Here's an interesting blog article: http://www.geekinthecockpit.com/2020/01/well-that-was-not-fun-at-all.html I wonder how often stuff like this happens. Good thing those passenger jets have some redundancies. P.S. It was a pleasant surprise to know that Airbus can run APU in flight. In old Russian jets such as Tu-154, the ram air effect in flight would spool up the APU and overspeed it. They had a check hatch to prevent the air intake in flight. In 1995, that door failed, the ram air oversped the APU, which exploded and took out all redundant hydraulic strings. The jet lost control and landed into a cow pen. Investigators had fun time separating human remains from animals.