Reely said: "
My vision of possible occurrences after reading the final report:
- both supply tanks did falsely indicated full on the CAD
(a 0.5ml (!) water globule at the capacitance based fuel sensors can do the trick, see p. 54, G-NWEM)
- "Low Fuel" Warnings (driven by correctly functioning thermistors), were considered as acting up "shi**y EC".
The were acknowledged as being irrelevant, because of (incorrect) triple "plenty fuel" indication on the CAD.
That is the reason why he flew that final task, although he just had acknowledged the Low Fuel warnings, multiple times!"
I have now read the report front to back three times and I have come to the conclusion that this is the most likely scenario. (I also went back and re-read the 170 odd pages of the first thread which was, errr, interesting).
I found 1.16.2, the G-NWEM incident, (just two weeks after this incident!), shocking. Not only were the supply tanks stuck on full during the ground test but the indicated level of the main tank was depleting with xfer pumps off! It would be easy for none of the crew to question that - (confirmatory bias). It would not prompt a check of the xfer pumps. I note with trepidation that neither would the fuel caution caption come on, and xfer pump captions do not come on if a pump that was switched off after running dry would not come on again if re-immersed. It only comes on after 3 mins of the pumps running dry or after 3 minutes of being switched off while immersed.
Falcon900 said
"The AAIB report makes reference to issues with the fuel probes on G-SPAO earlier in the year, and explains that these were resolved. It does not explain whether the faults became apparent while the aircraft was in flight, and who was flying it at the time. I am wondering whether the accident pilot had some history with spurious fuel warnings on this aircraft."
This is a really good point, we are all influenced by our past experience. It is easy to sit in an armchair and say it is inconceivable that 3 people ignored obvious warnings. Firstly, two of those people might have been comforted by a digital blue display more than a red lamp and audible tone (that the pilot had already acknowledged and cancelled several times).
Supposing I said to you the the oil pressure reading for your main rotor gearbox fluctuated wildly then suddenly went to zero, and that you knew that if it was correct you had 8 minutes max before you dropped like a stone out of the sky. Would you stake your life on that reading being wrong? I bet not a single person here would say that they would fly on and try to make base.
But that is exactly what happened here:
Investigation: Faulty filter cover, pilot error caused fatal Marine helicopter crash
The pilots were influenced by recent MRGB pressure sensor and transducer maintenance work and they were prepared to stake their life on a false indication.
The finding of the position of the prime and xfer pump switches are largely irrelevant, and in fact proven to be unreliable, although the photographic evidence favours at least one prime switch being OFF. I do not believe the pilot has confused the prime and xfer pump switches, for one thing, the caution captions for the prime pumps would have gone on if he has reached up for the xfer pumps in response to a xfer pump caution light coming on.
It has been said that the cause of the accident was the xfer pumps being off. Not strictly true, the cause of the accident was the pilot failing to put them on, their OFF position is the symptom not the cause.
I believe he had conflicting information and unfortunately, possibly due to past experience (someone on the previous thread mentioned running the tanks down to zero on a ground test and the Warning Unit red LOW FUEL 1 and 2 never coming on) chose to ignore procedure and rely on one of two information sources.