AircraftOwner Online

One of the oldest aviation clichés holds that a pilot certificate or rating is primarily a “license to learn.” Nowhere is that saying more appropriate than it is for the newly rated instrument pilot. Like many pilots, I was eager to exercise my new privileges by getting the wings wet almost before the ink on my temporary certificate dried. Having passed the instrument rating practical test, I was confident of my ability to operate in the system, to shoot approaches, and even to enter and fly holding patterns. I had mastered the art of the scan and the rhythm of cross-check, interpret, and control. My knowledge of instrument flight rules (IFR) and procedures was solid. As I quickly learned, though, my understanding of weather— specifically, how to think about weather in terms of a given flight—was as patchy as the clouds I so proudly passed through on my first IFR flight.

The gaps in my knowledge became crystal clear on a very cloudy day a few months later when I launched into rapidly deteriorating weather that eventually forced a diversion and an instrument approach to near minimums. I’m not proud of the “go” decision I made that day, but the experience does have a silver lining. As you might imagine, it provided powerful motivation to become a dedicated and lifelong student of aviation weather. Eventually, it also led to discovering a simple, but very effective, framework for deciding whither and whether to fly in weather of all kinds.

As Simple as 1-2-3

It is important to get a detailed weather briefing and I was always very dutiful about obtaining and printing out weather information from Flight Service (FSS) or one of the online direct user access terminal (DUAT) providers. Even more critical, however, is knowing how to pull the most important pieces of information from piles of printer paper and apply them to the flight you’re about to make.

Easier said than done. There was a time when I stared at those faithfully acquired weather printouts with the same expression of earnest confusion my Cocker Spaniel displayed when I tried to explain the importance of a bath. She didn’t get that picture any more clearly than I got the flick on weather. The Spaniel never did understand the bath rationale, but the light-bulb moment for my understanding of aviation weather came courtesy of a simple concept in Robert Buck’s Weather Flying

book. As Buck explains, there are just three ways that weather affects an aviator:

1. Weather can create wind.

2. Weather can reduce ceiling and visibility.

3. Weather can affect aircraft performance.

Eureka! With this framework, I began to notice that data in aviation meteorological reports (METAR) and terminal aerodrome forecasts (TAF) is structured to provide information on each of these three weather conditions. I finally had not only the tools needed to mine the most critical pieces of information from the printout, but also the foundation for evaluating a specific day’s weather in terms of both the specific pilot—me—and the specific airplane I planned to fly.

When the Wind Blows

In both METARs and TAFs, the first item provides information on an airport’s wind direction and velocity. A key to wise weather decision making is to consider these numbers in relation to both the pilot and the plane.

With respect to the pilot, the primary issue is proficiency and comfort with a known or forecast crosswind. If you are not comfortable with the crosswind component at the departure airport, it’s a good day to stay on the ground or, better yet, hire a qualified instructor to help scrub the rust off your crosswind takeoff, approach, and landing skills. If it is the crosswind at the destination airport that gives you pause, the next step in the windy weather decision-making process is to determine whether the winds are more favorable at alternate airports within range. When crosswind comfort is an issue at either end of the flight, it also pays to check wind at airports along your route in the event that diversion becomes necessary.

Regarding the airplane, the primary issue is its maximum demonstrated crosswind component, which is usually in the range of 12-17 knots for light GA aircraft. Though it is not a legal limitation, a GA pilot is wise to regard this value as a personal limitation. Here’s why. Aircraft manufacturers develop aircraft performance data through rigorous flight tests. These activities are conducted by professional test pilots who are, as the phrase goes, “simulating average pilot skills.” However hard we try, non-commercial GA pilots still may not obtain the aircraft performance that a professional who is “simulating” an average pilot’s skill level can achieve.

Also, even if the true maximum crosswind component is higher than the published (demonstrated) value, there is inevitably a point at which full deflection of a given airplane’s rudder, in combination with aileron input, will not be sufficient to correct for the drift resulting from a stiff crosswind. Pilots refer to this condition as “running out of rudder.” I speak from experience when I report that it does get your attention. That particular teachable moment came for me on a gusty autumn day when I was first learning to fly from the right seat of a Cessna 150. Even with the right rudder pedal jammed all the way to the floorboard, the trusty little trainer was no match for the crosswind at that particular airport.

Bottom line: Regardless of pilot proficiency in crosswind flying, it is also critical to consider whether the airplane is up to the challenge. A crosswind that is perfectly manageable in the beefy twin-engine Piper Aztec may well be too much for a tiny two-seat trainer.

Flying Blind

The next component of METAR and TAF reports ceiling and visibility, conditions that are the primary reason for learning to fly by reference to instruments. For legal instrument flying, an aircraft must be properly equipped and certified for IFR. Since, regardless of equipment, the airplane itself is not affected by the presence of clouds and precipitation, weather decision making in this area most logically focuses on the pilot.

For legal operation in instrument meteorological conditions (IMC), a pilot must be

both instrument rated and instrument current in accordance with Title 14 Code of Federal Regulations section 61.57. For safe operation in IMC, though, the pilot must also be proficient in basic attitude flying, instrument operating rules and procedures, course intercepts and tracking, holding, approaches, and all other aspects of instrument flying.

The existence of the IFR currency requirement bespeaks the perishable nature of instrument flying skills. As many pilots have discovered, though, maintaining just the legal minimum requirement for currency may not be enough for proficiency and confidence. If you haven’t flown in IMC recently, or if you have any doubts about your proficiency level, it behooves you to get some practice with a safety pilot or, better yet, some dual instrument-refresher training with a qualified instrument instructor.

Let’s assume you are rated, current, and proficient. Is that enough? Another part of being proficient and safe in IMC is knowing and adhering to your individual personal minimums. One way to approach this important task is to consider—honestly—how comfortable and proficient you are in the basic weather categories for aviation. VFR, marginal VFR (MVFR), IFR, and low IFR (LIFR). Be sure to account for day versus night operations in each category. For instance, I am very comfortable flying in day MVFR in my home airspace, but night is a different story. My own personal minimums also prohibit intentional operation into LIFR conditions. The minimums I set for IFR vary according to how much recent time I have flying in IMC, and how recently I have practiced flying instrument approaches. (Note: For specific tips and techniques for developing your own personal minimums see “Getting the Maximum from Personal Minimums” in the May/June 2006 issue of FAA Aviation News.)

The Little Engine That Couldn’t

The third major way that weather affects aviators is through its impact on aircraft performance. The temperatures in METARs, TAFs, and winds and temperatures-aloft reports can give you a good indication of two weather phenomena that will undoubtedly sap your airplane’s operating capability: icing and high density altitude.

An airplane is a machine, and all machines have performance limits. Consequently, a vital part of deciding whether to fly in weather likely to include such performance-reducing elements as icing or high-density altitude is to have a rock-solid understanding of what your airplane can—and cannot—do. The best piloting skills in the world cannot overcome the airplane’s physical performance limitations. Think of it this way: Even if you are super pilot, there are hard limits on what you can expect when flying a Super Cub.

A word about performance calculations: If the ground school memory of doing triple interpolations to calculate a two-foot difference in takeoff distance has discouraged you from regular use of the performance charts for your aircraft, rest assured there is an easier way. Simply use the next highest numbers shown on the chart to get a “ballpark” estimate, and then add a 50–100 percent safety margin.

For the purists: Yes, precision is important, but only to a point. If you calculate a takeoff distance of 1,242 feet in high-density altitude conditions and the last two feet (or even the last 42 feet) really make a difference in whether you can operate or not, you should stop and consider whether it is wise to fly at all in those conditions. As the saying goes, there are no emergency takeoffs.

Learning after Landing

A final thought: When you complete a challenging flight in weather, you may want nothing more than to go home and unwind. The immediate post-flight period, however, is one of the best opportunities to increase the weather knowledge and understanding that will guide effective decision making. Make it a  point to learn something from every weather encounter. At the end of a flight involving weather, take a few minutes to mentally review the flight you just completed and reflect on what you learned from this experience.

Still another way to develop your weather experience and judgment is simply to observe and analyze the weather every day. When you look out the window or go outside, observe the clouds. What are they doing? Why are they shaped as they are? Why is their altitude changing? This simple habit will help you develop the ability to read clouds and understand how shape, color, thickness, and altitude can be valuable weather indicators. As your cloud-reading skill develops, start trying to correlate the temperature, dew point, humidity, and time of day to the types of clouds that have formed. Take note of the wind, and try to visualize how it wraps around a tree or whips around the corner of a building. This exercise will help you become more aware of wind at critical points in your flight.

Weather is a fact of life for pilots. Developing your weather knowledge and expertise is well worth the time and effort you put into it, because weather wisdom will help keep you—and your passengers—safe in the skies.

Susan Parson (susan.parson@faa.gov) is a Special Assistant in the FAA’s Flight Standards Service. She is  an active general aviation pilot and flight instructor.

Ice Belongs in Drinks

- Meredith Saini

Any pilot who’s spent a drab winter day hangar flying at the airport over a pot of hot coffee with friends has probably heard stories like these before. There was the time when Joe took his Bonanza up to Boston to see a Celtics game and picked up a bunch of ice during the descent into Logan. He needed almost full power just to stay on the glide slope. Or when Bill’s Warrior looked like a hockey rink after crossing the Appalachians on his way home from Thanksgiving dinner with the inlaws last year. His wife hasn’t flown with him since.

These stories are often told with a touch of bravado, the pilot feeling a sense of accomplishment for having survived an ice encounter. “I got through it that time, so I’ll probably be all right next time, too.”

Nothing could be further from the truth for airplanes not certificated for flight in icing conditions, because the moment ice begins to accumulate on an airplane wing, that wing’s shape morphs into some new, untested airfoil design. At that moment, you become the test pilot of a new airframe, with no guarantee that the wings will keep flying as long as they’re covered with ice.

What Is Airframe Icing?

The Aeronautical Information Manual (AIM) describes the various types of airframe icing, the conditions under which it can form, and the negative effects it can have on airplane performance. It also offers guidance to pilots on how to give a pilot report (PIREP) on in-flight icing conditions. Depending on where the icing conditions are encountered and at what temperature and altitude, ice can form as clear ice, rime ice (cloudy appearance), or some combination of the two. Ice can form quickly, often

in just a few minutes—the time it takes to climb or descend a few thousand feet through a layer of juicy clouds. Unless the aircraft is equipped with some kind of anti-icing or de-icing system, ice can accumulate rapidly on the leading edges of the wings, the horizontal and vertical stabilizers, propeller, and windscreen.

The effects of ice on an aircraft are cumulative, and it doesn’t take much at all to severely reduce performance—as little as one-half inch of ice on an airfoil can reduce the lift it produces by up to 50 percent. Even a light coating of frost on the wings is enough to negatively affect the takeoff performance of most light airplanes.

Under what atmospheric conditions can a pilot expect ice to appear? As with many things in life, the answer is, it depends. There are many good tools on the Internet for making educated guesses about where ice is likely to be found, but there are no guarantees. AIM paragraph 7-2-21 says that a pilot can expect icing when flying in visible precipitation, such as rain or cloud droplets, and the outside air temperature is between +2 degrees and -10 degrees C. However, water can remain “super cooled” at temperatures as low as -40 degrees. Water can remain liquid at below-freezing temperatures until it contacts a solid surface like your airplane. Supercooled large droplets, or SLD (which include freezing drizzle or freezing raindrops within or below clouds), are particularly dangerous because they can coat large areas of the wing and tail very quickly.

What Is “Known Icing?”

In 2003, the FAA defined “known icing conditions” as “atmospheric conditions in which the formation of ice is observed or detected in flight.” This definition appears in paragraph 7-1-22 of the AIM. However, based in part on information provided by the Aircraft Owners and Pilots Association (AOPA), the FAA determined that this definition was not sufficiently broad enough to reflect the agency’s current policy. The FAA issued an interpretation addressing known icing conditions and other aspects of flight in icing conditions on January 16, 2009.

In this interpretation the agency noted that “the formation of structural ice requires two elements: 1) the presence of visible moisture, and 2) an aircraft surface temperature at or below zero degrees Celsius. The FAA does not necessarily consider the mere presence of clouds (which may only contain ice crystals) or other forms of visible moisture at temperatures at or below freezing to be conducive to the formation of known ice or to constitute known icing conditions.”

The letter to AOPA went on to say: “Most flight manuals and other related documents use the term ‘known icing conditions’ rather than ‘known ice,’ a similar concept that has a different regulatory effect. ‘Known ice’ involves the situation where ice formation is actually detected or observed. ‘Known icing conditions’ involve instead circumstances where a reasonable pilot would expect a substantial likelihood of ice formation on the aircraft based upon all information available to that pilot.”

The letter acknowledged the challenge to pilots in deciphering the many possible weather scenarios that could lead to an icing encounter, but urged pilots to dig deeper than the area forecast to determine whether icing conditions might exist. The letter specifically advised pilots to obtain the latest surface observations, temperatures aloft, terminal area forecasts, AIRMETs, SIGMETs, and PIREPs.

The letter also stated that pilots should incorporate new technology, as it becomes available, into their decision making. The letter further noted that, “If the composite information indicates to a reasonable and prudent pilot that he or she will be operating the aircraft under conditions that will cause ice to adhere to the aircraft along the proposed route and altitude of flight, then known icing conditions likely exist.”

Airplanes that meet certain design criteria can be certificated in the normal, utility, acrobatic, or commuter categories under Title 14 Code of Federal Regulations part 23 for “flight into known icing conditions.” These aircraft are equipped with systems that not only prevent ice from forming on critical surfaces like the wings, tail, and propeller, but can shed ice that’s already formed—within certain limitations. Such systems (often called Flight Into Known Ice, or FIKI, systems) typically use pneumatic boots that expand and push the ice off, heating elements, a solution that is mechanically distributed over the surfaces, or some combination of these systems. Aircraft that do not meet these regulatory criteria can still be equipped with ice-protection systems (such as the TKS™ system that comes standard on the Cirrus SR22) but they are not legal to fly into known icing conditions.

Find Ice, Then Avoid It

There are several really good tools available on the Internet for sleuthing the potential for inflight icing. NOAA’s Aviation Digital Data Service has a fabulous Web site that pilots can use to supplement the official Flight Service preflight briefing. From the home page, click on the Icing tab to view graphical depictions of the latest icing advisories, pilot reports of icing, and forecast freezing levels.

Click on the Supplementary Icing Information link to see plots of where icing is predicted to be severe, including the forecast location and altitude where you are likely to encounter SLD. The Current Icing Product (CIP) uses input from weather sensors to produce an hourly snapshot of where ice is likely to be found right now. The Forecast Icing Potential (FIP) is an automatically- generated forecast of icing potential. FIP examines numerical weather prediction model output (from the Rapid Update Cycle, or RUC) to calculate the potential for in-flight aircraft icing conditions. This icing potential demonstrates the confidence that an atmospheric location, represented by a three-dimensional model grid box, will contain super-cooled liquid water that is likely to form ice on an aircraft. RUC diagrams (also known as SkewT diagrams) provide another way to evaluate where ice might be found. The diagrams offer an easy way to figure out where the clouds are (and thus the potential for icing) in a given location, if you know what to look for. Go to http://rucsoundings.noaa.gov and in the form, type in the three-letter identifier for an airport along your route. Then, click the button that says “Simple java plots.” If there are data available for that location, you will see a chart with a blue line (dew point) and a red line (temperature). The numbers on the right-hand vertical axis show pressure altitude in thousands of feet. The altitudes at which the blue and red lines come together are where you are most likely to find clouds—and if the temperature is below freezing at that altitude, there is a potential for ice to form. (You can find a NOAA article on RUC diagrams at: http://aviationweather.gov/general/pubs/front/docs/feb-04.pdf.)

You’re in Ice...Now, Get Out!

If you are flying an airplane that is not certificated for flight into known icing, you need to get out of the clouds at the very first sign of ice. Don’t hesitate to tell ATC that you are picking up ice and need to exit the icing condition immediately. Declare an emergency if you are not able to maintain altitude. Above all else, don’t rely on the autopilot. Fly the airplane!

The January 2009 interpretation reiterates that, “Pilots should not expose themselves or others to the risk associated with flying into conditions in which ice is likely to adhere to an aircraft. If ice is detected or observed along the route of flight, the pilot should have a viable exit strategy and immediately implement that strategy so that the flight may safely continue to its intended destination or terminate at an alternate landing facility. If icing is encountered by a pilot when operating an aircraft not approved or equipped for flight in known icing conditions, the FAA strongly encourages the submission of PIREPs and immediate requests to ATC for assistance.”

Engage whatever equipment you have available to keep the situation from getting worse. Turn on the pitot heat if it’s not on already. If you have an anti-icing system, such as TKS™, turn it on, too. Depending on how much ice has already accumulated, it might be too late for the fluid to have an effect. Be sure to note the time you turned on the system pump so you can keep track of fluid usage, as some systems only carry enough fluid for about a half an hour of continuous use. When flying at night in IMC in near-freezing conditions, carry a highpowered flashlight you can shine out onto the wings to check for ice accumulation.

Depending on where you are flying and your clearance from terrain and obstacles, descend to a lower altitude where temperatures might be above freezing. If you are picking up ice while skimming the tops of a cloud layer, climb a few hundred feet to get above the clouds, but only if you are positive there is clear air above and the airplane has climb capability.

If you are wrong, you could end up spending more time in the clouds and accumulating even more ice. Maintain airspeed with ice on your airplane, and don’t rely on your airplane’s stall warning system. When you do your preflight planning to avoid ice, you should also plan your exit strategies. Use all available resources to exit icing conditions as quickly and safely as you can. Ice belongs in drinks, not on airplanes.