42 practice questions on Icing with answers and explanations, plus the key concepts and formulas, from the TrueHeading question bank.
Use this page to revise Icing for the DGCA Aviation Meteorology paper. Below are the key ideas first, then 12 practice questions with answers and explanations, picked from the 42 questions in the TrueHeading bank for this topic.
In short: In visible moisture (cloud or rain) with temperatures at or below freezing and supercooled water droplets.
Open the full set in the student zone to answer every question, track your accuracy and take timed mock tests.
5 ideas to know cold.
In visible moisture (cloud or rain) with temperatures at or below freezing and supercooled water droplets.
Differ by droplet size and temperature:
Ice in the carburettor throat from fuel evaporation and the pressure drop, which can cool the air by 20 °C or more.
Hoar frost: white ice crystals on a surface below 0 °C by direct deposition from the air. It must be removed before take-off.
Tip: Freezing rain under a warm front is the worst icing environment.
Rime: opaque, rough, small droplets, around −15 to −40 °C. Clear (glaze): transparent, heavy, large droplets, −0 to −10 °C. Mixed: both.
Tap “Show answer” after you have tried each one.
Answer: A. small supercooled droplets freezing quickly on impact
Rime ice is white and opaque, usually at temperatures below −15 °C in stratiform cloud.
Answer: B. large supercooled drops spreading before freezing
Clear ice is transparent and heavy; it is the most dangerous type and forms around 0 to −10 °C.
Answer: A. 0 to −10 °C
Large droplets are most common at these temperatures.
Answer: B. when it is on the ground at night and the surface temperature is below 0 °C and below the dew point
Deposition of ice from water vapour onto a cold surface; it must be removed before take-off.
Answer: B. a warm layer above a sub-zero layer near the surface
Snow melts in a warm layer then supercools in the cold layer, freezing on contact.
Answer: C. outside air temperatures up to about +20 °C with high humidity
Evaporation of fuel and the venturi effect cool the air by up to 20–30 °C.
Answer: C. reduced lift, increased drag and higher stall speed
Contamination alters the aerofoil shape, increasing the stall speed.
Answer: C. climb or descend out of the layer, or change route, if conditions allow
Move to warmer or colder air, away from visible moisture.
Answer: B. a combination of clear and rime ice
Forms in clouds with a range of droplet sizes.
Answer: A. between 0 and −15 °C
Between −15 and −40 °C the droplets are mostly frozen.
Answer: A. before entering visible moisture at temperatures near or below 10 °C
Typical engine anti-ice procedures use TAT +10 °C or below with visible moisture.
Answer: C. higher, due to ram rise
Compressibility heating adds to the static air temperature.
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