Investigators are trying to find out why a British Airways plane, carrying more than 150 people, crash-landed at London's Heathrow airport.Captain Peter Burkill was praised for his professionalism after all 136 passengers and 16 crew survived the crash-landing on the south runway.The Air Accidents Investigation Branch (AAIB) will interview the crew and file an initial report in 48 hours. Investigators are also examining the 'black box' flight data recorder.British Airways (BA) said it was planning to operate all its long-haul departures from Heathrow today and up to 90% of its short-haul departures. Passengers have therefore been advised to check with their airline before setting out for the airport.Wings damagedGordon Brown's own flight to China was delayed as the Boeing skidded across the grass short of the runway and pulled up about 1,000 metres from the Prime Minister's plane.Mr Brown, who is on a state visit to Beijing, praised the 43-year-old pilot's "professionalism" in managing to avert a major disaster.He said: "I think it's right to pay tribute to the calmness and professionalism of the British Airways staff and the captain and what he achieved in landing the aircraft. Captain Peter Burkill will be given as much time off as he needs, said BA."The speed of the evacuation we saw at first-hand, and the total professionalism and dedication of the staff.The AAIB will now be checking flight data and cockpit voice recorders at its headquarters in Farnborough, delivering a further preliminary report within 30 days. More than 200 flights had to be cancelled or diverted to other airports following the accident at lunchtime on Thursday.Witnesses described the plane coming in very low and landing short of the runway, before skidding across grass and tarmac. Part of the undercarriage, including two wheels, was torn off and there was some damage to the wings.Eighteen people needed treatment for minor injuries, including whiplash. But by Thursday night, all but one female passenger had been discharged.The 'Experienced pilot'British Airways chief executive, Willie Walsh, also paid tribute to the air crew, describing them as "heroes" and commending all of the crew as having done a fantastic job evacuating the 136 passengers. “Everyone at British Airways is very proud of them." Mr Burkill is described as an "experienced pilot" who has been with the airline for nearly 20 years.So far neither British Airways nor the authorities at Heathrow will speculate about the cause of the accident. However, Theories about the cause of the crash include: Mechanical or electronic failure, birds flying into engines, sudden wind change and pilot error.An unnamed airport worker interviewed by the BBC said that the captain had told him that the Boeing 777-200ER had lost all power after "all the electronics" failed while the plane came in to land.Witnesses on board the plane said they only became aware of a problem just before the plane was due to land.Passenger Jerome Ensinck said: "There was no indication that we were going to have a bad landing. When we hit the ground, it was extremely rough, but I've had rough landings before and I thought 'This is the roughest I've had'."'Extremely reliable'The Chief Inspector of Air Accidents, David King, warned it could take some time to discover the cause of the crash but said: "I have a duty to take any action we consider necessary as soon as we become aware of any safety-related aspects arising from the investigation."So far B.A is not grounding any of the 43 Boeing 777 planes in its fleet. The aircraft is generally thought by experts to be extremely reliable; with no serious accidents involving the 777 since the plane first went into production in 1996.SOURCE: BBC