AVmail: January 12, 2009

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Each week, we run a sampling of the letters received to our editorial inbox here in AVmail. One letter that's particularly relevant, informative, or otherwise compelling will headline this section as our "Letter of the Week," and we'll send the author an official AVweb baseball cap as a "thank you" for interacting with us (and the rest of our readership). Send us your comments and questions using this form. Please include your mailing address in your e-mail (just in case your letter is our "Letter of the Week"); by the same token, please let us know if your message is not intended for publication.

Letter of the Week: From an Ice Expert

Our company airplanes fly in icing as part of cloud-seeding and atmospheric research operations, so we have some experience in that area. The NTSB is completely missing the boat. They keep trying to dispel the myth of "ice bridging," which is what supposedly happens if you inflate the boots when the ice is too thin and it only stretches the ice. Now you supposedly have a "shell" of ice around your boots and they won't be effective. And guess what? That doesn't happen much, so the NTSB is right about that.

But, that is not the real reason you must wait for some ice to accrue on the leading edges before activating the boots. Here's how deice boots work:

Ice builds up on the leading edge. When the ice is a solid layer (1/8" to 1/4"), you inflate the deice boots. The ice is cracked, and the airflow catches the rough edges and rips the ice off of the plane. Repeat as needed, notice that you never get rid of all of the ice. It helps to make the boot surfaces as smooth as possible (so that the ice can't hang on, like why you sand something before you paint it), so we use boot treatment every so often and Pledge wax or ICEX to seal all the tiny imperfections in the rubber surface as much as possible.

The NTSB wants you to hit the boots as soon as you have any ice. Try it with a very light coating and see what happens. Right nothing. You have to let it build up at least a little.

Some other real-life icing tips:

  1. Keep your airspeed up. That keeps the angle of attack lower and keeps the ice on the leading edges, where you have boots.
  2. Never reduce power before initiating a descent with ice on the airplane. Always start it downhill and let some speed build before you reduce power if needed. You might be relying on that propwash for lift, and you might need every bit of the airspeed you currently have.
  3. If you don't lose all of the ice before landing, then keep your speed up until touchdown. Don't use all the flaps either. That might blank out airflow to the tail or change the angle of attack just when you don't want it.
  4. Remember that your horizontal tail will be affected more than the wings with the same amount of ice, because it is a thinner airfoil and the same amount of ice will affect it far worse than the thicker wing. That's why the tail stalls first if you load it up aerodynamically (like a steep bank, or a landing flare) when you have ice on.

Hans Ahlness


And It's Windy, Too ...

Hey, you guys -- go look at your charts. Midway Airport is not "near" Chicago, it's smack in the middle of the city. It's one square mile surrounded by the City of Chicago between 55th Street on the north, 63rd on the south, Cicero Avenue on the east and Central on the west.

Linda Pendleton


XM Outage

XM had a software failure that began Jan. 2 and lasted until Jan. 7. There was no notice I was aware of from either XM or Garmin. When I called both on Monday morning, Garmin responded, "The problem is with XM, not us." XM said they were working on it. It would have been nice to receive a broadcast e-mail or text message from either company about the failure. I can learn when runway lights are out; why not weather, which can be a tad more important? Garmin's attitude seemed cavalier. XM seemed not to comprehend that weather might be more important than a loss of music. And, of course, I am ultimately responsible for flying and weather. The weather on my 496 from XM has been very reliable. Maybe that's why the outage was a surprise.

W. Clarke Prescott

AVweb Replies:

Be sure to read AVweb Editorial Director Paul Bertorelli's take on the way the outage was handled.

Russ Niles
Editor-in-Chief

By Land or by Sea

How is crossing on the surface of the water like other "vessels" in a float plane affected by the new notification and manifest rule? Boats and cars don't have to do this. Do seaplanes that cross the border on the surface of the water? I hope not. I assume that they do not, because all that I have read says that this procedure is necessary when "flying" across the U.S. border.

Customs officials don't want to give a positive answer but can't find anything that says that my presumption is incorrect.

If the idea is to enforce the "No-Fly Rule," can we assume that soon we are going to have to notify Homeland Security on all small plane flights for every flight any place, any time, even in my non-electric (no starter, transponder battery etc.) Piper Cub on Floats?

Also, what happens if we send them the electronic manifest and then take off and it turns out that there is someone already in the airplane who is on their list *or has a name similar to names on their list)? They are already flying! What does Homeland Security/Customs do then with them/us when we show up to report to Customs?

P.S. I am sure that any persons seeking to do harm to our country will comply with all this bureaucracy. Aren't you?

Bradford Parker


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