Which component prevents cabin altitude from exceeding airplane altitude?

The component that prevents cabin altitude from exceeding airplane altitude is the cabin pressure regulator. This critical component is responsible for managing the differential pressure between the cabin and the outside atmosphere throughout the flight.

The cabin pressure regulator monitors various parameters, including the aircraft's altitude and the cabin altitude. As the aircraft climbs, it adjusts the outflow valve to control the rate at which air is released from the cabin, thereby maintaining a safe and comfortable cabin altitude. This ensures that the cabin pressure remains within operational limits and does not exceed the ambient atmospheric pressure as the aircraft ascends.

In contrast, the other options do have important roles in cabin pressure management but are not specifically designed to prevent cabin altitude from exceeding airplane altitude. For instance, the outflow valve regulates the flow of air out of the cabin but relies on the pressure regulator to determine how to operate. The negative pressure relief valve prevents negative pressure in the cabin but does not control the altitude itself. The safety valve is there as a precaution to protect the system from excessive pressure but does not actively maintain cabin altitude. Each component works together in the overall pressure management system, but the cabin pressure regulator is the primary mechanism for maintaining the proper relationship between cabin and airplane altitudes.