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Descent time in a microburst downdraft

Remote Pilot (Part 107) practice question 17 of 25 on Weather / Effects on Performance. ACS element UA.III.B.K1e · difficulty: applied. Want to answer it in a timed quiz? Use the Remote Pilot (Part 107) practice mode.

Question bank updated 2026-09-22

QUESTIONFAA guidance states that a microburst can produce downdrafts of up to 6,000 feet per minute. If a small unmanned aircraft at 400 feet above the ground were carried down at that rate, about how long would it take to reach the surface?

  1. AAbout 15 seconds
  2. BAbout 40 seconds
  3. CAbout 4 seconds
Show the answer and explanation

Correct answer: C. About 4 seconds

  • A — incorrect Fifteen is the upper end of a microburst's lifespan in minutes, not the descent time; at 100 feet per second, 400 feet takes 4 seconds.
  • B — incorrect This would correspond to only 600 feet per minute, a tenth of the downdraft rate stated in the guidance.
  • C — correct 6,000 feet per minute is 100 feet per second, so 400 feet takes 400 divided by 100, or about 4 seconds.

BACKGROUND

The study guide describes the microburst as the most severe type of low-level wind shear. A typical microburst has a horizontal diameter of 1 to 2 miles and a nominal depth of 1,000 feet, lasts about 5 to 15 minutes, and can produce downdrafts of up to 6,000 feet per minute together with headwind losses of 30 to 90 knots. Converting 6,000 feet per minute to 100 feet per second shows why an encounter at low altitude can end in terrain impact before the remote pilot can react. Microburst activity may be indicated by an intense rain shaft at the surface, but virga at cloud base and a ring of blowing dust are often the only visible clues.

STUDY TIP

Convert feet per minute to feet per second by dividing by 60; the tiny numbers that result explain why microbursts are treated as lethal.

KEY POINTS

  • Microburst downdrafts can reach 6,000 feet per minute (100 feet per second).
  • A microburst typically lasts 5 to 15 minutes and spans 1 to 2 miles.
  • Visible clues may be only virga at cloud base and a ring of blowing dust.

SOURCES

  • remote_pilot_study_guide.txt ch3b "Low-Level Wind Shear" (microburst paragraph)
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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.