The Nimrod Review - Official Documents

The Nimrod Review
98
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Comment
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92 On the basis of the limited testing carried out, in its report dated 16 September 2005, BAE Systems concluded
that the results of the tests were “typical for neoprene under these conditions and give no indications of
non-conformance to the supplied specification”. There was no discussion of, or even reference to, the carbon
content of the material. The Air Commodities IPT, for its part, accepted BAE Systems’ advice and actioned the
MOD Form 761 accordingly; however, it did note that the “Nimrod EA/DA may wish to consider more fuel
resistant material in future”.
In my view, these events in 2005 are redolent of the detection of the same inadequacies of the material
being used since 2000 to manufacture the Avimo seals as were subsequently discovered by QinetiQ in 2008.
Unacceptable swelling and deformity was observed by maintenance personnel at RAF Kinloss in 2005 which led
them to refer the seals to BAE Systems for conformity checking. It is likely that this was the same type of swelling
and deformity which has recently been observed and traced to non-conforming material. It is regrettable that a
more thorough examination of the reasons for the undoubted deterioration of the Avimo seals was not carried
out in 2005. BAE Systems was tasked to ‘test’ the seals to see if they had been manufactured in accordance with
the Avimo Drawing and the Material Specification. BAE Systems informed the Nimrod and Air Commodities IPTs
that it had been unable to conduct a comprehensive test programme due to various limitations but the results
of its limited tests suggested “typical for neoprene” (see above). Unfortunately, the matter was allowed to rest
there, despite the initial observation of a batch of seals which showed “swelling” and were “split and blistered”.
It is a matter of concern that none of those within the Nimrod and Air Commodities IPTs deemed it necessary to
question further. This does not suggest a rigorous attitude.
Current Position
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As a result of the discovery of the non-compliant formula being used for the Avimo seals, the MOD decided to
seek a replacement for the Neoprene material and this replacement is now used for all Nimrod Avimo seals. The
Nimrod IPT has advised the Review that the material is similar to that used in the FRS seals. An Interim DDP93 has
been issued which sets strict criteria on seal life.
Relevance as potential cause of loss of XV230
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The fact that there may have been Avimo seals fitted in the Nimrod fleet post-2000 manufactured from nonconforming
material which had a tendency to degrade and split is obviously significant as a potential cause of
the loss of XV230. As mentioned above, the starboard No. 7 Tank Dry Bay has one Avimo seal in the No. 7 tank
defuel line located immediately above the SCP elbow. This is one of the pipes that would have been in use and
under pressure during AAR.
It should be noted, however, that none of the seals identified by QinetiQ as having suffered mechanical damage
in September/October 2008 were showing any signs of actually leaking at the time of their removal from the
aircraft. QinetiQ explained, however, that the reason why these couplings had not failed was because the seals
initially tended to split underneath the clamshells and the examples seen had all maintained a seal between the
rubber and the clamshell. Depending upon where the failure initiation was, and the speed of propagation, the
failure progression could eventually reach the exposed seal between the two clamshell portions, whereupon the
seal would no longer be safe and it was simply a matter of time before it failed. None of the seals examined to
date had reached this point.
Since the loss of XV230, there has been more than one incident or Serious Fault Signal which could now, with
the benefit of hindsight, be assessed as most likely having been caused by the mechanical failure of an Avimo
seal due to the material used in its composition. By way of example, on 25 April 2007, an Annex A to Leaflet
070 was raised regarding an incident on XV236 on 18 April 2007, when an FRS coupling at the No. 7 tank
92 In their response to the IPT (CHD-TFN-M-ISA-QM-1423, dated 16 September 2005) BAE Systems clearly identified that they were “unable to execute
a comprehensive test programme”.
93 Taunton Aerospace DDP4126 Issue2-Interim, dated 3 June 2009.