Exit SeparationBy JC Fallo on 2013-12-23
On Saturday October 26, 2013 there was a near canopy collision by experienced jumpers. There were several factors which may have contributed to this event. I feel that a lack of understanding of exit separation was a major contributor.
The winds of the day were posted: 24 knots at 12,000 feet, 22 knots at 9,000 feet and so on. I was on the first load, first out with a three way formation. I turned to the group behind me and asked for 10 seconds of separation. The response was “Why? That’s a lot of time.” Both of these jumpers have around 500 jumps. One has been jumping for over 10 years, the other for 9 years. One of these jumpers was part of the group that was involved in the near collision later that day.
The incident: a near miss at opening time between two skydivers we will call jumper 1 and jumper 2. Jumper 1 left the plane first as part of an 8 way relative work group. Jumper 2, as part of a less experienced 2 way relative work group, left next with 5-6 seconds of separation. The second group left the plane flipping and having fun then got stable and continued a normal relative work dive. Jumper 1 was oriented to track up the line of flight decreasing his separation from the 2nd group. Jumper 1 further decreased his separation from the 2nd group by continuing to fly his canopy up the line of flight for 12 seconds. At which time he noticed one of the jumpers from the two way open pretty close. He then started looking for the other jumper from the two way group (jumper 2) and started a right rear riser turn. At this point, jumper 2 under a still deploying main fell past and within 20 feet of Jumper 1. Here is a link to the video of the opening sequence. This video was taken with a gopro camera and the jumpers in it are closer than they appear.
1. The initial flipping on exit of the second group may have had the two way in an orientation to slide down the line of flight and therefore contributed to the second group moving towards the first group. If so this would have been only momentary and not a large contribution. 2. Jumper 1 decreased separation by tracking up the line of flight. Although a contributing factor to the lack of separation, this was an appropriate action as on groups of 2 or larger all jumpers should track away from the radial center of the formation regardless of whether that puts them tracking up or down the line of flight as this will give them the greatest amount of separation from the members of their own group which would pose the greatest danger of collision at opening time. Jumpers tracking up the line of flight away from larger groups should always be aware of their direction and not “over track”.
3. Jumper 1 was flying a small fast canopy, continuing to fly up the jump run, holding into the wind with his brakes still set. This decreased separation with the following group. Every skydiver should know where jump run is planned to be before boarding the aircraft. All jumpers should upon opening orient themselves as quickly as possible to fly perpendicular to jump run at least long enough to ensure the groups before and after them have opened.
4. There is no question that mistakes were made on both sides, but there should also be no question that there would have been greater separation with 8 seconds at the door as called for in the chart below. In this case an extra 2 seconds separation would have equated to between 224-252 more feet of separation.
We are also reminded of another incident we had a while back. Jumper 1 on a hop-n-pop leaves opens and flies up the line of flight. Jumper 2 leaves with about 5 seconds of separation and tracks down the line of flight. Jumper 2 tracks through Jumper 1’s canopy ripping it in half. Luckily neither one was injured.
Another example is the video posted Iloveskydyving.org. This video clearly shows the following group giving 8 seconds of separation. Judging from their flying style it is obvious they are very skilled and not likely sliding through the air unintentionally. However, they still end up opening dangerously close to the group before them. We don’t know about what mistakes the group ahead may have made if any, but consider the problem may have been enough wind to dictate more time for adequate separation.Close Skydive Canopy Collision
As Jumpers, we must have a basic understanding of the effects the ground speed of the aircraft has on the amount of time that we need to allow for the same amount of separation. I have heard swoopers say that the only good wind is no wind. They are saying this because in a no wind situation all things remain constant and consistent. Likewise at altitude if the aircrafts speed relative to the ground was always the same we would always give the same amount of time for the same amount of separation.
What is adequate separation? In distance, the number I was taught is 1000 feet from center of formation to the center of the next formation for small groups. This number increases up to 2000 feet or more for groups of 8 or larger. Consider two 4 way groups lined up perfectly with jump run which will result in a jumper from each group tracking directly at one another. This allows each jumper to track 250 feet with 500 feet still left between them. The Skydivers Information Manual goes farther and recommends 1500 feet of separation for small groups and solos.
What is adequate separation? In time, that will depend on the speed of the aircraft and the wind the aircraft is encountering. In other words, it will depend on the ground speed of the aircraft on jump run. See the chart put together by Phil Litke. These numbers should be considered minimums for 1000 feet of separation to be doubled for following groups of 8 or larger.
Here are some examples of experienced jumpers and Tandem instructors giving between 13 and 31 seconds exit separation when the winds were very high. Also consider that these instructors are, for the most part, giving such separation on solos and 2 ways. As stated earlier, larger groups should be allowed more distance and therefore more time.
We are all concerned about hosing the guys in the back of the plane by taking too long. I am not advocating that we give more time unnecessarily. If the speed of the aircraft dictates a certain amount of separation between groups this should include your set up, climb out, and count. I am not suggesting anyone taking longer than the conditions call for as this would create different problems such as people landing off, unnecessary go arounds, and wasted fuel. Most of us have had experienced people in the back of the plane yelling for people to hurry up and get out. This is because they feel you are taking too long to exit and will end up with them getting too far from the airport to make it back. If the winds are strong enough to necessitate a certain amount of separation then likewise the plane is moving slower relative to the ground, Freefall drift will be greater, and the acceptable opening spot may be farther from the landing zone.
Every skydiver should know the acceptable exit and opening points for the conditions of the day. Many people land out without trying to make it back because it looks father than they are used to seeing. Without looking at the winds and calculating the opening spot before you go up you have very little chance of knowing for certain whether you will make it back, especially as the winds get higher and the spots get longer.
One thing that you cannot control when you leave the aircraft is what the group behind you will do. We all should look after each other. By knowing how much separation to give you are looking out for yourself and the group ahead of you. Don’t be afraid to confirm with the group behind you that they will also wait an appropriate amount of time before exiting.
Recommendation to reduce the likelihood of these type incidents:
1. Phil Litke’s exit separation chart should be posted near the jumper closest to the pilot for easy reference on jump run.
2. Upon turning onto jump run after the cut, the pilot will inform the close jumper of the aircrafts ground speed. This close jumper will look at the chart and determine how many seconds are needed. The number of seconds separation to give will be passed down to all jumpers on the load.
3. If this turns out to be too great a burden for the pilot we should install a GPS unit near the door so that the jumpers can determine ground speed themselves and make all jumpers on the load aware of how many seconds separation to give.
We all have to get on board for this to work. Our landing direction at our dropzone is mandatory. This has been the best proactive step towards promoting a safe landing area and smooth landing pattern I have seen since I have been with my dropzone. The chaos of 22 jumpers landing in every direction in light and variable winds seems to be behind us. Each of us knows no one landing against the assigned pattern will escape a talk with a staff member. Exit separation is as important a safety issue and should be treated with the same respect. It needs to be a matter of policy for consistency.
There is not an original idea on this subject here. This is the best knowledge which my mentors passed on to me. Here are a couple of related articles which go into greater depth about these concepts and solutions to these problems. I hope it is clear we must go about things in a more thoughtful and consistent way to avoid similar incidents in the future.http://www.dropzone.com/safety/Exit/Exit_Separation_Revisited_628.html
I prefer the "watch for the 45 deg. angle" method
Your spotter for your load watches the load before and when they are at a 45 degree angle behind the plane it's clear to climb out. In low winds this will be sooner than in higher winds.
|To the 45 degree rule people: we all probably prefer to employ the methods we learned first and are most familiar with. That doesn't always make them the most reliable methods. The article ( http://www.dropzone.com/safety/Exit/Exit_Separation_Revisited_628.html ) which I linked to near the end of my article goes into far more technical detail than I wanted to get into as to why the 45 degree rule is not a reliable method. I wanted to keep things simple and accurate for all levels of jumpers.|
|Great info! I've written a simplified version on how to calculate Exit Separation on my blog here: http://www.melissaairheart.com/exit-separation-time-really-matters/|
|*Miss Melissa, I also try to teach my students how to gather the necessary information and the education to think for themselves - to use the winds forecast to make an educated guess about ground speed of the aircraft and therefore separation. I feel this is a good exercise. However, I feel it is inadequate in practice due to the many factors which can change the actual ground speed of the aircraft such as incorrect forecast, winds changing over the course of the day, jump run being flown not directly into the upper winds. Unfortunately many jumpers are not interested in doing math when they arrive at the dropzone, especially some of the more experienced jumpers. With 23 people on an otter load, I do not want those I care for relying on someone's best guess of conditions that may have changed, much less the jumpers that don't bother. The key is getting ground speed from the pilot after the cut every load. This information is right in front of him on his GPS. It is the only accurate way which takes into account any changing conditions or off heading jump runs. You stated it very well in your Blog post, "Seconds Count." That statement couldn't be more true. As in my first example, the 2 extra seconds called for could have made the difference between having some fun and two jumpers having a very bad day. Most jumpers will do what is asked of them to insure safety. The rest will comply if it is a matter of policy with consequences. Without a policy and everyone on board we will just be waiting for the next incident. Last weekend we had a 23 knot ground speed at 14,000 feet. There were 20 jumpers on the otter, multiple groups and each group gave 30 seconds with no go-around. No one had any trouble making it back to the dropzone.|
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More articles in this category:
- Exit Separation - by JC Fallo (Posted: 2013-12-23)
- Launching 2, 3 and 4-Way Stars for Recreational RW - by Ed Lightle (Posted: 2010-09-14)
- Exit Separation Revisited - by Bill von Novak (Posted: 2006-05-10)
- Essay on Exit Order - by Bryan Burke (Posted: 2003-08-19)
- Another Look at Descent Kinematics - by Winsor Naugler III (Posted: 2003-08-19)
- Freefall Simulation Program - by John Kallend (Posted: 2003-08-19)
- Wind Drift & Exit Order Graphic - by Tim Wagner (Posted: 2003-08-19)