Something in a PBS broadcast tonight, followed by this item in Reuters ( [
www.reuters.com] ) suggests a way that the overspeed could happen. Apparently, the Amtrak NEC flavor of PTC (ACSES is the acronym, I think) wasn't installed on that section of track (yet). I thought it was active throughout the NEC, at least where Amtrak owns the tracks - apparently not.
Explains one thing I didn't understand - how on the NEC line you could carry that much speed so close to a restriction. With a clear signal and no externally enforced speed restriction absent the overlay system, the engineer may have recognized the curve and dumped the air too late.
NTSB did say in a press conference that the speed peaked at 106 mph, dropping to 102 in a couple of seconds after emergency braking started. Then their data stopped.