Attack Chopper (High-Rise Area)

Chapter: A5 · Lanshiang by Helicopter and the Quad Tower: the Dinosaur, the Rooftops and the Walkway
Where: 5-1 High-Rise Area: a tenement block; Ada flies her helicopter

Weak point

None: it's a damage sink, and missiles speed it up

A gunship by the building. Before it, enemy helicopters come down the street: one, another, then two at once. Against the gunship, use the left and right edges of the building as cover from its missiles, keep moving to dodge its machine gun and swing out of cover spraying.

Reward

On to 5-2 Quad Tower Entrance.

The guns don't overheat, but every missed shot counts against your accuracy. Missiles per attempt: 5 or 6 depending on the source.

Step by step

Street: cover Leon and Helena; kill zombies with the gun only and save the missiles. Serpent Emblem #17 first: the yellow truck bed, on the left.
Chase: one missile per helicopter, then the gun; one for the pair. Watch out for RPGs. Keep at least 3 missiles for later.
Serpent Emblem #18 before the gunship: drop altitude, on the right, on a signboard.
Gunship: use the edges of the building and drift slowly right during the shoot-out to dodge its missiles, which take a lot of health.
Arrive with good health: coming in hurt makes the dinosaur fight start badly.
Co-op: Agent sits in the co-pilot seat with his own gatling gun and aims with his own aim button; the missiles are shared.