The Nimrod Review - Official Documents

Chapter 6 – Overflow or Pressure from Air-to-Air Refuelling
CHAPTER 6 – OVERFLOW OR PRESSURE FROM AIR-TO-AIR
REFUELLING
Contents
Chapter 6 addresses Air-to-Air Refuelling. It answers the following questions:
Summary
What was the history of the Air-to-Air Refuelling modification to the Nimrod fleet?
How and why did Air-to-Air Refuelling pose a risk to the Nimrod?
Were the Air-to-Air Refuelling modifications in breach of design standards and regulations applicable
at the time?
Who was responsible for any breaches of design standards and regulations?
Causation.
1. The Nimrod MR2 and R1 fleet was first fitted with an Air-to-Air Refuelling modification as an Urgent
Operational Requirement for the Falklands conflict in 1982 (Mod 700). A permanent Air-to-Air
Refuelling modification was fitted in 1989 (Mod 715). Both modifications were fitted by the Nimrod
Design Authority, British Aerospace (now BAE Systems).
2. The fitting of Air-to-Air Refuelling gave rise to three risks which were insufficiently appreciated at
the time: (a) the risks associated with fuel being ejected from the blow-off valves during flight and
tracking back into the fuselage; (b) the risks associated with an overflow of fuel into the vent system
and fuel leaking from the No. 1 tank vent system around the aircraft; and (c) the higher flow rates
and the potential for pressure spikes associated with Air-to-Air Refuelling. The cumulative effect of
subsequent changes to the Air-to-Air Refuelling sequence and the tanker to be used (Victor, VC10
and Tristar) may have exacerbated (a) and/or (b).
3. The risks posed by blow-off valves operating in flight during Air-to-Air Refuelling and fuel tracking
back and entering the fuselage were raised during the Nimrod Mk3 Airborne Early Warning (AEW3)
project in the mid-1980s. However, only the risk posed on the port side was addressed and not the
equivalent risk on the starboard side. The AEW3 project was shelved and dye tests recommended
by BAE Systems which may have revealed the problem were never carried out. The MOD and BAE
Systems share responsibility for the failure to follow this up, or to read this knowledge across to the
MR2 and R1 fleets.
Responsibility
4. The Air-to-Air Refuelling modification in 1989 (Mod 715) carried out by British Aerospace was in
breach of applicable design regulations and standards at the time (Defence Standard (Def-Stan)
00-970) in two respects: (a) regarding blow-off valves being located where discharge of fuel could
pose a fire hazard; and (b) regarding fuel pipes being located close to high pressure hot air ducts.
In my view, it was British Aerospace’s duty as the Design Authority for the type to ensure that Mod
715 complied with Def-Stan 00-970 and validate the refuel system for its new in-flight Air-to-Air
Refuelling function. It failed to do so.
Causation generally
5. I am satisfied that the Board of Inquiry was right to find that overflow of fuel during Air-to-Air
Refuelling (from No. 1 blow-off valve and/or the vent system) was one of the two most probable
likely causes of the fuel which led to the fire on board XV230 (together with a Fuel Coupling Leak,
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