Clean Aircraft Concept (Anti-Icing vs De-Icing)

Clean Aircraft Concept

The Clean Aircraft Concept is a fundamental EASA and FAA safety principle: an aircraft must not take off with frost, ice, snow or frozen deposits on its wings, control surfaces, propellers, engine inlets, speed brakes or other critical surfaces — even thin, sandpaper-like roughness can have catastrophic consequences.

Legal basis:

• EASA Part-NCO.OP.180 (Ice and other contaminants — ground procedures): "The pilot-in-command shall only commence take-off if the aeroplane is clear of any deposits which might adversely affect its performance or controllability, except as permitted in the AFM."
• Part-NCO.OP.185 (Ice and other contaminants — flight procedures) regulates the same for flight.
• FAA "Clean Aircraft Concept" (FAR §91.527) — analogous rule.

Effects of ice accretion

On the wing:

• Lift decreases — even 0.8 mm of ice (roughness of coarse sandpaper) on the leading edge can reduce lift by 25–30% and increase drag by 40%.
• Critical angle of attack decreases — stall occurs at a lower AoA and higher speed (higher stall speed).
• Asymmetric ice accumulation → asymmetric lift loss → roll tendency.

On control surfaces:

• Tailplane icing is especially dangerous: with flaps up, often no problem, but on flap extension the elevator down-wash pushes the tail down → with iced elevator a "tailplane stall" with sudden nose-down pitch.
• Aileron icing → flutter risk, asymmetric roll.

On the propeller:

• Uneven ice accretion → vibration, balance issues → larger chunks cause structural damage.
• Loss of thrust due to altered blade shape.

On weight:

• Ice accumulation increases mass and may shift CG.

On engine performance:

• Iced air inlets restrict airflow → power loss.
• Carb icing (see separate lesson) → power loss in carbureted engines.

Anti-Icing vs De-Icing

Anti-Icing (preventing ice formation):

• Preventive: Before ice forms, the surface is heated or wetted with ice-repelling fluid.
• Systems: pitot heat, heated carburetor inlets, heated windshield section, anti-icing fluid (e.g. glycol-water mixture) on wing leading edges.
• "Weeping Wing" (TKS system): fluid exudes from micro-perforated leading edges.

De-Icing (removing ice that has already formed):

• Reactive: Ice has already formed and is mechanically or thermally removed.
• Systems: pneumatic de-icing boots (inflatable rubber tubes on leading edges that crack the ice off), thermal de-icing (hot bleed air), electrical de-icing (heating wires).
• Activation only after approx. 6–12 mm of ice has built up — earlier de-ice boot activation is ineffective (the ice does not crack off).

Components that can be protected

Relevance for PPL(A)

Most training aircraft (C172, PA-28, DA40) are "Not Approved for Flight Into Known Icing (NFIKI)". They typically have only:

• Pitot heat,
• Carb heat (carburetor pre-heat) for carbureted engines,
• Possibly windshield heating.

No wing anti-/de-icing. Therefore: in actual or forecast icing, VFR flight must be avoided.