comfortable focal distance which may range from
10 to 30 feet. For the pilot, this means looking
without seeing, which is dangerous.

pilot should consult an Aviation Medical Examiner
prior to aerobatic training and be aware that poor
physical condition can reduce tolerance to accelerative forces.

8-1-7. Aerobatic Flight

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 Incapacitation in Aerobatic Pilots: A Flight Hazard"
FAA-AM-82-13. These are available from the
National Technical Information Service, Springfield,
Virginia 22161.

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," "blackout," 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

8-1-8

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

8-1-8. Judgment Aspects of Collision
Avoidance
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 information 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.

Fitness for Flight