EXPLANATION OF IFR ENROUTE TERMS AIRPORTS Airports are plotted at their true geographic position. Airports are identified by the airport name. In the case of military airports, Air Force Base (AFB), Naval Air Station (NAS),  Naval Air Facility (NAF), Marine Corps Air Station (MCAS), Army Air Field (AAF), etc., the abbreviated letters appear as  part of the airport name. 59 Charted airports are classified according to the following criteria: High Charts:  On IFR Enroute Low Altitude Charts, airport tabulation is provided which identifies airport names, IDs and the panels they  are located on.  FAA Chart Users’ Guide - IFR Enroute Terms Low Charts:  Operational airports are shown on IFR Enroute Charts.  The explanations of symbols used on Instrument Flight Rule (IFR) Enroute Charts and examples in this section are based  primarily on the IFR Enroute Low Altitude Charts. Other IFR products use similar symbols in various colors. The chart leg- ends portray aeronautical symbols with a brief description of what each symbol depicts. This section provides more details  of the symbols and how they are used on IFR Enroute charts. FAA charts are prepared in accordance with specifications of the Interagency Air Committee (IAC), and are approved by  representatives of the Federal Aviation Administration and the Department of Defense (DoD). Some information on these  charts may only apply to military pilots. •  All IAP Airports are shown on the Low Altitude Charts (US and Alaska).  •  Non-IAP Airports are shown on the U.S. Low Altitude Charts (Contiguous US) have a minimum hard surface  runway of 3,000’.  •  Non-IAP airports are shown on the U.S. Low Altitude Alaska Charts are show if the runway is 3000’ or longer,  hard or soft surface.  •  Public heliports with an Instrument Approach Procedure (IAP) or requested by the FAA or DoD are depicted on  the IFR Enroute Low Altitude Charts.  •  Seaplane bases requested by the FAA or DoD are depicted on the IFR Enroute Low Altitude Charts.  •  Airports shown on the U.S. High Enroute Alaska Charts have a minimum hard surface runway of 4000’.  •  Airports shown on the U.S. High Enroute Charts (Contiguous US) have a minimum hard surface runway of 5000’.  LOW/HIGH ALTITUDE Blue  - Airports with an Instrument Approach Procedure and/or RADAR MINIMA published in the high altitude DoD  Flight Information Publications (FLIPs)  Green  - Airports which have an approved Instrument Approach Procedure and/or RADAR MINIMA published in  either the U.S. Terminal Procedures Publications (TPPs) or the DoD FLIPs  Brown  - Airports without a published Instrument Approach Procedure or RADAR MINIMA