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Maximum altitude below a cloud layer

Remote Pilot (Part 107) practice question 3 of 31 on Airspace / Operational Requirements. ACS element UA.II.B.K1 · difficulty: applied. Want to answer it in a timed quiz? Use the Remote Pilot (Part 107) practice mode.

Question bank updated 2026-09-22

QUESTIONA cloud layer has a base of 800 feet above ground level (AGL) over flat terrain with no structures nearby. To comply with the cloud-clearance requirement of § 107.51, what is the highest altitude at which the small unmanned aircraft may be flown?

  1. A400 feet AGL, the normal altitude limit
  2. B600 feet AGL, keeping 200 feet below the cloud
  3. C300 feet AGL
Show the answer and explanation

Correct answer: C. 300 feet AGL

  • A — incorrect At 400 feet AGL the aircraft would be only 400 feet below the 800-foot cloud base, less than the required 500 feet.
  • B — incorrect This exceeds both the 400-foot altitude limit in § 107.51(b) and the 500-foot cloud clearance in § 107.51(d).
  • C — correct § 107.51(d) requires 500 feet below the cloud; 800 feet minus 500 feet leaves a maximum of 300 feet AGL, which is also under the 400-foot limit.

BACKGROUND

Section 107.51 contains two limits that interact when clouds are low. Paragraph (b) caps altitude at 400 feet above ground level unless the aircraft is within a 400-foot radius of a structure, and paragraph (d) requires the aircraft to remain at least 500 feet below clouds. When the cloud base is below 900 feet AGL, the cloud-clearance rule becomes the binding limit. The remote pilot subtracts 500 feet from the cloud base to find the highest permissible altitude, then checks that the result does not exceed 400 feet AGL.

STUDY TIP

Practice subtracting 500 feet from the reported cloud base and comparing the result with the 400-foot ceiling; whichever is lower controls.

KEY POINTS

  • Required clearance is 500 feet below the cloud (§ 107.51(d)).
  • Cloud base minus 500 feet gives the maximum usable altitude.
  • That result must also stay at or below 400 feet AGL (§ 107.51(b)).

SOURCES

  • 14 CFR 107.51(b)
  • 14 CFR 107.51(d)
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MORE ON AIRSPACE / OPERATIONAL REQUIREMENTS

SkyDrill is not affiliated with the FAA. This is an original practice item based on 14 CFR part 107, 14 CFR part 89, and the FAA Remote Pilot – Small UAS Study Guide (FAA-G-8082-22). Regulations and handbooks are revised; confirm details against the current edition.