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Frost on a small unmanned aircraft before flight

Remote Pilot (Part 107) practice question 20 of 25 on Weather / Effects on Performance. ACS element UA.III.B.K1g · difficulty: standard. Want to answer it in a timed quiz? Use the Remote Pilot (Part 107) practice mode.

Question bank updated 2026-09-22

QUESTIONBefore a morning flight, a remote pilot finds a thin layer of frost on the wing of a small unmanned aircraft. What action does FAA guidance call for?

  1. ATake off normally, because frost is as harmless as dew
  2. BFly a short hover test first to let the frost melt off
  3. CRemove all frost from the aircraft before flight
Show the answer and explanation

Correct answer: C. Remove all frost from the aircraft before flight

  • A — incorrect Dew poses no threat, but frost is a definite flight safety hazard; the two are not equivalent.
  • B — incorrect Frost degrades lift and increases drag from the moment of takeoff, so the guidance requires it to be removed before flight, not flown off.
  • C — correct The study guide states that a small unmanned aircraft must be thoroughly cleaned and free of frost prior to beginning a flight because frost disrupts airflow, reduces lift and increases drag.

BACKGROUND

On cool, clear, calm nights the ground and objects on the surface can cool the surrounding air below the dew point, and moisture condenses on the ground, buildings, cars and aircraft as dew. If the temperature is below freezing, the moisture is deposited as frost. Dew poses no threat to a small unmanned aircraft, but frost is a definite flight safety hazard: it disrupts the flow of air over the wing, can drastically reduce lift, and increases drag, which together can adversely affect the ability to take off. A small unmanned aircraft must be thoroughly cleaned and free of frost before flight.

STUDY TIP

Treat frost as a no-go item on the preflight inspection until it has been completely removed.

KEY POINTS

  • Dew is harmless; frost is a definite flight safety hazard.
  • Frost disrupts airflow over the wing, reduces lift and increases drag.
  • The aircraft must be cleaned and free of frost before flight.

SOURCES

  • remote_pilot_study_guide.txt ch3b "Dew and Frost"
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MORE ON WEATHER / EFFECTS ON PERFORMANCE

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.