FAA clarifies ‘polished frost’ rule

 - November 6, 2006, 7:09 AM

The FAA issued a new Safety Alert for Operators (SAFO 06014) that seeks to clarify the conditions under which pilots can take off with frost adhering to airframes. At the same time, the SAFO might complicate the pre-takeoff decision-making process because it reminds pilots that takeoff with frost adhering to lifting surfaces and flight controls is legal.

FAA regulations (Part 91.527 and 135.227) permit takeoff with frost on the wings or stabilizing or control surfaces “if the frost has been polished to make it smooth.” While this seems to be a clear statement, the SAFO recommends that pilots do not take off with polished frost unless they have complied with an aircraft manufacturer’s specific procedure for preparing a frost-covered aircraft for flight.

The regulations are unambiguous, however, and make no mention of any requirement to adhere to manufacturer procedures. Lacking any mention of frost-mitigation procedures in the flight manual, pilots are under no obligation to do anything other than what the regulations require.

A SAFO provides safety recommendations but is not mandatory. While SAFOs are targeted at commercial operators, the FAA has used them to issue recommendations that affect all types of operator. SAFOs are available at www.faa.gov/othervisit/avia tionindustry/airlineoperators/airline_safety/safo.

SAFO 06014 is one page long and indicates that the FAA is concerned about takeoffs with frost on the wings and/or control surfaces. Using terminology such as “pending rule changes,” the SAFO hints that the FAA might be considering changing the regulations but meanwhile, the agency would prefer that pilots remove all frost before takeoff, unless complying with a procedure sanctioned by the aircraft manufacturer.

According to the SAFO, the regulatory basis for the frost-polishing rules dates to “at least 1960,” originating in a Civil Air Regulation draft release. While the SAFO seems to contradict FAA regulations, the FAA’s advice is clear: “Since 1960, operational experience and accident history have shown that contamination of any kind can adversely affect the aerodynamic properties of an airfoil, and that the safest course of action is to completely remove all contaminants from wing and flight control surfaces.”

AIN asked aircraft manufacturers if any of their aircraft have AFM-sanctioned frost-polishing procedures. By press time, only Cirrus and Gulfstream had responded, and both indicated that frost polishing is not approved.

“We don’t have such a procedure,” said a Cirrus spokeswoman.

“We recently reviewed this with the FAA (Atlanta Aircraft Certification Office),” said a Gulfstream spokesman. “Our cold weather and de-icing procedures call for removal of frost prior to takeoff and do not allow polishing of frost.”

AIN also asked readers of the AINalerts for opinions on frost polishing and whether they were aware of aircraft on which such polishing is permitted. Most respondents view frost polishing as a poor substitute for complete removal of all contamination, although one pointed out that the Hawker 800 AFM permits some wing frost due to cold-soaked fuel. “Let common sense, balanced decision making and experience guide the de-ice decision, not regulation,” wrote pilot David Mann.

The rest of the comments were uniformly against taking off with any frost adhering to the airframe.

• “The laws of physics, aerodynamics and so on do not alter just because the regulations or company operations manual allow for a particular procedure to be followed. All [contamination] must be removed and the aircraft must be clean before takeoff.”

• “The FAA allows ice to be polished. That in itself is against its own regs and is disgraceful. When you take off with anything clinging to an airfoil, you are a test pilot. You are flying an airfoil that is different from the one designed for your aircraft. As for polishing the ice, there is no statement as to how much accumulation is OK. Polishing ice is a joke.”

• “We operate a Learjet 36A from EHGG, a small airfield in the Netherlands. We keep the Learjet in the hangar, already refueled. Just before departure we tow it outside and get airborne immediately. We do not take off with any frost/ice on the wings/controls/T tail, even if it is a little.”

• “No frost any time! Remove all frost, snow and ice. We are not test pilots exploring the envelope.”

• “As a retired FAA inspector and an ATP with CFI/II, ASEL, AMEL and more than 35 years experience operating aircraft throughout the U.S. in all weather conditions, I still cannot believe that the regulations do not prohibit aircraft from taking off without all ice, snow, frost and so on removed before flight.”

AIN asked the FAA if it could identify any aircraft for which the AFM permits frost polishing. An FAA spokesman responded, “The FAA is currently unaware of any manufacturer that has an approved polished-frost procedure.” He added that the FAA is also polling manufacturers to learn their policies regarding frost polishing “to ensure we have the most current information on file.”

The SAFO is intended to emphasize the FAA’s current policy regarding frost polishing, that operators should use the procedure only when authorized by the aircraft manufacturer and not just because the regulations say it’s approved.

“Data analysis and research conducted by the FAA indicates that contamination from any source could be detrimental to aircraft performance,” the spokesman told AIN. “It is not the intent of the FAA, however, to unduly restrict a certificate holder’s ability to conduct operations. If a manufacturer has, or was to develop, a procedure for polishing frost on critical surfaces that resulted in no change to the aerodynamic properties of an aircraft and achieved an equivalent level of safety, the FAA would not preclude an operator from using such an approved procedure.”

A search through the FAA/NASA Aviation Safety Reporting System (ASRS) database showed that many pilots are concerned about taking off with airframe frost and there is still plenty of confusion about regulatory and operational restrictions.

Some pilots had lengthy discussions about how to measure the depth of frost on MD-80 wings; up to one-eighth inch of frost is permitted in specific areas near fuel tanks under certain conditions. In more than one case, pilots had heated arguments with ground personnel about the need to remove frost before takeoff. Airline pilots turn out to be surprisingly compliant when passengers reported contamination on wings before takeoff, and in almost every such case, they taxied back and asked de-icing crews to remove the contamination.

Interestingly, many of the ASRS reports involve flight crews trying to assess wing ice by looking out of passenger windows. This is a risky procedure and violates current recommendations on contamination assessment. In September, the NTSB issued a safety alert www.ntsb.gov/alerts/SA_006.pdf urging pilots not to take off with snow, ice or frost accumulation on the wing surface. The alert noted, “The NTSB believes strongly that the only way to ensure that the wing is free from critical contamination is to touch it. Pilots should be aware that even with the wing inspection light, the observation of a wing from a 30- to 40-foot distance, through a window that was probably wet from precipitation, does not constitute a careful examination.”

“I believe this SAFO to be a proactive attempt by the FAA at mitigating a growing myth that takeoffs with polished frost on wings are a sanctioned procedure,” said Antonio Cortes, assistant professor with the Department of Aeronautical Science at Embry-Riddle Aeronautical University.