11 minutes ago, threegreen said:

FMC navdata base updated to the current cycle I guess?

It’s current.

12 minutes ago, Fiorentoni said:

However since it's generally buggy for you (frozen cockpit), I'd say it's probably something else. Better open a ticket.

It’s the first time the frozen cockpit incident happened. I’ll keep flying and see if more issues arise. 

Well I’ve been doing some more testing and didn’t have any issue with altitude restrictions getting busted. Neither any frozen cockpit issues, luckily.

However the plane is very late to slow down to meet speed restrictions when in VNAV descent, so I usually have to manually intervene a few miles before the speed reduction indicator on the ND.

On 5/25/2022 at 12:55 PM, threegreen said:

Hard waypoint restrictions or target speed? Because in VNAV PATH there is a certain margin (10 or 15 kts, selectable in the FMC) that the aircraft will accept below or above the target speed. Also when the A/T is in arm mode you have to manually adjust thrust as needed until it goes back into FMC SPD or another speed mode.

Hard restriction as confirmed on navigraph charts - usually as part of a STAR.

16 minutes ago, Cpt_Piett said:

Well I’ve been doing some more testing and didn’t have any issue with altitude restrictions getting busted. Neither any frozen cockpit issues, luckily.

However the plane is very late to slow down to meet speed restrictions when in VNAV descent, so I usually have to manually intervene a few miles before the speed reduction indicator on the ND.

Yep, exactly what I have seen.

I saw it blow thru a SID alt restriction the other day leaving KDEN on the HHOTH departure, but, it could have been my poor flying that caused it.

Not been missing restrictions for me, have been using SIDs & STARs with restrictions AND manual restrictions and not had an issue aka ATC shout at me !!

 

G

I've not seen such busted restrictions at all and since all my flying is on Vatsim one has to be on top of such things. VNAV does at all times work within the art of the possible and if one tells it to do the impossible then it will ignore it, it can't just stop flying. I've certainly never had it descend below a hard floor and if it were doing that as a matter of course then it wouldn't have been released.

7 hours ago, Cpt_Piett said:

Well I’ve been doing some more testing and didn’t have any issue with altitude restrictions getting busted. Neither any frozen cockpit issues, luckily.

However the plane is very late to slow down to meet speed restrictions when in VNAV descent, so I usually have to manually intervene a few miles before the speed reduction indicator on the ND.

Do you get any "drag required" or "descent path too steep" messages on the CDU any time during descent? If so, you must intervene because the aircraft cannot with its available means.

3 hours ago, Fiorentoni said:

Do you get any "drag required" or "descent path too steep" messages on the CDU any time during descent? If so, you must intervene because the aircraft cannot with its available means.

Yes often. And I intervene when required. 

Been doing even more testing, and I still haven’t had any ALT restrictions busted. So it is down a single event which may well have been user error. 

Have to use speed intervene quite often though to meet the speed restrictions. 

1 hour ago, Cpt_Piett said:

Have to use speed intervene quite often though to meet the speed restrictions. 

It does seem to try and hit the speed restrictions very much at the last minute. I'm mostly flying heavy, so don't know if that makes it more or less likely to occur. Have been finding when P2A tells me to slow I am normally still about 12-15kts fast, but slowing to meet the restriction. That was pretty much what was happening in P3D as well....

 

G

Let me assure you all that the FMC's speed control in 'the real thing' is far from perfect and one has to keep a constant eye on the ASI.  However, it handles altitude restrictions pretty well but only, of course, responds to what has been programmed - hard altitude restrictions have to be complied with but there are lots of places where you can tell the aircraft what height/speed you want it to be at to make the approach more manageable.

Returning to the sim aircraft, I have had altitude busts by 2-3 hundred feet at times and they haven't been coming from either high climb or descent rates or excessive speed.  PMDG need to make some mods to the FMC, without doubt.

The VNAV working well is VERY dependent on having accurate wind data entered into the descent forecast.  also the spoilers are not overwhelmingly effective, so relying on them to  bail you out is not adviseable.  I haven't had trouble with it in msfs.  I used to rage about it in previous sims, but I realized the faulty component was me.  stay ahead of the airplane.  It's not a robot plane, the pilot is not merely an advisor/passenger to the flight.

 

1 hour ago, ShawnG said:

It's not a robot plane

That’s true. Have to stay on top of things and intervene when required. Even with all the automation. Have to stay in command 😉

For the last few flights I’ve let the plane manage itself in VNAV descent to see how it goes. And more often than not I’ll end up too high and too fast. 

Edited May 27, 20224 yr by Cpt_Piett

Let me ask you guys this.  If I have a SID dialled in, with the waypoints progressively increasing in altitude...and I have one waypoint that says "at 17000"...should I be setting 17000 in the MCP on climbout?

I think (as I recall) ATC had cleared me thru 31000 feet, and I might have had 31000 feet in the MCP.

This may be the reason for the departure busting of 17000, but I'm not sure how it /should/ be done.