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Fitness for Flight

comfortable focal distance which may range from

10 to 30 feet. For the pilot, this means looking

without seeing, which is dangerous.

8−1−7. Aerobatic Flight

a. Pilots planning to engage in aerobatics should

be aware of the physiological stresses associated with

accelerative forces during aerobatic maneuvers.

Many prospective aerobatic trainees enthusiastically

enter aerobatic instruction but find their first

experiences with G forces to be unanticipated and

very uncomfortable. To minimize or avoid potential

adverse effects, the aerobatic instructor and trainee

must have a basic understanding of the physiology of

G force adaptation.

b. Forces experienced with a rapid push-over

maneuver result in the blood and body organs being

displaced toward the head. Depending on forces

involved and individual tolerance, a pilot may

experience discomfort, headache, “red-out,” and

even unconsciousness.

c. Forces experienced with a rapid pull-up

maneuver result in the blood and body organ

displacement toward the lower part of the body away

from the head. Since the brain requires continuous

blood circulation for an adequate oxygen supply,

there is a physiologic limit to the time the pilot can

tolerate higher forces before losing consciousness.

As the blood circulation to the brain decreases as a

result of forces involved, a pilot will experience

“narrowing” of visual fields, “gray-out,” “black-

out,” and unconsciousness. Even a brief loss of

consciousness in a maneuver can lead to improper

control movement causing structural failure of the

aircraft or collision with another object or terrain.

d. In steep turns, the centrifugal forces tend to

push the pilot into the seat, thereby resulting in blood

and body organ displacement toward the lower part of

the body as in the case of rapid pull-up maneuvers and

with the same physiologic effects and symptoms.

e. Physiologically, humans progressively adapt to

imposed strains and stress, and with practice, any

maneuver will have decreasing effect. Tolerance to

G forces is dependent on human physiology and the

individual pilot. These factors include the skeletal

anatomy, the cardiovascular architecture, the nervous

system, the quality of the blood, the general physical

state, and experience and recency of exposure. The

pilot should consult an Aviation Medical Examiner

prior to aerobatic training and be aware that poor

physical condition can reduce tolerance to accelera-

tive forces.

f. The above information provides pilots with a

brief summary of the physiologic effects of G forces.

It does not address methods of “counteracting” these

effects. There are numerous references on the subject

of G forces during aerobatics available to pilots.

Among these are “G Effects on the Pilot During

Aerobatics,” FAA−AM−72−28, and “G Incapacita-

tion in Aerobatic Pilots: A Flight Hazard”

FAA−AM−82−13. These are available from the

National Technical Information Service, Springfield,

Virginia 22161.


FAA AC 91−61, A Hazard in Aerobatics: Effects of G−forces on Pilots.

8−1−8. Judgment Aspects of Collision


a. Introduction. The most important aspects of

vision and the techniques to scan for other aircraft are

described in paragraph 8−1−6, Vision in Flight. Pilots

should also be familiar with the following informa-

tion to reduce the possibility of mid-air collisions.

b. Determining Relative Altitude. Use the

horizon as a reference point. If the other aircraft is

above the horizon, it is probably on a higher flight

path. If the aircraft appears to be below the horizon,

it is probably flying at a lower altitude.

c. Taking Appropriate Action. Pilots should be

familiar with rules on right-of-way, so if an aircraft is

on an obvious collision course, one can take

immediate evasive action, preferably in compliance

with applicable Federal Aviation Regulations.

d. Consider Multiple Threats. The decision to

climb, descend, or turn is a matter of personal

judgment, but one should anticipate that the other

pilot may also be making a quick maneuver. Watch

the other aircraft during the maneuver and begin your

scanning again immediately since there may be other

aircraft in the area.

e. Collision Course Targets. Any aircraft that

appears to have no relative motion and stays in one

scan quadrant is likely to be on a collision course.

Also, if a target shows no lateral or vertical motion,

but increases in size, take evasive action.