If you turn your TAC on and check the waypoint & your assigned AI task, it usually says "descend & run to nearest airfield" whenever your flight leader decides he'd rather run away than take on whatever enemy group is nearby. So your flight lead is trying to save his bacon.

I tend to see this 'run away' behavior more in the first few missions with each new pilot. After a handful of missions, the flight leaders start engaging more often, unless outnumbered and/or at an altitude disadvantage. I just consider these early missions as training-like orientation missions rather than combat missions (which is probably appropriate).

You'll still see them run away later on, but not near as much. After being in some scrapes with a pilot and his flight, I've learned to follow them when they decide to run because by that point they're often making smart decisions regarding match-ups. I believe that the flight leader's personality will also have an effect on whether they fight or run either way.

I suggest just flying some more missions with the same pilot. You will start getting in entanglements before long, nearly every mission depending on which year you're flying.

What RoFfan said about AI is hunting the player seems right. I also saw often enemy planes attacking my group but it always seems that i am target nr.1 . Is that how it should be or is it only my impression?