Class E base converted to MSL

Remote Pilot (Part 107) practice question 8 of 21 on Airspace / Classification. ACS element UA.II.A.K1d · difficulty: applied. Want to answer it in a timed quiz? Use the Remote Pilot (Part 107) practice mode.

Question bank updated 2026-09-22

QUESTIONIn an area where the Class E airspace base is 1,200 feet AGL, the ground elevation is 3,000 feet MSL. At what MSL altitude does Class E airspace begin over that ground?

A1,200 feet MSL
B1,800 feet MSL (3,000 minus 1,200)
C4,200 feet MSL

Show the answer and explanation

Correct answer: C. 4,200 feet MSL

A — incorrect 1,200 feet is the height above the ground, not an MSL altitude; the ground elevation must be added.
B — incorrect Subtracting gives an altitude below the ground; an AGL base is added to the ground elevation, not subtracted from it.
C — correct A base of 1,200 feet above ground level over ground at 3,000 feet MSL is 3,000 plus 1,200, or 4,200 feet MSL.

BACKGROUND

The Remote Pilot Study Guide states that in most areas the Class E airspace base is 1,200 feet above ground level (AGL). An AGL value is measured from the ground, so its mean sea level (MSL) equivalent depends on the terrain elevation. Over ground at 3,000 feet MSL, a 1,200-foot AGL base lies at 4,200 feet MSL. Class E typically extends from that base up to, but not including, 18,000 feet MSL.

STUDY TIP

Convert AGL to MSL by adding the ground elevation; remember that the same AGL base sits at different MSL altitudes over different terrain.

KEY POINTS

In most areas the Class E base is 1,200 feet AGL.
AGL plus ground elevation equals MSL.
3,000 feet plus 1,200 feet gives a base of 4,200 feet MSL.

SOURCES

remote_pilot_study_guide.txt Chapter 2 "Class E Airspace"

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