weather theoryFAA-published question bank (Private Pilot, 2008)
Why is frost considered hazardous to flight?
A
Frost changes the basic aerodynamic shape of the airfoils, thereby decreasing 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
PHAK explains that frost disrupts (spoils) the smooth flow of air over the wing, causing early airflow separation that reduces lift and raises stall speed, and it can keep the airplane from becoming airborne at normal takeoff speed. Frost does not significantly change the airfoil's shape (that is heavier ice), and it certainly does not improve control effectiveness.
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