What is the maximum altitude for Class E airspace that encompasses domestic air space?

In the United States, Class E airspace is the controlled airspace that extends from either the surface or an altitude up to but not including 18,000 feet MSL (Mean Sea Level). Class E airspace typically begins at 1,200 feet AGL (Above Ground Level) and may extend up to 18,000 feet MSL in certain areas, but the upper limit is always below that altitude.

The maximum altitude of 17,999 feet MSL indicates the highest point Class E airspace can reach while still remaining below the threshold of Class A airspace, which starts at 18,000 feet MSL. This classification ensures that the transition between airspace classes is organized and safe, providing a structured environment for both VFR (Visual Flight Rules) and IFR (Instrument Flight Rules) operations.

Understanding these airspace classifications is crucial for pilots to navigate safely and comply with air traffic regulations while flying in the National Airspace System. Notably, other options present altitudes that either fall under the upper limit of Class E or do not appropriately represent the structure of controlled airspace.