The Nimrod Review - Official Documents

The Nimrod Review
8.23
154
Again, evident here are the signs of a somewhat ‘closed-loop’ thinking, i.e. the analysis of events in terms of their
perceived frequency, as opposed to in terms of their potential outcome or seriousness, such as to provoke a deeper
safety analysis. This was clearly not just a small fuel leak, confined to the immediate area of the coupling.
(4) December 2000: Nimrod XV229 incident – leak from FRS coupling onto hot duct
8.24
8.25
Just three months after the above incident, there was a further incident in December 2000 on XV229. Ground
crew were conducting ground engine runs while attempting to trace leaks in the SCP’s pressure regulating and
shut off valve (PRSOV). To do so, they had removed the insulating muff. During the ground runs, fuel began to
leak from an FRS coupling in the “stbd rib 1 rear spar compartment . As the fuel dropped onto the PRSOV and
associated ducting it began to smoke”. Investigation revealed that fuel was leaking from the FRS coupling on
the No. 6 tank transfer fuel pipe, rib 1, starboard side above the hot air duct. The FRS coupling seal was found
to be split and deformed, “presumably due to ageing, thus allowing fuel to leak out”. A Ground Incident Report
was raised10 . In the section for Further Actions/Comments, it was noted:
“Leak attributed to ageing seal and seal has been replaced. However, no trend of ageing
seal related faults apparent at 1st Line or through IRD(F&F) Report. This occurrence
suspected to be isolated incident and EA will monitor for future occurrences. AC has flown
several sorties without related incident and no further action is considered necessary.”
(emphasis added)
In the section for AV(Spey) remarks/Recommendations, it was then noted that:
“FRS couplings are susceptible to leakage if misaligned, fitted incorrectly or overtorqued,
and whilst we have no explicit evidence of these in this particular incident, we do believe
these causes are more likely than ageing. Furthermore, there is evidence on other airframe
types (Harrier) of FRS seals leaking due to causes other than ageing. Therefore, other than
monitor future arisings for trending [sic], the incident is closed.” (emphasis added)
8.26 In this report, therefore, one sees an awareness of some of the issues that I discuss in Chapter 5, namely the
fact that seals age and that FRS couplings may leak if incorrectly fitted or misaligned. Once again, however,
the incident was treated as an isolated one, without (it would appear) any detailed investigation of any earlier
incidents being made. Nor would it appear that the ‘smoking duct’ (which was admittedly uninsulated at the
time) caused anybody to think more widely about the potential risks posed by fuel dripping from a leaking
coupling onto one of the hot air ducts or perhaps penetrating the insulation.
(5) May 2002: Tornado GR4 ZA599 Incident – coupling fuel leak ignited by bleed air pipe despite
insulation
8.27
8.28
In terms of ignition sequence, the incident most similar to the fire which occurred on XV230, was the loss of a
Tornado GR4A ZA599 on 17 May 2002, as a result of a coupling fuel leak ignited by a bleed-air pipe.
Tornado GR4 ZA599 was flying from RAF Marham on a routine low level flying mission when it suffered multiple
control failures. Fortunately, the crew managed to eject successfully before the aircraft crashed into the River
Humber. The Tornado ZA599 Board of Inquiry (Tornado BOI) found that the aircraft had suffered a mechanical
control rod failure as a result of a fuel fire in the spine of the aircraft in Zone 23. The fuel source was a fuel leak,
caused by an incorrectly sealed elastomeric ‘O’ ring in a vent line, dripping and pooling onto the spine floor in
Zone 23. The ignition source was the bleed-air Hot Intercooler Ejector Pipe, which was insulated with a twopiece
Refrasil jacket which was not liquid or vapour proof. The insulation was found to be particularly vulnerable
where there were muffs over bellows attached with spring clips or locking wire. 11 Tests showed the lagging was
impregnated with fuel residues. 12
10 Ground Incident Report KIN/142/00.
11 BOI Report into Tornado ZA599 17 May 2002 incident, paragraph 41(a); and see Annex W: “Interim Evaluation by the Tornado Maintenance
School”, paragraph 21.
12 BOI Report into Tornado ZA599 17 May 2002 incident, Annex T: BAE Systems Report BAE-WME-RP-TOR-CHM-300940, dated September 2002.