Tuesday, March 22, 2005

Ice Ain't Nice

I flew for Ameriflight today. Yesterday one of their Chieftains threw an alternator belt in Klamath Falls; they sent a mechanic on this morning's UPS flight and I rode along on a later flight for the purpose of flying the plane back once it got fixed. The weather was okay but deteriorating on the way to K-Falls, and I was on the ground for a few hours while the mechanic worked on the plane. Would you believe that you need to take the propeller completely off just to change a stupid alternator belt? Somebody at Lycoming wasn't thinking that one out too well.

Anyways by the time it was together & we got headed back to Portland, the weather was worse & cumulus clouds were layered over the Cascade Range from the surface to FL200 (20,000 ft). I soldiered through the smaller ones and deviated around larger buildups. When I had no choice but to go through a decent buildup, I came out the other side with significantly more ice buildup. Fortunately, there was enough time between buildups for the deice boots to keep up.

Some explanation is in order for non-aviation types. When airplanes fly through visible moisture in freezing temperatures, ice can form on them. This is potentially dangerous; any amount of ice adds weight and drag, decreasing performance. Left unchecked, icing can and has brought airplanes down. Most ice occurs in clouds at temps between -15 and 0 degrees C; cumulus clouds usually contain more icing potential than stratus clouds, although the latter usually cover more territory.

To combat icing, many twin engine aircraft, a few singles, and nearly all turbines incorporate de-ice/anti-ice equipment. This usually consists of heated pitot tubes (airspeed sensors), windshield heat, prop heat and/or engine inlet heat, and wing/tail leading edge protection in one of the following forms: de-ice boots that inflate and break ice up, "hot wings" that heat the surfaces above freezing, or chemical anti-ice systems.

De-ice boots are the cheapest solution and the one used on most piston-powered aircraft; unfortunately, they lose effectiveness over time and cannot be used to fly in icing conditions indefinately. The best solution, no matter what your equipment, is to get out of icing by altering course or altitude, or even turning around if the situation becomes dangerous. Of course, with less power, speed, and altitude capability, your options are more limited in piston powered aircraft...which incidently have the least capable equipment. You've got to be smart flying this equipment in this area of the country in winter, or you can find yourself in a world of hurt, real fast.

Incidently, most of my icing experience took place in California. Yes, we have ice down there in the winter; it's usually not near the surface, but because of mountainous terrain, you're often forced to fly at higher altitudes where it's cold enough for airframe icing.