I agree - I think a little more than the instrument landing system was offline during that period of time. Surely ATC had them on radar and could have easily seen them coming in way too slow to properly land.
I'd be rather surprised if the radar could be useful in this capacity. You'd have to build a large database of all aircraft approach speeds, taking into account all the various factors (different weights and configurations) that could change. You'd also have to take into account wind speed and direction, since radar will measure ground speed, but airspeed is what matters. And not just wind, but wind at their precise altitude, which your ground weather station is not measuring. (Wind speed and direction can vary enormously over altitude, especially close to the ground, due to friction.) Finally, you'd have to catch it and communicate it in time to do something useful, which seems tough in this case, since the airspeed didn't get low until fairly shortly before the crash.
I wonder if a simple and effective thing to do here would be to simply display a velocity vector, either in a HUD on the windscreen itself, or on some kind of video display in the cockpit. Just a symbol on the screen that shows exactly which way the airplane is headed at any given moment. When it's on a runway, that's where you'll touch down if nothing changes. When it's on a seawall before the runway, that's where you're going to crash unless you fix things. Maybe I'm underestimating the difficulty, but it doesn't seem like it would be too hard to construct one based on GPS and a forward-looking camera.
Edit: thinking more about that last suggestion, more recurrent training for visual approaches would probably be a better idea. A normal human has a built-in velocity vector already. You look out the window and find the point on the ground that isn't moving relative to your view. That's the point you're headed toward. This is Aviation 101 stuff, literally one of the first things a pilot ever learns about landing an airplane. High and low comes later: the first thing you pay attention to is whether that non-moving point is, in fact, on the runway where you intend to touch down. (Or, because of the flare, slightly before where you intend to touch down.)
