The Nimrod Review - Official Documents

The Nimrod Review
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In the event, however, it was considered that the low rate of 30 leaks per year did not warrant any further
action. It would appear that, after a brief consultation with the Nimrod Major Servicing Unit and Nimrod Line
engineers at RAF Kinloss, it was agreed that there was no need to change the extant maintenance policy for
the Nimrod fleet. 4
In my view, there is much that is worthy of note in relation to the Harrier GR3 XW921 incident. First, it is
significant that the Harrier BOI considered that the alignment of fuel pipes and couplings was important and
recommended “geometric checks”, mirroring those made later for the Nimrod aircraft as a result of incidents
following the loss of XV230 (see Chapter 5). This reflected similar concerns over pipe misalignment as a cause of
leaks. It is also noteworthy that, as the sequence of correspondence developed (see above), the recommendation
of a “geometric check” was apparently overlooked. It is also interesting to note the comments by the Harrier
EA to the effect that this was a safety issue and that the drying-out of seals during Major maintenance was also
a factor. As explained in Chapter 5, these were all points that came to be recognised again in the aftermath of
the loss of XV230.
It is clear from the documents I refer to above that there was an attempt, following the loss of XW921, to consider
the accident’s implications for other fleets. However, the Harrier BOI’s recommendation was diluted (undoubtedly
unintentionally) and the subsequent analysis for the Nimrod was based solely on whether the current leak rate
was acceptable or not. It would appear that one of the Nimrod engineering officers considered that some
deeper analysis might be warranted in order to ascertain if any of the couplings were failing regularly and, if so,
whether they were in locations which could constitute a hazard to the aircraft (see above). Unfortunately, this
was not agreed and the decision was taken that the perceived low frequency of coupling leaks (30 per year)
did not justify further action. At no future time do any of the Nimrod documents seen by the Review make any
mention of the Harrier BOI recommendations (other than the Ground Incident Report considered below).
It should also be noted that, in 1988, the fuel leak rate for the Nimrod was believed to be 30 leaks per year.
This was well above the figures used by those who compiled the Nimrod Safety Case (NSC) some 15 years
later (see Chapter 10). In more recent discussions with Nimrod engineers at RAF Kinloss a figure of a leak a
fortnight (not including wing leaks) was suggested for operational aircraft. It is equally important to note that
such a rate was not considered excessive. However, one should bear in mind the point later made by the XV230
BOI and in this Report that any factor which might contribute to a fire should be minimised. In relation to the
Nimrod, it was the increase in leak rates over time which should have provoked at least the consideration of
remedial measures, not necessarily the absolute number of leaks. This sort of safety-related decision requires
maintenance of comprehensive records throughout the life of a platform and, equally importantly, an ability to
interrogate them effectively (see the Recommendations in Chapters 21 and 22).
(2) c.1999: Nimrod XV249 – history of fuel coupling leaks in Rib 1 area
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4 Ibid.
Nimrod XV249 was converted from a Nimrod MR2 to a Nimrod R1 in order to replace XW666, lost on 16 May
1995. The aircraft subsequently suffered from a continuous series of fuselage fuel leaks, which eventually led
to an extensive investigation and rebuild of the fuselage fuel system. Nonetheless, whilst the aircraft’s leaks
were eventually cured, it proved impossible to isolate a single system as the point of failure. Analysis of the
faults highlighted, inter alia: fuel couplings that leaked in flight, but not on the ground; fuel pipes that moved
in flight, provoking leaks; and fuel pipes of the same part number, but different construction and lengths. It is
noteworthy that fuel leaks originating to the rear of the Rib 1 area (the proximity of the No. 7 Tank Dry Bay)
were observed to track to the rear of the wing root, the pannier bay (equivalent to the MR2’s bomb bay) and
the tail cone. Fuel leaks were also noted to be associated with Air-to-Air Refuelling (AAR) sorties, although
not exclusively so. As the XV230 BOI observed, although XV249’s problems were attributed principally to its
conversion from an MR2 to an R1, coupled with the fact that it had been stored outside for some time prior to
conversion: “it does illustrate the potential for complex fault scenarios within the Nimrod’s fuel system and the
fact that the leaking fuel can potentially find its way to many areas of the airframe.” 5
5 BOI Report, Annex E [E-2].