The FAA already prohibits major and regional air carriers from operating with polished frost. Frost can affect the aerodynamics of wings and control surfaces, and the safest action is to completely remove it. Previous FAA guidance recommended removing all wing frost prior to takeoff, but allowed it to be polished smooth if the aircraft manufacturer’s recommended procedures were followed. But manufacturers never published standards of acceptable smoothness for polished frost, and the FAA has no data to determine exactly how to polish frost to satisfactory smoothness.  

“The FAA has advised pilots not to take off with frost or ice contaminating their wings for years because it made good sense,” said FAA Administrator Randy Babbitt. “Now, it’s the law.”  

The new rules include four alternatives to removing frost that operators may consider:  

• using wing covers to prevent frost accumulation on wings

• waiting for frost to melt

• storing the aircraft in a heated hangar

• deicing the wing surface.

The new rules also clarify that affected aircraft must have functioning deicing or anti-icing equipment for flights under Instrument Flight Rules into known or forecast light or moderate icing conditions, or under Visual Flight Rules into known light or moderate icing conditions.  

The FAA published an NPRM in the Federal Register on May 8, 2008 (73 FR

26049). The NPRM proposed to remove language permitting pilots to takeoff with polished frost adhering to the wings or stabilizing or control surfaces. The NPRM also proposed to restructure and to clarify the provisions of those sections. The comment period closed on August 6, 2008. 

As discussed in the NPRM, the FAA has recognized that adverse aerodynamic effects on lifting surfaces begin as soon as frost begins to adhere to the surfaces. For example, the presence of frost may: (1) reduce a wing’s maximum lift by 30 percent or more; (2) reduce the angle of attack for maximum lift by several degrees; (3) increase drag significantly; and (4) change unexpectedly the aircraft’s handling qualities and performance.  

The severity of these adverse aerodynamic effects varies significantly depending on: (1) the thickness, density, and location of the frost; (2) the degree of the surface roughness; and (3) the location of the roughness relative to the surface leading edge where significant variations may occur in the local airspeed and surface air loads.