I'm playing on Delta difficulty and am up to the objective to protect the marines' compound with Prophet from the flying thingies.

The glitch is that after a while the flying thingies disappear and don't come back, so there's no way to complete the objective. If I try to move to the next section of the game I get a warning that I will die unless I return to the compound within 5 seconds. In the distance I can see the flying thingies but you can't engage with them.

How do you complete the objective? I played the game on Normal difficulty and I didn't have this problem.

Is this a glitch? Is there a patch? When I'm online, there's no message saying that there are newer versions of the game (I bought it for my PS3 on the PSN).

I'm pretty rubbish at this section as the flying thingies deflect the alien bullets I shoot at it. I usually take cover but eventually the flying thingies disappear and they don't seem to come back.

Just wondering how to complete this objective!