Given their wide-reaching STC approvals, Garmin autopilots have dominated the aftermarket the past few years. But other full-featured autopilots like the dual-axis Trio Avionics Pro Pilot have gotten lost in the noise.
I thought the competitively priced Pro Pilot, originally designed for experimental aircraft, deserved consideration for replacing the aging S-TEC 50 autopilot in my Grumman. And so based on perceived value and its generous standard feature set, I decided to give it a try. Here’s an overview of the system and my experience with its installation.
Experimental Roots, STC approved
California-based Trio Avionics hit the market in 2000 by three pilots (hence the company name) who felt they had a better autopilot design than what was currently on the market. Together, Chuck Busch, Sid Tolchin and Jerry Hansen worked to bring their EX Pilot single-axis autopilot to the experimental market. Roughly 1600 EX Pilot systems are flying in models ranging from ultralights, Yak-52s and CJ-6s, though the majority are installed in Van’s RV models.
In 2003, a heavily modified RV-4 clawed its way to a near-record piston altitude of over 47,000 feet—and Trio’s EZ Pilot was still operating in that frigid environment (outside air temperature was about -60 degrees Fahrenheit).
Building on the EZ Pilot (and altitude hold add-on) successes and many lessons learned, in 2006 Trio created a two-axis autopilot with the Pro Pilot. It’s capable of horizontal and vertical course tracking via GPS, including coupled RNAV approaches with approved third-party WAAS GPS navigators. Interestingly, the Pro Pilot is only certified for vertical approach coupling down to 500 feet AGL, which might fit within the envelope of many instrument-rated pilots who don’t need (or want, for their personal minimums) to go down to minimums. The autopilot doesn’t stop working at 500 feet, but it’s only certified for ops above that altitude.
As for installation approval in certified aircraft, several years ago Trio teamed up with a company called The STC Group to work with the FAA for certified applications, while staying focused on the technology, production and support. The Pro Pilot focused on a value proposition that aimed for best bang for the buck—an installed cost significantly less than the competition, without skimping on advanced features like GPSV (GPS vertical), auto 180-degree turn and a safety mode to level the wings and hold altitude in case of spatial disorientation.
The Approved Model List STC process allowing the experimental Pro Pilot autopilot to be installed in certified aircraft was surprisingly quick, at least by FAA standards. Working closely with the FAA and, at the time, leveraging the FAA’s increasing recognition of the safety advantages of transitioning proven systems from the experimental world to certified platforms, The STC Group navigated the approval process in only about 12 months.
Compared to S-TEC and Garmin autopilot systems, the AML is by no means comprehensive, but is a good start at covering a lot of basic piston singles including the Cessna 170, 180 and 190 series, Piper PA-24/28/32 series and the Grumman AA-5 series (including the AG-5B). Approximately 1800 Pro Pilots have been installed in certified planes, with about 60 percent of those in Cessnas, roughly 25 percent in Pipers and the remaining approximately 15 percent in Grummans.
Trio and The STC Group continue to add aircraft to the AML, including a forthcoming announcement at AirVenture 2024 for an interface in Cessna 150/152 models (surprisingly, these were not included in previous Cessna additions to the AML since these models are a significant fleet that could benefit from Trio’s combination of advanced features and low cost).
EFIS interfacing
Trio has also been actively working on integration of the Pro Pilot into aftermarket EFIS models to allow the pilot to control the autopilot via the EFIS display rather than the Pro Pilot control head, providing paths for even more advanced features. Current experimental EFIS systems that have been tested and found to be fully compatible with the Pro Pilot include Garmin G5 and G3X Touch, Aspen’s EFD1000 Pro Max, Pilot and E5, the uAvionix AV-30, Dynon SkyView HDX as well as systems from Advanced Flight Systems and Grand Rapid Technologies. The current EFIS systems that are certified include the Aspen and G5, but there could be more announced approved certified interfaces soon (including the Dynon SkyView HDX) as Trio continues to certify the autopilot’s integration with other EFIS models.
It was in fact Trio’s announcement in 2023 of the certified integration with the Aspen Pro Max that launched me down the road of my own install of a Pro Pilot into my 1978 Grumman AA-5B Tiger, Li’l Blue. This Grumman started life equipped with 1970s-vintage Narco. It’s currently flying with an Avidyne IFD440 WAAS GPS/comm and an Aspen EFD1000 Pro Max PFD. My main objective was upgrading my capable (but aging) rate-based analog S-TEC 50 autopilot. While the S-TEC 50 had altitude hold and an add-on GPSS (GPS steering) module, it had no GPS vertical guidance capability for flying precision GPS approaches.
Still, I liked the way the Aspen PFD and the Avidyne interfaced with the S-TEC, allowing me to easily dial in ATC-instructed headings on the Aspen for the autopilot to follow, Essentially, I wanted to retain all of the current functionality while adding GPS vertical course tracking and other safety features to reduce workload and stress during light instrument flying (my personal minimums are more like MVFR than IFR).
Out with the old
The only two certified digital autopilot options for my Grumman Tiger were the Garmin GFC 500 and the Trio Pro Pilot. The GFC 500 is a phenomenally capable and generally well-regarded system from a performance standpoint, but with a couple of kids in college, I’m sensitive to saving the airplane budget where possible. The GFC 500 requires a G5 (or GI 275) instrument, so it would not just be replacing my autopilot but also the existing Aspen PFD. For about one-third of the full-up costs and based on some feedback from other Grumman owners, I decided to go with the Trio Pro Pilot. Full disclosure: I paid full retail price ($6545, including EFIS unlock) and did not get any discounts, compensation or other inducements from Trio Avionics or the shop to write about my experiences.
My installer was Yankee Aviation (a shop that specializes in Grummans) in Hamilton, Ohio (KHAO, just outside of Cincinnati). The shop was recommended by a fellow Grumman owner, plus Yankee’s avionics installer is Matt Wing of Wingman Aviation, who has installed more than a dozen Trio Pro Pilots in various Grummans. Wing installed a Trio in his own personal AA-5A Cheetah over a year ago and has flown over 200 hours with it. He was an enthusiastic supporter of both Trio as a company and the Pro Pilot as a product.
I flew up from my home base in Huntsville, Alabama, to combine an owner-assisted annual inspection with the installation of the Trio Pro Pilot autopilot. The first big task was removing the S-TEC 50 control head and associated servos. The pitch servo for the S-TEC was unfortunately located very far aft and required several hours of contortionist gymnastics to reach and remove. Trio notes that typical installation times are 30 to 40 hours, depending on the existing systems and rigging requirements. While Matt concurred with that estimate, as events would later reveal, we would exceed that range by a bit.
The rest of the S-TEC 50 removal proceeded smoothly and soon the Trio servos were ready for installation, this time in locations much more favorable for access (mid-fuselage, under the rear seats). Unfortunately, we discovered that the roll servo control arm threads were mis-machined to the wrong diameter and we had to wait for a new one to be machined and then shipped to us. Trio customer service response was excellent, but of course it would have been better if the control arm had been machined correctly to begin with as the waiting cost us about a day and half of work stoppage.
In with the new
Panel modifications were minimal. The Pro Pilot comes in two form factors—a 3-inch ATI instrument-cutout chassis or rectangular openings for a 6-inch-wide radio stack. With a relatively inexpensive adapter plate, the Trio fit right into the same spot as my S-TEC 50 control head. A small toggle switch needs to be installed (if using an EFIS) to switch the GPS source to the Pro Pilot either from the EFIS or directly from the GPS (in my case, switching between the Aspen PFD or the Avidyne GPS). Additionally, a push-button for the Level button is required (wing leveler and altitude hold) as well as a yoke-mounted switch for autopilot disconnect and PCS (pilot controlled steering).
If you aren’t familiar with autopilot control wheel steering, the PCS works like a pause button—as long as the pilot pushes it in, they can fly the plane manually—and then when the button is released, the autopilot picks up the new heading or altitude. A quick press of the same button disconnects the autopilot completely (or the pitch and roll servos can be independently turned on or off at the control head).
Once the control head was wired and interfaced to the Avidyne and the Aspen—a new procedure for Matt Wing as this was the first Trio he had installed with the Aspen EFIS unlock (a $250 extra charge for the software EFIS unlock from Trio)—we were ready for the installation of the servos. We left the Aspen ACU analog to digital converter in place, although we were a bit concerned about having an analog converter between the Aspen and Trio (both all-digital).
The roll and pitch servo (they’re identical) install was straightforward, with no additional major complications. Trio calls their servos The Gold Standard and considers them to be unique in the industry. Each servo contains dual microprocessors and sensors to allow it to disconnect itself from the controls if it senses anything that deviates from normal operational conditions, including motor currents, temperatures, short circuits and crank arm positions. Faults are announced on the LCD screen of the control head (such as clutch slip if the plane is significantly out of trim). Of course, as with all autopilots, the pilot can manually override the autopilot with the control yoke at any time in emergencies. The servos fully disconnect the internal gears when not engaged so that there is no drag on the control cables.
Not an insignificant task with any autopilot, programming the system came next. Configuration settings had to be adjusted on all three main components (Avidyne, Aspen and the Trio) to ensure that they were talking to each other at the same rate and in the same language. Some of this effort was really trial and error as the number of possible combinations of GPS and EFIS units is over 600. Eventually, it seemed like the units were happy and talking to each other so we took Li’l Blue up for a series of test flights per the Trio installation guidelines.
How does it fly?
The test flights seemed to go fine, although we had trouble with the Avidyne downgrading the LPV approach to LNAV+V and we had lost the VOR1 mode on the Aspen display. Back on the ground, we made some adjustments (per Trio’s recommendations) to both the Avidyne and Aspen settings to try to improve things.
After reassembly, the final tally for shop labor hours for the Pro Pilot install was 44.5—a bit more than the high end of Trio’s estimate, but not wildly so, and due primarily to the removal of the old S-TEC (especially the very aft- mounted pitch servo) and the additional integration with the Aspen.
I headed home on my 2.5-hour flight back to Huntsville. Unfortunately, several times during the flight, the vertical portion of the Trio had uncommanded 10- to 15-degree pitch-downs that would have resulted in my busting my IFR altitude had I not jumped on the controls to override it. These deviations occurred in relatively smooth air and with the aircraft properly trimmed for cruise. This was clearly not ideal and I was not happy with the Pro Pilot’s performance.
Reviewing the flight data, including video I shot in the cockpit and track log data visualized on www.flysto.net (the vertical rate tab was especially useful in picking up the sudden pitch changes), Trio made several suggestions for troubleshooting, but the uncommanded vertical deviations continue to occur randomly.
I flew back up to Yankee Aviation and Trio sent a temporary locked (not EFIS controllable) control head to swap out as well as a recommendation (which we complied with) that the legacy Aspen ACU converter be removed between the Aspen and the Pro Pilot. The removal of the ACU did restore the VOR1 to the Aspen so we celebrated that victory.
Warts and all
Here’s where I really saw the wisdom in holding off until the Aspen integration had been approved— the Trio may be a very capable unit without the EFIS, but it’s definitely more work. You have to enter the field elevation rather than being slaved to the barometric setting on the EFIS, and when ATC gives you a heading, you have to guesstimate based on wind since you’re setting a course in the Pro Pilot control head rather than a heading. Unfortunately, even with a new control head and no ACU, the random vertical deviations popped back up on my return flight and I ended up turning the pitch servo off and just trimming the plane to maintain altitude.
Three months after the initial installation, I received a new unlocked control head as well as a new pitch servo. The five test flight legs and associated coupled LPV approaches I’ve flown since then performed very well and indicate that the uncommanded vertical deviations may be a thing of the past. Although my install experience has been unusual, what seems to be common is that Pro Pilot customers I talked with tend to agree that the Pro Pilot handles lateral GPSS tracking better than vertical GPS. Whether that’s a reflection on the inherent increased variability of vertical navigation (trimming and rigging playing an even more important role) or of the limitations of the pitch servo is not clear.
Trio Pro Pilot customers I’ve spoken with are generally positive about Trio and the product. They cite excellent customer support and a feature-rich product that didn’t break their wallet. They like the safety features, including the 180-deg auto turns (for inadvertent encounters with IMC) and “panic” button to auto-level and hold altitude (for spatial disorientation or pilot incapacitation). Experiences like mine where control heads or servos had to be replaced do occur, but seem relatively infrequent. More common complaints were some nitpicks about trouble holding headings or altitude in turbulent or gusty conditions. Some pilots reported that a little rudder input can help and also pointed out the importance of having a properly rigged plane. This should be a question you ask any shop before installing any autopilot: Does the shop have the experience and manuals to properly rig the flight controls?
My S-TEC 50 was an excellent unit and seemed to do a much better job of holding headings and altitude. The S-TEC also had separate LEDs to quickly convey trim up/down needed (the Tiger does not have auto-trim) while the Trio announces the need for trim up or down on the LCD screen with words that are not as immediately obvious during an instrument scan.
The physical install of the control head and servos was not a major ordeal; Trio’s instructions are clear and their support has been outstanding, so I can give a qualified recommendation for installing a Trio system.
I’ll follow up with a long-term report on performance and reliability in a future report.
Visit www.trioavionics.com.
