sensor validation, If I am reading Wikipoodle correctly the speed of sound at commercial aircraft altitudes is around 660 MPH or 573 kn. That gives a speed of 7.8 nm/s for .82 Mach. If the plane flew on the entire time the radius would be 31 nm.
Just from ACARS it is pretty clear the plane was not at altitude by the last minute when the cabin pressure indication appeared. Unless the plane was intentionally driven into the ocean at the fastest speed possible without breakup it could not be outside the 31 nm radius. If it was falling, that would indicate, to me at least, that it had stalled. Perhaps some stall recovery could have taken place. However, in a stall my understanding is that the plane is making very little headway with a serious amount of altitude loss.
Admittedly this is in retrospect, basically because I am not a pilot, it seems fairly obvious the plane is not going to be immediately at LKP. And it's probably not going to be much past 4 minutes of flight minus the time it takes for it to fall the full 35000'. You might define an annulus about 5 nm to 15nm. Then erase the part "behind" the LKP. That's a more limited area to search and has the advantage of being the most likely region for the plane to crash. Instead they ass-u-me-d that the plane continued on for a good minute after the last message before deciding to plant itself forcefully into the ocean with small headway compared to vertical speed.
I repeat, what in heck were they doing out there so far from where the plane could possibly get to? (And how-in-'ell could it get 40 nm BEHIND LKP, which they were supposedly ready to search?)
I can buy it that this was ineptitude caused by the intense political pressure, just barely. I am suppressing comments from accident investigators about the reliability of reports. If the accident happens in a third world area, the report quality is poor because of the untrained and inexperienced investigators. If the accident is not politically charged and is in a "first world" nation the reports tend to be pretty good. If politics enters the picture the reports are what the politicians wanted them to say. That's from their experience. I suspect that is what this investigation started out to be. This latest search probably fell out of the unrelenting public oversight and demands. It would not go away. So the plane had to be found. At least that's what I get if I let my cynicism and "too many decades of real world experience" get out of hand. I still expect a political report. But I expect it's going to be as honest as the politicians permit. (And Wikileaks exists as a means of forcing honesty on politicians.)
(As a pair of side notes it has been reported here that the Russians, with (heh) more experience than others with crashes, have found that you start at or near the LKP when searching for crash locations. And I further note that mm43's current backtraces also placed the accident location fairly close to LKP but, if I recall, a bit South of where BEA hinted it actually fell.)