How to Determine Your Exit Point
- Obtain Winds Aloft Forecast. Ask your instructor, manifest or the pilot what the winds aloft forecast is for the day. If they don’t know, call Flight Service (800-992-7433). Tell them you are a skydiver and would like the winds aloft for your area (Stewart, Newburgh area for the Ranch). Ask for the winds at the altitudes that will be affecting your skydive. If the jump is made from 13,500 ‘, they are for 3,6,9 and 12 thousand feet for the time period of skydiving, usually from 8 am to sunset. The Weather Briefer will give the direction the wind is blowing from and the wind speed in knots that corresponds with the requested altitudes (eg. 280- 18 knots).
- Determine (Compass) position of dropzone. You need to relate these winds to your position on the DZ. If the wind is forecasted from 360 degrees, it’s blowing from the North. If the wind is forecasted from 180 degrees, it’s blowing from the South, etc. and so on. Most of us don’t carry a compass so we need to use something else as a point of reference. At Silicon Valley Skydiving we can use the runway as a reference point. The paved Runway has a heading of approximately 300 degrees (looking towards the mountain) and 120 degrees (looking away from the mountain). The Ranch also has a grass runway which is aligned 90 degrees and 270 degrees or approximately East-West .
- Determine Line of Flight for jump run.When you look at the winds aloft report the wind direction usually varies at 3, 6, 9, and 12 thousand feet. Average the wind direction from the winds aloft report and the surface wind. Use that average as a guide.
1330 / 5 = 266 Degree
- Determine Freefall Drift and Exit Point. To determine the exit point you need to approximate freefall drift. First, average the wind speed between 3000 and 12,000 feet and assume an average freefall time of 60 seconds. Plug the information into the following equation:
Freefall Drift=Average wind during freefall/duration of freefall x 5280 feetExample:AltitudeVelocity(knots)3000156000229000281200035100 / 4 = 25 knots25 knots/60 seconds x 5280 feet = 2,165 feetRounded to 2,000 feet of approximate Freefall Drift
With this information I know if I exit the aircraft on the proper Line of Flight approximately 2000 feet upwind of the target when I open my parachute 60 seconds later I should be right over the target.
- Locate a reference to estimate distance from the target. Normally , a good reference is to use the runway as a ruler. At Silicon Valley Skydiving in Gardiner, NY the runway is approximately 2400 feet long or about a ½ mile. Use a dropzone photo, plot your wind line as well as the nearest and furthest exit points that allow you to safely land at the target.
- Determine the exit window. How far upwind of the target is too far? Apply this information to an entire load of skydivers. You want the first and last to exit the aircraft to land at the target without being cut short or having to take a second pass. Ideally, we like to open upwind of the target, but how far? This depends not only on the wind but also opening altitude and the glide ratio of your parachute. Example: If you are open at 4000 feet with a normal student parachute, your descent rate is approximately 1000 feet /minute. This gives you a 4 minute canopy ride. The glide ratio of a typical student parachute is about 2.5 to 1 which means for every 2.5 feet you move forward you descend approximately 1 foot down in a zero wind condition. Referring back to our example of the winds, the average wind from the surface to 4000 thousand feet is about 15 knots. For our landing pattern, we like to be 500 feet high, opposite our target, on an imaginary line that runs perpendicular to the line of flight before turning downwind. This means we have about 3500 feet or 3.5 minutes to get to our 500 foot maneuvering position for the downwind leg. 15 knots/ hour which is our average wind speed plus the 20 knot canopy speed = 35 knot/hour ground speed if we open up on the wind line and fly right back to our 500 foot position opposite the target. 35 divided by 60 = .58 miles /minute x 3.5 = 2.03 miles or 10,718 feet. Now add the Freefall Drift of 2200 feet to 10,718 feet for a total distance of 12,918 feet or about 2.5 miles. In theory, using this example a Skydiver could exit the aircraft on the Wind Line about 2.5 miles upwind from the target and make it back to the target . If there is not a Main Frame computer to figure this out try rounding numbers off to make them easier to work with. For example, if your drifting in a column of air that’s moving at an average speed of 60 knots and you do this for 60 seconds (normal freefall delay) freefall drift will be about 1 nautical mile. If your drifting in a column of air that’s moving at an average speed of 15 knots (1/4 of 60 ) and do this for 60 seconds (normal freefall delay) freefall drift will be about ¼ mile or 1320 feet,.and so on…Use this same method when figuring out the maximum exiting point.
– Remember always check the winds and weather.
– Always calculate Freefall Drift.
– Use the Drop Zone photo to plot Wind Line for Jump Run.
– Use the Drop Zone photo to plot Exit points.
– Plan on deploying your parachute faced into the wind whenever practical, if you don’t, you could end up flying downwind wind of your target at over 40knots/hour usually making it impossible to get back to the original intended target area.
– Use the Drop Zone photo to plan Backup Landing Areas in case the Exit Point or Spot is bad!
So now you can figure out where to Exit the Aircraft. Here are some tips for Exiting.
- Exit the aircraft Upwind of the target and along the Line of Flight when practical.
- While checking for the exit area (Spotting) the plane should be flying straight and level. This can be determined by checking the relationship of the Wing to the Horizon.
- Belly Flyers should exit First , the larger the group the earlier the exit order.
- Free Flyers should exit after the Belly Flyers, they fall faster and have less freefall drift, the larger the group, the earlier the exit order.
- The stronger the Winds Aloft, the more time that is required between skydiving groups.
- The larger the skydiving group, the more time that is needed between groups.
- Avoid long Tracks up or down the Line of Flight. This could result in freefall collisions between groups that exited before or after you
- If opening altitude is going to be higher than normal (3000 feet) exit order needs to be adjusted to allow the higher opening groups to exit later.
- On a cautionary note, whenever the winds are light and variable at the Surface as well as Opening Altitude at Silicon Valley Skydiving we will sometimes exit the aircraft Downwind and Upwind of the Target. This is done to reduce the number of passes that the aircraft makes as well as reduce the possibility of dropping skydivers onto the skydivers that exited on the previous pass. If you open downwind of the target, do not head straight back to the target until you’ve seen the group that exited After you open up. If you do head straight back to the target you may end up flying in to the airspace of the following and experience a catastrophic collision.