VNAV at RJAA pt.2

[Guest LAX5x5]

So, after experimenting w/ the problem I had w/ VNAV not enaging departing from RJAA I finally got it to engage properly, at will. My ZFW: 384,257, fuel: 174,691 = GW: 558,948. OPT alt on CDU shows FL342, before TO so I was setting initial crz alt at FL350 and VNAV never engaged. I had to use FLCH and Speed or else I would stall or descend because of no VNAV. I tried FL340 once with the same result. While climbing under FLCH on one of my tests, I started to play around w/ the initial crz alt on the CDU. Only when I entered FL360 did VNAV engage(I know this because instead of being blank, Autothrottle Mode in Flight Mode Annunciation on the PFD went to THR REF). I reverted initial crz alt back to FL350 and VNAV would disengage(blank Autothrottle Mode in PFD), back to FL360 it would engage, and so-on and so-on, back and forth as I kept changing crz alt.I restarted the flight from RJAA again, this time w/ initial crz alt at FL360 to make sure that this wasn't a random occurance, that indeed the problems w/ the PSS FMS VNAV w/ regards to departure from RJAA was somehow linked to the initial crz alt setting. I also wanted to rule out other pausible causes for this particular problem such as spd/alt restrictions or something to do w/ the first several wypt's/hdg. After passing FL015, VNAV went active, THR REF indicator on Autothrottle Mode in PFD appeared and vertical cue from flight director started moving to indicate proper angle. Eliminating waypoints or setting or not setting spd/alt restrictions didn't effect it, either.So, PSS team, I hope this helps in tracking down and fixing the bizarre events that occur w/ the T7 VNAV that users such as myself have posted on this forum and hopefully you'll come up w/ a solution soon. Obviously, the solution to my problem is just another "workaround" solution. I should be able to enter any altitude(within reason of course) for initial cruise coming out of Narita and not have problems w/ the VNAV. Good luck, PSS Team.EDIT: Using 777-200LR, departing from RW34L CHOSH1.GUPPY-Ely

[truthknown 4]

It is somewhat comforting that I am not the only one experiencing this problem out of Narita. I will try what you did in this post tonight or tommorow and see if I have the same results.As for re-engaging the VNAV after switching to FLCH, i noticed that it would re-engage if i switched the altitude to the next useable flight level in either direction (not saying that it has to be 2000 ft exactly, but it is what I used). So starting off with an initial cruise alt of FL330, I would switch to either FL310 or FL350 to get VNAV to re-engage. If i did that and then tried to switch back, it would disengage again. So it looks like there is a problem with VNAV and the cruise alt set in the FMC at takeoff. Once in the air, if you take off VNAV or it comes off on its own, good luck on getting it back on without changing the cruise alt. Not that big a problem on long flights where you are going to step climb anyway which would solve the problem.Chris

[Guest Segwin]

>It is somewhat comforting that I am not the only one>experiencing this problem out of Narita. I will try what you>did in this post tonight or tommorow and see if I have the>same results.>>As for re-engaging the VNAV after switching to FLCH, i noticed>that it would re-engage if i switched the altitude to the next>useable flight level in either direction (not saying that it>has to be 2000 ft exactly, but it is what I used). So starting>off with an initial cruise alt of FL330, I would switch to>either FL310 or FL350 to get VNAV to re-engage. If i did that>and then tried to switch back, it would disengage again. So it>looks like there is a problem with VNAV and the cruise alt set>in the FMC at takeoff. Once in the air, if you take off VNAV>or it comes off on its own, good luck on getting it back on>without changing the cruise alt. Not that big a problem on>long flights where you are going to step climb anyway which>would solve the problem.>>ChrisHello Chris:Where did you change to crz alt? MCP, LEGS or VNAV?TIA

[Guest LAX5x5]

Hey(Hi) Chris."As for re-engaging the VNAV after switching to FLCH, i noticed that it would re-engage if i switched the altitude to the next useable flight level in either direction..."I've noticed the same thing. It seems that for some reason, eventhough the altitude a user chooses are within OPT and MAX altitudes shown on the CDU, sometimes the FMC just won't let it happen and will disconnect the VNAV. In the case of Narita, it just didn't want to go below FL360. OPT to MAX altitude in my situation was FL342-FL378(maybe FL379). FL360 and FL370 were fine, but when trying for FL340 or FL350, VNAV would not activate.Take it easy, Chris.-Ely

[truthknown 4]

I changed the altitude on the MCP, hit the altitude intervention button and checked that the VNAV cruise page was updated with the new cruise alt. This was done while still climbing to cruise in FLCH mode with VNAV "ARMED" (its armed because it would not engage without intervention). VNAV would then activate and VNAV SPD mode would display.