4/20/23 

AIM 

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 accelerative 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

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28, and “G Incapacitation in Aerobatic Pilots: A Flight Hazard” FAA

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13. These are 

available from the National Technical Information Service, Springfield, Virginia 22161. 

REFERENCE

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FAA AC 91

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61, A Hazard in Aerobatics: Effects of G

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forces on Pilots. 

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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

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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. 

f.  Recognize High Hazard Areas. 

1. 

Airways, especially near VORs, and Class B, Class C, Class D, and Class E surface areas are places 

where aircraft tend to cluster. 

2. 

Remember, most collisions occur during days when the weather is good. Being in a “radar environment” 

still requires vigilance to avoid collisions. 

g.  Cockpit Management. 

Studying maps, checklists, and manuals before flight, with other proper preflight 

planning; e.g., noting necessary radio frequencies and organizing cockpit materials, can reduce the amount of 

time required to look at these items during flight, permitting more scan time. 

h.  Windshield Conditions. 

Dirty or bug-smeared windshields can greatly reduce the ability of pilots to see 

other aircraft. Keep a clean windshield. 

i.  Visibility Conditions. 

Smoke, haze, dust, rain, and flying towards the sun can also greatly reduce the 

ability to detect targets. 

j.  Visual Obstructions in the Cockpit. 

1. 

Pilots need to move their heads to see around blind spots caused by fixed aircraft structures, such as door 

posts, wings, etc. It will be necessary at times to maneuver the aircraft; e.g., lift a wing, to facilitate seeing. 

2. 

Pilots must ensure curtains and other cockpit objects; e.g., maps on glare shield, are removed and stowed 

during flight. 

Fitness for Flight 

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