I am going to answer by just my own findings. It is indeed possible to destroy the gunship. On the screenshots I have posted the engine is circled in Red, if you look closely it sais 5x next to the health bar. The gunship starts with 10x, this means you need to shoot down the engines health bar 10 times to kill it. The blue circles are the turrets, now I can't remember where they all are but there is still one left, and one just got destroyed on the left. You don't need to destroy them but they will fire upon you and hurt like hell.
