Date: Thu, 25 Apr 1996 15:21:02 -0700
From: Rand Lindsly (Iconoclast at large)
Subject: Exit Order

Some very interesting information....
If you want to discuss, respond to Bryan
at Skydive Az.

Rand

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Bryan Burke writes:

  Subject: Exit order
  From: The Danger and Training Advisor at Skydive Arizona
  
  This is the text of a memo I put out to our freefly community.
  
  As more people come to Skydive Arizona to participate in skydives with a
  very fast fall rate, a serious safety problem arises. I am soliciting
  comments from the freefly community to determine drop zone policy. Please
  read over the following discussion of the problem and feel free to contact
  me if you have input. The issue in question is this: where should
  skydivers with a very fast fall rate exit? First, last, or in the middle?
  There are several considerations.
  
  From an aircraft operations standpoint, as a general rule whichever group
  will have the slowest climb out should leave first. On a calm day the
  aircraft on jump run covers about 175 feet per second, or one mile in 30
  seconds. Assuming the practical distance that a square canopy open at
  2,000 feet can cover is at most about one mile, that means that the first
  people out would just barely make the landing area from one mile short,
  while the last would be able to make it back from one mile long. In other
  words, all jumpers have to be out in a two mile long jump run or some will
  land out, or a second pass will be required. In time terms, on a calm day
  no more than 60 seconds can elapse from when the first jumpers leave the
  airplane to when the last jumper exits. At busy events with several
  aircraft flying, second passes are not an option.
  
  Let's take a sample jump run, where a large group will take up to 20
  seconds to climb out, a 4-way 12 to 15, 2-ways six to eight, solos five,
  and AFF students about 12 to 15. Our load has an 8-way, two 4-ways, two
  2-ways, a solo, and one AFF. That adds up to between 70 and 80 seconds
  from green light to last out. But it is possible to make it all on one
  jump run if the eight way gets out first, because the pilot figures at
  least 15 to 20 seconds for the first climb out. That brings us back to 60
  seconds from first out to last out, and one pass. Needless to say, we
  don't want to do an extra pass because 2-ways want to leave before 8-ways.
  (If the 2-ways get out first, the pilot can only count on a five to ten
  second climb out. He has to put the light on 1/3 to 1/2 mile closer to the
  dz than he would for the slow climb out.)
  
  That's the timing reason why small groups shouldn't leave first. Now lets
  talk about separation from other jumpers. First of all, anyone who counts
  on vertical separation for safety is out of touch with reality. I see
  people in freefall at 1,500 feet and lower routinely, so just because
  someone plans to open at 2,500 doesn't mean you should bet your life on
  it. Everyone needs to open in their own column of air. Horizontal
  separation is the only guarantee of security. The only real reasons - and
  they are good ones - why students and tandems get out last are that a
  student is more likely to balk or ride down, and that canopies opening
  high can get back from a longer spot. I repeat, horizontal separation is
  the only guarantee of safety. Vertical separation is a nice idea but
  cannot be counted on since a minor loss of awareness or a long snivel will
  eliminate it instantly. 
  
  Now, a quick digression about fall rates. Follow these categories out or
  time their videos if you don't believe me. Light freestylists doing
  routine freestyle do not fall significantly faster than a fast falling
  four way. Freeflyers fall about 30% faster than normal. Small skyboards
  fall fairly fast, if the rider is standing, but big ones fall very slow -
  slower than most RW, usually about the same speed as tandems. Because of
  their exits, they must leave first, and because of their complex emergency
  procedures, they must pull high. Leaving first and pulling high defies
  conventional wisdom, yet not once have we had a problem with slow falling
  skysurfers getting out first and pulling at 3,500. In fact, as long as the
  first person pulls higher than the break off altitude of the following
  group, they are a contribution to safety, not a detriment, provided
  adequate time was left between groups at the exit.
  
  We do have a recurring problem maintaining safe separation when the
  freeflyers get out first. Typically a freefly pair will have a forty five
  second freefall and open at 2,500 to 3,000 feet. Let's imagine that they
  are followed by an RW group that has a 10 second climb out. Now, let's say
  you are a freeflyer jumping a Stiletto. A Stiletto (assuming a 30 mph
  forward speed, which I can document is a reliable figure) covers about 45
  feet per second on a calm day. If you open 30 seconds (shorter freefall
  plus exit separation time) before the RW group leaving after you and turn
  directly towards the dz (which you will, since otherwise you can't make it
  back from getting out first unless you cheat on the climb out, spot for
  yourself, and force the pilot to go around, which REALLY pisses us off) in
  that 30 seconds you will cover over 1,300 horizontal feet. This would put
  you about 400 feet from the center of a group leaving the plane ten
  seconds after you. In theory, that would just barely be enough, except
  that a good tracker can do about 70 feet per second, so if they track
  towards you for six seconds they are right on top of you. Furthermore, a
  modern canopy descends about 800 feet in 30 seconds (also documented) so
  if one of you pulls at 3,000 to get back from a short spot, for camera
  effect, or whatever - by the time you are at 2,000 you are well into the
  danger zone of the group that followed you.
  
  So far, the big sky theory has taken care of us most of the time but I
  have heard of a couple close calls and more than once found myself
  directly over the freeflyers if they leave first. Having seen the
  consequences of a freefaller/canopy collision more than once, I want to
  minimize the possibilities. And they go way up as soon as we add wind to
  the exercise. Here's why. In a 30 mile per hour breeze, the plane only
  covers 130 feet per second, instead of 175. In ten seconds of exit
  separation, the airplane only covers 1,300 horizontal feet instead of
  1,750. Worse still, the RW group is in freefall for a longer time, and
  consequently gets blown further. Let's say the freeflyer is in freefall
  for 45 seconds, and the RW for 70. In 45 seconds you get blown nearly
  2,000 horizontal feet. The RW blows just over 3,000. That leaves only 300
  feet of horizontal separation without taking tracking or canopy movement
  into account! Make the winds 50 miles per hour, and the RW group drifts
  over 1,800 horizontal feet further than the freeflyers! Meanwhile, in ten
  seconds the plane only covers 1,100 feet. A 20 second exit separation will
  still have the RW group opening 400 feet from the freeflyers, not counting
  canopy movement or tracking! 
  
  Having opened right over freeflyers before, and having just heard from
  several expert skydivers who narrowly missed  freeflyers, and having
  watched RW groups blow over freeflyers on windy days, I think we have a
  problem. You might say, make sure the groups leave longer between exits.
  Well, we do tell them, but if they wait 20 seconds instead of ten, that
  still doesn't solve the problem because Freeflyers still fly under them
  under canopy. So for fast fallers your only choice if you want to get out
  first is to always fly perpendicular to the line of flight for 30 seconds
  before turning towards the dz. While I am confident most of you are aware
  enough to do this, it brings us back to the original time on jump run
  problem. Basically, Skydive Arizona isn't willing to do a lot of second
  passes just so freeflyers can get out first. 
  
  Getting out last except for students solves virtually every problem. You
  control the horizontal separation, so you can ensure you won't be
  overtaking anyone in freefall. The windier it gets, the safer you are
  because you get extra separation by having slower fallers blow away from
  you. Students take long climb outs and pull real high, so no problem
  there: just get open and fly off the wind line for a few seconds to be
  clear of them in the unlikely event that they are in freefall at 2,500
  feet.
  
  As for the argument that the canopy separation is necessary in the landing
  area, I don't buy it. Opening over the top instead of short, you can
  spiral down to make sure you get on the turn around loads. As for
  congestion at the landing area, no one else on the loads seem to have any
  problem, although you may not always get to land right by the fence.
  
  Please give this some thought. Unless one of you gives me an extremely
  convincing reason why you need to leave first, such as a safe spot for the
  skyball, I will make it standard policy that exit order will always be
  
  	1) skysurfers
  	2) freefall groups, largest to smallest, regardless of fall rate

             (Note (Skr): I believe this is a typo since the real rule is: )
             (2a - relative work groups, largest to smallest and then      )
             (2b - fast fall groups, largest to smallest and then          )
             (3  - AFF and tandems                                         )

  	3) AFF and tandems, plus any other very high openings. The main
  reason for high openings leaving last is not separation, it's that they
  can make it back from a long spot!
  
  Thank you,
  
  Bryan Burke
  DZ manager/Safety and Training Advisor
  
  So, that's the current thinking here. Yes, we have considered jump runs
  that are crosswind, offset crosswind, parabolic, and semi parabolic. There
  are good practical reasons why we don't use these, so don't bother
  bringing that up. And if ANYONE still thinks ground speed doesn't matter,
  they can e-mail me (skr/delete/spam) for a virtual flogging instead of
  bringing it up again on the public forum. Quit with the hypothetical
  boats, rivers, tractors, and sheep and get out and ride a few airplanes.
  Sit up by the GPS on a windy day to get in touch with the fact that if you
  put 20 people in the air in half the usual space you are greatly
  increasing the probability they will run into each other. However, if you
  persist in believing the sun goes around the earth and only airspeed
  matters, I will record your name and you will not be allowed to jump here
  until buying me a punitive case of green bottles and agreeing to wear a
  large scarlet A on your jumpsuit so everyone will know you are a moron and
  can plan accordingly.

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