Using Enhanced VNAV on The GTN Xi or GTN Navigators

Enhanced Vertical Navigation (VNAV) is a feature available for select avionics configurations that allow a pilot to plan a descent and couple the autopilot to fly it automatically.  The techniques seen in this article are basic, but can be expanded to meet multiple step-downs and even fly complicated arrival procedures.

REQUIRED EQUIPMENT AND SETTINGS

In order to have the enhanced VNAV feature, there are multiple hardware requirements and settings that must be met. 

• GTN™ Xi or GTN (SW 6.62+) Navigator  *Configured for VNAV.

• GFC™ 500 or GFC 600 Autopilot.

• G5 or G3X™ PFD or GI 275 Electronic Flight Instrument *GI 275 MOD 2 for GFC 500 interface. GFC 600 requires GDU such as G500TXi.

*If you would like to upgrade your panel to these items or have GTN configuration settings that do not support enhanced VNAV, see a Garmin Dealer.

All the procedures in the following example are extrapolated from the required equipment AFMS and Pilot Guides.  For further instruction, please reference those documents that were provided with your installation.  Examples can be found on Garmin.com under the “Manuals” tab on each product page. 

EXAMPLE

For this example, a Cessna 182 is flying from Emporia Municipal Airport (KEMP) to Lee’s Summit Municipal Airport (KLXT) at an altitude of 5,000MSL.  The plan is to arrive at pattern altitude (2,000MSL) for KLXT at 2 nm before the field making a gradual descent at 500 fpm.

PROCEDURE

1. Select your Navigation Source as GPS.

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2. Turn on your autopilot.

   1. Engage your autopilot with Lateral Mode: NAV.  This will ensure your autopilot is executing the navigation directive in the GTN.

   2. Engage Vertical Mode: ALT to hold your current altitude at 5,000MSL.

   3. Engaging the autopilot early in this process is a good use of Single Pilot Resource Management.  Never task deviate on the avionics to the point of distraction from flying the airplane.

3. After pressing any key on the autopilot, verify the desired mode is active on the AFCS annunciation bar on the corresponding flight display.

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4. Establish the KLXT along track waypoint of -2 nm with an altitude constraint of 2,000MSL.

   • To learn how to set up an along track offset and altitude constraint, see How do I add altitude constraints to waypoints on my GTNXi and GTN?.

   • You can add multiple waypoints with altitude constraints to create a detailed vertical flight plan or support an arrival procedure.

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5. Verify your VNAV settings on the GTN Xi.  From the flight plan page, select Menu > VNAV.

6. Ensure VNAV is enabled and set your Vertical Speed (VS) target.  In this case, -500 fpm.

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7. Altitude preselect: Set your altitude bug to the lowest cleared altitude. *If ATC clearance is required

   • The GFC will not command a descent below the altitude bug setting in VNAV.  This prevents accidental pilot altitude deviation when under instructions from ATC.

8. ARM VNAV prior to the TOD.

   • When “VNAV” shows in white to the right of ALT this means that it is ARMED.

   • All annunciations in green are ACTIVE

   • All annunciations in white are ARMED

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9. When the aircraft reaches the TOD the autopilot will command a descent at the rate established on the VNAV Profile page and capture the setting of the Altitude bug.  You will see “VNAV” in green as the ACTIVE and ALTV in white as the ARMED settings.

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COMMON ERRORS

Enhanced VNAV will not function if any of the following conditions are true.

• Navigation source is not set to GPS

• VNAV not enabled on VNAV profile page

• No waypoints exist in the flight plan with appropriate altitude constraints

• Lateral mode is not actively engaged to GPS

• OBS mode is active

• Dead reckoning mode is active

• Parallel Track is active

• Aircraft is on the ground

• Aircraft is between the FAF and MAP of an approach

SAFETY FIRST

While getting familiar with the Enhanced VNAV features of your avionics, it is advisable to fly with a Certified Flight Instructor or safety pilot.  Exercise a well-developed Crew Resource Management Plan to maximize awareness in flight and decrease distraction.

For more information on this procedure, see the Aircraft Flight Manual Supplement (AFMS) that was provided by your Garmin dealer for the GFC installed in your aircraft.  For screenshots and options on the navigator and flight displays, see the applicable Pilot Guides.

• GTN Xi  and  GTN Pilot Guides

• GFC 500  and GFC 600  Aircraft Flight Manual Supplement (AFMS)

• G5,  G3X Touch,  GI 275 Pilot Guides

• G500 TXi Pilot Guide

*All screenshots were taken from the free iPad trainer and Pilot Guides. 

*If you are on an iOS device, you can get the free trainer HERE.