When it is very dark you are subject to illusions. Your seat
position may make you more or less subject to these. Aircraft
seats are situated by a "Design Eye reference Point"
(DERP) that is supposed to give a view over the cowl and at the
instrument panel. It is not marked on the aircraft but is part
of the aircraft design.
If your seat is too low during dark conditions, you will only
be able to see runway lights if you are in a descent. The pilot
tends to set up a constant angle for their field of view on approach.
During daylight, you use the "point on the windshield"
to maintain this angle. If the aim point drifts upward you are
in an excessive descent; if it drifts downward you are too high.
It works the same at night but the references are fewer.
The black hole illusion begins out a few miles on final. The
field and lights will be foreshortened. Getting closer the runway
should rise in the field of view. If the aircraft is descending
the foreshortened view will remain constant. The eye/brain interpretation
of this is that the constant foreshortened runway is an indication
of a constant angle approach. This is the "everything is
fine" illusion of the black hole. During the final phases
the daytime depth perception does not work very well.
When flying into a black hole or 'featureless terrain' you
must use a correctly set altimeter to counter the illusion. Fly
a full pattern using your altimeter and a standardized procedure
for a stabilized approach. This is the best way to assure yourself
that you will not meet an obstacle on final. This is a combined
IFR/VFR approach and requires that you be capable of controlling
the aircraft accurately without visual references. The normal
order of viewing runway, lights, and dark areas is so changed
illusions of being higher occur. If the illusions are believed,
touchdown can occur before reaching the runway.
The "black hole illusion" has a dramatic effect on
straight in approaches to a runway. The stabilized constant angle
approach will appear to exist as an illusion while you fly an
arc that flies you into the ground. Do not fly a straight in approach
to a runway at night. Know the pattern altitude. Fly somewhat
farther out on down wind than appears appropriate. Use a standardized
configuration approach just as you would in daytime. Fly the VASI
or VAPI if available.
Failure to follow the above recommendations may cause you to
make a premature descent. Over flying featureless terrain without
lights on an approach that deprives you of the height clues can
fly you into the ground.
There are some optical illusions that relate to nearby aircraft.
An aircraft below you will appear to be above you. While getting
closer it will appear to descend through your horizon. All the
time it is straight an level below you. Avoid the temptation to
Last Modified October 26, ©2020 TAGE.COM