Fly-by-wire again?
What kinds fly-by-wire(FBW) system are we talking about?
Way too many loose references to FBW and not enuf details. Many planes have had electrical and electro-mechanical connections to the control surfaces and such for 50 years. Dampers, "control augmentation", control stick steering and the beat goes on. But few have had true fly-by-wire with zero mechanical connections from the yolk/stick to the ailerons, elevator and so on. Many, if not most jets from the early 50's drove the flight controls with pure hydraulic pressure or a combo of hydraulics and cables/pushrods. That ain't fly-by-wire. Electronic limiters and inputs that supplement basic hydraulic/mechanical implementations ain't FBW.
So the crew of the ill-fated plane may have turned off the autopilot, but what did the FBW system do? Was the system still using the bad air data? Were they in "direct control" as with the arbus implementation?
I have a very hard time understand a prolonged 30 degree dive until impact. I only saw that kinda pitch angle when delivering ordnance or performing aerobatics.
The scenario deeply disturbs me, and not just because the crew didn't turn on the heaters. The probes could have frozen anyway or ice crystals in the lines could have made things crazy. Oh well.......