Which class of airspace requires all aircraft to be IFR?

Class A airspace is unique in that it requires all aircraft operating within it to adhere to IFR (Instrument Flight Rules) standards. This regulation is fundamental because Class A airspace is situated from 18,000 feet MSL (Mean Sea Level) up to and including 60,000 feet, where the likelihood of encountering high-speed jet traffic is very significant. The IFR standards ensure that aircraft maintain proper separation and manage the complexities associated with high altitudes, where terrain and weather conditions can be challenging.

In Class A airspace, the use of radar and other air traffic control services is mandatory, which helps in preventing collisions by providing constant communication and situational awareness. This is essential when considering the high volume and speed of aircraft that often operate in these altitudes.

Therefore, the necessity for all aircraft to comply with IFR in Class A airspace promotes safety and efficiency in the national airspace system, allowing for seamless operations even in busy traffic environments.