The following is extracts from the report. Essential reading.
Check out the picture of the fire pattern:
http://www.aaib.detr.gov.uk/formal/gbgjl/bgjl8f.jpg
http://www.aaib.detr.gov.uk/formal/gbgjl/bgjl8i.jpg http://www.aaib.detr.gov.uk/formal/gbgjl/bgjl8j.jpg http://www.aaib.detr.gov.uk/formal/gbgjl/bgjl8kl.jpg
Although the wind was only some 5-7 kt - a strength so slight that it would have been a relatively insignificant factor in terms of aircraft handling - there is a powerful body of evidence which clearly shows that the influence of the wind onthis accident was paramount. Not only did it drive the static fire plume against and beneath the hull, making a more rapid penetration of the aluminium alloy fuselage skins inevitable, it created an aerodynamic pressure field around the fuselage which, once doors and exits had been opened on the side opposite to the fire, induced the products of the external fire into and down the length of the cabin interior. In turn, some interior materials ignited leading to the development of a fire inside the cabin.
The effect of a crosswind blowing over a fuselage is principally to create a region of high aerodynamic pressure on the upwind side of the hull, and a low pressure region on the downwind side, relative to the ambient pressure (Appendix 8 Fig i). Consequently, once the fuselage is opened to the outside atmosphere, whether as a result of penetration by the fire or because of doors and escape hatches being opened, there will be flows set up through the cabin interior dependent upon the pressure differential between the various apertures in the hull. (It is of extreme importance to appreciate that the wind strength necessary for this pressure-field mechanism to operate in practice has been shown to be very low17 - as little as 1 or 2 kt is sufficient.(Appendix 8 Fig j) These flows are crucial, because they have the capability to draw fire and toxic combustion products
62 The wind was the principal factor controlling the fire's behaviour. It carried the external pooled fuel fire against and beneath the rear fuselage, giving rise to rapid fire penetration. Subsequently the wind induced aerodynamic pressure field around the fuselage drew fire products into the hull, through the cabin interior and out through open exists on the right side of the fuselage.
63 The initial fire penetration of the fuselage occurred within 20 seconds of the aircraft stopping, when the lower skin panels on the left side adjacent to the aft cargo hold were burnt through, followed shortly afterwards by penetration of the fibreglass accoustic insulation blanket. This gave the fire access to a cavity surrounding the cargo hold, from which it entered the aft cabin via floor-level air-conditioning grills located on each side of the aircraft.
64 It is estimated that within 1 minute of the aircraft stopping, the fire penetrated the cabin sidewalls just above floor level adjacent to seats 17A to 19A, giving the fire direct access to the cabin interior
4.1 Procedures should be developed to enable the crew to position an aircraft, when a ground fire emergency exists, with the fire downwind of the fuselage. Visual indicators of local wind direction located within the manoeuvre areas would be valuable aids to the implementation of such a procedure. (letter to CAA 14 March 1986)
[ 30 September 2001: Message edited by: Propellerhead ]
[ 30 September 2001: Message edited by: Propellerhead ]