did i make a mistake?or why is it not working for the second airfield, while it works perfectly for the first??

I had the same problem, there are some fixes and work arounds like Salmo mentioned but sometimes they work sometimes they dont...

The best method I found and simplist was just block the "bad" spawns with a static aircraft or even a truck or buildings... Things that make the base a little alive. Then just let people spawn on the good ones. And a heads up, there is a massive dip in the field at Coquelles which you can only cover with the largest French hanger. ;)

In my oppinion I would not spend to much time trying to fight the spawns, it will drive you insane and never quite work as intended but its your mission so its up to you.

On another note:

David you know the RAF fields are call RAF Kenley etc, what would the LW fields be called?

If you are planning on having AI in an online mission take off or land at an airfield that could be used by players, you will run into big problems. Actually you could run into big problems without players lol. I tried this well over a year ago. Anything that gets in the way of their path while on the airfield can and will ruin the entire flight. This can happen on take off or landing. The final warping as you call it, is the AI's final resting point.

If something gets in the way of that final point, or even before, you can and most likely will have AI planes that look like that are dancing on the airfield. At this point they can not be destroyed, damaged, or despawned. They will bounce like that until the next mission. It's best to spawn them in the air and destroy them in the air as well.