If you've been flying at all this winter I suspect you've run into some delays due to the weather.
I've already had to deice more times than I care to this winter and there appears to be no end in sight.
You may be sitting in the terminal right now waiting out a 2-hour departure delay. I can't make it go any faster, but I can help with the "how" and "why".
Airplanes don't like ice. Period. Even a thin coating of ice on the aircraft adds weight, more importantly it adds drag and most importantly it destroys lift. How much? Well, we don't know, and that's part of the problem.
It's certainly not going to make it fly better. Millions of dollars and countless hours of engineering and wind-tunnel testing have gone into designing that airfoil. That inch of snow sitting on it certainly won't improve it any.
If you take off with ice or snow on your plane, congratulations, you're now a test pilot! Nobody has ever flown that particular aerodynamic configuration before. You might as well throw your takeoff data out the window.
So we have two problems to solve. First we need to get all the crud off the airplane. Then, if there's still precipitation we need to keep the snow and ice off the plane long enough for us to takeoff.
Clearing the snow and ice off the plane requires deicing. This is normally done by spraying the plane with a heated mixture of water and glycol called "Type I". Depending on the airport this may be done at the gate or at a designated spot on the ramp.
A deice truck looks a lot like the trucks the utility company uses to work on power lines. It has a long hydraulic arm, with a cab on the end. A person sits in the cab and sprays deicing fluid from a nozzle. I've seen as many as four trucks used to deice a jet.
You don't want to breath the fumes from deicing fluid so we shut down the air conditioning system while this process takes place. That way the fumes won't be sucked into the plane.
Hazards Associated With De/Anti-icing Fluids
Exposure to ethylene glycol vapors in poorly ventilated areas may cause throat
irritation, headaches, nausea, vomiting, and dizziness. Avoid breathing mists or
spray contact with eyes, or prolonged contact with the skin.
But what if we've still got snow or sleet coming down? Now it gets a bit trickier.
To keep plane from icing up again we have get a second squirt of a different type of fluid. This is normally done with "Type II" or "Type IV". These are thick fluids that stick to the airplane and keep snow or ice from building up on the plane. By the time we reach takeoff speed the fluid will have been swept away by the airflow, so we don't need to worry about it effecting our performance. It sticks around just long enough to do its job.
Once we've had the anti-icing fluid applied we look in a chart to find our "holdover time". This is how long we have before snow or ice will start building up on the plane again. It varies by type of fluid used, temperature plus type and intensity of precipitation. The fluid can only protect us for so long. If we don't get airborne by that time we'll have to go back and get another squirt.
Let's take a look at the chart. Let's suppose it's 27 degrees F outside and it's snowing.
We were deiced and then squirted with a 100% mix of Type IV fluid. According to the chart our holdover time is between 35 minutes and 1 hour + 15 minutes. Why is there a range? That leaves some of it up to our judgement based on how hard we think it's snowing.
Ice on the ramp and taxiways gives us problems as well. Airplanes will slip on ice just like your car will and once 200,000 pounds starts to slide it doesn't want to stop. We're going to taxi slowly and we'll especially slow down for the turns. We'll try not to taxi too close behind another jet because we don't want them to blow slush onto our freshly deiced airplane. We may keep our flaps up until just before taking the runway. They tend to collect snow and slush kicked up by the tires.
If there's any snow or ice on the runway it will affect our stopping ability but we'll have accounted for that in our takeoff/landing data calculations. Normally the airport will try to keep the runways plowed and swept. This may reduce the number of runways available which may delay us even further.
How do we know that ice is forming on the plane? Some planes have ice detectors. Don't ask me how they work, I've never flown a plane that had them.
We use the very high-tech method of looking at the windshield wipers. That's where ice is most likely to form where we can see it. Especially on the nut that attaches the wiper arm. So don't be alarmed if we talk about checking our nuts for ice. At night we'll occasionally shine a flashlight out the window at it. Like I said, very high tech.
We normally only encounter icing during the climb or descent. For us it's mostly a matter of remembering to turn the anti-ice on. I don't want to be the person who trashed a multi-million dollar Rolls Royce engine by letting ice get sucked through it.
Anything important on the plane is heated one way or another to keep ice from building up. Windshields, pitot tubes, static ports and drain ports are normally electrically heated. We can also take hot bleed air from the engines and use it to heat the engine inlets and even the wing leading edge if need be. The engine and wing anti-ice slightly increases our fuel consumption, which is why we don't just fly around with it on all the time.
So what happens to all that deicing fluid? That depends. Some airports have a dedicated deicing "pad" where they collect the used fluid and recycle it. Others just let it run into the storm drains where it probably finds its way into the local streams and rivers. I'm no expert, but I can't imagine that's good for the environment.
One last thing. If you should happen to find yourself walking on the ramp in the winter, take heed:
WarningI learned that lesson very painfully once. Once second I was doing my walk-around and the next I was flat on my back staring up at the sky. Deicing fluid? You're soaking in it!
Surfaces treated with de/anti-icing fluids are extremely slippery.
So now you know why we have so many delays in the winter. Rest assured that it's making us just as miserable as you are. Stay safe.