Adding Altitude Constraints to Waypoints on a GTN (Xi)

Adding altitude constraints to flight plan waypoints allows a pilot to use the Enhanced VNAV features of a GTN™ Xi touchscreen avionics or GTN (software version 6.50 and above) when integrated with the Garmin GFC™  500 / 600 automatic flight control system.  Even without Enhanced VNAV, the altitude constraint feature can be helpful in situational awareness and flight computer function to aid in your descent planning.

Note: 

*If you are below GTN software 6.50 or have the unit configured for VCALC, the following procedure will NOT be available to you. To update your software and/or configure the GTN for VNAV, please see an authorized Garmin Dealer

Situation

You are flying over Harrisonville Airport (KLRY) and are headed to Lee's Summit Airport (KLXT) to the north.  You want to enter the traffic pattern altitude of 2,000MSL at 2nm away from the field.  We can use the altitude constraint function to accomplish this. In order to configure an altitude constraint, you must have a course between two points.  You cannot add an altitude constraint to a stand-alone waypoint in a flight plan or just using the Direct To feature.

Procedure

1. Add KLRY and KLXT to the flight plan as shown on the map page below.
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2. Every waypoint (except for the first) will have a button just to the right of that waypoint that says ----FT.  It is under a column titled 'ALT'.  This is the Altitude Constraint field and is circled in the image below.  The color of the text in these fields can be an indicator of your options, especially when using procedures populated on the GTN. 

   • • Cyan: Signifies the field is pilot configurable
     • White: Signifies the field is locked  *Normally associated with pre-populated altitudes based on procedure requirements.
     • Magenta: Signifies the waypoint is the active navigation directive while operating with VCALC  *The procedure in this article is not applicable to your GTN, please see a dealer for a software update and VNAV configuration.
   • Select the cyan -----FT button next to the KLXT waypoint. 
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3. Set the following: Along Track to -2nm, Type should be set to 'At', and the Altitude Constraint button to '2000ft'. Select “Save”.

   • If you select the VNAV Direct to, this will issue a directive to the GFC 500/GFC 600 autopilot to initiate a descent when your VNAV profile constraints have been met.

   • If you are adding altitude constraints to waypoints in your flight plan and do not need an offset, just leave the along track field blank.  It is only used in this as an example of capabilities and pilot options.

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4. Now you will see that the GTN Xi has created a separate waypoint that is 2nm before LXT and has an assignment of 2,000MSL.
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5. Verify on the map to ensure it makes visual sense.  You will see the along track waypoint as an orange square on the course line, with two call-outs indicating its distance from the original waypoint and that altitude constraint.
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For further examples and explanations of your navigator’s capability, please see your Pilot’s Guide and Aircraft Flight Manual Supplement.