Some more modern aircraft indeed have such protections, but this was an old 737 without any such stuff. Simply pushing the control column fully forward would send the plane into a dive pretty quickly.

The controls are mechanically linked. Unless the perpetrator incapacitated the other flier, it’s a test of strength. There’s no method for disconnecting the second set of controls in a 737.

That is incorrect. There is a friction clutch between the controls in case there is a mechanical jam the other pilot can at least control half the control surfaces. It needs a significant amount of force to detach, though. It is documented on Egypt Air 990 however that both elevator surfaces turned into opposite directions.

Like @FeeJai already wrote, that's incorrect. Look up for Atlas Air Flight 3591 crash, boeing 767. Spatial disorientation, dual imputs on yokes, split elevator. https://www.pprune.org/rumours-news/628156-atlas-air-3591-nt...

I am not disagreeing with you, but I just want to point out the absolutely stunning safety of modern air travel. Using your 99.999% number against the number of FAA flights of 16,405,000[1] per year (that's just US FAA, not global). This would result in 16405 "incidents" per year. Luckily for us, the actual number is far lower than 16405.

[1] https://www.faa.gov/air_traffic/by_the_numbers/

Germanwings Flight 9525[0]

[0] https://en.wikipedia.org/wiki/Germanwings_Flight_9525

That was F/O without another pilot present