Using VNAV on an Approach

Pilots of GA piston singles don’t typically fly STARs, and usually ATC vectors us to join approaches that don’t require many step-downs as we intercept the final approach course. Instead, we tend to use the VNAV (or older VCALC) features in our avionics to meet crossing restrictions, manage the descent from cruise to an initial altitude for an approach, or to help us arrive near an airport at the appropriate traffic pattern altitude.

But when connected to a GPS navigator, such as a Garmin GTN 750 or 650, that supports vertical navigation, new digital autopilots like the Garmin GFC 500 and GFC 600 can automatically descend as you fly the initial legs of an instrument approach, reducing your workload and helping you spend more time monitoring your progress.

To watch VNAV fly a series of published step-downs, join me as I fly the RNAV (GPS) RWY 29 approach at the Skagit Regional airport (KBVS) north of Seattle, an approach that shows the value of using VNAV. I’m in my Beechcraft A36 equipped with the GFC 600 autopilot, a GTN 750Xi, and G500 TXi.

For more information about VNAV, see these additional posts here at BruceAir:

Video: Garmin GFC 600 Go-Around Test

My 1989 A36 Bonanza recently emerged from the shop at Pacific Coast Avionics with updates to several components. The most significant improvement, albeit one that doesn’t show off as obviously as the Garmin G500 TXi and GTN 750Xi, is the GFC 600 autopilot.

GFC 600 controller

The GFC 600 replaced the original KFC 150, a state-of-the art autopilot for light aircraft in the 1980s and 1990s. It was showing its age, however, and it lacks features available in the latest generation of digital autopilots, such as the Garmin GFC 500 and GFC 600 and the Genesys S-Tec 3100.

I will have more to say about the new avionics in subsequent posts, magazine articles, and videos, but for now, here’s a video that shows a test of the coupled go-around feature of the GFC 600. I flew the ILS Y RWY 16R approach at Paine Field (KPAE) in visual conditions for this familiarization flight. At the decision altitude, I pressed the Go-Around button, and the autopilot started the climb. My job was to add power and retract the landing gear and flaps.