Helgar, I hope I didn't give you the impression that I think you are the cause of a needless discussion. My criticism was directed to the media, who published an article that was clearly meant to stimulate a discussion, which I (and I forget that others do not have the opportunities that I have, to find the facts) wrongly described as needless. It should be needless in a Nimrod crewroom, but valuable in a bereaved family's home. For that slip of the tongue I apologise.
Dodgysootie:
when the second to last tank is shut off, would there not be a pressure increase or 'pressure spike' down the 5 tank refuel line as a result?
Yes, there would be a momentary pressure surge, which would be felt throughout the pipework (but not in the tanks), right back to the refueller's pump, which should react.
Mick,
As I have indicated above, I should not have used the word "needless". If Shona and Helgar are concerned about the QQ report, I agree that it needs discussion and clarification. QQ are not experts on the technicalities of all aircraft. I don't doubt their expertise in safety matters and specific subjects such as combustion analysis, fluid dynamics and aerodynamics, etc. Their suggestion that we consider re-installing the 5 tank overpressure warning is based on insufficient information (and thats our fault, I guess, for not giving them the full history), However, the IPT will doubtless give it due regard and for the reasons I have stated the device will probably not be needed. Its unfortunate that it provoked a headline moment for the press which then gave rise to family interest.
With reference to flow rates, yes, before the accident, we did experience fuel flow greater than the max permitted rate quoted by QQ. That specification in the QQ report was new to me (and most other aircrew, I believe) when I read it. I would be very interested to know where that max flow rate is published. There is no way that the Release to Service flight trials unit would approve the use of tanker pumps that would exceed manufacturers' published limits on the receiver's aircraft.
Since Dec 06, we have drastically reduced flow rates, markedly reduced the amount of fuel we can put into each tank and taken steps to obviate pressure surges. There are no more pressure surges any more. These changes in our proceures were done solely as a precautionary measure to ensure that AAR is now conducted even more comfortably within the bounds of safety.
Therefore, with the QQ report as a basis, the operational measures now in place make the fuel system, as designed, more secure than ever before.
The fuel leak on XV235 came out of the blue. We had not spilled a drop of fuel during AAR since Oct 06 before that incident. As I have mentioned before, the investigation into that incident is now complete. We await its publication. I would be very surprisd if the cause of that leak is down to flow rates, pressure spikes, age of the pipes or the reliability of the seals.
Ed Sett