Boeing 737-236 series 1, G-BGJL: Main document - Leonardo

approximately 42 square inch hole directlyinto the tank interior (Appendix 9). Fragments of this
accesspanel were recovered from the runway and one other fragment ofthe panel was recovered
from inside the tank cavity. Reconstructionof the access panel fragments revealed witness marks
and a patternof distortion which matched exactly the shape of the No 9 combustorcan dome and a
fan case fragment.
Outboard of the engine, the skins forming the tank roof were tornupwards from the spars and the
corresponding bottom skin, formingthe tank floor, was severely bulged downwards. The tank ribs
andinternal structure were distorted in a manner compatible withchordwise tensile loading of the
skins between the spars. Withthe exception of the damaged access panel, all damage to the leftmain
fuel tank was consistent with a rapid overpressure of thetank cavity due to the ignition of fuel
vapour in the outer sectionof the tank. The fracture surfaces at the upper skin/spar interfacewere
relatively clean, whereas the adjoining skin surfaces weresignificantly sooted - indicating that the
explosive overpressureoccurred after the fire had been burning for some time.
At the start of the accident sequence the aircraft fuel load isestimated to have been:-
each wing tank (full) 4,590 kg
centre tank
total
3,420 kg
12,600 kg
The fuel remaining in each tank could not be measured directlybecause of the practical difficulty of
emptying each tank separately.However, a tide mark of soot was found on the internal rib andspar
surfaces inside the left tank at a height which correspondedto the level of the damaged access
panel, enabling the post-accidentfuel contents of the left tank to be determined and hence thetotal
fuel loss to be estimated.
The total quantity of fuel lost from the punctured left wing tankis estimated to have been 2,109 kg
(689 US gals at specific gravity0.808), based on the position of soot 'tide-lines' on verticalsurfaces
wihin the interior of the left wing tank and the tankinitial contents and taxi fuel consumption data.
The leak rate was estimated by the manufacturers, based upon theirknowledge of fuel flow rates
through the various baffles and theinternal structure of the wing. This data suggested that the
leakrate would initially be very high, in the order of 16 US galsper second, but this would decay
rapidly as the tank compartmentimmediately above the puncture emptied. After about 40
seconds,the leak rate would have decayed to approximately 2 US gals persecond and would remain
at approximately that level until approximately200 seconds. Beyond that stage,the rate would taper
off and theflow would cease after a total time of approximately 250 seconds.(Appendix9 )
As an independent check on the validity of the leak rate estimate,the theoretical leak rate was
integrated with time and the resultingtotal compared with the leaked fuel estimate based on the
residualfuel contents. These figures agreed within 5%.
1.12.2.5 Oxygen
The emergency oxygen distribution system mounted in the overheadunits was destroyed in the fire,
but because the system was isolatedthere was no discharge of oxygen. Both passenger and crew
reservoirswere indicating full and the discharge discs were intact.
1.12.2.6 Doors and emergency equipment
Door slides