Minimum Obstacle Clearance Altitude, or ''MOCA'', is the lowest published

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

in effect between fixes on

VOR VOR or vor may refer to: Organizations * Vale of Rheidol Railway in Wales * Voice of Russia, a radio broadcaster * Volvo Ocean Race, a yacht race Science, technology and medicine * VHF omnidirectional range, a radio navigation aid used in a ...

airways or route segments that meets obstacle (like a building or a tower) clearance requirements for the entire route segment. Within the United States, this

also assures acceptable navigational signal coverage only within 22 nm of a

. 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 Minimum en route altitude (MEA), alternately spelled as Minimum enroute altitude, is the lowest published altitude between radio navigation fixes that assures acceptable navigational signal coverage (see MRA) ''and'' meets obstacle clearance requir ...

(MEA), and may put an aircraft below

air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airs ...

radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, we ...

coverage and also below

Minimum reception altitude In aviation, minimum reception altitude (MRA) is the lowest altitude on an airway segment where an aircraft can be assured of receiving signals from off-course navigation aids like VOR that define a fix. An MRA is determined by FAA flight inspectio ...

(MRA) for navigation aids; as a result, it is typically used only in emergencies, especially to get below icing.

See also