(09 Nov 2018, 9:36 pm)James101 wrote I don’t have the foggiest idea of how aircraft work, but why is setting auto pilot to 0ft even possible?

I've no idea! 
Tried making sense of this and it appears it is possible to use it during landing. 
https://en.wikipedia.org/wiki/Autopilot

Sure someone will know the reasons. Sure we have had a pilot or two on here in the past.