Which component of a pressurization system prevents the cabin altitude from exceeding airplane altitude?

The correct answer focuses on the role of the pressurization system component that specifically manages the cabin altitude in relation to the airplane altitude. The negative pressure relief valve is designed to open when the cabin pressure decreases significantly, preventing the cabin altitude from becoming greater than the external atmospheric pressure at high altitudes. It ensures that pressure differentials do not exceed specified limits, maintaining a safe and stable environment for passengers and crew.

The purpose of maintaining cabin altitude within safe limits is critical for passenger comfort and safety, as excessive cabin altitude can lead to hypoxia and other altitude-related health issues. In contrast, the outflow valve regulates the cabin pressure by allowing air to exit the cabin but does not directly prevent cabin altitude from exceeding airplane altitude. The delivery air duct check valve and the thermostatic expansion valve serve different functions related to air distribution and temperature control, respectively, and do not play a role in regulating cabin altitude relative to airplane altitude.