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Volume 20, Number 7c

August 21, 2013

Autopilot Repairs: Worth a Try

 

It wasn’t long ago that an entry-level, two-axis autopilot was priced around 10 grand—including installation. Today, that price is double. Add some options and the bottom line could soar toward $30,000.

These big proposals have many owners repairing older autopilots. But as service parts for older systems become obsolete, repair costs are high, downtime is increased and factory flat-rate pricing makes the repair questionable.

In this article, we’ll look at the reality of autopilot repair versus replacement. For basic systems, we think replacement is a better, long-term option.

Major-Level Repairs

We spoke with several respected autopilot repair facilities for their view of common, serviceable models. Surprisingly, repair capability for vintage systems—including Cessna/ Sperry and Piper/Century models—is good. It helps to use a shop that does high volume. That’s because they’ll have a good supply of core units for accessing hard-to-find parts. Better yet, many vintage systems can be returned to near-new condition. Still, everyone we talked with suggested that autopilot repair pricing is on the rise.

According to Bob Ferguson at Autopilots Central in Tulsa, Oklahoma, overhauling an older system is almost always going to be cheaper than replacing it.

“It might cost over $10,000 to overhaul an old system, but that’s still going to be cheaper than replacing it with a brand new model,” said Ferguson, who’s worked with autopilots for over 40 years.

Autopilots Central repairs and overhauls most systems in house, including King, Century and Cessna autopilots. According to Ferguson, one of the challenges his shop faces is dealing with S-TEC models, especially flight computers and servos. That’s because S-TEC doesn’t supply bench-level replacement components to the dealer network. Instead, major repairs will have to be accomplished at the factory.

Bruce Grammon at Mid-Continent Instruments and Avionics in Wichita, Kansas, told us that sourcing affordable, replacement parts is becoming a challenge.

“Parts. Whether it’s drive transistors for KC295 computers or servo motors for some King KFC150 systems for Mooneys, our biggest challenge is finding a healthy supply of replacement components for older systems,” said Gammon. According to Gammon, autopilot repair work has increased at his shop over the past couple of years. This, he says, is a direct result of other avionics upgrades.

“Owners might spend $15,000 on a retrofit PFD system but over-look an ailing autopilot system. In many cases, owners can’t handle the additional investment of a new autopilot,” Gammon noted. It’s easy to understand why repairing an old system seems appealing.

Factory repair comes at a premium. Cobham Avionics has three price structures for repairing the S-TEC line of autopilots. Minor-level repair covers component-level diagnostics, troubleshooting and repair but without replacing major components. If major component replacement is required, the repair turns into a major-level event—with a major price schedule. For instance, a 55X programmer/computer requiring a major level repair, has a flat-rate cost of $2927.

Cobham has an overhaul service—which covers replacement of most or all major components. That same 55X requiring overhaul has a price of $8441. This might be required for older computers with obsolete circuit boards. In some cases, Cobham might exchange the computer. Shops report long turn-around times, but our experience with the quality of S-TEC repairs is favorable, as is the quality of field technical support. Build time for a new system could be as long as five weeks, since each autopilot is airframe specific.

Old Standards 

With old systems, it’s not as easy. While the venerable King KFC200 is long out of production, field support is good but troubleshooting can be intensive. Earlier servos—including the KS270-series—are mostly obsolete, but interchangeable with newer, A-suffixed versions. Other troubles with the KFC200 could rest in the KC295 remote-mounted flight guidance computer. Problems related to the systems pitch and roll circuit boards might lead to expensive board replacement.

Still, we wouldn’t trash a KFC200, as it’s a good-flying and full-featured autopilot. Moreover, digital gyro emulators and GPSS steering might offer the KFC and other analog models a new lease on life.

The KFC150 and KAP150 (the latter has no flight director) utilize a panel-mounted controller/flight guidance computer. They have automatic pitch trim and can drive altitude preselect and alerter systems.

These and all attitude-based units from Bendix/King can be prone to gyro-induced flaws. Some possible symptoms of a gyro problem include shallow wing rocking and gentle pitch porpoising. The KI256 flight director gyro could be the problem. Overhaul exchange might cost around $3600, from a reputable shop with a one-year warranty.

What about pre-KFC autopilots, including the Bendix FCS810. Our sources told us these systems are repairable, but parts are becoming scarce.

The same is said for some Cessna 200-and-300 series autopilots. Higher-end Cessna systems—including the 800-series flight control system found in heavier piston twins and turboprops—are complex. You’ll want an experienced shop to handle repairs to these systems.

Early and mid-2000 model year Cessna models feature the KAP140,a rate-based autopilot with good performance and decent capabilities. There were, however, many service bulletins against these autopilots that required inspection and in some cases, replacement of servo assemblies. Look at this service record carefully when buying a used KAP140-equipped 172, 182 or 206.

If you have one of the Brittain AccuTrak or Accuflite systems, there’s hope. Brittain Industries in Tulsa, Oklahoma, still offers support for some models. One system that several repair shops warned against is the Bendix M4D. This system can be found in some Beech King Airs, some bigger Cessna twins, Mitsubishi MU2s and others. Servos for these systems can run close to $9000 each, if they can be sourced. Still, some shops might be able to work on them and bring them back to life, if you're lucky.

Avidyne’s Drop-In

The flagship S-TEC 55X is generally a good performer. But its rate-based turn coordinator drive isn’t always well matched for speedier airframes. For example, Cirrus pilots will attest that its weaknesses are most pronounced on coupled approaches, where it will often hunt left and right to keep the needles centered. GPSS steering helps, but not on an ILS, where the system might blow through the localizer. Nor does it work well on an LPV, because the 55X was conceived before the days of GPS approaches with vertical guidance. As a result, the system won’t fly the vertical segment of the approach in GPSS mode. But Avidyne’s DFC90 autopilot seems light years ahead, with sharper performance and useful features.

The DFC90 is partly a drop-in replacement for the 55X and it uses the same tray, wires and servos, but gets its reference directly from the PFD. This means it’s an attitude-based autopilot with access to an air data computer. It also eliminates the shortcomings of a rate-based system.

Realizing that pilots might have to overcome a learning curve when stepping up from the 55X, Avidyne retained as much of the buttonology as possible from the S-TEC control head to ease the transition. The new buttons are color-coded to show what modes are active or armed.

But more advanced is the straight-and-level mode. Similar to the Level button on the G1000-based Cirrus Perspective system, pilots might get a second chance at recovering from an unusual attitude. Pushing the Level button engages the autopilot and returns the aircraft to level flight. On a demo ride in the company Skylane, we witnessed the recovery from 60 degrees of bank and 30 degrees of pitch. The system is virtually stall-proof, with pitch logic that guards against decaying airspeed.

Avidyne retained the hidden turn coordinator from the original S-TEC installation as a fault comparator. If the DFC90 sees a mismatch between the PFD attitude and the turn-rate information from the old system, it will disengage and alert the pilot.

There’s also an STC that covers the DFC90 autopilot as a plug-and-play retrofit of existing 55X systems in 16 models of the Cessna 182 Skylane series and also various models of the Beechcraft Bonanza,  when installed with the Aspen EFD1000 PFD.

The Aspen Pro PFD provides attitude inputs to the DFC90 from its integrated ADAHRS, while displaying autopilot mode annunciations and alerts on the Aspen PFD. In addition to pitch and roll inputs, the Aspen Pro PFD also provides heading command, altitude preselect, indicated airspeed select and vertical speed command to the DFC90. The DFC90 has a starting price of $10,180 and the software unlock for integrating the DFC90 with the Aspen is $1995.

AHARS-Boosting Performance

A good way to breathe new life into an aging analog autopilot is to ditch the spinning gyro that drives it. Attitude-based autopilots rely on a horizon gyro for feeding pitch and roll output signals. These vacuum gyros—including the King KI256 flight director and ARC G550—are expensive to overhaul and add to the complexity of system maintenance. But both Garmin and Aspen have modern alternatives to sharpen the system’s performance while eliminating expensive gyro upkeep.

The Garmin GAD 43 is a remote box that converts AHARS digital pitch, roll, heading and  yaw rate data into analog signals used by attitude-based autopilots, to include the popular King KFC200/150 series and some ARC/ Sperry autopilots. The analog signals from the GAD 43 emulate those of traditional spinning gyros. The benefit here is two-fold: First, AHARS has proven more reliable than vacuum-driven gyroscopes. Further, the digital reference output from an AHARS system is more precise and stable than an aged spinning gyro.

Aspen offers a gyroless interface with the EA100 autopilot emulator. Like the Garmin GAD43, the EA100 remote unit receives pitch and roll reference from the Aspen 1000 AHARS and sends the data to the autopilot computer, just as the old spinning gyro did.

Installing the GAD43 and EA100 digital converters isn’t a slap-and-go project. Expect sizable amounts of configuration and calibration to make the autopilot fly true. This means you’ll want to select an installation shop that’s not only experienced with installing PFD systems, but one that’s also familiar with calibrating the analog autopilot it’s interfaced with. This analog-to-digital transformation is only as good as the installation—and the health of the servos and other supporting components in the system.

Caveat Emptor

For new retrofits, Cobham S-TEC still owns the market. The entry-level Thirty autopilot—which has altitude hold and basic nav tracking—will likely cost upwards of $17,000 after installation. We think it’s a good match for light airframes and is a better long-term solution than repairing a basic older system. It also offers more features than a basic wing leveler and couples nicely with nearly any panel-mounted GPS.

When buying a used aircraft, a little research goes a long way. Any work on the autopilot should be logged in the airframe logbooks. Look for descriptive entries, including teardown reports of replacement servos and gyros. They might offer clues as to the quality of the repair.

Buying an airplane with the intentions of upgrading or repairing its old autopilot is OK, as long as you understand the costs involved.

A version of this article originally appeared in the May 2013 issue of Aviation Consumer magazine.

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Leading Edge #20: Choosing Your Takeoff

If a nonpilot asks you "How do you take off?" how would you answer? Line up with the runway, add power, accelerate to liftoff speed, raise the nose and go. But is it really as simple as that? Every year airplanes fail to get off wet or muddy runways, or to clear obstacles past the departure end. Every summer we hear of airplanes that can't get airborne or, if they make it into ground effect, don't have the power to climb any higher. The answer to "How do you take off?" is "I have to choose the technique to match the takeoff conditions." So how doyou choose your takeoff?

Rolling Takeoff, Or Power Up On The Brakes?

Do you stand on the brakes and power up, or do you prefer to add power smoothly, letting the airplane roll as you advance thrust? A rolling takeoff is less stressful on the airframe (and occupants). Although some pilots have a personal preference one way or another, there is no "correct" answer; what you do depends on the requirements of that takeoff. Try this experiment: On a calm-wind day, put an observer in the copilot seat. Line up with the runway centerline on a specific spot, such as the runway numbers. Add power for a "rolling" takeoff ... that is, let the airplane accelerate naturally as you advance the throttle. Accelerate until you lift off, having your observer count the number of runway stripes and spaces from power-up to liftoff. If the runway has standard markings, each stripe-and-space combination is 200 feet long. Regardless, fly the pattern and land, having recorded your estimated runway requirement for takeoff. Now repeat the experiment, except from your identified starting point power up while holding the brakes. As soon as you achieve full power release brakes (you'll need more rudder initially than a rolling takeoff, because low air flow over the rudder reduces its effectiveness at countering torque). Accelerate to the same takeoff speed, with your observer counting the runway stripes-and-spaces. Do this a few times each way to gauge the difference at a variety of weights and density-altitude conditions. What you may find in many airplanes is this: A rolling takeoff results in a longer takeoff roll. The heavier the airplane and/or higher the density altitude, the greater difference you're likely to see. So back to answering that nonpilot's question: If the objective is to get off a short runway, or to take off when you have a nearby obstacle, or when departing with a high-density altitude (you'll have to explain that to a nonpilot), you'll probably choose to make a "power up on the brakes" departure. Otherwise, you'll likely make a rolling takeoff to reduce stress on the airplane.

Flaps Or No Flaps?

Do you use flaps on takeoff, or not? The effect is going to vary widely by airplane type, so you'll need to do another experiment. (Getting to better know your airplane's flight characteristics ... what a good excuse for doing a little proficiency flying!) First, look for any limitations on flap use for takeoff in your airplane's flight manual or POH (not just Performance section recommendations -- I mean Section II, Limitations, which are imperatives). Repeat the rolling/braking experiment, but this time using a consistent technique (i.e., rolling) but with any flap settings that is not prohibited by the manufacturer. On each takeoff, call out when you're 50 feet agl (or, if it's easier to read, 100 agl) and have your observer note where you are over the ground when you make that call. Determine what flap position gets your airplane off the ground soonest and what gets you to the altitude goal (50 or 100 agl) in the shortest distance. Again, it will vary by type, weight and density altitude, but you might find that your airplane gets off the ground sooner with flaps, but takes a shorter distance to meet the altitude goal without them. If that's the way your airplane flies, your answer to that nonpilot might be, "If the runway is short but there's no obstacle, I'll use flaps, but if there's a power line or trees off the end of the runway, I'll take off with the flaps up."

Liftoff Speed

"How fast is your airplane when you take off?" your nonpilot friend inquires. As you may have already figured, the answer is again, "It depends." Depending on the vintage and complexity of your airplane, the manufacturer may have specified a takeoff speed. It will even vary with airplane weight in heavier aircraft. For your experiment, pick a technique (rolling or braked power-up) and a configuration (flap setting) and have your observer note takeoff distance and the point you reach your altitude goal when lifting off at the "book" speed. Next, repeat the trial but let the airplane lift off "when it's ready" (the heavier the airplane, the less wont it has to do this). Finally, consistent with the airplane's capability, try a couple "soft-field" takeoffs, lifting off into ground effect at a slower airspeed. See what effect different liftoff speeds have on runway distance and initial climb. Can you generalize your airplane's performance for the nonpilot, and your own choice of takeoff technique?

VX or VY?

Closely aligned with liftoff speed is the target speed for initial climb. If your goal is to climb steeply over an obstacle, use VX. It'll be listed in the POH, perhaps modified (and thinly disguised) as a recommended 50-foot target airspeed, adjusted for airplane weight, on the takeoff performance chart. Note that the airplane may have different published speeds for different takeoff flap positions. On some of your "experimental" takeoffs, find the attitude that results in VX speed passing over that mythical 50-ft obstacle and have your observer record the distance it takes to reach that height from rolling/braked, flaps/no flaps conditions. Do the same at VY speed passing 50 agl. What you'll likely tell your nonpilot inquisitor is, "I will begin my climb at VY unless I have to clear a close-in obstacle, in which case I'll climb at VX. But wait: You may want to climb out even faster than that. If engine cooling is an issue, or in multiengine airplanes where speed is your best defense against loss of control in the event of an engine failure, you may want to climb out at an even shallower angle and higher airspeed if obstacles permit. Figure a few of these faster initial climbs into your exercise and see how much distance it takes to get to 100 agl. You may tell that nonpilot you'll normally climb out even faster than "book" unless conditions dictate otherwise. That's powerful information to know as you choose your takeoff technique on any given day.

Mixture Technique

Chances are your nonpilot friend won't think to ask you about fuel-mixture technique. But you need to make a conscious decision about it. Mixture technique for high density-altitudes is a common topic in aviation publications (see "Hot and High How-To" in the July 2008 issue of our sister publication Aviation Safety). Yet it's obvious from the summertime mishap reports that the lesson needs to be reviewed each time the weather begins to warm. The trend in more powerful engines is to crank up the fuel flows to their maximum to provide additional cooling at high power settings. This is especially true with turbocharged engines. The high flow rates now in vogue serve their purpose, but they may inhibit takeoff performance by creating too rich a fuel-air mixture. In hot weather (with a long runway), experiment with full rich and leaned mixture, measuring their effect on takeoff roll and the distance required to get 50 or 100 feet into the air. You may find to clear an obstacle, especially at a high density-altitude, you need to sacrifice a little long-term engine cooling (full rich mixture) for short-term performance (leaned for maximum horsepower). Afterward, if your nonpilot friend doesask you about mixture technique for takeoff, you might reply, "I use full rich except as need for takeoff performance, and if so, then I enrichen the mixture as necessary for engine cooling after transitioning to en route climb."

Choosing Your Takeoff

Planning, flying and interpreting these experiments would make a great instructional session. Combined with the required ground instruction and with a CFI as your observer, it could be a very informative flight review (see last month's Leading Edge column). Use a long runway so maximum performance isn't required for safety; adhere to all airplane and engine limitations. Airplane weight and density altitude will greatly affect performance, so be careful that you generalize only for a given set of conditions. Fly extremely conservatively when outside your area of experience. By thinking about how you'd answer that simple nonpilot's question, "How do you take off?" you'll ask yourself what technique you should use every time you choose your takeoff. Fly safe, and have fun!


Thomas P. Turner's Leading Edge columns are collected here.

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Podcast: NAFI Tackles Student Retention

It's one thing to get people in the flight school door; it's another challenge to bring them through to the check ride and beyond.  This week, Bob Meder, president of the National Association of Flight Instructors, hosted a webinar to discuss those issues and develop an action plan.  He spoke with AVweb's Mary Grady about the results.

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New airplanes sales may be a little soft, but we're seeing plenty of refurb work -- everything from new panels to fresh paint to full-up interiors. We would like to feature some of these airplanes in the pages of AVweb and spotlight the owners and shops doing the work. If you have photos of your restored aircraft -- single, twin or turbine -- send them to us at refurb-otm@avweb.com. If we select your airplane as refurb of the month, we'll contact you for more information.

AVweb/Aviation Consumer Avgas/Mogas Survey

As the quest for a replacement for 100LL drags into its third decade, our sister publication Aviation Consumer, is seeking opinions from owners, pilots and aircraft operators on how you think the process is going. The FAA has established a special office devoted to a replacement for 100LL and piston fuels in general. We would like to know if you've followed the process and, if so, what you think of it.

And what what about mogas? In some cases, it's $2 cheaper than avgas. Are you using it? If so, what are your experiences and if you haven't used it, why not? You can take the survey by clicking here. It'll take about five minutes.

We'll compile the results and compare them to the same questions we asked two years ago.

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AOPA's New Man

When I heard that Mark Baker was tapped as the new AOPA president, my first thought was...could he be the son of that other Baker, the one whose name almost always appeared appended to the word “colorful?” But no, no apparent relation.

By now, you will have perused Baker’s resume and formed your own opinions. Since the AOPA board never favors its membership with anything vaguely resembling a statement of intent, we can only surmise that when shuffling resumes, it was looking first for high-level executive experience from someone with lots of GA experience, both of which Baker seems to have. From his vitae, he seems to spring from that corps of professional executives, often peripatetic, that run the country’s thousands of small and mid-sized companies. Most recently it was Orchard Supply Hardware Stores Corp., a debt-ridden Sears spinoff that was supposed to compete in the Home Depot and Lowe’s realm. But it went bankrupt trying, thanks to the debt load. Its sale to Lowes was just approved a day ago. (AOPA’s Baker bio didn’t mention this and should have. It’s a basic fact readers are entitled to. They should have also been told Baker will continue to consult with his previous employer.)

So Baker brings to AOPA a strong background in management of shelter and lawn retail businesses, which, according to the association’s release, it considers a key asset. I’m not quite sure I see the connection, but in the name of give-the-guy-a-chance, I’m willing to indulge. If I were pawing resumes, I guess I’d look for marketing and management experience in general aviation businesses and/or political experience in Washington, which is what got the outgoing Craig Fuller a chair in the corner office. Retail experience implies a customer service tilt, but I’m not so sure AOPA has a membership service problem so much as it has a general direction problem.

As I noted in this blog last March, when Fuller announced his departure, I don’t think the association is irretrievably broken, although our surveys revealed significant membership dissatisfaction with AOPA’s direction and emphasis. That’s not a customer service issue, it’s a product issue, if you will.  

There’s no reason to believe that a competent, dynamic executive with good GA knowledge and involvement—Baker has that—can’t get things back on track, if he’s working with a cooperative, like-minded board. And that we don’t know, since the board lives behind the black wall. There’s also no reason that the exec has to be someone who’s well known in aviation, which Baker is not. Leadership is all about knowing the right direction to go and making the decisions to get there.

And that’s Mark Baker’s new job. We should all wish him every success at it and stand by to see the results.

Join the conversation.  Read others' comments and add your own.

Video: PS Engineering's PAR200 Multi-Function Audio System

There's a need for affordable audio system upgrades for basic aircraft.  PS Engineering attempts to answer the call with the PAR200 -- a three-in-one system that combines an advanced audio panel, a stereo intercom, and a remote comm radio.  In this video, Aviation Consumer's Larry Anglisano takes a look at the unit during it's introduction at AirVenture 2013 at Oshkosh.

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AirVenture 2013 Product Minute Video: ForeFlight 5.3 Preview

As AirVenture 2013, ForeFlight was showing off the latest version of its popular app, and it now includes Canadian charts, a unique plate overlay feature, and helicopter charts for U.S. pilots.  In this AVweb Product Minute, ForeFlight's Jason Miller gives us a tour of the app's new high points.

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AirVenture 2013 Product Minute Video: Dual Electronics' XGPS170 ADS-B

The XGPS170 is a combination GPS and ADS-B weather and traffic receiver from Dual Electronics.  Dual's Greg Lukins gives a tour of the unit at AirVenture 2013.

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