@Blake777:
We used a zero fuel weight of 175 tonnes. We let it run out of fuel at FL 250 in track hold and alt capture. However it would not make any difference what mode it was in as everything would drop out. In real life one engine uses fractionally more fuel per hour than the other* and there is typically a difference between main tanks of a few hundred kilos, so we had a 300 kg difference between the contents of the left and right tank.
When the first engine failed TAC (Thrust asymmetry compensation) automatically applied rudder. The speed reduced from 320 knots indicated to 245 knots indicated. It was able to maintain 245 knots and FL250. When the second engine failed the rudder trim applied by TAC was taken out and the trim went to zero. The autopilot dropped out and the flight controls reverted to direct mode.
*: With reference to the Factual Information Safety Information for 9M-MRO, Issued on March 8, 2015, page 28 states the following on an engine related Deferred Defect, deferred to the DDL:
3) 07 Nov 2013: From Daily Engineering Operations Report (DEOR) - Right engine consumes average 1.5T more fuel per/hour compared to left engine.
What would the implications be with this open DD if the crew were incapacitated after approx. one hour into the flight? If left unattended for the remaining hours the aircraft flew (no cross feed actions performed), a considerable imbalance could have developed between LH and RH fuel tanks with the right engine flaming out considerably sooner than the left engine. As you mentioned, airspeed and altitude would reduce and if systems were still functioning correctly, TAC would apply rudder to compensate. No telling where the aircraft ended up if TAC failed to correct with a relatively heavier LH wing in this scenario . . . . . probably nowhere near the current search area.
For fuel state see page 30 of the report:
"The investigation estimated that the aircraft would have had 41,500 kg fuel remaining after 41 minutes flying from KLIA to IGARI."