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737 Alt Intv & Spd Intv ?

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I can find no PMDG documentation on these buttons and what they actually do? Even the manuals that came with my 8-900 do not show these buttons on the MCP pictures, or talk about them.Am I not looking in the right place...or did I miss something. My forum search resulted in many talking about them not working as they thought they should, or only working in certain models. Not much good for me as I have no idea what they are :( . Where can I find info on how they (the PMDG ones, not RW) work? Thanks. Vic


Victor Buck

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SPD INTV: Speed Intervention. While in VNAV mode, allows you to give priority to speed instead of climb profile while not cancelling VNAV. For example, After normal takeoff and acceleration past flaps the aircraft will then accerate to 250KIAS but say ATC request you hold 230KIAS for traffic. Push the button, set to 230, and pitch will control speed to maintain 230KIAS. Then ATC says resume normal speed because you are now 2000 feet higher than traffic all you do is press the button again and speed goes back to whatever VNAV desires such as 250 if still below 10000.ALT INTV: Someone else needs to help... I've never used it because I don't use VNAV except to climb. Sorry.


Dan Downs KCRP

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ALT INTV: Someone else needs to help... I've never used it because I don't use VNAV except to climb. Sorry.
ALT INTV is exactly what SPD INTV is, you can enter this mode to climb or descend to a different ALT without altering the VNAV tracking in the FMC. Maybe you want to go higher or lower because of turbulence, Wx, or traffic.

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SPD intv: While in VNAV the autopilot commands the airspeed and the speedwindow is closed. You cannot set an airspeed manually. Say you want to fly a higher or lower airspeed you can either go to the FMC VNAV page and enter the required speed there (as has to be done on a lot of older 737's). Or you can push SPD INTV. This wil open the speedwindow, allowing you to manually enter an airspeed you want the airplane to fly. When you want VNAV to take over speedcontrol again you just push spd intv again. The speedwindow will close and VNAV takes over again.Alt intv: On the 737 you use the ALT INTV button to cancel VNAV altitude restrictions. Say you got a SID out of amsterdam which requires you to climb to FL060. VNAV will have an altitude restriction installed that requires you to pass the endpoint of the SID at this flight level. If ATC tells you you can climb to a higher FL, say FL200 and you want to keep using VNAV, you turn FL200 in the MCP and you push altitude intervention. This will cancel the FMC altitude restrictions between FL060 and FL200, allowing VNAV to climb. On the LEGS page you can find the altitude restrictions for each waypoint, you can cancel them here too. The ALT INTV logic works the same way for a descent. On the VNAV page there is also a CLB DIR button I believe (or is this only 747). Same function as alt intv. By the way, when you are in a climb and you set your MCP altitude higher than your VNAV cruise altitude, and push alt intv, this will change the VNAV cruise altitude to the altitude that is set in the MCP.Tom


Nicolas Maes

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SPD intv: While in VNAV the autopilot commands the airspeed and the speedwindow is closed. You cannot set an airspeed manually. Say you want to fly a higher or lower airspeed you can either go to the FMC VNAV page and enter the required speed there (as has to be done on a lot of older 737's). Or you can push SPD INTV. This wil open the speedwindow, allowing you to manually enter an airspeed you want the airplane to fly. When you want VNAV to take over speedcontrol again you just push spd intv again. The speedwindow will close and VNAV takes over again.Alt intv: On the 737 you use the ALT INTV button to cancel VNAV altitude restrictions. Say you got a SID out of amsterdam which requires you to climb to FL060. VNAV will have an altitude restriction installed that requires you to pass the endpoint of the SID at this flight level. If ATC tells you you can climb to a higher FL, say FL200 and you want to keep using VNAV, you turn FL200 in the MCP and you push altitude intervention. This will cancel the FMC altitude restrictions between FL060 and FL200, allowing VNAV to climb. On the LEGS page you can find the altitude restrictions for each waypoint, you can cancel them here too. The ALT INTV logic works the same way for a descent. On the VNAV page there is also a CLB DIR button I believe (or is this only 747). Same function as alt intv. By the way, when you are in a climb and you set your MCP altitude higher than your VNAV cruise altitude, and push alt intv, this will change the VNAV cruise altitude to the altitude that is set in the MCP.Tom

 

If in VNAV mode. when the ALT INTV is pressed and an altitude is selected how do you go back to VNAV PATH? I have to deselect VNAV and reengage and make sure the MCP ALT is higher. 

 

Thanks,

 

Abe


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Where can I find info on how they (the PMDG ones, not RW) work?

 

The PMDG ones behave exactly as the RW one work...

 

Additionally, while I appreciate your attempts to look for the info in the manuals, the buttons are very clearly explained in the tutorials.  I recommend that you fly them.


Kyle Rodgers

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PMDG 737 NG had a setup option to exclude ALT INTV? You fly the MCP differently when so equipped. Many airlines choose not to equip with ALT INTV. It may have been discussed before, but why is this setup option missing from NGX?

Sorry forgot to sign.

 

Ken Hair

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PMDG 737 NG had a setup option to exclude ALT INTV? You fly the MCP differently when so equipped. Many airlines choose not to equip with ALT INTV. It may have been discussed before, but why is this setup option missing from NGX?

 

Not entirely sure about this one. I thought that those operators who did not use ALT INTV just placarded it inop and covered it. I could be wrong, though.


Kyle Rodgers

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The MCP logic for VNV is different if you don't have ALT INTV. During climb or descents, VNAV disarms at each intermediate level off and has to be re armed each time. With ALT INTV you don't have to do that. Also, all waypoint restrictions have to be manually removed in the FMC.

Ken Hair

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