I read that he left the station sixteen minutes behind schedule. He was speeding to make up time. If the speed limit was 50 on that turn, like on a highway the turn probably could be taken in relative safety at 70 or 75 mph and in a pinch, it probably has been taken at 90 mph fairly regularly.
He just screwed up and was going too fast and then panicked. There was a retired Amtrak conductor on the radio last night who said that the train would have made that turn at 106 mph without too much problem except that he panicked and hit the emergency brakes. The brakes work from front to rear with the front cars slowing down first. Hitting the emergency brakes going that fast into a turn like that made all the back cars pile onto the front cars that had already slowed down first and caused the derailment.
It is like driving a car, the worst thing you can do is panic and lock up the breaks going into a turn.
From my railroad experience when the train goes into emergency, all cars brakes go on pretty much simultaneously, even on a train a mile long. The engine pumps the brakes off, ON is the default position once the air is pumped up. Air pressure pumps the brakes off, not on as some believe. Each car has an air tank to hold the air pressure that holds the brakes off.
It's easier to understand than it is to explain..
Old engines of my time had a dead man pedal but could be defeated with a case 50 cent piece wedged in to keep it down. If your foot slipped off, the train would go into emergency braking. Also if an air hose came uncoupled or if it burst, or the train broke a knuckle or draw head and separated, the train would go into emergency braking.
Time was there was a speed recorder on the engines. These were checked and engineers were subject to be fired for a period of time, if a speed violation occurred. My route between Savannah and Macon, Southern Train 135-136, was max 49 MPH on a freight train. We were in the dark with no electronic signals or tracking.
I'm sure things have changed since then but not much.
