Big "disagree" alarm for the pilots and let them decide to keep either computer or go direct. Airbus has the concept of flight control laws, surfaced and changeable by the wet backups.

http://www.airbusdriver.net/airbus_fltlaws.htm

>go direct

That's not really a thing in modern airliners. The computer is still heavily involved even when hand-flying the plane.

"Thankfully", the 737 series isn't a modern airliner, and isn't fly-by-wire. All control inputs are directly linked to the relevant outputs, though sometimes with power assistance.

It is on the Airbus, one of the control laws, see link above. It's still FBW though, so one might argue that "mechanical backup" is really what you want.

As for "modern", the A320 had control laws in 1984 and the 777 in 1994.

And Boeing will make that disagree alarm an optional extra?

Am optical extra that isn't actually properly functioning as intended in numerous delivered products? Almost as if it wasn't sanity tested in one production unit, let alone some random sample of units?

s/Am optical/An optional

https://www.aviationtoday.com/2019/05/06/boeing-angle-of-att...

Which computer calculates that there's a disagreement, and how can we ensure it's not indicating a false negative?

Either. The alarm must be an OR.

Then, IMO, it should be two independent indicator lights, not 1.

my CS201 class 19 years ago taught me this. education just isn't as good these days..