Chapter 2 - Theory and Aircraft Performance

Frost on the Fuselage

18.  Despite the requirement to clean contamination from critical surfaces, it is acceptable for aircraft with aft fuselage mounted engines to take off when hoarfrost is adhering to the upper surface of the fuselage if it is the only remaining contaminant, provided all vents and ports are clear. Also, aircraft with wing mounted engines can take-off in such conditions however, for both types this can only be conducted in accordance with the aircraft manufacturer's instructions.