Starting Jan. 30, 2010, all aircraft contaminated with "polished" (smooth) frost on wings, as well as on stabilizing and control surfaces will be prohibited from takeoff, according to the FAA final rule published today.

Majors and regionals are already prohibited from operating aircraft contaminated with polished frost. FAA's final rule removes language in Parts 91 (subpart F), 125 and 135, which allowed operators to take off with frost that was polished to make it smooth -- and requires operators to remove any frost adhering to critical surfaces before takeoff.

The final rule also restructures language in parts 91, 125 and 135 to clarify that aircraft must have functioning deicing or anti-icing equipment to fly IFR into known or forecast light or moderate icing - or under VFR conditions into known light or moderate icing conditions.

Previous FAA guidance recommended removal of all wing frost prior to takeoff, but allowed frost to be polished smooth if the operator followed the manufacturer's procedures. However, aircraft makers have never published standards of acceptable smoothness, nor is there supportive data to determine how to polish frost to a satisfactory smoothness, according to FAA.

The agency makes four recommendations for operators to use to comply with the rule: using wing covers to prevent frost accumulation -- which is the least costly method; waiting for frost to melt; keeping aircraft in a heated hangar, or deicing the wing surface.

The changes will affect 57 operators and 188 aircraft. Assuming operators would choose using wing covers, FAA estimates the cost of compliance to operators in the 2009-2018 period at aboout $164,000.

Total benefits in the same 10-year period are projected at $980,000. The presence of frost can cause adverse aerodynamic problems, including a 30% or more reduction in maximum wing lift, significant increase in drag and several degrees' reduction in the attack for maximum lift, notes FAA. Reducing dangers to aircraft flying in icing conditions is one of the NTSB's "Most Wanted" list safety improvements.

Photo credit: Airbus