Definition
The published vertical boundaries (floor and ceiling) of a defined block of airspace, expressed as altitudes that mark where one class of airspace ends and another begins.
Plain English
The top and bottom altitudes that show where a piece of airspace starts and stops.
Context Anchor
Seen when planning direct instrument routes that depend on ground-based navigation signals, such as VOR stations.
Derivation
Class' here refers to the FAA's lettered categories of airspace (A, B, C, D, E, G). 'Limits' means the boundaries — in this case, the upper and lower altitudes. Together: the altitude boundaries of a particular airspace class.
Why Pilots Care
Violating class limits can result in ATC rejection of the direct clearance or reduced navigation integrity, increasing workload and risk during instrument flight.
Analogy
It is like a radio station’s normal listening area. Inside the area, reception is expected; outside it, the signal may fade or become unreliable.
Intuition Check
Class limits do not mean passenger class or airspace class here. They mean the normal usable range and altitude boundaries for a navigation signal’s assigned category.
Example Sentence 1
Before filing the route, the pilot checked the class limits of the overlying Class B airspace to confirm their cruising altitude stayed beneath it.
Example Sentence 2
Because the aircraft met the required class limits, ATC approved the direct route without additional reporting points.