Definition
The actual height of the aircraft above mean sea level (MSL), as shown on a properly set altimeter. In pressurization discussions, aircraft altitude is the height the airplane is physically flying at, distinct from the cabin altitude, which is the pressure altitude maintained inside the cabin.
Plain English
How high the airplane itself is flying above sea level, regardless of what the air pressure inside the cabin is set to feel like.
Context Anchor
Seen in pressurized aircraft discussions when comparing how high the airplane is flying with the pressure being maintained inside the cabin.
Derivation
Altitude comes from the Latin word altus, meaning “high.” That helps because altitude is simply a measured highness above a chosen starting level.
Why Pilots Care
Knowing exact aircraft altitude governs terrain clearance, traffic separation, pressurization system settings, and regulatory compliance.
Intuition Check
Do not confuse aircraft altitude with cabin conditions. The aircraft may be flying very high while the cabin is kept at a lower, safer pressure level for people inside.
Example Sentence 1
At an aircraft altitude of 35,000 feet, the cabin was pressurized to 7,000 feet for passenger comfort.
Example Sentence 2
At the planned cruise aircraft altitude the cabin pressure differential remained within limits for the entire flight.