737NG LNAV & VNAV arm before engaging AP

[Guest davidbernard]

Hi There,Small question about takeoff procedures for the 737NG. I try to arm LNAV and VNAV before takeoff, so they will instantly activate when I engage AP after takeoff.I can now only select LNAV and VNAV after engaging the AP after takeoff. This means that other modes are activated first (HDG, SPD). Don't want that to happen..The FMC programming is complete and correct; A/T and FD are both armed; AP disengage switch is up. V2, cleared ALT and HDG are set on the MCP. Takeoff config is OK, no warnings or messages.With the 747 this works well. Am I doing something wrong or am I trying to do something that is impossible with the 737NG? Regards,David Bernard

[pschlute 37]

after takeoff (above 400 ft) i engage lnav and vnav while i am still in flight director mode. I can hand fly the departure as i wish, but if i want to i can engage a/p and it will be operating in lnav and vnav.Peter

[downscc 1,327]

I do the same as Peter. The LNAV/VNAV buttons don't light until after FD "comes alive." I find it's best to engage LNAV/VNAV during initial climb and use FD steering bar to align pitch with command bar; otherwise, the A/P will make an abrupt pitch change when engaged. It takes practice to get a smooth transition from inital climb (below 1000 agl) to cruise climb (below 10,000 msl) all before the first fix in a rnav departure (e.g., KLAS or KDFW).

[Mats_J 2]

David,>Am I doing something wrong or am I trying to do something that is >impossible with the 737NG?The latter!The A/P on the NG does not work exactly the same as the 744 A/P as you've noticed. You will not be able to arm any A/P modes on the ground.Hope it helps,

[basa 0]

Well, excuse me Mats, but I DO arm LNAV on the ground in my PMDG-737, I do it and it works fine (...is a procedure you can read in the PMDG-737 manual). It is VNAV that you can not arm on the ground.I don't know if that is the same in the real acft. Regards, Jose Luis.

[basa 0]

And, as I said before, here you have my 737 ready for departure with LNAV armed.Jose Luis.

[Mats_J 2]

Well,Seems my memory didn't serve me well in that instance. ;-) Thanks for putting me straight on that Jose Luis.And now I'll go to the corner...lol

[markadeane 272]

Shoo Mats! Shoo! :-DNice to see ya lurking here mate, how's Vdx coming along?If you have the FD's on and have carried out all the normal preflighting of the FMC then it should be possible to prearm those modes.If it doesn't work, check your FMA's, can you see TOGA modes in green?

[Pod562 0]

Jose Luis,Do you mind me asking where you got that little digital clock in your cockpit?ThanksRenzo

[downscc 1,327]

Easy on yourself, Mats, VNAV doesn't always arm on the ground and I haven't a clue why it will sometimes and not others. It's gotta have something to do with the programming that will be totally reworked for NGX (that's my guess).

[Mats_J 2]

Mark,Regarding vDX; Currently working on the route portion of the citypair setup. Import and XML serialization for FS default flight plan files and PMDG route formats. A lot to learn about the MSXML parser and XML. :+Check www.vdispatch.ca for latest news. I try to keep it current even if it can take a while between updates.I might have mistaken arming the A/P (which can be done in the 744 but not the NG) with arming A/P modes. TO/GA is indicated in the FMA.Cheers,

[KevMac 0]

This is the procedure for Delta Airlines 737-800:"At 400 ft the PF calls HDG SEL or LNAV depending on the departure. The SID or tower issued instructions will determine which one is apropriate. LNAV may be armed prior to departure if the first leg of the SID is within 5 degrees of the runway...in that case, you simply ensure that LNAV is selected at 400." Hope that helps.-Kevin

[Guest davidbernard]

>Easy on yourself, Mats, VNAV doesn't always arm on the ground>and I haven't a clue why it will sometimes and not others.>It's gotta have something to do with the programming that will>be totally reworked for NGX (that's my guess).So true; it just doesn't arm on the ground on my system.. No disaster, after takeoff it works just fine.Thnx for the help!David

[basa 0]

>Jose Luis,>>Do you mind me asking where you got that little digital clock>in your cockpit?>>Thanks>>RenzoIt is made from a clock gauge that I found in Avsim. I made some modifications and put it into my cockpit.Jose Luis.

[zubart 5]

Mats technically right. You can not engage the autopilot on the ground for takeoff. AFDS (autopilot flight director system)status is FD mode. LNAV is just a mode associated with the AFDS as a whole. I wouldn't call it an autopilot mode. It is also a FD mode.Also, LNAV is not ARMED in this case, it is already ENGAGED as seen by the green LNAV on the FMA because LNAV engagement criteria on the ground has been satisfied.Good luck,Floyd