Definition
The lowest altitudes at which certain fixes must be crossed when proceeding in the direction of a higher minimum en route altitude (MEA). MCAs ensure obstacle clearance on the segment beyond the fix when the airway ahead requires a higher altitude than the segment behind it.
Plain English
When the next leg of an airway requires you to be higher than the leg you are on, the chart tells you the lowest altitude you must already be at by the time you cross the fix. That altitude is the minimum crossing altitude.
Context Anchor
Seen on IFR en route charts and during arrival or route planning when the next part of the route requires more altitude.
Derivation
Minimum comes from a Latin word meaning “smallest.” Altitude comes from Latin altus, meaning “high.” In aviation, altitude normally means height shown in feet above mean sea level, so this term means the smallest allowed height at the point where you cross a specified fix.
Why Pilots Care
Maintains required obstacle clearance when climbing is necessary to meet a higher MEA on the next segment.
Grounding Statement
When the route ahead needs more altitude, the minimum crossing altitude tells you the point by which the climb must be complete.
Intuition Check
Do not read this as a suggested or comfortable crossing height. A minimum crossing altitude is the lowest altitude allowed at that crossing point for that route direction.
Example Sentence 1
The chart showed a minimum crossing altitude of 8,000 feet at the fix, so the pilot began climbing several miles ahead to be level by the time they crossed it.
Example Sentence 2
The pilot climbed early to meet the minimum crossing altitude required for the higher MEA ahead.