How Skydiving Works


Skydiving Image Gallery Skydivers in formation over Hawaii. See more pictures of skydiving.
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Skydiving is one of those things that you probably see­ all the tim­e. Pretty much every major soft drink has done a commercial with skydivers in it. Lots of action films feature skydivers. Skydiving appears in reality shows and is a mainsta­y of the military.

And it's easy to s­ee why. The sport definitely has an edge to it. There is something about leaping from a plane and falling through the air at 120 miles per hour that really gets people's attention.

­Have you ever wondered how skydiving works? What kind of equipment do skydivers use? How safe is skydiving as a sport? How do you become a skydiver and how much does it cost?

In this article, we will answer all of these questions and many more. The next time you watch someone skydiving on TV, you will have a whole new appreciation for what's going on!

Let's start by looking at what a typical jump is like for an experienced skydiver.

A Typical Skydiver Jump

There are thousands of experienced skydivers in the United States who have hundreds or thousands of jumps under their belts. They typically own their own parachutes, pack their own parachutes and skydive every weekend. A typical jump for this kind of enthusiast goes something like this:

  • The skydiver puts on his/her jumpsuit and parachute. Typically, another jumper will check the straps and the rig to make sure everything looks OK.
  • The skydiver gets on the plane. Depending on the size of the plane, there might be up to 20 jumpers sharing a ride.
  • The plane flies to the jump altitude. A typical altitude might be around 13,000 feet (4,000 meters), which gives the jumper about 60 seconds of free fall -- the term used in skydiving to describe the moment the jumper exits the plane. It is possible to go as high as 16,000 feet (4,900 meters) without supplemental oxygen, giving the jumper up to 75 seconds of free fall.
  • When the plane is lined up properly over the jump site, the skydivers jump out of the plane.
  • At about 2,500 feet (760 meters), the skydiver throws out a pilot chute, and it deploys the parachute. In the case of tandem skydiving, a drogue chute is used to regulate the fall rate.
  • The skydiver steers the parachute to line up for the landing, and lands.

We've used a lot of terminology here -- let's look at some of the actual equipment that a skydiver uses.

Skydiving Equipment

A parachute rig used by any sport skydiver today has six basic parts:

  • There is the parachute itself, also known as the main canopy.
  • There is the pilot chute -- a small (12 to 18-inch / 30 to 45-centimeter diameter) parachute that the skydiver uses to pull out and open the main canopy. The skydiver throws out the pilot. It catches the wind and pulls on a 7 to 10-foot (2 to 3-meter) long piece of nylon webbing (known as the bridle). The bridle pulls the main canopy out of the container so that it can inflate.
  • There is a second parachute, known as the reserve, that is available in case the main canopy fails for some reason. The main canopy might not come out of its container, it might not inflate properly, it might get tangled in its lines, and so on. If it fails, the skydiver can cut it away and deploy the reserve.
  • There is the container, which is a backpack that holds the main chute and the reserve chute. The container also includes thick shoulder and leg straps that keep the container firmly attached to the skydiver.
  • There are the lines, which run from the parachute to the container through a pair of thick straps called the risers. Most modern parachutes have five sets of lines called the A-lines, B-lines, C-lines, D-lines and brake lines.
  • There is the AAD, also known as the automatic activation device. If something goes wrong -- for example, the skydiver passes out or gets distracted -- the AAD will automatically release the reserve parachute at about 750 feet (230 meters).

Just about everyone today uses ram-air canopies. This type of parachute is square or rectangular and is made completely out of lightweight nylon. There is a top and bottom sheet of nylon, and then a set of fabric ribs between them. The ribs divide the parachute into a set of individual cells. Air enters, or rams, into the front of the canopy to inflate the cells and give the parachute an airfoil shape. This shape makes the parachute act like a wing (see How Airplanes Work for a description of wings). Instead of coming straight down like you would with a round parachute, you actually glide in with a ram-air chute.

You also have a lot of control with a ram-air chute. You have two sets of lines connecting to the rear edge of the parachute on the left and right sides. You control these lines with two handles called toggles. When you pull on the left toggle, you lower the back part of the left side of the wing. This causes the left side of the parachute to slow down, so you turn to the left. You can turn to the right in the same way. If you pull both the left and right toggles together, it slows the whole wing down and acts like a brake. This allows you to flare to a stop during landing. This level of control makes extremely precise landings possible.

Next, we'll look at how a parachute is packed.

Packing a Parachute

A parachute is like a little nylon machine with all of the parts designed for light weight, durability and as few problems as possible during deployment. Considering the speed at which a skydiver is typically free falling -- about 120 mph (193 kph) -- and the lack of options if something goes wrong, a parachute rig needs to be incredibly reliable.

There's a lot of popular interest in the fine art of parachute packing. It has all the elements of great drama -- a person is folding a piece of fabric and stuffing it into a very small bag, and there's another person whose life literally depends on that fabric unfolding properly. When a parachute deploys, it needs to:

  • Unfold reliably, so the entire parachute inflates correctly
  • Unfold consistently, so the skydiver knows what to expect when the parachute opens
  • Unfold without twisting, so the skydiver is facing the right direction after deployment
  • Unfold without tangling the lines
  • Unfold at the right pace - If it unfolds too quickly, it can hurt the skydiver and/or damage the equipment.

The best way for a skydiver to make sure that all of this happens is to pack the parachute carefully and follow the manufacturer's folding instructions. Most experienced skydivers do their own packing, and it takes 10 to 15 minutes to do the job.

One of the things that makes modern parachute packing so interesting is the use of zero-porosity fabric. Zero-porosity means that the fabric has a coating so that air cannot move through it. Zero-P gives the canopy better performance, but it also means that it can be very hard to get all the air out of the parachute during folding.

Now let's take a detailed look at what happens when a parachute is deployed.

Parachute Deployment Sequence

Here's what happens when a parachute deploys normally:

  • The skydiver uses the pilot chute to start the deployment sequence. The drogue normally rides in a little pouch attached to the bottom of the container (BOC). To deploy, the skydiver pulls the drogue out of the pouch and lets go of it.
  • The pilot chute catches the air and inflates. It pulls out a 7 to 10-foot long (2 to 3-meter) piece of nylon webbing called the bridle.
  • As the bridle is coming out of the container, it pulls a pin, called the closing pin, on the container. This pin holds the main canopy inside the container. Pulling the pin opens the container with a small pop.
Click here to watch a short video of how the pin is pulled!
Click here to watch a short video of how the pin is pulled!
  • The bridle continues to pull out of the container.
  • One end of the bridle connects to the pilot chute. The bridle's other end connects to a bag called the deployment bag, or D-bag. When you pack the parachute, you stuff it into the D-bag, and then load the D-bag into the container. The bridle pulls the D-bag out of the container.
Click here to watch a short video of the D-bag!
Click here to watch a short video of the D-bag!
  • All of the parachute's lines have been stowed in a zig-zag pattern by looping them underneath rubber bands attached to the D-bag. As the pilot chute and bridle continue to pull on the D-bag, all of the lines unfold and stretch out.
Click here to watch a short video of how the lines unfold!
Click here to watch a short video of how the lines unfold!
  • As the lines completely unfold and start to pull with the tension from the pilot chute, they pull the risers out of the container. The risers are heavy nylon straps that connect the lines to the container. (The risers also contain a release mechanism for the main canopy's lines in case you need to cut the main canopy away.)
  • The tension on the lines also pulls the parachute itself out of the deployment bag.
  • The wind inflates the cells of the canopy. What you do not want, however, is for the canopy to open instantaneously. If it opens instantaneously, you go from 120 mph to 10 mph too quickly. This hurts and can also damage equipment -- it can snap lines or rip the canopy. Therefore, all ram-air canopies have a piece of nylon called a slider that holds the lines together and slides down the lines as the parachute opens. This slows down the opening and keeps the lines from tangling as the parachute inflates.

Once the parachute is out and open, the skydiver looks up to make sure everything is OK. Then the skydiver can grab the two toggles and start steering the parachute toward the landing site.

Next, we'll look at what happens when the parachute doesn't deploy correctly.

Reserve Deployment

Click here to watch a short video of the three-ring release!
Click here to watch a short video of the three-ring release!

Let's say you try to deploy your main canopy and something goes wrong. For example:

  • The main canopy never comes out of the deployment bag.
  • The main canopy does not inflate.
  • The main canopy gets tangled in the lines.
  • Some of the lines break, or the canopy rips during opening.
  • Part of the main canopy inflates while another part does not.

In all of these cases, you have a canopy that you cannot use to land safely. You need to cut away the main canopy and deploy the reserve.

All modern rigs have a mechanism called a three-ring release that connects the main canopy to the container.

To cut away the main, you reach down and pull the release handle attached to one of your shoulder straps. This handle releases the lines on both risers simultaneously. You are now in free fall again. Then, one of two things happens:

  • On some rigs, there is a cord called the reserve static line that automatically pulls out the reserve when you cut away the main.
  • On other rigs, you pull a second handle to deploy the reserve manually.

In either case, you are praying that the reserve deploys cleanly and you have a good canopy when you get done. Most experienced skydivers pack their own parachutes, but it is common for the reserve chute to be packed by a certified rigger. Every few months, the reserve is unpacked and repacked to keep it from getting stiff.

Automatic Activation Device

There's not a lot of room for error in skydiving. Let's say that one of the following three things happens during a skydive:

  1. You lose consciousness as you are exiting the plane or falling.
  2. You lose track of your altitude because you get distracted.
  3. Something completely unexpected happens -- maybe an airplane or a second skydiver flies too close to you and either damages your equipment or makes you unstable.

In any of these situations, you may be unable to deploy your parachute yourself, and you need some help. An AAD (automatic activation device) is a small computer that constantly monitors the altitude and activates the reserve chute for you.

One of the best-known AADs is the CYPRES AAD. CYPRES is short for "Cybernetic Parachute Release System." According to the manufacturer, there are more than 65,000 CYPRES units in the field.

The CYPRES unit has four parts:

  • A small display that lets your turn it on and monitor its activity
  • The computer itself
  • The battery
  • The cutter, which actually deploys the reserve chute

The cutter is fascinating. It is essentially a bullet, and the computer sends it a signal when it is time to deploy the reserve chute. The cutter fires. The tip of the cutter is wedge-shaped, like a knife, and it cuts a piece of cord called the closing loop. The closing pin for the reserve chute hooks through the closing loop to hold the reserve chute in the container. Cutting the closing loop is the surest way possible to deploy the reserve.

The computer has the non-trivial job of deciding when it is time to deploy the reserve. The basic goal is to always deploy the reserve chute if the skydiver is in free fall and makes it down to 750 feet (230 meters) in altitude. However, this is not as easy as it sounds. Here are some of the situations that the computer has to handle to avoid erroneous deployments:

  • Normal flying under a successfully deployed main cute
  • Quick, unexpected pressure changes caused by rolling over (front to back) or flying around other skydivers in free fall
  • Return to the ground in the airplane (rather than jumping)
  • Significant pressure changes caused by the weather (e.g., a low-pressure system moving into the area)

Only if the skydiver is in free fall at 750 feet will the CYPRES unit cut the reserve loop.

The skydiver turns on the CYPRES on the ground. The CYPRES computer takes a measurement of air pressure on the ground and uses this to determine the skydiver's altitude throughout the day. Whenever the skydiver is on the ground, the unit recalibrates every 30 seconds to handle weather-based changes in atmospheric pressure.

In the next section, we'll see how inexperienced skydivers get into the sport.

Getting Into Skydiving

If you have never been skydiving before, one popular way to make the first jump is called tandem jumping. In a tandem jump, you get strapped to your instructor and the two of you fall together. The instructor carries one large parachute on his back -- big enough to support your weight and his together. Your instructor controls all aspects of the jump to make sure nothing goes wrong.

A typical tandem jump looks a lot like a normal jump. Here are the big differences:

  • An experienced skydiver can simply leap from the plane. In a tandem jump, the student and the tandem instructor are strapped together, so there is a little more maneuvering to get ready for the jump.
  • Just after jumping out, the instructor throws out a large (approx. 4-foot/1.2-m diameter) drogue chute, and this drogue is out during the entire free fall. Without this drogue, the combined weight of the instructor and student would cause the pair to fall at 180 to 200 mph (290 to 320 kph) -- much faster than the normal 120 mph. The drogue slows the pair down to the normal falling speed.
  • When it is time to deploy the parachute, the instructor or student pulls a cord that lets the drogue do its normal job -- the drogue pulls the parachute out of the container.
  • The instructor and student land together.

Skydiving Costs

One of the most popular skydiving techniques in use today is called Accelerated Free Fall (AFF). In the United States, the student might go through the following steps to become a licensed skydiver:

  • The student probably starts with one tandem jump in order to get a little experience jumping out of the plane and working in free fall. This jump typically costs between $150 and $200.
  • The student then takes ground school to prepare for the first AFF jump, and then makes the first jump. In the first several AFF jumps, the student leaves the airplane with two instructors and they all fall together, with the instructors holding on to the student. The cost for ground school plus the first jump with two instructors is typically $300 or so.
  • The student then makes two to three more jumps with two instructors, at a rate of around $180 to $200 per jump.
  • The student then makes four to five more jumps with just one instructor, at a cost of about $150 for each jump.
  • The student is then cleared to jump solo with minimal supervision. The student must complete 20 jumps, pass a test and meet other criteria to get an A License from the United States Parachuting Association.

Once you have your A license, you are generally free to jump at most drop zones, and you pay $15 to $25 per jump.

Skydiving Variations

Once you have your A license, there are many different variations on the basic "falling through the sky at 120 mph" theme:

  • You can jump in formation with four or more other people.
  • You can jump with a skyboard and do tricks.
  • You can jump with the goal of maximum speed in free fall.
  • You can take up more extreme aspects of the sport, like BASE (Building, Antenna, Span, Earth) jumping.
  • You can try night jumping.

There are also the professional aspects of skydiving, like teaching and stunt skydiving in movies and TV shows (see, for example, Joe Jennings Freefall Cinematography or SkydivingStunts.com).

Risk of Skydiving Accidents

Skydiving is a remarkably popular sport. The United States Parachuting Association has nearly 35,000 members. It estimates that about 350,000 people complete more than 3 million jumps in a typical year.

The big question is always, "How dangerous is skydiving?" In 2012, 19 people died in parachuting accidents in the United States, or roughly one person per 100,000 jumps. Look at the US Skydiving Incident Reports to get an idea of the types of problems that lead to fatalities. If you make one jump in a year, your chance of dying is 1 in 100,000.

How does the fatality rate in skydiving compare to other common activities? Since most adults in America drive cars, let's compare skydiving to driving. Roughly 34,000 people died in 2012 in traffic accidents in the United States ref. If you drive 10,000 miles per year, your chance of dying in a car wreck in any given year is something like 1 in 6,000. In other words, we accept a higher level of risk by getting into our cars every day than people do by occasionally skydiving. The fatality rate for skydiving is 0.006 per 1,000 jumps, according to the U.S. Parachute Association.

A logical question to ask here is this: Given these statistics, why do we think of skydiving as dangerous and driving a car as safe?

  • The first reason has to do with frequency. At 19 per year, fatal skydiving accidents are infrequent. That tends to make each one newsworthy, so you are likely to hear about them. On the other hand, there are about 93 fatal car accidents every day in the United States. If you heard about every car accident, you would go insane, so you only hear about a few of them. That leaves you with the impression that car accidents are infrequent even though they happen constantly.
  • The second reason has to do with familiarity. Most people drive every day and nothing bad happens. So our personal experience leads us to believe that driving is safe. It is only when you look at the aggregated statistics that you realize how dangerous driving really is.

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