Is it possible for a pressure loss in the cockpit to not extend to the cabin?

Question

I have done research into the question of pressure differences between the cabin and cockpit and the theoretical answer I receive the most is that the pressure difference would equalize almost instantly, as cockpit doors are not capable of an airtight seal — and it makes sense, but I recently came across an incident that happened a couple years ago: Sichuan Flight 8633.

On that flight, the windshield actually exploded, and based on the passenger recordings, the cabin seemed a little messy from objects flying around, but they could still hold onto their phones and the flight attendants were able to stand up.

The only comment I could find on that matter had to do with insulation and sealing that protected the passengers from the low temperature and pressure loss. So with that information in mind, is it possible for a cockpit to experience extreme loss of pressure while the cabin suffers minor loss of pressure as on Flight 8633 (an A319)?

Answer 1

The internal walls in an aircraft are not designed to withstand any significant pressure difference. Since the accidents of American Airlines flight 96 and Turkish Airlines Flight 981 where explosive decompression in the cargo hold caused the passenger cabin floor to partially collapse and damage the control cables running below it, the internal walls and floors are intentionally designed so that the pressure has a way to equalize without causing damage to any of them (with enough openings or loosely fitted panels that will blow out if needed). Therefore it is not possible for pressure loss in cockpit not to extend to the cabin, or the cargo hold.

The information I found about Sichuan Flight 8633 only says the passengers were not exposed to cold, nothing about pressure. During decompression, the air rushing out is not doing much work, so it does not lose much energy, and therefore only cools down a bit. What is going on is not an isentropic expansion, but something closer to free expansion. The air still has to do some work to push the outside air out of its way, but not as much as if it was expanded gradually from the 8,000 ft cabin altitude (in which case it would get down to similar temperature as outside).

The only reason for exposure to cold would be if the cold outside air was rushing into the cabin. Which the wall between the cabin and cockpit minimized, plus the engines were still running and supplying warm air.

Answer 2

Great question with an interesting history.

The barrier between the flight deck and the cabin of commercial aircraft is engineered to blow out in a controlled fashion upon sudden decompression like the other barriers discussed in Jan's answer.

However, after 9/11, the FAA mandated reinforced doors to prevent unauthorized access. These doors are much heavier than their predecessors, and the security requirements basically dictate that they be one single hunk of material.

Now, consider a decompression event in which the big, heavy door gets rocketed one direction or another. Bad news for anything or anyone in its path:

The pressure differential and the force on the sealed cockpit door might be too much for the frame structure to handle if the cockpit depressurizes first. Passive and active internal venting (dado panels) may malfunction, get clogged by flying debris, or simply not react fast enough to relive [sic] the pressure differential on the security door. A loose, heavy, armored door can be much more dangerous than no door at all (or light door), as it could seriously injure or kill the flight crew, jam and/or destroy flight controls, damage and destroy flight instruments, and create mayhem in the cockpit. Such a scenario is incredibly dangerous, as it may prevent emergency descent. The rise of pressure differential and the force across the cockpit security door may well be much quicker than the designed venting system is capable of handling.

A solution was needed to nearly instantaneously unlock the door when a major pressure difference was felt. Enter the decompression sensing module, some variant of which is almost universal at this point. It integrates with the other components of the flight-deck access system and can unlock the door in a small fraction of a second:

In 2001 the commercial aircraft OEMs needed a solution to rapidly unlock the cockpit door in the event of a decompression event. NAT Engineering developed an electrical solution that responded to a decompression event in the millisecond range. In a matter of months it was taken from concept, through engineering design, computer modeling, prototyping, R&D testing, formal qualification testing, and into production for delivery to the OEMs. The NAT electrical device included integration of control for the keypad, thus providing for a secure keyless entry solution.

A fun thing about the DSM is that one way to test it is by shooting it with a high-powered handgun loaded with a blank cartridge. Makes for an interesting day in the lab.

Answer 3

There are two different factors to consider: First, there is the ambient air pressure - cabin and cockpit are not really separated in regard to pressure. So both would suffer from the "leak" nearly the same. On the other hand, there are wind effects - and these are considerably stronger close to the leak, especially when in front of the airflow.