Autorotation works on the premise of keeping your rotor blades spinning after engine power has been lost, and then using that stored energy at the last moment to arrest your descent and allow for landing. Arma more or less gets this right, but it does have some dangerous quirks you need to be aware of.
Autorotation in Arma is harder than in ACE, so if you can do an Arma autorotation, you can do an ACE one.
In Arma, the instant you hear your engine dying or see the engine damage indicator go red, press and hold down collective. You’ll hold this throughout the remainder of your flight. Simultaneously, get your aircraft as level as possible. This is essential. If you don’t do this, if your nose is pitched down even a pinch too much, you’ll probably die. Once you’re level, you can do one of two things. One, you can use whatever speed you had to keep flying forward (or turn slightly in the process), or you can reduce your speed if you’re at too low of a level or don’t want to overfly a potential landing zone.
Once you’re level and descending, do a hasty scan for an LZ. A slight curving path can help to reveal potential LZs as you’re descending.
As you’re descending, try to assess the LZ as best you can. Slow your forward speed as you descend – landing at high forward speed is to be avoided and often fatal. Since there’s no vortex ring state in Arma, you can even autorotate straight down if the situation requires.
Once you’re 30 meters above ground level, release down collective and hold up collective. This will take the stored rotor energy and give you enough thrust to set down lightly. When setting down, do your best to land as level as you can – striking the tail first in Arma can do an incredible amount of damage to the aircraft, and if you’ve already taken damage to the engine, it can easily result in an explosion.
The quirk mentioned earlier comes into play when pitching your nose down after losing engine power. Autorotation in Arma requires the aircraft to be fairly level, with very low tolerance for deviation. If you pitch too far forward, you’ll see the rotors spin down, and even if you try to correct it, you’ll almost certainly run into one of two things – either the aircraft will no longer be able to pitch up, or even after pitching up you’ll be in far too fast of a descent to stop. I guess you’ll technically run into something else as well, as either route will have the ground in your immediate future.
So, to rehash the key points – as soon as you lose engine:
• Immediately drop collective
• Level out
• Find an LZ, drift towards it
• Slow your forward speed as you reach the LZ
• When you're 30 meters above the ground do full up collective and try to land as level as you can.
If you do all of those steps, 99 times out of 100 you'll be fine.