[gvb]

How many aircraft are lost that satellite link "crash data" would have been useful? I recall three, MH370 would make four. I imagine there are more, but compared to the number of aircraft that don't crash, the total is a rounding error.

http://en.wikipedia.org/wiki/TWA_Flight_800

http://en.wikipedia.org/wiki/China_Airlines_Flight_611

http://en.wikipedia.org/wiki/Air_France_Flight_447

Of the three, TWA flight 800 is the only one whose cause is controversial, and in-flight data transmission likely would not have helped identify the cause of that crash.

Of all the above accidents, the causes are understood and have not been repeated. In fact, the cause of Air France 447's instrumentation failure was understood before the crash - there was an an active airworthiness directive to fix the pitot icing.

Extraordinary expense with no(?) payback.