Cessna 500 N511AT

During the landing descent in instrument meteorological conditions , the copilot of the Cessna 500 noticed that the windscreen was picking up a trace amount of rime ice. Neither crewmember saw any ice on the wings, and the crew did not activate the deicing boots. The approach seemed normal until reaching approximately 100 feet above ground level, when the crew experienced what the copilot described as a "burble," and the airplane rolled "steeply" to the right. The pilot stated that there was "no buffet and no warning." The crew attempted to recover, but were unsuccessful, and the right wingtip struck the runway overrun area. Postflight inspection revealed "light rime ice" on the wings, horizontal stabilizer, and radome. The airplane was certificated for flight into known icing conditions, but no ice detector, or stall warning system was installed. The Citation 500 was certificated with full span deicing boots on the wing leading edge, but this airplane had been modified with electrically heated anti-ice panels on the inboard wing leading edge. The deicing boots had no automatic or continuous mode. Both pilots had taken Federal Aviation Administration (FAA) approved systems training for the Cessna 500. The pilot stated that he had heard about "ice bridging," at the training provider and his company. The copilot stated that "unless you have 1/4 to 1/2 inch of ice" the boots should not be activated. A review of the Cessna model 560 airplane flight manual (AFM) revealed that like the Cessna 500 operating manual, it advised pilots to wait for ice to build before inflating the pneumatic de-icing boots. Both the study guide and the AFM stated that, "Early activation of the boots may result in ice bridging on the wing." In 1996, the FAA conducted icing evaluations of the Cessna 560. These evaluations resulted in modifications to the stall warning system to increase stick shaker speed in icing conditions, but did not change the procedures for pneumatic de-ice boot operation. In 1997, the Safety Board recommended that, "leading edge deicing boots should be activated as soon as the airplane enters icing conditions because ice bridging is not a concern." A 1997 industry workshop reported that there was no substantiation for the phenomenon of ice bridging. In 1999, the FAA proposed several airworthiness directives (ADs) on 17 airplane models (including Cessna 500, 501, 550, 551, and 560 ) that would have required manufacturers to change the AFMs so that pilots would be required to inflate de-ice boots as soon as ice accumulation began. Cessna Aircraft Company succeeded in convincing the FAA to withdraw the proposed ADs. In December 2002, the FAA issued advisory circular AC 91-74, which stated that there were few, if any, documented cases of ice bridging on modern boot designs. In February 2005, the Safety Board investigated an icing accident involving a Cessna 560, and review of the AFM again revealed guidance that stated that the pneumatic de-icing boots should be activated when ice is 1/4 to 1/2 inch thick. In December 2006, the FAA released a report stating that test results supported "the activation of lifting surfaces" deicers at the first detection of ice formation on the aircraft's lifting surfaces and for the operation of pneumatic deicers in an automatic cycling mode." Although more than 10 years have passed since it was established that ice bridging does not occur, the FAA has not taken any regulatory action, and Cessna Aircraft Company has only removed the references to ice bridging in it's AFMs but, still advises to wait until the ice thickness is 1/4 to 1/2 inch before activating the surface de-ice. Since 1982, the Safety Board has investigated 43 icing occurrences involving turbine-powered airplanes. These events have resulted in 201 deaths and 16 serious injuries. In the past 4 years, the Safety Board has issued 18 recommendations and one Safety Alert related to icing. As of June 2008, actions to reduce dangers to aircraft flying in icing conditions remain on the Safety Board's 10 Most Wanted List. The Safety Board has classified the FAA response to this issue as "Unacceptable."

Quoted verbatim from the NTSB record.