The Nimrod Review - Official Documents

Chapter 4 – Cross-Feed/SCP Duct
4.58 AvP 970 Chapter 715 (paragraph 2.2.2) required that “Any compartment in which inflammable fluids may be
liable to accumulate accidentally or from a drain on or in the aeroplane shall either drain automatically in flight
or be capable of being drained as a servicing operation.” Fuel leaking from one of the numerous fuel pipes and
couplings in starboard No. 7 Tank Dry Bay was liable to accumulate in the lower (corrugated) panel tray at the
bottom of the bay because the design and placement of the drainage holes in the panel was ineffective, in that
it was possible for fuel to pool on the upper surface of the panel, between stiffeners, in volumes of up to 300ml
(these drainage holes have since been rectified).
(3) Non-conformity with design safety standards regarding the use of absorbent lagging
4.59
The Nimrod designs were arguably not in conformity with the original safety standards of 1969 and 1979
regarding the use of absorbent lagging for the protection of flammable liquids.
4.60 AvP 970 Chapter 715 (paragraph 6.4.1) required that “Heat insulating material shall be non-inflammable and
preferably non-absorbent” The laced muffs in the No. 7 Tank Dry Bay were unable to prevent fluid ingress at
their ends and seam, were liable to retain liquid, and were, therefore, on this basis ‘absorbent’. (The capability
of such laced muffs to absorb and retain fluid is demonstrated by the XV225 incident in which the muff was
found to be soaked in fuel).
Design Handbook
4.61
It should be noted that the Design Handbook at the time provided as follows:
“Section 3:...leakage or drainage of combustible substances such as fuel, oil, hydraulic fluids
etc, near a heat source is a fire hazard ... lines should, therefore, be placed as remotely as
possible from heat sources and away from or below other equipment to avoid leakage on
to controls, components (especially electrical equipment) or absorbent materials. The use
of protective shrouding or trays (with adequate drainage) should be considered to protect
vital equipment or contain the fluid from a coupling failure.” (emphasis added)
BAE Systems’ denial of breach of original design standards
4.62
In its submissions and evidence to the Review, BAE Systems denied there was any breach of any of the original
design standards. The Review heard from two senior BAE Systems executives: the Military Airworthiness Solutions
(MAS) Chief Engineer¸ Martin Breakell, and BAE Systems MAS Head of Airworthiness, Tom McMichael. They
accepted the fact that fuel could access the muff, but sought to argue on behalf of BAE Systems that the
single point failure scenarios postulated above were ‘incredible’ because: (a) very large volumes of fuel would
be required to create the conditions for soaking and ignition and the required catastrophic fuel pipe failure of
this nature was not ‘credible’; and (b) a failure of the Cross-Feed/SCP duct would ‘blow the fuel away’ and that
ignition was, therefore, not ‘credible’. In my view, both arguments were grasping at straws.
First, it is clear
4.63 e.g. from the recent videos of leaks on board XV250 and XV229 (see above and further
Chapter 5) that fuel couplings could suddenly spring significant fuel leaks which could provide a substantial
and continual fuel source feeding any fire. Second, it is clear from the configuration of starboard No. 7 Tank
Dry Bays that fuel from such leaking couplings might well find its way onto the Cross-Feed/SCP duct and into
the gaps and crevices in and about the Refrasil insulation and muffs and pool in the lower panel tray. Third, it is
clear from the QinetiQ fire study that only a very small quantity of fuel is required to start the initial fire which,
if fed, would quickly lead to a catastrophic conflagration in the bay. Fourth, it is clear from the XV227 incident
that, if the SCP duct rupture had occurred earlier in the sortie when the No. 7 tank had been full, the result
could have been catastrophic.
59