Re: [Deimian] Canopy Collision SDAZ 30 December 2016

[Pendragon 1]

You can manage that easily enough by leaving the appropriate amount of time between groups in the door - and for the first RW group after the freeflyers to leave a little extra time (which usually happens anyway given the inevitable faffing! )

It's far more difficult to manage lack of vertical separation once everyone is under canopy, and where the smaller (faster) and larger (slower) canopies are mixed across the various groups

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BASE #1182
Muff #3573
PFI #52; UK WSI #13

[Deimian 43]

Pendragon

You can manage that easily enough by leaving the appropriate amount of time between groups in the door

Appropriate in this context means longer than the other way around. Which would imply more off site landings for the last ones in the load, which depending on the DZ might imply more chances of getting injured. And that is assuming that people are able to wait enough time.

[Pendragon 1]

Hardly.

If the aircraft run-in is fast, then differential wind drift isn't a problem because the wind down jump run is minimal: there is no real advantage to putting RW flyers out first. If it's strong, then run-in would be slower and the gaps would need to be longer - but you wouldn't be so far from the DZ. Also, due to drift, RW flyers will want to be deeper than Freeflyers.

Furthermore, take an example where it's 10 seconds between groups and freefly speeds imply 45s freefall rather than 1min RW. Deployments would be 25 seconds apart: the preceding group would be far away from their opening point by that point.

Besides, what about a go-around if you get too deep? Skydivers still retain a personal responsibility to get out in roughly the right place to be able to make it to a suitable LZ.

Putting RW groups out before freeflyers gets more skydivers opening on the same level, which in turn increases the chances of collision under canopy, and is done to solve another (largely theoretical) problem that can be addressed in other ways.

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BASE #1182
Muff #3573
PFI #52; UK WSI #13

[DJL 232]

Pendragon

Hardly.

If the aircraft run-in is fast, then differential wind drift isn't a problem because the wind down jump run is minimal: there is no real advantage to putting RW flyers out first. If it's strong, then run-in would be slower and the gaps would need to be longer - but you wouldn't be so far from the DZ. Also, due to drift, RW flyers will want to be deeper than Freeflyers.

Furthermore, take an example where it's 10 seconds between groups and freefly speeds imply 45s freefall rather than 1min RW. Deployments would be 25 seconds apart: the preceding group would be far away from their opening point by that point.

Besides, what about a go-around if you get too deep? Skydivers still retain a personal responsibility to get out in roughly the right place to be able to make it to a suitable LZ.

Putting RW groups out before freeflyers gets more skydivers opening on the same level, which in turn increases the chances of collision under canopy, and is done to solve another (largely theoretical) problem that can be addressed in other ways.

Sorry man, but your statements don't reflect the consensus of industry knowledge. I don't even know where to start but there are plenty of threads on this website that go into this issue in immense detail.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[Pendragon 1]

I know there's a bunch of threads on it. In my belief, whilst the concept of freefall drift is correct, the proposed solution (fast fallers out after slower fallers) is wrong for a variety of reasons - and there's a whole bunch of DZs that agree with me. My home DZ is one. To infer that it's a closed discussion is rubbish. The skydiving industry is full of opinion that's constantly recycled.

Putting freeflyers out after RW flyers out of a larger capacity skydiving aircraft (Twin Otter, Grand Caravan etc) increases the chance of large numbers of skydivers deploying at the same time - and it's pretty obvious to conclude that must be increasing the risk of collision under canopy. Correct separation on exit can be managed by leaving an extended gap between freeflyer groups (out first) and the RW groups when upper winds demand it, whilst maintaining vertical separation between groups and minimising the risk of canopy conflict.

--
BASE #1182
Muff #3573
PFI #52; UK WSI #13

[pchapman 261]

Pendragon

correct separation on exit can be managed by leaving an extended gap between freeflyer groups (out first) and the RW groups

Well the question is, to what degree would the industry sustain it? Longer passes, more go arounds. Maybe you could start a thread about the DZ's who do the 'reverse order -- but with larger gaps'.

I mean, you're right in a sense. If the Otters and Caravans of this world dropped 5 jumpers max per pass, 2 minutes between passes, we'd have all the separation we had back when we only jumped C-182s. And everyone could swoop every jump without restriction. Not sure about the fuel burn though....

[EDIT : Ok, this chunk of the thead did get moved to S&T!]

[DJL 232]

How do you determine your exit separation between FF and Belly? If you wouldn't mind, be specific with an example using ground speed and winds aloft.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[billvon 2,391]

Quote

I know there's a bunch of threads on it. In my belief, whilst the concept of freefall drift is correct, the proposed solution (fast fallers out after slower fallers) is wrong for a variety of reasons - and there's a whole bunch of DZs that agree with me. My home DZ is one. To infer that it's a closed discussion is rubbish. The skydiving industry is full of opinion that's constantly recycled.

While that's true (that skydivers are opinionated) there are things that are fairly settled. Novas are unsafe, you should check the spot before you exit, the 45 degree rule doesn't work, blast handles shouldn't be used, RSL's and AAD's are very good ideas (especially for students and low time jumpers) you shouldn't jump through solid cloud decks etc. For every one of those things, someone's going to say "but . . . but . . . ." - but overall those things improve safety for everyone.

Quote

Correct separation on exit can be managed by leaving an extended gap between freeflyer groups (out first)

Yes, it can be. In practice it is not maintained. Almost no one is willing to stand in the door for 30 seconds as the plane gets farther and farther away from the spot and while everyone else on the plane is screaming for them to go. And even those who are generally count faster in those situations. That's why most DZ's use the foolproof fast-fallers-out-last method.

[tsalnukt 1]

It is far easier to manage vertical separation than horizontal separation.

People under parachute have a duty to pay attention to where everyone is in the sky with them. It is also their responsibility to create their own vertical separation in order to land safely.

When groups are at the mercy of FF drift it is not as simple to say, "just leave more time."

This has been debated since Freeflying was invented. It has been widely accepted that it is generaly/more often/best practice/to put flat flyers out first followed by freefly. Some places do it differently, yes, but I have yet to hear a decent enough argument to stray from the 'norm'

Yeah dude, there are some exceptions but I am speaking generally.

and I'm also not talking about moving groups and wingsuits.

[sammielu 3]

IMO it's less risky to have all groups opening at the same time (vs 25 seconds later). Sure there are more obstacles in the sky and there is a possible mathematical higher chance that we will hit each other - but canopy collisions happen when we're all heading to the same place for landing, not due to chance.

Everyone open at the same time and altitude gives us more time to see each other, more time to establish vertical separation and to stay out of each other's way. Staggering opening times with the example of FF out first with huge separation between groups means I'm less likely to see the other canopies and more likely to be surprised or in their way.

[DJL 232]

It seems to me that with openings occurring anywhere between 2000 ft and 4500 ft and varying canopy speeds that rearranging FF vs FS to coordinate vertical separation for canopy traffic in the landing pattern is futile.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[Mark4 0]

IMO, if there is only one aircraft flying then you should be able account for all the canopies and create enough vertical separation whatever order you get out.

The issue with Eloy is that it's pretty usual for multiple aircraft to be flying. Even with flat flyers out first, people out of the following aircraft are likely to catch and overtake the stragglers from the previous load. Your solution will exacerbate that problem by decreasing the time separation between loads.

[skytribe 16]

A collision occurs not just through lack of vertical separation. It requires 3 things to happen vertical separation, horizontal separation and time. If only two of these occur.

So fly through the same spot in 3 dimensional space 30 seconds after someone - no collision.

Fly at the same position horizontally at the same time but 1000 ft vertical separation - no collision.

Fly at the altitude but 1000 ft horizontal separation at the same time - no collision.

We don't determine exit order based upon canopy sizes - and how would we when you have jumpers in same group with small and large canopies. Neither do we determine that all jumpers open at the same time on larger aircraft. The 1st group are opening before the last group may have even exited.

The exit order is a rough determination to avoid as much conflict as possible. ie. people drifting over other groups due to freefall drift (putting them in same horizontal area) and also opening altitudes (creating vertical separation for opening).

However once opened it may be difficult - if impossible for a later jumper to remain above earlier exiting jumpers. Due to size wing loading. So vertical separation will be an issue.

With all jumpers converging on the same area - the 20 yards square closest to the spectators/beer line/packing area etc. This is the problem as ultimately the horizontal, vertical and time components are all converging to a very small area.

The simple solution is for jumpers to be aware of others and fly predictable patterns (Doh !!!!) and for dropzones to separate high-performance landing areas from general landing area (As USPA member DZ have agreed) and to encourage full use of the landing area not just the 20 yards square closest. This maximizes the horizontal area that people are in.

I look at this incident and see issues with both jumpers but the upper jumper had ample opportunities to avoid a collision. The lower jumper was visible albiet a little bit unpredictable on final - the higher jumper could have made decisions earlier on to land a little further out rather than in the high making a choice that they would overtake the bigger slower lower canopy close to the ground and have both jumpers landing in the same area at roughly the same time. (All 3 components converge).