That bit's not that hard, just go to the top and then drop down again until it flies away a bit. Take out the gunner and then it's plain sailing.
Or throw a grenade, I got this from the forum but even without going up the ladder you can kill the heli by throwing a nade into it

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But erm, Far cry is very hard indeed, especially later ingame, I'm now replaying it on medium and it's terrible even though I'm only halfway through.
iirc on hard, the last few miltary levels of pharaoh were hard to beat, was hard finding a balance between income and strength, I either got wiped out by invaders or got broke as I spent too much on military early on...
Also the last boss in ut2004, very hard to beat even bunny hopping all around he manages to hit me from insane distances ( I can hit him too, but that's not the point, even in mp people just can't hit you when you move around too much and are very far, but this ai had like a target lock on me lol).
Also, some red alert 1, ''no base'' missions are so damn tough...