Thank you Oner but the first time I did it in that way, I've been tried couple of times but always happens the same, I have to load the last checkpoint in the Safehouse and then start the mission.
I just started to play this game and when I tried to replay the first mission, the one in the airfield, there was only one enemy, teh rest dissapeared. This game needs a patch A.S.A.P.!!