For what it's worth, I've had two AI failures in the past month in different aircraft, one VMC, one IMC.
VMC, easy to detect. IMC, a few moments of 'this feels f'ing wrong' before I picked it up. Autopilot off and recovered on Standby AI from about 20 AoB and 5 degrees nose down. No biggie at altitude.
Having an AI let go on rotation on a cloudy night with a black hole in front of you: That is a biggie.
Perhaps this pilot was trained well and new all about OEI performance requirements and the somatographic illusion. Perhaps, like me, he knew about AI failures. Perhaps, unlike me, he didn't have enough sky below...
