A minimum off-route altitude (MORA) provides a quick way for an
aircraft pilot to read the minimum altitude required for terrain and obstacle clearance. MORAs give at least 1,000 feet altitude clearance above terrain and obstacles such as
radio masts
Radio masts and towers are typically tall structures designed to support antenna (radio), antennas for telecommunications and broadcasting, including television. There are two main types: guyed and self-supporting structures. They are among the t ...
, and 2,000 feet where the terrain and obstacles exceed 5,000 feet.
MORAs are given feet, rounded up to the nearest 100 and omitting the last two figures. For example, 7,550 feet would be given as 76.
There are two types of MORAs: the route MORA and the grid MORA. Route MORAs provide an obstacle clearance within on both sides of the airways and within a
radius
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
around the ends of the airways. Grid MORAs provide an obstacle clearance
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 ...
within a latitude and longitude grid block, usually of one degree by one degree.
MORAs were created by
Jeppesen and used on their
airways charts. Some countries specify Minimum Enroute Altitudes (MEAs), minimum obstruction
clearance altitudes (MOCAs), and Off Route Obstacle Clearance Altitudes (OROCAs), which have slightly different rules. An MEA gives a minimum altitude for reception of navigation aids and radio communications, and is found only within controlled airspace. An OROCA gives 2000 feet of clearance only in mountainous areas.
References
Air navigation
Air traffic control
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