, while relatively new, had accumulated 832 landings and 1,670 flight hours.
Findings
- The tire burst because the brake manifold valve malfunctioned, causing the brake to lock during taxi.
- The locking of the brake caused the tire to skid, wearing through the tread until the tire deflated and the tread separated from the carcass.
- The fragments from the disintegrated tire struck the landing gear, causing the hydraulic leak and damage to the gear door fasteners.
- The crew was unable to detect the brake lock during taxi or takeoff because the aircraft's onboard systems do not monitor this specific failure.