747-400X Autopilot, VNAV and LNAV problems

[Guest Jpadua]

For some reason, the LNAV function on the autopilot won't come on or activate at all, even if I have a route set up in the FMC and is shown on the NAV display. To make matters worse, the VNAV function has problems as well. Not only won't it also function, but I always get an FMC message saying "Unable crz alt". Even though the aircraft is not that heavy and my selected crusing altitude is reachable, it still gives me that message. Please, can anyone figure it out why?

[jobepilot 7]

For some reason, the LNAV function on the autopilot won't come on or activate at all, even if I have a route set up in the FMC and is shown on the NAV display. To make matters worse, the VNAV function has problems as well. Not only won't it also function, but I always get an FMC message saying "Unable crz alt". Even though the aircraft is not that heavy and my selected crusing altitude is reachable, it still gives me that message. Please, can anyone figure it out why?

How long have you been flying this plane ???? Can you post some screen shots, I dont think you programed the FMC correctly, Lnav/Vnav will not work if the parameters are incorrect or you dont have the aircraft in correct config.

[Guest Jpadua]

For some reason, the LNAV function on the autopilot won't come on or activate at all, even if I have a route set up in the FMC and is shown on the NAV display. To make matters worse, the VNAV function has problems as well. Not only won't it also function, but I always get an FMC message saying "Unable crz alt". Even though the aircraft is not that heavy and my selected crusing altitude is reachable, it still gives me that message. Please, can anyone figure it out why?

I've only had it for about a couple of days. And when you mean some of the parameters of FMC must be correct, which parts? P.s. Here's something I just realized. I only program one of the FMCs; I only work the captains side but leave the copilot's untouched. Does that have something to do with it?

[jobepilot 7]

I've only had it for about a couple of days. And when you mean some of the parameters of FMC must be correct, which parts? P.s. Here's something I just realized. I only program one of the FMCs; I only work the captains side but leave the co-pilot's untouched. Does that have something to do with it?

Ok you have to read the manual in ref to the FMC its would be too hard to explain here, just go to start PMDG then the FMC user's guide and follow it, then you will understand. And yes only set the captains FMC, but you must know the parameters before going any further, you will need fuel weights etc and distance in order to program it fully, the manual is a must, I think also there is a tutorial on youtube,

but even so you will need to read. The sim has been made/designed to work like the real thing, and you really just cant take off without some knowledge. I have had the plane well over a year, and even now still read things I never knew. The devil is in the detail

[slip-stream 5]

I assume you have the Flight Director on and A/T armed? If the FMC states that crz alt not attainable it may mean that you are flying a short route and the aircraft does not have time to climb to your selected alt before having to descend again.

[Sun_King_135 0]

I, too, have the problem that VNAV will only flicker one or two seconds and extinguish again, while activating VNAV.I tried this on a Riyadh to Dubai flight. Cruising Alt was FL310. I think this should be ok for this flight, or not?The Manual didn

[downscc 1,327]

If VNAV will not activate, it is usually because it doesn't have a vertical navigation solution. This could be caused by a discontinuity in the flight plan. Be sure to check your flight plan using the ND in the plan view to verify all the legs look right. If altitude is a problem, it has an error message to tell you that.There are tutorials available in the pmdg ops wiki-based knowledge base here: http://ops.precisionmanuals.com/wiki/Main_Page