weather theoryFAA-published sample question (PAR, Aug 2021)
Why is frost considered hazardous to flight?
A
Frost changes the basic aerodynamic shape of the airfoils, thereby increasing lift.
B
Frost slows the airflow over the airfoils, thereby increasing control effectiveness.
C
Frost spoils the smooth flow of air over the wings, thereby decreasing lifting capability.✓ Correct Answer
Explanation
Frost roughens the wing surface and disrupts the smooth airflow over it, causing early airflow separation; as PHAK Ch. 12 explains, this reduces the wing's lifting capability and increases drag and stall speed, possibly preventing the airplane from becoming airborne. Frost never increases lift, and it does not improve control effectiveness.
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