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.