What characterizes the unpressurized range of an aircraft?

In the unpressurized range of an aircraft, cabin altitude equals aircraft altitude. This means that as the aircraft climbs or descends in altitude, the cabin's altitude changes in direct relation to the external atmospheric pressure. In this range, the cabin does not use pressurization systems to maintain a lower altitude than the outside environment, leading to a direct correlation where the cabin environment mirrors the outside altitude levels.

This understanding is crucial for aircrew as it impacts passenger comfort and safety, emphasizing the need for supplemental oxygen at higher altitudes, where the decreased air pressure affects oxygen availability for breathing.