This is kind of an "oldie but a goodie" in the aircraft biz, and it's making the rounds again, so I thought I would share.
One of the things we do after a major structural repair is what is known in the industry as a "high blow". We pressurize the airplane a wee bit more than it experiences at altitude, which accomplishes a number of things for us. I don't want to get off track and delve into the details of all of that, suffice to say we run up the cabin pressure. It's actually one of my responsibilities as the tool/equipment engineer on site.
Airplanes are fitted with outflow valves to relieve over-pressure situations. We plug those and monitor pressure on a pretty simple gauge. We go higher than where the outflow valves are designed to open.
So, what happens if something goes wrong? In this case, a mechanic used his own, un-certified gauge. It was broken. No one caught it, so they kept running the pressure up. Eventually, something had to give:
