VNAV Confusion

[clayton4115 56]

i was given departure vectors out of Kennedy tonight and i pressed VNAV then FLCH then VNAV and also pressed the Select button so the plane could track a 100 course after departing 04L,however when i was cleared on the SID and i finished with all the flaps up, i pressed VNAV, but look what happened!here folks, we have VNAV, LNAV and FLCH all lit up!!!!then the plane, instead of tracking the next waypoint on the route, started drifting! this is crazy!http://forums.avsim.net/user_files/147660.jpg

[Byrna 0]

Clayton, I noticed your AUTOPILOT LIGHT IS OFF (A/P).Anyone correct me if I'm wrong but A/P has to be on for VNAV and LNAV to function. ONLY the AUTOTHROTTLE functions without requiring A/P to be engaged. So naturally, your plane WILL DRIFT as it is not set to autopilot!John

[clayton4115 56]

hi Johnhaha good observation, but i didnt know what to do so this shot was taken AFTER the A/P was off, i was seeing what would fix this, but even with AP off or on it wasnt working.

[Guest mao1968]

The autopilot can be off and you will have VNAV and LNAV commands directed to the flight director in order to manually follow them . As clear as I see this is a huge bug because Flight level change and VNAV can not be lit at the same time . After the patch I am not happy with this plane so in my hangar unfortunately she will be grounded forever. Beware I am not an expert on 777 but as a real Boeing 767 captain I can tell you the MCP is not right on this case.Mauricio Villada

[Byrna 0]

Mauricio,What do you mean when you say that "VNAV and LNAV commands directed to the flight director in order to MANUALLY follow them"? What happens here when you say MANUALLY? Is the plane able to follow your VNAV and LVAN WITHOUT a/p on?...or do you mean using MCP input to MANUALLY follow the plan by your (pilot's) control of the MCP?John

[FOD 23]

JohnWith AP off and fd selected, you fly the flight director on the PFD - its bars are locked to required LNAV and VNAV flight paths.BTW - its a very effective tool.John R

[Guest mao1968]

Hi JohnWHat I mean is that you are able to manually fly the aircraft using the control wheel (in flight simulator the joystick or yoke) just following flight director commands that are provided by the FMC using LNAV and VNAV or by the MCP if you are using different combinations of pitch and roll modes (for instance flight level change and heading select) When you fly manually, help from the other pilot is required because all the commands given to the mcp or fmc must be done by the monitoring or non flying pilot.best regardsMauricio

[Guest NormanB]

Looks like others have already answered your thoughts Clayton.>this is crazy!Following the steps outlined in the tutorial should restore your sanity ;)

[FOD 23]

YesI have tried to replicate every switch selection he made several times but could not get both VNAV & FLCH lights to stay on!John R

[clayton4115 56]

hi John,thats a pity, but the proof is in the photo, try this, upon dep press HED SELECT then FLCH then AP then after she is clean LNAV VNAV and see if the FL CHG is still lit.

[psolk 3,040]

You can get this error if the VNAV CRZ ALT is set too high for the CDU's liking. Try flying the same situation and reducing your CRZ ALT. Worth a try right...-PaulLiquid CooledAMD 4000 San Diego2 Gigs Kingston Corsair XMS CL2Dual 7800 GTX 24 inch widescreen dual 19 inch LCDRaid-0

[clayton4115 56]

well im just doing a short flight PHX to ABQ and took off with VNAV armed and HED SEL "HOLD" lit and she was went fine, i also am doing a derated take off as im very light and im climbing at the moment and all looks good.

[Guest Remotec]

>Beware I am not an expert on 777 but as a real Boeing 767>captain I can tell you the MCP is not right on this case.>>Mauricio Villada>On another VNAV subject, Mauricio maybe you can help me.Im positive that with VNAV selected when you get to Top of Descent providing you have set the MCP ALT to lower than you current Alt the aircraft SHOULD descend. You should not have to tell the aircraft to descend. Im sure this is the case for all Boeings with that function - what do you think?Tim

[Guest Remotec]

ClaytonI believe you - I have had this happen!! More than once. Next time Ill get a screen shot. I think for me it happened at top of descent when I was on VNAV but I had to press FLCH to make the thing descend.

[miguelpp 25]

Sorry.Deleted.Miquel Egea.