Flying at night can be a very pleasant experience. The
air is generally cooler and smoother, resulting in better
helicopter performance and a more comfortable flight.
You generally also experience less traffic and less radio
congestion.
NIGHT FLIGHT PHYSIOLOGY
Before discussing night operations, it is important you
understand how your vision is affected at night and
how to counteract the visual illusions, which you might
encounter.
VISION IN FLIGHT
Vision is by far the most important sense that you
have, and flying is obviously impossible without it.
Most of the things you perceive while flying are
visual or heavily supplemented by vision. The visual
sense is especially important in collision avoidance
and depth perception. Your vision sensors are your
eyes, even though they are not perfect in the way they
function or see objects. Since your eyes are not
always able to see all things at all times, illusions and
blindspots occur. The more you understand the eye
and how it functions, the easier it is to compensate for
these illusions and blindspots.
THE EYE
The eye works in much the same way as a camera. Both
have an aperture, lens, method of focusing, and a sur-
face for registering images. [Figure 13-1].
Vision is primarily the result of light striking a photo-
sensitive layer, called the retina, at the back of the eye.
The retina is composed of light-sensitive cones and
rods. The cones in your eye perceive an image best
when the light is bright, while the rods work best in low
light. The pattern of light that strikes the cones and rods
is transmitted as electrical impulses by the optic nerve
to the brain where these signals are interpreted as an
image. The area where the optic nerve meets the retina
contains no cones or rods, creating a blind spot in
vision. Normally, each eye compensates for the other’s
blind spot. [Figure 13-2]
CONES
Cones are concentrated around the center of the
retina. They gradually diminish in number as the dis-
tance from the center increases. Cones allow you to
perceive color by sensing red, blue, and green light.
Directly behind the lens, on the retina, is a small,
notched area called the fovea. This area contains only
a high concentration of cone receptors. When you
look directly at an object, the image is focused
mainly on the fovea. The cones, however, do not
The rods and cones (film) of the retina
are the receptors, which record the
image and transmit it through the optic
nerve to the brain for interpretation.
Light passes
through the cornea
(the transparent window on
the front of the eye) and then through
the lens to focus on the retina.
The pupil (aperture) is the
opening at the center of
the iris. The size of the
pupil is adjusted to
control the amount
of light entering
the eye.
Lens
Iris
Pupil
Cornea
Optic Nerve Retina
Rods and □
Cones
Fovea□
(All Cones)
Rod □
Concentration
{
{
{
{
{
Figure 13-1. A camera is able to focus on near and far objects
by changing the distance between the lens and the film. You
can see objects clearly at various distances because the
shape of your eye’s lens is changed automatically by small
muscles.
Figure 13-2. This illustration provides a dramatic example of
the eye’s blind spot. Cover your right eye and hold this page
at arm’s length. Focus your left eye on the X in the right side
of the visual, and notice what happens to the aircraft as you
slowly bring the page closer to your eye.
function well in darkness, which explains why you
cannot see color as vividly at night as you can during
the day. [Figure 13-3]
RODS
The rods are our dim light and night receptors and are
concentrated outside the fovea area. The number of
rods increases as the distance from the fovea increases.
Rods sense images only in black and white. Because
the rods are not located directly behind the pupil, they
are responsible for much of our peripheral vision.
Images that move are perceived more easily by the rod
areas than by the cones in the fovea. If you have ever
seen something move out of the corner of your eye, it
was most likely detected by your rod receptors.
Since the cones do not function well in the dark, you
may not be able to see an object if you look directly at
it. The concentration of cones in the fovea can make a
night blindspot at the center of your vision. To see an
object clearly, you must expose the rods to the image.
This is accomplished by looking 5° to 10° off center of
the object you want to see. You can try out this effect
on a dim light in a darkened room. When you look
directly at the light, it dims or disappears altogether. If
you look slightly off center, it becomes clearer and
brighter. [Figure 13-4]
How well you see at night is determined by the rods in
your eyes, as well as the amount of light allowed into
your eyes. The wider the pupil is open at night, the bet-
ter your night vision becomes.
NIGHT VISION
The cones in your eyes adapt quite rapidly to changes in
light intensities, but the rods do not. If you have ever
walked from bright sunlight into a dark movie theater, you
have experienced this dark adaptation period. The rods
can take approximately 30 minutes to fully adapt to the
dark. A bright light, however, can completely destroy your
night adaptation and severely restrict your visual acuity.
There are several things you can do to keep your eyes
adapted to the dark. The first is obvious; avoid bright
lights before and during the flight. For 30 minutes
before a night flight, avoid any bright light sources,
such as headlights, landing lights, strobe lights, or
flashlights. If you encounter a bright light, close one
eye to keep it light sensitive. This allows you to see
again once the light is gone. Light sensitivity also can
be gained by using sunglasses if you will be flying from
daylight into an area of increasing darkness.
Red cockpit lighting also helps preserve your night
vision, but red light severely distorts some colors, and
completely washes out the color red. This makes read-
ing an aeronautical chart difficult. A dim white light or
carefully directed flashlight can enhance your night
reading ability. While flying at night, keep the instru-
ment panel and interior lights turned up no higher than
necessary. This helps you see outside visual references
more easily. If your eyes become blurry, blinking more
frequently often helps.
Your diet and general physical health have an impact
on how well you can see in the dark. Deficiencies in
vitamins A and C have been shown to reduce night acu-
ity. Other factors, such as carbon monoxide poisoning,
smoking, alcohol, certain drugs, and a lack of oxygen
also can greatly decrease your night vision.
NIGHT SCANNING
Good night visual acuity is needed for collision avoid-
ance. Night scanning, like day scanning, uses a series
of short, regularly spaced eye movements in 10° sec-
tors. Unlike day scanning, however, off-center viewing
is used to focus objects on the rods rather than the fovea
blindspot. When you look at an object, avoid staring at
it too long. If you stare at an object without moving
your eyes, the retina becomes accustomed to the light
intensity and the image begins to fade. To keep it
clearly visible, new areas in the retina must be exposed
to the image. Small, circular eye movements help
eliminate the fading. You also need to move your eyes
more slowly from sector to sector than during the day
to prevent blurring.
Focus on□
Fovea
Cones Active
Night Blindspot
Rods Active
Figure 13-3. The best vision in daylight is obtained by look-
ing directly at the object. This focuses the image on the
fovea, where detail is best seen.
Figure 13-4. In low light, the cones lose much of their visual
acuity, while rods become more receptive. The eye sacrifices
sharpness for sensitivity. Your ability to see an object directly
in front of you is reduced, and you lose much of your depth
perception, as well as your judgment of size.
AIRCRAFT LIGHTING
In order to see other aircraft more clearly, regulations
require that all aircraft operating during the night hours
have special lights and equipment. The requirements
for operating at night are found in Title 14 of the Code
of Federal Regulations (14 CFR) part 91. In addition to
aircraft lighting, the regulations also provide a defini-
tion of nighttime, currency requirements, fuel reserves,
and necessary electrical systems.
Position lights enable you to locate another aircraft, as
well as help you determine its direction of flight. The
approved aircraft lights for night operations are a green
light on the right cabin side or wingtip, a red light on
the left cabin side or wingtip, and a white position light
on the tail. In addition, flashing aviation red or white
anticollision lights are required for night flights. These
flashing lights can be in a number of locations, but are
most commonly found on the top and bottom of the
cabin. [Figure 13-5]
VISUAL ILLUSIONS
There are many different types of visual illusions that
you can experience at any time, day or night. The next
few paragraphs cover some of the illusions that com-
monly occur at night.
AUTOKINESIS
Autokinesis is caused by staring at a single point of
light against a dark background, such as a ground light
or bright star, for more than a few seconds. After a few
moments, the light appears to move on its own. To pre-
vent this illusion, you should focus your eyes on
objects at varying distances and not fixate on one tar-
get, as well as maintain a normal scan pattern.
NIGHT MYOPIA
Another problem associated with night flying is night
myopia, or night-induced nearsightedness. With noth-
ing to focus on, your eyes automatically focus on a
point just slightly ahead of your aircraft. Searching out
and focusing on distant light sources, no matter how
dim, helps prevent the onset of night myopia.
FALSE HORIZON
A false horizon can occur when the natural horizon is
obscured or not readily apparent. It can be generated by
confusing bright stars and city lights. [Figure 13-6] It
can also occur while you are flying toward the shore of
an ocean or a large lake. Because of the relative darkness
of the water, the lights along the shoreline can be mis-
taken for the stars in the sky. [Figure 13-7]
White
Red
Green
Your Helicopter
White
Green
Red
Red Green
White
Figure 13-5. By interpreting the position lights on other aircraft, you can determine whether the aircraft is flying away from you
or is on a collision course. If you see a red position light to the right of a green light, such as shown by aircraft number 1, it is
flying toward you. You should watch this aircraft closely and be ready to change course. Aircraft number 2, on the other hand,
is flying away from you, as indicated by the white position light.
Apparent Horizon
Actual Horizon
Apparent Horizon
Actual Horizon
Figure 13-6. You can place your helicopter in an extremely
dangerous flight attitude if you align the helicopter with the
wrong lights. Here, the helicopter is aligned with a road and
not the horizon.
Figure 13-7. In this illusion, the shoreline is mistaken for the
horizon. In an attempt to correct for the apparent nose-high
attitude, a pilot may lower the collective and attempt to fly
“beneath the shore.”
LANDING ILLUSIONS
Landing illusions occur in many forms. Above feature-
less terrain at night, there is a natural tendency to fly a
lower-than-normal approach. Elements that cause any
type of visual obscuration, such as rain, haze, or a dark
runway environment also can cause low approaches.
Bright lights, steep surrounding terrain, and a wide run-
way can produce the illusion of being too low, with a
tendency to fly a higher-than-normal approach.
NIGHT FLIGHT
The night flying environment and the techniques you use
when flying at night, depend on outside conditions.
Flying on a bright, clear, moonlit evening when the visi-
bility is good and the wind is calm, is not much different
from flying during the day. However, if you are flying
on an overcast night over a sparsely populated area,
with little or no outside lights from the ground, the sit-
uation is quite different. Visibility is restricted so you
have to be more alert in steering clear of obstructions
and low clouds. Your options are also limited in the
event of an emergency, as it is more difficult to find
a place to land and determine wind direction and
speed. At night, you have to rely more heavily on the
aircraft systems, such as lights, flight instruments, and
navigation equipment. As a precaution, if the visibility
is limited or outside references are inadequate, you
should strongly consider delaying the flight until con-
ditions improve, unless you have received training in
instrument flight and your helicopter has the appropri-
ate instrumentation and equipment.
PREFLIGHT
The preflight inspection is performed in the usual man-
ner, except it should be done in a well lit area or with a
flashlight. Careful attention must be paid to the aircraft
electrical system. In helicopters equipped with fuses, a
spare set is required by regulation, and common sense,
so make sure they are onboard. If the helicopter is
equipped with circuit breakers, check to see that they
are not tripped. A tripped circuit breaker may be an
indication of an equipment malfunction. Reset it and
check the associated equipment for proper operation.
Check all the interior lights, especially the instrument
and panel lights. The panel lighting can usually be con-
trolled with a rheostat or dimmer switch, allowing you
to adjust the intensity. If the lights are too bright, a glare
may reflect off the windshield creating a distraction.
Always carry a flashlight with fresh batteries to pro-
vide an alternate source of light if the interior lights
malfunction.
All aircraft operating between sunset and sunrise are
required to have operable navigation lights. Turn
these lights on during the preflight to inspect them
visually for proper operation. Between sunset and
sunrise, theses lights must be on any time the engine
is running.
All recently manufactured aircraft certified for night
flight, must have an anticollision light that makes the
aircraft more visible to other pilots. This light is either
a red or white flashing light and may be in the form of
a rotating beacon or a strobe. While anticollision lights
are required for night VFR flights, they may be turned
off any time they create a distraction for the pilot.
One of the first steps in preparation for night flight is
becoming thoroughly familiar with the helicopter’s
cockpit, instrumentation and control layout. It is rec-
ommended that you practice locating each instrument,
control, and switch, both with and without cabin lights.
Since the markings on some switches and circuit
breaker panels may be hard to read at night, you should
assure yourself that you are able to locate and use these
devices, and read the markings in poor light conditions.
Before you start the engine, make sure all necessary
equipment and supplies needed for the flight, such as
charts, notepads, and flashlights, are accessible and
ready for use.
ENGINE STARTING AND ROTOR
ENGAGEMENT
Use extra caution when starting the engine and engag-
ing the rotors, especially in dark areas with little or no
outside lights. In addition to the usual call of “clear,”
turn on the position and anticollision lights. If condi-
tions permit, you might also want to turn the landing
light on momentarily to help warn others that you are
about to start the engine and engage the rotors.
TAXI TECHNIQUE
Landing lights usually cast a beam that is narrow and
concentrated ahead of the helicopter, so illumination to
the side is minimal. Therefore, you should slow your
taxi at night, especially in congested ramp and parking
areas. Some helicopters have a hover light in addition
to a landing light, which illuminates a larger area under
the helicopter.
When operating at an unfamiliar airport at night, you
should ask for instructions or advice concerning local
conditions, so as to avoid taxiing into areas of con-
struction, or unlighted, unmarked obstructions. Ground
controllers or UNICOM operators are usually coopera-
tive in furnishing you with this type of information.
TAKEOFF
Before takeoff, make sure that you have a clear, unob-
structed takeoff path. At airports, you may accomplish
this by taking off over a runway or taxiway, however, if
you are operating off-airport, you must pay more atten-
tion to the surroundings. Obstructions may also be dif-
ficult to see if you are taking off from an unlighted area.
Once you have chosen a suitable takeoff path, select a
point down the takeoff path to use for directional refer-
ence. During a night takeoff, you may notice a lack of
reliable outside visual references after you are airborne.
This is particularly true at small airports and off-airport
landing sites located in sparsely populated areas. To
compensate for the lack of outside references, use the
available flight instruments as an aid. Check the altime-
ter and the airspeed indicator to verify the proper climb
attitude. An attitude indicator, if installed, can enhance
your attitude reference.
The first 500 feet of altitude after takeoff is considered
to be the most critical period in transitioning from the
comparatively well-lighted airport or heliport into
what sometimes appears to be total darkness. A takeoff
at night is usually an “altitude over airspeed” maneu-
ver, meaning you will most likely perform a nearly
maximum performance takeoff. This improves the
chances for obstacle clearance and enhances safety.
When performing this maneuver, be sure to avoid the
cross-hatched or shaded areas of the height-velocity
diagram.
EN ROUTE PROCEDURES
In order to provide a higher margin of safety, it is rec-
ommended that you select a cruising altitude somewhat
higher than normal. There are several reasons for this.
First, a higher altitude gives you more clearance
between obstacles, especially those that are difficult to
see at night, such as high tension wires and unlighted
towers. Secondly, in the event of an engine failure, you
have more time to set up for a landing and the gliding
distance is greater giving you more options in making a
safe landing. Thirdly, radio reception is improved, par-
ticularly if you are using radio aids for navigation.
During your preflight planning, it is recommended that
you select a route of flight that keeps you within reach
of an airport, or any safe landing site, as much of the
time as possible. It is also recommended that you fly as
close as possible to a populated or lighted area such as
a highway or town. Not only does this offer more
options in the event of an emergency, but also makes
navigation a lot easier. A course comprised of a series
of slight zig-zags to stay close to suitable landing sites
and well lighted areas, only adds a little more time and
distance to an otherwise straight course.
In the event that you have to make a forced landing at
night, use the same procedure recommended for day-
time emergency landings. If available, turn on the land-
ing light during the final descent to help in avoiding
obstacles along your approach path.
COLLISION AVOIDANCE AT NIGHT
At night, the outside visual references are greatly
reduced especially when flying over a sparsely popu-
lated area with little or no lights. The result is that you
tend to focus on a single point or instrument, making
you less aware of the other traffic around. You must
make a special effort to devote enough time to scan for
traffic. You can determine another aircraft’s direction
of flight by interpreting the position and anticollision
lights.
APPROACH AND LANDING
Night approaches and landings do have some advan-
tages over daytime approaches, as the air is generally
smoother and the disruptive effects of turbulence and
excessive crosswinds are often absent. However, there
are a few special considerations and techniques that
apply to approaches at night. For example, when land-
ing at night, especially at an unfamiliar airport, make
the approach to a lighted runway and then use the taxi-
ways to avoid unlighted obstructions or equipment.
Carefully controlled studies have revealed that pilots
have a tendency to make lower approaches at night
than during the day. This is potentially dangerous as
you have a greater chance of hitting an obstacle, such
as an overhead wire or fence, which are difficult to see.
It is good practice to make steeper approaches at night,
thus increasing any obstacle clearance. Monitor your
altitude and rate of descent using the altimeter.
Another tendency is to focus too much on the landing
area and not pay enough attention to airspeed. If too
much airspeed is lost, a settling-with-power condition
may result. Maintain the proper attitude during the
approach, and make sure you keep some forward air-
speed and movement until close to the ground. Outside
visual reference for airspeed and rate of closure may
not be available, especially when landing in an
unlighted area, so pay special attention to the airspeed
indicator
Although the landing light is a helpful aid when mak-
ing night approaches, there is an inherent disadvantage.
The portion of the landing area illuminated by the land-
ing light seems higher than the dark area surrounding
it. This effect can cause you to terminate the approach
at too high an altitude, resulting in a settling-with-
power condition and a hard landing.