The Nimrod Review - Official Documents

FRS or Avimo?
5.141
5.142
5.143
Chapter 5 – Leak from Fuel Coupling
Is an FRS or an Avimo coupling more likely to have been the cause of the fuel leak on XV230? In my view, the
probabilities favour an FRS seal rather than the Avimo seal having failed in the starboard No. 7 Tank Dry Bay of
XV230 leading to the fatal fire. It is, however, a finely balanced matter. I have come to this view principally for
three reasons:
5.140.1 First, there has been recent powerful empirical evidence that FRS couplings can and do suddenly spring
major leaks and maintain a flow rate which would provide more than sufficient fuel for the fire observed
on XV230. Two instances were recorded on video. In February 2007, the BOI was given a video of a fuel
leak on XV250 which was in theatre at the time. In December 2008, a further video was taken of two
fuel leaks on XV229. A still from the video of XV250 is set out below.
Figure 5.13: Leaking fuel coupling
5.140.2 Second, whilst it is true that we now know Avimo seals fitted post-2000 are made with non-conforming
material which makes them prone to deterioration and splitting, so far, no Avimo seal has actually been
found leaking. This may be due to the fortunate construction of the encircling metal flange.
5.140.3 Third, numerically, the probabilities favour an FRS coupling being the culprit on this occasion because
there were eight FRS couplings in the starboard No. 7 Tank Dry Bay and only one Avimo seal.
As I have said, however, this is a finely balanced matter and there is a significant possibility that it could have
been the Avimo seal which failed on this occasion, particularly given its prime location immediately above the
SCP elbow.
I deal elsewhere with the question of whether a fuel coupling leak or AAR was the more likely source of the fuel
which led to the loss of XV230.
Responsibility
5.144
Fuel leak from coupling in the No. 7
Tank Dry Bay at a rate of approx ½
pint per minute
The MOD must bear a share of responsibility for the probability that the failure of an FRS or Avimo fuel seal
contributed to the loss of XV230 principally for three reasons. First, the failure of the MOD to do enough to
monitor fuel leak rates over the years. Second, the failure of the MOD to give better guidance for the fitting of
couplings and elimination of fuel pipe leaks. Third, the failure of the MOD to give consideration at any stage to
a pro-active approach to fuel couplings, e.g. a seal inspection and replacement programme, notwithstanding:
(a) the five-year inspection regime stipulated in the original DDP for FRS couplings99 (which was the predicate
for stipulating ‘indefinite life’); and (b) the substantial increases in the Out-of-Service date of the MR2 fleet as a
result of delays in the MRA4 programme.
99 BOI Report, Exhibit 75.
103