A single player mission doesn't seem to be completable for me.
 

The mission where you have to fly to Calais to redeem yourself doesn't seem completable for me.It's now the sixth time of me flying over there, shooting down some 109's, flying around the airfield and flying back exiting and being told I somehow failed and can't advance.Help would be appreciated.

could someone tell what I need to do for this mission to be successful?

It would help if you told us what mission and who made it...

Oh sorry it's in the RAF stock campaign.Mission number 17