Under which condition should stall heat be used?

Stall heat is primarily utilized in aircraft operation to prevent ice formation on critical surfaces, particularly the leading edges of wings where airflow is crucial for maintaining lift. The correct condition for using stall heat is during icing conditions. In these scenarios, atmospheric moisture can freeze on the wings and control surfaces, leading to a significant decrease in aircraft performance and an increased risk of stalling. Activating stall heat in these conditions ensures that the ice does not accumulate and disrupts the airflow, thus allowing the pilot to maintain control and flight safety.

The other conditions presented may not warrant the use of stall heat. For example, in clear weather, where icing is not a concern, activating stall heat would be unnecessary. High altitudes might present other challenges, but they are not directly related to the need for stall heat unless ice is also a factor. Similarly, during night operations, visibility is reduced, but this does not inherently equate to the necessity for stall heat unless icing conditions exist. Therefore, stall heat should be specifically used when flying in conditions where icing is present to ensure optimal performance and safety.