Airframe icing is probably at the top of most aviators' hazard list. As such we need to not only understand the condition, but have an effective game plan to deal with it. This information below pertains equally as well to both de-iced and non-deiced aircraft, however, much greater caution needs to be exercised when applied to non-deiced aircraft as if caught in very adverse conditions, one's options are much more limited.
I have been flying all types of aircraft for 35 years, in all manner of winter conditions and have found that icing does not have to be feared if planned properly. Different aircraft have different characteristics in icing conditions. Generally speaking, an aircraft such as a Piper Seneca with a very fat leading edge wing can carry a significant load of ice with only 10 or 20 knots loss of airspeed. Other types such as the Beech Barron or Cessna 310 do not do so well. The thinner the leading edge on an aircraft, the bigger the airflow disruption under icing conditions.
As with everything else in aviation, success begins with a good plan of action. In preparing for a flight that has the potential to encounter icing conditions, there are a few critical tests to run before departure.
1. Escape Hatch 1 - What does the route look like ceiling and visibility-wise. Are the bases higher, perhaps above 4000 feet AGL, or are the very low across the route. A reasonable ceiling across the route is preferable. If things get dicey in icing conditions at a particular altitude, you always have the option of descending below the conditions under IFR.
2. Escape Hatch 2- Where are the tops? Your flight altitude in cruise will hopefully be able to keep you in top and out of icing conditions enroute. Tops reports can be had, although it takes a little effort. The first place to look is in PIREPS form the weather service. Pilots often make reports to NWS or ATC about tops and icing conditions. Another effective method that I have found extremely valuable on departure and arrival it to call the towers by phone before departure and get the information from them. Often they will know this from in and outbound aircraft. If they are not aware of the tops, if you ask, they will usually ask an inbound or outbound aircraft to call the tops. There is no better and more current way to get area tops and icing conditions, as this information will be as current as it can get.
3. Escape Hatch 3 - Air temperatures. As part of your preflight, know what the temperatures aloft are and take them with you for departure. Ideally you want to see freezing levels of at least 4 to 5 thousand feet, but there are many days in winter when the temperature is freezing at the ground. On days where there is a freezing level aloft, you will have warmer air to descend to should you be in icing conditions.
Preflight - Your aircraft. Thoroughly pre-flight your de-ice equipment. Wing and tail boots, props boots, pitot heat, windshield heat (if you have it), should all be thoroughly check and proven before departure. Propeller anti-ice boots are 4 or 6 separate components (depending on whether you have two or three bladed props) dependent on each other to function properly. This can only be dome by turning the system on, stepping outside the aircraft and putting a hand on the blade itself for warmth. Most systems have an ammeter in the cockpit that will indicate the various phases of heat being activated on each blade. Amperage varies, but the target for most systems is somewhere in the area of 20 to 30 amps. If the ammeter indicates this range of draw, chances are pretty good that the system is working correctly. It cycles down to say 5 or 10 amps, then return to 20 to 30, you most likely have a weak or no power to at least one blade. I have found that when this condition occurs, it is most often a frayed wire in the prop hub ground or partially grounding to the prop cone. Another telltale sign is static in you r headset that you do not normally hear. This would be that voltage getting to the radios and causing slight interference. Discovering a blade out in-flight can often render the entire system useless under certain conditions where ice could build up on the weak or dead blade and create a violent shaking of the aircraft. The only way to recover from this condition is to shut the entire system off, power back the engine to reduce the shaking, and find warmer air if possible as quickly as possible.
If your aircraft checks out properly and you have at least one escape hatch that passes the test, you are in pretty good shape for departure. I like to have at least two. Not to say you should not depart with none, but in such case be very confident of you aircraft's ability to deal with icing conditions. Non de-iced aircraft should NOT depart without at least 2 of the escape hatches available to them.
Flying In Icing Conditions
Prior to entering any icing conditions, turn any available anti-icing devices on. I most cases this will be t propeller heat and pitot heat. This combination is also appropriate before taking off into possible icing conditions when icing can be expected soon after takeoff.
Should you find yourself in a situation where ice is beginning to accumulate, most aircraft will take at least a ¼ inch give or take with out too much negative effect on flight. Once any more than that begins to accumulate, the first symptom will probably be a noticeable loss of airspeed starting with 5 or 10 knots, increasing as the accumulation of ice increases. Adding bit of power can help counter this airspeed loss. Your most important task is to take positive action immediately. Where are the tops? Can you request clearance to climb above them. Ask ATC where the tops are. Often they will know or can ask another aircraft in the area where they are. Where is the warmer air? Another option is to descend to a point above the freezing level. Once you attain 32 degrees or more, any ice will peel off within a minute or two at most. If you find yourself in conditions that have changed to afford no escape hatch options, find the nearest airport and land.
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