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03.2001

30

Collidingwithatower,powerline,an-
other balloon, orother obstaclecan ruin
your flight, not tomention your day. The
number onecauseof collisionsreported
by pilots is theirfailure to see theobstacle.
Hand-in-handwiththatismisjud ging
clearance.
Accidentstatisticsdonotrev eal
whetherthe new,inexperiencedpilotor
the older, more experiencedpilot is most
likelytobe involvedinan in-flight colli-
sion with powerlines or other obstacles. A
beginning pilot has so much to think about
theymayforgettolookaround.Onthe
otherhand,themoreexperiencedpilot,
having had manyflightswithoutcoming
closetoanyhazardousobstacles,may
grow complacentandforgetto scan. No
pilotisinvulnerable.
Vision,sensoryillusion,meteorol-
ogy, planning, regulations, physiological
andpsychologicalconditionsare all fac-
tors that play a part in successfully avoid-
ingobjectsin flight.
The eye is one of the most important
and complex systemsinthe world. Of all
our senses it has been estimated that 80%
of our total information gathering is done
by the eye. During flight we use our eyes
toprovide informationlike speed, direc-
tion,andproximitytothings.Knowing
theeye’slimitationinseeingpotential
hazards can help the pilot from flying into
objects thatcanspoil the beauty of fight.
The eye, andconsequentlyvision, is
vulnerable to just about everything: dust;
fatigue; emotion; germs; fallen eyelashes;
age;opticalillusionsand,thealcoholic
content of last night’s party. In flight our
visionisalteredbyatmosphericcondi-
tions, too much oxygen ortoo little, accel-
eration, glare, heat, aircraft design and so
forth.
Most of all the eye is vulnerableto the
vagariesof the mind.We can“see” and
identifyonlywhatthemindletsussee.
For example, a daydreaming pilot staring
out into spacesees no obstacles ahead and

is probably the No. 1 candidate for anin-
flight collision.
Onefunctionoftheeyethatisa
source of constant problems to the pilot is
the time required foraccommodation.Our
eyesautomaticallyaccommodate for (or
refocuson) near andfar objects. But the
change from something up close, like the
instrument package in the basket two feet
away, toa well-lightedlandmarka half-
mile away,takesonetotwoseconds, or
longer, for eye accommodation. That can
be a long time when you consider that you
need10seconds(the minimum,accord-
ingtotheFAA)forapilottospotan
obstacle, identify it, realize it’s a collision
threat,andreact.Addtothatthe time it
will take a balloon to respond to an action
(burner, rip, etc.) bythe pilot.
Anotherfocusingproblemusually
occursatveryhighaltitudes,butitcan
happenevenatlowerlevelsonvague,
colorlessdayswhenthereisnodistinct
horizon visible. If there is little or nothing
tofocus onat infinity, we do not focus at
all. We experience somethingknownas
“empty-fieldmyopia”;westarebutsee
nothing,evenanon-comingtower,ifit
shouldenter our visualfield.
The effects ofwhat is called “binocu-
lar vision” have been studied seriously by
the National Transportation Safety Board
(NTSB) during investigations of in-flight
collisions.Toactuallyacceptwhatwe
see,weneedtoreceivecuesfromboth
eyes. If an object is visible to one eye, but
hiddenfromtheotherbyanuprightor
otherobstruction, the total image is blurred
and notalways acceptable tothe mind.
Another inherent eye problem is that
of narrow fieldofvision.Althoughour
eyesacceptlightraysfromanarcof
nearly200º,theyarelimitedtoarela-
tivelynarrowarea(approximately10-
15º) in which they can actually focus and
classifyanobject.Thoughwecanper-
ceive movement in the periphery, wecan-
not identifywhatishappeningout there,

and wetend not to believe what we see out
of the corner of our eyes. This, aidedby
the brain, oftenleadsto “tunnel vision.”
This limitation is compounded by the
factthatatadistanceanobjectthatis
motionlesswillremaininaseemingly
stationary position, without appearing ei-
thertomoveortogrowinsizefora
relativelylongtime,andthensuddenly
bloom into a huge mass. This is known as
“blossom effect.”We need motion or con-
trast toattract our eyes’ attention.
Inaddition tothe built-inproblems,
theeyeisalsoseverelylimitedbyenvi-
ronment. Optical propertiesof the atmo-
spherealtertheappearanceofobjects,
particularlyonhazydays. “Limitedvis-
ibility” actuallymeans“limitedvision.”
Glare, usually worse when the sun is
low and shinning through particulatemat-
ter inthe air or during flight directly into
thesun,makesobjectshardtoseeand
scanning uncomfortable. With the sunin
front of you objects are “back lighted” and
hardto see because there is nocontrast.
Another contrast problem is trying to
findanobjectbetweenyouandterrain
that is varicolored or heavilydotted with
buildings,itwillblendintotheback-
grounduntil it isquite close.
Andthereisthemind,whichcan
distract ustothe point of not seeingany-
thing at all, just starring into space. As you
cansee,visualperceptionis affectedby
many factors.
On approach to landingkeep a clear
fieldofviewinyourdirectionofflight
fromwithinthebasket.Scancontinu-
ously, and not just straight ahead but 360º.
Use the eyes of others that might be in the
basket to helpyou identify potential haz-
ardstoflight.
“Seeing”whatisaroundthe balloon
and inthe flight path takes constant visual
awareness. Planning ahead, knowing what
problemscandevelopandscanningfor
both theexpected and unexpected will help
you to avoid life threatening situations.

“Seeing” is the key to a successful landing.

Obstacle Avoidance

by Tom Hamilton

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