**4.3 Aerial Application Operations (crop dusting, fire fighting):**

Special nature of aerial application flying (multiple take-offs and
landings, low level flight, heavily loaded, tight maneuvers, protective
equipment)

Flight profile

Thermal stress

Effects of exposure to aerial application chemicals

Crash survival and crash worthiness

**Section II 4.3 AERIAL APPLICATION OPERATIONS (Crop Dusting, Fire
Fighting)**

This chapter is designed to provide you with a basic understanding of
the activities of specialized aircraft that provide low level delivery
of agricultural products. Their activities of crop dusting and fire
fighting require specialized equipment and training. Emphasis is placed
on understanding unique requirements for low level flight, the
physiologic demands of high frequency, short flights in demanding
conditions of high heat and repeated acrobatic activities. Toxic hazards
are present due to the use of pesticides and herbicides by some aerial
applicators. Due to the low altitude flying, collision with the ground,
trees, wires and other objects is a constant risk and occur with greater
frequency than in other aviation events. These aircraft are designed to
provide protection and survivability to their pilots in the event of a
crash. You will understand the process of creating and evaluating an
aircraft for crashworthiness.

Aerial application operations consist of agricultural spraying and
dispensing of materials from low-flying aircraft. This can include
insecticides and pesticides, herbicides, fertilizers, defoliants, seed,
fire control substances, and other potentially toxic materials.
Dispensing materials from low-flying aircraft for agricultural or fire
control purposes is hazardous, due to the proximity of ground,
repetitive low level maneuvers, the potential of striking objects on the
ground, and some of the chemicals being dispensed. Commonly referred to
as crop dusting in the United States, this includes fire fighting
aircraft and what is termed top dressing in New Zealand and Australia.

The initial testing of aircraft for dispensing airborne dusting
equipment began in 1922 at Delta Laboratory in Tallulah, Louisiana as
part of a United States Department of Agriculture experiment. As part of
this program, the Starman C3B biplane became a primary dispenser and
became widely available when the Army Air Service and the U.S. Navy
adopted it as a primary trainer. Following World War II, thousands of
these aircraft became available and were converted to duster/sprayer
activities. Soon they became an essential contribution to American
agriculture. A number of other aircraft were converted for agricultural
application operations, but in 1957, Grumman Aircraft designed and built
an aircraft specifically for crop dusting needs. This aircraft became
the Grumman Ag-Cat. This biplane had a large capacity for carrying
agricultural chemicals, as well as structural designs to make it highly
maneuverable at low altitude and crashworthy.

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height="2.8229166666666665in"}

Grumman Ag-Cat

Aerial application pilots are covered by FAR Part 137. These regulations
govern agriculture aircraft in the United States and encompass the
dispensing of any chemical designed to treat the soil or crops. Special
certification rules for these pilots include knowledge and skill tests
for the safe handling of poisons, agricultural chemicals, and basic
medical knowledge of the symptoms of poisoning. There is also a special
flight test and many of the rules of other aircraft operations are
altered for Part 137 aircraft. These include a requirement for a safety
harness, operating without positioning lights, and restrictions from
operating over congested areas. Special record keeping must be
maintained. If a private individual dispenses spray over their own
property, they may operate as a private pilot, with a third class
medical certificate, but those individuals flying for hire are required
to have a commercial license and a second class medical certificate.

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height="4.864583333333333in"}

The flight profile of an agricultural applicator is typically a day of
short flights from a small, uncontrolled airfield where the aircraft's
tanks are filled. The flight then proceeds to the target track and
several passes are made at a low level of three to five feet above the
crop, at a typical speed of 110 miles per hour. The agricultural
applicator pilot must have inspected the field prior to flight and be
aware of obstructions to flight, such as power lines and poles and
trees, the relative flatness of the field, and adjoining fields, and
must be extremely knowledgeable of the weather and wind conditions. Wind
drift must be taken into account to avoid having the spray contaminate
adjacent fields. A typical run will be straight downfield. At the end of
the field a "P" turn is executed, using a bank angle of 45° to 60° and
approximately 2-4 g of force on the aircraft. This increases the
aircraft's stalling speed by over 40%. The P turn completed, the
aircraft flies back down the field and sprays the next lane.

One applicator estimated that he performed over 9,000 P turns in one
summer. Since crop dusting is often done in summer under high
temperature conditions, thermal stress may be an added problem.
Repetitive turns at even these modest G loads coupled with dehydration
can lead to g-induced loss of consciousness (G-LOC). Under these
circumstances, the pilot will wake up in the wreckage of the aircraft.

Considerable care must be taken during the application of agricultural
chemicals. In some parts of the country, application of chemicals is
limited, but, in others, most notably the Sacramento River delta of
California, virtually all crop care is provided from the air. Within
this delta are a number of islands with dikes around them, making them
resemble Dutch farmlands. However, unlike Holland, these delta islands
are not reclaimed, but instead have been leveled, using laser surveying
techniques so that an entire field will differ in altitude by only a few
inches. At the beginning of the season, the island is flooded and
aircraft will dispense rice seed, performing the planting. Subsequent
flights will provide fertilizers and herbicide for weed suppression.
Later flights will deliver pesticides to the area. The farmers need not
actually enter their fields until the harvest is ready.

The nature of chemicals used in aerial application varies widely. The
greatest concern is with pesticides, especially organophosphate
insecticides, which include malathion and parathion. These are
acetylcholinesterase enzyme inhibitors, which are, in general, slightly
more toxic to mammals than insects. A special license from the United
States Department of Agriculture is required to obtain and dispense
these pesticides.

Related to organophosphate insecticides are the carbamate insecticides,
which are also acetylcholinesterase inhibitors, but do not bind
irreversibly to the enzyme. Both organophosphates and carbamate
insecticide poisoning in humans can be treated by atropine, which
provides a cholinergic blockade, preventing the symptoms of excess
acetylcholine caused by the poisoning. In addition, pralidoxime can
reactivate the acetylcholinesterase enzyme. Plasma cholinesterase enzyme
measurements should be taken periodically of any individual involved in
cholinesterase or carbamate insecticide applications.

Other pesticides include the chlorinated insecticides, which are being
used less and less. The prototype of this group is
dicholordiphenyltrichloroethane (DDT), which is now banned in the U.S.
but still used elsewhere in the world. Others, such as aldrin and
dieldrin are rarely used in the United States. There may be some central
nervous system irritation due to overexposure to these chemicals, which
can be treated by intermediate acting barbiturates.

Herbicides are commonly used, the most potent of which is paraquat. This
is a powerful skin irritant and inhalation can cause pulmonary edema,
which can only be treated symptomatically. Similar reactions occur with
its chemical analog, diquat. Survivors typically have severe pulmonary
fibrosis. Other herbicides, such as 2, 4D and 2, 4, 5T have a minimal
toxicity in humans, although one combination of this, known as Agent
Orange, was used in Vietnam and its contaminant 2, 3, 7, 8-TCDD (dioxin)
was suspected of causing significant problems. Aerial applicators can
also dispense insects directly used for fighting infestations, such as
ladybird eggs and larvae or indirectly used such as sterile male screw
worm flies.

Recent events have led operators of agricultural spray aircraft to take
precautions to prevent their aircraft from being used for terrorist
attacks. This includes greater security measures. However most
applicators use fairly large nozzles, dispensing liquids and solids with
a particle size on the order of 50 microns or larger: Large particles
tend to settle out onto crops. Biological and chemical terrorism
requires a much smaller particle size on the order of 1-5 microns in
order to be inspirable and remain airborne for long periods.

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height="3.946527777777778in"}

Helicopters participate in aerial application operations as well
beginning in the 1950's. Experienced pilots are able to fly at low level
at the more traditional altitudes for helicopters. Helicopters must be
equipped with special wire cutting blades in the event of impact of
power and telephone lines, but wire strikes still take a high toll.
Crash worthiness is being designed into newer helicopters.

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A variation on aerial application is employed by fire suppression
aircraft. Water bombers, which include helicopters, will be loaded with
water, either from a tanker on an airfield or, in the case of amphibious
planes and helicopters, at a nearby lake. Aerial fire fighting began
with surplus amphibious aircraft after World War II. Special use
designed fire fighting aircraft did not appear until the Bombardier
CL215 in the 1960s. Water bombers quickly became and remain the
preferred method of fighting deadly crown fires, which can spread
rapidly and jump fire breaks cut by ground personnel.

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height="5.285416666666666in"}

This aircraft and its successors can land in a lake, rapidly fill its
tanks with water, and take off to dispense water on a nearby fire, using
adjustable openings in its tanks for different water spread patterns.

In the U.S., many organizations operate firefighting aircraft, include
state and federal programs (the Air National Guard converts some C-130
Hercules for firefighting in the summer) plus special fire districts and
the U. S. Forrest Service. Flying through fires creates additional
hazards for the water bomber pilot. Visibility is often reduced and
there are significant updrafts created from the fires themselves, which
may not be occurring on perfectly flat terrain, but are often in hilly
or mountainous areas, where no other fire suppression can be brought to
bear. Usually the water is mixed with foam to provide better penetration
of the bolus though trees and a colored nitrogen-based fertilizer is
mixed with the water to provide additional fire suppression, creating an
orange cloud that marks the target and provides for later growth of
plants that will fill in the burned out areas. The use of aging aircraft
such as World War II vintage planes and 1950s era transports in water
bomber missions led to two catastrophic crashes in the summer of 2002
when the wings failed on a 40-year-old C130 Hercules, followed shortly
thereafter by a similar failure in a converted B-26 Intruder.

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Water bombing with fire retardants added give the solution an orange
color.

The risk of crashing an agricultural spray aircraft is very high and
accident rates are many time higher than for general aviation. Risks
include G-LOC syndrome, tree and wire strikes, spatial disorientation
during turns, and low altitude stalls. Because of the dangers of low
altitude flying, crashworthiness was first built into aerial application
aircraft, beginning with the Ag-Cat and its many successors.
Crashworthiness is an engineering design concept based on aeromedical
principals, intending to "improve the odds of crash survival". It was
first used in agricultural application aircraft because the risk of
crashing was so great that it made the benefits of building additional
structural changes in the aircraft to be cost effective. Crash injury
research, conducted in the 1940's and 1950's by Drs. Ross McFarland and
John Paul Stapp led to understanding the physics of crash dynamics and
how to protect the occupants of an aircraft, not to mention cars and any
other form of motor vehicle. These are stated in the acronym of CREEP,
which stands for:

C-container

R-restraint

E-environment

E-energy absorption

P-post crash hazards

In using this acronym to analyze aircraft accidents and crashworthiness,
we begin with the Container, that is, the crew compartment. This
structure must protect the occupants and remain intact. If it is crushed
or collapses so that survivable space does not exist, the occupants will
suffer injuries. In the case of agricultural aircraft, the pilot's
compartment has become a structure of reinforced steel rods, creating a
roll cage. This compartment is structurally extremely strong and
separate from the rest of the aircraft imbedded within it. Such designs
for roll cages have been transferred to racing cars and, later, in a
different form, to passenger cars, where the passenger compartment
becomes reinforced with side bars and structural supports to the roof,
in case of rollover. All aircraft crashworthiness research is
transferable to any other form of motor vehicle.

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Crashworthy design places the pilot's compartment far behind the engine
and hopper tank within a structurally reinforced cage. The pilot has a
five point restraint system. Energy-absorbing wheel struts, cable
cutters and self-sealing fuel lines all reduce risk of pilot injury.

The R represents the restraint system. Restraints were initially lap
belts only. By 1914, most aircraft were equipped with lap belts for the
pilots. In the 1930's, shoulder harnesses were discovered to prevent the
torso and head from moving forward and impacting other objects within
the compartment, creating a "strike envelope". Similarly, seatbelts have
been installed in American cars since 1965 and shoulder harnesses since
1984. Additional restraint systems in aircraft have included a fifth
point, consisting of a strap securing the lap belt and going between the
legs. This prevents the occupant from submarining and going underneath
the lap belt. Sometimes, a six point restraint is used where there are
two crotch straps. Additional restraint systems for the head and neck
have been necessary in racing cars, particularly on the NASCAR circuit.
A restraint and container for the head alone, known as a crash helmet,
was developed by the Stapp team in the 1940's. This modified old
aviation helmets of padded leather, which were basically modified
football helmets. The crash helmet consists of an outer hard shell that
prevents penetration of the container and an inner energy-absorbing
material that restrains and reduces the energy applied to the wearer's
head. Crash helmets are now, of course, used by motor cyclists,
bicyclists, and skiers.

The Environment includes the cockpit itself and the potential for loose
objects to become missiles. Propelled unrestrained objects may break
loose and fly around the occupant's compartment, causing additional
injuries. Likewise, there may be toxic chemicals carried by the
aircraft, which provide additional hazards.

Energy absorption has to do with decelerating the occupant at levels
below those capable of causing human injury. In conjunction with
restraints, which should be broad and thick to distribute energy and
positioned to cross bony structures, such as the pelvis and thorax,
other structures of the aircraft itself crush and absorb energy. In an
agricultural aircraft, this will include placing the engine at the far
front of the aircraft, accounting for the somewhat unusual long-nosed
appearance of modern agricultural aircraft. In helicopters, the engine
may be mounted above the cabin. This way, during deceleration, the
engine itself is separated from the cockpit. Structures built into the
aircraft can absorb energy by collapsing slowly at a designed level of
acceleration. For example, the belly of an aircraft may be built of
crushable aluminum, designed to be collapsed at a level of 14 g's
acceleration. This is common in newer helicopters. Likewise, the seat
structure of aircraft can be designed to bend and deform at a limit of
14 g's. This is now applied to most commercial aircraft and helicopters.
The 14 g level derives from research indicating that this level of
acceleration will cause no permanent injury to a normal human being.
Higher levels of acceleration are required to cause injuries, such as 50
g's to break long bones and approximately 250 G's to fracture the human
skull. Agricultural aircraft will also have specially designed features,
such as landing gear cut struts designed to collapse, wire cutters built
in front of the windscreen to avoid decapitating the pilot, and full
restraints and attachments for the seatbelts.

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height="4.979166666666667in"}

Fire is the greatest post crash hazard.

Finally, Post crash hazards include escape from the aircraft, fire,
survival, and potential toxic exposures. Fire is the greatest hazard and
65% of all aircraft fatalities occur in the 15% of aircraft that burn.
The chances of survival in a crash where there is no fire exceed 90%. A
method of crash-proofing an aircraft is to use fuel lines that quick
disconnect when too much stress is applied and self-seal. The result is
a fuel line that struck by a metal post on impact will simply disconnect
rather than rupture and only a small amount of fuel will be spilled,
reducing the chances of fire. Some effort has been placed on finding
fuels that are less likely to burn, but, so far, this research has been
frustrated by the primary reason for having fuel, which is to burn it in
the engine. Other items that can burn in a crash include the upholstery
of an aircraft, which, if they are nylon or other synthetics, may
produce toxic fumes, including cyanides and carbon monoxide. This has
caused commercial aircraft to be refitted with safer material, such a
Nomex. If there is a risk of landing in water, additional precautions,
such as life vests or flotation devices, must be provided. Finally, an
emergency locating transponder (ELT) must be installed in all new
aircraft. This device, which is triggered by high acceleration levels,
automatically broadcasts on 121.5 MHz and 243.0 MHz. An ELT will be
immediately detected by Federal Aviation Administration air traffic
controllers, military rescue centers, and orbiting satellites, which are
equipped with special location devices. Within minutes of any activation
of an ELT, the crash site can be localized by these means. Search and
rescue will be activated and coordinated.

References

Aldman, B. and Chapon, A., editors. [The Biomechanics of Impact
Trauma]{.underline}, International Center for Transportation Studies,
Washington, D.C. 1984.

Federal Aviation Administration, "Transport Airplane Cabin Interiors'
Crashworthiness Handbook", U.S. Department of Transportation Advisory
Circular No. AC25-17 July 15, 1991.

Gurdjian, E.S., Lange, W.A., Patrick, L.M., and Thomas, L.M. [Impact
Injury and Crash Protection]{.underline}. CC Thomas, New York 1970.

Mohler, S.R. Civil Aviation Medicine. [Fundamentals of Aerospace
Medicine]{.underline}, 2^nd^ edition. R.L. de Hart, editor. Williams &
Wilkins, Baltimore 1996.

Petersen, R. [So You Want to Be a Spray Pilot?]{.underline} AgAir Update
February 2002. The National Agricultural Aviation Association and the
National Agricultural Aviation Museum.