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.  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.  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.  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.  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.  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 Clearance Surface (OCS). An inclined or level  surface associated with a defined area for obstruction  evaluation.  Non-RNAV DP. A DP whose ground track is based on  ground-based NAVAIDS and/or dead reckoning navigation.  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.  G-7 