Shy Torque
Thank you for your post - I'll address your points in order:
TANS It is the basic accuracy that is the problem - esp after crossing water - it so happened that ZD576's TANS last reading was accurate at the end but this should be regarded as fortuitous - the father of one of the pilots recalled a flight where the TANS had been out by (as I recall) nearly 2 miles - one of the pilots had actually warned the Flight of the accuracy concerns of the TANS - I do not believe this system would have been used by this crew for anything other than en route nav - certainly not for a close in turn a few hundred metres from danger. DME on the other hand, in normal circumstances, is often more accurate than radar and does not require interpretation - it would have been ideal for this manoevre.
SPEED May I direct you to Boeing's report (on the web) - the sums are done for you but you can use them as a guide to do it yourself from the various timings etc - basically, to get where it did when it did, the a/c must have maintained its speed (at the top end of cruise) for most of the passage over the sea - there was insufficient reserve of speed for it to have ever been going slow (or doing any sort of significant manouevre) and then make up the time - this rather leaves the only scenario as a straight and (approx) level flight at the top end of cruise speed right up to the last moments (when the a/c had apparently responded to an intuitively obvious avoidance manouevre - suggesting to me at least that there was not a control problem or any other kind of mechanical problem and also suggesting that only at the last moment did they realise just how close they had got - by actually seeing the shoreline pass under them, entering the mist, or getting the radio altitude warning, all just about the same time).
SH NOT USING BEACONS This is the kind of input needed. If you could push a bit further and get similar input from those in SH who had actually done this crossing, then this line could indeed be put to bed - my persistence in pushing this line has been due in part to its being summarily dismissed previously with generalisations, simplistic VFR/IMC arguements, what I consider to be deliberately misleading descriptions of the conditions, etc, and a general obfuscation as to the flight plan. However, on the strength of your input alone we cannot yet discount it - although I accept that its likelihood is considerably deminished.
It does sound to me that you may be able to pursue the actual practice through social contacts?
And, there's always a first time for everything - I don't suppose we'll ever know (at this rate) what was the equipment that the American SEALS were looking for near the crash site.