Thursday, January 23, 2014

Anti-Icing Mythologies

Well-developed ground de-icing/anti-icing mythologies have been developed for the airlines.
         - My misreading of an icing education document

The document said "methodologies" not "mythologies" and that's true for the airlines, but I was anticipating what it was going to say for general aviation. It's not that GA pilots are stupider, just that we aren't supported by the infrastructure the airlines are and we usually have to do our own de-icing. And it always takes place in the stupidly freezing cold, and usually in the dark, because people want their airplane ready to depart at the beginning of the day, but the sun doesn't come up in the winter until it has confirmed that the day is well underway. And even then it only comes up far enough to clock in.

Like the sun, GA pilots' first line of defence against icing is to try to take the winter off. This is actually working pretty well for me these days, especially when combined with our "keep the airplane in a warm hangar" strategy, but when the chips are down I still have to resort to the well-developed mythologies.

Sun will take the ice off, even if the air temperatures are below freezing. In temperatures that are just below freezing, sunlight will warm dark areas enough to melt, or at least soften, the ice on them, and even when it's especially cold the air is dry and the frozen moisture will sublimate into to the air as it warms with the morning. Meanwhile we whack the airplane with brooms or mitten-clad hands to crack the ice and then sweep it to dislodge frost or ice chunks. The official video on not taking off with any ice adhering to your airframe ever recommends sawing a rope back and forth across the surfaces. I've never tried that. Never had a rope. Last year I bought a broom at a northern hardware store, just a regular straw broom, and shared it with a Maule pilot stuck in the same snowfall. When I walked into the office at the end of the trip one of my bosses asked, lightning fast, "What's the broom for? Is that how you got home?" It was too funny to take offense at.

One reason we resort to mythological forces, like windshield antifreeze is that it's available. Most GA airports have no deicing services available at all. Even if de-icing is an advertised service of the FBO on the field, you have to find the phone number and persuade the person who answers to come out and do the work. Let's say you're paid by the hour to do a job that mainly involves driving a fuel truck around and pumping fuel into tanks, plus a bit of sitting in an office and answering the phone. How many hours pay would you want to get up at four am, start a different vehicle that you're not sure is going to work and stand on a ladder spraying poisonous fluids on yourself and some cranky pilot's airplane? If an airport is used by an airline, they may have their own deicers, but generally don't have the staffing, spare fluid, insurance, or billing apparatus to deice other peoples' airplanes. If you happen to be departing shortly after the scheduled airline flight, and have a case of beer handy, you may be able to get a few squirts of the pre-heated deicing fluid from the guys that came out for the flight, but you can't count on that. And you have to know what you're allowed to spray on your airplane and where.

Quick rule of thumb, the odd-numbered ones are okay for me. That is Type I deicing fluid, which looks like thick orange Gatorade, gives virtually no holdover time and can be used on any speed of aircraft is safe and so is Type III. Type III looks like urine, requires a minimum rotation speed of 60 knots, and, if you pay first, has a holdover time sufficient to get you to the runway and airborne in light snow. Holdover time is the time period during which you probably won't get more contamination while standing or taxiing. It's measured from the beginning of the application (i.e. measuring by the area that is treated first). Types II and IV have holdover times sufficient to queue with everyone else on the taxiway at Pearson, but they work by enveloping your aircraft surfaces in cozy ooze, so to use them safely you have to have a rotation speed over 100 knots, to ensure they will shear off before rotation and not interfere with wing performance.

Holdover time is just a mythological luxury for me. In ground icing conditions I need to do everything, including a run up, and then shut down, deice and go right away. That can be a tough call because batteries and starters are not at their best in the cold. If you've got the incantation right to start the engines once in a morning, you don't like to shut down and risk having the magic not work the second time.

1 comment:

europeanPilot said...

You have my sympathies, Aviatrix. In the winter I am really glad to operate from large airports with de-icing trucks readily available...