Tuto du Djetdail

TOD calculation
3° slope
Calculation of the descent rate
3° / 5% slope
1 If you don't know the wind component you have to calculate it
Enter the data
Click on "Calculation of the wind component".
The field in part 3 will be filled in automatically.
Wind speed
Wind direction
Aircraft heading

Calculation of the speed to be lost between the beginning of the descent and the target
Speed GS start TOD :
Target IAS speed :

3 Enter altitudes in feet

Cruising altitude in feet (mandatory)

Target altitude in feet (mandatory)

If target Alt < TA indicate local QNH


Indicate the speed to be lost
between cruise speed (GS)
and initial approach speed or use part n°2

Indicate the wind component
(- sign for forward component)
or use part 1

From Mach speed


From ground speed GS

From the indicated speed (IAS)

Speed > FL100 =

Speed < FL100
(without data leave 250)

Distance additionAjouter

IAS = Indicared AirSpeed >> speed directly indicated by the instruments, it comes directly from the external probes (Pitot), it is thus impacted by the density of the air mass.
TAS = True Air Speed >> speed of an aircraft in relation to the air mass in which it is located, independently of its density.
GS = Ground Speed >> speed relative to the ground.
MACH = is the ratio of the speed of the aircraft in the air mass to the speed of sound in the same air mass.

Ratio between the speeds:
GS=TAS+-Wind component

Formulas used :
TOD distance = ( Cruise altitude (ft) - Target altitude(ft) / 𝟏𝟎𝟎 ) / 3°
TOD distance = ( FL cruise -FL target) / 3°
VS (ft/min) = GS x 5
VS (ft/min) = MACH x 3 x 3000

The calculation of the SV from the MACH and IAS speeds takes into account the wind component
The calculation of the VS from the IAS speed uses the formula TAS=IAS+(FL/2). The FL used is the intermediate FL between the cruise FL and the target FL.
Source : https://mediawiki.ivao.aero/index.php?title=Top_of_descent_calculation

Descent speed (source Eurocontrol)
Aircraft code ICAO Cruise >> FL 260 FL260 >> FL100
A319/A19N//A320/A32N//A321/A21N .78 290
A332 .80
A333/A338/A339 .81
A342/A343/A345/A346 .81
A388 .83 300
B722 .72 280
B731 .68 270
B732/B733 .70 280
B734/B735 .74 280
B736/B738 .78 280
B737 .76 280
B742 .84 290
B748 .85 250
MD11 .83 300
DH8D - 270
CL60 .75 250
T154 .72 290
AN24 - 240