One recent Saturday morning, a member of our editorial staff tried to get an early start on a planned cross-country. It proved impossible—not because of low weather or mechanical trouble, but because she arrived on the ramp to find her airplane coated in heavy frost. It was too solid to wipe away with rags, and it would be hours before the sun would be high or strong enough to melt it off. Twenty minutes and $120 worth of de-icing fluid later, she was finally on her way—regretting that she hadn’t thought to request transient hangar space the night before. It would have been faster, cleaner, and cost less than half as much.
Still, she was wise to cope with the delay and financial distress rather than trying to cut corners. No sane pilot would think about trying to fly off in an airplane covered in a quarter inch of clear ice, but that wouldn’t degrade aircraft performance as much as a layer of frost the thickness of a fingernail. It’s the extreme demonstration of the fact that the perils of ice don’t lie in its weight, but in the unpredictable ways it disrupts airflow. Because of its rough texture, a few ounces of the stuff—enough to make you scrape the windshield of your car—can cause a 30-percent loss of lift and a 40-percent increase in drag. The latter is the reason it’s necessary to remove the frost from the entire airplane, not just the wings and tail.
Perhaps because we’re used to just scraping the windows while the engine warms up, then driving off, pilots regularly underestimate the hazard of leaving visible frost anywhere on the airplane. (It is primarily a fixed-wing problem: Since helicopters don’t depend on forward airspeed for lift, frost on the fuselage is less of a problem provided it’s completely removed from the rotor blades.) In fact, the loss of climb performance can be devastating. In January 2015, a lightly loaded Cessna 182—just the pilot and one passenger on board—tried to take off from Santa Fe, New Mexico. The pilot had “scraped the frost off the windshield and…wiped off the frost from the wings,” but apparently didn’t clean the rest of the airplane. The Skylane attained an altitude of about 50 feet before banking hard to the left and stalling into the runway. Thankfully, both the pilot and passenger escaped unhurt.
The Santa Fe airport sits at an elevation of 6,348 feet, but higher altitude merely aggravates the basic problem. A solo pilot was unable to get a 150-horsepower Super Cub off the ground in Wasilla, Alaska (elevation 353 feet msl) because he failed to clear “heavy frost” from the airplane. (In one of those only-in-Alaska details, the takeoff attempt was made from a city street, not a runway.) Similarly unsuccessful takeoffs have been tried in Anchorage, elevation 136 feet; Lewiston, Maine, elevation 287 feet; and Chesapeake, Virginia, elevation 18 feet. Density altitude wasn’t a factor in any of those.
Knowing that the frost has to go is the first step. Knowing how to get rid of it comes next. The Anchorage pilot had the shrewd idea of pouring hot water over his Skyhawk, then trying to remove it with a squeegee. Unfortunately, enough remained to form a fresh layer of ice on the skin. Some also got into the aileron hinges and froze there. He wound up stalling into power lines and trees a half-mile from the runway’s departure end. If it’s too tenacious to brush off, then warmer ambient temperatures, a heated hangar, or approved de-icing fluid are the only tenable solutions.
One source of pride (or maybe relief) is that the flight training industry seems to do a pretty good job of managing this particular risk. A quick search turned up just one instructional accident in the past 15 years in an undefrosted airplane. In that one, the “student” was a commercial pilot taking familiarization training in a de Havilland Beaver floatplane. Not surprisingly, the accident occurred on their first flight of the day. After stalling into a marsh from an altitude of 50 feet, the 9,600-hour CFI noticed “an accumulation of frost on the wings.” Surely both should have spotted that on preflight.
Our editor’s experience leads us to wonder whether opportunities to fill underused transient hangars might be going overlooked. Discounts are always attractive, though we can understand a reluctance to devalue the going rates. A better approach might be to compile an email list of pilots who’d appreciate an update when space is available and frost is in the forecast. Most owners planning early departures would prefer to pay less and leave on time than pay more to leave later—and many might choose to scrub the flight before parting with that $120.
David Jack Kenny is aviation safety manager for the AOPA Air Safety Institute.