The NTSB recently issued a Safety Alert advising pilots that the procedures they have been taught regarding the use of de-icing boots may not be safe, but the National Business Aviation Association said this week that operators "should continue to base their decisions about de-icing on their experience and judgment." The NTSB alert said that pilots shouldn't wait "for a prescribed accumulation of leading-edge ice before activating the de-ice boots because of the believed threat of ice bridging." Ice bridging has never been implicated as the cause of an accident, and is extremely rare, and may not exist at all, the NTSB said, and delaying the use of the boots has been noted in "numerous incidents and accidents." NBAA said it believes "proving the existence of ice bridging after an accident is difficult, and many documented cases resulted in successful outcomes due to the skill and professionalism of the flight crew." Misuse of the de-icing boots was cited as a factor in the NTSB report on the crash of a Cessna Citation 560 in Pueblo, Colo., in February 2005, in which all eight people on board were killed. At that time, the NTSB asked the FAA to require all manufacturers and operators of airplanes equipped with pneumatic leading-edge de-ice boots to revise their manuals and training programs to emphasize that the boots should be activated as soon as the airplane enters icing conditions.
The safety board also asked the FAA to require that all pneumatic de-ice boot-equipped airplanes certified to fly in known icing conditions should have a mode that would automatically continue to cycle the boots once the system has been activated.