1994. A twin-engined French-made ART commuter plane is approaching O'Hare in Chicago but it's busy so they are put in a holding pattern through cold and cloudy skies over Indiana. Everything is normal. Some ice is noted but the rubber boots that de-ice the wing's leading edge are turned on, as they should be. Without further warning, the airplane rolls to the right, plummets, and crashes with no survivors in a farmer's field.
Investigators go to extraordinary lengths to test the most likely hypothesis -- that thick ice formed on the wings BEHIND the de-icers because the airplane was flying through droplets of supercooled liquid. That means water droplets that are below freezing but don't turn from liquid to solid unless they hit something solid, in this case the wings. And they tend to build up behind the de-icers so they continued to accrete as the ATR flew round and round in circles through these icy clouds.
The French manufacturers blame the pilots. The NTSB blames the manufacturers and places restrictions on ATR flights through icing conditions. Most of the ATRs are moved to the South, where icing is less likely. Basta! The manufacturers respond by making the de-icing boots larger and issuing warnings.
As usual the technical details regarding supercooled liquids (like glass) and the function of de-icing mechanisms is explained in such concise but simple terms that even a non-techie like me can understand them.
Investigators go to extraordinary lengths to test the most likely hypothesis -- that thick ice formed on the wings BEHIND the de-icers because the airplane was flying through droplets of supercooled liquid. That means water droplets that are below freezing but don't turn from liquid to solid unless they hit something solid, in this case the wings. And they tend to build up behind the de-icers so they continued to accrete as the ATR flew round and round in circles through these icy clouds.
The French manufacturers blame the pilots. The NTSB blames the manufacturers and places restrictions on ATR flights through icing conditions. Most of the ATRs are moved to the South, where icing is less likely. Basta! The manufacturers respond by making the de-icing boots larger and issuing warnings.
As usual the technical details regarding supercooled liquids (like glass) and the function of de-icing mechanisms is explained in such concise but simple terms that even a non-techie like me can understand them.
