Having been castigated for previous posts exploring scenarios where the supply tanks could run out in other than the prescribed fashion,it is with some trepidation that I enter the fray again!
However, the latest AAIB bulletin does raise several issues which would seem to corroborate a number of the scenarios which were previously dismissed. Posts since the latest bulletin have already picked up on some of these, but one which hasnt been picked up relates to whether the aircraft was afflicted with the fuel probe fault which was the subject of the subsequent Eurocopter service bulletin.
Having read the prescribed checks which had to be undertaken, it may not have been feasible to ascertain after the accident whether the probes were reading accurately on this aircraft, but it does seem clear that there was a major anomaly in relation to actual versus perceived fuel contents.
Had the transfer pumps been switched on, it would still be the case that the aircraft would have landed with fuel contents below MLA by an unhealthy margin. And yet on the return flight from Dalkeith, it seems to have diverted to not one but two non urgent tasks. If the pilot had any worries at all about fuel he would not have undertaken this tasking, not just because they were non urgent, but because they were so close to base that he could have RTB, refuelled, and relaunched in a short time.
Everything points, IMHO, to the fuel probe fault being present, misleading the pilot in relation to his actual fuel state.
The consequent late illumination of the yellow fuel warnings, followed too quickly by the (correctly functioning) red warnings would have been very confusing.
Also of relevance, again IMHO, is the fact that the total fuel on board was less than the total capacity of the supply tanks. In "normal" operations, at this stage should both transfer pumps not be switched off, as there would be nothing left in the main tank to transfer? Throw in the ability of fuel to spill assymetrically back into the main tank from the assymetric supply tanks, which could only be filled symetrically by the transfer pumps (had they been on) and you arrive at a situation where the supposed designed in delay between each supply tank emptying could be drastically reduced.
Still trying to join all the dots up, but keep coming back to the fuel probe fault as starting the sequence of events that caused this.