Effects of Icing

By disrupting the airflow over the ailerons or elevator, small amounts of ice can alter the aerodynamic balance of the controls and potentially render the aircraft uncontrollable.

Aircraft are designed to warn the pilot of incipient handling anomalies with clean airframes. However, ice contamination can cause handling anomalies to occur without warning. Ice accretion can lead to both roll and pitch upsets caused by wing stalls and tail stalls.

An ice-contaminated wing will stall at a lower angle of attack or higher airspeed than a clean wing.

Clean vs. Iced Wing

Minute amounts of ice (equivalent to medium grit sandpaper) covering the leading edges or upper surfaces of wings can increase the stall speed up to 15 knots. Ice on the wing also can disrupt the airflow over the ailerons and cause the aircraft to behave in unusual ways. The aileron may deflect without pilot input and cause an uncommanded roll.

Tail Stalls

The center of gravity is forward of the wing center of lift. The forces acting through these two points generates a nose-down moment. The horizontal stabilizer counteracts this nose-down moment by generating downward lift, it acts like an upside-down wing. Ice contaminated tail stalls are almost always associated with flap extension. Lowering the flaps increases the wing downwash, and thereby greatly increases the horizontal stabilizer’s angle of attack, potentially leading to a tail stall. The elevator may oscillate without pilot input and cause an uncommanded pitch change. In extreme cases, the yoke might snatch forward, immediately pitching the nose down.

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