Climbing in VNAV with CHECK MCP ALT annunciation...?

[JSACKS 0]

I simulated a step climb to cruise just now but on several occasions during the ascent, I got CHECK MCP ALT annunciations in the FMC having levelled off at an altitude below the programmed FMC cruise alt. I fixed this by clicking the MCP ALT button and then could generally re-engage VNAV for a further step climb.I am not clear as to why this annunciation has occurred like this. Can anybody explain, please? Thanks!Jonathan

[Guest Hawkeyeted]

Did you try to climb with a LVL CHG, or by resetting the cruise alt in the FMC first, then pressing VNAV? try setting the FMC first, then the MCP alt to your new desired altitude, then set the V/S to 500 and let her lumber the way up (MCP will come out of VNAV and go to SPD. Once at the new cruise alt, reengage the VNAV.

[JSACKS 0]

The intermediate (climb) cruise ALT was already set in the MCP ALT window earlier and I clicked ALT INTV to re-engage VNAV SPD for the climb. That's why this is puzzling to me. Why would it say CHECK MCP ALT after levelling off sometimes? It's just another VNAV-related mystery to me!VNAV is a major angst provoker both going up and particularly coming down. The plain vanilla up-cruise-down VNAV works fine; it's the "fine tuning" of VNAV that baffles me with these annunciations. (At least I can handle CWS P and R OK now!)Jonathan

[Mats_J 2]

Jonathan,Tell us what version you are using.I am assuming you are not talking about a STEP CLIMB at CRUIZE? You want to CLB to your CRZ altitude using VNAV but intervene it with intemediate MCP ALTs?First I think this would generally call for a LVL CHG climb. But if you chose to use VNAV you should be able to intercept it with the MCP ALT window. You should get the CHECK MCP ALT though if you are hitting the ALT INTV before changing the MCP ALT window to a higher altitude.The fine-tuning of VNAV is mainly done in the FMC and that's where the VNAV really is flown. Hope it helps,

[zubart 5]

Jonathan,Did FMC message maybe say RESET MCP ALT or CHECK ALT TGT instead of CHECK MCP ALT? I've never seen CHECK MCP ALT in the real airplane.With U10.5, RESET MCP ALT message would be caused by not flying away from the MCP altitude. Corrective action would be to select a MCP altitude value in the proper direction (higher for a climb, lower for descent).CHECK ALT TGT message is caused when VNAV disengages while the airplane is between MCP and FMC altitudes or VNAV button is pressed while the airplane is between the MCP and FMC altitudes. The corrective action is to clear the message. I believe this is with the No VNAV ALT option selected.Good Luck.Floyd

[Jim Harnes 13]

Jonathan,You are not alone. During a flight from KIAD to KORD at FL240 to avoid high winds aloft, got the CHECK MCP ALT annunciation when I tried to engage VNAV at 15,000 ft. Noticed the FMC-calculated TOD was way past where it should have been - inside the FAF!Never was able to engage VNAV druing that flight. Jim Harnes

[Guest Moviedirector20]

huh, I actually never had a problem with this. IE I just did a flight yesterday ORD-MSP, was cleared to 5000 initial, did that with LVLCHG because I needed to get up there fast. But then I was cleared to 13,000 stuck 13K in the MCP and hit VNAV, it brought me up to 12,000 where ALT AQuisition took over and held me at 13, then was given FL220 my cruise, punched that into the MCP and hit VNAV, brought me all the way up.

[JSACKS 0]

Floyd, it definitely did not say RESET MCP ALT, it was CHECK MCP ALT each time. Has happened 5-6 times so far.I shall experiment further and make notes next time and post results.Mats, this is for climb to cruise not cruise-climb mode. I am using a saved flightplan that I modify with waypoints from climbout to about 15,000 feet and then have a straight climb to cruise at about FL290 or 330.In this plan, I am stepping up in stages from say 5,000 to 30,000 feet and leveling off every 2000 or 3000 feet for practice with VNAV, VNAV ALT (which is an option set in my PMDG options window), VNAV SPD, etc. Thanks for your responses. Will be back in a bit with more specific observations and the results.Jonathan

[JSACKS 0]

Mats:I change the ALT in the ALT window first and then hit ALT INTV to resume VNAV climb; or a I then hit the VNAV button twice to disconnect briefly and then reconnect it, but generally I use the ALT INTV button because it's easier and more logical to me.I am determined to "break" VNAV and get mastery over it one way or another in this fine machine !Jonathan

[JSACKS 0]

Jim:Thanks for this "encouraging" post! It's easy to "lose" VNAV and not be able to connect or reconnect; but it can be done, you just need to know how to do it from other non-VNAV modes.See my other replies in this thread.Jonathan