VNAV Behavior Takeoff after SP1b upgrade?

[DrumsArt 270]

Concerning the problem I think I found...In the second page of Takeoff Ref in the FMC I had ACCEL HT=3000agl then REDUCTION 1500agl !With this setting when the plane reaches 1500agl N1 change in Climb1 or 2 if selectionned but the climb ATTITUDE don't change so speed decrease (N1 less power). Question : Is it like this in real ?Btw I don't remember putting this setting but anyway I put the same number in ACCEL and REDUCTION and everything worked as planned.Regards,Richard Portier

[martin-w 3,263]

Well my dads m8 flys 738 and he said that he has never done this in his whole life of flying always after takeoff what happens if you arm the LNAV then forget you have and arm the CMD the plane will go into a very sharpe turn depending on your waypoint etcI will just say everyone has there own way of flying

what happens if you arm the LNAV then forget you have and arm the CMD the plane will go into a very sharpe turn depending on your waypoint etcExactly, thats why you arm it. To follow the SID straight after takeoff.It's been discussed before on the forum, perfectly acceptable to arm VNAV and LNAV after the Honeywell software update.Section 3.3 and 3.31 of the Flight Crew Training Manual. [Takeoff Profile Using VNAV (FMC U10.8 and Later]It's not just permisable, it's prefered!

With FMC U10.8 and later, VNAV is normally armed for takeoff and engages at 400 feet AGL. The use of VNAV for takeoff, flap retraction and climb out is the preferred method of managing the AFDS for takeoff. This provides the VNAV profile and acceleration schedule compatible with the planned departure.

Sorry to side track the thread Richard.

[Spin737 102]

Concerning the problem I think I found...In the second page of Takeoff Ref in the FMC I had ACCEL HT=3000agl then REDUCTION 1500agl !With this setting when the plane reaches 1500agl N1 change in Climb1 or 2 if selectionned but the climb ATTITUDE don't change so speed decrease (N1 less power). Question : Is it like this in real ?Btw I don't remember putting this setting but anyway I put the same number in ACCEL and REDUCTION and everything worked as planned.Regards,Richard Portier

Yep, that's standard procedure. Lot's of power to get off the runway and airborne and less for the climb.

[flygarn1 0]

Arming Vnav on ground, when engage TO/GA, Vnav goes off, then at about 1000 re engage and engage AP... then steep climb with stale... using fsbuild to create flightplan than importing into FMC

I am pretty shure that this one was a BIG NO,NO when SP1b came out becouse your life would be realy bad if you made a flightplan outside of FMC and imported that one?

[mrdfw 0]

This is my screenshots for problem on climb out, VNAV and AP engaged, steep clim causing stall..

[DrumsArt 270]

Please Mister Mrdfw what setting have you in the SECOND TakeOff Ref page if possible with a picture ?Regards,Richard Portier

[DrumsArt 270]

@ MartinNo problem, it was what I thought and at least it ended the "controversy" ;-)@ Matt"Yep, that's standard procedure. Lot's of power to get off the runway and airborne and less for the climb."Yes I know that.May be I expressed myself poorly...This is what happens :1-If the altitude of Accel Ht is greater than Reduction. Ex : ACCEL HT=3000agl REDUCTION 1500aglAt 1500agl the power change to climb, climb1 or climb2 it's normal (no problem with that).The problem is that the plane keeps the same pitch than takeoff with less power. In our case the speed decreases ! Then after passed 3000agIs, things back to normal. The pitch decreases to accelerate at 250 etc....So my question was : is it normal that Vspeed mode keeps the same pitch like takeoff while we are in Climb mode 1 or 2 ?If it is, that would mean that it's dangerous to have ACCEL HT greater than REDUCTION.Second page of TakeOff in FMCPassed 1500aglPassed 3000agl2-When ACCEL HT is equal or less that REDUCTION all seems work like expected.Not completely sure but I had not observed that before SP1b.Hope I'm clear ;-)Regards,Richard Portier

[mrdfw 0]

Please Mister Mrdfw what setting have you in the SECOND TakeOff Ref page if possible with a picture ?Regards,Richard Portier

Second page of takeoff ref

[RYR738 9]

Richard !Why are you at flaps 15 and not retracting the flaps ??also......For flight training, Boeing use 1000 ft for thrust reduction and 1500 ft as the acceleration height.( otherwise 1500 is a good setting for both )Fred.

[Ben Cap 89]

also......For flight training, Boeing use 1000 ft for thrust reduction and 1500 ft as the acceleration height.

I've wondered this for a while... Thanks!! :)

[DrumsArt 270]

@mrdfwIt seems you have the same altitude (1500agl). With this setting have you the same problem you describe ?If yes I don't know. It's that we do not have the same issue.Richard Portier

[DrumsArt 270]

Frederic !! ;-)The flaps are not the subject in this case. No ? I just take the picture to show then I stopped FSX...To answer why the flaps is at 15, it's because I configured the FMC with this setting.I will test with 1000 ft for thrust reduction and 1500 ft as the acceleration height.Regards,Richard Portier

[RYR738 9]

Frederic !! ;-)The flaps are not the subject in this case. No ? I just take the picture to show then I stopped FSX...To answer why the flaps is at 15, it's because I configured the FMC with this setting.I will test with 1000 ft for thrust reduction and 1500 ft as the acceleration height.Regards,Richard Portier

I know the flaps are not the subject but they do have a lot to do with the pics in this case.You are very light on fuel so I would use flaps 5 and derate 2 and climb 2 for good VNAV behaviour.The pics also show that the Yaw Damper is not on !Have fun !Fred.

[DrumsArt 270]

I know the flaps are not the subject but they do have a lot to do with the pics in this case.You are very light on fuel so I would use flaps 5 and derate 2 and climb 2 for good VNAV behaviour.The pics also show that the Yaw Damper is not on !Have fun !Fred.

And you have not seen it all No lights, no cabin signs, no pressurization.More seriously because you seems to know many things (not ironic). Thank you for your advice, its how I proceed. It was just to test a special situation under particuliar circumstances.Is the following setting ACCEL HT=3000agl REDUCTION 1500agl is never used ? Regards,Richard Portier

[Spin737 102]

And you have not seen it all No lights, no cabin signs, no pressurization.More seriously because you seems to know many things (not ironic). Thank you for your advice, its how I proceed. It was just to test a special situation under particuliar circumstances.Is the following setting ACCEL HT=3000agl REDUCTION 1500agl is never used ?Regards,Richard Portier

That's a standard setting for NADP1, so it's used all the time.