738 for MSFS: why does speed drop to 212 around TD when...

[Noel 4,503]

...when descent speed is set for 250?  I'll be flying level til around 140m out when speed drops way down and before I've initiated descent...

Thanks in advance!

 

[G550flyer 1,014]

I think you are experiencing a feature where the aircraft slows down when you don't descend when it's expecting you to. May be a 737 thing, but I don't like my aircraft doing anything without me setting it up or initiating it.

[Noel 4,503]

Thanks Rick it is something the 737 in P3D did not do so was puzzled by it.  Just now I descend to FL270 and descent goes at 250 as it's supposed to but when it hits Fl270 same same right back to 214.  That is bizarre!

[threexgreen 3,139]

Just now, Noel said:

Thanks Rick it is something the 737 in P3D did not do so was puzzled by it.  Just now I descend to FL270 and descent goes at 250 as it's supposed to but when it hits Fl270 same same right back to 214.  That is bizarre!

It's not bizarre and the P3D version does the same thing just like the real airplane. Like Rick said, it reduces speed to clean maneuvering speed when you go past the top of descent or any point of descent on your descent profile without actually descending (most likely due to not resetting the MCP altitude to a lower altitude in time) trying to maintain the descent profile.

 

[Chock 17,769]

As others have noted, the 737 is quite slippery on descent - in fact it's not unknown for crews to have dropped the landing gear on their 737 to help keep the speed under control on a descent, so it's giving you a margin to keep you well below Vne when you are going 'downhill', which of course if you don't then take advantage of by actually descending, will slow you down a lot as you maintain altitude with the throttles backed right off. 

[G550flyer 1,014]

3 hours ago, Noel said:

Thanks Rick it is something the 737 in P3D did not do so was puzzled by it.  Just now I descend to FL270 and descent goes at 250 as it's supposed to but when it hits Fl270 same same right back to 214.  That is bizarre!

Here's what I would do. As you close on your T/D, select the speed intervene button on the right of the speed knob. Dial in the speed you want and the jet should keep it. In my jet, we call this manual speed. It should keep this speed from cruise down through landing. Keep in mind that you are the speed control in this case. If you are not careful, you could bust a restriction so stay progressive!

Rick

Edited September 6, 2022 by G550flyer
Wrong Quote

[Noel 4,503]

Thanks all.  The problem comes from using default ATC to direct descent which sometimes is after when the FMC thinks it ought to be in VNAV mode.  Anyway thanks I just switch to FLC and up the speed so I can play along w/ default ATC.

And yes I notice the speedbrake isn't real effective in this plane so, once again because of MSFS' tardy descent calls often end up applying flaps and gear down to help control the plane's speed during approach.

Cheers

Edited September 6, 2022 by Noel