A Frosty Situation

Here we are, on the edge of another season change. The air is cooling, the nights are crisp, and the leaves are starting to turn. Now is the time to start thinking ahead to the days of winter. As a pilot, this can mean more days of bad weather and less days for flying. Winter brings with it its own set of flying challenges. We have much colder temperatures both on the ground and aloft. Anytime we have the combination of cold temperatures, moisture, and an aircraft surface, this can be a potential problem. We want to look at frost specifically here. There is nothing more frustrating that showing up at the airport on a brisk winter morning to find the airplane covered with a layer of frost. It may look harmless; after all, its only a thin layer. But that thin layer can literally be the difference between life and death for us.

In the many studies done on frost, it has been found that a thin layer of frost, the thickness of medium coarseness sandpaper, will reduce lift by 30 percent and increase drag by 40 percent. In the smaller general airplanes we fly, we do not have the excess power to overcome that loss of performance. That doesn’t stop some pilots from trying it each winter and finding out the hard way that they still can’t overcome the excess weight and drag.

The airlines are required to make sure that the plane is completely clean of any ice/frost buildup before they fly. The same rules legally don’t apply to us, but it makes sense that the only safe airplane is a clean one. Even if it is legal for us to fly with frost, if something does happen, the FAA will still probably find you guilty of careless or reckless operation which is a violation of FAR 91.13

So now that we hopefully agree that frost and flying don’t mix, what can we do about it? If your airplane is parked in a hanger, you shouldn’t have any problems. If it is left out overnight and has a layer of frost, our options are to clean it off or wait to fly another day. A layer of snow or loose frost can be fairly easily cleaned off with a broom or ice brush, but care must be taken to not damage paint. At some airports you can have the plane de-iced with a glycol solution, but that is usually an expensive option. If that is not available, we can use automotive de-icer in a can. If you know you will have frost to deal with ahead of time and are set up for it, you can use Polypropylene antifreeze, the pink stuff used in RV’s. When sprayed on from a small garden sprayer, it can be quite effective (composite aircraft owners should test this on an out-of-the-way area first to make sure it doesn’t stain). If you pull the plane into a heated hanger for a bit to melt if off, make sure we clean all the water off before we take it back out. We don’t want all the just melted frost to re-freeze.

For further information, check out this ASF Safety Brief PDF.