How to determine exit separation times

[billvon 3,120]

Since this has come up a few times, I figured I'd mention some easy tricks to use to figure out separation times.

First off, decide how much distance you need. For larger groups (larger than 4-6 way) or novice freeflyers or _very_ novice RW groups, 1000 feet is a good separation at opening time. This lets people track a good distance (400 feet) and still have some separation when they open.

For smaller groups (an experienced 4-way team, experienced 2-way freelfly) you can leave 500 feet. For solos 500 feet is usually OK as long as care is taken not to track or backslide too much.

Using these distances, you can put 6 big way groups, or 12 smaller groups, out over the course of a one mile jump run. This is usually plenty for even large planes - a CASA can only hold 5 6-ways.

How do you tell how long this is in time? If you can see the groundspeed indication on the GPS, it's pretty easy. Multiply that number by 1.5 and you have your speed in feet per seconds. That makes it easy. At 200 fps, wait 5 seconds and you have 1000 feet. (This makes some common assumptions about winds at opening altitudes.)

If not it's a little harder. If you know the windspeed at altitude, and jump run is into the wind, then you can do the math. The plane's airspeed indicator gives you IAS, or indicated airspeed. Multiply by about 1.3 to get true airspeed at 14000 feet. Subtract winds-aloft. Multiply by 1.5 to get feet per second. Since winds aloft don't change too quickly, you can do this once at the beginning of the day and have a good idea for the number for the rest of the day.

A final way is to just look out the door. Pick any spot you can see. Wait until that spot moves 1000 feet relative to the plane and go. Or wait until that spot moves 500 feet and give a count and go. It's pretty foolproof because you are actually seeing your ground separation. In areas where there are a lot of 1000 foot wide fields it's easy; in open deserts it's a lot tougher.

[Michele 1]

Cool. Thanks, Bill...

Now, can you explain how to determine 1000 feet if you've never done it before?

Ciels and Pinks-
Michele

~Do Angels keep the dreams we seek
While our hearts lie bleeding?~

[billvon 3,120]

>Now, can you explain how to determine 1000 feet if you've never
>done it before?

Find something on the ground that's 1000 feet long and use that; I think the paved part of the Perris runway is about 2000 feet, so half of that would work. The entire runway is about 3600 feet, so you can divide the whole thing visually into 4 parts if you want to do that. (Ask Jack for the exact distance.) The student circle looks like it's about 500 feet across.

[freeflir29 0]

Quote

can you explain how to determine 1000 feet if you've never done it before?

Thats what we call a "Yardstick" in the Forward Air Control business. We used to pick out something like a runway, section of road between 2 obvious intersections, or the distance between two easily recognizable points. Then use that known distance to move the pilots eyes around the target area. Of course, you want to pick something that is close to the jump run so you can easily refer to it. Just get a map, like off "Terra Server" or find someone that has the area on a GPS map disk. Find your 1000ft yard stick in the area and you're set.