The Nimrod Review - Official Documents

The Nimrod Review
6.6
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this intake, it may be necessary either to switch off the tail pack before commencing an
air-to-air refuel, or to carry out a modification on the blow-off valve outlets of Tanks 1
and 6 to prevent the fuel running down the skin. 5 ’ (emphasis added).
This report was distributed to 11 addressees (10 BAE Systems staff, and the MOD’s representative on site –
the Resident Technical Officer (RTO)). However, the report’s distribution list does not indicate who, if anyone,
was supposed to take forward the recommendations, and no evidence has been found that further work was
undertaken on the threat presented by fuel entering ports and intakes after blow-off.
6.7 In May 1985 British Aerospace issued a Report entitled: “NIMROD AEW3 MK 3 TESTING AND ASSESSMENT
OF AIR TO AIR REFUELLING SYSTEM”, 6 which summarised a number of ground and air tests of the AEW3 AAR
system. The Report also referred to the report discussed above, which it said stated:
“4.1 The report also concluded that there may be some hazard from residual fuel running
down the fuselage following a blow-off from Tanks 1 or 7, which should be the subject
of further investigation.” 7 (emphasis added)
6.8 In July 1985 British Aerospace issued a Report entitled: “NIMROD AEW3 MK 3 OPERATING INSTRUCTIONS FOR
AIR TO AIR REFUELLING”. 8 The report set out operating instructions for the AEW3 during AAR, but made a
number of points relevant to AAR operations generally:
6.9
“3.7.3. During the refuel operation, it is recommended that a look-out is kept through
the escape hatch windows for fuel venting, in which case the blow-off valves of Tanks 1
and 7 may have discharged fuel. If venting is seen, and Tanks 1 and 7 are full, refuelling
should be discontinued. (see also paragraph 3.13).” 9 (emphasis added)
“3.13. After landing. WARNING If fuel spillage has taken place in flight due to venting or
to a probe mishap, do not run the APU until the APU has been inspected and declared
clear of fuel.” This highlights continuing concern about fuel entering ‘ports and intakes’
and reinforces that fuel entering fuselage panels was a possibility, even though the APU
external panel lies flush with the fuselage.
These reports show that blow-off during AAR was recognised as a potential hazard. Although the potential
hazard of No. 5 tank blow-off on the port side was dealt with, the hazard from the blow-off from No. 1 tank
on the starboard side (and Nos. 6 and 7 tanks) was not. The threat of fuel entering the fuselage compartments
was raised, but there is no evidence that it was ever investigated further. It is surprising that there is no record
of any decision process which may have curtailed further work on these reports, particularly in view of the clear
implications for flight safety.
1987: Changes to Refuelling Sequence
6.10
6.11
10 In a letter dated 15 January 1987, BAE Systems advised the RAF that the extant sequence of refuelling
could potentially cause structural problems because of wing bending relief. Following trials, the sequence was
changed, such that rather than filling all tanks simultaneously, the wing tanks were refuelled first, followed by
the fuselage tanks, once the wing tanks were full.
It is important to note that this had the incidental effect of increasing the instantaneous flow rate at which
individual tanks were refuelled; the significance of this is explained later when the operation of the blow-off
valve is discussed.
5 Ibid, page 6.
6 HAS MPP F AEW 0065 (BOI Report, Exhibit 6).
7 The reference to No. 7 tank may been error as the earlier report talked of Nos. 1 and 6 tanks.
8 HAS MPP F AEW 0068 (BOI Report, Exhibit 58).
9 This may be a perpetuation of the previous report’s error in substituting No. 7 tank for No. 6 tank.
10 JNG/CSN, dated 15 January 1987.