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TOD calculation


Jov

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I do have problems with the TOD calculation.

 

If the flighplan in the MCDU contains only the destination airport and no specification of a runway yet,
obviously no TOD is computed and the plane keeps on flying past the destination because the "pause at TOD"
option is not invoked.

 

To circumvent that problem I started entering a runway and STAR into the flightplan.

So today, as in other flights b4, the plane stopped 21 mi b4 TOD en route to KLAX at FL 400, apporx. 140 mi away
from destination.

However, when I pressed "P" to restart the sim, the PFD showed that I was
already 6800 ft too high for the proper descent.

 

Plus, the plane accelerates even in high altitudes pretty much if descent rate is greater 1800 ft/min.

This is strange, since IAS should increase only at lower FLs, whereas with the 330 one can even
descend with 1800 ft below 18000 ft without picking up too much speed.

 

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  • Deputy Sheriffs

And you are sure, that you configured the aircraft correctly, with weights, fuel etc.? Best show us screenshots of the PFD, ND, FCU and MCDU (INIT A and B, flightplan page), ECAMs...

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Yes I am sure, that I configured the aircraft correctly.

Yesterday, the TOD was 180 mi away from KLAX.

With a 777 from PMDG the TOD is 140 mi away, but with a much steeper initial
descent, (approx 2700 ft) so the glideslope is doable.

 

With your a330, such a steep descent would accelerate the plane too much.
At least in my sim.

 

I will try to recreate some flights to show my point.

 

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Here is one example. TOD @ FL400 180 mi out.

Target descent rate at FL 345  around 1500 ft.

 

That seems odd to me.

Or are these standard procedures for a A330

I can hardly imagine

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  • 1 month later...

What was your Tailwind on the flight?

 

As a rule of thumb in the real airplane we (my airline)  use the following profile calculation to check that the managed profile is relevant:

 

4* FL when above FL150.  At FL200 and around 300KTIAS you should see 80Nm to run on the MCDU

3*FL plus 1NM per 10kts above 150Kts. Example: at FL100 and 250kts your track miles to run as read on the MCDU should be 40Nm. 

 

example:

at FL400 your TOD should be at 160NM with no wind. More if tailwind (+/- 2NM/10kts of wind roughly ). If this calculation is within 20NM of the aircraft computed TOD, then the computed TOD is relevant. Therefore in your scenario if you had close to 100kts tailwind I would say 180NM TOD looks correct.

 

The A330 is pretty "slippery" and is hard to decelerate so you don't want to get high on profile.

In high workload  environment I tend to use the following gates which are pretty conservative and are based on the profile calculations described above with nil wind:

FL200 80NM

FL150 60NM

FL100 40NM 250Kts

FL50 20NM at Green Dot

15nm 4500ft 180kts

this should take you to intercept the ILS at 10nm, 3000ft, 180Kts. Speed will then be easily under control once in F2 and gear down.

 

Disclaimer: I have not tested the Aerosoft A330 much as I bought it recently but I am mostly flying vintage airplanes on the sim at the moment.Make sure you get the descent winds in the MCDU so that the FM can compute an accurate descent profile.

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