Leeward side of a mountain

Remote Pilot (Part 107) practice question 11 of 25 on Weather / Effects on Performance. ACS element UA.III.B.K1b · difficulty: standard. Want to answer it in a timed quiz? Use the Remote Pilot (Part 107) practice mode.

Question bank updated 2026-09-22

QUESTIONA remote pilot operates a small unmanned aircraft near a mountain while a strong wind blows across the ridge. On the leeward side of the mountain, the pilot should expect

  1. Aincreasingly turbulent air that tends to push the aircraft toward the terrain
  2. Bsmooth upward currents that help carry the aircraft over the peak of the mountain
  3. Ccalm air, because the mountain blocks the wind from reaching the downwind side
Show the answer and explanation

Correct answer: A. increasingly turbulent air that tends to push the aircraft toward the terrain

  • A — correct On the leeward side the air follows the terrain downward and becomes increasingly turbulent, which tends to push an aircraft into the side of the mountain.
  • B — incorrect Smooth upward flow occurs on the windward side; the leeward side behaves differently.
  • C — incorrect The mountain does not shelter the leeward side; the descending air is turbulent, and the stronger the wind, the greater the turbulence.

BACKGROUND

The effect of obstructions on wind is even more noticeable in mountainous regions. Wind flows smoothly up the windward side of a mountain, and the upward currents help carry an aircraft over the peak. On the leeward side, the air follows the contour of the terrain as it flows downward and becomes increasingly turbulent. This tends to push an aircraft into the side of the mountain, and the stronger the wind, the greater the downward pressure and turbulence become.

STUDY TIP

Picture the wind as water flowing over a rock: smooth on the upstream face, churning on the downstream face.

KEY POINTS

  • Windward side: smooth upward flow.
  • Leeward side: descending, increasingly turbulent air.
  • Stronger wind means greater downward pressure and turbulence.

SOURCES

  • remote_pilot_study_guide.txt ch3b "Effect of Obstructions on Wind"
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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.