What legitimate reason would a pilot have to depressurize a plane at altitude, incapacitating or killing the passengers? Just wondering if and if so why that system / function is available.
If some part of that system was on fire or an engine was damaged and it was pumping smoke into the cabin. Basically every system can be switched off, sometimes it’s necessary to be able to switch them off completely (normally for pressurisation they would already be on the way to a breathable altitude), or to be able to power cycle something to try and fix an issue.
At the end of the day, there are so many other ways for the pilots to down an airliner and kill everyone, they are ultimately the only people you can’t practically have the system distrust. The only thing you can do is the rule to always have two people in the cockpit but it doesn’t always help.
It's more that they have the ability to control the pressurisation manually in case the automatic system fails.
Ultimately the pilots have to be able to turn anything off that might malfunction.
Also even if you (try to) take capabilities away they are by definition quite smart people and could probably figure a way round if they really wanted to.
Pilots have access to virtually all critical systems on board; if they wanted to kill everyone on board, they could simply fly the plane into a mountain. Pressurization is mostly automatically managed, but if it fails, the pilots must be able to manually depressurize before landing.
Because if you have control of the aircraft you already can kill everyone if you wanted. Manual control of cabin pressure could be useful if the pressurization system malfunctioned and needed to be manually overridden.
All vehicles that can be steered have that possibility, even cars: If there is a steering wheel, it is possible to deliberately crash the vehicle. If it is possible to shut down engines, it can also be used for malicious purposes. In other words, there is always the possibility of using everything for malicious purposes.
On the other hand, the ability to shut down a system that has failed can save everyone on board.
There are approximately 40,000,000 flights each year. Almost all occur without incident. In the entire 120-year history of aviation, only a few accidents have resulted from the pilot intentionally crashing the plane.
