Part 107 Study Guide
Weather & METARs
Decode METARs and TAFs, understand density altitude, wind shear, fog formation, and how weather affects sUAS operations. Know Part 107 visibility and cloud clearance minimums.
39 questions in this topic
Sample Questions
In the METAR observation 'METAR KJFK 121856Z 21015G25KT 3SM BR OVC007 04/02 A2990', what does 'BR' indicate?
BR is the METAR code for mist, reported when visibility is 5/8 to 6 statute miles. FG (fog) is used only when visibility is less than 5/8 SM. AIM 7-1-29.
💡 Memory tip
BR = mist, visibility 5/8 to 6 SM. Below 5/8 SM the same obscuration is reported as FG (fog).
A temperature/dewpoint spread of 3°F and decreasing suggests:
The dew point is the temperature at which the air can hold no more moisture. As the temperature/dew point spread decreases, relative humidity increases; when temperature and dew point are close together and the air reaches saturation, fog, low clouds, and precipitation are highly likely to form. One way air reaches saturation is by cooling at night through contact with the cooler ground. FAA-G-8082-22 Ch. 3b; FAA-H-8083-28B Sec. 6.6.
💡 Memory tip
Dew point is where air can hold no more moisture. When the temperature drops to meet it, the air saturates: fog or low clouds.
What weather phenomenon poses the greatest risk to a small UAS operating below 400 ft AGL?
Buildings, terrain, and other obstructions break up the wind into gusts that change rapidly in direction and speed, and low-level wind shear is especially hazardous because the aircraft is close to the ground. Jet streams are bands of strong wind in the upper levels of the atmosphere, and clear air turbulence is a higher-altitude turbulence, normally above 15,000 ft. FAA-G-8082-22 Ch. 3b; FAA-H-8083-28B Sec. 9.4, 19.2.3.2.
💡 Memory tip
Below 400 ft you fly among buildings, terrain, and other obstructions that break the wind into fast-shifting gusts.
In a METAR, the altimeter setting 'A2992' means the barometric pressure is:
The 'A' prefix means the altimeter setting is in inches of mercury, in inches and hundredths: A2992 = 29.92 inHg, which is standard sea-level pressure. Outside the U.S., METARs may instead report the altimeter setting in hectopascals with a Q prefix (e.g., Q1013). AIM 7-1-28, 7-1-29; FAA-H-8083-25 Ch. 11.
Density altitude increases with:
Density altitude rises when it's hot, humid, and at high elevation (the 3 H's: High, Hot, Humid), as well as with low atmospheric pressure. This means thinner air and degraded performance for both manned and unmanned aircraft. FAA-G-8082-22 Ch. 3b.
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What are the Part 107 weather minimums? ▾
Under 14 CFR 107.51, the remote PIC must ensure: visibility at least 3 statute miles from the control station, and at least 500 ft below and 2,000 ft horizontally from any cloud. These are minimum conditions — exercise greater caution as appropriate.
What does OVC007 mean in a METAR? ▾
OVC007 means overcast cloud layer at 700 feet AGL (the number represents hundreds of feet). An overcast layer is sky coverage of 8/8. Because Part 107 requires staying at least 500 ft below clouds, a 700 ft overcast limits a sUAS to 200 ft AGL.
How does high density altitude affect drone performance? ▾
High density altitude (high elevation, high temperature, high humidity, or low pressure) means thinner air. Thin air makes the propeller less efficient and produces less lift, so aircraft performance decreases compared with standard conditions. 14 CFR 107.49 requires assessing local weather conditions before flight.