On 22 June 2009, an Airbus A340-300 being operated by Finnair suffered a single tyre failure during take off on a scheduled passenger flight to Helsinki and malfunction assessed as consequential by the flight crew occurred to the hydraulic system. The flight proceeded to destination and carried out a daylight landing there without any further aircraft damage. Because of a further deterioration in the status of the aircraft hydraulic systems during the landing roll, the aircraft stopped on the runway and was towed into the gate. No persons were injured in this incident.
An Investigation was carried out by Accident Investigation Board Finland. It found that the take off from Shanghai had been normal but that the Electronic Centralized Aircraft Monitor (ECAM) had subsequently indicated the caution ‘BRAKES HOT’ followed, about six minutes after take off, by a caution because of a leak in the green hydraulic system and about four hours after take off an annunciation of green hydraulic system fluid at minimum level. Examination of runway debris led to the conclusion that they were from the inner wheel of the left main landing gear and the flight crew were informed accordingly.
A review of hydraulic system status by the flight crew revealed that they would have to extend the landing gear by free fall, which meant that the centre body gear would not extend and no nosewheel steering would be available. Because of the assessed risk of landing gear damage, the aircraft commander decided that the cabin should be prepared for a possible emergency during landing.
The landing was uneventful but during braking, the blue hydraulic system began to leak through a fractured brake line coupling, emptying completely after the aircraft had stopped.
It was found that the tyre tread on one of the wheels of the aircraft left main landing gear had detached at takeoff causing pieces of rubber to impact the wheel well and other structures at high velocity. Hydraulic lines in the wheel well sustained a rupture and a dent. The brake line coupling on wheel number 2 was damaged. A trailing edge flap also sustained a tear but this did not hamper the functioning of the flap. There were also impact marks elsewhere on the aircraft. The green hydraulic system drained below the minimum fluid level which caused the following faults:
- normal gear down selection inoperative
- no extension of the body gear
- no nosewheel steering
- reverse thrust on engines number 1 and 4 unavailable
- one pair of spoilers was inoperative, lengthening the landing roll by approximately 15%
- the green hydraulics braking system was inoperative.
However, since a brake line coupling on wheel number 2 had also been broken, the blue hydraulic system also drained after the aircraft came to a stop and its brake pressure accumulators depressurized rendering the blue system inoperative.
During the course of the investigation, Airbus informed the investigation commission that they would amend the text of the Aircraft Maintenance Manual in respect of hydraulic system check valves so as to better explain their true function and this amendment was published on 1 April 2010. Also, since the incident, Finnair has changed its instructions on fault inspection and damage reporting procedures in respect of tyres sent for retreading.
The Final Report was published on 27 April 2010 and may be seen in full at SKYbrary bookshelf: Serious incident at Helsinki-Vantaa Airport due to tread separation and hydraulic failure, 22 June 2009.
It contained one Safety Recommendation:
That Airbus Industries evaluate the need and possibilities of shielding hydraulic and electric systems in wheel wells. Justification: The investigation revealed that the hydraulic fault was caused by high energy rubber pieces impacting the fully exposed hydraulic lines in the wheel well. The rubber pieces also damaged electrical wiring shrouds.