The Nimrod Review - Official Documents

The Nimrod Review
6.72 Cognisant of the above Incident Report, the BOI noted that the “vent lines from No 1 tank are of light construction
and secured by jubilee clips, which if overtightened can leak”, 34 and recommended that they be modified to
reduce the risk of fuel leakage.
2009: XV235 incident
6.73
6.74
6.75
124
A very recent incident involving XV235 has brought to light important evidence.
35 On 20 April 2009, during maintenance of XV235 at RAF Kinloss, a Serious Fault Signal was raised for a fuel
leak from a No. 1 Tank Cell 4 rear vent connection. The signal goes on to describe what was found as follows:
“Further investigation carried out suspect that fuel soaked pre-cooler muff Part No BA205123 located at the
forward face of 7 tank dry bay may have been result of above leak” (emphasis added).
Part No. BA205123 is the flexible muff located immediately aft of the SCP elbow. The incident on XV235
therefore provides powerful evidence in support of the BOI’s conclusion that, if fuel had leaked from the vent
connection during AAR on XV230, that fuel would have found its way to the No. 7 Tank Dry Bay and could
have gathered at the flexible muff to provide the fuel source for the fire. Furthermore, such fuel would have the
potential to pool on the lower panel.
2008: QinetiQ report on XV236
6.76
6.77
Subsequently, during the teardown conducted by QinetiQ on Nimrod XV236, a fault report was raised concerning
the No. 1 Tank Vent Connections (see further Chapter 15). 36 In order to investigate the matter further, the
connection was pressurised and leaked at 0.5psi gauge pressure; well below the blow-off valve setting of 2.7psi.
The design features of the connection were described as follows: “The metal vent pipe was fabricated from
two diameters of tube: a 1.25” diameter tube, which had both a raised bead to form a seal with a ‘push fit’
rubber pipe and a bonding tag attachment; and a second approximately 1.5” diameter tube. The rubber hose
was found to interface with the larger metal pipe section of approximately 1.5” diameter, which had no sealing
bead present. Thus the joint was reliant on a single Jubilee clip to both seal and clamp. .... Due to the lack of
a witness mark on this larger pipe, there is a lack of control of the position of the hose clip, which could lead
to the hose being clamped only over the welded portion of the pipe assembly or only over part of the surface,
which could lead to complete detachment.”
QinetiQ, therefore, raised similar concerns to the BOI in relation to the design of the vent pipe design and go
further by positively suggesting that the jubilee clip could slip under pressure, allowing the rubber extension
to reposition itself over the narrower section of the metal pipe, resulting in a significant leak of fuel. Also, the
QinetiQ Report explained that the rubber extension had been positioned on top of a clear plastic tape which
labelled the pipe as a fuel vent pipe; the tape further reduces the effectiveness of a seal between rubber and
metal. It should be noted that other aircraft were subsequently checked at RAF Kinloss and found with the same
condition, i.e. with the rubber extension positioned on top of the clear plastic tape.
34 BOI Report, paragraph 40(d)1.
35 Serious Fault Signal 181300, dated May 2009.
36 QINETIQ/MS/SES/TR0902158/1, dated 02 July 2009.