What is the maximum frost thickness allowed on the underside of the wing caused by cold soaked fuel?

What is the maximum frost thickness allowed on the underside of the wing caused by cold soaked fuel?

• A. 1/8 Inch
• B. 1/4 Inch
• C. 1/16 Inch
• D. 1/2 Inch

Answer: (A)

Frost forming on the underside of the wing from cold soaked fuel can change the wing’s surface enough to disturb the smooth airflow that creates lift. Even a very thin frost layer increases drag and can raise stall speed, narrowing the safe margin for takeoff. The limit is set to be conservative, allowing only a tiny amount of frost before takeoff is no longer considered safe. If frost is thicker than that, the aircraft should not depart until it’s removed or conditions improve. The other options imply much thicker frost, which would produce larger aerodynamic penalties and unsafe takeoff performance, so the smallest permissible thickness is the one that keeps safety margins intact.

Frost forming on the underside of the wing from cold soaked fuel can change the wing’s surface enough to disturb the smooth airflow that creates lift. Even a very thin frost layer increases drag and can raise stall speed, narrowing the safe margin for takeoff. The limit is set to be conservative, allowing only a tiny amount of frost before takeoff is no longer considered safe. If frost is thicker than that, the aircraft should not depart until it’s removed or conditions improve. The other options imply much thicker frost, which would produce larger aerodynamic penalties and unsafe takeoff performance, so the smallest permissible thickness is the one that keeps safety margins intact.