Why do people duck under a helicopter?

[coachTanthony]

[RebelinSteel]

Because the ground is not always even, with larger helicopters the blades droop towards the outer edges as they idle, it’s an actual safety brief. It’s the same with ensuring there is a net out on the ship (on the do not leave this side door) for those exiting a helicopter, as people will leave from the wrong door and can get wet, it’s a long way down.
in the photo (and it may be an illusion), it looks like they are leaving in the wrong direction as the ground slopes slightly upwards, they should leave to the right until clear of the blades then move upwards.

[Lliam]

Helicopters can and do decapitate people on a regular basis—often because rotor tilt (possible in some types of craft), mechanical failure, or an inopportune gust of wind, brings a rotor tip down to head level—just for an instant.

I suppose it depends on size and type of helicopter, though.

I also think people duck instinctively when walking under a spinning blade.

[DeeDeeDeVour]

To me, it's initially because of that fear my head would get sliced off my body.

I guess it's my basic instinct to take a necessary precaution even though I'm short and unlikely gonna get struck my those spinning blades.

[Daniela1982]

People often do not pay attention. They walk into tail rotors occasionally from being inattentive. If you don't duck you might suck!

[OlderAndWiser]

Nobody wants to take a chance on getting their head chopped off!!!

[AviatorTom]

... and the rotating blades create a lot of wind. Ducking reduces the effect of the wind... a little.

[Fireguy17]

force of habit.
The blades are very flexible, so a gust of wind can change the angle of the blades in an instant.
And probably force of habit, if they have been on smaller ones they have a lower blade height.
Better safe than sorry.
It makes a real mess when that happens.

[purplepoppy]

Same reason we all tuck our arms in when driving through a tight space.

[BetaBucks]

Former helicopter crew, and you never want to lose that habit. Different clearances, fluctuations in blade tip, and more. Seen brains form not ducking...

[Red_Arrow]

The blades will droop when not spinning at full speed. On many helicopters it would be possible for them to connect with your head. Don't assume you are safe. You should get in the habit of always protecting yourself.

[Paul_in_Indy]

Newer rotor discs are much more rigid. The risk is much lower. -but traditionally, soldiers were taught to take a low crouch because gusts of wind could deflect the blades downward.

[Smashingdoozy]

Because there's a lot of force coming from the blades

[OfMiceandMen]

I think it's just a reactionary/ounce of prevention thing.

[avery58]

I'm guessing it has more to do with the noise than anything else

[katiesmuff]

Just keeping face down due to wind from blades rotating.

[FunkyMonkee]

The blades are flexible and MIGHT swoop down far enough to chop off your head. Remember Vic Morrow?

[on_my_knees]

They walk that way so they can drag their knuckles on the ground.

[Anpu23]

Down wash. There's no concern of chopping off your head. But the down wash is pretty intense.

[PsychicBoobs]

People tend to only walk past the tail roter once.

[Dargil]

Some impulse that the blades sink low. I always did it even though I knew better.

[DrPepper12]

Instinct? Irrational fear? Too many Hollywood movies? 🤷‍♂️🤔

[Jamie05rhs]

You can never be too careful when decapitation is at stake.

[CaptainSmartass]

So their heads don't get chopped off.

Simples...

[Wiredone]

They are trying to avoid getting a haircut from the blades

[electromagnetic]

Risky to do otherwise.

[onedarkcloud]

Normal human instinct. Better safe than brainless! LOL

[normalice]

Because everyone else does.

[exitseven]

they think it looks cool..

[andreasderjuengere]

Because they are Donald's?

[Pterodon]

The blades are known to flap

[noohair]

They don't need a haircut.

[Irene97]

So they don’t lose their heads.

[paledreams]

Well 🤕🤕🤕

[Babygirl_S]

lol.

[Ladsin2]

Probably loud.