Airport Security Prize Announced
Now, assume the bullet hits the ceiling and almost immediately the aircraft will start de-pressurizing (venting oxygen too) which is a very bad thing (read Hypoxia). In general, commercial aircraft are pressurized at a maximum cabin altitude equivalent to about 8,000 feet, where it is possible to breathe normally without an oxygen mask. This is when the oxygen masks come in handy as you are venting oxygen into the atmosphere. An aircraft fuselage is not a completely sealed tank, pressurization happens by either drawing air from one or more of the engines or a separate compressor. Putting more holes in it will not suddenly stop the plane from bleeding air into the cabin.