The Nimrod Review - Official Documents

The Nimrod Review
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combination of consistently pessimistic Design Authority predicted lives for the hot air ducts and a minimal
number of failures detected during inspection 47 seems to have engendered an atmosphere of ennui among
those responsible for ensuring the integrity of the hot air system, such that no positive action had been taken to
resolve and explain the discrepancy in views. However, while rejecting the duct lives determined by BAE Systems
in June 2005, the Nimrod IPT was nonetheless convinced that the ducts should be lifed, but that more credible
figures should be determined. As a result, BAE Systems was tasked with further work (see below).
As regards the UI’s recommendation that a hot air leak warning system should be introduced for the duct which
failed on XV227 and for the Cross-Feed bleed air-duct, even following the UI Report, the IPT continued to hold
the view (relying on the presence of the centre section overheat detectors) that the only duct not covered by
such a system was the one that had failed on XV227 and which was subsequently being replaced throughout
the fleet. 48 In any event, the IPT ultimately decided not to proceed with the proposed warning system, on the
basis that it was not practicable to do so given the length of time it would take to introduce such a modification
into service compared against the MR2’s OSD. 49 As mitigation in support of this decision, the IPT noted that the
aircrew procedures in relation to SCP malfunctions had been amended so as to increase awareness of SCP duct
failures.
Further investigations into the life of the ducts
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The IPT did, however, adopt the other recommendations of the UI into XV227, including that the ducting which
had been removed from XV227 should be the subject of a test programme in order better to inform decisions
on a safe life for each duct. BAE Systems was tasked to carry out this exercise. From late December 2006 into
2007, BAE Systems issued a number of reports to the Nimrod IPT with the results of its pressure testing and
examination of the ducts. 50 At a strategy meeting held at BAE Systems Chadderton on 20 February 2007, it was
agreed that that BAE Systems would categorise the different sections of duct identified in its June 2005 report
according to the likelihood of significant collateral damage to fuel pipes and tanks in the event of duct failure,
and therefore the priority for their replacement. It was further agreed that BAE Systems would provide the IPT
with a lifing policy for all of the relevant ducts.
51 BAE Systems reported back to the IPT in a letter dated 8 March 2007, setting out its conclusions in relation
to these two tasks. A replacement category of 1 (i.e. the most important) was attributed to the ducting which
was close to the No. 7 fuel tank, and also to ducting which was close to fuel pipes in Rib 2. For the vast majority
of the ducts, a safe life of 2,500 flying hours was given. For reasons which remain obscure, the Nimrod IPT did
not receive a copy of BAE Systems’ February or March 2007 reports until June 2007 (and hence these were
not available to the BOI when preparing its report on XV230). Subsequently, in response to an IPT request
for clarification dated 3 December 2007, BAE Systems confirmed that its lifing policy recommendation also
covered non-critical, non-bellowed ducts and that its intent was that the life of all ducts in the system should
be the same, i.e. lifed at 2,500 flying hours. This decision was agreed between the IPT and BAE Systems, based
on a combination of BAE Systems’ theoretical calculations and the results of tests on actual ducts. The life is
significantly greater than the purely theoretical figures previously quoted, but also significantly less than the life
displayed by the great majority of the aircraft’s hot air ducts. The simple fact is that, having been replaced, the
ducts will not need further replacement within the predicted life of the remaining Nimrods.
47 This attitude does appear to be contradicted by an IPT generated document following the XV227 incident which states: “many ducts have already
been changed across the fleet due to leaks from the bellows or corrosion”: ES(Air)(WYT)/512752/8, dated 6 October 2005.
48 See the IPT’s memo on the “Supplementary Cooling Pack Damage Sustained by Nimrod MR2 XV227 – Unit Inquiry Recommendations”, ES (Air)/
(WYT)512752/8, dated 6 October 2005.
49 “XV227 Hot Air Duct Failure – Requirement for Leak Detection System”, DLO (Strike) (Wyt)/512752/21/227, dated 5 July 2006; BOI Report, Exhibit
24. In fact, the Out-of-Service Date was at the time 2010, not 2012.
50 e.g. Letter “Nimrod – Testing of Hot Air Ducts Removed from XV227” dated 8 December 2006 and BAE Systems’ Document No. CHD-TFM-R-ISA-
MB1486 “Pressure Testing and Examination of Nimrod Hot Air Ducts taken from Aircraft XV227 and XV228”, dated 28 February 2007.
51 BAE Systems’ Reference: FAT/801R/07/009