Autopilot vertical inaccuracy after takeoff

sg_aviation

When engaging autopilot after takeoff the aircraft is unable to maintain the vertical mode settings. When engaging:

AP after takeoff, the PITCH mode does not maintain the pitch, but nose moves up further;
VS on ground or in the air, the aircraft pitches heavily above/below the set value;
IAS after takeoff, the aircraft pitches heavily above/below the set value.

Only after disengaging and re-engaging the autopilot everything works as expected.

I haven't been able to run in-depth test flights. However does anyone expericence similar and has a quick advice/fix?

PS. This is with PMS50 Garmin GTN 750 in WTT mode!

sg_aviation

@sg_aviation PPS. Before takeoff FD, then TO/GA have been engaged.

BAEflyer

I've observed said behaviour where nav would only trigger if you reengage it. Don't know if it's a bug or a feature though ...
No Toga for takeoff, as per the real world manual and respective normal procedure

Regards

sg_aviation

@BAEflyer Can't confirm this on my side.

However I found out that the TBM did not like reducing the flight_model.cfg elevator_maxangle_scalar too much. After setting to a moderate value the autopilot works OK.

Remaining question is why the autopilot was previously not OK with first engaging, but upon second engaging.

Gabe777

Activate FD and horizontal/vert modes to guide you after take off.

Clean up, then ensure you trim aircaft correctly before activating AP.

It's not a 747.