Flying the PMDG 737-800 in VNAV mode, I noticed that the plane is not descending when it reaches top-of-descent. Is the plane supposed to automatically start descending itself based on the next lower altitude waypoint or does it require pilot intervention in the MCP. 

The same question for Decel. Does the plane automatically decrease speed or does it also require pilot intervention in the MCP?

Did you set new altitude. Works for me

It should descend itself along the path as long as you have manually entered your lower altitude first on the MCP. You should have also entered your approach winds in the forecast page along with the QNH at your arrival airport and your flap setting into othe relevant pages in the FMC before reaching TOD.

2 hours ago, JamesIL said:

Did you set new altitude. Works for me

18 minutes ago, El Diablito said:

t should descend itself along the path as long as you have manually entered your lower altitude first on the MCP.

So I guess the answer is "yes, there is manual intervention ie. a new lower attitude has to be manually entered on the MCP"? 

At what point in time then should I manually enter the lower altitude?

I don't believe I have an answer for my second question ie. Does the plane automatically decrease speed or does it also require pilot intervention in the MCP?

You set the MCP altitude according to ATC clearance. VNAV is restricted by the MCP alt.

If you're not using ATC, set the MCP alt to your cruise altitude before takeoff, and at cruise before TOD, set the MCP alt to the glide slope interception on the approach. VNAV can then operate freely.

28 minutes ago, anavsun said:

 Does the plane automatically decrease speed or does it also require pilot intervention in the MCP?

Yes, it will automatically decrease if VNAV is activated and it will decrease according to the speeds entered in the flight plan. For example, if there are any altitude constraints and those speeds are entered in the flight plan beside the waypoint where the restriction is, then the aircraft will slow itself down to the restriction speed. Just an FYI, when the aircraft reaches its TOD and starts to descend it will automatically increase speed because it will be nose down, but it will slow itself according to its altitude as it goes down the flight path, ie: it will slow to 250kts at or above FL100.

Just to note there are 2 types of VNAV cruise , VNAV ALT & VNAV PATH, you will need to be in VNAV PTH for the aircraft to start its descent automatically ( with a lower altitude set in the MCP)

5 hours ago, anavsun said:

Flying the PMDG 737-800 in VNAV mode, I noticed that the plane is not descending when it reaches top-of-descent. Is the plane supposed to automatically start descending itself based on the next lower altitude waypoint or does it require pilot intervention in the MCP. 

The same question for Decel. Does the plane automatically decrease speed or does it also require pilot intervention in the MCP?

https://downloads.pmdg.com/supportfiles/Docs/PMDG_737_MSFS_Tutorial.pdf

Here's is the full tutorial flight they give you for the plane in case you couldn't find it after install. Deals with this subject and everything else for a basic flight. 

3 hours ago, anavsun said:

So I guess the answer is "yes, there is manual intervention ie. a new lower attitude has to be manually entered on the MCP"? 

At what point in time then should I manually enter the lower altitude?

I don't believe I have an answer for my second question ie. Does the plane automatically decrease speed or does it also require pilot intervention in the MCP?

You should see RESET MCP ALTITUDE in the FMS about 5 nautical miles from T/D. That is when I select a lower altitude on the MCP. You will also have to manually reduce the speed on the MCP when required. The autothrottle adjusts the speed based on your manual inputs.

Edited February 5, 20251 yr by Christopher Low

8 hours ago, El Diablito said:

Just an FYI, when the aircraft reaches its TOD and starts to descend it will automatically increase speed because it will be nose down, but it will slow itself according to its altitude as it goes down the flight path, ie: it will slow to 250kts at or above FL100.

Great info. Thank you.

6 hours ago, jon b said:

Just to note there are 2 types of VNAV cruise ,

How? Do you know of a tutorial on how to get to these two modes?

5 hours ago, Christopher Low said:

You will also have to manually reduce the speed on the MCP when required.

When is it required?

5 hours ago, sloppysmusic said:

Here's is the full tutorial flight they give you for the plane in case you couldn't find it after install. Deals with this subject and everything else for a basic flight. 

Thanks for the suggestion. I tried to follow the tutorial but the default ATC was giving me difficult to follow waypoints when it cleared me for a VECTOR. For instance it required a sever U-Turn since the aircraft is coming from the north (KPDX) and the runway (28R KSFO) is facing north.  It was suggested that I use 3rd party ATC, eg. BeyondATC which unlike SayIntentions does not require a subscription. I need to check FSHud too. 

Also, the tutorial is for a 700 (I have the 800) and it does not explain how it came up with the route plan and how and why it selected or did not select a SID or a STAR.

17 minutes ago, anavsun said:

the default ATC was giving me difficult to follow waypoints when it cleared me for a VECTOR.

Definitely do NOT use ATC when learning a complex plane! After you understand lnav/vnav and want to learn the MCP with heading vectors, manual flight level/altitude selection and manual (with at) speed control any ATC is great for that. The more diversions the better!

Regarding the route, I believe it gives you the full route assuming clear skies, no wind. Again this is a good way to practice the ac first. I find making my own routes a lot of fun, so I get to pick what scenery i see on the way. If you want to do your own flight me or someone here will gladly help you with a complete route with sid/star before you learn how to do it yourself.

I usually train a new ac with route to and from the same airport. Short flights are good for practice plus the wind is usually the same so runway is too!

4 hours ago, sloppysmusic said:

Definitely do NOT use ATC when learning a complex plane! After you understand lnav/vnav and want to learn the MCP with heading vectors, manual flight level/altitude selection and manual (with at) speed control any ATC is great for that. The more diversions the better!

Regarding the route, I believe it gives you the full route assuming clear skies, no wind. Again this is a good way to practice the ac first. I find making my own routes a lot of fun, so I get to pick what scenery i see on the way. If you want to do your own flight me or someone here will gladly help you with a complete route with sid/star before you learn how to do it yourself.

I usually train a new ac with route to and from the same airport. Short flights are good for practice plus the wind is usually the same so runway is too!

Good advice. I've been doing that. Thank you. Time for ojt (on-the-job training) for me. 🙂