Some aircraft may not be adequately protected against this threat. When ice forms on the wings, the airflow is disrupted, resulting in reduced pressure on the top of the ailerons, Bragg said. Because the auto-pilot was engaged, the pilot was unaware of the changes occurring in the lateral control forces due to the accretion of ice. When the auto-pilot disengaged, the right aileron rotated up violently and the aircraft rolled rapidly to the right. As the pilot fought to regain control, the aircraft rolled further and crashed into a field.
Large jetliners use hot air from the engines to prevent ice from forming on the wings.
Instead, pilots of commuter aircraft rely upon inflatable rubber boots along the wings' leading edges to 'pop' off accumulated ice. In the case of the ATR-72 accident, because the ridge of ice formed aft of the rubber boot, inflating the boot had no effect. Although the ATR-72 deicing boot has been redesigned and now extends farther back on the wings, this is only a partial solution, Bragg said. The potential accretion of ice remains a problem for other aircraft and other icing conditions. Bragg hopes to minimize this risk by better understanding the effects of icing.