Originally Posted by
ACARS
I have tried to find the relevant post, still looking.
As I remember it the autopilot can fly LNAV (preprogrammed route), Heading Select or Track Select. The heading/track reference can also be changed from magnetic to true (as done over the North Atlantic). So I would imagine a true track could be flown with no end point entered into the computer.
It is simple logic that one can only fly a great Circle route if one has a start point and a finish point since one has to compute several calculations.
You can't just point MH370 south and say to the autopilot fly a Great Circle Route because if the autopilot could answer back it would have to say, okay but to where?
I imagine on a FANS 1/A aircraft for oceanic flights there might be such a function, but it would require a start and finish waypoint. I know of no waypoints between Cocos Islands and Australia which MH370 could have been commanded to calculate a great circle route for.
http://skyvector.com/?ll=-20.6821281...rt=304&zoom=10
I do know that if an autopilot reaches a waypoint with no further instructions it will just continue to fly the last magnetic heading.
It is far more logical that they were having electrical problems, loss of on-board navigation systems so continued past BITOD towards the VOR beacon at Con Son so they could fly the VOR radial back to Singapore for an emergency diversion.
Over Con Son I postulate they selected L-Nav to divert to Singapore, perhaps even inputted the code for Singapore itself intending a descent from 35,000ft, but then a blaze erupted and engulfed them?
Once MH370 flying depressurised and on autopilot reached Singapore it just kept flying the last heading (196 True?). It is worth noting too that magnetic variation would distort any magnetic track towards Australia no matter which heading MH370 was pointing at the start which could imply intercepting the southern arc higher along the Southern Arc than just a straight track flying 196 degrees True. The limiting factor would have to be the fuel endurance from Con Son island of 5.5 hours. approaching IGARI the airspeed was 473kt, then about IGARI it reduced to 471kt perhaps as a result of the turn?