Ice is a silent examiner. It doesn't announce itself, it doesn't wait for you to be ready, and a layer no thicker than coarse sandpaper on a leading edge can raise your stall speed and quietly delete your climb performance. In the EASA ATPL theory exams, icing hides mainly in Meteorology (050), but it leaks into Principles of Flight, Aircraft General Knowledge and Operational Procedures too.
The problem isn't that icing is hard. It's that students carry hangar myths into the exam hall and lose easy marks. Here are eight of the most common, with the EASA-correct principle behind each.
1. "Airframe ice only forms below zero"
Half true, and the missing half is what catches you out. Airframe icing needs two things at once: visible supercooled liquid water, and a surface at or below 0 °C. Supercooled droplets can stay liquid down to roughly -40 °C, so the water is often colder than you would expect. Add kinetic (ram) heating at speed and the skin temperature can differ from the raw outside-air reading. Learn the clean statement: supercooled water striking a sub-zero surface. Temperature on its own is not the whole answer.
2. "The colder it gets, the worse the icing"
This one is backwards across most of the range. The most severe clear ice clusters between about 0 °C and -15 °C, where large supercooled droplets and high liquid-water content live. Go deep enough, below roughly -40 °C, and the cloud is essentially ice crystals, which mostly bounce off and fail to adhere. The danger zone is moderate cold, not the deep freeze.
3. "Rime and clear ice are basically the same"
They form differently and they punish you differently. Rime ice forms when small droplets freeze on contact, trapping air. It is opaque, rough, milky and follows the airfoil shape, favouring colder temperatures. Clear (glaze) ice forms when large droplets flow back before freezing. It is smooth, dense, glassy and builds near 0 °C, growing "horns" that wreck the airflow. Mixed ice is both. Clear ice is heavier, harder to see and generally the more dangerous of the two.
4. "Carburettor icing needs freezing weather"
No. Carburettor icing can form with an outside air temperature as high as +30 °C, and it is most likely in humid air at low power, such as a descent. The pressure drop through the venturi plus the cooling from fuel vaporisation can chill the charge by 20 to 30 °C, dragging moist air below freezing inside the carburettor on a mild day. Fuel-injected engines escape carburettor icing but can still suffer impact or inlet icing.
5. "Freezing rain is less of a threat than cloud"
The opposite. Freezing rain and freezing drizzle are supercooled large droplets (SLD). They build fast, extensive clear ice that reaches behind the protected leading edges, onto surfaces with no ice protection at all. Freezing rain also tells you something: there is a warmer layer aloft, a temperature inversion, with precipitation melting higher up and refreezing as it falls into sub-zero air below.
6. "Anti-icing and de-icing mean the same thing"
Different jobs, different timing. Anti-icing is preventive, switched on before ice forms: heated leading edges from engine bleed air, electrically heated probes, or a weeping wing releasing fluid. De-icing is corrective, removing ice that has already accumulated, typically pneumatic boots that inflate to crack it off. On the ground the same split applies: de-icing fluid removes existing contamination, while thickened anti-icing fluid buys you holdover time before take-off.
7. "A little frost on the wings is fine for take-off"
It is not, and EASA is blunt about it. The clean aircraft concept requires critical surfaces to be free of frost, ice and snow before take-off. Frost no rougher than sandpaper spoils the boundary layer, cuts maximum lift and raises the stall speed enough to end a take-off run badly. "Polished frost" is a myth. The rule is: remove it.
8. "Ice just adds weight"
Weight is the least of your problems. Ice increases drag and reduces maximum lift, so the wing stalls at a lower angle of attack and a higher speed. It can jam or unbalance controls, block the pitot-static system and feed you false airspeed and altitude, disturb fuel venting and shed into engines. Because the thinner outer wing is a better ice collector, it often stalls first, which is why an iced-up aeroplane can roll off without much warning.
How this shows up in the exam
Expect icing as a Meteorology question on droplet size and temperature bands, an AGK question on ice-protection systems, or a Principles of Flight question on the iced-wing stall. One rule ties them together: if ice remains on the wings, your stall speed is higher, so any approach flown with ice should carry a suitable speed increase. Know the why, not just the number, and the marks follow.
Frequently asked questions
At what temperature is aircraft icing most severe?
Most severe clear icing typically forms between about 0 °C and -15 °C, where large supercooled droplets and high liquid-water content are common. Below roughly -40 °C the cloud is mostly ice crystals, which largely fail to adhere.
Can carburettor icing happen in warm weather?
Yes. Carburettor icing can occur with outside air up to around +30 °C, and is most likely in humid conditions at low power settings such as a descent, because the venturi and fuel vaporisation cool the charge below freezing.
What is the difference between anti-icing and de-icing?
Anti-icing is preventive and used before ice forms, for example heated leading edges or a weeping wing. De-icing is corrective and removes ice that has already accumulated, for example pneumatic boots.
Is it legal to take off with frost on the wings under EASA rules?
No. EASA's clean aircraft concept requires critical surfaces to be free of frost, ice and snow before take-off, because even a thin, rough layer significantly raises the stall speed.
Ice questions are pure marks once the principles click. Drill Meteorology and AGK with exam-standard questions and worked explanations at atpltraining.io.
Photo by Bornil Amin on Unsplash
