Under what condition can an aircraft take off with frost present?

An aircraft can take off with frost present on the top of the fuselage due to the aerodynamics and operational requirements of flight. Frost can significantly impact lift and control surfaces, such as wings and horizontal stabilizers, because they are crucial for the aircraft's ability to generate the necessary lift and maintain stability during flight.

The wings and horizontal stabilizer are key to producing controlled airflow and generating lift; any frost or contamination on these surfaces can alter their shape and airflow characteristics, drastically reducing performance and potentially leading to unsafe flying conditions.

While frost on the top of the fuselage may not directly affect lift as much as frost on control surfaces does, it should still be noted that the presence of frost anywhere can introduce risks and is generally not ideal. However, when frost is strictly present on the fuselage and not affecting critical aerodynamic surfaces, takeoff may still be possible. Nonetheless, it is essential for pilots to conduct proper inspections and adhere to specific guidelines set forth by aviation authorities or manufacturers before proceeding with a flight under such conditions.