FMC problems on take off

[baw079]

Sorry to keep up the questions about thie FMC, but...
After take off, above 400 ft, I select Autopilot and either select LNAV or HDG. So far, so good, B737 flies excellent.
I then clean up the flaps, etc and select N1 with speed set at 220 kts. Again so far so good.
Next part is now becoming a very major problem...
Whenever I select either VNAV, LVLCHG or V/S - the B737 only wants to nose dive into the ground killing me and my passengers. Even when I disconnect the autopilot completely, I have extreme difficulty regaining control.
I have followed the manuals and wlak throughs, etc but cannot get the B737 to stop wanting to nose dive into the ground.
Please keep me sane and help!!!

[ToddNicholson]

LAST EDITED ON Dec-30-01 AT 03:54PM (EDT)[p]It sounds like you're not trimming the airplane during the climb. What's happening is that you're probably engaging VNAV then letting go of the stick back pressure which results in the nose pointing down because the aircraft hasn't been trimmed properly. VNAV is not going to be fast enough to trim the airplane up and out of that condition.

Todd

[baw079]

Todd,

Will give this a try asap, however, I set the trim before take off to ensure it is correct.

I appreciate the trim requirements change throughout flight.

Cheers

Willie G.

[ilh]

Todd, I thought that as well. Yesterday I tried to mistrim very badly so I had a lot of back pressure when engaging the A/P, and it actually worked just fine. I wonder if these folks are having a different problem.

Lee Hetherington (KBOS)

[ToddNicholson]

Lee, I was also thinking it could be a problem with left-over autopilot settings from another flight in FS that isn't cleared out of the system. Not sure from the descriptions if these are from first-session flights or not.

Todd

[baw079]

Guys, many thanks, it was an untrimmed aircraft!

Apologies for not thanking you all sooner but I have only just managed to get back on line after line problems.

Works excellent.

[Sim]

Hi

The minimum altitude to engage Autopilot is 1000 feet..for a 737
In reality, they engage LNAV at 400 feet AGL and VNAV at min 3000 feet..then, after take-off checklist..they can engage autopilot..
After t/o, aircraft must be trimmed..
Regards
Sim