Icing and the TKS system
With winter now upon us (if you live somewhere other than
Scottsdale or Los Angeles), and the number of TKS-equipped Cirrus airplanes on
the rise, I thought it might be helpful to have an open discussion on icing
encounters and proper techniques for using the TKS system.
First, a caveat: we all know that the TKS system is not certified for known icing conditions. But as the Cirrus magazine ads last year pointed out, “Ice Happens”. So let’s not digress into the regulatory aspects of how one managed to get into icing conditions in an uncertified airplane. Instead, let’s focus on real experiences and suggestions, so that we can all learn from each other. Frankly, I didn’t find a single instructor during my training that had any knowledge about ice: they all thought the wings would instantly fall off. Presumably the COPA membership has a more enlightened view on the subject.
Here are several observations I’d like to throw into the discussion:
1. The POH Supplement says nothing about the use of alternate air when using the TKS system. On the other hand, the emergency checklist for icing encounters on the Avidyne says “use alternate air”. So I’ve opted to use alternate air whenever TKS is on, and with totally unscientific methods I’ve determined that it has a 4-6 knot negative impact on KTAS. I am not aware of any deleterious effect from keeping alternate air open throughout the flight, other than a minor speed penalty. Does anyone think otherwise?
2. The TKS system does an admirable job at normal flow rate of removing the slushy ice that accumulates below 6,000 feet when going through a snowshower. It does an excellent job of removing light rime ice at any altitude. It takes about 3-5 minutes for the flow to build up, and then most of the stuff just slides off. In the interim, there is a 5-10 knot speed penalty. However, if one waits for buildup before turning on the system, there’s at least a 50/50 chance that one or more of the TKS outlets on the prop will get clogged, and it won’t clear up until the plane is back in the sunshine. Plus some of the slush or rime ice can turn into hard ice which does not dissipate (but as best I can tell it did not impair speed at all). So its preferable to turn on TKS before entering those clouds where ice may arise.
3. Climbing to the highest possible altitude is the preferable strategy, because the cold air of winter gives a very fast rate of climb (10,000 feet in six minutes), and there’s a decent chance that it will get you above the weather or that it will be cold enough to avoid icing. This is a particularly valid strategy in the Cirrus because there is only an hour of TKS reserve, so its vital to conserve it for any surprises on the descent. I use the count up function on the transponder to track accumulated usage during a flight, and then refill on landing.
4. As Scott D. teaches in his “Weather or Not” seminar, there is no hard and fast rule on the temperature at which one is safe from ice. The common belief is that at colder than –20 Celsius ice won’t form, and this is certainly a good target to aim for. But I ran into light rime ice at 11,000 feet and –24 Celsius during a morning flight, so there are no guarantees. On the other hand, during an afternoon flight there was no ice on the same route at 10,000 feet and –25 Celsius.
5. Don’t be surprised if the throttle doesn’t pull back smoothly after a visit through the ice. My guess is that there is some ice buildup inside the cowling on a cable or linkage, notwithstanding the use of alternate air. Working the throttle lever back and forth smoothes out the friction, but not entirely.
6. Flying through ice substantially increases the pilot’s workload. A lot of energy is devoted to watching the wings and tail, checking speed and setting the throttle and mixture, setting the timer and alternate air, etc. Plus there’s the factor of figuring out whether to climb, descend, divert or conserve TKS for later on. If ever there’s a time to “use all available resources” on the aircraft, this is it.
7. I get my TKS fluid from my SC in 2.5 gallon jugs. They’re much too heavy and unwieldy to pour into the small inlet port, so I keep my backup supply on board in smaller jugs with built in spouts. Be prepared for wind and mess when you’re refilling the TKS tank; it helps to be wearing clothes that like getting dirty because the stuff blows and spills all over the place.
8. This may not be obvious to everyone, but the sections of the wing which do not have the TKS strip will accumulate a decent layer of ice, and there's nothing you can do about it. The good news is that its against a white background, so you can't see it unless you look real close or after landing.