If you have followed the instructions in this walkthrough, you should now be in the base, in the north-eastern part of the map. The pilot's body is in the center of the map, in the church (M3,9). You will get there along the tunnel underneath the road between the center of the map with the base.
Watch out for the sniper there (M3,5). He is next to the cannon, on the bridge. At high difficulty level, it will be nearly impossible to take him down.
After you exit the tunnel, you will simply have to follow the edge of the rocks until you reach the river, and by following the river, you will reach the church. Climb up a little, hide in the bushes and toss a stone to the left of the church's main entrance.
After the soldiers react to that, run behind the church - there you will find the entrance. Eliminate quickly the guard there and toss his body into the church. In the church, there also is an officer. If you have been fast enough, he will now be looking in the direction in which you have thrown the stone. Hide his body under the tower.
It is best to snatch the tape next to the dead pilot and exit to the rooftop of the building, where you will have to wait for a moment until the soldiers calm down. You can also distract enemies by destroying the truck at the eastern rocks, using a suppressed weapon (M3,3).