Keyboard Controls, help please!

I am having some trouble making my flying airoplane map: first I had a problem with trigger nesting, but with the help of some nice people I could figure that out. Now I have another problem, I think I know what is wrong but if my theory is correct the way I am doing it may be the only way:

My plane seems to randomly change directions in mid air, or not turn or do all sort of random stuff you would never expect. This as I have been told, may be because I am telling the plane to go to:
"position of plane offeset by 999999 ; 0" for example

I ignored this problem for a bit and added accerleration and a few other things that do work but they are all useless if the very basic doesn't.

If i revert to the original form of "ever 0.5 seconds (...)" it jerks and the plane moves very very slowly... What should I do?

this is a version of the map that works wondefully in terms of steering but the plane jerks so much that it could be outrun by a banished wisp! In air battles the planes need to do faster I would say... but what do I do?

this one is not done by me. The person who helped me with the trigger nesting made it. His name is on the credits on the map. I gave the original to him and continued on it myself, this is the one he gave back.

I didn't won't to edit it incase I broke somthing I didn't understand, I am past thinking I know everything there is to know about triggers since nesting. Hence no acceleration.

ok. I have worked out somthing to stop the jerking but there does remain one problem, I need to have missiles, when fired, moving to the extremities of the map in the same way as the first version of the map. there must be a way of doing it...