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Conditions required for structural icing

Remote Pilot (Part 107) practice question 19 of 25 on Weather / Effects on Performance. ACS element UA.III.B.K1g · difficulty: recall. Want to answer it in a timed quiz? Use the Remote Pilot (Part 107) practice mode.

Question bank updated 2026-09-22

QUESTIONWhat two conditions are necessary for structural icing to form on an aircraft in flight?

  1. AVisible moisture and an ambient air temperature of 32 °F or colder measured at the surface
  2. BHigh humidity and a temperature below the dew point at any altitude
  3. CVisible moisture and a temperature of 0 °C or colder at the point of impact
Show the answer and explanation

Correct answer: C. Visible moisture and a temperature of 0 °C or colder at the point of impact

  • A — incorrect The temperature that matters is at the point where moisture strikes the aircraft, and aerodynamic cooling can bring an airfoil to 0 °C even when the ambient air is a few degrees warmer.
  • B — incorrect Humidity alone is not enough; the aircraft must be flying through visible water such as rain or cloud droplets.
  • C — correct The study guide lists two conditions: the aircraft must be flying through visible water such as rain or cloud droplets, and the temperature where the moisture strikes the aircraft must be 0 °C or colder.

BACKGROUND

Two conditions are necessary for structural icing in flight. First, the aircraft must be flying through visible water such as rain or cloud droplets. Second, the temperature at the point where the moisture strikes the aircraft must be 0 °C or colder. Aerodynamic cooling can lower the temperature of an airfoil to 0 °C even though the ambient temperature is a few degrees warmer, so icing can occur when the outside air temperature reads slightly above freezing.

STUDY TIP

Learn the pair "visible moisture plus freezing at the surface of the aircraft," and remember the airfoil can be colder than the air.

KEY POINTS

  • Structural icing needs visible water (rain or cloud droplets).
  • The temperature where moisture strikes the aircraft must be 0 °C or colder.
  • Aerodynamic cooling can chill an airfoil below the ambient temperature.

SOURCES

  • remote_pilot_study_guide.txt ch3b "Structural Icing"
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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.