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Budget Autopilots: Growing STC Approvals: The lower-priced autopilot market is finally turning the page as installation approvals expand. You can now get the latest digital tech for under $10,000 installed..

Second to engine replacements, autopilots top the list of the most expensive aftermarket retrofits you can make to the aircraft. Until recently, pricey entry-level systems didn't offer much more than basic wing-leveling functions.


But thanks to a welcomed switch in FAA regulatory mentality, the certified market has recently seen no fewer than three new budget-based and full-featured autopilots (priced under ten grand) trickle down from the experimental aircraft world. This includes the Garmin GFC500, the Trio Avionics Pro Pilot and TruTrak Vizion, which all earned STCs last summer.

Still, the buying decision is muddy mostly because of their limited STCs and third-party interface potential (although that's changing for the better). In this article we'll take an updated look at all three systems to help ease a complicated buying decision.

Since we covered the Garmin GFC500 extensively in the September 2017 issue of Aviation Consumer, we won't dive too deep in it here, other than taking a fresh look at interface potential, required instruments and an update of its STC approvals.


California-based Trio Avionics has been building autopilots for the experimental market since 2003, but it was the outside firm The STC Group (founded by Paul Odum) that earned the initial STC for the Cessna 172/182, and recently announced approvals for the Cessna 175, 180, 182 and 177. There's also the Piper PA28.

The STC Group is currently knee-deep working on other STCs, including ones for the Piper PA32, Grumman AA5, Cessna 195, plus older Beechcraft Bonanzas and Debonairs. Trio and The STC Group are separate entities; Trio sells the autopilot, while The STC Group sells the installation kits and permission to use its STC, although orders are coordinated seamlessly through Trio.

The Trio Pro Pilot is a rate-based autopilot, but unlike other designs that use a mechanical turn coordinator for roll input (S-TEC and BendixKing's KAP140), the Trio has self-contained solid-state inertial rate sensors. It also receives position data from panel and portable GPS navigators, providing automatic corrections to the sensor data to correct for drift due to thermal shifts, inherent sensor drift and noise errors. In panel-mounted navigator interfaces the system uses serial and Arinc 429 data input, while portable interfaces use NMEA serial data. The autopilot also uses pitot/static air input for computations.

Worth mentioning is that given the age of some pitot/static systems, expect to pay for additional labor (and parts) to get the system back in shape. Of course, you should be addressing problems in the system (mainly leakage) when shops perform the two-year FAR IFR inspections.

The Pro Pilot, which is completely digital, has three lateral modes including nav track, course/track command and wing leveling. In Track mode, the autopilot follows the flight plan coming from the GPS (including GPS roll steering). In WAAS-equipped installations, the autopilot can fly precision LPV approaches, but it won't fly raw nav ILS or localizer approaches. This is a GPS-functioned autopilot only, at least in terms of course tracking. Forget about connecting it to your old King KX155 nav radio for tracking.

At this point, the Pro Pilot doesn't interface with third-party directional gyros or HSIs for flying a commanded heading, although Trio's Chuck Busch told us the company is pursuing interfaces with popular EFIS systems, including the Aspen PFD. Technically, it would be an easy interface to accomplish, but we're told the FAA is treading cautiously when it comes to interfacing with external third-party flight instruments. While any pilot-initiated directional changes are done through the autopilot by selecting a desired course, we'd still like to see external mag heading command from a DG or EFIS.

Installation is flexible because the Pro Pilot is offered in two configurations, including a version that fits in a standard 3-inch instrument cutout and also a flat-pack style control head that mounts in the radio stack. Both versions are covered under the existing STC and offer the same functions, just packaged differently.

The systems ships with a complete wiring harness and two servos for the autopilot's pitch and roll axes. At this time the STC'd autopilot has no electric pitch trim option. Instead, the system has trim prompting, which triggers an annunciator so the operator can manually trim the aircraft in the pitch axis.

Speaking of servos (they weigh 27 ounces each), we like that the digital smart-servo installation is traditional and attaches via pushrod to an aileron or elevator bell crank, but without bridal cables. This means less upkeep and less worry about loosening bridal cable tensions, which degrades performance. In a Cessna 182/172 application, the roll servo is installed in the wing, while the pitch servo is in the tail. The servos are failsafe, with slip clutches and feedback circuitry. In some experimental applications, the system comes with an elevator pitch trim servo and Trio says this could be a future offering for certified aircraft, too.

As for advanced functions, the Pro Pilot has altitude preselect, vertical climbs and descents, plus stall and overspeed protection. There is also an automatic 180-degree turn feature to back away from inadvertent IMC, and it's nearly impossible to take off with the system engaged because the sensed GPS groundspeed during the takeoff roll will make it disengage.

The experimental version of the autopilot has a fuel endurance computer built in, but the current STC doesn't yet cover the function.

The Pro Pilot has a list price of $3495, and installation kits are between $2500 and $3000.


To differentiate it from its experimental line, Arkansas-based TruTrak calls its STC'd system PMA Vizion. The company partnered with the Experimental Aircraft Association (EAA) and earned a growing number of Vizion STCs, plus PMA approvals, initially for the Cessna 172. Recall that EAA was instrumental in the STC for the Dynon D10A experimental EFIS display (it owns the STC), which incidentally got the ball rolling for the swift FAA approval of Garmin's low-cost experimental G5 flight instrument, which is the backbone of the company's GFC500 autopilot. More on that coming up.

In addition to the Cessna 172, current PMA Vizion autopilot STC approvals include the Cessna 177 Cardinal, Cessna 175, Piper PA28 and PA32. As we got to press, TruTrak says it's finishing the STC for the Cessna 182 and will pursue an STC for retrofit in Mooney models.

Providing an autopilot for the Virgin Atlantic Global Flyer, TruTrak has been building autopilots for the experimental market since 1999 (it has sold over 10,000) and the STC/PMA version of the Vizion system is a rework of the company's most popular autopilot, the Digiflight II. When TruTrak redesigned the system as the Vizion, it retained nearly all of the features that worked well for experimentals but added altitude select/altitude preselect as well as an emergency level button.

We've installed TruTrak systems in experimentals and after removing some inspection plates on a PMA Vizion-equipped Skyhawk, remain impressed with the TruTrak's installation hardware and components. Even more, we like that the installation is technician friendly.

In the Skyhawk, the pitch servo mounts up front between the two sets of rudder pedals rather than in the confined space of the tail section. And like the Trio and Garmin, the servos ride the controls directly without the use of bridal cables.

TruTrak's servo technology doesn't have built-in software. Instead, it's a simple slip/disengage-clutch design and has velocity limited torque. This means the faster the drive motor spins, the lower the torque output. In the early days of autopilot design, servo runaway and hardovers was an ugly failure mode, made even worse by heavy control forces. TruTrak says such failure is impossible with its PMA Servos because of the wave form design that works in unison with lower torque outputs. The servos attach to the control systems via pushrods and each servo (pitch and roll) weighs 3.4 pounds.

Like the Trio, the TruTrak Vizion can interface with both panel-mounted and portable GPS systems for flight plan tracking (and GPSS roll steering), a feature TruTrak calls GPS Nav. The published GPS interface list is fairly substantial and includes the Garmin GNS430/430W and GTN650, the vintage Garmin GNC250XL and Avidyne IFD550 with version software. Portable models include the Garmin 496, aera 500/510/550/560 and the newer aera 660.

A word or two on software is in order. While you might rely on your avionics shop to alert you of available software updates, we suggest taking a proactive approach and staying current with firmware updates. The latest software is often critical to successful third-party interfacing and in the case of autopilots, it's specific to the STC.

The PMA Vizion has a shallow feature set with limited bezel controls. Three versions are offered and include a 3-inch instrument mount, a 2-inch instrument mount and a rectangular flat pack, all with the same functionality.

TruTrak added a feature called AEP, for automatic envelope protection. It's a gotta-have capability because any modern autopilot is simply lacking without it. When AEP is armed in the background, the flight computer monitors the bank angle and if it senses anything greater than 45 degrees, sends a command and subsequent corrective input to the roll servo. TruTrak said its AEP is different than in other autopilots because it doesn't take command of the flight controls. The idea is to get the pilot's attention with an automated input on the controls.

There's also a push-of-the-button emergency wing leveling mode, control wheel steering, vertical speed select for programmed climbs and descents, altitude hold/select/preselect, plus LPV approach coupling when connected to select WAAS GPS navigators listed earlier.

As for external interfaces, the TruTrak (which isn't analog compatible) won't work with round-gauge directional gyros or HSI systems for heading command. TruTrak told us it's working on an approved interface that would connect the TruTrak with Aspen EFD1000 series PFDs. The system doesn't require external pitch and roll input. In the experimental world where almost anything goes, TruTrak systems connect with a variety of EFIS systems (including Garmin) for heading select. When asked if the system will someday work with Garmin's G5 electronic directional gyro, TruTrak told us it's working on it. There's no analog raw nav data interfacing. That means the interface is limited to GPS navigators with digital outputs.

GFC500              $9144           Cessna 172 F through S, plus
                    including G5    F-series models
                                    Cessna 182 E through T,
                                    plus T182 T, P, Q models
                                    Future: Piper PA28150, 160, 161,
                                    180, 181 models
                                    Beechcraft Bonanza S35, V35A, V35B
PRO PILOT           $S995-$6495     Cessna 172, 175, 177, 180,
                                    182 (all models)
                                    Piper PA28 (all models)
                                    Future: Cessna 190, 195, 210, Beech
                                    35 to S35, Debonair
                                    Grumman AA5
VIZION              $5000           Cessna 172 (all models), 175 (all
                                    models), 177 (all models)
                                    Piper PA28 (all models), PA32 (all
                                    Future: Beechcraft Bonanza, Mooney

The list price of the all-inclusive TruTrak (for all approved airframes) is $5000 and includes a wiring harness and install kit.


Since we've already covered it, we won't look at the Garmin GFC500 user feature set, but it's worth reviewing the interface because an installation will affect the existing flight instruments. Where the other two autopilots are almost entirely self-contained, a required element of Garmin's GFC500 is the popular G5 electronic flight instrument. It channels in pitch and roll reference to the GMC507 electromechanical mode controller.

Think of the G5 serving as the autopilot's main source of mode annunciation and also for inputting flying commands like altitude changes and setting vertical speed and indicated airspeed holds. The GFC500 has a flight director function, so the magenta-colored command bar cues are placed over the G5's attitude display. The G5 electronic DG provides heading command to the autopilot.

The G5 DG can work with third-party autopilots (maybe you have an existing S-TEC or King autopilot), which requires the GAD29B adapter, but it's not yet approved.

The Garmin GFC500 system has a base price of $6995 for the two-axis configuration and doesn't include the G5 attitude and G5 directional instruments. The primary attitude indicator is $2149 and the G5 heading indicator is $2449. Add all that up and the system comes in at around $12,000, without installation. It goes up from there with major options. If you want the pitch trim kit, it's an additional $2100, including the installation kit, plus the yaw damper is $1500. But if you can live without heading command, you can skip the G5 DG, which puts the system a touch under $10,000.

As we go to press, the aircraft that are currently approved for GFC500 installations via the STC are limited to a wide range of Cessna 172 and 182 models. Garmin says it's working on STC approval for Piper PA28 models, in addition to S- and V-series Beechcraft Bonanza models.


As you can see by the STC list for each of the three systems, the market has become refreshingly competitive. Trio has the most approvals to date, followed by TruTrak, while Garmin comes in last, at least for now.

We're not sure why it's taking so long for manufacturers (and the FAA) to secure STC approval for interfacing with external heading sytems. It's an option we think most buyers will want. Garmin has a distinct advantage because it makes the G5 electronic directional gyro/EHSI, which is approved under the GFC500 STC.

Given the popularity of Garmin's G5, we think it would be foolish for Trio and TruTrak to not pursue approvals with this instrument and it appears this is in the works. The Aspen EFD1000 is also on Trio and TruTrak's radar for future interfacing and there are a lot of Aspens flying around.

Since Garmin's GFC500 requires the G5 electronic attitude indicator as part of the STC, its autopilot is the most expensive of the three. Add a G5 DG for heading command and the system is priced north of $10,000 not including installation.

As for installation, none of the manufacturers would offer labor estimates, which is understandable. We've been involved in enough autopilot projects to know there are plenty of variables that effect downtime and the price, especially when removing old systems and wiring. Use one working week as a reference.

For certain, any of these budget-based autopilots will be a much cheaper investment with more performance than any aftermarket system we've seen to date. That's something buyers have waited a long time for.

by Larry Anglisano
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Author:Anglisano, Larry
Publication:The Aviation Consumer
Article Type:Product/service evaluation
Date:Apr 1, 2018
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