It’s a grayish fall day with a 900-foot ceiling and two miles visibility as a turboprop breaks out of the clouds on an instrument approach to a nontowered airport. The runway is in sight—and there’s a Piper J–3 Cub taxiing on it.
Do you have a problem with that?
It’s unknown whether the perturbed pilot made the report. Doing so might have proved embarrassing by unmasking his confusion about airspace—specifically Class E airspace, Class G airspace, and what happens when you descend from one into the other, as you do at many nontowered airports.
That’s a topic that makes a good opener for the ground portion of an IFR proficiency session, and the scenario described above illustrates the confusion that can arise if a pilot arriving on an approach is unprepared for what might be going on down below.
Class E airspace is good review material because although it seems less onerous to occupy than airspace classes B, C, and D, Class E has the unusual element of flooring out, so to speak, at different levels in different places. Those levels could be 700 feet agl, 1,200 feet agl, or at the surface at some airports, where it has the effect of prohibiting transit or arrival under VFR when visibility goes below three statute miles (beneath 10,000 feet msl) or five statute miles (above 10,000 feet msl). Note that surface-based Class E airspace is depicted on VFR charts within dashed lines approximating instrument-approach corridors to keep nonparticipating aircraft out of IFR traffic’s way.
When a Class E airspace floor sits at 700 feet agl or 1,200 feet agl, however, Class G airspace lies below, and if the daytime visibility is one statute mile, and an aircraft can remain clear of clouds, it can fly VFR in the Class G below 10,000 feet msl. Translation: If you are flying an instrument approach to such an airport, you could encounter a VFR aircraft—possibly with no radio—when you descend from the Class E into Class G.
As noted, that scenario is typically posed to pilots in proficiency checks and flight reviews strictly as a what-if question. But with satellite navigation adding instrument approach procedures to many formerly VFR-only airports, IFR and VFR pilots alike need to face up to their boundary issues.