Hunted mission helicopter glitched?

[アウトコールド]

So I killed the helicopter gunner like 11 times and then after like 15 seconds, a new one just appears out of no where where the old gunner was and is just continuously spawning. Is this a glitch or are you just not supposed to be able to kill the gunner? It's annoying if they just added an infinite spawn to the gunner and not tell you.