VNAV: What is it and why is it important? [Vnav basics and how the Airliners descend!] 

This video is about VNAV or Vertical Navigation.
When flying in a small aircraft at low altitudes is easy to know when to start the descend for the landing.
However, when operating in an Airliner into busy airspace the calculation of the Top of Descend becomes more complicated.
This is so because, in busy Airspaces, such as Madrid for example, you have in your Standard Arrival multiply altitude and speed restrictions.
So, you can imagine that to calculate your top of descend correctly and fly a continuous descend to the next restriction is not an easy task.
And what happens if you have more tailwind or your aircraft is heavier, or you need to use the Anti ice, etc?? Your descend path will be different compared to an ideal world descend without all these variables.
Here is when the VNAV plays its rule. The Vertical Navigations takes into account all these variables and provides you with an accurate Top of descend.
In order to have a correct VNAV path descend you need to insert the data into the FMS accurately, otherwise, the VNAV will make some mistakes.
The Vertical Navigation calculates the descend path going backward from the runway.
It starts from the runway or the missed approach point and calculates a constant 3 degrees from the last restriction, then it will give you a segment for your declaration, a segment for every altitude restrictions, then it takes into account the weather, the weight and any other factor the may affect your descend.
And in the end, it will give you a correct Top of Descend.
Comparing an ideal world descend (without external factors, deceleration and altitude restrictions) with a real descend you will notice that the Top of descend position will change substantially.
If you want to know more about the Standard Arrival watch the RU-vid video below:
• Standard Arrival Route...
If you want to know more about IFR watch the video below:
• IFR vs VFR flight - In...
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Disclaimer:
THIS VIDEO IS FOR ENTERTAINMENT PURPOSES ONLY.
NOT FOR REAL-LIFE OPERATIONS.
PLEASE REFER TO THE OFFICIAL MANUAL AND DOCUMENTATION.
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