id: descent-planning title: Descent Planning meta: Learn how to plan your descent in Infinite Flight. order: 1 #

Descent Planning #

@vimeo

Descent preparation is a crucial step in any flight, the following tools will help you achieve a well planned descent:

You as the pilot - we will show you how you can calculate the Rate of Descent (ROD) required, your Top of Descent (TOD) point, and how many track miles you need to lose the altitude.
The Altitude Arc, also known as a “banana”
Vertical Navigation (VNAV)

Manually calculating Rate of Descent (ROD) Required #

To calculate the Rate of Descent (ROD) required to fly a 3 degree flight path angle, simply use the calculation below:

ROD = Groundspeed x 5

e.g. 500kts GS: 500 x 5 = 2500

Therefore a vertical speed (v/s) of 2500fpm (feet per minute) is required

The ROD calculation is a great tool to use in your initial descent as you will likely still be quite far from your destination and there is no need to dive down. You can then continue to adjust your ROD by redoing the calculation based on your current groundspeed.

Manually calculating Top of Descent (TOD) #

To calculate your Top of Descent (TOD) point, simply use the calculation below:

Distance = Altitude / 1000 x 3

e.g. FL380: 38000 / 1000 x 3 = 114

Therefore, with 38,000ft of altitude to lose, the distance required will be 114nm (nautical miles)

Tip

: Not sure what Top of Descent (TOD) means? Click here

Altitude Arc #

The Altitude Arc, commonly referred to as the “banana”; is a blue, curved line that depicts on the map/mini map where you will reach the bugged altitude that is currently selected on your Autopilot FCU.

The Altitude Arc/Banana takes into account your current groundspeed, vertical speed and altitude to place the arc on the map/mini map - because of this, you’ll notice that the arc can move around quite a lot. For the altitude arc/banana to work, you must have the autopilot engaged with an altitude selected

Tip

: Can’t find your altitude arc/banana? Open the map/mini map and look in the 12 o’clock position relative to your aircraft nose. Even if you have a turn in your flight plan, the arc is always directly in front of the aircraft. Also, don’t forget; if you have a low vertical speed set, the arc could be very far away!

See Vertical Navigation (VNAV) for more info.

Descent Management #

So you have now calculated your initial ROD and where to start your descent, perhaps you’re going to let VNAV take care of it for you. But if you decide not to use VNAV, how can you make sure you’re on profile?

Tip

: Don’t forget about your altitude arc/banana - adjust your ROD so that the arc is before the point on the map where you want to be at that selected altitude

The following steps will help you keep on top of your descent:

Step 1

: Calculate the platform altitude for the approach that you intend on flying (e.g. for a three degree ILS approach, with a Final Approach Point at 9 miles, this would be approximately 3000ft AAL)

Step 2

: Take the platform altitude away from your current altitude (e.g. FL380: 38000 - 3000 = 35000)

Step 3

: Divide this figure by 1000 and then multiply it by 3 (so in the above example 35000 / 1000 x 3 = 105)

Step 4

: Again using the above example, we now know that to be at 3000ft for the approach, you need 105nm from your current position to lose the altitude

Step 5

: Look at how many track miles you “think” you have to go before the Final Approach Point where we want to be at 3000ft

Tip

: Not sure how many track miles you have? Look at the map/mini map to help you, watch where the other aircraft are flying and use that to determine the most likely path you’ll be taking, it doesn’t need to be too accurate!

Step 6

: If it is less than 105nm, you’re high and need to increase your ROD. If it is more than 105nm then you can just maintain your current ROD or even reduce it

If you find you are high on the profile, there are two methods you can use:

Method 1

Reduce thrust to idle
Pitch for a high speed (e.g. 300kts IAS)
Extend speedbrakes

Method 2

Reduce thrust to idle
Shallow your descent and allow aircraft to decelerate
Extend speedbrakes
Get an intermediate stage of flaps out (e.g. Flap 2 for Airbus)
Then adjust pitch to maintain the speed

Method 1 is very effective but tends to be better at high to intermediate altitudes. Method 2 is more appropriate when you are at lower altitudes, closer to terrain or surrounded by high levels of traffic. Regardless of what method you use, make sure to always follow ATC speed control if issued.

Tip

: If you’re still high, don’t forget you also have the gear!

You’ve seen how to calculate how many miles you need and how to recover the profile if you’re high/low, now it’s time to look at how to monitor your descent:

Step 1

: Continue to do the above calculation and compare how many track miles you “need”, with how many track miles you “have”