With NO hardware controls connected, and with all Auto-Assist turned OFF, the pitch trim on all planes sets itself to full nose down, making even taking off impossible. Plugging in hardware controls (e.g. Velocity One) makes no difference. Removing all key/control assignments to pitch trim makes no difference. This makes the simulator completely unusable.
Moved to Tech Talk which is more appropriate whilst others help you troubleshoot 
Does it occur witth all addons removed?
Does it start directly at full down or does it take a few seconds to get there, like the trim is being held.
Try with empty community folder.
If you have just installed anything market place or updates, restart msfs.
Double check your mapping/bindings for any duplicate trim on every controller.
Make sure your autopilot is off while on the ground and check mappings for ap on, in case something is turning it on.
I discovered that one of my controllers was somehow still active, even though I thought that the USB port was off. So please consider this issue resolved.
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