The Nimrod Review - Official Documents

7.49
Chapter 7 – Damage from Cross-Feed/SCP Duct Failure
The XV227 incident amply demonstrates the risk of potentially catastrophic damage to the aircraft structure and
adjacent fuel system seals from an engine bleed-air hot pipe fracture. If the incident had occurred earlier in the
sortie, when fuel was present within the No. 7 tank and its adjoining pipes, there could have been a serious fire
similar to that which befell XV230 and XV227 could have been lost. The XV227 incident accordingly caused the
BOI to give careful consideration to the possibility that a similar hot air duct failure caused the loss of XV230,
notwithstanding that it had not been provided with a copy of BAE Systems’ February and March 2007 reports
(see above).
Did a hot air leak cause the XV230 fire?
7.50 The incident on XV227 is indicative of a potential causal chain of the fire on XV230, i.e. a failure of the SCP duct
leading to the escape of hot bleed-air causing damage to adjacent fuel seals leading to the escape of fuel and
ignition. The BOI concluded, however, that, whilst the SCP was in use at the time and a Cross-Feed/SCP duct
failure could not be ruled out, as a causal mechanism for the fuel source, it was much less likely than the other
two potential causes (fuel seal failure or over-flow during AAR igniting on the SCP duct). I agree. Nonetheless,
I turn below to consider the two ways in which the BOI suggested that a fractured bleed-air duct could have
been causative of the XV230 fire, either: (a) a large hot air leak as a result of a major failure of the duct (as with
XV227); or (b) a small hot air leak as a result of a smaller fracture.
(a) Large hot air leak
7.51
7.52
A major failure of a hot air duct within, or proximate to, the starboard No. 7 Tank Dry Bay could have led to a
large hot air leak damaging adjacent fuel seals, resulting in fuel leaks which might have been ignited by hot
and exposed elements of the broken duct. The principal reason given by the BOI for discounting such a leak
was that it was unlikely “to have gone unnoticed by the experienced Flight Sergeant Davies”, or the crew who
“would all have noticed the pressure change concomitant on the loss of conditioning air”. 62 It is important to
note that XV230 was operating with a pressurised cabin, 63 whereas XV227 was unpressurised; this would have
masked the change in cabin pressure caused by the loss of XV227’s SCP. Although the crew intercom recording
shows that XV230’s SCP tripped-off at 11:09:23 hours, Flight Sergeant Davies clearly did not think it significant
and probably linked the event to AAR. Flight Sergeant Davies was one of the most experienced and able Nimrod
Air Engineers in the RAF, with 7,817 flying hours on type; 64 an engineer of his experience would have had no
difficulty in recognising the symptoms of a duct failure. Further possible explanations of the event are discussed
below. Moreover, if this event had been the SCP duct failing, Flight Sergeant Davies could not have received the
subsequent warning (reported concomitant with the bomb bay and elevator bay warnings) of an overheated
SCP since an SCP failure would have removed most of the hot air from the SCP system.
There are two entries on the Mission Tape which indicate events associated with the SCP at the time:
7.56.1 The Mission tape at 11:09:23 records a remark from Flight Sergeant Davies (Air Engineer) as the SCP
trips-off, causing a pressure change within the cabin: “: …we’ve just lost the tailpack sorry about your
ears.” 65 This remark is made to inform the crew that he is aware of the event and is dealing with it, i.e.
normal crew courtesy and co-operation on an MR2.
7.56.2 The Mission tape records at 11:12:01 Flight Sergeant Davies commenting, 28 seconds after the fire
warning at 11:11:33 and reports of smoke coming from the rear bay: “Yeah I have an under er an
overheated SCP which could be the cause. Attempting to reset the warning”. 66
62 BOI Report, paragraph 38 [2-27].
63 When the Nimrod MR2 is operating at low level the crew will depressurise the cabin.
64 BOI Report, Annex B, B-2.
65 BOI Report, Exhibit 1.
66 Ibid.
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