Modern passenger airplanes are by their nature complex – but in most cases, that’s a good thing. The mental attention of air crews is a precious resource, and automated systems allow this to be conserved for when it’s most needed. On top of that, the fly-by-wire systems pioneered by the Airbus SE A320 mean that most planes these days self-correct when pilots move the controls too aggressively – one reason why fatal loss-of-control accidents have fallen by three-quarters over the past three decades.

The problem comes with split-second decisions. Using autopilot to preserve a crew’s mental energy is all very well. Over time, though, mental muscles that go unused end up atrophying. That’s a problem because most air accidents occur in odd, unexpected situations where pilots are having to diagnose a baffling problem under high pressure. One 2014 study of highly experienced Boeing 747 pilots found that 15 out of 16 failed to react properly to misreadings of airspeed in simulator tests, to the extent that the “aircraft” started to stall.

Boeing should be worried about that, because a recurring comment of pilots who’ve flown the 737 Max and predecessor versions is that changes to the basic design and flight control systems make it feel like a different aircraft. Such differences risk breeding confusion.