Arming LNAV/VNAV

[Vagabondo 23]

Hi Ithink you've probably got the answer by now, but if not I don't arm the L/Vnav until above 450ft. you have to arm the autopilot first ,then L/Vnav.

There is no order of sequence with the use of autopilot and lnav/vnav. The selection of pitch and roll modes with the FDs on drives the FD pointers on the PFD. The autopilot will automatically follow the FD pointers or display CWS P/CWS R if no pitch or roll mode is selected.

 

Also, be careful with the use of the term "arm", the A/P is never armed, it is either on or off. lnav/vnav can (should!) only be armed on the ground. In flight they are selected either on or off. Minimum height for manual selection is 400' RA (AGL) for hdg sel or lnav. Some aircraft have the option for automatic selection of heading select when nothing is armed on the ground after takeoff.

[avhpilot 156]

you have to arm the autopilot first ,then L/Vnav.

 

 

There is no order of sequence with the use of autopilot and lnav/vnav.

 

I would say that it makes more sense to switch on lnav/vnav and keep handflying by following the FD. Once the aircraft is trimmed and pressure from yoke is gone turn on the autopilot,

 

I think that makes more sense then first autopilot and then l/vnav

 

It also gives the pilot more sense of controlling the aircraft and prevents sudden uncomfortable corrections the autopilot would have to do otherwise.

[Spin737 102]

I would say that it makes more sense to switch on lnav/vnav and keep handflying by following the FD. Once the aircraft is trimmed and pressure from yoke is gone turn on the autopilot,

 

I think that makes more sense then first autopilot and then l/vnav

 

It also gives the pilot more sense of controlling the aircraft and prevents sudden uncomfortable corrections the autopilot would have to do otherwise.

As long as you are trimmed and following the F/D, it really shouldn't make any difference what mode is active when you engage the A/P. 10 ANU and 25 bank is the same regardless of mode.

[Q_flyer 766]

Greg not quite.

 

regarding autopilot activation

 

Airbus can mostly arm at around 50FT off the deck and for some companies that is SOP..I kid you not.

 

With the NG for example it is physically impossible to engage the autopilot below 400FT.

 

The turn is dependant upon the rules; whether it be TERPS or ICAO PANSOPS, and whether its conventional type nav or RNAV

 

That's right.  The Iran Air SOPs for their A300-600s and A310s was A/P engagement between 50' and 200'.   (You can see this in action in the Just Planes Iran Air DVD, where the PF litetally rotates, relaxes the back pressure on the yoke, and instantly calls for "Autopilot").

 

 

 

You have to arm the autopilot first ,then L/Vnav.

 

                     Best of luck   pontious

 

Hmm, that's incorrect I'm afriad.  You don't need to engage the AP before activating LNAV/VNAV.   

[Porthos 9]

Pontious as Q400_flier said

 

SOP for some airlines is arm LNAV/VNAV prior to pushback then engage AP airborne.

 

Thats only arming the modes, not executing them. That happens once AP is engaged.

[ESzczesniak 128]

I suppose in similar vein, I have a question about vertical modes for NADP1 procedures.  I've read SOPs that engage LVL CHG at 1500' AFE (climb thrust, continue at V2+20) and wait until 3,000' AFE (acceleration height) to engage VNAV.  Others engage VNAV right away, skipping LVL CHG.  If programmed properly in the FMC with 1500' climb thrust and 3000' acceleration height, VNAV will give the correct commands to fly V2+20 until 3,000' AFE.

 

Can anyone share the thought process for choosing one or the other method?  It seems they are both safe methods of flying the NADP1 profile.

 

Eric Szczesniak

[Spin737 102]

I suppose in similar vein, I have a question about vertical modes for NADP1 procedures.  I've read SOPs that engage LVL CHG at 1500' AFE (climb thrust, continue at V2+20) and wait until 3,000' AFE (acceleration height) to engage VNAV.  Others engage VNAV right away, skipping LVL CHG.  If programmed properly in the FMC with 1500' climb thrust and 3000' acceleration height, VNAV will give the correct commands to fly V2+20 until 3,000' AFE.

 

Can anyone share the thought process for choosing one or the other method?  It seems they are both safe methods of flying the NADP1 profile.

 

Eric Szczesniak

There are threads on this subject if you search. You can arm VNAV on the ground and set it for an NADP-1 if you fill in the boxes correctly. NADP-2 is a bit more tricky.