IFR en route low-altitude charts
IFR (instrument flight rules) en route low-altitude charts
En route low-altitude charts provide aeronautical information for navigation under IFR conditions below 18,000 ft MSL (mean sea level). This four-color chart series includes the jet route structure; very high frequency navigational aids (VHF NAVAIDs) with frequency [only very high frequency omnidirectional radio-range (VOR) but not terminal VORs], identification, channel, and geographic coordinates; airports with terminal air-to-ground communications; minimum en route and obstruction clearance altitudes; airway distances; reporting points; special use airspace; and military training routes. Scales vary from 1 in = 5 NM (nautical miles) to 1 in = 20 NM; 50 λ 20 in can be folded to 5 λ 10 in. Charts are revised every fifty-six days in the United States. Area charts show congested terminal areas at a large scale.