C2/2009L Serious incident at Helsinki-Vantaa Airport due to tread separation and hydraulic failure, 22 June 2009

An incident occurred on the Finnair scheduled flight AY58 flew from Shanghai, China to Helsinki-Vantaa Airport, Finland on the 22 June 2009. The aircraft type was an Airbus A340-313, registration OH-LQE. There were 195 passengers and 12 crew members on board.

The tread of the inner rear wheel in the left landing gear detached and broke into pieces during takeoff at 02.17 (all times are in UTC time). Rubber debris damaged hydraulic lines on the aircraft´s landing gear and brake systems. The flight proceeded to Helsinki-Vantaa, landing at 11.53 without any further damage. No persons were injured in this incident.

The incident was classified as a serious incident. On 26 June 2009, Accident Investigation Board Finland appointed investigation commission C2/2009L to this occurrence. Investigator Vesa Kokkonen was named investigator-in-charge, accompanied by investigators Jouko Koskimies and Niina Aintila as members of the commission. Fire Officer Heikki Harri was invited to assist the commission as a rescue service expert.

The takeoff was otherwise normal except for the fact that the Electronic Centralized Aircraft Monitor (ECAM) generated the amber caution BRAKES HOT. Approximately six minutes after takeoff the ECAM generated a caution related to a leak in one of the hydraulic systems (green). The crew acted according to the instructions displayed by the monitoring system. Four hours from takeoff the ECAM annunciated that the hydraulic fluid in the green hydraulic system had been depleted to the minimum level.

After the aircraft departed Shanghai, pieces of tyre with the marking Finnair were found on the runway. The pieces were delivered to the Lufthansa mechanic who performed the turnaround check on the aircraft. He then reported the matter to Finnair in Helsinki, photographed the pieces and e-mailed the photos to Helsinki. The photos indicated that the pieces came from OH-LQE’s tyre number six, on the rear inner wheel of the left main landing gear. Preliminary information regarding a tyre failure was reported to the flight crew approximately three hours before landing. This was supplemented by precise information regarding the tyre in question 21 minutes prior to landing.

During the flight the crew assessed the problems caused by the hydraulic fault as well as the required corrective action. It became evident that, among other things, they had to extend the landing gear by gravity extension, which meant that the center gear would not extend and no nosewheel steering would be available. Later, the information of a tyre failure added to the uncertainty regarding the extent of the damage and the condition of the landing gear. Therefore, 40 minutes before landing, the captain decided that the cabin had to be prepared for a possible emergency during landing. The air traffic control at Helsinki-Vantaa arranged a priority approach and landing for the OH-LQE on runway 22L.The emergency response service was also alerted. The landing was successful but, during braking, the other hydraulic system (blue) began to leak through a fractured brake line coupling. After the aircraft had become stationary the blue system drained completely. Since nosewheel steering was inoperative the aircraft had to stop and stay on the runway. After approximately 20 minutes the aircraft was towed to the apron, where the passengers deplaned.

Investigation revealed that tyre number 6 delaminated during takeoff and the tread shredded into pieces. Chunks of loose rubber flying off at high velocity damaged hydraulic lines on the green hydraulic system as well as the brake line coupling on wheel number 2. Wheel number 2 is in front of the damaged wheel number 6. The green system depleted to its minimum level through a rupture on the gear-up line. After the aircraft had come to a standstill, the blue system drained through the damaged brake line coupling.

The damaged tyre had previously been on another aircraft. The tyre had been sent for retreading because a pinhole had been discovered. The hole was not reported to the retreading company nor was it detected during the retreading process. Later, the tyre was installed on the OH-LQE. Pressurised nitrogen had been gradually seeping between the tread and the belt plies, causing the tread to begin to detach and finally separate at take-off in Shanghai. Rubber discoloration caused by overheating was detected during the inspection. It is possible that overheating degraded the integrity of the tread and the belt plies, thereby accelerating delamination.

The leaks on the green and blue hydraulic systems were caused by the impact energy of the tyre shreds when they hit at high velocity the hydraulic lines in the wheel well as well as the brake line coupling on wheel number 2.

The investigation commission recommended that Airbus Industries evaluate the need for and possibilities of shielding hydraulic and electric systems in wheel wells.

C2/2009L Report (pdf, 1.97 Mt)