Freezing rain that fell on O'Hare International Airport on Tuesday coated everything it touched with a thin layer of ice.
As temperatures fluctuated above and below the freezing mark, many aircraft had to be de-iced before takeoff. Although that led to additional delays on a day when hundreds of departures were canceled, it still allowed many flights to proceed despite the nasty conditions.
The success, albeit limited, was the result of a carefully choreographed production among the airlines, the Federal Aviation Administration and city aviation officials.
It could not have been accomplished without roving teams of ice-busters wearing waterproof suits and smelling like vegetable oil, an ingredient used in de-icing fluids with names such as Kilfrost.
Once an airliner was loaded and its doors shut, as many as three de-icing trucks went to work thawing out the wide-body jet as passengers inside pressed their faces against windows to see the colored fluids splash onto the wings.
Each de-icing takes about 20 minutes, depending on the size of the aircraft. The plane then immediately pushes back from the gate in a race against the clock to take off before the de-icing fluids stop working.
Even planes landing in warm climates such as Miami or Palm Springs in the California desert sometimes will require de-icing because condensation that builds up during flight can turn to frost. At cruising altitude, the temperature outside an aircraft can plunge to 45 degrees below zero Fahrenheit.
About 95 percent of the de-icing operations at O'Hare typically involve snow, making Tuesday's struggle against an ice storm advancing across the country a bit unusual, officials said.
"We don't get a lot of freezing rain in northern Illinois," said Capt. Jay Rud, a chief pilot for American Airlines at O'Hare. "This is only the second event this winter."
American gave the Tribune access to its behind-the-scenes operations at O'Hare on Tuesday to offer a glimpse into how the de-icing process works on a chaotic weather day.
Ray Morgan, the de-icing manager for American at O'Hare, began his shift at 5:30 a.m. in a squat mini-tower that sits atop Terminal 3 and overlooks the airline's aircraft gates. Morgan monitored and reacted to cycles of ice turning to rain, and rain turning to ice.
Outside the mini-tower, crews floating several stories high in the buckets of de-icing trucks pointed their hoses at McDonnell Douglas Super 80 jets parked at the gates.
"The buckets sway a lot and you get soaked," Morgan said. "It's a job where you cannot be afraid of heights."
The first coating on each plane was about 300 gallons of a pink vegetable-oil based alcohol that cleared away ice and other contaminants. It was followed by about 100 gallons of a green chemical cocktail of anti-icing fluids that prevent icing for up to two hours, in case planes are forced to sit that long waiting to take off.
A wide-bodied jetliner such as a Boeing 777 could need as much as 900 gallons of the pink Type I de-icer and 400 gallons of the green Type 4 anti-icer, Morgan said.
American, which handles about 40 percent of O'Hare flights, could go through 100,000 gallons of de-icing fluids on a single day like Tuesday, Morgan said. It isn't inexpensive for airlines, with the cost of the fluids ranging from $5 to $8 a gallon.
The chemistry represents a remarkable improvement over the de-icing fluids used as recently as a decade ago. Back then, de-icing fluids were effective for only about 20 minutes and planes delayed on the ground for takeoff often had to get out of line and receive a fresh dousing.
One of the worst icing accidents occurred on Jan. 13, 1982, at Reagan National Airport in Washington. The pilots of an Air Florida jet that was delayed for departure failed to request additional de-icing. Ice formed on the wings, and the plane crashed during takeoff, killing 78 people, including four in vehicles on the ground.
Tuesday's weather at O'Hare would have been a lot easier to deal with if Mother Nature had just made up her mind. But late in the morning, the color graphic on Morgan's computer screen showed the airport right on the border of freezing rain and rain. Snow was farther north in Wisconsin and the makings for a possible ice storm were hours away from the Chicago region.
"Storms are dynamic experiences, so you must have a dynamic operating plan based on forecasts," said American spokeswoman Mary Frances Fagan.
If given a choice, the airlines would choose snow over ice any time. Snow can be blown away and plowed, while ice is harder to remove.
The airlines must ground their planes in conditions of ice pellets, moderate and heavy freezing rain, heavy snow and hail. The FAA prohibits any ice on wings and other lifting surfaces of aircraft.