The Nimrod Review - Official Documents

8.29
8.30
8.31
8.32
A report commissioned by the Tornado ZA599 Board of Inquiry concluded:
Chapter 8 – Previous Incidents and Missed Opportunities
“Most of the sections of bleed air pipe are insulated with Refrasil material ... Anecdotally
the stainless Refrasil jackets are frequently damaged during maintenance activities ...
Assuming that a fuel leak either drips or is splashed onto the pipe the fuel will ignite
if the temperature is hotter than 240C. There will be an ignition delay time while preignition
reactions take place. This is about 4 minutes at 240C but rapidly reduces as the
temperature increases (for example it is about 20 seconds at 400C). Of course the same
fuel has to be held in contact with the hot pipe for this time but this does not seem to
present a problem because the fuel can easily be trapped in damaged Refrasil or under the
PTFE grommets. In some ways, in spite of the longer delay time, the lower temperature
is the most threatening because the fuel remains liquid and stays in contact with the hot
surface rather than quickly evaporating into the passing airflow.” (emphasis added)
The Tornado thermal insulation or Refraisal blanket appears to have been similar to that used on the Nimrod
fleet. It was described in the AAIB report into the incident to the Tornado BOI as comprising “a fibrous
insulating material sandwiched in a thin stainless steel jacket” which completely enclosed the intercooler
ejector supply pipe. However, the AAIB expressly noted that it was “not designed to be fluid or vapour tight”. 14
This was confirmed by the Design Authority, BAE Systems, who said it was not intended within the design
requirement that the Tornado muffs be hermetically sealed so they did not provide a liquid-proof seal15 (see also
Chapter 4).
The ignition sequence for the Tornado incident would, at first glance, appear to be directly comparable to the
loss of XV230. This therefore raises the obvious question why information gained (by both the MOD and BAE
Systems) as a result of the Tornado incident was not read across to the Nimrod fleet (and other fleets), i.e. why
did the Tornado incident not prompt anyone to consider the fire risk in the No. 7 Tank Dry Bay given the presence
of fuel couplings above similar hot pipes covered with Refrasil insulation? Why did the Tornado incident not
prompt anyone to question the effectiveness of the insulation in the No. 7 Tank Dry Bay and whether it provided
a liquid-proof seal in the event of a fuel leak?
In both its oral and written evidence to the Review, BAE Systems sought to dispute that the findings of the
Tornado BOI (and its own reports appended thereto) were “directly applicable” to the Nimrod fleet. Its primary
basis for doing so was that the type of insulation covering the hot intercooler ejector pipe on the Tornado was
different from that utilised on the Nimrod (other than within the engine bays), in that the former comprised
two ‘half shells’ secured together with a spring clip, the ends of which were not secured and did not overlap
with other fixed insulation. Be that as it may, it seems to me that this response somewhat misses the point and
again highlights the dangers of assessing incidents on an individual basis, without anyone taking a more global,
holistic view of the lessons that can be learnt from that incident. If any of those responsible for carrying out
the Hazard Analysis of the risks present in the No. 7 Tank Dry Bay and preparing or checking the NSC in 2003
and 2004 had read a copy of the Tornado BOI report, the contents of the report would (or should) have caused
them to consider more acutely the risk presented by the presence of the SCP elbow in the No. 7 Tank Dry Bay.
It is apparent that no-one connected with the NSC did (see Chapter 10).
(6) November 2004: Nimrod XV227 incident – SCP duct failure leading to near catastrophic loss
8.33 As discussed in Chapter 7, on 23 November 2004, Nimrod MR2 XV227 suffered a potentially catastrophic inflight
failure of an expansion bellows in the SCP system. This expansion bellows is located immediately aft of,
and just below, the No. 7 Tank Dry Bay, enclosed in a fairing external to the fuselage. The Unit Inquiry (UI) into
the event concluded that the expansion bellows had failed due to corrosion and that the failure had probably
occurred some 20 to 40 minutes before the SCP was closed down. This leak of air at up to 420ºC caused, inter
alia, a significant weakening of the rear spar, damage to aileron and flap control cables and pulleys, the melting
13 BOI Report into Tornado ZA599 17 May 2002 incident, Annex S: QinetiQ, Examination of Fire-Damaged Components from Tornado ZA599,
paragraph 4.0 on Ignition Sources
14 BOI Report into Tornado ZA599 17 May 2002 incident, Annex X: AAIB Report, page 15.
15 BOI Report into Tornado ZA599 17 May 2002 incident, Annex Y: BAES report BAe-WAW-RP-TOR-PDS, dated February 2003.
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