Take the NPC "McMillian" to the Pripyat Flyer

but don't put him in the designated spot on the hill first. Now scout the area and know where the enemies are going when they come. Face back to the direction of the wheelbarrow and see an alley facing southeast (use the compass to identify the direction), there is a closed apartment building, the door will be opened when the firefight later the enemy will come out from there. After watching, place the NPC on the hill at the designated location and prepare for the enemy. When the enemy helicopter appears, the door will be opened just now.