Prevailing Cultural / Organizational Factors

At the time of this accident there was an industry-wide belief that for deicing (boot) systems to effectively remove ice from protected surfaces, an ice buildup to a discrete thickness was required. This necessitated flight crews being aware that they were in icing conditions, and being able to accurately assess the amount of ice buildup on the airplane. Once the procedurally recommended thickness had been attained, the system could be activated and the ice would be removed.

There was a concern throughout the industry that premature actuation of the deicing system would result in a phenomenon known as ice bridging, which would result in plastic deformation of newly formed ice, and formation of a "bridge", or void, between the boots and the accreted ice. The ice bridge would be the same shape and volume as the expanded deicing boots, effectively forming a new wing leading edge. As the ice bridge would basically be a mold of the expanded deicing boots, the deicing system would become ineffective at removing the ice, and the contamination would continue to accrete on this bridged section of wing. Over a relatively short time period in icing conditions, ice could then build on top of this "bridge" to a thickness sufficient to produce profound effects on airplane performance and handling.

Subsequent to this accident, several studies concluded that for the modern class of deicing boot systems, activation of a boot deicing system at the first indication of icing conditions (prior to any actual ice accretion) would prevent ice accumulation and provide better protection for the wing. A 1997 icing conference addressed the subject of ice bridging and disseminated these conclusions to industry at large, resulting in recommendations to activate deicing systems upon entry into icing conditions, and many operators/manufacturers have adopted this philosophy.

Article on ice bridging, © Aviation International News Online, April 1, 2007.

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