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Comment by 13of40 | Hacker News Reader

When you're getting on the plane, if you look down and to the right there's a little wheel resting against the side of the plane and connected to the skybridge. It says do not touch. That's because it's the sensor that allows the skybridge to automatically level itself when the plane moves up and down on its suspension due to fueling, loading, unloading, etc. I wonder if this is what happens if it gets touched?

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I would hope / imagine that the amount of force necessary to move that wheel is well greater than what an average person could exert without being noticed and stopped by one of the crew! (i.e. only genuinely large movements of the 2 very heavy objects involved)

Another design to accomplish this same goal seems to be called the "safety shoe" [1]. I believe this is a horizontal bar placed under the open door which moves the airbridge down if it gets too close.

https://www.youtube.com/watch?v=4Ir5b0GzfiE

I've wondered what that is when seeing it during boarding! The video doesn't explain anything though... Is it some proximity sensor? How? It doesn't seem to require extremely accurate positioning.

I found a product manual [1] from one manufacturer which describes stepping on it as part of a maintenance test (bottom of page 6), so it seems like some type of switch or pressure.

The idea seems to be that if the door touches the top of the sensor, it automatically lowers the jetbridge a few inches to prevent the door from being damaged. And I guess this can happen if the plane is being loaded improperly causing it to shift.

[1] PDF, 4MB: https://www.acesincusa.com/wp-content/uploads/2020/07/Safety...

Oh, I see, thanks for that! Yes it looks like a contact strip sensor kind of thing.

I have also noticed in some jet bridges, you will see some kind of air sensor probe on the end of a coiled cord, which is very odd to me that this would inform the operation of the bridge. I can't find a photo of it readily, but it is definitely something I have noticed and puzzled about.

The wheel is the primary sensor and the safety shoe is a backup.

If you look down you also see how far away the ground is.

Always find myself subconsciously wondering how to react if the bridge/plane somehow separate.

Ride either of them down, preferably the plane. Don’t fall out!

I hate the moment of having one foot on plane, one on bridge.

Jump with both feet.

Then you probably won't enjoy watching video footage of elevator failures.

I'm fine with that, but I rode in a boat a couple times, and the first step in/out from the pier was a doozy! Aircraft don't bob and float in the surf!

I still remember old trains where you could look down and see the track while stepping from one carriage to the next. Child me always thought it was cool.

Jump forward, either into the plane or into the bridge, or rest on the back foot? I think that either we train reflexes or our body will take a guess but who trains for that?

I always figured it was a pinching hazard.

> That's because it's the sensor that allows the skybridge to automatically level itself when the plane moves up and down on its suspension due to fueling, loading, unloading, etc.

And if you pay attention while you're on the jetbridge, it's not entirely uncommon to feel it move as it adjusts. (Although I find the movement a bit disconcerting, even though I know it's normal.)

I work in aviation and have moved that wheel out of curiosity. As expected, the jet bridge moved up and down with the wheel!

Judging from the photos, not unless "touched" means "was pulled back and rolled about 7 turns downward".

Sometimes it doesn't have the warning and I think it should be mandatory. Any passenger can go and play with the wheel and wreck havoc.

Aren't those reachable by boarding passengers? Never put anything sensitive like that near passengers. With millions of passengers, including kids, walking by it each day, someone is going to touch it for fun, especially when you put up a sign saying "touch me!"

This tech is on thousands of bridges around the world, has been for a lot of years now, and yes, millions of people have passed it, and we haven't heard of any incidents of passengers touching it and causing big issues... so I would say whoever engineered it knew what they were doing and don't need the Internet commenter expert knowledge...

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