Call for availability and to place an order The IFR Enroute High Altitude Charts for the Conterminous U.S. are designed for navigation at or above 18,000 feet MSL. IFR Charts are updated every 56 days.  AL H1/2 ALASKAH1/2 NORTHWESTH3/4 SOUTHWESTH5/6 SOUTH CENTRALH7/8 SOUTHEASTH9/10 EAST CENTRALH11/12 EAST/NORTHEAST