MINIMUM OBSTRUCTION CLEARANCE ALTITUDE (MOCA)

The MOCA is the lowest published altitude in effect between radio fixes on VOR airways, off-airway routes, or route segments which meets obstacle clearance requirements for the entire route segment and which assures acceptable navigational signal coverage only within 25 statute (22 nautical) miles of a VOR.

The MOCA seen on the NACO en-route chart, may have been computed by adding the required obstacle clearance (ROC) to the controlling obstacle in the primary area or computed by using a TERPS chart if the controlling obstacle is located in the secondary area.

This figure is then rounded to the nearest 100 foot increment, i.e. 2,049 feet becomes 2,000, and 2,050 feet becomes 2,100 feet.

An extra 2,000 feet is added in mountainous areas, 1,000 in non-mountainous.

The MOCA is based upon obstacle clearance over the terrain or over manmade objects, adequacy of navigation facility performance, and communications requirements. The MOCA is always at or below the Minimum en route altitude (MEA), and may put an aircraft below air traffic control radar coverage and also below Minimum reception altitude (MRA) for navigation aids; as a result, it is typically used only in emergencies, especially to get below icing.

A MOCA is only shown on the Enroute Low Charts and only published when it is lower than the MEA. When shown, it is preceded by an asterisk.