Managing VNAV – Vertical Navigation and ATC Crossing Restrictions.
The Garmin Perspective Touch avionics platform is feature-rich and highly capable. Will show you how VNAV Vertical Navigation is set up… I will show you a VNAV pilot technique in the video below.
Several viewers asked me to demonstrate how vertical navigation profiles and ATC crossing restrictions are entered in the Garmin Perspective Touch avionics system. A crossing restriction occurs when ATC tells a pilot to cross a specific point on the earth at a specific altitude. The point of the restriction can be over a specific waypoint or fix or navigational aide, or a specific distance before or after that fix. It is always associated with a crossing altitude restriction.
Normally, an aircraft has to descent at a specific time and at a vertical speed in order to meet the restriction. It can involve complicated speed, distance and time calculations. No worries though since it is made easy by the avionics system IF you pay attention to set up.
This is an example of what a pilot might receive during a flight. Special thanks to Terry T for asking to see how this works in the SF50 Vision Jet. Follow along using the video below if you would like a visual reference.
ATC: “N379JM Cross 25 miles east of the Belcher (EIC) VOR at 11 – eleven thousand feet. Shreveport Altimeter is 30.42.”
N379JM: “Cross 25 miles east of the Belcher VOR at 11 – eleven thousand feet, 30.42”
The Three “B” VNAV Technique is used to set up and verify the crossing restriction has been set up completely.
1) Build It using a VNAV Profile (in the flight management system). Select the Fix, select the distance before or after the fix and the crossing restriction altitude.
2) Bug It (change altitude selector) Change altitude selector to the crossing restriction altitude.
3) Button It (press VNAV button) on the mode controller.
View the map on the Multi-Function Display (MFD) to look at the TOD Top of Descent and BOD Bottom of descent to verify the setup. Look at the VNAV target descent rate to make sure you can meet it. The avionics system will announce “Vertical Track” one minute prior to the TOD to remind the pilot to check the NVAV set up. Look for the cyan (blue) “Banana Bar”, which is the Selected Altitude Intercept Acr (SAIA) and make sure it is where you expected it to be along your flight plan route. SAIA will be displayed along your flight path and designate where you will reach the altitude selected when you set up VNAV. If is not where you expected it, verify your set up and fix the error.
Verifying VNAV After Entering a Crossing Restriction in the Garmin Perspective Touch+ Avionics
One of the biggest mistakes pilots make is assuming that because the FMS accepted a crossing restriction, the airplane will automatically descend correctly. Before every VNAV descent, take a few seconds to verify the automation. Think of it as confirming the airplane’s “game plan.” Above, I described the three-B process for the set up. Now we can discuss some of the critical areas that require monitoring and verification.
1. Confirm the Crossing Restriction
Start by reviewing the flight plan. Look at GTC2 and look for the crossing restriction you created.
Verify:
- The correct waypoint was selected.
- The correct altitude was entered.
- “At,” “At or Above,” or “At or Below” matches the clearance.
- No unexpected altitude constraints exist later in the arrival.
A single incorrect waypoint or altitude can completely change the VNAV profile.
2. Review the Vertical Profile
Open the Vertical Flight Profile page, or change the map inset to show the vertical profile.
Ask yourself:
- Does the descent profile look reasonable?
- Is the descent beginning where you expected?
- Are there any unusually steep segments?
A quick glance often reveals data-entry mistakes before they become a problem.
3. Determine the Required Descent Rate
The VNAV page on GTC2 or the flight plan inset on the MFD will show the required vertical speed to satisfy the selected crossing restriction.
This is one of the most valuable pieces of information.
Ask:
- Is the required descent rate comfortable?
- Is it realistic for passenger comfort?
- Think about avoiding overspeed condition in turbulent air or if the required decent rate is greater that 1500 feet per minute.
- If using auto-throttle – is AT engaged and what speed reference is being used?
For example:
- 600–1,200 FPM is generally comfortable.
- 1,500–2,000 FPM may be perfectly acceptable.
- 2,500+ FPM should immediately get your attention.
If the airplane needs an aggressive descent, consider slowing earlier or requesting an earlier descent from ATC.
4. Find the Top of Descent (TOD)
Locate the Top of Descent symbol on the map.
Verify:
- Where is it?
- How many miles away?
- How much time remains before reaching it?
This allows you to mentally prepare instead of being surprised by the descent.
Many experienced pilots also compare the TOD location with outside references or nearby fixes to ensure it makes sense.
5. Verify the Flight Mode Annunciator (The “Scoreboard”)
The Flight Mode Annunciator across the top of the Primary Flight Display is the airplane’s scoreboard.
Never assume.
Look specifically for:
- V PATH armed (typically shown in white)
- Lateral mode correct (usually NAV but could be HDG)
- Appropriate autopilot, auto-throttle and flight director modes
- Altitude preselect correctly set
If V PATH is not armed, the airplane will not automatically capture the descent path.
Many automation surprises begin with pilots simply not checking the scoreboard.
6. Verify the Altitude Selector
One of the most overlooked items:
Is the altitude selector set correctly?
If ATC has not yet cleared you to descend, leave the assigned altitude in the selector.
Once descent clearance is received:
- Set the newly assigned altitude.
- Confirm the altitude selector matches the clearance.
- Verify V PATH remains armed.
7. Cross-Check Time and Distance
Before reaching TOD, mentally compare:
- Miles remaining
- Altitude to lose
- Required descent angle
Ask:
“Does this profile look reasonable?”
If something doesn’t look right, it probably deserves another look before the airplane begins descending.
8. Monitor Path Capture
As the airplane approaches TOD:
Watch for:
- V PATH changing from armed (white) to active (green)
- Smooth pitch transition into the descent
- Expected descent rate developing
- Power reducing as anticipated
If the airplane does something unexpected, disconnect the automation if necessary and fly the aircraft while determining what changed.
9. Continue Monitoring Throughout the Descent
VNAV is not a “set it and forget it” feature.
Continue monitoring:
- Required descent rate
- Groundspeed changes
- Winds aloft
- Crossing restrictions ahead
- Any changes issued by ATC
Strong tailwinds, increase in airspeed, or amended clearances can require updating the vertical plan.
A Simple Verification Flow
Before every VNAV descent, I like to mentally run through this checklist:
- ✓ Crossing restriction correct
- ✓ Vertical profile looks reasonable
- ✓ Required descent rate acceptable
- ✓ Top of Descent location identified
- ✓ Flight Mode Annunciator (“scoreboard”) shows V PATH armed
- ✓ Altitude selector matches the current clearance
- ✓ Aircraft is configured and ready for descent
Spending 15 to 20 seconds verifying these items dramatically reduces the chance of an unexpected descent or a missed crossing restriction. Automation works exceptionally well when it’s monitored, but the pilot’s job is to continuously confirm that the airplane is doing exactly what was intended.
