Minimum Reception Altitude (MRA). An MRA is determined by FAA flight inspection traversing an entire route of flight to establish the minimum altitude the navigation signal can be received for the route and for off-course NAVAID facilities that determine a fix. When the MRA at the fix is higher than the MEA, an MRA is established for the fix, and is the lowest altitude at which an intersection can be determined. 

Minimum Safe Altitude (MSA). MSAs are published for emergency use on IAP charts. For conventional navigation systems, the MSA is normally based on the primary omnidirectional facility on which the IAP is predicated. For RNAV approaches, the MSA is based on the runway waypoint (RWY WP) for straight-in approaches, or the airport waypoint (APT WP) for circling approaches. For GPS approaches, the MSA center is the Missed Approach Waypoint (MAWP). 

Minimum Vectoring Altitude (MVA). Minimum vectoring altitude charts are developed for areas where there are numerous minimum vectoring altitudes due to variable terrain features or man-made obstacles. MVAs are established for use by ATC when radar ATC is exercised. 

Missed Approach Holding Waypoint. An approach waypoint sequenced during the holding portion of the missed approach procedure that is a fly-over waypoint. 

Missed Approach Waypoint (MAWP). An approach waypoint sequenced during the missed approach procedure that is a fly-over waypoint. 

National Airspace System (NAS). Consists of a complex collection of facilities, systems, equipment, procedures, and airports operated by thousands of people to provide a safe and efficient flying environment. 

Navigational Gap. A navigational course guidance gap, referred to as an MEA gap, describes a distance along an airway or route segment where a gap in navigational signal coverage exists. The navigational gap may not exceed a specific distance that varies directly with altitude. 

Next Generation Air Transportation System (NextGen). Ongoing, wide-ranging transformation of the National Airspace System (NAS). NextGen represents an evolution from a ground-based system of air traffic control to a satellite- based system of air traffic management. 

Non-Directional Radio Beacon (NDB). An L/MF or UHF radio beacon transmitting nondirectional signals whereby the pilot of an aircraft equipped with direction finding equipment can determine bearing to or from the radio beacon and “home”on or track to or from the station. When the radio beacon is installed in conjunction with the ILS marker, it is normally called a compass locator. 

Non-RNAV DP. A DP whose ground track is based on ground-based NAVAIDS and/or dead reckoning navigation. 

Obstacle Clearance Surface (OCS). An inclined or level surface associated with a defined area for obstruction evaluation. 

Obstacle Departure Procedure (ODP). A procedure that provides obstacle clearance. ODPs do not include ATC related climb requirements. In fact, the primary emphasis of ODP design is to use the least erroneous route of flight to the en route structure while attempting to accommodate typical departure routes. 

Obstacle Identification Surface (OIS). The design of a departure procedure is based on FAA Order 8260.3, a living document that is updated frequently. Departure design criteria assumes an initial climb of 200 Ft/NM after crossing the departure end of the runway (DER) at a height of at least 35 feet above the ground. Assuming a 200 Ft/NM climb, the departure is structured to provide at least 48 Ft/ NM of clearance above objects that do not penetrate the obstacle slope. The slope, known as the OIS, is based on a 40 to 1 ratio, which is the equivalent of a 152 Ft/NM slope. 

Off-Airway Routes. The FAA prescribes altitudes governing the operation of aircraft under IFR for fairway routes in a similar manner to those on federal airways, jet routes, area navigation low or high altitude routes, and other direct routes for which an MEA is designated. 

Off-Route Obstruction Clearance Altitude (OROCA). An off- route altitude that provides obstruction clearance with a 1,000-foot buffer in nonmountainous terrain areas and a 2,000-foot buffer in designated mountainous areas within the U.S. This altitude may not provide signal coverage from groundbased navigational aids, air traffic control radar, or communications coverage. 

Operations Specifications (OpSpecs). A published document providing the conditions under which an air carrier and operator for compensation or hire must operate in order to retain approval from the FAA. 

