[mgsouth]

Watch the Mentour Pilot video; there was a display in the cockpit which showed the actual control surface movement. Why didn't they catch it? I'd guess it was because they were just a regular flight crew as opposed to acceptance test pilots, had never ever seen cross-connected controls before, and when they tested the controls they saw "yep, the surfaces moved" and it just didn't register that some of them were in the wrong direction.

[mjg59]

The primary issue is that once the ailerons were fully deflected, the control display turned green - even if they were deflected in the wrong direction. It seems that despite this test having been performed multiple times, everyone involved was subconsciously looking for "It goes green" and not "It moves in the right direction".