From the report
http://www.atsb.gov.au/media/4911984...370-report.pdf
"- loss of radio communications
- long period without any en route manoeuvring of the aircraft
- a steadily maintained cruise altitude
- fuel exhaustion and descent
This suggested that, for MH370, it was possible that after a long period of flight under autopilot
control, fuel exhaustion would occur followed by a loss of control without any control inputs.
Note: This suggestion is made for the sole purpose of assisting to define a search area.
The determination of the actual factors involved in the loss of MH370 are the responsibility
of the accident investigation authority and not the SSWG
.
Also allowing for the fact that a maximum glide distance of 100+ NM would result in an
impractically large search area, the search team considered that it was reasonable to assume that
there were no control inputs following the flame-out of the second engine. Accordingly the aircraft
would descend and, as there would be some asymmetry due to uneven engine thrust/drag or
external forces e.g. wind, the descent would develop into a spiral."
I still haven't got that. Maybe because I'm just a CPL/MEPL, but why should fuel exhaustion under autopilot end in a spiral dive? Is the auto pilot on the B777 completely disconnecting on fuel starvation? I'd guess the Ram Generator would deliver the power for autopilot + controls, the envelope protection of the AP would prevent a stall and the AP would maintain the track. That would place the center of the search area about 100 NM forward in flight direction.