What could be a major consequence of improperly applied de-icing fluids?

Improperly applied de-icing fluids can significantly increase the risk of stall during flight. De-icing fluids are designed to prevent and remove ice accumulation on an aircraft's wings and control surfaces, which are essential for maintaining proper aerodynamic performance. When these fluids are not applied correctly, ice can form or remain on the surfaces, altering the airflow around the wings and reducing lift.

As the aircraft approaches certain angles of attack, especially during takeoff and landing, the presence of ice can lead to a loss of lift and an increased stall risk. This situation is particularly dangerous, as it can occur without warning, leading to potential loss of control. Therefore, proper application of de-icing fluids is critical to ensuring that flight surfaces remain clear of ice, thereby maintaining the safety and performance of the aircraft.