The Nimrod Review - Official Documents

Fuel Seal Replacement Programme
15.16
Chapter 15 – BOI Recommendations and Post-XV230 Events and Measures
18 As a result of a key BOI recommendation, a Fuel Seal Replacement Programme (FSRP) was instituted. This
targeted for replacement 42 fuel seals in areas where an independent study19 had shown that a fuel leak would
be particularly undesirable. This programme is being undertaken by a specially trained team who ensure that
their work does not disturb the alignment of the fuel system pipes. Contrary to some prognostications by those
who believed that fuel seals were best left undisturbed, the FSRP has so far produced encouraging results.
Hot Air Duct Replacement Programme
15.17
20 As a result of a further key BOI recommendation, a Hot Air Duct Replacement Programme (HADRP) was
instituted. The BOI recommendation was made in the light of the disintegration of part of the SCP duct at the
‘elbow’ on XV227 in November 2004, following which BAE Systems was commissioned to complete a survey
of the ducting within the system and, if necessary, recommend the ‘lifing’ of the components. The initial BAE
Systems report21 recommended setting lives for the ducts which were significantly lower than those that the
RAF had experienced in actual use. As a result, BAE Systems was tasked to reconsider its proposals in the light
of practical experience and fatigue tests of actual ducts. BAE Systems produced a further series of papers and
letters in 2007 and 2008; the result of this activity was a decision, agreed with the Nimrod IPT, that a life of
2,500 hours for the aircraft’s hot air ducts would be appropriate. This in turn triggered the HADRP. The residual
risk inherent in continuing to use the system was mitigated by the fact that the prohibition on SCP use would
continue, the Cross-Feed ducts would only be used on the ground for engine start and all high-temperature
ducting in use in the air is contained within a fire zone.
15.18 As explained in Chapter 7, as a result of BAE Systems’ work and the BOI’s recommendation, in June 2008, the
Nimrod IPT issued a Special Technical Instruction (STI 926) regarding a fleet-wide duct replacement programme,
requiring the replacement of the high pressure hot air ducts between the ECU and the Cross-Feed valves, and
also those that formed the Cross-Feed system. The Nimrod IPT determined that, for the risk to the aircraft to
remain ALARP, the replacement programme should be completed by 31 March 2009 and that aircraft that
had not had their hot air ducts replaced by this time would not be flown until the work had been completed.
Although it had originally been planned that the programme would be completed by 31 March 2009, delays in
the provision of replacement parts made this unachievable. As at the date of writing, eight Nimrod MR2s and
two R1s have been through the HADRP. The only aircraft that have not been through the HADRP are those in
scheduled maintenance; these aircraft will have their ducts replaced before returning to service.
Teardown by QinetiQ commenced August 2008
15.19
While scoping the work necessary to complete the AASyA, the IPT concluded that the most effective means of
achieving the BOI’s intent would be physically to dismantle a Nimrod to identify areas of concern; indeed, this
would enable an examination of the condition of the entire aircraft, not just its systems. The Chief of Defence
Materiel authorised a forensic ‘teardown’ of a Nimrod to be carried out. I understand that this may be the first
full-scale forensic teardown of an aircraft to examine systems that has ever been conducted anywhere in the
world. On 1 August 2008, QinetiQ was contracted to undertake this major task. The task was completed in
July 2009 and the total cost is estimated to be £2.6 million. The aircraft chosen (XV236) was one which would
have been due a Major maintenance procedure; by virtue of the time since it had last undergone an extensive
maintenance procedure, this aircraft would exhibit the greatest range of defects and degradation. This approach
proved fruitful. A large number of issues were found and raised by QinetiQ. The majority of arisings were of a
relatively minor nature and would have been identified and corrected during the previously planned Major. 22
18 Following the decision not to life fuel system seals (BOI Recommendations 5 and 6 at paragraphs 65a (1) and (2)), other means were sought to
address the issue of fuel leaks; the Fuel Seal Replacement Programme was one of these measures.
19 “Nimrod Fuel System Zonal Hazard Assessment”, QINETIQ/EMEA/IX/SA0701788, Issue 1.
20 BOI Recommendation 11 at paragraph 65 c of the BOI Report recommended measures to prevent the hot air system acting as a source of ignition,
including that “the study into corrosion....undertaken following the hot air leak on XV227 is completed and its recommendations acted upon”. The
decision to replace the hot air ducts was a direct result of this study.
21 MBU-DEB-R-NIM-FF0786, dated 1 June 2005.
22 Comment by QinetiQ personnel to Review member during Review inspection of XV236 at Boscombe Down.
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