Welcome to the VNAV Tutorial! VNAV, a long awaited feature has finally made its appearance. However, it does require a little bit of playing around with though before we can maximize its potential. This tutorial will cover most of the basics to get you familiar with and get comfortable using this autopilot feature.
How does it work?
VNAV works by taking into account, groundspeed, distance from the next waypoint, and the difference in altitude between your initial altitude and your target/final altitude to calculate a desirable rate of climb/descent. This rate of climb will adjust accordingly with a change in groundspeed.
At the end of this tutorial you’ll be able to:
- Utilize VNAV on STARs & Approach phases of flight.
VNAV – Vertical Navigation: VNAV is an autopilot feature that allows the aircraft to pitch for a predetermined altitude at a specific waypoint. SIDs, STARs, and Approaches have specific altitudes at various waypoints that need to be met. By allowing VNAV to control your rate of descent, you’re ensuring you’ll cross these waypoints at the correct altitude.
TOD – Top of Descent: This is the point at which you initiate a descent from cruise altitude to another altitude in preparation for the arrival phase of flight. TOD in Infinite Flight is not depicted on the map. Our TOD is displayed on both our VNAV toggle button as well as the VNAV advisory tool found in your toolbar (you will need to select this if you wish to have it displayed) . TOD is displayed in two formats for us: Time and Distance . See (Part 2) “Image 1.2” for more info about this.
SIDs, STARs, & Approach: Refer to the following tutorials for flight planning,
- Part 1: The Departure Procedures Tutorial VNAV is for descent only for now
- Part 2: The Arrival Procedures Tutorial
- Part 3: The Approach Procedures Tutorial
Route of Flight
Route of Flight
For the purpose of this tutorial, we’ll be planning a flight from Flagstaff Airport (KFLG) to Phoenix Sky Harbor International Airport (KPHX) via the FLG1.RW21 Flagstaff One Runway 21 Transition – INW.EAGUL6 Eagle Six Arrival Winslow VOR Transition – ILS08 to land on Runway 08 .
Route: KFLG FLG1.RW21 INW.EAGUL6 KPHX
To utilize VNAV to your advantage, there are a few things that are worth noting. VNAV will not work for climbs. Right now this will only work on a descent.
In Image 1.1, you’ll see that we have our VNAV control pulled up as found in the Autopilot menu. In your toolbar at the bottom, there is also a VNAV tool that you can use to see how long it will be before you will be required to or will be descending. The VNAV advisory tool in the toolbar will display data regardless if VNAV is in use or not.
Note: You will need to have at least one waypoint with an altitude plotted on your FPL for this data to come into view.
Seen here, [VNAV 3nm] indicates that you will be required to descend to your next altitude for the waypoint in front of you. If you have VNAV enabled, the autopilot will descend at a 2 degree angle to capture your next altitude. Your altitude and VS will turn to the color magenta when VNAV is armed and active. This is normal. If you have altitudes on your waypoints, there is no need for you as the pilot to change your altitude in the autopilot menu. VNAV will change ALT and VS automatically to hold that 2 degree angle.
Refer to Image 1.2 for this section. Keep in mind some of the features pointed out in “Part 1” as you will see some changes made in this part. As we continue along our flight, we have come to a point along our flight that we would call the “Top of Descent” or TOD. Our TOD indicates to us that we have come to the point where our final cruising altitude and our 2 degree descent angle meet so that we can cross a waypoint at a specified altitude. In this example, our final cruise altitude was FL280 and our first waypoint that has an altitude we need to cross at is EAGUL at FL180.
When VNAV in both the Autopilot menu no longer show a “XXnm” distance, you are at the 2 degree angle and need to descend.
- If no altitude exists at a waypoint prior to a waypoint with an altitude, the autopilot will still look for the next altitude and descend at that specified 2 degree angle.
- If you forget to turn on VNAV and you have passed the TOD, you will be greater than the 2 degree angle and you will see a higher descent rate. This will max out at -3000ft/min. Additionally, VNAV will begin to read out a negative value for distance.
Pilots are also sent an advisory messages that VNAV has begun descent as well as a message that indicates VNAV will begin a descent in “XXnm” after crossing a waypoint.
VNAV can be verified to be functioning properly via the the Altitude Arc or the “Banana”. In Image 1.3, this can be seen. In continuation from our descent of FL280 to FL180, you’ll note that we’ll indeed cross EAGUL at FL180.
Once VNAV captures 18,000ft at EAGUL, it will do either one of two things:
1. The autopilot will level off and display a new distance under “VNAV” indicating where your next TOD is for that segment of your FPL. Because our new altitude is FL180, 18,000ft is being used as our “final cruise altitude” and it’s now looking for our next step down altitude.
- VNAV and the autopilot will continue to work together to repeat the Part 1 - 3 to complete each step down. It will look for its TOD, then Descend and then look for its next level off altitude. Then repeat until you are on the ground or no other altitudes are present.
2. The autopilot will continue descending if it determines that you will be at or above the 2 degree glide angle. The best way to describe this is to picture it as an ILS. You will hold an altitude until you capture the glideslope before the aircraft begins a descent.
What do I do when I’m talking to approach or being vectored?
This part is rather simple and straight forward as it requires the tap of a couple buttons.
- Disable/Turn OFF VNAV
- Set altitude, speed, and/or heading to what ATC instructs you to fly.
- Select the approach in your “Procedures Menu” that you were assigned or told to expect as directed by ATC if not done already. If you’re unsure how that’s done, please see, Part 3: The Approach Procedures Tutorial.
- Tune into the ILS frequency in the [RWYS] tab if flying an ILS approach. Tap on NAV, and change your NAV source from GPS to NAV1
NOTE: You the pilot will be responsible for energy or speed management. Flying too fast on some of the arrivals will cause steep descent rates which could lead to overspeeding situations. It’s important to pay close attention to your speed while VNAV is commanding.
To add an altitude to a waypoint, simply tap on the waypoint you wish to add the altitude to, click on “SET ALT” at the bottom of your FPL menu, and type in the altitude you wish to be at for that given waypoint.
Ensure you have at least one altitude on a waypoint within your FPL if you wish to have the autopilot run VNAV.
If you forget to turn on VNAV and you have passed the TOD, you will be greater than the 2 degree angle and you will see a higher descent rate. This will max out at -3000ft/min. Additionally, VNAV will begin to read out a negative value for distance.
Be mindful of your aircraft speed on STARs in particular as overspeeding situations are more prevalent due to the likelihood of increased descent rates.
When flying under ATC, its important that you follow the instructions that they instruct. VNAV does not have priority over ATC. Its crucial, that once ATC tells you to change altitude, that you disengage VNAV and operate your altitude change with Vertical Speed.
VNAV can be used on approach so long as it doesn’t interfere with ATC or the instructions they issue.