Reestablishing VNAV after runway change

[curt1 79]

VNAV is working fine for the most part, but how can you reestablish VNAV when changing the landing runway? At cruise altitude, once you line select a different runway and transition, VNAV disconnects. The waypoint speeds are deleted from the legs page and the TOD info is missing from the Descent page. From this point on I'm having to rely on Flight Change and/or vertical speed only, but there must be a way to get VNAV usable again. Any tips would be most welcome.

[Lusche 3]

This is strange ... I don't think this should happen ...I did change my arrival runway last flight and no disconnect of vnav ...how far were you from the runway ? maybe you were to close and the A/P couldn't calculate a descent route ? otherwise no idea

[curt1 79]

I was at cruise altitude and still over 100+ miles from the airport.

[Dean19 11]

VNAV is working fine for the most part, but how can you reestablish VNAV when changing the landing runway? At cruise altitude, once you line select a different runway and transition, VNAV disconnects. The waypoint speeds are deleted from the legs page and the TOD info is missing from the Descent page. From this point on I'm having to rely on Flight Change and/or vertical speed only, but there must be a way to get VNAV usable again. Any tips would be most welcome.

Did you check for any route discontinuities in the legs page after you made the change?

[curt1 79]

Did you check for any route discontinuities in the legs page after you made the change?

Yes, I closed the discontinuities. The key here I think is none of the speed data adapted to the new runway selection, speeds were all - - - -. Also, the TOD was no longer displayed on the Descent page. The NGX is so complex (in a good way), that I don't know if this is pilot error or a bug in the product.

[Warchild 0]

Thank you thank you.You just gave me a new idea to test the VNav problem some of us have been seeing..

[znypan 0]

Can you provide the route you were flying including the runway changes and the altitude? It would also be great if you remember any approx. payload/fuel values

[RYR738 9]

Did you Execute the change ?

[NGXfanatic 85]

I have seen this problem, most notably when resorting some saved flights, but also when I was on a flight from KSLC to KSEA, and tried to change the runway about 100 or so miles before TOD.It has to be a bug, no way the real deal will be this fussy. At least I can resort to FLCH or V/S to finish the descent, but I hope PMDG takes note of this glitch. Once it's lost, VNAV is unrecoverable, and that is really the most important autopilot mode for the NG. EDIT: I found something that could be used as a hint of what is wrong when this happens. Go to the PERF INIT page, under trip/crz alt it will have a very low figure (probably about 2197ft) in the trip altitude. At least that is what I see whenever I get the "VNAV DISCONNECT" FMC message.

[VARIG 0]

I experienced this issue while flying SBRJ-SBSP and the wind changed at SBSP. I had to assign a different RWY, covered all discontinues, executed the change, and my VNAV died. I was flying 800kg of cargo + 152 pax, fuel was about 40%.

[znypan 0]

I experienced this issue while flying SBRJ-SBSP and the wind changed at SBSP. I had to assign a different RWY, covered all discontinues, executed the change, and my VNAV died. I was flying 800kg of cargo + 152 pax, fuel was about 40%.

Route?

[VARIG 0]

Route?

SBRJ SID-RASA1 MOTOB UW64 STAR-LITRE1 (RWY 35), then changed to LITRE4 (RWY17). Edit: I forgot to say, it was 738 SFP

[Thunderbird8 1]

I often get runway changes due to flying with real world or server based weather. My first questions as I read down the thread was to ask if you had pressed EXEC, sounds obvious but easy to forget to do. Hmmmm...I'll try and recreate this tonight as this (potential) bug interests me. Did you enter the new runway length on the pedestal? Not sure if that would make any difference....don't think so but.....

[curt1 79]

My route was KCLE DJB HERAK APE KCVG (straight from flightaware). I attempted this flight again today, changed the runway and no problem with the VNAV. I did however load up a saved flight starting at cruise with the same waypoints, and that caused a VNAV disconnect with no way to resume VNAV. So in my case, I believe the issue is from the saved flight file.

[wildwally 0]

Is there a resolution for this, I change runway and the aircraft still fly's and seems to react; however, I can no longer manually fly the thing. Like the change screwed things up.