Proficiency: Icing primer

Having an out (or three) and knowing when to use it

November 20, 2013

airplane icingFew hazards scare pilots more than icing, and rightfully so. But if we didn’t fly on days when icing was in the forecast, we wouldn’t get very far from the local airport. What follows are some guidelines when it comes to operating in icing conditions and the characteristics of some deicing and anti-ice equipment.

First, the potential for icing exists any time there is moisture (clouds) and freezing temperatures, which is nearly every winter day in parts of the country. Does that mean you can’t fly? No. There have to be pilot reports of icing conditions in the area and altitudes at which you plan to fly. In the early morning there may be no pireps, so you could be the pathfinder for everyone else. If so, knowing where the freezing level is, having an idea of where the tops are, VFR conditions under the clouds, and having a number of airports along your route all are excellent backups in case you encounter ice. Keep in mind the minimum en route altitude (MEA) on the route if you’re IFR. If the MEA is above the freezing level you’ve just eliminated one of your escape plans. If your airplane is equipped for flight in known icing, the sage advice is to only use the equipment while activating your plan to get out of icing conditions (see “Safety Pilot Landmark Accident: Unpredicted, Unadvised, Unaware,” page 64). Today, I still fly by this rule in my airline job.

A word of caution when flying in areas of busy airspace such as the Northeast: Often, the routes and altitudes are determined by air traffic control, regardless of what you may have filed. While your filed route and altitude would keep you ice free, ATC may well put you right back in it. This happened to me on a frigid day flying from Teterboro, New Jersey, to Gaithersburg, Maryland. I filed for 4,000 feet on a route over the flats of central New Jersey. Unfortunately, I was assigned 6,000 feet—above the freezing level that day—on a route that took me toward mountains.

I’ve never gotten so close to using the “E word” (emergency) as I did that day when I had a couple inches of ice on my family’s Beechcraft Baron and had lost nearly 30 knots of airspeed. My final plea to ATC was to accept any vector to get higher or lower to escape the icing. With that urgency duly noted, I was granted a climb to 8,000 feet, where the ice stopped accumulating. I was very happy to be in a lightly loaded twin that had the excess power to affect a climb with that draggy load. In hindsight, I never even thought of simply saying, “unable” to the initial clearance—or, upon encountering the ice and ATC’s resistance to budge from my clearance, to say, “I have to land.” I had a number of airports along my route with decent weather that I could have dropped in on, but I stubbornly plodded on. Lesson learned.

Often, icing can be escaped by climbing or descending 3,000 feet—sometimes it’s more, sometimes less, and sometimes not at all. In my experience, some of the worst icing can occur when reaching the tops of stratus clouds. Just as your ice-laden airplane is running out of performance, clawing for the blue sky on top, you very well may encounter the heaviest accumulation. More than one pilot has stalled just shy of reaching his salvation under these circumstances.

It may sound obvious, but stay in non-icing conditions as long as possible. If you’re flying above the clouds and have to descend through them to land, the prudent action is to minimize your exposure to ice by staying in the clear as long as possible and rapidly descending through the icing area. Because ATC may not have a clue what your flight conditions are, it may descend you early and vector you through the clag for many minutes, increasing your exposure to icing. Ask ATC if they can accommodate your plan to stay in the clear as long as possible.

Once in the icing, avoid using flaps and extending the landing gear (unless needed to descend), as these items can accumulate ice as well, adding unnecessary weight and drag. If your airplane is already iced up, in most cases it’s advised to leave the flaps retracted for landing. Since the horizontal stabilizer provides a downforce to balance the airplane, extending flaps requires more downward “lift.” Just like the wings’ upward lift is hobbled by ice, the tail’s downward force is reduced. Leaving the flaps up minimizes the chance of a tailplane stall.

As for icing protection, there are three main options: bleed-air heat, fluid excretion, and pneumatic boots. Some are more effective than others. Bleed-air heat is mostly used in jets, where gobs of excess power allow some hot engine air to be tapped and distributed along leading edges of the airplane to prevent ice accumulation. Jets also have the tremendous advantage of climbing and descending quickly through icing altitudes, minimizing their exposure to ice. In eight years and more than 6,000 hours of flying the Boeing 737, I’ve only been significantly iced up once. And despite the alarming load of ice, the airplane continued to handle normally.

I can’t say the same for the thousands of hours flying light airplanes and turboprops equipped with pneumatic boots. Several times over the years, I’ve been exposed to conditions beyond that which the equipment could handle. I’ve noticed that boots with a nice, shiny finish on them blast off the ice far more effectively than those that are pockmarked and dull. Unfortunately, the Jetstream 41 turboprop I flew for a regional airline didn’t sit still long enough to get boot TLC, unlike the Cessna Conquest I that I flew occasionally for a corporation. The Conquest’s slicked-up boots worked great. In the Jetstream, I often inflated the boots to see them remove only about 50 percent of the ice.

Finally, the weeping-wing systems such as those used on Cirrus airplanes and some jets—such as the Hawker series—force-feed an anti-icing fluid through tiny holes drilled into leading-edge panels on the airframe. One night I ran into the pilot of a ratty-looking old Baron C55 on the ramp in Cleveland on a particularly icy night. He parked next to our Jetstream, which sported an ugly coating of rime ice from our arrival. His leading edges were clean and equipped with a weeping-wing system installed via STC. He said his choice of ride for the night cargo run was the battle-worn C55 with TKS or a newer Baron 58 with boots. “With ice like tonight, the decision was a no-brainer,” he told me. Some years ago, Cessna began equipping Caravans with fluid-deice systems rather than boots in reaction to a number of icing-related accidents involving the type.

But having all the right equipment still won’t save a pilot from bad icing conditions. The only savior in such a case is having multiple plans of action for escape. If those plans are executed and you’re still in ice, it’s time to land. You did make sure there was decent weather below you, right?

Pete Bedell is a pilot for a major airline and co-owner of a Cessna 172M and Beechcraft Baron D55.