What type of airspace do civil and military aircraft operate above FL245?

Civil and military aircraft operating above Flight Level 245 (FL245) are in controlled airspace with full ATC service. This designation is important because it ensures that aircraft are operating under the supervision of Air Traffic Control, which is crucial for maintaining safe and efficient flight operations.

Above FL245, typically referred to as the "high altitude" airspace, specific standards and regulations come into play, including requiring separation from other aircraft and adherence to instrument flight rules (IFR). Controlled airspace at high altitudes allows for the organization and management of a greater volume of air traffic, as aircraft may be traveling at higher speeds and altitudes where there's an increased risk of intersecting flight paths.

The other airspace types listed do not offer the same level of control or oversight. For instance, uncontrolled airspace allows pilots to operate without air traffic control guidance, which is not the case above FL245. Class D and G airspace signify less or no ATC service and are not applicable to the conditions experienced at high altitudes. Therefore, the designation of controlled airspace with full ATC services is essential for ensuring safety and order in the busy airspace above FL245.