When Mother Nature throws travelers a curve ball and freezing fog descends over the airport in Medford, Oregon, it can delay takeoffs and landings. But ground crews there and at several other Western airports have an unusual tool at their disposal to bust the fog.
The same dry ice that can create make-believe fog at a theater or a rock concert can also clear away real fog.
"The dry ice collects the moisture in the air and it falls to the ground as just basically snow or ice,” said Howard Volkman, the operations and maintenance supervisor at Rogue Valley International-Medford Airport.
First, they load crushed dry ice into a hopper suspended under a big helium balloon. The 18-foot diameter balloon is tethered with a winch cable to an airport pickup truck.
"We detach from the vehicle and let the tether hang on to it,” Volkman said. “We fly the balloon at about 500 feet."
Volkman said a driver and an operator make loops around the runway with the balloon and its dry ice spreader in tow.
"We're basically driving along five to seven miles an hour and we're clearing a hole in the fog -- just for the airplanes to be able to see the runway,” Volkman said.
Volkman said this fog busting method only works at temperatures of 32 degrees and below. So this is not that useful for airports in coastal cities where it's usually warmer when fog forms.
Reducing cancellations and diversions
Medford Airport Director Bern Case said the staff nicknamed their white balloon Casper, after the friendly cartoon ghost. The nickname was then "reverse-engineered" into an official acronym CASPER - Cable Attached System Providing Effective Release.
CASPER has deployed 14 times this winter. Case described it as "very effective." It reduced flight cancellations to near zero.
"It's all about dollars,” Case said. “Cancellations and diversions for airlines are very expensive, not only to the airlines, but if a person is trying to get to Tokyo and they can't get out of here, it can ruin an entire trip."
Regional airline Horizon Air, operating under the Alaska Airlines brand, has the most scheduled flights at Medford airport. Horizon Air flies Bombardier Q400 turboprop planes which need a half-mile minimum runway visibility to land with instrument assistance and at least one-quarter mile visibility to takeoff.
"Medford is plagued with freezing fog certain times of the year and CASPER definitely improves our operational performance when the airport has the chance to use it," Horizon Air Air Traffic Liaison Kevin McKennon said. The Q400 captain said via email that he looks forward to refinement and expanded use of the system.
Case said the Medford airport provided the blueprints for the one-of-a-kind balloon system to the airport authorities in Spokane and Anchorage. CASPER is on its eighth winter of tweaking and improvement.
More fog-fighting systems
In Missoula, Montana, airport ground staff try to clear away freezing fog, but not with a balloon-based system like Medford invented. When the need arises in Missoula, two to four trucks sweep down the runway spraying supercooled liquid carbon dioxide to disperse fog that impedes regional jets.
Missoula Airport Director Cris Jensen said his airfield uses its 11-year-old fog dispersion system about ten times in an average winter, but less often this year as luck would have it.
"What the liquid CO2 does, it basically cools the fog in the air. It crystallizes and essentially precipitates out," Jensen explained. He said it is not 100 percent effective when the fog settles in the Western Montana valley, more like 70 percent effective. But he said that success rate easily justifies the effort.
Jensen said Kalispell, Montana's airport has adopted Missoula's fog clearing system and a representative from Pullman-Moscow Regional Airport came for a look about a year ago.
New navigation technology
Medford’s airport operations team fabricated the CASPER system themselves. Their balloon first flew in the winter of 2010. The apparatus achieved wider renown last year when a delegation organized by the North American Weather Modification Council visited. Since then, Case said he has fielded inquiries from counterparts as far away as Russia.
But some airports have already moved past actively fighting the fog.
At Ted Stevens Anchorage International Airport, manager John Parrott said his airport inquired about Medford's system when it was first introduced, which was right after the Anchorage airport stopped using a hired small plane carrying shaved dry ice to attack fog.
"Using their (Medford's) technique with a pickup truck would have been significantly cheaper than having an airplane fly it over. But even at that, we just no longer had a requirement,” Parrott said. “The older aircraft that needed the help have all been mothballed."
Anchorage and other Western airports such as Salt Lake City, Boise and Reno that once actively fought winter fog, no longer do. Parrott said recent advances in precision navigation technology mean newer jets can take off and land with barely any visibility.
"We talked to the airlines and we all came to the conclusion that there just was not a good business case for continuing this,” he said.