Nuts and bolts of TKS: TKS is one of the most popular ice-busting systems for light aircraft, but its utility is all in how you use it.
For the record, I am not your local FAA inspector, CFI, insurance agent, defense lawyer, or mother. I will not proselytize about doing a 180 at the first sign of icing, get into a debate about what constitutes "known ice," or preach about airplanes not approved for known icing. These things are a matter for you and your conscience.
I don't know exactly why ice doesn't stick to a TKS-coated wing and, for the purposes of this article, I don't care. Finally, the context for my comments is a TKS-equipped Mooney 252 with extended-range tanks (106 gallons) based in the Northeast.
The Need for Alcohol
A winter cold front is approaching from the west. Ahead of it, there is southerly flow bringing above-freezing temperatures aloft. You are IMC at 7000, happily cruising north in ice-free conditions and an OAT of +4 degrees C with a southerly tailwind. Life is good.
The forecast guarantees that the overrunning warm air will raise temperature above freezing all the way to the ground, but this is not happening in a timely fashion. Not only that, but the clouds reach nearly to the ground and the visibility is on the raggedy edge for getting in. You scribble yourself a note to ask for your money back on the forecast as you descend to 5000 and see the OAT drop to freezing, meaning ice is likely on the approach and the missed approach. The approach takes 1015 minutes, and the missed and the climb-out another 10-15. That's 20-30 minutes in icing conditions, with some nagging concern for being able to climb out if you picked up ice on the way down.
With TKS, you would have turned on the system about 20 minutes before initiating the descent to get the wing, horizontal stabilizer and rudder nice and coated with glycol, and you would shoot the approach with the confidence of Abraham's hand resting on your shoulder, knowing you can make a miss if you have to.
There is nothing like the joy that comes from completing a tight approach when the forecast bombed and looking at ice-free leading edges with ice on the unprotected features of the airplane. This, and tankering tons of fuel, are the two finest reasons that TKS pilots don't get high blood pressure or take Prozac instead of vitamins.
How Much, How Fast?
People ask how much ice TKS can handle. The best answer is, "Much more than the ice you'd like to carry around in a non-TKS airplane." Put differently, it may keep an airplane ice free in conditions that would put an inch of ice in a half an hour on an unprotected airplane. Still, "How much ice?" is the wrong question. The right question is, "What kind of ice accretion rate can a TKS system handle?"
The system will save your bacon in light or moderate mixed icing conditions usually found in stratus layers. This covers more than half our icing in the Northeast.
You can do research on optimum altitudes all day, but around here the altitude you get is what ATC gives you. Going anywhere near Boston? You'll get something between 6000 and 9000. Heading south to Raleigh, N.C., (KRDU) in the winter time, it will be 6000 over JFK and then 8-9000 until Approach hands you off to New York Center (even if it's the wrong altitude for the direction of flight). Although you can get lucky and work an altitude that puts you between layers, you can also get unlucky and be stuck in icing temperatures in IMC.
If there happens to be ice at those altitudes, and the ice comes from stratus clouds, accretion rate will be within the capabilities of a TKS system and you can cruise in peace until Center gives you a climb to the low- to mid-teens. That is, of course, if you can handle getting up there. (Hint: turbocharging helps.)
Say you're headed west to Chicago in the winter or even spring and PIREPs say, "tops 13,000, clear above." At 6000, you're in ice and wicked turbulence. The headwinds are "only" 30 knots, but it's a thoroughly unpleasant flight. Headwinds at 14,000 are 60 knots, but the sun is out and the air is smooth.
You would not hesitate to go upstairs with TKS. (Two hints: turbo-charging and long-range tanks.) On the way up you have to climb through 6-7,000 feet of icing clouds. If you are TKS equipped, you would ask for 14,000 just as soon as you get handed off to Allentown Approach (who hands you to New York Center, who gives you the 14,000 pretty routinely). Since TKS coats both top and bottom wing surfaces, there is no need to worry about ice building up on the under-side of the wings in the climb, which is a great benefit.
Approaches often mean loitering in clouds at ice-producing altitudes while on vectors to get lined up. In rural settings, you may count on staying on top--or at least in an ice-free environment--and making a last-minute, rapid descent to minimize exposure. This isn't the case at busy metro airports. Assume that you will be at altitudes assigned by Approach. Unless the approach is into freezing rain, a TKS system can handle light to moderate mixed ice under these circumstances.
TKS is generally unable to handle the sudden and rapid build-up of clear ice. Ice of this type abounds above the freezing level in developing cumulus. Tops may be only in the high 20s, but with the freezing level around 10,000 feet, penetrating these build-ups at the high teens assures you of notable turbulence and a large, and immediate, helping of clear ice. It is possible to accumulate a half an inch of clear ice in a few minutes--more if you loiter.
This scenario can play out at surprisingly low altitudes in the early spring. You may be cruising at 12,000 with the tops at 12,500 and the freezing level at, say, 8000. The cumulus heads will have an etched, sharp-edged appearance; the sharper the edges, the more water and the more ice. Bumbling into one of these sounds like someone is sandblasting your airplane as the ice piles on. In this situation, get out of Dodge to the above-freezing temperatures that are generally available below.
The same sane advice goes if you are planning to cruise in the tops of the stratocumulus in the lee of the Great Lakes. Just don't do it. These layers rarely go higher than 12,000 feet, so operate on top knowing the TKS will handle a descent through these icing layers (provided you turn it on early enough to coat the surfaces with glycol).
Occasionally a huge, wet system parks over your route and kicks out accretion rates that a TKS system on a single-engine airplane cannot handle. On those days you have to pack a sandwich and take the jets. (For god's sake don't eat airline food.)
A TKS system is also not equal to substantial freezing rain. I suppose light freezing drizzle has a better sound to it, but I cannot give you any observations from personal experience, nor do I plan to.
TKS systems are not instantaneous. The propaganda may say that you "turn it on when you encounter icing conditions" but that is nonsense. TKS works only if you anticipate well in advance.
Unless you have "warmed up" the system on the ground before departing, it needs time. Expect at least five minutes to get glycol to the prop and the windshield; 10 minutes to come up to pressure in every panel on the wings, horizontal stabilizers, and vertical stabilizer; 15 minutes to coat all the leading edges with glycol; and 20 minutes to put a coating of glycol on the wings as the fluid runs back. Personally I like the 20-minute option.
You have to test the system during preflight. Turn it on while on the ground, walk around the airplane, and confirm that glycol fluid is coming out of every panel. It saves a little time if you first run it in de-icing mode (instead of anti-icing mode) because the pump runs faster and brings the piping and panels everywhere to the required operating pressures a few minutes faster.
Once you have the engine running, turn on the system in anti-ice mode as you taxi out if you are about to depart into suspicious clouds. You can activate it later in the flight; just give the system the time to coat the surfaces before penetrating icing conditions. For night operations, the system gives you a cute ice-light. If you don't like what you see, turn the light off.
If you neglected to pressurize the system in time and you picked up ice, use the deicing button. The pump puts out more fluid out at higher pressure to remove ice already accreted, although it may take 20 minutes to get rid of all of it. That time obviously depends on whether you are continuing to pick up ice and the accretion rate. Still, the deicing setting will overcome light-to-moderate ice. Use the deicing setting whenever the anti-icing setting starts falling behind.
Six gallons of TKS glycol lasts three hours. That should cover several flights, because surely you aren't going to loiter in icing conditions for three hours, are you?
Installations vary between inadvertent icing and known-ice systems and range from around $30,000 to north of $50,000. A case of TKS with two 2.5-gallon containers costs around $150, so the six gallons in your TKS tank are worth $180. A short ice episode, one that uses up, say, one gallon in a half an hour, will cost $30.
At the price of $5.00 aviation fuel, that equates to six gallons. Not bad compared to what you might waste dragging an ice-laden airframe around. And, yes, you simply have to use the approved stuff. Why would you put an expensive installation at risk? Some Hawkers use TKS and FBOs that service them carry TKS fluid.
All that said, you have to forget about the cost of glycol. It would be silly to get all iced up because you decided to save a few dollars. Besides, traveling in icing conditions with no ice on the prop, windshield, wings, horizontal stabilizers and rudder is as close to heaven as wintertime mortals get.
RELATED ARTICLE: Weeping wings 60 way back.
According to Jeff Holden at AS&T, Inc., "TKS stands for Tecalemit, Killfrost, Sheep-bridge-Stokes. They are the three companies that were brought together during WWII to design and produce the first TKS anti-ice systems. The system was designed as a metal (backthen steel-mesh) leading edge for protection from barrage-balloon (anti-aircraft) cables that the bombers with TKS flew through. The boots with which they were originally equipped would tear off or, worse, catch the cable instead of allowing it to slide along the leading edge to the cutting charges."
The TKS installation covers the leading edges of the wings, horizontal stabilizers, and rudder with a thin strip of titanium. This strip has millions of tiny holes--some 800 per square inch. Each hole 0.0025 inches in diameter.
An electric pump forces glycol through these holes. The glycol coats the leading edges and runs back, top and bottom, on the surfaces. Ice, which loves to stick to paint, is unable to stick to the glycol-slick surfaces and, bingo, the airplane does not collect any.
The pump also puts some glycol along the leading edges of the prop blades and keeps ice from sticking there, which is important. The prop throws off the glycol and air carries this mist to the windscreen, keeping that ice-free too. There is a separate spray-bar for the windshield, although I have never had to use it. Moreover, the air stream carries the spray over the top of the fuselage to the VHF antennas. (Who says there is no free lunch?)
Other wonderful benefits include not having to repaint the leading edges or worry about bugs in the summertime. Titanium looks pretty much the same after 10 years. These benefits alone ought to give you cause to install TKS.--E.S.
Emery Stephans owns a well-equipped Mooney 252, which he flies nationwide.
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|Date:||Jan 1, 2008|
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