Hi, I have Maddog 2010 Pro and FS9 and a problem: the altitude constraints entered in the LEGS page during VNAV descent are not taken into account! I tried several times, but always the same result.
Attached is a screenshot: from cruise FL 300 I descend to FL 250 BUT I want the aircraft to be at FL 270 at NORNI. Nothing, it doesn't level off at FL 270, but continues descending to FL 250 as if there were no constraints.
Please, tell me where I make a mistake!
Thank you,
James

Altitude targets can be inserted preceeded by a slash in the corresponding field. The format can be:

- /10000 or /FL100 or /100 “ AT FL 100 “
- /10000B or /FL100B or /100B “ AT FL 100 OR BELOW “
- /10000A or /FL100A or /100A “ AT FL 100 OR ABOVE “
- /8000A10000B or /FL080AFL100B or /080A100B “ BETWEEN FL80 AND FL100 “

Speed constraint (NOT IMPLEMENTED YET)can be inserted only followed by an associated altitude constraint. If in doubt about wich altitude constraint to utilize, use the altitude of the immediately preceeding wpt followed by letter B. E.g.: If the altitude of the preceeding wpt is FL080, enter a speed constraint of 280 Kts for the next wpt as 280/080B.

Massimo, do you mean I did not enter the correct format for the altitude constraints?
Do you also mean that in Maddog 2010 speed constraints are not implemented?

By the way, I found out that the "AT" is quite followed, while what is often overlooked is the "AT OR ABOVE" constraint, the aircraft overflies the waypoint too high. But it doesn't happen all the times, I'm trying to understand why at times it is respected and at times not.

Its impossible to overfly a waypoint too high if the contraint is "AT OR ABOVE".

Your constraints are ok anyway. Try to select 250A.

What I have reported is the correct FMS constraints syntax format input.

By the way, as I have mentioned in others reply, the FMS functions aren't 100% reliable, specially for computation and predictions related to vertical path.

I have seen your picture, and you are 0.3 NM outbound NORNI. So if you have armed a lower altitude before reaching or before passing the active waypoint, the system will follow the speed and the precomputed altitude or, if inserted, the speed and/or constraint altitude for the active waypoint.
In this case if the FMS for the waypoint before NORNI wpt, it was precomputed a lower altitude or a lower constraint altitude it was selected, arming a lower altitude will cause a change in the vertical profile that will bring the aircraft to catch (as probably in your case) the lower level.

I apologize, but unfortunatly it is difficult to found on the web a complete Honeywell FMS literature; for this reason the complex FMS system it isn't 100% reliable. I hope as soon, some simmer will help the community in this way.

Thanks Massimo, I did some more testing and overall I can say I am quite satisfied with the VNAV behaviour.

To wims80: sorry, I meant "while what is often overlooked is the "AT OR ABOVE" constraint. Often the aircraft, while descending, doesn't "realize" there is an AT OR ABOVE constraint and passes the waypoint below the constraint altitude" .

Hi,

Because you armed a lower altitude (see the ALT ARM line on the FMA) the FMS ignores all constraints in the FMS leading to that altitude.

If you want it to obey the FMS, do NOT arm an altitude - simply dial the altitude down. It will obey FMS altitude constraints, and will not descend lower than the selected altitude (check - I think this is the case as it is VNAV flying and not a basic vertical mode).

Best regards,
Robin.

Hi Robin,
I don't understand how I can dial an altitude without arming it. If I dial say 25000 on the FGCP it automatically becomes armed on the FMA ALT ARM. Can you please elaborate a little bit about that?
I did some more tests today and the aircraft never respected the "at or above" constraints, it keeps descending tp the FGCP altitude without changing the rate of descent, as if there were no constraints at all.


By the way, Davide, I found this old thread (2007):
http://www.flythemaddog.com/forum/index.php?showtopic=2693
Reading that thread it seems to me that now the code has been modified and a restriction without "A" or "B" works well during descent. But what if there is an "A" or a "B"?

Thank you very much and best regards,
James

Check the "Auto-arm Altitude" option in Manager & Setup Tool > General ("Aircraft setup" on the right side).

I did tests without the auto-arm but I hardly see any changes.

**BUT** I did some more tests and I found out something strange...
Say I am descending from cruise level to 16000 ft and there is a waypoint with an altitude constraint "at or below" ("B"), for example FL280B: the aircraft descends in VNAV DES and approaches 28000 before reaching the waypoint, then enters VNAV CAP and levels at 28000 in VNAV LVL. In order to continue descend the VNAV button needs to be pushed, otherwise the aircraft will continue at 28000 ft forever, even after the waypoint.

Then there is a waypoint with a constraint "at or above" ("A"), for example FL250A: the aircraft descends in VNAV DES and doesn't care of the constraint, continuing in VNAV DES below 25000 ft before reaching the waypoint.


What does that mean? That the "A" and "B" are inverted!! FL280B should be FL280A, so that the airplane can't go below 28000 and MUST level (even if I don't understand why it doesn't start descending again after the waypoint, if you don't remember to push VNAV the maddog will remain at that altitude forever).
On the other hand, FL250A should be FL250B! Indeed, the aircraft continues below 25000 because it must not be above 25000 but no problem below.

What do you think Davide? It seems to me that there is a "bug" in the code so that "A" should be changed into "B" and viceversa.

*EDIT*: some more testing after changing VNAVN=98 into VNAVN=65 in the maddog2008.ini file: now it seems that it's working correctly, levelling off when there is "at or above" or continuing descending when there is "at or below". What does the VNAVN parameter change??

I have auto-arm altitude arm disabled here. Regardless - I explicitly stated that the altitude must *not* be armed for the FMS altitudes to be respected.


Interesting. I'll have a look at this next time I fly.

Best regards,
Robin.

It's really strange:I tried several times after changing VNAVN from 98 to 65 and it workscorrectly, except for the first waypoint with constraint I encounter after I start a DES NOW early descent. If that waypoint has an "at or above" constraint, it is not taken into account. The next waypoints are honored, either they have an "at or above"or an "at or below"!
I tried the same thing at work, where I installed FS and the Maddog just for testing purposes, and there no constraint is honored, as if there were no constraints at all! Really strange.
The important thing anyway is that at home it works well the other day I did an entire descent with waypoint constraints down until the runway and I almost did a "precision" approach with only VNAV

That would be an RNAV approach, aka FMS approach. Is the LSH MD RNAV capable? I thought it leveled off at the waypoints...

Still yet to check your observation...

Best regards,
Robin.