The Nimrod Review - Official Documents

6.47
Chapter 6 – Overflow or Pressure from Air-to-Air Refuelling
panel during AAR, much of it would have already drained via the drain holes. Although the BOI noted that
approximately 300ml of fuel could remain on the panel below the level of the drain holes, if left there for any
amount of time, it would tend to slowly drain as aircraft manoeuvres brought it to the level of the drains; and
once on the ground any residual fuel would remain on the panel until it evaporated.
I am satisfied, in the light of the above, that it is clear that blown-off fuel can enter chambers within the aircraft
fuselage.
(d) Could blown-off fuel enter the SCP fairing and the No. 7 Tank Dry Bay?
6.48
It is evident from the foregoing that: No. 1 tank blow-off can occur; that blown-off fuel will run down the
surface skin of the aircraft fuselage; and that fuel can enter fuselage openings and bays. The remaining issue is,
however, whether fuel could enter the SCP fairing and the starboard No. 7 Tank Dry Bay, in particular. The issue
turns on the dynamic behaviour of the fuel once it leaves the blow-off outlet on the aircraft’s starboard side.
No experiments have been undertaken to replicate the fuel’s behaviour and, now that Nimrod AAR has been
halted, the results of any experiments would be purely of academic interest. I nonetheless turn next to analyse
the evidence that is available.
XV230 witness trail
6.49
At the Inquest much was made of the fact that the ‘fuel witness trail’ (described by Witnesses 22 and 28 to
the BOI) observed following a sortie around 9/10 August 2006 was a ‘crescent’ shape, descending from the
No. 1 tank blow-off valve exit and crossing the bomb door hinges. It was suggested that, if this marked the
flow of fuel, then logically it could not reach the No. 7 Tank Dry Bay. However, the MRA4 liquid release trial is
instructive on two counts in explaining this. First, after the liquid had been released from the MRA4, the aircraft
was landed as soon as possible. The simple fact is that traces of liquid flow (water or fuel) on the fuselage
exterior will be erased after a period of time and BAE Systems needed an accurate record of the liquid’s flow.
After tanking, XV230 may well have spent a further eight hours in the air in August 2006. Second, the liquid
trail in the MRA4 trial proves how the liquid goes directly backwards and spreads out, even when an aircraft
is flying at a slower speed than XV230 would have been. In my view, the witness trail observed on XV230 on
this occasion in question was probably residual fuel draining from the blow-off system as the aircraft made its
approach to land.
Boundary layer of air
6.50
It is clear that ejected fuel can take a wide range of paths along the fuselage, as my discussion above of the
observed fuel flows following a probable blow-off event show. Fuel escaping from the No. 1 tank blow-off will
be ejected at pressures in the region of 2.7psi. On the ground, this may well allow the ejected fuel to appear to
spurt out with some force. However, in the air, any blown-off fuel will need to breach the boundary layer of air
on the fuselage before reaching the free-flow air. During AAR, the free flow air will have a velocity in the order
of 400 knots at right angles to the much lower velocity of the expelled fuel. This matches the simple airflow
diagrams provided by BAE Systems to the BOI. 28 However, the expelled fuel (of which there would be several
hundred litres) is unlikely to execute a neat right angled turn, parallel to the fuselage, in an orderly stream and
depart safely behind the aircraft. Common sense would suggest that, as the fuel stream hits the air flowing past
the aircraft, random interaction between air and fuel will cause a more random dispersal of the fuel, such that
it spreads out as it travels to the rear of the aircraft. The evidence from previous incidents supports this and also
suggests that significant amounts of ejected and dispersed fuel will flow along the fuselage.
28 BOI Report, Exhibit 60
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