What should be done if cabin altitude CAS warning occurs?

When a cabin altitude CAS (Caution Advisory System) warning occurs, the appropriate response is to don oxygen masks. This action is crucial because a cabin altitude warning indicates that the cabin pressure has dropped to a level that may cause hypoxia, which is a deficiency in the amount of oxygen reaching the tissues. By donning oxygen masks, the crew and passengers can obtain supplemental oxygen, thereby ensuring their safety until corrective actions can be taken to address the cabin pressure situation.

While adjusting cabin pressure, reducing airspeed, or activating emergency landing procedures may be part of the overall response to a cabin altitude issue, the immediate priority is to ensure that everyone onboard has adequate oxygen. This step helps to mitigate the potential for in-flight incapacitation due to low oxygen levels, thereby allowing the crew to focus on troubleshooting the underlying issue with cabin pressure and safely managing the situation.