Final answer:
The airspace from 18,000 ft MSL to FL600 is known as Class A, where IFR operations occur and the FAA regulates a minimum separation of 2,000 feet vertically between aircraft, reduced to 1,000 feet below 29,000 feet.
Step-by-step explanation:
The airspace you're asking about, from 18,000 ft MSL up to and including FL600, is known as Class A airspace. In this airspace, aircraft operations are conducted under Instrument Flight Rules (IFR), and positive air traffic control is provided to all aircraft. It's designed this way for safety, ensuring that all aircraft are separated from each other to prevent collisions. The Federal Aviation Administration (FAA) regulates this, requiring a minimum of five miles lateral separation and 2,000 feet vertical separation between aircraft at these altitudes, which is reduced to 1,000 feet below 29,000 feet. This controlled airspace is designed to create an organized flow of traffic where each aircraft has a specific altitude block to maintain during flight.
The airspace generally from 18,000 ft MSL up to and including FL600 is known as the stratosphere. The stratosphere is the second major layer of Earth's atmosphere, located above the troposphere and below the mesosphere. It extends from about 10 to 50 kilometers above the Earth's surface.
Within the stratosphere, the temperature increases with altitude due to the presence of the ozone layer. This temperature inversion prevents turbulent convection, making it a stable layer for aircraft.
Aircraft flying in the stratosphere enjoy smoother flights and reduced atmospheric drag, which results in increased fuel efficiency for long-haul flights.