In the last article, we left off with our shiny new Garmin GFC 500 autopilot fully configured for departure. We’d been instructed to “fly heading 180, climb and maintain 3,000 feet.”
Takeoff: From runway to airborne
With the preflight work done, take off as normal. Saying “Gear up, flaps up, yaw damper on,” will make you feel like one of the big kids, as you press the “YD” key and let the servos handle the rudder. Above 800 feet agl with the airplane cleaned up, reach over and enable the autopilot by pressing the “AP” button whenever you’re ready.
If on a GPS direct track for the first leg, I’ll press Direct To-Enter-Enter on my navigator first, to recenter the course from the present position, then press the “AP” button to engage the autopilot.
George is now flying the airplane…or is he?
Important: Develop this habit! Whenever you select a new mode on the autopilot, always bring your eyes back to the top of your G5 or G3X and verify the modes selected. Every. Single. Time.
I developed this habit shortly after finding myself in the clouds on a departure, thinking George was flying—very poorly, I might add, and my scan was confirming that—and then discovering that nobody had been flying the plane for about 60 seconds. Talk about a wake-up call!
The correct lateral/vertical modes were selected, but the autopilot itself hadn’t enabled. Maybe I didn’t quite push the button while getting bounced around in those Houston afternoon thermals. Verify the modes! Some people call it “checking the scoreboard,” with the “scoreboard” being the autopilot status line at the top of your PFD.
Do you have green AP and YD annunciations on the scoreboard? No? Fix that! Yes? OK, then George is flying. But what is he doing? Verify the annunciated lateral and vertical modes. It’s showing a green IAS 90? Great, George is flying you at an indicated airspeed of 90 knots. Or is he? Cross-check! Is that what your airspeed indicators read? Great.
Where will George level off? Check to see that the cyan altitude bug is set at your expected level off altitude (did tower give you a last-minute change?), and that a white (armed) ALTS mode is annunciated next to the IAS 90. If so, “George” will level off at that ALTitude Selected.
I can’t stress this enough—always “check the scoreboard” after doing anything on the GMC 507. Every. Single. Time.
Fair warning. You’re going to be bored.
The GFC 500 is going to do such a fine job flying the airplane that you’ll find you get bored, unless you fill that time with other activities. Of course, I’m not suggesting you read a book or get caught up on Netflix! You now have time to focus on other important pilot duties.
Check the weather ahead and develop options. Refine your Plan B if needed. Scan those engine instruments more often. Check out the approach plates and arrival airport diagram. Which runway are they using? What taxiway do you think you could make, and what taxi route to your FBO makes sense?
It’s amazing the amount of “thinking time” you get back with a well-running autopilot as your co-pilot. But don’t get so busy you forget to monitor George frequently!
Tip/trick: While in NAV mode, tracking that GPS course, reach over every few minutes and push the “HDG/TRK” knob on the GMC 507 to sync the heading bug to your current heading. The difference between the heading bug and your actual track, as shown on the HSI, will give you a good idea of the winds aloft, and how they are changing over time.
If you have a GAD 13 installed and the recent G5/G3X firmware, you’ll see winds aloft and OAT displayed on the instruments. Having that heading bug already synced up is especially helpful when ATC says, “Turn 10 degrees right for traffic.” Note the current bugged heading, spin it right 10, then reach over and press “HDG” on the GMC 507. What’s next? You know: Check the scoreboard. Every. Single. Time.
What’s this VNAV thing?
Vertical navigation can be thought of as a magenta path, not over the ground, but rather through the vertical profile. It is a GPS-computed path to help you meet the step-downs in a “descend via” clearance on an arrival procedure, to help you with that crossing restriction ATC just gave you, or to ensure you get from your cruising altitude to pattern altitude 3 miles before you arrive at your destination airport.
The “VNAV” button on your GMC 507 enables the autopilot to fly that vertical path precisely—all you must do once it’s engaged is manage the throttle to keep your airspeed where you want it. But there’s the catch: “once it’s engaged.” There are some gotchas that trip people up and keep VNAV from working when expected.
First, you need your GFC 500 system to be coupled to an IFR navigator capable of VNAV. The GTN 650 and 750 are two such navigators. If you’re flying a GNS 430/530 series, even if it’s WAAS enabled, you’re out of luck. The 430/530 units do have a vertical descent planner that can tell you the VSR (vertical speed required) to meet a defined crossing restriction, and I use that feature—but it won’t couple to that fancy “VNAV” button on the GFC 500 autopilot.
If you’re flying a GTN series navigator, though, and load a procedure that has crossing restrictions or add your altitude constraints to your flight plan, then VNAV should be available on the GFC 500.
Second, to activate VNAV, you must perform certain steps in order. The most often missed step is that you must set your selected altitude (ALT SEL) to a lower altitude than you’re currently flying.
Here’s a scenario. You’re at 9,000 feet msl, and your flight plan says you want to be at 3,000 feet msl at GOTHI intersection, and your MFD properly shows a TOD (top of descent) and BOD (bottom of descent), and the “VNAV” button is lit up on the GMC 507, and you hear that voice that announces, “VERTICAL TRACK,” one minute before the descent begins. All of this looks good!
But the airplane will remain at 9,000 feet and never actually descend, flying right past your TOD marker and remaining at your current altitude, if you leave that selected altitude bug on the G5/G3X set to your current 9,000 feet.
Why? Think of it this way: the autopilot will always err on the high side to avoid flying you lower than you want. If you want to descend lower, you must set the selected altitude lower than the altitude you’re currently flying.
Tip/trick: If you want to use VNAV, set up the altitude profile in your navigator’s flight plan. Verify you see the TOD/BOD markers on your moving map. One minute before descent, you’ll hear that nice lady’s voice in your headset announcing “VERTICAL TRACK.” That’s your cue!
You’re going to do three things after that audible prompt:
Set the ALT SEL bug to the lowest altitude you’ve been cleared to by ATC, or the lowest altitude in the published arrival procedure.
Press the “VNAV” button on the autopilot.
Check the scoreboard! Every. Single. Time.
Several other factors determine if VNAV will engage or not, such as the requirement to be navigating on a course (i.e., direct to a fix, or between two waypoints). If you’re just wandering around on your own, VNAV isn’t an option.
Garmin recently published a 20-minute training video that thoroughly covers all aspects of VNAV training. If you fly with a navigator capable of doing VNAV, I strongly recommend you take the time to view it.
Some final tips
- Pressing the “AP” button before selecting lateral or vertical modes will activate the Flight Director (FD) and engage the autopilot in the default PIT (pitch) and ROL (roll wings level) modes. That’s probably not a mode set that you will ever really want, so always select your desired lateral/vertical modes before pressing the “AP” button.
- If lateral/vertical modes are selected, but the autopilot and flight director are not engaged, you can engage the FD separately from the autopilot by pressing the “FD” button, and then hand-fly to match the flight director’s cues. Pressing the “AP” button enables both the autopilot and FD since the autopilot works by following the flight director’s commands.
- If, while climbing or descending, ATC tells you to level off immediately, simply reach over and press the “ALT” button twice. It will grab your current altitude and lock onto it.
- If you find your ALT hold is off by 20-40 feet, using the pitch trim wheel on the GMC 507 while ALT mode is engaged, will change the selected altitude reference UP or DN in 10-foot increments. Utilizing this method, you can tweak your altitude by up to 200 feet. If you need to “tweak” your altitude by more than 200 feet, you’re really “changing” your altitude, so just dial in a new selected altitude and use another vertical mode (VS, IAS, or PIT) to make that change. If ATC gives you a new barometer setting, setting the new value on the G5/G3X is all you need to do. The autopilot will seek up or down a few feet to capture your selected altitude at the new pressure level.
- GA (Go Around) mode is great! You’re allowed to use the autopilot down to 200 feet on an approach (which is the only exception to the STC’s “don’t use the autopilot below 800 feet AGL” limitation). When you get to your missed approach point or decision height and don’t have the runway environment in sight, push the throttle forward and let that index finger reach forward to touch the “GO AROUND” button as you do the rest of your gear/flaps cleanup. Your PFD will command a pitch up and straight-ahead climb, and the autopilot will immediately follow that guidance. Once the initial part of the go-around procedure is completed (which may be a straight-ahead climb to a specific altitude before making any turns), unsuspend your IFR navigator to resume waypoint sequencing, and select the appropriate lateral/vertical modes on the GFC 500. The autopilot will fly the entire missed procedure, including holds. Practice this in VMC first!
- If you change navigation sources (i.e., toggle your navigator from GPS to VLOC), the autopilot will sense this, and the lateral mode will revert to ROL (wings level, it doesn’t even hold a heading). Thus, anytime you do any work on the navigator, do your scoreboard check afterward. Switching from GPS to a LOC or ILS course will require you to reselect the appropriate lateral mode. Speaking of which…
- On an approach, should you use APR or NAV mode? The answer is easy: If the approach you’re flying has vertical guidance (think ILS, LPV, LNAV+V, or LNAV/VNAV), then use APR mode. If the approach you are flying doesn’t have vertical guidance (think LOC, VOR, or a BC approach), then use NAV mode. You can select either mode (NAV or APR) as soon as ATC has cleared you for the approach. You’ll see a green HDG for active mode, and a white annunciation for the armed mode.
- Related to the last tip: one time, ATC had me on a vector (HDG mode) to intercept the GPS LPV approach, and I had APR mode armed. Shortly before intercept, ATC told me they were going to fly me through the course and then bring me back for sequencing purposes. If this happens to you, you’ll need to reach over and disable the armed approach by pressing the “APR” button to deselect the mode. This will leave HDG mode as the only active lateral mode and allow you to follow the controller’s vectors. Once inbound to the approach course again, reactive the approach by pressing “APR.” If you fail to deselect/deactivate the approach mode once it’s armed, the autopilot will turn you inbound, which is not what the controller told you to expect or do.
- GPS approaches (especially LPV) are the simplest approach to fly with the GFC 500. If you have the option, choose it. There’s no mode to change when inbound, simply press “APR” when you get close, outside the FAF, and have been cleared for the approach. That’s it. Other approach types involve more button-pushing. Get out the flight manual supplement, grab a buddy in VMC, and go practice the detailed step-by-step in the manual until it is ingrained in your subconscious. IMC is not the place to figure things out.
I hope you found these tips helpful. The GFC 500 is an amazing piece of equipment, but as with all things in aviation, it demands respect for its capabilities and its limitations. Learn both well, practice before doing it for real, and leverage its ability to make your flying safer.
Taking Off and Going Around
The first phase of flight is just getting airborne and away from the ground on runway heading to 400 feet agl before making any turns, especially when IFR. The GFC 500 can help you there, too. Simply press the GO AROUND button, probably installed near your throttle, and the GFC 500’s flight director command bars will command a straight out wings-level climb at an appropriate pitch attitude, as specified by your aircraft make and model’s STC, and the lateral/vertical modes annunciated on your G5 or G3X Touch will both indicate “TO” for “takeoff.”
Tip/trick: The same GO AROUND button also commands the pitch bars for a go-around at the start of a missed approach, and you’ll see the lateral and vertical modes annunciated as “GA.” How does the same button handle both “TO” and “GA”? If you’re not flying (i.e., your groundspeed is slower than 30 knots), the system knows you’re setting up for TO (takeoff); if you are flying, then you must want to GA (go around). Boy, this system is smart!
Tip/trick: Use of the “TO” mode is optional. I might use it for positive flight director guidance when departing into a very low overcast, but if the ceiling is at least 800 feet agl (the minimum autopilot engagement altitude), I actually find it easier to preselect my NAV/HDG and IAS values and modes, and just fly straight ahead on runway heading, ignoring any turn the flight director command bars are providing cues for, during that first phase of flight. It reduces workload a little, as my only task then becomes pressing the AP button at 800 feet agl—lateral and vertical modes/values were already set on the ground.
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 to catch a sunrise or sunset, 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 editor@cessnaflyer.org.
Part 1 of this series can be found here: Tips & Tricks for Flying with the Garmin GFC 500 AFCS Autopilot, Part 1
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