Class A airspace

Class A airspace covers the United States from 18,000 ft MSL up to and including FL600 (60,000 ft on a standard altimeter setting of 29.92). Above 18,000 ft everyone flies on the standard pressure setting, so altitudes are expressed as flight levels (FL180, FL310, etc.).

The defining rule is simple: Class A is IFR-only. Every aircraft must be operated under instrument flight rules, on an ATC clearance, with an instrument-rated pilot and an IFR-capable aircraft. There are no VFR operations and therefore no VFR weather minimums to discuss — ATC separates all traffic.

Because it's a single nationwide block, Class A isn't drawn on sectional charts with a boundary the way Class B or C is; pilots simply know it begins at 18,000 ft. To climb into it you need an IFR clearance and the equipment that IFR requires (including the transponder and ADS-B Out called for above the relevant altitudes).

For a VFR pilot, the practical takeaway is a hard ceiling: VFR cruising tops out below 18,000 ft. Long cross-countries that would benefit from the smoother air and winds aloft up high require an instrument rating and an IFR flight plan.

*Reference and training only. Consult the FAA AIM and current charts.*