The Nimrod Review - Official Documents

5.104
5.105
Chapter 5 – Leak from Fuel Coupling
As explained above, Contractor B contracted with Thales, who in turn sub-contracted the production of the
Avimo seals to Cellular. Thales’ Purchase Orders to Cellular stated as follows: “THIS PURCHASE ORDER HAS
BEEN RAISED TO COVER THE COST OF SUPPLYING THE FOLLOWING ITEM/S STRICTLY IN ACCORDANCE WTH
CURRENT DRAWING AND/OR SPECIFICATIONS REQUIREMENTS UNLESS OTHERWISE SPECIFIED HEREIN.”
Each delivery of seals to Avimo/Thales by Cellular was accompanied by a Certificate of Conformity in the terms
set out above. Each subsequent delivery of seals by Avimo/Thales to Contractor B was accompanied by a
Delivery Note, which provided as follows: “Certified that the whole of the supplies detailed hereon have been
inspected, tested and, unless otherwise stated, conform in all respects with the requirements of the contract of
order. The quality assurance and control arrangements adopted in respect of these supplies have accorded with
the conditions of our ISO9001 approval and MOD registration.”
5.106 Each Delivery Note appears to have been stamped “Q.A. PASSED”. It is not entirely clear whether this stamp was
made by Avimo/Thales or Contractor B upon receipt of the seals.
5.107
Notwithstanding the statements contained in the various Purchase Orders, Delivery Notes and Certificates of
Conformity, the fact of the matter is that the Avimo seals supplied by Cellular did not conform to the material
specification in the Avimo Drawing. It would appear both that Cellular did not appreciate the significance of this
and that neither Thales, Contractor B, Contractor A or the M&GS IPT were ever made aware, or became aware,
of the changed composition of the rubber compound used in the Avimo Seals. I set out below my analysis as to
where responsibility lies for this failing.
Warning sign in 2005 missed
5.108
Some three years prior to the discovery of the problem in 2008, there was an occurrence in 2005 which is likely
to be related to the non-conforming Avimo seals. On 7 July 2005, a Form 760 (Narrative Fault Report) was raised
after an Avimo seal (Part No. 52/29B) was seen to swell excessively when immersed in fuel. As a result of this
discovery, maintenance personnel at RAF Kinloss conducted informal tests by leaving a selection of seals in a
bucket of fuel for a few days. They reported that: “...the results don’t look good. All of the seals have shown
signs of swelling! Some have split and blistered”. 89
5.109 At about the same time ( i.e. end of July 2005), the Nimrod IPT, on behalf of the Air Commodities IPT, tasked
BAE Systems to investigate the issue, by way of the testing of four seals in order to ascertain if they had
been manufactured in accordance with the Avimo Drawing and the Material Specification for ZCOM 533
Polychloroprene (Material Specification) supplied by Cellular, 90 copies of which were sent to BAE Systems. In its
written submission to the Review, BAE Systems stated that, following the initial request for assistance from the
Nimrod IPT, it informed the IPT that it was unable to execute a comprehensive test programme due to various
limitations. Whilst no record of the limitations exists, BAE Systems stated that the limitations were believed to
include the short timescale within which a response was required and a lack of capability within BAE Systems to
determine all aspects of the specification (such as ozone resistance).
5.110
Amongst other things, the Material Specification provided to BAE Systems identified the hardness of the material
as 60+/-5. 91 It contained no reference, however, to the number of carbon parts (used as filler) per 100 Neoprene
parts (although this was specified on the Avimo drawing also sent to BAE Systems). The tests conducted by BAE
Systems were carried out using aviation fuel AVTUR F34 and involved placing samples of the seals for periods
of 74 hours in air at room temperature, in air at 100°C, in fuel at room temperature and in fuel at 100°C. The
parameters monitored were hardness, weight and a single dimension (the width). BAE Systems confirmed in
its evidence to the Review that the testing did not consider, inter alia, the chemical composition of the rubber.
Nonetheless, chemical analysis in isolation would not be able to determine the amount of carbon used as filler
(it could only determine the total amount of carbon in the compound, some of which would be part of the
compound’s molecular chain). This could only be determined by discussing the manufacturing process with the
manufacturer.
89 Unreferenced e-mail, dated 25 July 2005, from Nimrod Major Servicing Unit (now Nimrod Servicing Group) to Nimrod IPT.
90 Dated 27 July 2005 (by hand).
91 The distinguished expert from MOD Materials Integrity Group confirmed that this does for all practical purposes accord with the 65% hardness
requirement laid down in the Avimo Drawing.
97