Which requirement is NOT applicable to Class A airspace?

In Class A airspace, pilots are required to operate under instrument flight rules (IFR) and must have an ATC clearance before entering. This airspace is typically located from 18,000 feet mean sea level (MSL) up to and including 60,000 feet MSL over the United States, where air traffic control services are essential for maintaining safe separation between aircraft, given the high density of traffic and the nature of operations.

While flying in Class A airspace, it is mandated that pilots operate on an IFR flight plan. This requirement ensures that airplanes are managed efficiently and safely within this complex airspace environment. DME, or Distance Measuring Equipment, is often utilized for navigation in various flight operations; however, it is not specifically required to operate in Class A airspace, which is where the misconception around the other options may arise.

The key point is that there is no requirement for a flight plan in Class A airspace, primarily because all aircraft must be on an IFR flight plan. Hence, having no flight plan is indeed not applicable in this context.