Arming VNAV mode

[Dazza74 1]

As a recent newbie to this aircraft I have been following the 'Tutorial #1' but cannot seem to arm VNAV mode prior to takeoff as instructed. I press the VNAV button on the MCP, but it does not illuminate green like the LNAV button does after pressing. Has anybody else experienced this? Can someone please help. Regards Darren.

[aentwis 61]

VNAV can only be armed when the necessary criteria are fulfilled. Make sure the FMS is fully configured, the flight plan is activated and so on. Do you have the v speeds displayed on the speedtape on the PFD? Make sure the takeoff page is fully configured including the T/O centre of gravity and so on. Andrew

[Guest]

Same here, anyway I can arm the VNAV few seconds after takeoff so that's not a problem. Sometimes a pilot have to pilot a plane by himself :(

[badderjet 181]

Same here, anyway I can arm the VNAV few seconds after takeoff so that's not a problem.

At 400R. To the OP: Common mistake is to fail executing the PERF INIT page. Fill out all the required fields, then the EXEC light should illuminate. And you need to sign your full name here.

[Guest]

At 400R.

Is that considered normal ? I think to remember I am used to fill the whole Perf Init FMC page but I may recall wrong. Thx

[Dazza74 1]

Thanks guys for the prompt responses, I definately found out the hard way that you must fill out all the required fields in the PERF INIT page, then press the EXEC light once illuminated. 'It Worked'. I guess it was a case of a trap for new players, and getting used to it, but I am enjoying learning the 737. Thanks again.

[badderjet 181]

Is that considered normal ? I think to remember I am used to fill the whole Perf Init FMC page but I may recall wrong.

What do you mean? Yeah it's perfectly normal. It's just system design. LNAV becomes active at 50R, VNAV at 400R, where you can also engage the AP if you need to.

[Guest]

What do you mean? Yeah it's perfectly normal. It's just system design. LNAV becomes active at 50R, VNAV at 400R, where you can also engage the AP if you need to.

First, thanks for the answer. I told that because I think to rememeber that a real 737 pilot here stated that you can arm the VNAV before taking off. Again my memory may fails so I am not sure but I think so.

[ESzczesniak 128]

You can arm VNAV on the ground if all criteria are met. It won't become the active FD mode until 800' RA (or was it 1,000' RA?) though. TO/GA will be the vertical mode before that.Eric Szczesniak

[Spin737 102]

At 400R. To the OP: Common mistake is to fail executing the PERF INIT page. Fill out all the required fields, then the EXEC light should illuminate. And you need to sign your full name here.

Is that considered normal ? I think to remember I am used to fill the whole Perf Init FMC page but I may recall wrong. Thx

What do you mean? Yeah it's perfectly normal. It's just system design. LNAV becomes active at 50R, VNAV at 400R, where you can also engage the AP if you need to.

First, thanks for the answer. I told that because I think to rememeber that a real 737 pilot here stated that you can arm the VNAV before taking off. Again my memory may fails so I am not sure but I think so.

You can arm VNAV on the ground if all criteria are met. It won't become the active FD mode until 800' RA (or was it 1,000' RA?) though. TO/GA will be the vertical mode before that. Eric Szczesniak

I wouldn't say it's normal to select VNAV at 400RA. Normal would be on for takeoff or after flaps are up. If you screwed something up [eg. forgot to turn on the FDs ((what kind of idiot would do that? cough cough))] VNAV wouldn't arm. If you intend to takeoff in VNAV, find the problem and fix it. Oh, and VNAV engages at 400agl if it's armed for T/O (FCTM).

[Guest]

Assuming the perf init page is properly filled ( and the FDs are both on ) , what in your opinion could be the cause of the VNAV not arming until few seconds or 400R after takeoff ?

[Spin737 102]

Assuming the perf init page is properly filled ( and the FDs are both on ) , what in your opinion could be the cause of the VNAV not arming until few seconds or 400R after takeoff ?

Do you mean that you can't select it on the ground but you can a few seconds after airborne? Beyond not setting up the FMC and the MCP correctly, I don't know. I don't think there are tricky arming issues like LNAV.

[martin-w 3,239]

VNAV won't arm on the ground if the first waypoint is at an acute angle. Has to be within a certain number of degrees. Don't remember exactly how many.

[Guest]

Do you mean that you can't select it on the ground but you can a few seconds after airborne?

Exactly what you said. I also catch the Autoland 3 once every 6-8 landings and each time I do the same things. Anyway no problem, I like to land her by myself when I am around 500 feet. I came to the conclusion that I have a ghost floating around the cockpit, well, I am not alone therefore over the skies

[Spin737 102]

VNAV won't arm on the ground if the first waypoint is at an acute angle. Has to be within a certain number of degrees. Don't remember exactly how many.

You're probably thinking of LNAV.

track of first leg within 5 degrees of runway heading

FCOM:

VNAV Armed for TakeoffVNAV may be armed on the MCP prior to takeoff provided the followingrequirements have been met:• a valid flight plan has been entered• performance data has been entered and executed• both flight director switches have been switched on• NG aircraft equipped with Collins P4 FCC or later; or Honeywell -710FCC or later; and CDS BP06 software.Note: If an older version of FCC or CDS software is installed, VNAV will notengage nor arm on the ground.