During normal operation the entire fuselage is pressurized equally:
An aircraft fuselage does not contain separate compartments with different pressure values in each. The entire vessel is pressurized equally from the forward pressure bulkhead to the aft pressure bulkhead. This normally includes the cabin, cockpit, and lower-deck cargo holds. (source)
If my understanding of physics is correct, this means that there must be airflow between the cockpit and the cabin (otherwise a pressure difference would occur). The airflow equalizes the atmospheric pressure in the cockpit and cabin.
Question: Can the pilot completely stop the airflow between cockpit and cabin, i.e. hermetically sealing off the cockpit from the cabin ?
3 scenarios for which this question is interesting:
If there is smoke in the cabin, the pilot would need to prevent the smoke from entering the cockpit.
Does cabin depressurization (due to a hull breach for example) directly lead to cockpit depressurization? Or can the pilot prevent this by stopping the air outflow from the cockpit to the cabin?
One working hypothesis in the MH370 mystery is accidental or deliberate cabin depressurization. Assuming the latter, is there any way the perpetrator in the cockpit could prevent the cockpit depressurization ?
I would appreciate if your answers included these 3 scenarios. Since the third scenario deals with a B777, please use this type as an example. Technical airflow diagrams very welcome!
Concerning scenario 1 (fire), my research into this question seems to suggest, that the cockpit is indeed designed to be sealed off in case of fire. I could not find the relevant information for a Boeing-777, but here is a description of how smoke entered the MD-11 cockpit in the Swissair 111 crash and how it was supposed to be prevented (smoke barrier, etc):
Airflow patterns in the MD-11 are affected by the aircraft configuration. In the forward portion of the aircraft, this configuration includes the valve position of individual air outlets in the cockpit and throughout the cabin, and the position of the louvres in the bottom part of the cockpit door. Also, all MD-11s are equipped with a smoke barrier installed laterally across the aircraft in the attic area above the cockpit aft wall (see figure 3). Inspection of Swissair MD-11s showed that the smoke barrier was sealed relatively tightly in some aircraft, while in others there were gaps in the barrier at the edges and at the seams where conditioned air ducts pass through the barrier. These gaps allowed air to flow past the smoke barrier. The holes in the barrier, designed to permit the engine fire shut-off cables to pass through the barrier, would also be a path for smoke to pass between the cabin and cockpit.