Definition
The lowest altitude at which an aircraft must cross a specified fix when proceeding in the direction of a higher minimum en route altitude (MEA). It is published on charts at fixes where the MEA increases ahead, ensuring the aircraft has reached the higher altitude by the time it crosses that fix.
Plain English
If the required altitude on the next leg of your route is higher than the one you're flying now, the MCA is the altitude you must be at — or above — by the time you cross the fix where that change happens. It gives you time to climb before you get there.
Context Anchor
Seen on IFR en route charts near fixes where the next route segment requires a higher altitude.
Derivation
Crossing' here means crossing a specific point — the fix — not crossing terrain or airspace. The 'minimum' is the floor: you can be higher, but not lower, when you reach that point.
Why Pilots Care
Flying below the MCA at the designated point risks collision with terrain or obstacles even when the MEA is lower.
Grounding Statement
If an MCA is shown at a fix, plan the climb so the aircraft reaches that altitude before crossing the fix.
Intuition Check
Do not read MCA as an altitude to start climbing toward after the fix. It is the minimum altitude required at the moment you cross the fix.
Example Sentence 1
The chart showed an MCA of 8,000 feet at the fix, so we began our climb several miles early to be level by the time we crossed it.
Example Sentence 2
Even though the MEA on this segment is 4000 feet, the MCA at the fix ahead is 5000 feet, requiring us to reach that altitude before the crossing point.