Some really thought provoking posts recently, the last 4 or 5 pages should really have informed all of the fuel system and it's display and caution/warning systems. Hats off to Sid for explaining and illustrating the CAD and the Warning panel. In my opinion it should now be clear to all that if the systems worked as advertised and the CAD was in fact working, the pilot would have and should have taken decisions to land well before the fuel configuration got to the point the AAIB have found.
That really does leave only 2 possibilities, display/warning system faults, or HF, it will be critical that the AAIB find out what this display fault was and if the sensors where contaminated. Once that is known it could be time to move on to the HF.
If it all worked perfectly the chain of events would be as follows.
Ac departs with 400kg fuel with transfer pumps both ON.
Fuel system transfers from main to supplies keeping them full.
Main tank contents reduce to a point where transfer pump cautions appear according to fuel level and aircraft attitude, in accordance with the RFM the pilot will carry out switch position changes.
The main tank fuel contents reduce to empty. The Full supply tanks then start to reduce.
The Supply contents reduce to the point where the amber low cautions and master caution and beep occur, 2 occurences.
The supply tank contents continue to reduce to the point where the Red Fuel Warnings on the Warning panel illuminate with audible gongs and the master caution illuminates, again 2 occurences.
Around 8 to 10 minutes later the first engine flames out. The master caution illuminates along with many other cautions, the police role equipment high power consumers fail. The role equipment screens, camera etc.
Around 2 minutes later the last engine flames out. Many services are lost, many warnings, both visual and audible. The battery becomes the only source of electrical power.
The low rotor audio warning sounds, and warning illuminates if Nr drops below the set parameter. The Nr continues to drop, the hydraulics cease to function and the flight controls become immobile.
This sounds stark, but is a factual timeline/sequence of how the aircraft COULD end up in uncontrolled freefall if NO faults have occurred and the pilot took no action at all other than the transfer pump switch manipulation whils the main tank fuel reduced.