The Nimrod Review - Official Documents

Lack of Trend Analysis
5.49
5.50
Chapter 5 – Leak from Fuel Coupling
48 As required by Maintenance Policy, and as the BOI correctly emphasised: “...it is important that corrective
maintenance trends are analysed and, where appropriate, reflected in changes to preventative maintenance
schedules” 49 . Unfortunately, as explained above, the maintenance data for the Nimrod fuel system was never
subject to any trend analysis at a component level which would have allowed the increase in leak rates to be
detected. In his comments on the XV230 BOI Report, whilst noting that fault trends had been analysed and
that the direction contained within JAP 100A-01 had been followed, the RAF Kinloss Station Commander went
on to note that: “…the analysis was not effective as it did not identify the increase in fuel leaks that the BOI
uncovered.”
Nimrod was not part of the Logistics Information Technology Strategy (LITS) because the Nimrod’s (perceived)
impending out-of-service date (OSD) was thought not to make this worthwhile. However, the data relating
to the maintenance record of the aircraft did exist and it is regrettable that insufficient effort was applied to
analysing fault trends to inform maintenance decisions. In order to analyse the trend of fuel leaks, the BOI was
forced to sift through a database containing summaries of several thousand aircraft job cards, examining each
record individually to see if it contained any relevant data. The inadequacies of the official Nimrod data recording
systems are illustrated by the fact that the Nimrod Line Engineers at RAF Kinloss felt the need to develop their
own database, which unfortunately fell into disuse when the individual Line engineer with the Information
Technology (IT) skill to construct and maintain the system was posted elsewhere. From my discussions with
personnel at RAF Kinloss, it is plain that it was regarded as a valuable asset and its passing is much regretted
now.
5.51 Following the accident to XV230, the Nimrod IPT introduced mandatory reporting of fuel leaks using a form
known as a Leaflet 70 from AP101B-0500-2(R1). These were to be sent to the IPT when completed to highlight
any ongoing problems with fuel leaks. As a result of the F765B investigation into the fuel leaks on XV229 in
December 2008, one of the observations made by the Investigating Officer, was that his review of a significant
number of Leaflet 70s listed ambiguities, factual inaccuracies, and non-standard practices: “It was concerning
that there seems to be no follow up action by the IPT to address these anomalies ... it is considered that the
robustness of the reporting and reviewing process is questionable and requires a process review.”
5.52
This lack of follow up is a matter of concern, particularly since Leaflet 70 was meant to serve as the primary
monitoring tool for fuel leaks and the effectiveness of any new procedures to deal with them, such as the
enhanced inspection regime.
Prevailing attitude that fuel leaks ‘inevitable’
5.53
There was (and remains) a prevailing attitude that leaks in aviation fuel systems are an inevitable fact of life.
5.54 This is reflected in, e.g., the DE&S “Review of Lifing and Maintenance Policy for Aircraft System Seals”, 50 dated
22 November 2007, which stated that: “ultimately, leaks from seals are inevitable and the system design
principles used for aircraft in both the civil and military environments to mitigate against leak hazards (sic)”.
The term ‘leak tolerant’ (a term which seems to have sprung up since the loss of XV230) appears intended to
convey the sense that fuel leaks in themselves should not pose a significant hazard because aircraft should be
designed and constructed such that leaks would never reach a point of ignition. This is undoubtedly true in
theory: any competent designer should naturally do everything to eliminate the risk posed by sources of ignition.
Nonetheless, as the TWA 800 case51 and XV230 have starkly illustrated, however careful you think you have
been, you cannot be sure you have anticipated all potential ignition sources.
48 JAP 100A-01, and BOI Report, paragraph 32(a)(5).
49 As mirrored by civilian maintenance procedures: see Civil Aviation Authority (CAA) IP leaflet 1-7, BOI Report, Exhibit 12.
50 DE&S(WYT)/365/8/2/CASD, page 18.
51 TWA 800 exploded on a flight from Paris to New York on 17 July 1996 over Long Island. Investigators determined that fuel vapour in the almost
empty central fuel tank had been ignited by an unknown source, most probably an electrical short.
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