The UK’s Air Accidents Investigation Branch (AAIB) is recommending that the FAA change its regulations to make it illegal for aircraft to take off with so-called “polished frost.” The AAIB also urged all aviation authorities that follow the FAA’s current practice to delete references to polished frost within their regulations and expunge the term from approved operations manuals.

Under FAR 91.527(a)(3) and Part 135.227 (a)(1), pilots can take off in an airplane with frost on the wings or other control surfaces if the frost has been “polished to make it smooth.”

The AAIB’s recommendations follow its investigation into the fatal crash of a Challenger 604 at Birmingham International Airport on Jan. 4, 2002. Investigators concluded that the pilots elected not to have the airplane de-iced and that frost on the wings caused the jet to go out of control and crash on takeoff.

“It is considered that the concept of ‘polished frost’ is particularly inappropriate and potentially dangerous to modern aircraft types and detracts from the importance of strictly observing the clean-wing principle,” the final report said.

The AAIB issued the report and recommendations last August, but it wasn’t until the fatal crash of a Challenger 601 in Montrose, Colo., on November 28 last year that the FAA acknowledged publicly that it was reviewing the AAIB’s recommendations. According to the NTSB, the pilots of the Challenger 601 declined to have the aircraft de-iced; however, investigators have not yet determined whether icing was a factor.

In support of the AAIB’s recommendation, the international organization Flight Safety Foundation in Alexandria, Va., said the polished frost provisions of Part 91 and Part 135 are “misleading and can instill a false sense of security that a little contamination is acceptable.”

Moreover, the FSF noted that the Part 91 and Part 135 provisions contradict the clean-aircraft concept of the FARs for airlines. FAR 121.629 states, in part, that “no person may take off in an aircraft when frost, ice or snow is adhering to the wings, control surfaces, propellers, engine inlets or other critical surfaces of the aircraft.”