I get to the airport ,Itake the guard at the gate ,the guard with the dog and the guard on the shack inside the parking,also took out all the cameras and entered the room where is one guard dead,but still can continued because whe i try to open the other door ,a recieve a message that indicate that do not let any terorist behind and that there is one more terrorist active ,my cuestion is where is him because i look every where and i can find him, help me plese.

Make sure the 'orange' terrorists in thermal vision are dead.

To get you off on the right foot, the guard in the shack is the terrorist. Use thermal vision and you'll see that he'll be reddish/orange, just like the other 9 terrorists throughout the level will be. Put a bullet in his head and you'll be able to proceed. Be sure to kill, not just KO, the terrorists as you come across them, otherwise you'll get more messages like the one you got.

By the time you get to that dead body that's laying between some server/electronics, you should have already KILLED 5 terrorists.

First is in the second guard shack, delivery area.
Second is in the first luggage area.

There are 3 in the second luggage area:
One is patrolling on the right side lower floor.
Another is sitting in the chair on the lower floor.
Last is patrolling near the dead body upstairs.

DON'T kill the civilians or regular guards, just the 'orange' ones. You can actually stealth past them without KO's, but that takes practice and skill. If you'd like to see how a pro does it check out DanielHac's videos HERE.

The key is to kill the terrorists- knocking them out is not good enough on this level. If they are dead, they will fade to blue and eventually black on thermal vision. I KO them and then shoot them with the pistol to keep it quiet.

thanks to all of you for the hints