Originally Posted by RadioGirl

Inmarsat have not (AFAIK) released information about any 'pings' other than the final one. Before the data source (ACARS, transponder, other) was disabled, what the aircraft (presumably) sent to the satellite was not just a "ping" but a proper telemetry message.

Even so, any satellite-based range information obtained before the transponder was disabled or ground-based radar lost track of the aircraft is redundant information. ATC and/or the radar tells us "the plane was exactly at this point at this time" while a 'ping' at the same time tells us "the plane was on a circle X km from the sub-satellite point" where the circle includes the exact point known from ATC/radar.

None of that tells us whether the plane flew north or south after ATC/radar lost track of the plane.

No, planes don't usually fly like that, but pilots don't usually turn off the transponder, or make a sharp turn off the scheduled course, or fly a zig-zag path after that, or fly to 45,000 feet and then drop to 23,000 feet. MH370 is known (or suspected) to have done those things. We are not talking about a normal flight. It is already clear that either the pilot was flying an unpredictable route to avoid detection or the flight was erratic for other reasons.

If the plane was on the northern route and under intelligent control, there is quite reasonable speculation that the pilot was flying close to the terrain, which would involve more zig-zagging to use terrain as well as trying to avoid population centers which might have radar. It may also (maybe CaptainMiles or another pilot can help us) mean it was flying somewhat slower than the ideal cruising speed.

If it was on the southern route and under intelligent control, it looks like someone was planning to ditch in the ocean. It's not obvious that one needs to fly as far as possible in a straight line to achieve that.

In short, I don't think you can assume the plane took a straight line at a constant speed after the last radar contact.

No, of course it can't fly at very low or very high speeds, but I assume that the speed is variable within a range (CaptainMiles can you help here?) and ground speed varies with wind speed as well as load, as CM already explained. And the plane was "missing" for 5 or 6 hours between the last radar contact and the final 'ping', it is not completely impossible that it touched down somewhere; it could have even stopped at a point on the final 'ping' arc close to where it went missing and stayed there sending 'ping's until 0811.

But what if his intended destination was not "distant"? He could have flown a non-linear complicated route to avoid radar, knowing he had fuel to spare and not being in a hurry, to get to a point somewhere between KL and the end points of the ping 'arc'. If he had a hidden base in, Bhutan, for example, he didn't have to fly that far to get there.

Or again, it might not have been a deliberate plan; there may have been an inexperienced (unexperienced?) pilot at the controls who couldn't keep a straight course, or there could have been damage to the aircraft controls or navigation system that made keeping a straight course impossible.