Why do helicopters/choppers need to do circles in the air before landing?
In: Engineering
You don’t want to be standing still (hovering) at low but non-trivial altitudes in a helicopter.
When a helicopter loses power it can do something called “autorotation”, which basically uses the force of air moving through the rotor to force the rotor to turn. The problem is this doesn’t work very well unless you have significant forward speed. So if you’re hovering at say 100ft and lose power it’s possible to hit the ground at a potentially fatal velocity. [The specific altitudes/velocites required by a helicopter are reported in a helight-veloicty diagram](https://en.wikipedia.org/wiki/Helicopter_height%E2%80%93velocity_diagram). This means it is in the helicopter pilots interest to maintain forward air velocity at low altitudes.
So if the pilot has a reason to hang around the landing area while not in the actual process of landing (like say checking wind directions, or verifying that the landing area is clear) the slow circling is the safest way to operate at low altitude while also remaining in the area of the landing pad.
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