Shortly after departing Melbourne en route to Port Vila, Vanuatu, the crew of a Boeing 737 (B737) aircraft received advice from Air Traffic Control (ATC) that a following aircraft had observed rubber and debris on the runway. As nothing unusual had been noticed during take off, the flight crew of the B737 considered that the debris was possibly from the BAe 146 ahead of them and asked ATC if the debris could be identified. Assessment by ground engineers confirmed that the debris was a section of the left main landing gear door and tyre tread from a B737.
On receiving that information the crew checked their flight controls for any signs of restriction or abnormal handling. As the left wing trailing edge was checked for damage through the cabin window by one of the cabin crew, a passenger advised her that a bang had been heard from under the wing during take-off. No damage was observed but the flight crew decided to divert the aircraft to Sydney. Approaching Sydney, the crew contacted ATC and requested a gear-down fly-past to assess the condition of the landing gear.
The fly-past confirmed that part of the left main landing gear door was missing but the wheels appeared to be intact. An emergency was then declared and the flight crew consulted the operator's emergency procedures manual. After burning off excess fuel, the cabin crew and passengers were briefed for the emergency. The flight crew then commenced their approach with the cabin crew and passengers in the brace position and an uneventful landing was carried out.
The aircraft was stopped on the taxiway and inspected by ground engineers where it was found that the left outboard tyre had lost its tread but was still inflated, although at a lower than normal pressure. The aircraft was then cleared to taxi under its own power to the terminal and the passengers disembarked normally. Both left main wheels were deflated and replaced. Further inspection of the aircraft revealed damage to the left main gear mid door, the left inboard trailing edge flaps and the underwing false structure. Temporary repairs were carried out to the aircraft and it was flown, without passengers, to a maintenance facility in Melbourne for further repairs.
The investigation revealed that there had been impact damage, marked with black rubber, to the flaps and underwing, and ductile overload damage to the landing gear door tie rod and underwing panel support links. The left outboard main wheel and tyre were sent to overhaul and retread facilities for examination and testing.
An examination of the wheel and tyre showed evidence of air leakage from the bead area and on the tyre surface. After a pressure retention check, the wheel was disassembled and the hub-halves examined with no evidence of damage to the hub seal or mating surfaces found. The tyre liner was found to be intact with no air leakage apparent and there were no signs of delamination of the carcass inner plies. An inspection of the separated surfaces revealed areas of shiny polished rubber. That indicated that there may have been localised ply movement and separation prior to failure.
A blueing of the rubber around the tyre's shoulders and on the separated sections of tread was also noticeable. That indicated that the tyre had been overheating. Factors contributing to overheating can be, low tyre pressures, high taxi speeds, long taxiing or heavy landings. There was no evidence of cuts or foreign object damage on the tyre or tread segments.
The aircraft normally operated with moderate to high payloads and at airports with long taxiways. Both those factors would have affected the temperature of the tyre and increased the importance of maintaining correct tyre pressures. The company's standard operating procedures specified a maximum taxi speed of 30 knots, which was within the tyre manufacturer's limit. An inspection of the operator's maintenance records revealed that the tyres were checked for correct pressure daily before the first flight and every 30 flying hours on an ancillary check. However, the pressures were not recorded if they were found to be within the serviceable limits.
The failed tyre had been fitted to the aircraft for 4 weeks and during that time only one occurrence of lower than normal tyre pressure had been recorded. It was established that the tyre was at its fourth (R4) retread, with that tyre type permitted to have up to seven (R7) retreads. The failed tyre's service history, and the retread and wheel assembly processes were assessed but nothing was found that may have contributed to the tyre failure.
It was not possible to conclusively determine why the tyre tread separated from the tyre and, due to the damaged condition, if the results of the tests carried out were representative of the condition of the tyre prior to its failure. The air leakage observed on the tyre's surface during the tyre pressure testing was consistent with gas venting from between the damaged plies. This was verified by the liner integrity test. The air leak from the bead area of the tyre could not be confirmed as being pre-existing as the tyre had been deflated and reinflated since the failure.
The shiny areas observed on the tyre surface indicate that movement between the ply layers had occurred. This may have been a result of overheating, which was also evident by the blueing around the tyre shoulders or may have been from another form of adhesion failure. The overheating may have been due to low tyre pressure, although the service history of the tyre's pressure was not sufficient to conclude that the tyre had an ongoing leakage problem. The tyre pressure was found to be low after the aircraft landed, but that may have been as a result of the failure of the tyre itself and not a pre-existing condition.
Low tyre pressure and consequent overheating may have contributed to the tyre's failure. The physical recording of actual tyre pressures whenever they are checked would give a more accurate record of a tyre's pressure retention rate.
|Date:||02 August 2001||Investigation status:||Completed|
|Time:||1244 hours EST|
|Release date:||11 December 2001|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Minor|
|Departure point||Melbourne, VIC|
|Departure time||1244 hours EST|
|Destination||Port Vila, Vanuatu|
|Role||Class of licence||Hours on type||Hours total|
|Co-Pilot/1st Officer||Senior Commercial||2000.0||10400|