Autopilot and Trim

[pcartier 0]

Hello Pilots,Can someone tell me what causes my aircraft to picth-up over 20+ degwhen the autopilot is selected (around 1000 ft)On take off the aircraft is trimmed, I take-off with a 15 deg nose up pitch - looking good reaching 1000 ft, HDG is selected on the MCP, and then the AP is turned on around 1000 ft and there goes my smooth climb, the pitch goes to around 20+ unless I select LNAV and VNAV.Thanks for any help or hints you can provide!Paul Cartier

[Guest amerton]

Paul,If you engage the AP with no vertical mode on prior to engagement, you'll be in "CWS pitch - control wheel steering mode" *which is not yet modelled*. You have to handle pitch yourself, the AP will not issue any control surfaces commands.If you took off with TOGA mode, then engaging the AP will force LVL CHG pitch mode, and the AP will maintain your MCP speed - which is updated at +20, as you had to set V2 on the MCP prior to engaging TOGA.Use TOGA to take off, or engage a pitch mode (LVL CHG / VS / VNAV) BEFORE engaging the AP, or else after AP engagement, fly pitch by hand.Makes sense ?anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

[pcartier 0]

Thanks Anthony,I engaged LVL CHG before selecting AP and it was perfect!What take-off method do you use?Thanks for you help and a GREAT aircraft!Paul Cartier

[Guest]

Please explain easy,what should i do?the auto pilto is crazy, picth to 4000FPM and the alt doesnt respond to my MCP command.what should i do?

[Guest amerton]

You are required to sign your posts with your name.If you engage the AP when not in TOGA pitch mode, with no pitch mode already selected, then NO pitch mode will be active.So BEFORE engaging the AP, select a pitch mode (VS, FL CH, VNAV...)Before I can answer precisely, please describe exactly all the steps you go through (phase of flight, the buttons you press, the knobs you turn etc...).anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

[Guest tmetzinger]

>Paul,>>If you took off with TOGA mode, then engaging the AP will>force LVL CHG pitch mode, and the AP will maintain your MCP>speed - which is updated at +20, as you had to set V2 on the>MCP prior to engaging TOGA.>Since the autopilot will use pitch first to achieve the MCP speed, the reason many of you see a big pitch change when you engage the autopilot is that you've already sped past the V2+20 speed - thus the autopilot raises the nose to slow down the plane.If you follow the tutorial, you're at 1000 AGL and have almost certainly hand flown the aircraft to a higher speed.So, here's a hint - if you've taken off in TOGA and haven't engaged the autopilot, check your airspeed and make sure the MCP speed is higher than your current speed before you engage the autopilot.

[Guest amerton]

Very true !I will add that flying the FD cue pitch-wise will result in holding V2+20, provided you entered V2 in the MCP before engaging TOGA. This is the correct thing to do ;-)During the first phase of take-off, the pilot should pitch to hold V2+15/V2+20...anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

[Guest amerton]

Well, generally :- set correct V2 in MCP (see FMC TAKEOFF REF page)- then spool up the engines to +- 70% N1- then TOGA- after rotation, pitch smoothly - following the FD cue - to maintain V2+20 until thurst reduction alt, then reduce pitch to follow the flaps retraction schedule to accelerate to 250.- you *can* engage VNAV at 400ft AGL. The FD will give correct pitch indications and the FMC will set speed targets that correspond to flaps settings.Engage the AP in CMD mode when you like (I usually engage it before 1000ft AGL, after having engaged VNAV (if applicable), but then... I guess this is not done often in the real world).At takeoff, it is difficult to fly the aircraft, retract gear and flaps being alone, with no first officer to help... ;-)In a nutshell : whatever pitch mode you engage (or not) after TO, it is very important to pitch the aircraft so it maintains V2+20. This will give you a high altitude gain (you want to get "out of here" as quickly as possible), while still flying a safe speed.More recent Boeing aircraft like the 777 have CMD which can be driven by TOGA after take off. In aircraft like the 737/757, TOGA is FD assisted only, meaning hand fly following FD indications, and engaging the AP in CMD mode will disengage TOGA (and go to FL CH).BTW 1 : if the aircraft is very light, maintaining V2+20 can result in a very high pitch attitude. Pilots are encouraged to relax it a bit to V2+25 or more as to not cause discomfort to the passengers.BTW 2 : it is great fun to hand fly the aircraft VNAV LNAV APP, following the FD ! Try it. anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

[Guest]

Hi,that what i did,i used the TO/Go, and the MCP shoed 200 and the airspeed was 185, just turn on the autopilot and agian the plane started to jump up like mad, 4000FPM the spped didnt changed a bit.i tried decrease the VS to 200 FPS but noting the plane stalled and agin picthed up like mad.i did as follow and correct what i'm doing wrong:1)Switch the speed ARM2)TO/GO switch on3)MCP speed HIGER then the TO/GO speed.4)before engaging autopilot checking to see that the MCP speed is higer then the real speed.but agin it's start jumping and IGNORE all ALT, VS.thanks,

[Guest Ian_Riddell]

"Since the autopilot will use pitch first to achieve the MCP speed, the reason many of you see a big pitch change when you engage the autopilot is that you've already sped past the V2+20 speed - thus the autopilot raises the nose to slow down the plane."Hi, Tim.In the Boeing 737NG Maintenance Manual it says that...."If the pilot pushes the LVL CHG mode selector switch when in TO/GA, the MCP IAS/MACH indicator shows the higher of these:-Present airspeed-Speed set in the MCP"Would engaging the autopilot after taking off in TOGA mode simulate pushing the LVL CHG mode selector switch? If so, might the aircraft simply stay at the current airspeed in the scenario above, rather than pitching up to slow the aircraft back down to V2+20?At this point, I'm not even sure if the Maintenance Manual is talking about TOGA after takeoff, or TOGA during a missed approach.... or both(???)Thanks.Cheers.Ian.

[Guest]

i followed your tutorial it is great but sorry nothing help the aircract continue to jump like crazy.today i've reached 5000FPM madness.

[Guest]

i followed your tutorial it is great but sorry nothing help the aircract continue to jump like crazy.today i've reached 5000FPM madness.

[Guest amerton]

Udis,Please SIGN your posts, as I've asked you kindly in the forum, and in response to your email.Have you re-installed as I suggested ?Where do you come from, BTW ?anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

[Guest]

sorry for my english,i'm from israel, my native is hebrew,inappropriate question by the way.i've reinstalled the aircraft 3 times with the removal tool and i made fresh installation, and full patch SU1.1.still same problem.thanks.

[joherszch 21]

I think my message fit in this topic =) Why does the FMC say "UNABLE CRZ ALT" When I push the VNAV button? Best RegardsJohan Adolfsson