British Airways 777 crash – not an easy investigation

The UK Air Accidents Investigation Branch (AAIB) has issued its third update on the British Airways Boeing 777 accident at Heathrow on 17 January – and it’s making it pretty clear that it’s going to be a long, detailed investigation. No surprise to be honest.

There is next to nothing in the way of new findings being released. The only thing I noticed was the addition of the single word “fresh” to describe the cavitation damage to the outlet ports of the high-pressure fuel-pump. I think it’s reasonable to observe that that might in fact be significant.

There is one other subtle change – in its last update the AAIB said the cavitation evidence led them to believe that there had been “either a restriction in the fuel supply to the pumps or excessive aeration of the fuel”. The aeration clause has been dropped – but I’m not clear that that is in fact significant since a restriction could, I think, result in aeration.

More substantially, the AAIB talks a bit about the technical work now underway. It says that Rolls-Royce has modified its engine test-cell to enable it to introduce “calibrated restrictions” in the engine and fuel-feed systems in order to replicate the “engine fuel and control system response”.

And it says: “The primary challenge at Boeing is to create the environmental conditions experienced on the flight over Siberia at altitudes up to 40,000ft, in which to test a representation of the aircraft fuel system.”

Qinetiq has been called in to review and analyse similar data on “a large sample of flights on similar aircraft”. But the AAIB says “no individual parameter from the flight of G-YMMM has been identified to be outside the previous operating experience” and also confirms that “no operational changes are currently recommended” by the AAIB, Boeing or Rolls-Royce.

A long summer ahead for the investigators I suspect.

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One Response to British Airways 777 crash – not an easy investigation

  1. kws June 12, 2008 at 2:03 pm #

    Having been involved with aircraft fuel systems for a few years (off and on) I mooted to the AIB that the fuel pump damage suggested partial starvation, allowing enough flow for flight idle during descent and cruise, but not for full power or pump lubrication and cooling. (Normally, an engine pump delivers close to max flow all the time but some recirculates via blow-off bypass valves.)

    There are two likely causes for flow impedance – either ice build-up in fuel filters or fuel wax accumulation in pipes. Either would vanish post crash in the warmth at ground level. Very difficult to replicate or prove.

    I wonder.

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