The Nimrod Review - Official Documents

8.19
8.20
8.21
Chapter 8 – Previous Incidents and Missed Opportunities
6 On 26 January 1999, BAE Systems issued a report into the persistent fuel leaks on XV249. It pointed to four
potential differences between ground and flight conditions, one of which was that “there will be structural
movement due to flight loads and cabin pressurisation, causing sympathetic movement of the fuel piping and
the interconnections.” The BAE Systems report went on to make the following observations:
“Past problems with Flight Refuelling couplings leads us inexorably towards understanding
the reasons for the system leakage. The catalogue of problems causing fuel leakage due
to airframe build difficulties when using FRS110 couplings relate back to the Lancaster,
Vulcan, Lightning, AEW MK3 Nimrod, and VC10 CMK1. The Hawker Siddeley Engineering
Standard SO8 sets the FRS standard for the manufacture of pipes, the beading of pipe
ends and the gap tolerance between mated pipes. The integrity of the coupling demands
that these criteria are met at each and every joint, a difficult achievement for the Nimrod
airframe especially when each production aircraft has build differences that exceed the
permitted tolerance banding for the couplings. …”. (emphasis added)
The BAE Systems report went on to suggest two particular causes of the problems. First, the fact that XV249
had been placed in storage and was subject to conversion in 1996: “Couplings previously wetted by fuel
and then allowed to dry out, will suffer from deterioration of the rubber, especially if the cycle was repeated
again…”. Second, BAE Systems concluded that maintenance work may have led to “assembly stresses” being
built into the system. Therefore, some seven years before the loss of XV230 and the consideration subsequently
given to the lifing of seals, there was already a recognition of some of the factors I discuss in Chapter 5, i.e.
that the ‘drying out’ of seals may present a problem and the difficulties of actually fitting the FRS couplings on
the Nimrod within the required tolerances.
It would nonetheless appear that, once the specific problem of the fuel leaks on XV249 was satisfactorily
addressed, no wider thought was given to these issues in the context of the Nimrod fleet as a whole. For example,
no steps were taken to address the ‘drying out’ issue during Major Maintenance. Rather, and notwithstanding
that the precise cause of the leaks on XV249 was never identified, once XV249 had been proved to operate
satisfactorily, the matter was considered closed. Thus, a report on the fuel leak problems on the XV249 by No.
51 Squadron’s Senior Engineering Officer, dated 23 July 1999, 7 concluded:
“Over the past 6 months, XV249 has undergone extensive investigations to identify an
elusive and potentially hazardous major fuel leak, accumulating over 500 manhours
maintenance effort. Despite the extent of this work, it has not been possible to pinpoint a
specific component within the fuel system as being the sole cause of the leak. However, it
can be stated that … the fuel system [has been] completely overhauled. Furthermore, the
test flights using fuel dye and with couplings bagged were highly successful in identifying
couplings which leak only in the air and allowed correctly targeted rectification to be
carried out.” 8
(3) 13 September 2000: Nimrod XV245 incident – leak from FRS coupling during AAR
8.22
On 13 September 2000, midway through an AAR sortie, the Tristar tanker reported that XV245 was venting fuel
from the underside of the fuselage. After landing, fuel was found to be covering the rear fuselage and to be
leaking from the No. 6 tank defuel valve outlet FRS coupling. Further investigations revealed that the seal was
split. An Incident Report9 was raised. In the section for Further Actions/Comments, it was noted “NLS Prop TM
[Trade Manager] reports that this is an isolated incident and there is no history of leaks from the subject valve.
This statement is supported by both the seal Range Manager and EA who confirm that there is no history of
faults with the subject seal.” The AV(Spey) Remarks/Recommendations then went on to state: “This incident
occurred following a fuel leak resulting from a split coupling seal. Discussion with NLS and confirmed by the seal
EA indicates there is no history of leaks associated with this seal. Closed”.
6 BAe letter PJP/AF/402, dated 26 January 1999: “Nimrod XV249 Persistent Fuel Leaks” (BOI Report, Exhibit 35).
7 51S/402/1/1/Eng (BOI Report, Exhibit 26).
8 Ibid, paragraph 18.
9 Incident Report KIN/103/00, dated 13 September 2000.
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