INSTRUMENT AIRWAYS VOR LF/MF AIRWAY SYSTEM (IFR LOW ALTITUDE ENROUTE CHARTS) AIRWAY/ROUTE DATA FAA Chart Users’ Guide - IFR Enroute Terms The FAA has established two fixed route systems for air navigation. The VOR and LF/MF system-designated from 1,200'  Above Ground Level (AGL) to but not including FL 180 is shown on IFR Enroute Low Altitude Charts, and the Jet Route  system designated from FL 180 to FL 450 inclusive is shown on IFR Enroute High Altitude Charts. In this system VOR airways - airways based on VOR or VORTAC NAVAIDs - are depicted in black and identified by a "V"  (Victor) followed by the route number (e.g., "V12"). LF/MF airways - airways based on LF/MF NAVAIDs - are sometimes called "colored airways" because they are identified  by color name and number (e.g., "Amber One", charted as "A1"). In Alaska Green and Red airways are plotted east and  west, and Amber and Blue airways are plotted north and south. Regardless of their color identifier, LF/MF airways are  shown in brown. On both series of IFR Enroute Charts, airway/route data such as the airway identifications, magnetic courses bearings or  radials, mileages, and altitudes (e.g., Minimum Enroute Altitudes (MEAs), Minimum Reception Altitudes (MRAs), Maxi- mum Authorized Altitudes (MAAs), Minimum Obstacle Clearance Altitudes (MOCAs), Minimum Turning Altitudes (MTAs)  and Minimum Crossing Altitudes (MCAs)) are shown aligned with the airway. As a rule the airway/route data is charted and in the same color as the airway, with one exception. Charted in blue, Global  Navigation Satellite System (GNSS) MEAs, identified with a "G" suffix, have been added to "V" and "colored airways" for  aircraft flying those airways using Global Positioning System (GPS) navigation. Airways/Routes predicated on VOR or VORTAC NAVAIDs are defined by the outbound radial from the NAVAID. Airways/ Routes predicated on LF/MF NAVAIDs are defined by the inbound bearing. •  Minimum Enroute Altitude (MEA)  - The MEA is the lowest published altitude between radio fixes that assures  acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes. The  MEA prescribed for a Federal airway or segment, RNAV low or high route, or other direct route applies to the en- tire width of the airway, segment, or route between the radio fixes defining the airway, segment, or route. MEAs for  routes wholly contained within controlled airspace normally provide a buffer above the floor of controlled airspace  consisting of at least 300 feet within transition areas and 500 feet within control areas. MEAs are established  based upon obstacle clearance over terrain and man-made objects, adequacy of navigation facility performance,  and communications requirements. •  Minimum Reception Altitude (MRA)  - MRAs are 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. •  Maximum Authorized Altitude (MAA)  - An MAA is a published altitude representing the maximum usable  altitude or flight level for an airspace structure or route segment. It is the highest altitude on a Federal airway, jet  route, RNAV low or high route, or other direct route for which an MEA is designated at which adequate reception  of navigation signals is assured. •  Minimum Obstruction Clearance Altitude (MOCA)  - The MOCA is the lowest published altitude in effect be - tween radio fixes on VOR airways, off-airway routes, or route segments which meets obstacle clearance require - ments for the entire route segment and which assures acceptable navigational signal coverage only within 25  statute (22 nautical) miles of a VOR. A MOCA is only shown on the Enroute Low Charts and only published when  it is lower than the MEA. When shown, it is preceded by an asterisk. 64