PILOT TRAINING ARTICLE
It’s Just a Little Ice…Right?
As the weather has turned cold and areas of the country are seeing their first dustings of snow, it is time to begin thinking about one of aviation’s greatest hurdles, icing. While most pilots recognize the danger posed by flying through icing conditions, there are still myths that persist about the problem.
Icing, as the name suggests, is a phenomenon where an aircraft begins to experience ice build-up on the fuselage, wings, engine nacelles and tail assembly. Ice can develop internal to the engine(s) and pitot tubes, as well, but that is beyond the scope of this article. As ice continues to build, it begins to disrupt the standard laminar boundary layer of air, most readily seen on the plane’s wings. When the laminar flow becomes turbulent it has a tendency to detach from the airfoil itself, creating a stall, at much higher than normal airspeeds.
Intuitively it is assumed that icing is only a real threat when surface weather is extremely cold and there is snow or sleet in the forecast. However, this is the first icing myth. Icing is often seen even when ambient ground temperatures are quite mild. For example, while living in the state of Florida, icing was often a concern even during spring! This is due to a unique combination of high moisture and low temperatures that exist in the skies of such a state. At even just 10,000 feet, the temperature can drop significantly, often close to freezing, and when coupled with high humidity and cloud layers, one can develop ice rather quickly and unexpectedly.
Another icing myth is that it cannot develop in clear air. While unusual, this is not entirely true. One area where you may witness clear-air icing is in the vicinity of convective storms. During times of updraft supercooled droplets can be expelled through the tops of the “anvil” and fall outside of the storm itself. In other words, it could be raining even though there is no cloud above the area. If an aircraft is in this rainshower of supercooled droplets, it may experience icing despite being VMC. However, the droplets from the nearby storm satisfy the requirement of visible moisture necessary for ice formation.
But it is not good enough to just understand icing and its effects on aircraft, we must also understand how to react; any encounter with icing is serious and must be addressed quickly. First, if able, leave the area of icing by either exiting visible moisture, or flying at an altitude where icing is less probable. A good rule of thumb is to look for outside air temperatures greater than 5°C or less than -20°C. Likewise, if icing conditions are expected or encountered, pilots must ensure that their anti-icing/deicing systems are on and functioning properly before icing develops. As icing continues to accumulate, this may lead to severe problems where control surfaces become sluggish as lift is decreased. Pilots may encounter engine problems as thrust is reduced or even aircraft upsets and departures as lift generation is compromised.
Ultimately, if icing poses a significant control problem for a pilot, the only option may be to land. Look for an appropriate airport with a field length long enough for a high-speed, no-flap landing. Realize that the runway may be wet/snowy when considering length. If possible, pilots may wish to perform a controllability check at altitude, but only if they can arrest icing build-up first. If controllability is in question, and a controllability check is not possible, pilots should consider a faster landing speed, perhaps with no flaps. And remember, if you encounter icing, so will other pilots. Be courteous and submit a PIREP.