Minimum crossing altitude

In aviation, a minimum crossing altitude (MCA) is the lowest altitude at which a navigational fix can be crossed when entering or continuing along an airway that will allow an aircraft to clear all obstacles while carrying out a normal climb to the required minimum en route IFR altitude (MEA) of the airway in question beyond the fix.

The definition given here concerns primarily United States airspace; procedures and practices may vary in other countries.

Airways are normally designed such that an aircraft moving from one segment with one MEA to another segment with a higher MEA can safely begin a normal climb (see below) to the higher MEA upon crossing the fix that divides the two segments and still remain well clear of obstacles.

When obstacles along the airways are such that a normal climb beginning at the fix defining an airway segment is not adequate to provide proper obstacle clearance, a minimum crossing altitude (MCA) is published for the fix indicating the minimum altitude at which the fix must be crossed when entering that specific airway segment in order to make it possible to safely climb to the MEA while remaining clear of obstacles.

In this case, a segment of an airway ending at fix ABC has a MEA of 5200 feet MSL, and the minimum obstacle clearance altitude (MOCA) required to clear an obstacle six nautical miles from the fix within the next segment is 6620 feet MSL.