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Comment by robryk | Hacker News Reader

Usually tying an in-flight helicopter to the ground is a huge no-no. E.g. there's a subtle sequence of steps for airlifting a casualty from a steep hillside that prevents the helicopter from ever being connected by a rope to the ground (the reasoning, AFAIK, is that the helocpter migth need to depart or move at a very short notice and the line may hinder it and injure people if it breaks).

It seems that there are reasonably long period of time here when the helicopter is still connected to a tower segment when the workers are in the process of screwing bolts in. Why isn't this problematic?

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I suspect it is because the context of construction operations are calendar based. This allows for detailed planning; careful logistics and protocols that suspend flight operations under anything other than 'ideal' conditions. Protocols for rescue operations are designed around an expectation that operations are likely to happen in adverse weather conditions in rough terrain when minutes might be the difference between life and death.

The operations depicted are not uncommon on construction sites (e.g. when mounting rooftop equipment) and there are OSHA regulations for helicopter cranes. https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=...

Google how the canadian navy lands helos on ships in heavy seas. They drop a line, tie the helo to the boat, and literally winch it down onto the deck. The helo pulls against the line so as the deck rises so does the aircraft. Joined by the line, boat and helo move up and down as one. It sounds crazy but really works.

I googled it, but didn't find anything involving a rope. Can you post a link?

https://www.youtube.com/watch?v=tAbm2XDpx9w

You need to see it in HD to see the rope. It's called "recovery assisted landing" or sometimes "hauldown".

The high-tension power-line tower people have a better approach.[1] They have a way to make the tower segments self-align, using a square of cables that fits around angled guides atop the section already in place. So the helicopter puts a section on without help from the ground, and with no workers near the tower. Once the helicopter has cast off, workers climb up and bolt the sections together, and remove the alignment guides.

Ski lift installations are rare, but power line towers go up by the tens of thousands. So the power line people need a way to do this routinely and safely.

[1] https://www.youtube.com/watch?v=YdynKxCloUQ

I'd assume the sequence of states is:

1. Tower segment is hanging from helicopter.

2. Tower segment is in place with pins preventing it from falling over, but can be lifted away by the helicopter.

3. Tower segment is in place with pins preventing it from falling over, and will be released if the helicopter needs to fly away.

4. Tower segment is in place, fully secured by bolts.

The key point here is that under good conditions -- and they only ever do this under good conditions! -- a few pins is all it takes to stop the tower segment from falling over, but they won't stop the helicopter from lifting it off again. Securing the tower with two dozen bolts is only necessary when you want it to stay in place during strong winds and with the added load of the lift cable + chairs.

Good summary but what is not shown here is that once the lifted element "settles" on element below and all pins are in, the helicopter releases the hold immediately.

This is due to the calculated risk of something going wrong: workers on the pole can quickly move around if the unmounted pole starts falling, similar to lumbar can quickly change position when tree falls. With helicopter however, a violent pull of attached line could probably end up with part of helicopter being chunked out of the hull.

There's no escaping the fact that this is a dangerous operation. The guys bolting the segments together can easily sustain a solid knock to the head, or get a finger squashed, etc. The helicopter pilot has a lot of responsibility hanging from his vehicle!

There's a difference between "not white collar safe" and "dangerous".

Deck hand on Indian fishing trawler is more toward the dangerous end. This is pretty in the middle. Very few variables are uncontrolled here. Anything involving confined spaces and chemicals is definitely more on the dangerous end.

In an emergency the helicopter can just drop the load: the pilot can release the hook and fly away. Unlike carrying a casualty, this is unlikely to be anywhere near as dangerous. If the tower is somewhat bolted on, it'll probably stick there long enough for the other bolts to go in. Worst case, it tips over and falls to the ground, but in any case it's unlikely for there to be any injuries.

Drop the load while there are hardhats waiting on the ground below? Uh ya that's probably not happening here.

As far as I know, one of the reasons why dropping the load is considered dangerous is that the line that was holding the load will be suddenly released from high tension, so it will go flying at fast enough speed to injure someone.

Did we watch the same video? There were people below that helicopter quite often. I'm not sure how you'd go about just dropping the pole.

They are referring to releasing the load when it's connected to the ground through the tower. Meaning some bolts are in place, therefore is probably unlikely to tip over.

Medical helicopters usually have a firing bolt/cuter that the pilot controls.

In the event there is a risk to the helicopter due to the winch operation (such as the line becoming stuck in some tress below) - the pilot has the ability to cut the cable to ensure the helicopter is not compromised.

So why does the following manual go to such lengths to prevent the winch line from ever being tied to the ground?

http://www.raf.mod.uk/rafsearchandrescue/rafcms/mediafiles/7...

That is a really good question. Its possible that the helicopter has a quick disconnect on top which simply drops the pole segment although that would seem to endanger the people on the ground.

The use of guide cables/pins was really neat. Assuming the camera is 'real' time (it wasn't sped up for the video) it looks like about 15 seconds between starting to pull the guide cables through to the point where they have two bolts installed. So a pretty narrow window for problems, of course you wouldn't do it when it was windy out either.

Such a mechanism might also endanger the helicopter: releasing a line under high tension will cause both ends of the release mechanism to rapidly accelerate away from the connection point.

And if the connection point being released is on the helicopter... Think about it.

Don't some Navy and Coast Guard helicopters land by getting winched down onto a rolling deck?

Yes it's called RAST or "beartrap". https://www.curtisswrightds.com/products/naval-systems/helic...

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