Here is my question(s)
How does a plane just start breaking up at cruise altitude? I am no expert, so this is why I am asking.
Also, How can you not track an airplane? even if the transponder was disabled, how can there not be a backup system for the plane? Seems pretty logical to me?
I know there are more variables. I think your guess is very plausable, just would like the details.
Good questions. An aircraft can break up for many reasons. Faulty equipment, usually in the flight controls or flight surfaces are likely. Improper maintenance, whether it be preventative, inspection, or part replacement can also be a factor. In aircraft, some parts have a lifespan based on how many flight hours they've been on the aircraft. For example, a turbo-prop engine on let's say a Beechcraft King-Air(used for corporate companies) HAS to be overhauled at 2000 flight hours. No questions asked. Doesn't matter how good it's running at that TBO(time before overhaul) time, it has to be done for safety reasons. You can't just pull over when you have an issue at altitude.
I watched a documentary not too long ago on a regional jet being operated by United Express Airlines and an overnight mechanic crew was supposed to replace both leading edge horizontal stabilizer skin's on the tail. That's the part of the tail that creates lift and aerodynamics to control the pitch of the aircraft. Anyway, the crew finished one side a little later than scheduled and rushed the other side. They forgot to reinstall all of the hardware and the aircraft flew fine until the initial descent into their destination. The increased airspeed created enough stress on the leading edge that it ripped the part off, so that half of the tail no longer produced any lift or contol, creating an uncontrollable dive, ripping one of the wings off, becoming what we call a "powered lawn dart," unfortunately plumeting to the ground at a high rate of speed, killing everyone on board. This series is VERY interesting and if this stuff intrigues you, check it out! It's called "MAYDAY, Air Crash Incestigation." It was a TV series but full episodes are on Youtube.
The ONLY way to not be able to track an aircraft in a Radar coverage area, is to "fly below the radar." By that, it means that you literally have to fly low enough for the radar to think your aircraft is a building, car, ect. So this usually means less than 200 feet, but over a sea like that, I would guess you could lose radar coverage under 3000 feet or so, give or take. But the transponder in the aircraft doesn't work how I think you're assuming. It's essentially the receiver, and the radar station being the transmitter sending out a ping, and the transmitter sends back a pulse, letting the radar station know how far away it is, and a Mode C transponder can entail it's altitude in the ping as well. Those are required in commercial aircraft amd aircraft flying in more congested areas.
Now the transponder has adjustable code settings, in a series of 4 digit numbers, assigned by the FAA to designate your aircraft is that blip they see on the screen. So in your clearance, they will give you your "squak code" so they cam identify you on the radar. It gets much more detailed, but I can go on all day about it.
So there is not a requirement for ALL aircraft to have a transponder. For example, Older aircraft that were not equipped with them do not have to use one, but they are restricted to where they can and can't fly. But the radar can still identify their blip, as an object and estimated altitude. The radar will pick up anything of decent size in the air, whether it has a transponder or not, the transponder just helps the controller identify which blip they are on the screen.
I can go even further in detail or send you a couple links if are still intrigued, but check out that TV series I was talking about. It's cool the things you'll learn about the aviation industry amd accident investigation.