Speed Control upon glideslope capture

[kmw510 0]

I am getting inconsistent results with auto throttle speed control upon glideslope capture. When in VNAV and selecting APP I obtain VORLOC and then G/S and the speed is controlled properly with auto throttle. When using the MCP to hold altitude and control speed until I get to the IAF I get inconsistent control of speed upon glideslope capture. There are times the speed is controlled in the same way as when I enter via VNAV and other times the speed control window flashes and the speed is not controlled. I am not totally sure what the proper operation is so don't know if this is a bug or my lack of understanding

 

 

Kevin Wilson

[rfresh737 36]

Hi Kevin,

 

You may want to watch my free 737NGX ILS tutorial videos at my YouTube Channel. The link is in my signature.

[kevinh 409]

Ralph's videos are excellent to learn about the whole procedure. Well worth studying in detail. But if you want a quick answer to this specific question:

 

If you aren't in VNAV you shouldn't expect MCP speed to be controlled automatically. If a number is shown in the MCP window you are in control of the speed. You need to manually reduce the speed to the flap manoeuvre speed shown on the speed tape (as a green numeral for the current flap setting). Then after glideslope capture you select Vref plus corrections.

[kmw510 0]

Hi Kevin,

 

You may want to watch my free 737NGX ILS tutorial videos at my YouTube Channel. The link is in my signature.

Thanks Ralph, I will take a look

 

 

Kevin Wilson

 

 

If a number is shown in the MCP window you are in control of the speed

 

Thanks Kevin, do you know why the speed is still indicated in the speed window after disengaging both autopilot and auto throttle?

[scandinavian13 5,192]

 

 

Thanks Kevin, do you know why the speed is still indicated in the speed window after disengaging both autopilot and auto throttle?

 

Reference. Just like the heading and altitude windows. That, or it's pre-selected for use if you needed to throw the AP/AT on quickly.

[kmw510 0]

Reference. Just like the heading and altitude windows. That, or it's pre-selected for use if you needed to throw the AP/AT on quickly.

Thanks Kyle

 

Kevin Wilson

[scandinavian13 5,192]

Thanks Kyle

 

Kevin Wilson

 

Welcome. Kevin might have something more profound, but I figured I'd chime in since I saw it.

[NM5K 1]

In addition to Ralph's tutorial, here is another one I ran across a while back that shows almost

everything you are asking about, and also the procedure that Kevin is referring to.

This one is from the real world, and they yellow outline each step as they go through the descent

down to an autoland. Note how they use the flaps guide on the speed tape. Pretty good video..

 

https://www.youtube.com/watch?v=Bm02l989PUw

 

[kevinh 409]

Welcome. Kevin might have something more profound, but I figured I'd chime in since I saw it.

The only thing I could add to what you said is that even with AP and A/T disengaged, if the FD is on you will still get command bar guidance controlled by the MCP selections. So the windows need to remain active.