Chapter Three: ENVIRONMENT

Weather

The environment in which you fly your parachute includes a large number of variables, any one of which can contribute to an accident. Let's look at some of the many things that affect your canopy.

Turbulence
Turbulence can be described as a disturbance in the air. Several things can cause turbulence that can affect a canopy in flight. Among them are wind, heat and wake turbulence.

Wind over an uneven surface or a temperature gradient creates turbulence. The amount of turbulence increases geometrically with the wind speed. In other words, a building that creates negligible turbulence in a 10 mile an hour wind can create extremely dangerous turbulence in a 20 mile an hour wind. Turbulence extends far downwind of an obstacle. Visualize the wind as flowing water. A line of trees or a long building will have a definite downward wave behind it. A single obstacle such as a building will have both sideways and downward turbulence. For a graphic demonstration, stand behind a large building on a windy day and note which way the wind currents are where you stand. Odds are they will be quite different from the general wind direction.

Dust devils are caused when a small area of air is heated above the temperature of the surrounding air. These miniature tornadoes create severe turbulence in an area up to a hundred or more yards wide. They can easily collapse all or part of a canopy. They can also cause downwind landings, either by causing a false reading on wind indicators or by changing the wind direction in their immediate area.

Wake turbulence is a common cause of hard landings in a crowded landing zone. A canopy's passage through the air leaves a wake similar to the one behind a boat. The wake has two characteristics. One is general turbulence directly behind a canopy that can drastically increase the descent rate of a parachute flying through it. This occurs because the "bumpy" air reduces the lifting force of the canopy by disturbing the airflow over the wing. The other wake turbulence is from "tip vortices," which spiral out from the edges of the canopy. These occur because air tries to move from the high pressure bottom skin to the low pressure top skin. It takes the path of least resistance, which is towards the sides of the canopy. As it spills off the end cells it creates a circular wake trailing behind each wing tip - just imagine the V shaped wave behind a power boat. These are essentially miniature dust devils and can easily collapse an end cell or two. Both types of wake turbulence extend well behind the canopy - as much as fifty feet or more - before becoming insignificant. An interesting exercise is to open high with a friend and intentionally fly through their canopy wake to get an idea of how your parachute handles turbulence.

Last but not least, don't land behind the airplanes when the engines are running!

Density altitude
Thin air reduces a wing's performance. Two things cause air pressure to drop: heat and altitude. Therefore, you can expect that a canopy that performs well at sea level on a cool day will fly significantly worse at high altitude on a hot day. As a rule of thumb, count on a 3 to 4 percent performance loss for each 1,000 foot elevation gain or each 10 degrees temperature increase. Using this rule of thumb, a parachute taken from sea level to a 3,000 foot high dz would lose about 10% of its efficiency if the temperature remained constant. Or, jumped at the same sea level dz on a 70 degree day and a 100 degree day it would show a comparable change in performance. Humidity also decreases performance slightly.

Traffic
At a large drop zone it is not uncommon for twenty or more skydivers to share the landing area. As more and more of these jumpers use fast canopies, traffic becomes a real hazard. We all know that auto traffic follows certain universal guidelines to minimize collisions. The same is true of aircraft and boats, and even in the freefall portion of skydiving. Yet for some reason, skydivers have been reluctant to adopt standard traffic patterns under canopy even though this simple idea could prevent several injuries and fatalities annually. By following some simple guidelines, you can be a good citizen in the skydiving community, minimizing risk to yourself and others while still having fun.

Break-off and Deployment
Traffic management actually begins at the dirt dive. Be sure you plan a break off altitude that will allow plenty of time to get away from others and still be open by at least 2,000 feet. USPA’s Basic Safety Requirements specify container opening by 2,500 feet for intermediate level jumpers (A and B license) and 2,000 feet for advanced jumpers (C and D license.) The custom for many years has been to break off at 3,500 for small RW groups and USPA recommends 4,000 feet for groups of six or more. But in the modern canopy environment, we should reconsider these numbers. The advent of "fast" canopies has had two effects on the break off and deployment section of the skydive. One is the issue of how much separation from other canopies is enough. The other is how much time a jumper might want to deal with a malfunction on a modern canopy.

At Skydive Arizona, canopy collisions at the deployment phase cause one third of fatalities - more than any other type of accident. To minimize risk skydivers need to minimize the causes of these collisions: off heading openings and inadequate separation. In an ideal world where canopies would always open on heading it would suffice for everyone to turn away from the center and deploy. We’ll discuss controlling the openings later, but right now, let’s talk about the real world of canopies that occasionally open off heading. That’s when adequate separation becomes essential.

How much separation is enough? Typical modern canopies fly forward at about 35 feet per second while the brakes are still set in deployment configuration. When facing another canopy as a result of off heading openings the closing speed can be up to 70 feet per second. With brakes off, it is more like 90 feet per second. Given that it will take about three seconds to recognize the emergency and begin appropriate action, deploying within 200 feet of another skydiver is very hazardous. A good skydiver can attain speeds of 80 to 90 feet per second in a track - but it takes time to turn, build up speed and then wave off and slow down the track. To turn 180 from the formation, begin a track, sustain a good track for at least three seconds, and then wave off is the work of at least eight seconds - 1,500 feet of altitude at the minimum. That means that if you want to initiate deployment at or above 2,500 feet, you need to break off at or above 4,000 feet. More tracking time means a higher break off.

Although details on tracking skills fall outside the scope of a treatise on canopy control the collisions that might result from poor break offs are part of the subject. Learn how to "flat track" from an experienced RW jumper - just watch the break offs from the ground and you will be able to figure out who has mastered the technique. But there is much more to separation than how effectively you can track. An important thing to keep in mind is that the fundamental goal of break off is to deploy your parachute in clear airspace - not necessarily the same as being able to track fast and far.

For example, if two skydivers find themselves tracking in roughly the same direction at 4,000 feet, they have a traffic problem. If both continue to track, at 2,000 feet they will have the same traffic problem and no altitude in which to fix it. In this situation, the higher (or further behind) skydiver should wave off and deploy as soon as he knows there is no one above, behind, or deploying to the side. Similarly, it makes sense to have one person pull in place (customarily the video man, if there is one) while the others track away from the center person.

Separation is one way to minimize the risk of collisions. Controlling the deployment is another. Most off heading openings, line twists or snivels are caused by either packing or body position. Be sure to pack as symmetrically as possible. Since this discussion is on canopy flight, not packing, you will need to get this information elsewhere. BASE jumpers and canopy formation enthusiasts are good sources for packing tips that will contribute to on heading openings.

Body position is as crucial as packing technique. To understand this, next time you are under canopy raise your right knee as high as you can and twist your shoulders to the left. You should notice a left turn (assuming your canopy flies straight in normal flight!) The turn will be more pronounced on higher performance canopies. Now imagine how much more air is affecting your canopy during the deployment phase, when you have considerably more speed. Having a shoulder down (looking behind is a common cause) can result in off heading openings or line twists. To prevent this, as you track away clear the air to the front, sides and below. Looking behind is largely a waste of time and awareness. Your job is to ensure no one is deploying below you.

When the time comes to deploy, wave off and throw your pilot chute. As you do so, pick a point on the horizon straight ahead. When the canopy deploys, it may have an inclination to turn right or left. Concentrate on holding your shoulders square and towards your heading point. If the canopy turns right, twist your shoulders back towards the heading. As the canopy fully inflates, grab risers or toggles and steer towards your heading. Turning back onto the heading will keep you flying away from others until you have a chance to ensure the space around you is clear.

Traffic management under canopy
Once under canopy, immediately clear your airspace. This means checking for potential collisions before you do anything else. Releasing brakes, stowing sliders and heading for home are all secondary to collision avoidance. If you are faced with a collision, the general rule is to turn right. Practice using front and rear risers for this. Front risers will cause sink, rear risers cause float. Altering descent as well as direction should be practiced until it becomes second nature.

As you head for the dz, there are a couple things you need to check as soon as you have cleared your air and have your canopy in hand. Is anyone under their reserve? If so, go to their aid by following them or their equipment - the main and free bag. Ideally someone will follow each item to ensure recovery. This is your duty to all fellow parachutists, whether you know them or not. Sooner or later you will be under your reserve, watching your main canopy drift away from the dz at sunset. When it happens, you will be glad to have some company.

Assuming all is well your next task is to obtain as much vertical separation from the other skydivers as you can, assess the spot and choose your landing areas. We’ll hold off discussion of bad spots until later, while we continue to look at traffic. Assuming you can make it back to the intended landing area, while you are flying along take stock of the other canopies. With practice you will be able to recognize the types, speeds and altitudes of other canopies. Compare them to your own and begin the process of vertical sorting. Low canopies with high descent rates should maintain a fast descent rate to increase separation from higher canopies, while higher canopies should slow their descent.

Regardless of design specifics a typical modern canopy will have a broad range of descent speeds. In full glide most canopies will descend at 1,000 to 1,500 feet per minute. The same canopy in one half to two thirds brakes will descend at 600 to 900 feet per minute. In a turn, it can easily reach descent rates of 2,000 feet per minute. Therefore, most canopies have a range of descent rates of at least 1,500 feet per minute. By taking advantage of this a wise canopy pilot can ensure that of the twenty people he was on the plane with only two or three will be landing at the same time he is. A helpful hint: most people are better at sinking than floating. Learn how to slow your descent rate and you can have the landing area to yourself. The added advantage is that you get to watch everyone else land, giving you extra information about ground winds.

Final Approach
Eventually it will be time to enter the landing pattern. Like the break-off, this is a very dangerous part of the skydive. A good approach is more than aesthetically pleasing - it can be the difference between life and death. What makes for a good traffic pattern? Whether your style is aggressive or conservative, an elegant landing is characterized by these features.

• The initial approach is easily understood by other canopy pilots in the air.
• The turn on to final approach does not intersect the flight path of other canopies.
• The entire approach and landing is done in such a way that it does not cross a straight ahead, conservative approach to the center of the landing area.
• The approach is not directly over or next to any bystanders.

Most landing areas will have some buildings, roads, fences or other obstacles that affect the pattern. With airplanes, the convention is to use a left hand pattern - one that uses only left turns onto the different legs of the approach. That makes sense because the pilot sits on the left of the plane and has better visibility that way. With parachutes the situation is different. Some drop zones like a left hand pattern so everyone does the same thing. Some allow either left or right patterns to allow skydivers of different experience levels to split up the landing area and control what obstacles they will have to fly over.

Canopy and pilot types also affect the pattern. Generally I find they can be broken down into two classes: conservative approaches used by novices or other people inclined towards caution, and aggressive approaches used by skydivers with high performance canopies. Since these types may be about equal in numbers, the vertical separation mentioned earlier is critical. Even so, we can expect a few of each category to be landing simultaneously. How do we keep the two incompatible styles safe?

Let’s use Skydive Arizona as an example. We allow skydivers to choose either a left or right pattern. Our primary landing area is about 80 meters wide from north to south. On a day when landings are to the west, people using left hand patterns should approach over the buildings and land within 20 meters of the fence. By local custom this pattern is reserved for fast canopies and experienced pilots. They have the skill to land near obstacles, and it keeps them out of the rest of the landing area. People using right hand patterns should land well to the north of the gravel target in the center, leaving that area free for people using a straight in approach.

The less experienced jumpers stay out over open desert and land further away from the fence. Their main concern is to avoid overshooting the landing area and ending up on the asphalt taxi way. But imagine the wind shifting to either the north or the south. Now a new set of problems arises - the danger of undershooting or overshooting the landing area.

In general, overshooting is a problem on calm days; undershooting, windy days. Instead of thinking of landing on a circular target, imagine a runway. Depending on your skill level and canopy type, always give yourself a long enough runway so that whether you land long or short you will not be faced with hitting obstacles or people. Sometimes that will mean picking an alternate landing area with a little more room, since on a calm day most modern canopies need at least a one hundred yard runway to be safe. The dart board style idea of a landing area has become obsolete - always think of a runway!

Finally, we need to consider the combination of traffic and obstacles. Look at our sample landing area again. Let’s say the wind is out of the west and you are approaching along the fence. If a canopy on a more southwesterly heading lands in front of you, you have no place to go. Choices are collide with the canopy, collide with the fence, or do a sharp right turn out into any other traffic, with the hazards of wake turbulence and low turns thrown in. Many canopy pilots develop the habit of thinking of a certain area is "theirs." If you find someone in "your" airspace, what will you do? Learn to maintain a flexible approach!

Low speed approaches have their own set of problems. Using deep brakes or "S" turns in a crowded landing area is as dangerous as "hook" turns. Do not employ student flying techniques in an area for advanced jumpers.

Regardless of your personal style, the etiquette is:

• Low man (including people on the ground) has the right of way, as do students and tandems.
• Never use an approach that will force traffic behind you to use evasive action or fly through your wake.
• Don’t intentionally land crosswind or downwind: this not only presents a huge traffic hazard, but leads everyone still in the air into a state of confusion.

Any discussion of landing areas needs to address so called "hook" turns. I dislike this term; to me a hook turn is a low toggle turn, not necessarily intentional, that shows a lack of planning or respect for the surroundings. High performance landings are another thing altogether. It is acceptable to blend the turns onto crosswind and final into a single, smooth, carving 180 if it is "round" enough to allow you to alter it in the event of traffic conflict and is intelligible to others as a transition through the customary downwind, crosswind and final approach. A detailed discussion of good high performance technique will follow in the chapter on flying skills.

Just as there are some things that define exemplary landings, there are some that define unacceptable technique. Some common approach errors that are rude or dangerous are:

1) Downwind approaches over the center of the landing area.
In this situation, no one in the air knows which way you intend to turn. For all practical purposes you are obstructing the entire landing area. In addition, you are putting yourself in a situation with no escape routes - if traffic eliminates your intended turn you will be forced to land downwind or execute your turn too low. Therefore, all downwind legs of the approach must avoid flying over the center of the landing area.

2) Sudden, "snap" turns, especially more than 90 degrees.
These turns have several problems. From the standpoint of other traffic, they do not allow you a good view of where you will be going and greatly increase the possibility of a collision. They are also confusing to other canopy pilots.

3) Approaches that may cause you to land crosswind/cross traffic
Due to traffic, obstacles, turning too low, or other factors.

4) Approaches that cross through some or all of the normal straight in approach pattern.
Imagine a line along the wind through the center of the target. No approach should cross this line. If you use a left hand approach, finish on the left side of the line. If you use a right hand approach, stay on the right side of the line.

5) Final approaches that put the pilot over or next to bystanders.
Always remember that many skydivers have poor hearing and may not know where you are if they don’t see you. Wuffos have no idea where parachutes will go. Never assume they will stay in place - or move - if you need them to. While striking people on the ground is rare, it should be considered as reprehensible as a motorist striking a pedestrian.

The final aspect of controlling the landing area takes place after you land. Collapse your canopy quickly so no one will hit it. Leave the area promptly; you can discuss the dive somewhere other than an active landing area. In particular avoid the area downwind of obvious landing spots such as the pea gravel. This is where incoming canopies will tend to concentrate. If you are in the pea gravel assume someone is right behind you and clear the area at once. As you depart the landing area, scan constantly for incoming canopies: never assume they see you or that they are in control.