There have been quite a number of accident reports referenced here at Aviation.SE about commercial (passenger or freight) flights executing controlled flight into terrain on approach for landing. The accident reports always seem to revolve around the pilots not knowing they are too low, failing to recognize or respond to the GPWS, etc.
While I understand that the pilot in command has the final say on what happens on board the aircraft, ATC is responsible for giving the PIC instructions to get him safely to the end of the runway.
In the case where ATC has given the PIC the approach route, whether VFR (flight following) or IFR, how much time, ability, and requirement does ATC then have to monitor that flight to ensure that it's on the expected course and at expected altitudes? In other words, how much responsibility does ATC have for failure to monitor the situation and allow these accidents to happen?
If necessary, differentiate between different CAAs, but I would think the answer would be fairly similar around the world.
There are a couple of nice answers, but they're not addressing (in my head, at least) the question I was attempting to ask, so it seems I didn't ask it well. I'll clarify further:
In a situation such as Eastern 401, the pilots had already contacted the tower to indicate that they had an issue - the nose gear lock light failed to illuminate. While attempting to determine what the cause of the problem was (bulb burnt out or gear not actually locked), they forgot to aviate and flew into the ground. In a situation like this, particularly where ATC has been notified that there was an issue with the flight, it seems to me that they (ATC) would have been more alert to the flight and notified the pilots that they were descending when they should have been holding a steady altitude.
This is the type of situation that I'm asking about (though not specifically EA401), and I'm wondering what role, if any, ATC should or does take in monitoring and alerting flight crews to altitude deviations, especially on approach.