When i'm climbing to my cruise alt FMC FL390 and ATC only clear me to lets say 250 when i level off and VNAV ALT shows, then once ATC resumes my ascend to FL340, i punch in FL340, i then hit ALT INVT and i get a VNAV disconnect?

 

Can anyone see if this happens to them aswell? I know there is a similar bug when descending as rfresh has already mentioned this.

 

 

Can anyone see if this happens to them aswell? I know there is a similar bug when descending as rfresh has already mentioned this.

 

Definitely not the same bug Ralph mentioned, or it would have popped up a lot more before now. This function is used extensively in the tutorial flight, so that would've set off a lot of posts to bring it up.

 

You're rolling the MCP ALT up and then hitting ALT INTV once and it's just disconnecting? What do you have set as the cruise altitude?

I've let paul know over at PMDG.

 

Exactly, thats why i'm scratching my head.

 

I did have a step climb with PFPX. First alt was FL250 so i set that in the FMC as my initial alt. Along the route i was coming up for my final climb FL390, Requested RC for a climb to FL390, they only cleared me to FL340. So i set FL390 in the FMC, also set the pressurization controller to FL390. Rolled MCP ALT to FL340 and hit ALT INV.

 

 

I did have a step climb with PFPX. First alt was FL250 so i set that in the FMC as my initial alt. Along the route i was coming up for my final climb FL390, Requested RC for a climb to FL390, they only cleared me to FL340. So i set FL390 in the FMC, also set the pressurization controller to FL390. Rolled MCP ALT to FL340 and hit ALT INV.

 

For what it's worth, you're not using the proper procedure.

 

You should be setting your expected initial cruise alt in the FMC and the pressurization controller. In your case, this would be FL390. The intermediate alts are handled by setting the MCP altitude at that level. In your case, this would've been FL250, and then FL340 with the FMC/Press seeing FL390 the entire time.

This is what you told me a while back kyle thats what i have been doing. I'm doing a quick climb again to see what happens

Ok got a vnav disconnect it says in the FMC CHECK ALT TGT

 

If i select an alt in the MCP ALT below 390 i get the disconnect

If i set the alt to 390 and hit alt inv its fine it will climb

 

 

This is what you told me a while back kyle thats what i have been doing.

 

The above doesn't match up with the below:

 

 

 

First alt was FL250 so i set that in the FMC as my initial alt.

 

I'm trying to think of other reasons why you got a "check target alt," but there's no reason FL250 should've been in the FMC.

I can hit alt inv while climbing to FL250 my FMC cruise alt. But when its time for my step climb to FL390 i enter that into the FMC set the press controller to 390 and RC only clears me to FL340, so i enter 340 in the alt window hit ALT INV and VNAV DISCONNECT.

 

But i don't get VNAV DISCONNECT if i enter FL390 just anything below it.

 

I think there could be a problem with step climbs. You could possibly check this kyle if you have time...

I think there could be a problem with step climbs

There is no problem with step climbs. Enter your final altitude on the INIT page as your cruise altitude. Control intermediate altitudes levels by using your altitude window and ALT INTV. Don't make any entries in the FMC for altitude changes. Put 390 in the FMC and leave it alone.

 

I assume that you have verified that the plane can fly at the various altitudes by entering them on the ACT ECON CRZ page and seeing that they don't exceed the maximum altitudes.

Yeh doing it the way you mentioned is fine, it works. But setting a cruise alt lower first in the FMC and then increasing it to my final alt i get a VNAV DISCONNECT if i do a climb lower than my final alt.

On the ground when you are entering data into the FMC, what would you enter for CRZ ALT on the PERF INIT page and what is the altitude shown to the left of the five boxes?

If i don't have a step climb i input my cruising alt.

 

If i have a step climb of FL250 and final cruise alt FL390 i will enter FL250 and set the press controller to FL250

If i don't have a step climb i input my cruising alt.

 

If i have a step climb of FL250 and final cruise alt FL390 i will enter FL250 and set the press controller to FL250

I would not consider a climb from FL250 to FL390 to be a step climb. I would say ATC has restricted you to FL250 until they tell you to climb to FL390. I associate step climbs with a with optimum altitudes and climb of 2000 or 4000 feet to save fuel and these climbs would start a lot closer to your final altitude. Say FL370 to FL390 or FL390 to FL 410. I would imagine that flying in the EU they are very few occasions when there would be a step climb. I am doing a 2500 mile flight right now and there is only one step climb from FL360 to FL380.

 

In your situation I would enter 390 in the FMC as your cruise altitude. I would let the plane level off at FL250 by having that dialed in the altitude window. At that point the MCP will switch from VNAV to ALT HOLD. When you receive clearance to FL390, dial that into the altitude window and press ALT INTV. Once you have reached FL390 if VNAV does not engage press the button and see what happens.

I just flew an old Continental legacy route from KSAN to PHOG (the 737-700 COA livery has ETOPS, much to my delight). I had one step climb in the 5 hour flight.  I'm glad I read this thread because I am fresh from lots of B777 flying and was trying to use those techniques, which turned out to be wrong of course.  However, even when I set the FMS up to initial cruise and then used MCP controls to perform the step (I always prefer a gentle 800 fpm climb in VS mode) I never had a problem. Next trip is going to be a UAL 738 that is flying the KSFO PHNL route, so next chore is looking for a UAL livery in ETOPS mode or setting it up myself. Too much fun.

If i don't have a step climb i input my cruising alt.

 

If i have a step climb of FL250 and final cruise alt FL390 i will enter FL250 and set the press controller to FL250

 

That's not a step climb. FL250 is an intermediate restriction. FL390 is your cruise alt. Step climbs are climbs to remain at optimal cruise altitude as fuel burns off. Just like I mentioned earlier: FL390 in the FMC. All else in the MCP.

Thanks so much for the help. Yeh FL250 sounds more like a REST. But still can't figure out why i get a VNAV DISCONNECT?

 

What about a STEP CLIMB in my FP ? Will i enter the first cruise alt in the FMC first?