I find it funny how some people are claiming that Chris & Piers used guns to kill it (and thus reasoning it could be gunned down easily on land). Only problem is, it wasn't guns that killed it at all. It was Piers lightning blast (it tried to attack Chris' escape pod and a super concentrated lightning blast came out of the facility and struck it from behind). Some people might argue that the lightning blast only weakened it and it was the exploding facility that killed it, but even though HAOS falls towards the facility as it blows up, the scene clearly shows that explosions don't reach him (at least by the time the scene cuts away anyway).
Xbox 360 Gamertag & Playstation Network ID: LegendKillerRAB Wii U Nintendo Account: LegendRAB