Jump to content

Sign in to follow this  
Guest WomBat151

VNAV question

Recommended Posts

Guest WomBat151

Hi everyone,A couple of days ago i bought the PMDG 737NG, and at first i wanted to get familiar with automatic flight. I entered the flight route with a SID and a STAR for the arrival airport. After takeoff (after gear retraction) i engaged AP(A), LNAV and VNAV. Everything went ok, until the VNAV disengaged around 10000ft. When i tried to engage it again, i get the message "CHECK MCP ALTITUDE". What does this mean? The altitude for the next leg in the legs page was FL240. Yesterday i got more strange VNAV disengagements i don't know the cause of :S.I like your product very much btw!Cheers,Ian Udinga

Share this post


Link to post
Guest Daniel Pimentel

Sounds to me like you left your altitude on the autopilot at 10,000ft. You need to raise it in order for the plane to continue to climb. When it levels off, raise the altitude, and it should resume the normal climb. I usually select 5,000ft as initial altitude, and as I reach that I put the FL180, FL250 and cruising altitude as my stops. Step climbing is not needed with the NG, but I am used to it from flying the big ones. lolDaniel P.

Share this post


Link to post
Guest boxjockey99

VNAV is a complex mode and takes some figuring out if you haven't already gotten accustomed to the more advanced autopilot systems. The up and down of VNAV is that it flies the vertical profile (altitudes, climbs and descents) that the FMC has calculated to be the most economic according to the set cost index. As a safety feature to prevent VNAV going barrelling through any cleared altitudes Boeing added the feature whereby the VNAV will not climb above or descend below a set altitude in the MCP window.FOr example if you set 10,000 in the MCP but the FMC is set to climb to FL240 it will not be allowed to climb past 10,000 until you reset the MCP window (as said in the previous post). The same is true in the descent, if the MCP is set for 10,000 and the FMC is set to go to 5000 then it again will level off at 10,000 till you reset the MCP alt window. This is becase the system assumes any ATC restrictions will be dialed into the MCP ALT window so if 10,000 was set in the window in the climb that would be becuase that is your cleared alt, when you are cleared to climb further you would reset the alt window and engage VNAV and away it will go. When you do get into the situation look on the Flight mode annunciator you will see that you have gone from VNAV to ALT HOLD and the VNAV will have dropped out, you must therefore re-engage a climb descent mode to get out of ALT HOLD. Again this is a safety measure to ensure you haventt accidently reset the alt window, you must then push a button to confirm and doing both accidently is unlikely! Hope that helpsKris

Share this post


Link to post
Guest WomBat151

This is what i call great support!Thank you!Cheers,Ian Udinga

Share this post


Link to post

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  
×
×
  • Create New...