Where does frost typically form on an airframe?

Frost typically forms on an airframe outside and overnight due to radiational cooling. During clear nights, the airframe can lose heat rapidly, leading to a temperature drop of the metal surfaces below the dew point of the ambient air. This cooling allows moisture in the air to condense and then freeze upon contact with the cold surfaces, resulting in the formation of frost.

Frost is more prevalent in the early hours of the morning when temperatures reach their lowest point, especially when the conditions are clear without cloud cover. The other options do not align with the conditions under which frost accumulates. While frost can occur when an aircraft is parked outside under the right night-time conditions, it does not typically form during the day when heat from the sun would prevent freezing. Additionally, frost would not form inside heated hangars, as the warmer temperatures and controlled environment negate the cooling effects necessary for frost formation.