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22nd of June 2009

An Airbus A340-313 was being prepared for a flight from Shanghai (China) to Helsinki (Finland). Onboard the aircraft were 12 crew members and 195 passengers. The relief pilot performed an external inspection of the aircraft after the local engineer had performed his turnaround inspection. Neither of the two inspections revealed any abnormalities.

The mainwheel with the missing tread, the red line indicated the trajectory of the separated tread. (© Finish Accident Investigation Board)

There was a slight delay to the 01.40 UTC departure due to traffic. The engines were started at 02.01 UTC and after receiving taxi clearance the aircraft taxied to runway 17L. Due to traffic, it took 16 minutes to reach the runway. No abnormalities were observed during the taxi.

At 02:17 takeoff was initiated, and during the take-off roll, a BRAKES HOT caution message was presented on the ECAM ( Electronic Centralized Aircraft Monitor). The takeoff was continued as this was not a requirement in the Aircraft Operating Manual.

The aircraft lifted off the runway normally, and due to the BRAKES HOT caution, the gear was not immediately retracted. After which the configuration of the aircraft was cleaned up and the flight continued to climb.

At 02.23 UTC the ECAM alerted the crew that there was a leak in the Green Hydraulic system, with a G SYS LEAK caution. (one of the 3, Green, Yellow, and Blue). As per procedures, the crew monitored the hydraulic quantity and noticed that it was slowly reduced. At 02.54 the crew decided to turn off the Engine-Driven Pumps for the Green Hydraulic system on engines 1 and 4, causing a low-pressure warning for the system. During the cruise phase of the flight, at 06.39 UTC the crew received a low-level caution for the Green reservoir, in accordance with the ECAM procedure the electric pump for the system was turned off.

The damaged tire after landing in Helsinki with the missing tread (© Finish Accident Investigation Board)

During the flight, the crew was in constant contact with their maintenance organisation in Helsinki via ACARS ( Aircraft Communication Addressing and Reporting System). The required procedure for the loss of the Green hydraulic system informed the crew that the following system would be affected;

  • Normal landing gear extension (alternate extension required)

  • Due to alternate extension landing gear doors would remain open and the center main gear would not extend.

  • Nosewheel steering inoperative

  • Thrust reversers are inoperative on engines #1 and #4

  • two of the six spoilers are inoperative

This would result in a 15% longer landing roll.

At 11.09 UTC the crew was informed by maintenance that pieces of tire tread were found in Shanghai and that these pieces were conformed to have originated from their aircraft. this information let the captain to decide to prepare the cabin for an emergency.

Although the gear had to be lowered manually the approach and landing were uneventful with the aircraft decelerating normally and no handling issues observed. After the aircraft came to a stop a hydraulic leak was observed on one of the brakes, causing the blue hydraulic system to empty in ~4 minutes. Firefighters cooled the brakes using fans to reduce the risk of fire.

Damage to the aircraft consisted of;

  • Tread separated on the #6 main wheel

  • Green hydraulic line suffered a 10 mm rupture as a result of impact by tire debris

  • Damaged hydraulic connector on brake #2 as a result of impact by tire debris

  • Left inner flap as a result of impact by Damaged wiring in the wheelbay tire debris (© Finish Accident Investigation Board)

  • electrical wiring shrouds and landing gear door damaged

  • Impacts on Fuselage

  • Impacts on Horizontal stabiliser

The incident was investigated by the Finish Accident Investigation Board (FAIB). They concluded that the tread separation was caused by a pinhole in the tire that was not found during the retreading process of the tire. This caused a gradual build-up of pressure between the carcass of the tire and the tread. The full report, with more details, by the FAIB is available by clicking here.

Airbus A340 Hydraulic Schematic (© Finish Accident Investigation Board)

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