The Nimrod Review - Official Documents

The Nimrod Review
5.123
5.124
5.125
100
Second, can Cellular be criticised for complying with the ‘hardness’ criteria in the component drawing but
not the ‘100 part neoprene/100 part carbon black’ criteria? It appears that Cellular focused on the ‘hardness’
criteria in the component drawing and paid less heed to the carbon content criteria. In my view, this focus
was understandable in the circumstances. ‘Hardness’ is the key property which defines the tensile properties
of the polymer; it is therefore the key attribute which the manufacturer of a polymer, especially a general
purpose one, will focus on producing. Once the hardness criterion is achieved, I share the opinion of the
MOD’s MIG expert that a reasonably prudent manufacturer in Cellular’s position would probably consider
that they had met the (limited) requirements specified in the Avimo Drawing. That conclusion is reinforced by
two factors: first, the fact that this is also what BAE Systems (which does have specialist aviation knowledge)
focused on when testing the material in 2005; and, second, the MIG expert’s evidence that Neoprene with 100
parts carbon black content is no longer manufactured and the maximum level found is about 60 parts carbon
black. In these circumstances, given a reasonable belief that the seals were for general purpose, in my view, a
reasonably prudent manufacturer in the position of Cellular could not properly be criticised for thinking that it
had reasonably satisfied the specification.
Thirdly, can Cellular be criticised for not raising a query about the ‘100 part neoprene/100 part carbon black’
criteria with Avimo/Thales at any stage? In my view, whilst Cellular might have raised an issue, a criticism on this
basis would be unfair. Cellular was a small, non-aviation specialist rubber manufacturing company unaware that
the seals were for aviation use. It was also only charging a very modest sum per seal (varying between £3.35 and
£15.00 for the various types of seal manufactured between 2000 and 2007, see further below).
In summary, therefore, I do not consider that Cellular is properly open to any criticism, and have instead
concluded that responsibility lies elsewhere for the fact that the composition of the Avimo seals (as fitted to the
Nimrod post 2000) did not accord with the Avimo Drawing.
Avimo/Thales
5.126
The position of Avimo/Thales is potentially more complicated given that, unlike Cellular, Avimo/Thales was aware
that the seals were being supplied to the MOD (and hence that they were being used for military equipment).
However, like Cellular, Thales was able to point to the fact that the Avimo Drawing contained no mention at all of
the seals being an aviation or a ‘controlled’ part, or indeed any reference to fuel. Thales’ Aerospace Division does
in fact have its own “Guide for the Grading and Traceability of Parts and Joints” procedure, which is mandatory
for all Thales’ airborne products and which seeks to ensure that specific procedures are followed, so as to ensure
compliance with the requirements of Def-Stan 00-970 and Def-Stan 05-123, in respect of “Identifiable Parts” 95
and “Grade A” and “Grade B” 96 parts, respectively. An equivalent company procedure existed at the date of
Thales’ acquisition of Avimo Ltd. 97 There was, however, nothing in the Avimo Drawing to indicate that the seals
should be treated as a controlled part for aviation use and/or that any particular procedures therefore needed
to be followed as regards their manufacture.
Inadequacy of the Avimo Drawing as a specification
5.127
In my view, the real root of the problem lies in the fact that the original Avimo Drawing was not in reality a material
specification at all, but merely a component drawing. Indeed, as an aircraft specification, it was described to the
Review by an expert as “atrocious”. It is important for aviation parts that specifications are crystal clear and that
the key requirements are spelled out clearly. There should have been a full material specification of the Avon
company rubber mixture and the actual polymer. When drawing up a particular specification of this nature, it
is necessary to look at the specific requirements of the application which might not be covered in any generic
specification. In the present case, the generic specification did not cover details of physical properties required,
such as swell limits etc. If you purchase an off-the-shelf polymer, this might meet a generic specification but the
generic specification might not be sufficient for the specific application. Either the procurer needs to ensure that
its requirements are fully articulated in the procurement contract, or it needs to work to some defence standard
above the generic one. It should be noted that there is no Defence Standard for polychloroprene.
95 Def-Stan 05-123, Part 2, requires that a list of Identifiable Parts is generated for inclusion with equipment design records. Identifiable Parts are
defined as those parts deemed most likely, in the case of a fault, to affect equipment airworthiness or operational effectiveness.
96 Def-Stan 00-970 requires all metallic joints, with the exception of standard or component joints, to be graded A or B. The consequence of grading
a part, or joint, ‘A’ is to invoke airworthiness traceability of the part material and manufacturing process.
97 Company Procedure “Control of Hull Integrity/Quality Assured Items, Identifiable Parts and Grade A Aircraft Parts”, dated June 1996.