The Nimrod Review - Official Documents

8.10
8.11
8.12
8.13
Chapter 8 – Previous Incidents and Missed Opportunities
“Following a Harrier accident, the integrity of the FRS couplings was suspected. Some
FRS couplings in the Harrier vent system are already changed at major servicing but the
remainder are replaced on-condition. Although a fuel leak check is carried out after a
servicing, there remains a risk of a major fuel leak from the FRS seals if they have either
dried out or been subjected to any shear force. With a design life of some 20 years, age
is not a significant factor. Nonetheless, for flight safety reasons we do not wish to leave
Harrier FRS seals unchanged indefinitely. It is during a Major servicing that the FRS seals
are most likely to dry out and this servicing is also the most desirable opportunity to
change the seals. Consequently, we wish to introduce replacement of all Harrier GR3/T4
FRS seals during Major servicing.” (emphasis added)
The Harrier EA’s letter was sent to (amongst others) the MOD’s Inspectorate of Flight Safety (IFS). On 17 July
1989, the IFS issued a letter entitled “Servicing of Fuel System Couplings” 2 in which it requested that other
aircraft types consider the applicability of the Harrier EA’s changes to their FRS coupling servicing schedule
to their own type. This letter was circulated to Headquarters Strike Command who would then have been
responsible for deciding whether further distribution to Groups (including 18 Group, the then operators of the
Nimrod) was necessary. The IFS’s letter stated as follows:
“The accident to Harrier GR3 XW921 in Aug 88 followed engine stagnation and an
airborne fire. Although the precise mechanism for these pre-crash occurrences could not
be positively determined, inter alia, the Board of Inquiry recommended that the Harrier EA
investigate the integrity of the FRS couplings in the aircraft fuel system. As a result of their
investigation, at the Reference (enclosed), the Harrier EA tasked the CSDE Schedules Flight
with amending the Topic 5 series for the Harrier GR3 and T4 to introduce replacement
of all FRS – the more commonly used name – coupling seals during Major servicing. ... I
understand that FRS couplings are installed on a number of other aircraft types; you may
wish to consider whether the Harrier EA’s policy is relevant to your aircraft EAs.” (emphasis
added)
The two letters above, issued pursuant to the Harrier BOI recommendation on FRS couplings, appear to
demonstrate a coherent and structured organisation attempting to ensure that an issue raised during the
investigation of the loss of one type of aircraft was carried over to other aircraft types. However, neither of the
two subsequent letters refer to the Harrier BOI’s suggestion to consider “geometric checks of the coupling on
fitment”. Although not explicitly referenced, it is clear that this recommendation stemmed from a concern that
couplings not assembled within the strict FRS parameters might leak.
A subsequent internal MOD Minute dated 26 July 1989, addressed to the engineering officer with responsibility
for Nimrod and Shackleton, stated: “Please see the attached copy of reference A, which reports the Harrier EA’s
decision to replace all FRS coupling seals during Majors as a result of a previous accident. Do we use similar
couplings on the Nimrod and Shackleton? If so, please investigate to see whether we should follow the same
policy. If not, are our seals analogous, and should we therefore consider introducing this policy? I would
appreciate your response by the end of Sep.” (emphasis added)
The Review’s investigations revealed that the internal Minute referred to above was copied internally to other
specialist Nimrod engineering staff, asking for advice in relation to the Nimrod. Following receipt of a data
printout on fuel coupling leaks covering the period March 1987 to February 1989, the specialist staff advised
that there were approximately 30 such leaks per year on Nimrods and noted that: 3
2 D/IFS(RAF)/48/32/64.
“[You] will wish to consider the more difficult question of the Nimrod seals. Perhaps an
AEDIT task is called for to look more closely at the fault history to identify whether any
particular types of coupling seals fail more frequently and establish the potential dangers
involved in fuel leaks where the couplings are located. This may narrow down a range of
seals which could justify replacement at Major”.
3 Strike Command Minute sheet – file STC/13004/10, Part 8, minute sheet.
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