old topic has been/will be shut, permission from a mod for this
VNAV?! What’s VNAV, you might ask. It stands for Vertical Navigation. But what does it do? You probably know what LNAV is (Lateral Navigation), and that it basically follows your flight plan for you. Well VNAV is similar, but slightly different. When you see your FPL, it is from a top-down perspective. Now imagine looking at it from a side perspective. The lines would show the altitude of the aircraft, not location.E.g
Ignore the reserves part
Here you can see the pilot climbed, leveled off, climbed again, cruises, step climbed (explained later) and then descended, leveled off and landed. Simply, VNAV controls your climbs and descent.
But why is this useful? Climbing only takes 15 mins and I’ll set an alarm to remind me to descend
Aha! You see, VNAV is less useful for initial climbs or the final descent, but more for step climbing and climbing/descending during the middle of your flight when you aren’t with your device.
But why would I climb or descend in the middle of my flight? And what’s step climbing?!
Simple. Imagine you’re on an airway with certain cruising altitudes and transition to a different one with different altitudes, or cruising one direction and turning around requiring a different altitude (SWEVENNEODD). You would set VNAV to climb/descend at that waypoint to the correct altitude.
Step climbing: On long flights, with very fuel-heavy aircraft that weight alot, the ceiling (and therefore cruise altitude) is restricted to lower, thicker air where the wings have enough lift to keep from stalling. When some of this fuel burns, it is important to climb so you aren’t cruising to low and wasting fuel, so VNAV climbs for you. Let’s see an example. We are EY878, an a340 from OMAA-RJAA. As we are so heavy, for the first half of the trip we can only cruise at FL290, but as we pass over Tibet (China) we can go up to FL350. As we may not be by our devices at this point, VNAV would make the climb for us.
I suggest to set a VNAV profile you click on a waypoint in your fpl (either in map or fpl) and set an altitude for it. Then you could have an ALT view along with the map, map/FPL and FPL views we have currently that shows the vertical profile.
In summary, VNAV would help a lot with fuel efficiency through step climbing and also help on routes that change direction, as well as increasing realism a lot.