XV230 Accident Report is Out

The XV230 Board of Inquiry has travailed, and brought forth many PDFs. And some appalling numpty discposter has printed out the clearly wordprocessed documents, tippexed classified information, and scanned them chunk by chunk as huge uncompressed graphics files, before pdf-ing them into a round dozen fat-arse documents. Still, anything to keep google out, right – except robots.txt…

If I felt stronger I’d OCR the lot and turn it into something useful; but I don’t have the time, so you’ll have to rely on the art of exegesis. Here are the killer (in every sense) conclusions:

1. The 38-year old rubber seals

I am not joking; there may very well be seals in the Nimrod fuel system that have been there ever since the original aircraft were built in 1969. Better yet, according to BAE engineering documents shown to the inquiry, the RAF has had problems with the Flight Refuelling Ltd 110 kit leaking from the seals on the following aircraft types: AEW Mk3, VC10, Vulcan, Lancaster.

The seals were under “corrective maintenance”; this means that they were replaced if they blew. The manufacturers originally suggested they would last indefinitely but must be checked every 5 years; this has never actually been done. The current makers, Eaton, think they are likely to start leaking after 25 years; the MOD, however, thinks that the problems on the aviation museum catalogue list of aircraft given above were caused by doing maintenance, and that if they just left well alone it might work better.

2. Stats

Between 1983 and 2006, the average number of annual fuel leaks on Nimrods went from 10 to 40, despite the fact the number of aircraft fell and one of the two bases in the UK was shut down. Nobody, it seems, thought that the maintenance policy should be changed as a result.

3. Hot Air

A pipe runs through the No.7 tank dry bay, the compartment where the fire began; this pipe carries compressed air taken directly from the engines at around 400 degrees C, which is used for a wide range of purposes (electricity, pressurisation, pumps, cross-bleed engine start, etc). Crucially, one of its uses is to drive the supplementary conditioning pack, or SCP, which provides extra pressurisation and air conditioning. Naturally the Nimrod’s designers realised that 400-degree compressed air is stuff that ought to be kept separate from essentially everything else, so the pipes are heavily insulated.

Just as naturally, the insulation is only replaced if it goes wrong; the maintenance handbook does not state how much insulation is tolerable. An experiment on a dodgy section showed the insulation was only 16 degrees cooler than the bare metal. “In some areas on other aircraft it was noted the laces have loosened and there are visible gaps between the blanket edge and the main pipe insulation, leaving exposed sections of pipe surface”, saith the Board. There’s a further problem; a previous incident on XV227 occurred when hot air leaked from the pipe and caused a rubber seal on the fuel line to melt. The Board considered this a possibility.

There are several of those famous seals in the No.7 bay; on the 15th of February this year, XV250 had a fuel leak right there, fortunately on the ground.

4. Too Much of a Good Thing

The crisis aboard XV230 began immediately after an air-to-air refuelling. Nimrods were converted for this task in a tearing hurry in 1982, and the capability was then officialised in 1989. There are some concerns about sudden over-pressure in the system; BAE, however, reckons it’s OK. Now there’s reassurance.

Much more seriously, though, there was a problem in the event that too much fuel went into tank number one. In this event, the excess should overflow through the vent and into the air; the pipe provided is not meant to stand pressure and isn’t tested for it. A related cockup in October, 2006 demonstrated that fuel overflowing from tank 1 could end up in bay 7, with the hot pipe. And the delivery of fuel from a Tristar tanker is faster than a ground refueller; more pressure. XV230 had refuelled from a Tristar more often than any other Nimrod; more strain on those seals.

Worse – much worse – though, something similar had happened to XV230 in August, 2006; a ground engineer noticed fuel had escaped from the overflow during an AAR sortie, and after this decided not to fill tank 1 over 15,000 lbs of fuel. Even worse still, BAE had noticed the problem whilst working on the disastrous Nimrod AEW project in the 1980s, and had decided that the SCP must be shut off before refuelling; but the knowledge had been lost. Nimrods are long-range aircraft; they don’t need to refuel in the air often, or at least not until they had to operate over Afghanistan rather than the Western Approaches. And the SCP doesn’t get that much use in the North Sea.

Tristars are fast; to keep up, the Nimrod had to use 94% power, at which setting the compressed air from the engines would have been around 420 degrees. Fuel entered the No. 3 cell faster than it emptied into the tank; eventually the valve operated and it vented, but quite a lot went into the No. 7 bay. Although there was a hole in the bottom, there was space for about 300ml of the stuff below it, enough for 100 seconds of fire. There was no way of knowing about the fire until it had already spread beyond the compartment, still less doing anything about it. Eventually the fuel in No. 1 tank boiled and a BLEVE occurred; and that was it.

5. Killer Powerpoint

“Changes to RAF Kinloss’ management structure as a result of Project Trenchard removed the SO1 Engineer/OC Engineering Wing from the station structure. Engineering personnel are now distributed between the station’s 2 remaining Wings under non-specialist leadership…”

“Service training courses were perceived by a number of witnesses no longer to impart the skill of hand or depth of knowledge necessary to maintain an aircraft built around a design philosophy now some 40 years old.”

Engineers – who needs ’em?

6. Comic Relief

“Some Nimrod aircraft at both DOB [CENSORED] and Kinloss had elements of the acoustics mission equipment removed and the resultant voids had been masked with cardboard, held in place with tape..”

7. Now’s The Time For Your Tears

“The body bags, which had been provided by the US mortuary at Kandahar and manufactured in the USA (NATO Stock No 9930-01-3316244) were not provided with impermeable membranes.”

I don’t think I have anything to add.

  1. 1 and now for some truly appalling stupidity « Alternate Seat of TYR

    […] XV230 accident occurred in part because the RAF traditionally relied on the responsibility of senior engineers, […]

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