Flying in Winter Weather? Don’t Let Your De-Icing Spray Expire

A new system aims to end costly delays on the runway during ice storms.


With a major winter storm bearing down on the U.S. East Coast this weekend, here’s a chilling thought: When Chicago’s Midway airport got hit with freezing weather earlier this winter, nearly 90 Southwest Airlines flights had to be canceled due to delays with de-icing operations.

The folks at Vaisala hope to fix that.

The Finland-based environmental services company is developing a new system called CheckTime designed to make sure the chemical de-icing fluid used at airports—which has a limited “shelf time” before losing its effectiveness—doesn’t expire before takeoff.

CheckTime trials are currently under way with several major U.S. and European carriers, says Nick Demetriades, Head of Aviation Digital Solutions at Vaisala. If the trials go well, he expects that “airlines will be taking this service into much greater use.”

If you’ve ever come out to your car on a cold morning to find the windows glazed over with frost, you’ve experienced ground icing. While a quick scrape or shot of hot air from the defroster is usually enough to get you on your way, the process is much more complicated for aircraft.

Ground frost, sleet, ice pellets, freezing rain, and snow are all capable of producing icing on an airplane’s surface, says Memphis-based Senior Aviation Meteorologist Jeremy Smith. “Icing increases the drag and weight on the aircraft while decreasing lift,” he says. “If that happens, it…can prevent the aircraft from taking off.”

It doesn’t take much ice, either. According to the National Transportation Safety Board, just one ice particle the size of a grain of salt per square centimeter over an airplane’s surface is enough to affect lift and prevent flight.

In order to combat this, aircraft go through a thorough de-icing process before takeoff. Sprayed-on chemicals remove any ice that’s present and prevent new ice from forming. Unfortunately, these chemicals are only effective for a finite period—typically an hour or so. If the airplane fails to take off before their effectiveness expires—known as the holdover time—the whole de-icing process has to be done all over again.

“One of the worst scenarios for an airline, and for us as passengers, is you go through the de-icing process, then you sit in line at an airport like JFK or Chicago O’Hare and your protection from the fluid runs out,” says Demetriades. “Then you have to go back and do it again, and get in line again. The delays cascade, so airlines want to reduce re-sprays.” (The decision not to get in line for a second de-icing was a contributing factor in the 1982 Air Florida tragedy, when a 737 crashed into a bridge in Washington, D.C., killing 78.)

CheckTime reduces delays and re-sprays by providing pilots with up-to-the-minute estimates of how much holdover time is remaining based on current weather conditions as measured by a pre-installed suite of sensors. The system monitors wind speed, direction, temperature, humidity, and how much water is present.

At present, pilots awaiting takeoff in winter weather typically calculate holdover times manually, using FAA holdover tables based on the type of de-icing mixture and current weather conditions. “We determine our holdover times by finding the corresponding fluid mixture, freeze point of the mixture, the strength of falling precipitation, and outside air temperature,” says Joshua Hjemvick, a pilot for a major airline based in the Northeast. “The holdover times derived do not provide an exact end time…it provides a window.”

One of the advantages of CheckTime is that the system automatically recalculates the holdover time based on current weather, which can vary greatly from minute to minute during winter storms, says Demetriades. “One of the huge selling points is allowing airlines to operate when they couldn’t operate before, based on more accurate and more timely weather measurements.”

Hjemvick, although he has yet to use CheckTime himself, thinks the combination of real-time weather monitoring and ending reliance on the holdover tables would be popular among pilots. “Without a question the system would be beneficial,” he says.

If it works as advertised, CheckTime could lead to big savings for airlines. De-icing fluid isn’t cheap—it can cost up to $10,000 to de-ice a midsized jet, according to the National Business Aviation Association. “The case for being able to use less fluid, or the ability to use diluted fluid has already been proven,” says Demetriades.

CheckTime already is in operational service with the UPS cargo fleet, and Demetriades says feedback from the current airline trials has been very promising. “The fact that we have all these major carriers trialing at once, I think it’s a really good sign of the industry recognizing the benefits this kind of technology can provide,” he says.