how are the altitudes in DIR INTC decided vs LEGS?

[eag_a 9]

Hello,

 

on the DIR INTC page that is extremely useful for descent planning, you also get an altitude for each waypoint.

I do not understand how this altitude is decided by the FMS. Notably, it doesn't necessarily match the altitudes set in the LEGS page. For example, I have a waypoint at 3500A in the LEGS page. It shows as 3900 altitude on DIR INTC.

 

Thanks

[Aplato 133]

This is something I reported a long time ago that hasn't been addressed. One of the review videos by a real-world CRJ pilot highlighted this as a bug as well. 

 

[Jonas S. 466]

Hi,

 

I've forwarded this to the testing team.

[SinusJayCee 38]

On 24.9.2021 at 16:08, eag_a sagte:

I do not understand how this altitude is decided by the FMS. Notably, it doesn't necessarily match the altitudes set in the LEGS page. For example, I have a waypoint at 3500A in the LEGS page. It shows as 3900 altitude on DIR INTC.

I actually don't see an issue here. When the LEGS page shows 3500A for a waypoint, this means that there is an altitude constraint saying the plane needs to be above 3500ft when passing that waypoint. For the actual descent planning, the FMS may decide to actually fly higher at that point because it may be more appropriate or efficient regarding other altitude constraints, the TOD or whatever. This is the value you see on the DIR INTC page. A difference of 400ft sounds absolutely reasonably here to me.

 

If the DIR INTC fails to meet altitude constraints (i.e. being above a "below" constraint or a deviation at an "at" constraint"), this wouldn't be correct.

[Aplato 133]

4 hours ago, SinusJayCee said:

I actually don't see an issue here. When the LEGS page shows 3500A for a waypoint, this means that there is an altitude constraint saying the plane needs to be above 3500ft when passing that waypoint. For the actual descent planning, the FMS may decide to actually fly higher at that point because it may be more appropriate or efficient regarding other altitude constraints, the TOD or whatever. This is the value you see on the DIR INTC page. A difference of 400ft sounds absolutely reasonably here to me.

 

If the DIR INTC fails to meet altitude constraints (i.e. being above a "below" constraint or a deviation at an "at" constraint"), this wouldn't be correct.

 

This behavior is definitely not correct. This page should be displaying the altitudes specified on LEGS, not a calculated glide path. If there's a between restriction, it should show the top altitude if you're above it, and then change to the bottom altitude after it is reached. See this explanation from a real-world CRJ pilot that Aerosoft itself posted.  Starts at 1:39:10. 

 

 

[SinusJayCee 38]

vor 26 Minuten, Aplato sagte:

 

This behavior is definitely not correct. This page should be displaying the altitudes specified on LEGS, not a calculated glide path. If there's a between restriction, it should show the top altitude if you're above it, and then change to the bottom altitude after it is reached. See this explanation from a real-world CRJ pilot that Aerosoft itself posted.  Starts at 1:39:10. 

 

 

That's actually not the behavior that I would expect. For all non-constrained waypoints, the DIR INTC displays the planned/expected altitude. So I expected that this is also true for constrained waypoints except for that the altitude need to meet the constraints.

 

But since a RL pilot says it's differently, I would agree with you that this is not the correct behavior. Given that this is *advisory* VNAV and not classical VNAV, it also make sense to have the DIR INTC page behave as stated by that pilot.