PMDG B737 Climbing Question

[Langeveldt 279]

Hi all

I just wondered what the best procedure is for climbing out in the PMDG.  It's all a bit overwhelming.

I have everything set up correctly in the FMC and ATC clears me to say 15,000 feet.  When I reach 15,000 feet I get cleared to say 21,000 feet.  When I dial this into the altitude selector nothing happens.  How do I initiate the climb?  I am in VNAV mode and I would expect this to happen automatically.  There are no constraints.  Do I have to click LVL CHG and then VNAV again?  If I just click LVL CHG it stays out of VNAV mode when I reach the target altitude. I see there is the ALT INTV button too, but haven't used this yet.

Just wondering how the pros do it.

TIA. 

[SAS443 1,721]

VNAV "ALT" INTV. button will solve this

[Bigbluss 304]

On this topic, what is the difference between LVL CNG and manually setting altitude + hitting ALT INTV? The tutorial didn't explain the difference and I've been unable to clarify it online.

[SAS443 1,721]

1 minute ago, Bigbluss said:

On this topic, what is the difference between LVL CNG and manually setting altitude + hitting ALT INTV? The tutorial didn't explain the difference and I've been unable to clarify it online.

Level Change will not honor any intermediate restrictions regarding speed/altitude.
ALT INTV is associated with FMS VNAV mode, which caters FMS climb speed/alt restrictions. (SPD INTV can be used to alter speed profile)

in short, use ALT INTV to transition from VNAV ALT- annunciation to VNAV SPD and begin climb in VNAV again.

 

 

[Bigbluss 304]

1 minute ago, SAS443 said:

Level Change will not honor any intermediate restrictions regarding speed/altitude.
ALT INTV is associated with FMS VNAV mode, which caters FMS climb speed/alt restrictions. (SPD INTV can be used to alter speed profile)

in short, use ALT INTV to transition from VNAV ALT- annunciation to VNAV SPD and begin climb in VNAV again.

 

 

Much appreciated - thank you.

[Langeveldt 279]

Thank you, much appreciated.  I'm at work but would like to test this tonight.  When being given a new altitude and on pressing ALT INTV there is nothing more to do?  It stays in VNAV mode? 

[SAS443 1,721]

2 minutes ago, Langeveldt said:

When being given a new altitude and on pressing ALT INTV there is nothing more to do?

If your current Autopilot vertical mode is VNAV ALT - then yes. It will transition to a VNAV SPD climb.

If it reads ALT HOLD, then nothing will happen AFAIK, you need to select higher MCP altitude and press VNAV button.

[SierraHotel 976]

1 hour ago, Langeveldt said:

Hi all

I just wondered what the best procedure is for climbing out in the PMDG.  It's all a bit overwhelming.

I have everything set up correctly in the FMC and ATC clears me to say 15,000 feet.  When I reach 15,000 feet I get cleared to say 21,000 feet.  When I dial this into the altitude selector nothing happens.  How do I initiate the climb?  I am in VNAV mode and I would expect this to happen automatically.  There are no constraints.  Do I have to click LVL CHG and then VNAV again?  If I just click LVL CHG it stays out of VNAV mode when I reach the target altitude. I see there is the ALT INTV button too, but haven't used this yet.

Just wondering how the pros do it.

TIA. 

 

 

Edited May 12, 2022 by SierraHotel

[Langeveldt 279]

1 minute ago, SierraHotel said:

https://www.youtube.com/watch?v=v7J9M_0M0Gg&ab_channel=737NGDriver

 

Thank you.  Appreciate the quick and detailed help.

[SierraHotel 976]

 

[SierraHotel 976]

Just now, Langeveldt said:

Thank you.  Appreciate the quick and detailed help.

You are most welcome, don't forget to watch "Climb Theory" as well

[Nadsy 0]

Was this the same on 737-800 in FSX? I don't recall having to do that... but it's been a while since I've been in the seat.

 

[Stearmandriver 2,266]

It was the same in FSX, but I think maybe not at first. It may have been a later update that made Alt Intv functional.  I can't really remember. 

It's worth noting that not all aircraft have the VNAV ALT mode, and I don't think it's tied to a software version so much as it is a specific option. I mention this because folks are grabbing various 737 manuals off the internet, and depending on the aircraft being described, VNAV ALT may or may not exist. 

On fleets that don't use VNAV ALT (mine does not), when the aircraft is climbing or descending in VNAV and it reaches an FMC altitude constraint, it will level off and remain in VNAV PTH until it's time to start down again... but if it intercepts (and therefore is forced to capture) an altitude set in the MCP, vertical mode just reverts to ALT HOLD.  Thus, when you reset the MCP altitude to continue your climb or descent, you have to re-select VNAV (or another vertical mode).  We have and use the ALT INTV button, but we use it for other things (that are modeled correctly on the PMDG too.)

So, the above paragraph does NOT apply to the PMDG 737, which is also accurate.  I just mention it in case someone finds this in a manual and wonders why. The rest of this thread explains the (accurate) behavior of the PMDG.