Manufacturer surprised by damage after brake heat caused tyre pressures to rise

Airbus has to modify its A340-600 wheels and main gear design before it can pass the rejected take-off (RTO) certification tests, admits the company. Many of the wheels suffered structural failure in a 12 February RTO test when tyre pressure rose dramatically because of brake heat.

At the Istres test centre, France, Airbus carried out the prescribed tests using the A340-600 prototype, because regulations require that the brakes must be worn and gear frequently used to represent performance in an ordinary line aircraft.

The real damage, however, was more than Airbus bargained for. After the maximum braking to a standstill required in the RTO test there must be a 5min wait before fire services are allowed to attend the aircraft. Fire broke out in the port main bogey of the Messier Dowty undercarriage, and several of the Goodrich wheels broke under the stress of increased tyre pressure before the tyres' fuse-plugs could operate. The aircraft was fitted with Michelin's new NZG radial tyres, which are believed to have performed adequately.

Debris damaged gear bay doors and the fuselage but not fuel tanks. The stopping distance, however, was within planned performance requirements, says Airbus. By 21 February the company had repaired the undercarriage and flown the aircraft back to Toulouse.

Airbus says the wheels have been shown to have an "insufficient strength margin" and will be reinforced. Also, heat-shielding between the brake discs and tyres is to be improved to slow heat transfer.

There will be no delay to the three-aircraft test programme, Airbus insists, because the RTO tests are always done last in the programme since they usually cause fire and some damage.

The 1,600h flight-test programme for the -600 is in its final stages, with route-proving flights expected to begin soon ahead of European Joint Aviation Authorities and US Federal Aviation Administration certification, which is scheduled for May. Launch customer Virgin Atlantic is due to receive its first A340-600 in late June.

Source: Flight International