However, a pilot can only choose to fly IFR if they possess an instrument rating which is above and beyond the basic pilot's license that must also be held.
The difference between Class E and A airspace is that in Class A, all operations are IFR, and pilots must be instrument-rated, that is, skilled and licensed in aircraft instrumentation.
E 级和 A 级空域的区别在于，在 A 级空域，所有操作都需遵照仪表飞行规则，飞行员必须要有仪表等级，也就是说，要有操作航空仪表方面的技术和执照。
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On a clear day, a pilot in controlled airspace can choose a VFR or IFR flight plan, and the FAA regulations were devised in a way which accommodates both VFR and IFR operations in the same airspace.