What happens if the cabin differential pressure exceeds 8.7 psi?

When cabin differential pressure exceeds 8.7 psi, a controlled descent becomes necessary to ensure the safety of the aircraft and its occupants. This limit is established to prevent pressure-related injuries or issues, such as hypoxia, that could arise if the aircraft is operating at unsafe pressures. A controlled descent allows for a reduction in altitude to a level where the cabin pressure is more comfortable and manageable for passengers and crew, typically aligning with a safer altitude for continued flight, such as below the service ceiling where the atmosphere is denser and safer for oxygen availability.

The specific pressure limit reflects the aircraft's design capabilities and operational protocols intended to maintain passenger and crew safety. Exceeding this threshold indicates a potentially dangerous situation that cannot be left unattended, thus necessitating immediate action such as a controlled descent instead of simply notifying maintenance or terminating the flight, which might not address the urgency of the situation as effectively.