Icing

Ice and frost on the wing can be serious flying hazards. Hence, the responses to a recent question about the best method for de-icing or de-frosting a wing on the Ask a Flight Instructor website is well worth reading. The question poster had also wrote:

I’ve heard either Glycol or a little bit of rubbing alcohol can be sprayed on the wings.  Then what?  Just rub it off GENTLY with a towel or nylon bristle brush?

-Also, when is it appropriate to use pitot heat?  When visible moisture is present?

In response, Paul Tocknell noted several aircraft icing resources that are well worth mentioning again:

• AC 91-74 Flight in Icing Conditions
• AC 135-17 Pilot Guide: Small Aircraft Ground Deicing
• AC 20-117 Hazards Following Ground Deicing and Ground Operations in Conditions Conductive to Aircraft Icing
• AC 91-51AEffect of Icing on Aircraft Control and Airplane Deice and Anti-Ice Systems
• Aircraft Icing Tutorials / Modules developed by NASA

In addition, Paul noted that you should never take off if you have frost on the wing as even a small amount can impair lift. He also noted that the best way to de-ice a wing is to warm it up in a hangar and once it starts to melt, simply wipe the wing down with a towel so that the water won’t refreeze again once you are out of the hangar.

Paul then wrote that he uses pilot heat whenever he is in any visible moisture regardless of the temperature as you never know when you might pick up icing. In fact, he wrote that he once picked up serious icing on the edge of a summer thunderstorm once and that more than a few aircraft have been lost because a pilot forgot to turn the pilot heat on.

After Paul’s response, Lance, a pilot based up in Alaska, added:

Snow, absolutely none is allowable, however frost that fits between the wing covers and the wings is typically considered flyable.  The other thing you want to watch for is whether conditions aloft will allow the frost to sublimate off as you are flying, (same principle as to why if you get into icing conditions descending is not always the only solution).  Also the way most pilots up here clean frost and excess snow off of their wings is a clean, soft bristle, push broom, since hangar space comes at a very high premium.

Hence and if you are planning to fly this winter, keeping the above de-icing and de-frosting tips in mind will keep you safe in the air.

With winter well underway, anyone flying at higher latitudes and altitudes at this time of year will likely encounter frost or ice. However, not everyone understands the similarities and differences between frost and ice and when either can form. Hence, a question about the technical difference between aircraft icing and frost that was recently posted on the Ask a Flight Instructor site along with the answers given are well worth reading. The poster had also asked:

-In order for aircraft icing to occur, there needs to be visible moisture present.  But what about temperatures?  Do temperatures HAVE to be at or below freezing for icing to occur?  What OTHER conditions are necessary for ice to occur?

-As for frost…The collecting surface must be at or below the dewpoint of the air..and the dewpoint has to be below freezing.

Paul Tocknell responded by pointing out that frost is a form of ice and both are considered to be frozen contaminants. He also noted that:

Frost will occur on aircraft surfaces if the aircraft’s surface temperature is below the ambient dew point and the surface temperature is below freezing.  Frost can occur even when the surrounding air temp is above freezing.  For instance, an airplane parked overnight will radiate heat and become cooler than the ambient air.  If it cools to it’s dewpoint (and it’s dewpoint is below freezing) then frost will occur.

Paul then pointed out that according to the FAA’s AC 91-74, nearly all icing will occur in supercooled clouds where liquid droplets are present in temperatures below 0° C while at temperatures near 0°, the cloud may actually consist entirely of such droplets with few or no ice particles present. In addition, he noted that the right type and size of water droplet will also matter as large droplets will tend to lead to in flight icing conditions.

In addition, Wesley Beard responded by noting that the Aeronautical Information Manual states that icing is most prevalent in temperature ranges from +2deg C to -10deg C and in most of the corporate jets he flies, the manufacturer considers icing conditions to exist when inside visible moisture and the temperature is between +10deg C and -40deg C.

However, Wesley also pointed out that:

There are a lot more variables than just visible moisture and temperature in determining whether or not ice will form.  The size of the droplets also matter.  Droplets smaller than 40 mu meters don’t have a chance on sticking they are simply too small.  Conversely, droplets that are too big and are not supercooled probably will not form ice either.

In other words, there can be many unpredictable variables with the formation of frost and ice that pilots need to consider and be aware of at this time of year.

With winter fast approaching, icing during a flight should be a concern in the back of every pilot’s mind. After all, ice can quickly build up during a flight and this can be particularly dangerous if it were to happen in a remote area or in poor weather conditions.

Hence John Fiscus, the Chief Pilot of The Flight Academy, has recently written a post on the Cirrus Owners & Pilots Association (COPA) blog listing a couple of useful resources to help USA based pilots make an informed decision about ice conditions in the air before leaving the ground. Some of the resources mentioned by John are listed under the icing tab on the ADDS (Aviation Digital Data Service) website and these resources include an icing airmets map and two other useful tools that measure maximum icing severity and the potential for icing at 7,000 feet. John does an excellent job of explaining how to use all of these tools that were created to help you plan a safe flight this winter.