Author TROY WHISTMAN walks you through preparation for a flight with the state-of-the-art Garmin GFC 500 digital autopilot.
With Garmin’s introduction of the GFC 500 digital autopilot, more accurately an Automatic Flight Control System (AFCS), capabilities previously absent in small General Aviation aircraft are now available for about $25,000 installed.
Your vintage Cessna may have come from the factory with a single-axis Cessna Nav-o-Matic that could “kind of” hold a heading or scallop along a VOR course utilizing analog inputs, while you managed altitude and trim settings. Newer digital systems like the GFC 500 from Garmin, the DFC90 from Avidyne, or the S-TEC 3100 from Genesys Aerosystems provide full two-axis pitch and roll control with amazing levels of accuracy and stability.
Full installations with all options can include automatic electric trim, allowing the autopilot to control your pitch trim; as well as yaw damper capability. The latter is an advanced feature previously reserved for cabin-class twins, single-engine turboprops, and jet aircraft.
A yaw damper (often abbreviated as YD) uses a dedicated servo to automatically provide just the right amount of rudder to keep the ball centered in all phases of flight. Passengers in the back seat enjoy a smoother ride without the side-to-side yaw or Dutch roll that can occur without a yaw damper, and it makes the pilot’s job easier—and the autopilot’s too.
This article will focus on how you can effectively utilize the features of the Garmin GFC 500 autopilot in VFR and IFR flight, including some tips and tricks learned after flying behind the unit in both VFR and IFR conditions since last summer.
My installation was covered in the October 2019 issue of Cessna Flyer and utilizes dual G5s and a Garmin GNS 430W. I’ve also flown from Oregon to Texas in a friend’s dual G5/GFC 500/GTN 650 setup. Where there are differences with the Garmin G3X Touch, or GTN navigators, I’ll try to point them out.
First things first: RTFM (read the Flight Manuals)!
While it’s tempting to just “hop in and go” when new toys are installed in our airplanes, it’s critical that you have a solid understanding of the equipment before your feet leave the ground. For the GFC 500, that means reading not only the generic Pilot’s Guide but also the airframe-specific Airplane Flight Manual Supplement (AFMS), cover to cover.
Get to know all the symbology, failure modes, and how these are annunciated (as well as how to respond to them). Both referenced documents are available for free download from Garmin’s website. (“Annunciate” is used in this article to indicate a lighted display. This follows the usage in Garmin manuals. —Ed.)
Also consider watching training/familiarization videos, such as Sporty’s excellent in-depth one-hour webinar featuring a Garmin training specialist, which is available for free on YouTube. (Find a link below in Resources. —Ed.)
Not much is more disconcerting than being in the clouds, wondering, “Why is the autopilot doing that?!” Which leads us to our first, and arguably the most important, topic…
Know how to kill the autopilot
Whether the autopilot is misbehaving, or you need to make a course change right now to avoid traffic, or it’s time for you to hand-fly at the end of an approach, you need to know every means at your disposal to disconnect the autopilot and return control to you, the human pilot.
With the GFC 500, there are four ways to cancel autopilot operation:
1.) The most common way to disconnect the autopilot is to momentarily press and release the red “AP DISC/TRIM INT” button (“Autopilot Disconnect/Trim Interrupt”), typically installed on the left horn of the pilot’s yoke. A disconnect tone will sound, and an amber AP will be annunciated on the G5 or G3X autopilot status box.
If the optional yaw damper is installed, pressing this red button will also disconnect the yaw damper, and the amber YD will also annunciate to indicate this function is disabled. Since it disables all modes, including the yaw damper, this is the preferred method to quickly disconnect all autopilot modes before landing.
Tip/trick: The disconnect tone is a series of three loud DOO-dah tones; pressing and releasing the button quickly more than once will cancel/mute additional tones, which can be nice for passengers (and you).
2.) Use the manual electric pitch trim switches. This makes sense! If you have the optional automatic electric pitch trim, then the autopilot is managing trim while it is engaged. If you subsequently use the trim switches, the autopilot is going to (metaphorically) say, “Fine buddy, you wanna fly? She’s yours,” then play the disconnect tone and relinquish the flight controls.
When disconnecting the autopilot using this method, the yaw damper will stay engaged, so you can keep your feet flat on the floor while managing pitch and roll yourself. Do remember to disconnect the yaw damper before landing. You’ll want full control of the rudders!
Tip/trick: I’ve modified my GUMPS checklist to be GUMPSY, a reminder to verify the YD is disabled before landing.
3.) Press the “AP” key on the GMC 507 mode controller. This method will also leave the yaw damper enabled, until the “YD” key on the mode controller is pressed, or the red “AP DISC/TRIM INT” button is pressed.
4.) Pull the autopilot circuit breaker. Obviously, this is a final resort, but you should know in advance where the breaker that provides power to the system is located—commit it to memory. Pulling the breaker will remove power from all servos and the GMC 507 control head. I had my breaker installed at one end of the bottom left row on my avionics subpanel so I could find and pull it without looking. In the Cessna TR182 Turbo Skylane RG I fly, that’s down by my left leg on the sidewall.
Tip/trick: Talk with your avionics installer about selecting a location that is easily identifiable by touch and feel. Being able to do this quickly (and “blind”) could save your life if you ever need it.
One more note on regaining control from a misbehaving autopilot: If the autopilot is engaged, don’t try to overpower the GFC 500 without disengaging it first. The automatic electric trim will operate in the direction opposite your overpowering force, which could result in large out-of-trim forces when you finally do get smart and turn the autopilot off.
Always disengage the GFC 500 first, then hand fly.
In an extreme errant autopilot behavior scenario, rather than pressing and releasing the red “AP DISC/TRIM INT” button as described above, press and hold the button instead, while you hand fly.
Pressing and holding the button will both disconnect the autopilot and remove all power from the servos as long as the button is depressed, so they can’t fight against you. Then, reach down and pull that breaker (you know right where it is, remember?) before you release the red button.
A quick tour: lateral on the left, status in the middle, vertical on the right
A quick look at the G5’s autopilot status line and the GMC 507 control head reveals some conscious thought about functional layout; both are divided into three sections.
The leftmost section displays (on the G5) and selects (on the GMC 507) your lateral navigation modes. You can track your heading bug (HDG) if you have a GMU 11 magnetometer installed, a specific GPS track (TRK), a NAV course (GPS, VOR, or LOC), or an approach (APR) with vertical guidance, such as an ILS or GPS LPV approach.
You’ll find the dedicated “HDG/TRK” knob is easier to use for setting the heading bug on the G5 than using the knob on the G5 itself. Train yourself to make all heading (and altitude) selections on the GMC 507.
The center section displays and selects autopilot status/modes. Enabling the autopilot (AP) will also enable the flight director (FD). The FD can also be enabled with the AP disabled, which is a cool mode where the GFC 500 will tell you how it would fly, but leave the flying up to you (see the “What About the Flight Director?” sidebar for more information).
The yaw damper is enabled/disabled with the “YD” button, and then, of course, there’s the famous blue “LVL” (Level) button, which will recover you to straight and level flight.
Important: Read the Limitations section and the Electronic Stability and Protection (ESP) details in the manuals to avoid surprises. The blue “LVL” button, and basic autopilot engagement, is predicated on not being outside certain limits of roll, pitch, and airspeed. Fly outside those specified limits, and none of the modes will engage.
Finally, the rightmost section covers your vertical navigation modes. A dedicated pitch trim/vertical speed wheel and “Altitude Select” knob provide for easy entry of desired values (see “The GMC 507 Vertical Mode Wheel” sidebar for more information on intuitive use of the wheel).
You can climb/descend in any of three modes: IAS (hold a specific airspeed), VS (hold a specific vertical speed), VNAV (track a GPS-computed descent profile; more on that next month). The “ALT” button enables altitude hold. Pushing the “ALT SEL” knob syncs the altitude bug to your current altitude.
White triangles illuminate above any selected mode to positively identify active selections, which you should cross-check on the status line of your PFD to ensure the desired modes are activated.
Modes that are active are depicted by green text on the PFD autopilot status line. Armed modes are depicted by white text. In the example depicted at left above, where we see VS +500 in green, and ALTS in white, it’s telling us the autopilot, and flight director are “actively” (green) set to climb the airplane at a vertical speed of 500 fpm up (+), and it’s “armed” (waiting) to capture the ALTS: the ALTitude you have pre-Selected with the altitude bug.
Gotcha: While Garmin follows this “lateral on the left, status in the middle, vertical on the right” layout convention consistently across the G500, G600, and G5 product lines, the G3X Touch swaps two of these, breaking the convention. The AP mode is on the left, the lateral mode in the center, and the vertical mode on the right. It’s not a deal-breaker, by any means, but something to be aware of for those flying the GFC 500 behind the G3X Touch.
Now that you know every possible way to disable the thing if you need to, and how the interface is laid out, let’s go fly! (Before disconnecting the autopilot, firmly grasp the controls and be prepared for the worst. It's also a good idea to glance at the aircraft's trim indicators to verify that the controls are trimmed for that flight condition. -Ed.)
Setting things up before departure
OK, you’re sitting in the runup area, ready to depart. The autopilot is disabled and will stay that way for a while because you’ve RTFM and know that Section 2 (Limitations) of your AFMS specifically calls out 800 feet agl as the minimum altitude for autopilot engagement.
Legally, you can’t use the autopilot below 800 feet agl (except while on an approach, then you can use it down to 200 feet agl). Note your field elevation, add 800 feet: that’s the altitude at which you can enable the autopilot. However, you can preset some things to reduce your workload after departure, and you can use the Flight Director to guide you, even below 800 feet.
Using the GMC 507, let’s configure the autopilot for the lateral and vertical modes we’ll want to engage after departure, and assume that you’ve received the following departure instructions:
“After departure, fly heading 180, climb and maintain 3,000 feet.”
Step-by-step, here’s how you’d set that up:
Set the heading bug on your PFD and HSI to 180 degrees by turning the “HDG/TRK” knob on the GMC 507 mode controller.
Press the “HDG” button to enable that mode. A white triangle will appear above the button, confirming it was selected. At the same time, you’ll see HDG appear in green as the active armed lateral mode on your PFD.
Astute pilots will notice that the FD (Flight Director) mode has now become active, even though we didn’t press any buttons. Magenta-colored Flight Director command bars will appear on your PFD, indicating the bank angle required (left or right) to turn from your current heading to the selected heading. You’ll also see a green PIT (pitch) vertical mode armed, even though you haven’t selected a vertical mode, because that’s the default vertical mode.
Set the altitude bug on your PFD to 3,000 feet msl by turning the “ALT SEL” knob on the GMC 507 mode controller while viewing the cyan altitude bug at the top of your PFD’s altitude tape. When you stop turning the knob, you’ll see the GFC 500 has armed ALTS mode, as indicated by white text, and it still plans to get there by flying a specific pitch (PIT is still in green).
We want to climb at an indicated airspeed to 3,000 feet msl, so press the “IAS” button. PIT will be replaced by green IAS 90 (or whatever Vy speed is defined in your airplane’s STC), indicating the aircraft will climb at 90 knots, and ALTS will be in white text, indicating that it’s “armed” (waiting) to capture the ALTitude you have pre-selected with the altitude bug.
A link to a video demonstration of this specific scenario is available in the resources for this article, if a picture is worth a thousand words to you.
We covered a specific scenario above, but other options are available to you as well to help you fly any departure clearance or route you might receive. Let’s talk about those while we’re here getting ready to depart.
If you’re going to track a course, make sure the correct flight plan is programmed in your GPS, or tuned and course selected if flying a VOR radial. Then, press the “NAV” mode button.
You might be flying a specific heading to intercept that course, so it’s totally legitimate to press “HDG” and then press “NAV,” in which case HDG mode will be active (green), and NAV mode will be armed (white). The autopilot will fly the heading until the NAV course starts to center and will smoothly intercept and track it.
I like to climb in indicated airspeed (IAS) mode and descend in vertical speed (VS) mode. If you’re climbing out of an area with terrain concerns, perhaps you’ll set Vx as your initial speed instead of the default Vy speed. You can adjust that speed using the little wheel in the vertical modes section of the GMC 507 (again, see “The GMC 507 Vertical Mode Wheel” sidebar for how to effectively use the wheel).
Tip/Trick: You can’t stall the airplane if you climb in IAS mode! If you have a long climb at a fixed vertical speed, and engine horsepower decreases as you climb, pitch must increase to maintain that vertical speed. Result? Airspeed drops off as you climb, threatening a stall. To prevent this possibility from ever occurring, just set an IAS mode for all climbs, and reserve VS mode for descents.
OK, now that we have our GFC 500 configured to “fly heading 180, climb and maintain 3,000 feet,” we’re ready for departure. In the next installment, I’ll cover the use of the GFC 500 from takeoff to touchdown, as well as more tips and tricks for getting the most out of this incredible digital autopilot.
The GMC 507 Vertical Mode Wheel
My first few flights, I found myself struggling with that little wheel in the vertical mode section on the GMC 507 autopilot mode controller, because it seemed to behave differently in VS versus IAS mode, even though it’s labeled “DN” at the top, and “UP” at the bottom.
Scrolling the wheel up would increase the value when in IAS mode, but decrease the value when in VS mode. Exactly opposite each other! I never seemed to know in advance which direction to roll the wheel to get the value I wanted.
But it all made perfect sense when I started thinking of the little wheel as a trim wheel.
If you’re trying to set a higher vertical speed (climb rate) with the standard manual trim wheel in your airplane, you’d trim the wheel toward nose up (wheel down), while that same movement of the aircraft’s trim wheel would create a lower indicated airspeed (fly slower).
The opposite is also true. Rolling the wheel toward nose down (wheel up) would give you a lower vertical speed/higher indicated airspeed.
Thus, if you think of the wheel on the GMC 507 as a trim wheel, you’ll always turn it the right direction, regardless of which mode (IAS or VS) you have selected.
Troy Whistman is the father of three grown daughters and has been married 30 years to his lovely redhead bride, affectionately called “Lady Red.” Together, they base their airplane at the Mid-Way Regional Airport (KJWY) south of Dallas, Texas. Whistman holds a commercial airplane SEL certificate with instrument airplane rating. When not flying for fun, he enjoys using his toys as tools to help others: he flies for and is on the board of directors for Angel Flight South Central, and thinks flying kids for Challenge Air is some of the most rewarding flying he does. Send questions or comments to .
Part 2 of this series can be found here: Tips & Tricks for Flying with the Garmin GFC 500 AFCS Autopilot, Part 2