What is the purpose of the cabin pressure relief valve?

• A. To protect the cabin from overpressure by venting excess air to the outside.
• B. To regulate cabin temperature.
• C. To vent cabin air into the cockpit.
• D. To seal the cabin during pressure changes.

Answer: (A)

The main idea is protecting the cabin from overpressurization by venting excess air to the outside. The cabin pressure relief valve acts as a safety backup in the pressurization system: under normal flight, it stays shut, but if the differential pressure between the inside and outside becomes too high, it opens and releases air outside to prevent damage to the fuselage from excessive pressure.

This is not about regulating temperature, which is handled by the environmental control system, nor is it about venting cabin air into the cockpit. It also isn’t about sealing the cabin during pressure changes—sealing would trap pressure and could lead to structural problems. The relief valve works with the primary outflow valve to maintain safe, controlled cabin pressure, stepping in only when overpressure could occur.