Little off topic but let us not get carried away with the capabilities of HMS Echo....
I spent 3 years on board and her sister ship as a civilian contractor providing support for the survey equipment and teaching Navy operators how to use it - (yes as a civilian - really!).
The vessel is fitted with survey equipment for up to 1000m depth. It is great at finding wrecks. A sidescan sonar can only see a 200m wide swathe and you can only survey at 4.5knots. Her hull mounted multibeam will see a much larger swathe, but it is not designed for detecting objects - just changes in seabed. The 'hit' rate per metre squared is too low.
While Echo is a valuable asset, but it is not magic and is limited by the equipment. What may be of more use is her ability to act as a command platform.
I now work as a Survey Party Chief running geophysical surveys (as well as a flight instructor) - so I do know this industry as well as flight instruction.
Excellent bit of insight into how difficult the task is going to be to find the aircraft. This thread has gone into over kill with suggestions and hypothesis of what actually happened. Either way we wont know for sure until the plane is found and and even then we may never find out. The time is well and truly over for any thoughts of working out what happened.
On a side note, I find it rather tedious now watching the day after day updates (or non updates) in the press conferences. It is doing nothing more than fueling speculation and adding to the tension of the families. I know they want answers, but if there isn't any, then there isn't any.