Minimum Crossing Altitude (MCA)
Minimum Crossing Altitude (MCA) is the lowest altitude at which an aircraft must cross a particular fix when proceeding in the direction of a higher MEA segment. It ensures the aircraft reaches the required altitude before encountering the higher terrain or obstacle clearance requirements of the next segment.
When MCA Applies
MCAs are depicted on IFR en route charts as a flag symbol with an upward-pointing arrow at the applicable fix. If a pilot approaches a fix with an MCA below the MCA, the aircraft must not cross the fix until it has climbed to MCA, even if the current MEA would otherwise permit a lower altitude. This is particularly relevant near mountainous terrain where the MEA steps up significantly.