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ganter

Wild nose pitch up on engaging LNAV

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Hi fellow Aviators,

 

I'm experiencing a rather peculiar event in my take off procedures.

 

I'll rotate at my PNF's callout to 15 degrees and make the climb out at that pitch to 1500 ft where NADP measures will cause me to tuck her in to about 8 degrees for the 1500 ft duration to 3000 ft or so. When N1 comes on strong again I'll see her up to about 4000 ft and engage AP/ and LNAV to take care of the SID course while I continue to hand fly the VNAV. 

The problem is as soon as I hit LNAV at or around 4000 ft the nose pitches wildly up to about 23-26 degrees and I have to wrestle it down to a practical pitch in order to prevent a stall.

 

I fly relatively light with Fuel invariably 1/3 full on short European hikes.

 

I haven't fallen out of the sky doing this yet but it does rather take the immersion away from take off.

 

What am I doing wrong?

 

 

 

 

 

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What am I doing wrong?

 

Not sure, but mostly because terms are being used incorrectly here...

 

If you have the AP on with LNAV, "hand flying" is no longer in play. What do you mean by "continue to hand fly the VNAV?" If the AP is on, then your hands should be off.

 

What do you mean by "as soon as I hit LNAV at or around 4000 feet?" LNAV is lateral. 4000 feet implies vertical.

 

As far as the pitch up goes, do you have any trim axes on your hardware?

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I'm confused: you're letting the A/P fly LNAV but you're handflyjng the VNAV? I'm not sure how you could do that. Is there a reason why you're doing it as you describe?

 

I would suggest either handflying or full A/P.

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 Thanks for replying - sorry for incorrect use of terminology - still learning to fly this superb machine.

 

I engage AP at 4000 ft and select LNAV to fly the course to steer for the SID. I do not select VNAV so vertical navigation is still in my hands at this point in time. Or is it?

 

As I understand it, with LNAV engaged and AP on but not VNAV, I'm still controlling speed and pitch.

 

Is this where I'm going wrong?

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I engage AP at 4000 ft and select LNAV to fly the course to steer for the SID. I do not select VNAV so vertical navigation is still in my hands at this point in time. Or is it?

 

If the AP is on, your hands should be off. If not, you're going to end up disconnecting the AP.

 

 

 


As I understand it, with LNAV engaged and AP on but not VNAV, I'm still controlling speed and pitch.

 

No.

 

 

 


Is this where I'm going wrong?

 

It's very likely.

 

Please fly the tutorials to get the hang of using the various AP modes.

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Thank heavens someone sorted this out. I was going around in circles trying to make head or tail of the ' hand flying' with A/P engaged.

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Also if your not properly cleaned up (e.g. flaps still out etc) this would couse the A/P to pitch up violently as well.

Make sure you are in trim and not flying harder than selected speed. (FMC or VNAV)

 

Mark Visch

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You can select all the lateral and vertical modes as you desire so that the F/D on the PFD "directs" you while you hand-fly. I recommend you select LNAV and VNAV on the ground before take-off, that way you wont have to do anything but follow the F/D bars once airborne.

 

It's very simple like Kyle said: If A/P is engaged and you see a "CMD" green tag on the PFD, the A/P is flying -> Hands off the yoke (applying too much pressure on the control while the A/P is engaged will disconnect it).

 

If A/P is disengaged and you see "F/D" on the PFD, then YOU are flying.

 

The A/T goes by its own. You can hand-fly with A/T taking care of thrust, or you can in theory let the A/P do the flying with the A/T off (which is rather unusual, I can't think of a situation where you would do that, maybe during turbulence penetration to prevent the A/T from going whild).

 

BTW: To be "in control" and to be "flying" are different things. As a single pilot operation, you'd better ALWAYS be "in control", hehe. Now, the A/P can be "flying" or you can. But it's always you who is in control, that is, to be held responsable for what the A/P is doing.

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Unless you're using a configuration that results in CWS pitch mode when you engage the A/P. It is technically possible to have the A/P flying the LNAV course while you (kind of) control the pitch... but I'm not seeing why that would happen here.

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