The passenger mode is way too buggy and annoying to deal with, especially when organizing bank robberies. I have not seen this issue being addressed on the forums before, despite how serious it is.
The main issue is being able to shoot using TAB (people frequently check scoreboard which is bound to TAB, and it also happens to be bound to 'Fire' by default) while in passenger mode, causing damage to the plane or sometimes even blowing it up using grenades.
I am sure the majority of SAES are aware of this issue, but I am still gonna leave LAW's video below which shows a few cases of this issue:
Some possible fixes could be: Disallowing weapons in passenger mode, not being able to deal damage as a passenger, or just simply disabling tab.