The Nimrod Review - Official Documents

The Nimrod Review
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significant safety margin to prevent blow-off. This 10,000lbs limit remained in force notwithstanding that the
original problem had been caused by an incorrectly constructed fuel tank.
Enhanced fuel and vent system maintenance regimes: 2007
15.12
14 An independent fuel system hazard analysis carried out by QinetiQ identified the requirement to inspect the
fuel system in a number of areas not previously considered. 15 Pressure testing of the fuel system vent pipes was
also introduced, to check and ensure their integrity. 16
XV235: November 2007 incident led to total cessation of AAR
15.13
In November 2007, whilst carrying out AAR from a Tristar over Afghanistan, XV235 experienced a fuel leak in
the bomb bay. A crew member noticed what appeared to be a spray of fuel emitting from the fuel system and,
in view of the crew’s understanding of what had occurred to XV230, the aircraft issued a Mayday and diverted
to Kandahar. The aircraft was examined on landing and traces of fuel in the bomb bay confirmed that there had
indeed been a leak. However, despite extensive trials, the aircraft’s engineers were unable to replicate the leak
on the ground. The inability to reproduce the leak, even when subjecting the fuel system to pressures similar
to those experienced during AAR, meant that there could be no guarantee that leaks could be detected during
pre-flight inspections. The increased risk to the Nimrod crews should they continue flying AAR sorties was
balanced against the increased risk to ground forces inherent in any reduction in Nimrod coverage concomitant
on a cessation of AAR. Following considered analysis of the issue, the AOA decided that Nimrod AAR should
cease. It should be noted that, during the investigation into XV235, an Avimo coupling was dismantled and
was found to have a pipe-to-pipe gap which was outside specified limits. A leak had been noticed from it by
the ground crew at about 1 drip per minute and so it was thought unlikely to have been the cause of the leak
seen in the air.
BOI recommendations implemented from December 2007 onwards
15.14
15.15
The BOI made a total of 33 formal recommendations in its Report which was published on 4 December
2007. 28 of the BOI’s recommendations were accepted. Five of the BOI’s recommendations were rejected. Of
these, the effect of three was achieved by an alternative course of action. Of the remaining two, a study was
undertaken into the utility of parachute escape from the Nimrod, but it was decided that any solution could not
be incorporated within the remaining life of the aircraft; a similar decision was made as to the recommendation
to fit a crash protected means of recording position and intercom voice. The most recent update on progress
with the BOI’s recommendations is to be found at Appendix A at the end of this Chapter.
Implementation of the BOI’s formal recommendations began in December 2007. Amongst the first of these was
the inclusion of more detailed information within the aircraft’s Topic 1 engineering manuals on the assembly
of FRS and AVIMO fuel system couplings. A number of the BOI recommendations, such as the review of
maintenance policy, a review of the Nimrod Safety Case to correct errors within it and the conduct of an Ageing
Aircraft Systems Audit (AASyA), 17 were extensive tasks and it was realised that they would take some time to
complete. As the Review went to publication, it was predicted that all remaining recommendations, with the
exception of the Safety Case Review, would be completed by the end of October 2009. The Safety Case Review
has resulted in the production of Safety Case 3 (SC3), as explained further below.
14 Nimrod Fuel System Safety Review Report QINETIQ/EMEA/IX/SCRO702915.
15 RTI 207.
16 RTI 196.
17 BOI Recommendation 2 at paragraph 65 a (2) of the BOI Report.