Criteria for arming VNAV after t/o

[WebMaximus 372]

Hi fellow PMDG captains,I know there have been numerous postings about this and I've spent some time searching the forum before posting this without really finding the exact answer I'm looking for...namely - what (if any) criterias are there for arming VNAV after t/o?Reason I ask is I'm using FS2Crew and when asking the FO to start retracting the flaps after t/o that should also make him arm VNAV but it hasn't on my last flights and I can't quite figure out what's wrong...or rather where I go wrong...;-)Any help would be much appreciated!All the best,

[Tabs 2,790]

The only restriction I'm aware of is that you must be at least 400AGL or higher to engage the AP and the FMC must beo properly preflighted to calculate the VNAV parameters etc.

[crvm 0]

Well for ENGAGEMENT, on the classic 737, you can do it prior to flap retraction but on the NG it is the perfered method to perform flap and acceleration first. I believe if you *ARM* it prior to flap retraction that the F/D will not command flap speeds but insted go to the REStriction, or VNAV target whichever is current (someone correct me if I am wrong-going off of memory here) so better to be at UP SPD or better yet, speed up to target then engage..[h4]Randy J. Smith[/h4]

[WebMaximus 372]

Thanks for your replies guys!Did another try now and made sure calling for LNAV at 400' and then VNAV passing 1000' and this time it worked flawlessy.Cheers,

[Guest ahmedem]

Out of interest would anyone know how it works on the 747-400, I know it is armed prior to take off, but will it fly certian speeds prior to flap retraction or will it go to the restriction/VNAV target as Randy correctly stated the NG does?

[WebMaximus 372]

Another question now related to my first question, is it imperative that you arm LNAV before you arm VNAV? Haven't tried it out myself yet, but a thought crossed my mind that maybe you must first arm LNAV before you will be able to arm VNAV - anyone knows?

[Guest BenBaron]

In my opinion it aint necessary to arm LNAV prior VNAV... .The only thing which has to be kept in mind is that the FD modes like LNAV, VNAV, HDG select etc. and the AP can not be activated below 400ft RA. But it is possible to select VNAV prior selecting any roll mode.

[WebMaximus 372]

OK, I'll experiment abit with this during my next flights and see what happens. Reason I asked is I'm using FS2Crew and had problem when the FO was supposed to arm VNAV but nothing happened and I thought it might have been because I didn't tell him to arm LNAV first. Might be a FS2Crew issue perhaps.

[crvm 0]

>In my opinion it aint necessary to arm LNAV prior VNAV...>.The only thing which has to be kept in mind is that the FD>modes like LNAV, VNAV, HDG select etc. and the AP can not be>activated below 400ft RA. But it is possible to select VNAV>prior selecting any roll mode. Many RL operators ARM lnav on the ground, something you cannot do with VNAV on the "NG", so it might not be always be "necessary" but is perfered in *certain* situations...[h4]Randy J. Smith[/h4]

[WebMaximus 372]

Gave it another go now and this time I had no problem with VNAV although I hadn't asked for LNAV first so I guess I went wrong somewhere before even thought I can't see what I made different from now.Thanks for the replies in this thread!