What type of weather condition requires the use of a Pre-Takeoff Contamination Check?

The requirement for a Pre-Takeoff Contamination Check is primarily associated with ground icing conditions. This check is essential to ensure that the aircraft's critical surfaces, such as wings and tail, are clear of any contamination that could adversely affect lift and control during takeoff. When temperatures are at or below freezing and conditions are conducive to ice formation, any accumulation of ice or frost can significantly increase the risk of an accident due to reduced aerodynamic performance.

In contrast, while heavy thunderstorms can present a variety of hazards, including wind shear and lightning, they do not specifically necessitate a Pre-Takeoff Contamination Check like ground icing conditions do. Clear skies typically indicate favorable conditions for flight without the presence of ice or snow, negating the need for this particular check. Similarly, light rain alone is generally not a cause for concern regarding aircraft surfaces being contaminated to the extent that snow or ice would be. Therefore, it is the acknowledgement of the risks associated with icing situations that underscores the necessity of conducting a Pre-Takeoff Contamination Check before flight operations in those conditions.