Private Pilot Private Practice Exam

The most favorable condition for the formation of carburetor icing is indeed when the temperature is between 20ºF and 70ºF accompanied by high humidity. This phenomenon occurs because when fuel vaporizes in the carburetor, it absorbs heat from its surroundings, which can lead to a drop in temperature sufficient to form ice, particularly in the presence of moisture in the air.

At temperatures within this range, the likelihood of icing increases as the dew point can be reached or exceeded, allowing for water vapor in the air to condense. High humidity provides the necessary moisture for ice to form at these temperatures, therefore creating an ideal set of conditions for carburetor icing to occur.

In contrast, cold temperatures and low humidity do not provide enough moisture for ice to form, while high temperatures generally reduce the likelihood of ice formation altogether, especially with low humidity as there is insufficient moisture available. Thus, the conditions outlined in the chosen answer establish the perfect scenario for carburetor icing to manifest.