Features

January 2018 Issue




Confronting The Ice Queen

FIKI or no-FIKI, the rules are the same: Have an icing escape plan and use it.

Years ago, when a good friend and airline captain heard I had earned my IFR rating, he congratulated me: “You’ll be a much safer pilot.” And then he startled me by adding, “Just don’t ever use it here in the West.” He went on to explain that since IFR often means thunderstorms or icing, “You have no business in either of them.” To a large degree, he was absolutely right.

In the Western United States, minimum en route altitudes (MEAs) and freezing levels tend to coincide, even in the summer, bringing the possibility of airframe ice. And no one has any business flying through a thunderstorm, whether it’s in Colorado, Wisconsin or Florida. Now that my day job has me flying Part 135 cargo and passengers in aircraft certified for flight into known icing (FIKI), I can offer similar advice: “A FIKI aircraft allows you to fly into icing conditions, but don’t think it means you can fly in ice.”

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There Are Limits

Certification for FIKI allows pilots of such aircraft to depart into conditions conducive to forming ice on an airframe. The certification means your aircraft has either anti-icing or de-icing equipment that will protect you from specific kinds of icing encounters as specified in the aircraft operating manual. Even when flying a FIKI-equipped aircraft, however, there are limits and you do not get to linger in clouds in icing conditions indefinitely or with impunity. You use your FIKI capabilities when you encounter ice. And, in most cases, that is also when you begin to execute your plan to find better conditions.

The main aircraft I fly in the winter season is one of the few (perhaps only) aircraft with an AD for the pilots. A decade or longer ago, Cessna Caravans got a bad reputation for falling out of the sky after encountering in-flight icing. To a great extent, the problems centered around a small airplane being asked to do a large airplane’s job and less-than-exhaustive pilot training. As a result, all Caravan drivers today are required to take an annual cold-weather operations class geared to conveying the gravity of flying in icing conditions. (See “Saving The Caravan,” January 2008.) It’s one of the reasons the Caravan’s ice-related record has substantially improved.

Run Away!

That training, plus some operational experience, has taught me there are three basic rules for dealing with airframe ice, and they are same whether you have an aircraft supposedly capable of dealing with —FIKI’d—or not. They’re very simple.

Rule #1: Know where the ice is. Check freezing level forecasts as part of your preflight briefing. Look at the temperatures on winds aloft to identify good altitudes that are above freezing or below -15 C. Where there’s so little water vapor, airframe ice is less likely to form. Remember, though, there’s nothing magic about -15; you may need to hit -20.

Check ice-forecasting products to identify the good, bad and the ugly altitudes and routes. Watch out for fronts and zones with high liquid water content. And don’t forget: Timing is everything. Can you leave early or wait a day? Icing conditions are both temporal as well as spatial. 

Icing Pireps are helpful. However, the lack of icing Pireps is not an indication that there is no ice. Even Pireps for negative icing should be treated as a snapshot, not a reality. Ice-related Pireps are always past tense. They tell you where icing was, not where it is. But forewarned is forearmed.

• Rule #2: Have a preflight plan to avoid it. Pick the altitudes that give you the greatest opportunity to avoid ice. Route your flight path away from fronts or areas where MEAs, clouds and freezing levels are working against you.

If you have to cross a front, do so at the best altitudes and as perpendicular to the frontal line as possible. Or land and let it cross you, then fly out behind the front. Will the warmer air be above you or below you when you pass?

• Rule #3: Have a preflight escape plan if you encounter it. If you encounter ice, will you climb or descend? If FIKI equipped, what are the best airspeeds for your boots or the amount of priming time or fluid levels needed for your TKS system? Are your FIKI systems functional and ready? How much TKS fluid do you have on board? Has the system been tested lately? Is there enough TKS in the system to dispatch? Are the leading edges of weeping surfaces clean? Is there any de-lamination or weeping wing membranes on preflight?

Are your boots working? Do they have fresh anti-ice product coatings? Do your boots have the legal number of patches? (In my case, the required number according to the Boise FSDO is as many patches as there are holes.)

Where are your alternate airports? If you have a load of ice, where are the longer runways you will need? Which direction gets you to better weather? Which direction gets you higher? Which direction doesn’t?

Preflighting For Ice

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While you’re planning your winter flight, make sure you stop by and consider some of the graphical weather forecasting tools available from the Aviation Weather Center (AWC) Aviation Digital Data Service (ADDS) web site at www.aviationweather.gov/icing. These graphics usualy are incorporated into popular tablet-based electronic flight bag apps, like ForeFlight. There are three basic graphical products you’ll want to consider, at minimum.

Figure 1 is the new graphical forecast, which replaced text-based area forecasts for the CONUS. In this image, the product is set to show icing Airmets. Figure 2 is the AWC’s current icing product (CIP) and future icing product (FIP). The CIP/FIP combination “are computer-generated three-dimensional analyses of information related to the likelihood of encountering icing conditions,” according to the AWC. Figure 3 is the AWC’s graphic presentation of the forecast lowest freezing level, an important data point.

Types of Ice and Icing

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Science geeks like me enjoy plowing into the FAA’s 2015 Advisory Circular on airframe icing (AC 91-74B, “Pilot Guide: Flight in Icing Conditions”). It is a good read with lots of details about the different types of ice, the behaviors of super-cooled water droplets of various sizes—from sub-micron level to super-cooled large water droplets—and the differences between freezing drizzle and freezing rain. There is clear ice, rime ice and mixed ice. From it one can learn that different temperature and moisture regimes can result in novel mixes of both ice crystals and supercooled water droplets in the same air mass. Here is the gist of it.

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There’s really only one kind of airframe ice: the bad kind. But it does accumulate in two basic ways. At top right is an example of clear icing on a Bonanza wing. The ice in the photo is concentrated on the leading edge while some clear ice may run back along the wing’s upper surface before freezing. The FAA says clear ice is denser, harder and sometimes more transparent than rime ice, and may develop larger structures called horns. Temperatures close to the freezing point, large amounts of liquid water, high aircraft velocities and large drops are conducive to the formation of clear ice.

Freezing precipitation, such as freezing rain, freezing drizzle and supercooled large droplets, fall outside the capabilities of most small FIKI-equipped aircraft. The statistics show they also account for a disproportionate number of icing accidents. The most common form of precipitation in the U.S. is rain, making up 66 percent of reported precipitation in the study period, yet it was only associated with 25 percent of icing events. In the same period, 32 percent of precipitation events involved snow and was associated with 38 percent of the icing-related incidents/accidents. 

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The other basic type of airframe ice is rime, which the FAA says has a “rough, milky, opaque ice formed by the instantaneous or very rapid freezing of supercooled drops as they strike the aircraft.” The rapid freezing traps air pockets in the ice, giving it an opaque and rough appearance, making it porous and brittle. The ice in the photo appears to be rime, but it’s trying to adhere to the wing of a Cirrus equipped with the TKS anti-ice system, so it’s hard to be sure.

Supercooled large drops (SLD) are one of the more dangerous forms of airborne moisture. These drops of liquid water have not actually turned to ice, but they have cooled below the freezing point. When they contact a surface, such as an airfoil, they freeze on contact. Pilots should be concerned about ice accretions from SLD when outside air temperatures are below five degrees C and/or there is visible rain or drizzle, or when precipitation drops splash or splatter on impact, indicating freezing is occurring.

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Above is a Beech Baron’s wing with an accumulation of what we’d call mixed ice. Note how the ice extends forward from the wing’s leading edge. This photo was taken just before cycling the Baron’s boots.

Whenever ground stations report rain, sleet, ice pellets, drizzle, freezing drizzle or snow, and whenever outside air temperatures at altitude are near freezing, pilots should be on the lookout for SLD. But even when there is no reported SLD precipitation on the surface, SLD are often present aloft. Because SLD pockets are not easily predicted, it is important to watch for evidence of it on the airplane. 

When the Iceman cometh

To be blunt, there are two types of ice: survivable and not survivable. If you are flying in a non-FIKI aircraft, assume any encounter with ice will be non-survivable if you don’t execute your exit strategy immediately. This includes immediately confessing your sin to ATC (unless your actions are pretty egregious, no one’s going to turn you over to enforcement for wanting to get out of icing), act and declare an emergency to get out.

In “A Study of U.S. Inflight Icing Accidents and Incidents, 1978 to 2002,” the author noted how pilots failed. They either expected a blanket clearance from ATC once they explained that they encountered icing or, in many cases, failed to make ATC aware of the gravity of the situation. 

The FAA circular is clear, “In the event of an inadvertent icing encounter, the pilot should take appropriate action to exit the conditions immediately, coordinating with ATC as necessary, and declaring an emergency.” 

When an emergency is not declared, encounters with ice fall under the category of hazardous weather conditions. When icing conditions are encountered reporting of meteorological hazards is required under FAR 91.183, FAR 121.561 and FAR 135.67. Pireps provide your fellow pilots with data to assist them in their planning and provide helpful data that helps the NWS refine its forecasting products.

Strategies

Pilots in non-FIKI aircraft should have a strategy that starts with declaring an emergency. The pilot who lingers in a state of indecision wondering what to do and failing to seek ATC assistance has a much greater chance of becoming a statistic. 

Pilots of FIKI-equipped aircraft must assess whether the icing encounter is manageable and within the capabilities of their particular set of equipment. This isn’t easy because ice encounters can be transient. Ice buildup may be within tolerance for a time, but it only takes a few short minutes for ice accretion to become extreme and urgent.

Freezing precipitation, such as freezing rain, freezing drizzle and supercooled large droplets, fall outside the capabilities of most small FIKI-equipped aircraft. They also account for a disproportionate number of icing accidents. While freezing rain and freezing drizzle make up less than two percent of U.S. precipitation events, they account for more than 36 percent of the icing accidents and incidents studied between 1978 and 2002.

The best practices in icing conditions are the same whether you are flying a FIKI or non-FIKI aircraft. Start flying the conditions when you are on the ground. Know where the ice is, have a preflight plan to avoid it and, if you encounter it, have an escape plan you are immediately ready to enact. If you encounter freezing precipitation, take urgent evasive action, and have the humility to declare an emergency to secure priority handling.


Mike Hart flies his Piper J3 Cub and Cessna 180 when he’s not schlepping people and packages. He’s also the Idaho State Liaison for the Recreational Aviation Foundation.