The Nimrod Review - Official Documents

The Nimrod Review
66
Prevailing Approach
5. There was, and remains, a prevailing belief that: (a) fuel couplings leaks are ‘inevitable’ but seals
should generally be left undisturbed because prophylactic replacement might actually increase the
number of fuel leaks by disrupting the system and/or because of high failure rates of recently fitted
seals; and (b) there should be a concentration on eliminating ignition sources. This is a not an
uncommon approach amongst civilian and military operators.
Increased leak trend
6. The Nimrod fleet experienced a four-fold increase in fuel coupling leaks during the period
1983-2006. 3
Warnings
7. There were a number of incidents in the years before XV230 which should have raised awareness of
the fire risks inherent in fuel coupling leaks (see Chapter 8).
Maintenance regime unsatisfactory
8. The RAF’s maintenance regime of the Nimrod fuel system prior to the loss of XV230 in September
2006 was unsatisfactory because: (a) there was insufficient emphasis on analysing fuel leak trends
and, as a result, the four-fold increase in leak rates went unnoticed; (b) fuel system tests were not
done under pressure; (c) there was no system of sampling seals; (d) there was a lack of proper
guidance in Maintenance Manuals as to how properly to replace seals; and (e) the RAF failed to
address the apparent discrepancy between the manufacturer’s original recommendation in 1968,
namely, that the FRS seals should be inspected every five years, and actual practice.
Avimo seals
9. A serious manufacturing defect has been found in Avimo seals: Avimo seals fitted to Nimrods after
2000 have been found to contain 50% less carbon black filler than earlier seals. This has made them
prone to swelling and splitting and reduced their fatigue life.
10. From 2000 manufacture of the seals was subcontracted to a new small general rubber manufacturing
company, Cellular Developments Ltd, who was not told that it was an aviation part and was given
a 1947 specification drawing which was unclear and had also never been updated. In my view,
Cellular Development Ltd was not to blame for using a British standard Neoprene material which
complied with the 60/65 hardness requirement. There was a lack of effective quality control because
of the convoluted and inappropriate procurement chain.
11. A warning sign regarding the quality of Avimo seals was missed in 2005. In July 2005, maintenance
personnel at RAF Kinloss observed abnormal “swelling” and “splitting and blistering” in some Avimo
seals. The Nimrod Integrated Project Team (IPT) requested BAE Systems to test them for “conformance
to specification”. In September 2005, BAE Systems reported that its limited test showed results which
were “typical” for Neoprene and gave “no indications of non-conformance to...specification”. Given
the earlier observations, the Nimrod and Aircraft Support IPT should not have let the matter rest
there.
3 BOI Report, Part 2, paragraph 39(b).