In-Flight Icing
In-Flight Icing
Lesson duration is: 120 minItems in this lesson
In-Flight Icing
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Learning goal
I can explain how aircraft icing forms, identify its main types, and describe how it affects aircraft performance.
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What problems might ice cause for an aircraft in flight?
Use this as a prior-knowledge activation. Likely responses: lift, drag, weight, engine, wing shape, stall speed, safety. Briefly surface misconceptions, then connect to the learning goal.
Why ice is dangerous
Ice can build up on wings and other exposed surfaces
It changes the shape of the aerofoil
It can also affect engine air intake systems
Even a thin layer can reduce performance
Open with the familiar idea that ice adds weight, then broaden to the less obvious aerodynamic and engine effects that the lesson will explain.
Conditions needed for icing
Aircraft icing forms when three things come together:
cold conditions
visible moisture
contact between droplets and the aircraft surface
Warm, dry air does not provide the same conditions for ice to form.
Keep this rooted in atmospheric conditions rather than ground frost. The lesson focus is in-flight icing and related induction icing.
How aircraft icing forms
Suitable conditions → aircraft meets supercooled liquid water droplets → droplets hit the aircraft surface → droplets freeze → ice accumulates
This causal chain is a load-bearing idea for the whole lesson. Reuse the same wording later when discussing airframe icing.
Supercooled droplets
Supercooled droplets are liquid water below 0°C.
They are not already ice.
When they strike an aircraft surface, they can freeze rapidly.
A common misconception is that icing comes from snow or ice crystals sticking on. Emphasise that the key source here is liquid droplets below freezing point.
What forms first
Ice usually starts where airflow meets the aircraft first, especially at the leading edge of the aerofoil.
That is why small changes at the front of the wing can have large effects on airflow over the whole aerofoil.
This slide sets up the later aerodynamic section without overexplaining it yet.
Which condition set is needed for in-flight icing?
Warm air, dry air, sunlight
Cold air, visible moisture, surface contact
Hot air, rain shadow, turbulence
Clear sky, low wind, low pressure
Checks the three required conditions from slides 3–4: cold conditions, visible moisture, and droplet contact with the aircraft surface.
How icing forms
Aircraft icing forms in cold conditions when an aircraft meets supercooled liquid water droplets. When the droplets strike the surface, they freeze and ice begins to accumulate, often first at the leading edge of the aerofoil.
All blanks are load-bearing terms already taught in slides 4–6.
Rime ice
linked with smaller droplets
droplets freeze rapidly on contact
forms a rough surface
usually looks opaque
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Clear ice
linked with larger supercooled droplets
water can spread before freezing
forms a harder accumulation
often appears smoother
Students sometimes assume 'clear' means harmless or easy to see through. Stress that it can be especially hazardous because it spreads and can be hard to remove.
Rime ice and clear ice
Rime ice: smaller droplets, rapid freezing, rough and opaque.
Clear ice: larger droplets, spreading before freezing, harder and smoother.
The droplet behaviour explains the different appearance and texture.
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Mixed icing
Mixed icing is a combination of characteristics from rime ice and clear ice.
If an ice build-up shows features of both types, it is described as mixed icing.
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Classifying icing
small droplets + rapid freezing → rime ice
larger droplets + spreading before freezing → clear ice
combined characteristics → mixed icing
hard accumulations are more associated with clear ice
This slide consolidates the type-identification language students will need for short-answer assessment.
Which description best matches clear ice?
Small droplets, rough, opaque
Large droplets, smooth, hard
Mixed features, soft, powdery
Dry air, rapid melting, thin
Distractors reflect confusion with rime ice or invented properties. Correct answer draws on slides 8–11.
Classifying icing types
Rime ice is linked with smaller droplets that freeze rapidly on contact. Clear ice is linked with larger droplets and water can spread before freezing.
Reinforces the causal distinction between rime and clear icing rather than just memorising names.
How would you recognise mixed icing?
Expected elements: mixed icing combines characteristics of both rime and clear ice; a student might mention rough plus hard, or rapid freezing plus spreading behaviour. Use for brief verbal follow-up rather than exact marking.
A clean aerofoil
A clean aerofoil has a designed shape that helps air flow smoothly around it.
That shape is essential for producing lift efficiently.
Use 'aerofoil' consistently. This is the reference point for understanding why any ice build-up matters.
Ice changes the aerofoil
When ice builds up on the leading edge, the aerofoil is no longer its intended shape.
That changed shape disrupts normal airflow.
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The main aerodynamic effects
Airframe icing can:
increase drag
decrease lift
increase weight
increase stall speed
change aerofoil shape
These are the core consequences the rest of the lesson unpacks one by one.
Why drag increases
Ice changes the aerofoil shape and makes airflow less smooth.
Ice → altered airflow → increased drag
With more drag, the aircraft needs more power or more effort to maintain flight.
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Why lift decreases
Lift depends on the aerofoil shape and smooth airflow.
When ice disrupts that airflow, the wing becomes less effective at producing lift.
Ice → disrupted airflow → reduced lift
Avoid going beyond the lesson scope into advanced airflow theory. The key idea is reduced effectiveness of the aerofoil.
Weight and shape
Weight: ice adds mass to the aircraft.
Aerofoil shape: ice build-up changes the contour of the wing, especially near the leading edge.
These effects happen together, not separately.
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Why stall speed can increase
Ice accumulation → aerofoil shape changes → aerodynamic performance changes → less lift available at a given condition → the aircraft needs a higher airspeed to produce enough lift
That is why icing can increase stall speed.
Students often memorise this without linking it to lift. Keep the causal chain explicit: changed shape leads to reduced lift efficiency, so a higher airspeed is needed.
The full airframe icing chain
Ice → changes aerofoil shape → disrupts airflow → increases drag → reduces lift → can increase stall speed → aircraft performance becomes more hazardous
This is the summary chain students should be able to reproduce in assessment answers.
What is the main reason icing can increase stall speed?
The aircraft becomes quieter
The aerofoil produces less lift
The engine always freezes
The wing becomes longer
Targets the causal link in slides 13–19: ice changes shape, disrupts airflow, reduces lift efficiency, so a higher airspeed is needed.
The aerodynamic chain
Ice changes the aerofoil shape and disrupts airflow. This increases drag and reduces lift, so stall speed may rise.
This is the load-bearing summary chain students need for later assessment answers.
Why does leading-edge ice matter so much?
Expected elements: the leading edge meets airflow first; small shape changes there disrupt airflow over the whole aerofoil; this links local ice build-up to wider aerodynamic effects.
Induction icing
Aircraft icing is not only an airframe problem.
Ice can also affect the engine air intake system.
This is called induction icing.
Make the contrast clear: airframe icing affects aerodynamic surfaces, while induction icing affects engine intake airflow.
Carburettor icing
In some piston engines:
pressure reduction + fuel evaporation → significant cooling → ice forms in the carburettor → airflow becomes restricted → engine performance decreases
Keep the wording close to the chain in the source material. The key effect is restricted airflow and reduced engine performance.
Airframe icing or induction icing?
Airframe icing
changes aerofoil shape
can increase drag
can reduce lift
Induction icing
can restrict engine airflow
includes carburettor icing
can reduce engine performance
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Scenario: ice builds up
In cold conditions with visible moisture:
ice accumulates on the aircraft
the aerofoil shape changes
drag increases
lift decreases
stall speed may increase
Some piston engines may also face carburettor icing.
Use this as a narrated walkthrough of the cause-and-effect sequence rather than a new set of facts.
Why icing is hazardous
Ice can act in several harmful ways at once:
it changes aerofoil shape
it increases drag
it reduces lift
it increases weight
it can increase stall speed
Together, these make aircraft performance less safe.
The danger is the combination of effects, not a single isolated change.
Why clear ice can be especially hazardous
Clear ice is linked with larger droplets that can spread before freezing.
This can produce a hard accumulation over more of the surface.
Because it changes shape and can be difficult to remove, it can be especially hazardous.
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What does carburettor icing mainly do to the engine?
Increases fuel flow
Restricts airflow
Improves lift
Reduces wing weight
Checks understanding of induction icing from slides 20–22. Students often confuse engine icing with airframe effects.
Which hazard would worry you most in the scenario?
Reduced lift
Increased drag
Higher stall speed
Carburettor icing
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Why is clear ice especially hazardous?
Expected elements: several effects happen together; shape changes, drag rises, lift falls, weight rises, stall speed may rise, and some engines may also suffer induction icing. Best answers stress combined impact on performance and safety.
GCSE-style answers
What is aircraft icing? Ice forms when supercooled water droplets strike an aircraft surface and freeze.
Describe rime ice. It is linked with smaller droplets, rapid freezing, and a rough opaque appearance.
Describe clear ice. It is linked with larger droplets, spreading before freezing, and a harder smoother accumulation.
Model concise 2-mark responses. Students should notice how each answer includes defining features rather than long explanation.
Explaining effects in assessment
Three effects of airframe icing: increased drag, reduced lift, increased stall speed.
Why stall speed increases: ice changes the aerofoil shape, so less lift is available at a given condition and a higher airspeed is needed.
This slide keeps the assessment focus aligned to the content already taught rather than introducing new examples.
Induction icing in assessment
What is carburettor icing? It is ice forming in the carburettor of some piston engines.
What effect can it have? It restricts airflow and can reduce engine performance.
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GCSE-style recall
Aircraft icing forms when supercooled water droplets strike an aircraft surface and freeze. In some piston engines, ice can also form in the carburettor and reduce engine performance.
Final knowledge anchor before reflection, tying together airframe icing and carburettor icing in assessment language.
What idea from this lesson will you remember best?
Reflection prompt for the end of the lesson. Invite short personal responses about understanding, not factual correctness.
Which part of icing still feels hardest to explain?
Reflection prompt. Useful for planning reteaching: students may mention icing types, the stall-speed chain, or induction icing.
Glossary
aircraft icing - ice that forms when supercooled water droplets strike an aircraft surface and freeze
supercooled droplets - liquid water droplets that remain liquid below 0°C
aerofoil - the shaped surface of a wing designed to help produce lift
rime ice - ice linked with smaller droplets, rapid freezing, and a rough opaque appearance
clear ice - ice linked with larger droplets that spread before freezing, forming a harder smoother accumulation
mixed icing - icing that combines characteristics of rime ice and clear ice
airframe icing - icing that builds up on external aircraft surfaces such as wings
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Glossary
drag - the resisting force that opposes an aircraft moving through air
lift - the upward aerodynamic force produced by the aerofoil
stall speed - the speed below which the wing can no longer produce enough lift in that condition
induction icing - icing that affects the engine air intake system
carburettor icing - ice forming in the carburettor because cooling causes moisture to freeze there
leading edge - the front edge of the wing that meets the airflow first
visible moisture - cloud, precipitation, or other moisture in the air that can provide droplets
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