Minimum obstacle clearance altitude
Encyclopedia
Minimum Obstacle Clearance Altitude, or MOCA, is the lowest published altitude
in effect between fixes on VOR
airways
, off-airway routes, or route segments that meets obstacle (like a building or a tower) clearance requirements for the entire route segment. Within the United States, this altitude
also assures acceptable navigational signal coverage only within 22 nm
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 enroute 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.
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
in effect between fixes on VOR
VHF omnidirectional range
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
airways
Airway (aviation)
In aviation, an airway is a designated route in the air. Airways are laid out between navigational aids such as VORs, NDBs and Intersections ....
, off-airway routes, or route segments that meets obstacle (like a building or a tower) clearance requirements for the entire route segment. Within the United States, this altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
also assures acceptable navigational signal coverage only within 22 nm
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
of a VOR
VHF omnidirectional range
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
. 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 enroute altitude
Minimum enroute altitude
Minimum en route altitude , alternately spelled as Minimum enroute altitude, is the lowest published altitude between radio navigation fixes that assures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes.The definition given here is that of the...
(MEA), and may put an aircraft below air traffic control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
RADAR
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
coverage and also below Minimum reception altitude
Minimum reception altitude
In aviation, minimum reception altitude is the lowest altitude on an airway segment where an aircraft can be assured of receiving signals from navigation aids like VOR or NDB. Typically, the greater the distance between navigation aids, the higher the MRA...
(MRA) for navigation aids; as a result, it is typically used only in emergencies, especially to get below icing.
See also
- Above ground levelAbove ground levelIn aviation and atmospheric sciences, an altitude is said to be above ground level when it is measured with respect to the underlying ground surface. This is as opposed to above mean sea level , or in broadcast engineering, height above average terrain...
- Minimum safe altitudeMinimum safe altitudeMinimum safe altitude is a concept used in planning and executing aircraft flights. It is an altitude which allows adequate vertical clearance from nearby terrain and manmade obstacles, and allows proper navigational functions.-IFR flights:...