**4.7 Skydiving:**

Free fall aerodynamics

Air blast effects during free fall

Thermal stress

Traumatic injuries (opening shock, midair collisions, landing)

This chapter is designed to provide you with an overview of parachuting
activities. This will include the basic operations, physics and
acceleration forces acting on jumpers. You should understand the various
activities of parachutists and the medical issues concerning their
maneuvers. The lesson emphasizes the hazards involved in these
activities, including the rates and various causes of injuries to
participants. You will be able to objectively evaluate and counsel
individuals who participate in skydiving, provide medical care and
certification as needed.

Thousands of people parachute every year for recreational purposes. The
majority of them jump from aircraft, although balloons and ground
objects are used as well. This latter is termed BASE, for jumping from
tall Buildings Antennas, Spans (bridges) or Earth (cliffs such as El
Capitan in Yosemite National Park).

In skydiving, the individual will fall free of the aircraft and then
deploy a parachute. Parachutes have changed from their original concept,
that of saving the pilot from going down with their crashing airplane.
Parachutes have been modified extensively from the early versions. These
parachutes were typically circular, and were designed to open as rapidly
as possible after exiting the aircraft. Today's parachutes were designed
to open and then lower the pilot to the ground, with minimal control on
the pilot\'s part.

Studies performed in World War II, under the leadership of Dr. Randall
Lovelace, demonstrated that freefall velocities were extremely high at
upper altitudes and that by delaying parachute opening to a lower
altitude, the shock of the canopy opening could be significantly
reduced. These findings by Dr. Lovelace led to the development of the
sport of skydiving.

The basic aerodynamics of freefall involve jumping or falling free of
the carrier aircraft and having gravity accelerate the parachutist to
\"terminal velocity\". This velocity varies with altitude and can exceed
300 miles per hour 500 kph) at 30,000 feet. Below 10,000 feet, it is
approximately 120 to 180 miles per hour (192-288 kph), depending upon
the position of the parachutist's body. A skydiver falling headfirst
will present minimum air resistance and have maximum velocity, while a
jumper positioned with the body in the "spread eagle" or stable position
with back arched and arms and legs extended, will fall at a slower
speed. A typical position is the "delta" with head down, legs spread and
arms abducted at 45°, using the hands as ailerons to control attitude.
Part of the basic training of the parachutist is to develop techniques
for remaining stable and for maneuvering in freefall. The ability to
maneuver, alter position, and perform acrobatics has led to various
competitive leagues and international competitions in skydiving.

The basic training for skydiving involves learning how to exit an
aircraft and stabilize oneself in freefall and then deploy the
parachute. Initial training is performed with a minimum of eight jumps
and often requires 15 to 20 jumps. Parachute training may be by static
line, where once the student exits the aircraft, a line fixed to the
interior of the aircraft automatically deploys the parachute as the
parachutist leaves the aircraft.

A second technique involves an automatic timer that is pulled before the
student leaves the aircraft and automatically opens the parachute a
predetermined number of seconds later or at a preset altitude.
Additional training is called accelerated freefall, with instructors
controlling line deployment. Finally, a tandem jump can be performed
with an instructor pilot firmly attached within the harness to the
student or passenger, who rides in front.

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Tandem Jump

There are significant air blast effects during freefall and fatalities
have occurred when two freefalling parachutists have collided at speed.
Appropriate clothing, particularly with higher altitudes, which brings
the risk of hypoxia, as well as hypothermia, includes helmets for
protecting the head and eyes from both air blast and injury on landing,
as well as appropriate gloves and boots to protect against trauma upon
landing.

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Freefall

There are on average, 30 to 40 fatalities amongst skydivers in the
United States every year, an extraordinarily high rate of nearly 2 per
thousand. Fatalities may occur during several phases of the operation.
First, there may be a failure of the aircraft prior to the parachutist
departing, and this can involve problems with the aircraft or with the
pilot. Pilots are not required to hold a second class medical
certificate, unless they are performing their operations under Part 91,
which demands commercial operations. It would be extremely unusual to
see a parachute in operation conducted under Part 135, which would
involve carrying the parachutist a significant distance from the airport
to their drop zone (DZ).

A second source of injuries and fatalities is during freefall by
collisions between parachutists, or with dropped objects. These most
often occur when multiple parachutist exit near-simultaneously, often
from several aircraft flying in formation, in order to provide the
maximum number of people for formation jumps.

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Formation Jump

A third source of injury occurs when the parachute fails to deploy
properly. Parachutes are handmade fabric, usually of synthetic
materials. The life expectancy of a parachute ranges from 300 to 2000
jumps, depending upon the nature of the material, as well as its
handling and storage. Sections of the parachute may fail, or as the
chute opens, lines may deploy over it, leaving an insufficient amount of
parachute to slow descent.

The normal sport parachute used today has a flying speed of 25 to 40
miles per hour. The typical descent angle is 1: 1; therefore, if the
actual flight speed is 25 miles per hour, forward speed and vertical
speeds are approximately 17 miles per hour. However, all modern
skydiving canopies can be flown. They are essentially fabric wings
functioning much like an aircraft wing. Through controls operated by the
parachutist, the speed can be altered as the flight path is flattened or
steepened on the parachute maneuvered side-to-side. Even stalls can be
performed. Typically, upon landing, the parachutist will "flare" the
parachute, by turning speed into climb, reducing vertical velocitiy
speed to under 5 miles per hour.

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Landing flare "Sky Surfing", note square parachute

Prior to landing, if the primary chute fails, a backup or reserve
parachute can be deployed. The highest number of injuries occur during
landing, often resulting in sprained ankles or other similar trauma.
However, if the parachutist has been dropped away from the DZ,
fatalities can occur when landing on extremely rugged ground or in
water.

Federal Aviation Regulation Part 105 concerns civil Parachute jumping
from aircraft for non-emergency purposes. Any jump that could create a
hazard to flight or on the ground is prohibited. Jumps must be conducted
from aircraft equipped with radios and in appropriate airspace. Class A,
B, C and D airspace use is prohibited and jumps over airports is
strictly limited by this regulation. Jumps from aircraft must be
conducted during daylight, using VFR rules and from more than a 1,200
feet minimum altitude. Use of drugs and alcohol is strictly prohibited.
Parachute equipment must be packed by a certificated parachute rigger
within 120 days of use and all planned jumps must be with a two canopy
(main and reserve) system.

FAA medical regulations do not apply to parachutists' or their
instructors. However, the manufacturers of tandem parachutes require
that the instructors maintain FAA Class 3 Medical Certificates for
insurance and certification, but this is not a federal requirement. In
addition, many DZ operators will require some sort of medical
certification for sport parachutists.

The most common medical condition seen among sport parachutist are ear
problems, due to the rapid rates of descent. Parachutists may also
encounter difficulties when trying to transport their parachutes by
commercial airlines, as some of these parachutes contain explosive
devices, and there may be concern about in-flight hijacking if the
parachute were to be carried within the cabin.

Reference: United States Parachuting Association and Skydiving Magazine.