What went wrong with BA flight?
Air accident investigators have released their first information about the events that led to the crash-landing of BA flight 038 at Heathrow.
A final report will be released once a much more extensive inquiry has been carried out.
LOSS OF POWER
An initial assessment from the Air Accidents Investigation Branch (AAIB) said that the Boeing 777 failed to respond to demands for extra thrust during its final descent towards Heathrow.
"At approximately 600ft and two miles from touch down, the autothrottle demanded an increase in thrust from the two engines but the engines did not respond," the preliminary report said.
"Following further demands for increased thrust from the autothrottle, and subsequently the flight crew moving the throttle levers, the engines similarly failed to respond."
The lack of thrust meant the speed of the aircraft reduced, and it came down on the grass short of the runway, the report added.
The findings confirm early theories that the pilots were pitched into a struggle to control the crucial final moments of descent. Only hours after the crash, an airport worker had told the BBC that one of the pilots had described how the aircraft "just shut down".
What remains to be revealed is why both engines failed to respond.
A simultaneous failure of the highly-reliable engines seems unthinkable, so investigators will focus their attention on the plane's systems.
The initial report says that "the range of aircraft systems that could influence engine operation" will now be examined in greater detail. Information from various modules within the plane will be gathered and studied.
The plane's fuel supply, hydraulics, electrical and computer systems are all likely to be examined in this phase.
Theories floated earlier relating to a loss of power also included:
· Fuel contamination or starvation - if water got into the system, or some blockage occurred, it would explain loss of power, although not why both engines were hit at the same time
· Running out of fuel - although this continues to look unlikely in itself, as the AAIB report says that a "significant amount" of fuel leaked from the aircraft, and in any case that would not explain why no early warning of fuel shortage was apparently given to the crew.
· Bird strike - if a flock of geese or other large birds had been hit, the damage could conceivably have been sufficient to knock out or seriously compromise both engines - although the engines are put through rigorous testing to ensure they can withstand this
· Wind shear - rapidly-changing winds in very squally conditions can cause planes to stall - but no reports from the area at the time suggest significant wind shear conditions
GETTING THE FULL PICTURE
The task of investigators from the Air Accidents Investigation Branch (AAIB) will be proving much easier than in many cases, as the flight recorders and wreckage have been easily accessible and not deep under water or damaged by fire.
As well as the recording of cockpit conversations, the inquiry team have accessed the plane's technical data from the second so-called "black box" recorder.
The fact that all crew and passengers survived will also help build up a detailed picture of exactly what happened and over what timescale.
Already it is clear that passengers were given no early warning of a problem with the plane.
Most accidents are caused by a chain of events rather a single catastrophic one, so investigators will be keen to explore all aspects of the incident before reaching their final conclusion.
A fuller report is due to be released within 30 days.
