There is some cognitive limit of how many variants of procedures pilots can be expected to memorise and execute. Detecting a classic constant runaway trim is a

There is some cognitive limit of how many variants of procedures pilots can be expected to memorise and execute. Detecting a classic constant runaway trim is an old drill for pilots. Detecting a trim that gradually runs away, then stops to make the situation look normal, then runs away again until the plane is way off level flight is a new failure pattern. It works for non-critical software where users can learn workarounds for only those problems they happen to encounter. But it doesn't, in the long run, work for cases like aviation where there is a known but growing set of special conditions that the pilots need to learn and remember even if they don't ever bump into them.