Top of descent procedure

Hi guys, i m having a question about TOD…checked related posts, but couldnt find the answer.

so, lets say i flying at 30,000, and the next waypoint is at 21000…will the aircraft descend automatically…
I m flying mostly a320. I tried the defalut version and the FBW (both stable and development), and i noticed this :

with the default one, when i set 21,000 and press the AP for automanaged altitude, it wouldn’t descend until a specific distance…so i can not descend in “advance”…
with the FBW ones, same scenario, and when i press, it will start the descent immediatly (so not respecting the proper waypoint of descent)

and the arrow for TOD in both vesrions is not accurate…or may be it is me ?..

so, if someone would be so kind and explain me, how do a descent properly kinda close to real life.
and also, what to use ? the default version or the FBW ?
Thanks in advance.


As far as I know, FBW does not have VNAV capability (vertical navigation) only LNAV (lateral navigation). You have to monitor and adjust your altitude from takeoff to landing. As far as I know, none of the current aircraft in MSDS 2020 have this functionality. Even in other sims,
only the study level aircraft have this functionality.

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I have the same questions… and all I do is start to descend toward 3,000 or 4,000 at the last assigned FL as stated in my flight plan.

So if I’m near the end of the flight, I set for 3,000 or so and let the AP take me down. This usually results in me being at or near the level that the ILS can take hold. However, I’m quite often well below the constraints for much of my descent and approach.

I’ve tried to dial in the prescibed altitudes from the flight plan, but many are unattainable (dropping 10,000 feet in 15 miles, for example). I’m not good enough to do that and I don’t think the flight management system would allow such a steep descent.

But, I’m no pilot, so I don’t know any other way to do it. I suppose I’ll learn in due time…

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so guys, thanks for the answers…i think i will do it thej old way, just descned kinda manually and just adjust the VS to reach the correct altitude at the spec ific waypoint…and just feel it…i think that pilots do it also in real life…better being too low at some point than too high and avoid a steep descent…happy flying…and learning…

MSFS does not have VNAV but at times, for reasons I don’t understand, a320 automatically started the descent much ahead of the TOD.

It happened just twice or thrice with me, but, it did happen.

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There’s one aircraft with LNAV: The working Title Mod of the CJ4 has VNAV capability like the real plane since the last big update. :wink:


Yes, I noticed waypoint constraints would not always take entries also

The Airbus doesn’t automatically descend at TOD like Boeing. You can either wait until exactly at or past TOD and the AP in managed will descend to catch up or follow the vertical path constructed with the programmed altitude constraints and speeds. Or, before the TOD, in managed descent the AP will descend at a rate of -1000 until the aircraft either meets the vertical path or any altitude constraints programmed, whichever is reached first while complying with any programmed speeds.

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Thank you for the insight. I was mid-flight from KORD to KLAX when I read this and decided to do as you stated… I waited until I was inside the last waypoint in my flight plan that had FL360 assigned and then dialed in 3,000 and initiated my descent using the “managed” altitude in the AP. There were several constraint levels above 3,000 feet as I traversed the waypoints on the way in and the AP held those levels until we went past them.

After that, when I finally acquired the ILS and then, subsequently, the LOC, the AP picked up on that. And when I finally selected APPR, we started the final descent on the G/S.

It worked just as you said. I guess I’d just never trusted it enough and fought it by coming down way too early and… well, you get my drift here.

Thank you again… I’m off to do more short flights so I can practice this and get better and more trusting of the system.

Do you know if it is implemented in the FBW A320 yet?

For what it’s worth, I only use the developer version of the FBW A320neo… update it just prior to all flights to make sure I have all the goodies installed.

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Yeah, I can feel you. Also only using the dev version. But I think it didn’t catch up any altitudes the last time I tried. Also RNAV approaches aren’t working for me, I only get the indication when turning on LS. Were you ever able to fly any altitude constraints automatically?

no, not yet, that’s whhat i m trying to find out…i see the constraints and i adjust the VS too get righgt there at a certainn time…boring but i think nnnnnoothing else to do for now…

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I’m still experimenting… I thought the AP held the majority of the constraints, but was too busy trying to understand other stuff to make sure that it did.

I’m trying to develop a workflow, as it were, so I do the same things at the same points in each approach. I’m hoping that will help me gain consistency and not miss a step.

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the Working Title CJ4 does have working VNAV. You have to manage climb with v/s (same as IRL) but descent it will do for you.

Hi All
In aviation, the rule of three or “3:1 rule of descent” is that 3 nautical miles (5.6 km) of travel should be allowed for every 1,000 feet (300 m) of descent . In the early days of aviation, few aircraft were pressurized. A pilot who descended rapidly would cause his passengers the discomfort of rapid pressure changes on their eardrums .

Don’t forget to drop three digits from the end.
Example 30000 ft x 3 = 90miles.

I’ve used this site to assist…

Just a couple points here from A320 driver…

The real A320 does not have VNAV (The button doesn’t eve exist). The 4 modes we use for descent : VS, FPA, DES, Open Des. From them the most common are VS, DES, Open DES.
I’ll try to keep it straight forward and simple :

VS - is very obvious, the plane descending using the vertical speed you selected by pulling on the VS knob.

Open Des - Known as open descent, is pretty much the FLC mode, the plane goes to idle and maintaining the target (Selected or Managed) speed using pitch.

Des - Is what’s getting confusing… It’s not a VNAV but it will capture the vertical profile from a specific point “white Hockey stick” to your first crossing restriction. I’m not going in depth how this TOD stick is calculated, but pressing the ALT selector know before the “TOD Stick” will initiate a -1000 fpm descent until it intercepts the “Path” from there the plane will go to idle and continue for crossing the first altitude restriction. If you press it exactly at the “TOD Stick” the it will capture it perfectly, but if you press it late it will struggle sometimes depending on winds and the message “MORE DRAG” will appear and sometimes speed brakes will be necessary (On the A320 it’s only half while using the AP).

Airbuses philosophy in the automation is either “Managed” or “Selected” while managed is your calculated FMGS/FMS inputs.


Thank you for the explanation. It seems most helpful except for one thing–how, where and when is the “TOD” delineated, created, pointed out to me so I can make the selection I want and start the DES at the proper time and place?

I don’t know where to find the “TOD” in the overall scheme of things and that leads me to guessing. I’ve seen and tried to figure out equations that take into account many of the parameters at the arrival, but I am unable to determine when to start the calclations.

Add to that there are always several “steps” of constraint altitudes in my flight plans… do I need to do the TOD white hockey stick procedure for each “step”? If so, I’ll most certainly blow the approach as I’ll be too busy calculating and trying to hit waypoints and their restricted altitudes.

I am not trying to be obstinate here… I’m trying to figure out the flow of steps from cruise to landing. I just can’t see it at this point.