Following the Roselawn commuter crash of 1994, aircraft icing became the FAAs Public Enemy Number One. In the months since, the government has thrown big money at the icing bogey man. Forecasts and reports have improved, ADs have been issued, research marches boldly forward. But light airplane drivers still slog around with either boots or juice. Or nothing at all.
Boots are the old standby but more aircraft are being fitted out with weeping wing TKS systems. Since our last report on this subject six years ago, Mooney has certified its Bravo and Ovation for flight into known icing and a third single, the Encore, will soon have that option. New Commander singles are also being certified with TKS.
So much for new airplanes. How about the options for a prospective owner bent on tackling an icy overcast? Which is the better choice, boots or TKS? And does it matter if the airplane is certified for known ice or not? (Many de-ice systems arent.) Should you buy an aircraft already equipped or add boots or TKS to what you already own?
Right out of the blocks, pneumatic boots have one sizable advantage over TKS: Theyre approved for and may already be installed on some 36 models or series of light aircraft, ranging from Beechcraft Bonanzas to Cessnas heavy singles and twins to Pipers Malibu, plus many of its singles and twins. TKS, on the other hand, is found on just a handful of aircraft models or series.
If ice protection is a must, it takes but a casual perusal of Trade-A-Plane to find a suitable boot-equipped model, thanks to that long list of eligible airframes. However, some caution is advised: Some of those ads sport claims that the airplane is certified for known ice but many actually arent. Yes, theyve got the boots all right, and maybe a windshield hot plate and hot props, but in many cases, the model was never officially certified with a known-ice package or even if the model was certified, the particular airplane youre looking at may lack all the required features, such as protection for the inner wing section on twins.
Many boot systems are installed under STCs and specifically lack known-ice certification. Check the approved flight manual for that particular airplane to be sure or contact BFGoodrich for details.
Does certification for known ice really matter? Yes, if thats what you think youre buying. But frankly, unless the aircraft will be used for Part 135 charter work, we think the known-ice certification is a distinction without a difference. Even known-ice packages arent certified for continuous flight in severe icing and regardless of conditions, prudent pilots use boots for knocking off a layer of rime while searching for an ice-free altitude or route.
As the Roselawn accident demonstrated, some icing conditions will overwhelm the boots or, at the very least, raise beads of sweat on the pilots brow. But since none are certified for those conditions anyway, the outer limits of boot protection are unknown.
The same is true of TKS, although with glycol streaming back over the wings, theres little likelihood of the kind of runback icing behind the boots that did in the Roselawn ATR-72.
A typical certified boot system covers the wings, horizontal and vertical tail, plus heated pads for the props and either a heated windshield, a surface-mounted hot plate or an alcohol spray bar. A larger-than-standard vacuum pump runs the system and a back-up pump is recommended equipment.
One sticky dilemma is whether to install boots on an existing airframe or buy an airplane already equipped. Typically, an STCd boot system will cost something like $20,000, if you include a hot prop and-if available-a heated windshield plate. (Some aircraft STCd for boots arent approved for any windshield protection.) If an already-equipped airplane has a hot plate, make sure it works. Replacement costs for these devices can be ruinously high.
An across-the-board comparison between the only aircraft STCd for boots and for TKS-the Beechcraft A36-reveals that boots will cost about $25,000, to include wings and tail surfaces but not windshield de-ice, while the TKS system will cost about the same, but with all surfaces protected, including a slinger for the prop and a spray bar for the windshield. (By comparison, the certified system in new Mooneys is a $40,000+ optional add on.)
Not that having a de-ice system-certified or not-always adds much to the airplanes resale value. According to the Aircraft Bluebook, on a Cessna 310, boots add about $2600 to the aircrafts base value; on an Aztec, theyll bring less than $2000 over a similar airframe without boots; on a Cessna 210, theyre worth $3000 to $5000, depending on model year. TKS is strictly eye of the beholder; there are too few systems to establish meaningful price points.
Pneumatic boots were first developed by BFGoodrich during the 1930s and although theyve been improved over the years, the operating principle has remained the same. Air from the pressure side of a vacuum pump is pumped into tubes (usually spanwise) in each boot, causing it to inflate and breaking the ice off mechanically.
As any owner of a de-iced aircraft will tell you, boots work like a charm, except when they dont, which is none-too-rare if they arent maintained properly.
Freshly installed boots dont leak air and they inflate with vigor, blowing ice into the slipstream with a touch of the switch. But as the systems age, they often become cranky, developing leaks and absorbing water.Owners occasionally complain about boots that shed ice poorly or unpredictably. Surface treatments such as AgeMaster and Icex help, as do regular maintenance look-sees before the icing season arrives. And using boots is itself a practiced art, requiring a good eye for activating the system at the right time, just as the ice is brittle enough to break off but not before its accumulated past the protected areas.
Although runback icing was implicated in the Roselawn accident and its a favorite FAA buzzword, theres little evidence that this is a major risk factor for GA owners. The Roselawn ATR was holding in large droplet icing; GA pilots tend to-or should-exit serious icing without delay.
De-icing systems exact a penalty in weight, if not drag. A typical boot system, including the pumps and plumbing, weighs between 20 and 30 pounds, while a TKS system weighs about 40 pounds empty and 90 to 107 pounds when fully charged with fluid. (Weight varies with aircraft type.) TKS leading edges are satin smooth while boots introduce a transition line between the rubber and the metal wing. (Goodrich disputes that this causes a speed penalty.)
The serious disadvantage of boots, of course, is that they must be replaced. Even the best rubber doesnt last forever, suffering from the ravages of time, sunlight, slipstream-driven rain and industrial pollution. BFGoodrich says a typical boot installation should last seven to 10 years, although this varies widely with use and maintenance.
Replacement price varies with type, of course, but figure a reboot job will cost between $8000 and $12,000. This work can be done by dealers in the field or by Goodrichs Akron, Ohio factory in a day or two. (Advice: Have it done in the spring or summer, well before the first ice hits in the fall.) Further improving the longevity of boots is a new repair process developed by Boots, Inc., an Oklahoma company with distributors around the country. (See sidebar on page 14.)
Some shops-De-Ice System International, in Harrisonburg, Virginia is one-sell deeply discounted boot installations, using surplus boots whose shelf life has passed. For 30 to 50 percent less than the price of factory new boots, the company promises satisfaction out of the bag, but once you leave the shop, youre on your own; no warranty. Goodrichs new boot warranty is two years.
Aware of the limitations of boots, BFGoodrich has recently developed a high-tech add-on for its de-ice systems called SMARTboots. These consist of a conventional pneumatic boot with electronic ice detectors cured into the rubber along the leading edge stagnation line where ice first forms. Ice detectors have been around for awhile, too, but have been limited in their ability to detect ice in its many forms.
The idea is that the improved detectors-which consist of a bundle of conductive fibers encased in an erosion-resistant elastomer-sense ice when it interrupts electrical field lines. This illuminates a warning light in the cockpit, letting the pilot know that ice is forming even before it may be visible on aircraft surfaces. The detectors grew out of concern about tailplane icing, which came into focus during the early 1990s, even before Roselawn. It has long been known that small radii tail surfaces collect ice more efficiently than blunter wing surfaces and may have ice when the wings do not.
As shown in the photo on page 14, the SMARTboot panel has five warning lights. The ice-detected light illuminates when .02 to .05 inch of ice has accumulated. The de-ice light comes on when 1/4 to 5/8th inch of ice has formed, at which point the boots can be activated or the ice allowed to build. A residual ice light illuminates if boot activation fails to dislodge the accumulation.
The FAA awarded Goodrich an STC for SMARTboots on the Piper Malibu last summer and the company plans to pursue additional STCs in early 1998 with follow ons every few months, if the market interest warrants. Since no systems have yet been installed, we dont have any owner feedback to report. The SMARTboot system can be installed as a new de-ice installation or as an upgrade replacement to a certified system. However, its not cheap: Goodrichs Gary Plummer told us that the SMARTBoot detector system will add $12,000 to the cost of standard boot installation, plus an additional 10 pounds of weight.
Plummer says the boots operate in a conventional manner; the detectors dont improve their ability to shed ice, they only help in detecting it when it might not otherwise be visible.
Although most pilots believe TKS is a relatively new development, it actually dates to World War II, having been developed by the British to de-ice the armored leading edges of heavy bombers. For reasons not entirely clear, pneumatic boots have dominated the de-ice market in the U.S., although TKS enjoys more widespread use in Europe. (Its found on the British-made Hawker jet, for example.)
As we report on page 15, TKS owners seem uniformly enthusiastic about the system. Compared to boots, theres little knack to operating a TKS system. It has two modes: de-ice and anti-ice, with the higher fluid flow used to rid surfaces of accumulated ice. The fluid is called AL-5 and is a mixture of ethylene glycol, isopropyl alcohol and water.
The fluid is pumped at constant volume through tubing routed through the wing and tail surfaces, where it weeps through leading edges made of laser-drilled titanium or, in earlier systems, stainless steel mesh. The panels are backed by a membrane that maintains differential pressure to force the fluid out against the slipstream. A slinger similar to that used for alcohol protects the prop and a spray bar behind a fairing in front of the windshield keeps the pilots side clear. (The spray bar is controlled with its own dedicated switch.)
According to Kevin Hawley, of Aerospace Systems & Technologies, which markets TKS, there are about 200 TKS installations in the U.S., with the number growing by a couple a month. As does Goodrich, TKS supports dealers around the country, who consult on sales, service and installations. If your aircraft is on the approved list, a TKS install will require between 70 and 175 shop hours and the basic kits cost between $17,700 and $20,600. Figure on a nice round number of about $25,000 for a complete TKS. Other than new Mooneys and soon new Commanders, none of those systems are certified for known ice.
For that princely sum, you get what owners describe as superb ice protection. Although no one will officially say it, TKS appears capable of handling any level of icing, whether certified or not; big drops, little drops or freezing rain. In fact, except for a back-up pump, non-certified TKS systems are essentially identical to certified systems. Given that GA de-icing equipment is normally used as an escape hatch, we dont think the back-up pump is critical.
On the negative side, TKS is heavier than boots. Depending on the aircraft, the penalty is between 90 and 100 pounds, with the system charged and capable of providing 2.5 to 3.5 hours of anti-ice protection. (AL-5 weighs 9.2 pounds per gallon.)
Some owners address the weight problem by carrying minimum fluid levels or draining the system during the summer. Owners also say the fluid runback which keeps the wing free of ice also creates a minor mess on the hangar floor, since the goo continues weeping for a bit after the system is switched off. On the other hand, after the summer stand down, it may take 15 minutes to get the wing panels juiced up and flowing.
Maintenance wise, TKS seems to require very little. The panel membranes are sensitive to some solvents and paint, but bugs and other detritus dont seem to harm them. The wing panels can be replaced, if damaged, but other than occasional fluid filter changes, owners report no maintenance headaches.
Deciding on how to get de-iced has a chicken-and-egg quality to it. We think the chicken-that is, the airplane-comes first. The most effective way to get into de-icing is to buy a suitable airplane already equipped, allowing the previous owner to take the depreciation hit, whether for boots or TKS.
In a single, our first choice would be a TKS-equipped model, but these are relatively rare beasts and unless youre willing to accept any single on the TKS STC list, youll have a limited choice of models. Certification is a non-starter; none of the early TKS systems were certified.
Boots are found on singles and twins and, again, depending on model, we would trade-in or trade-up before installing a new system on an aircraft that has no ice protection at all. Boot installs are expensive and, in our view, the failure-prone and pricey heavy-duty vacuum pumps finish a close second place to the more effective, albeit heavier, TKS system.
As for BFGoodrichs SMARTboots, well reserve judgment until more are in the field. Thats a lot of money to spend for an ice detector that offers no appreciable improvement in the ability to shed ice, although admittedly, if tailplane icing is a major concern, the detector may prove to be a significant safety-of-flight addition.
Also With This Article
Click here to view “Restoring Old Boots: Replacement Isn’t the Only Option.”
Click here to view “TKS Owners Report.”
Click here to view the De-icing Checklist.
Click here to view “Electrical De-icing: If You Can Find the Power, It Works.”
Click here to view the De-icing Addresses & Contacts.
Click here to view the Booted & TKS Aircraft Lists.