Definition
A published altitude representing the highest usable altitude for an airspace structure or route segment. It is the maximum altitude at which an aircraft may be operated on that segment, established because of design limitations, frequency protection, airspace restrictions, or other operational factors.
Plain English
The highest altitude you are allowed to fly on a particular route segment. Going above it is not permitted on that segment.
Context Anchor
Seen on IFR charts and route information when planning or flying along published airways or route segments.
Derivation
Maximum from Latin maximus meaning greatest; altitude from Latin altus meaning high; authorized indicating official permission. Together they specify the greatest height controllers are allowed to assign on that route.
Why Pilots Care
Staying at or below this altitude keeps the aircraft within reliable navigation signal coverage and maintains proper separation from other traffic.
Intuition Check
Do not read “maximum authorized” as the highest altitude your aircraft can fly or the highest altitude ATC could ever clear you to. Here it means the published upper limit for using that specific route with reliable navigation signals.
Example Sentence 1
The pilot checked the enroute chart and saw a maximum authorized altitude of 15,000 feet for that airway segment, so they planned to cruise at 13,000.
Example Sentence 2
The pilot requested a lower altitude after passing the point where the maximum authorized altitude dropped due to terrain.