77 Airspace Information (Continued) VHF/UHF LF/MF LOW CHARTS LOW CHARTS  HIGH CHARTS HIGH CHARTS  MEA-29000 MEA-FL240 LOW CHARTS HIGH CHARTS 65 279 $J505$ 91 MEA GAP MEA-24000 108 TWISP LOW / HIGH LOW / HIGH  CHARTS CHARTS LOW CHARTS LOW CHARTS LOW CHARTS LOW CHARTS LOW / HIGH LOW / HIGH  CHARTS CHARTS MINIMUM ENROUTE ALTITUDE (MEA) All Altitudes Are MSL Unless Otherwise Noted. Directional MEAs MEAs are shown on IFR High Altitude Charts when MEA is  other than 18,000’. MINIMUM ENROUTE ALTITUDE (MEA) GAP MEA is established when there is a gap in navigation signal  coverage. Maximum Authorized Altitude (MAA) All Altitudes Are MSL Unless Otherwise Noted. MAAs are shown on IFR High Altitude Charts when MAA is  other than 45,000’. Minimum Obstruction Clearance Altitude (MOCA) All Altitudes Are MSL Unless Otherwise Noted. Minimum Turning Altitude (MTA) and Minimum  Crossing Altitude (MCA) See Low Enroute Chart Example below for examples of  both MTAs and MCAs. MINIMUM RECEPTION ALTITUDE (MRA) ALTITUDE CHANGE MEA, MOCA and/or MAA change at other than NAVAIDs CHANGEOVER POINT Changeover Point giving mileage to NAVAIDs (Not shown  at midpoint locations.) HOLDING PATTERNS RNAV Holding Pattern Magnetic Reference Bearing is de- termined by the isogonic value at the waypoint or fix. Holding Pattern with maximum restriction airspeed 210K  applies to altitudes 6000’ to and including 14000’. 175K ap- plied to all altitudes. Airspeed depicted is Indicated Airspeed  (IAS) RNAV LOW CHARTS HIGH CHARTS  MEA for GNSS RNAV  aircraft MEA-24000G MEA for DME/DME/IRU  RNAV aircraft MEA-24000D N/A LOW / HIGH  CHARTS LOW CHARTS LOW CHARTS N/A N/A FAA Chart Users’ Guide - IFR Enroute Symbology