How did using the wrong oil in an override piston for the elevator trim system on an Airbus 320 lead to the simultaneous failure of all five fly-by-wire flight computers, reversion to purely manual pitch control by the trim wheels only, two dead side-stick controllers, and eventual hull loss and write-off of the airplane?
The sequence of design choices, implementation bungles, and opaque human interface decisions that led to this accident makes you wonder whether Airbus had contracted out the development of their fly by wire software to Microsoft. And sometimes, “Have you tried turning it off and on again” is not the best course of action when a computer appears to be misbehaving.
Here is the complete “Investigation Report: Accident, Loss of Control with Airbus A320-214 near Tallinn Airport on 28.02.2018” [PDF, 102 pages] by the Estonian Safety Investigation Bureau.