Normal view Astigmatic view
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.
Rods and
cones
Fovea
(All Cones)
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.
PUPIL
Light passes through the cornea (the
transparent window on the front of the
eye) and then through the lens to
focus on the retina.
CORNEA
Iris
Retina
Lens
Optic nerve
Rod concentration
Figure 12-2. Example of a view that might be experienced by someone with astigmatism.
Figure 12-3. The human eye.
Visual Acuity
Normal visual acuity, or sharpness, is 20/20. A value of
20/80 indicates that an individual reads at 20 feet the letters
that an individual with normal acuity (20/20) reads at 80
feet away. The human eye functions like a camera. It has
a camera. A camera is able to focus on near and far objects
by changing the distance between the lens and the film.
With the eye on the other hand, objects can be seen clearly
at various distances because the shape of its lens is changed
automatically by small muscles.
Once a target is detected in the peripheral
field of dark-adapted vision, aircrews
maintain continual surveillance by using
the off-center vision technique. They look
10 degrees above, below, or to either side
of the target, viewing it no longer than two
to three seconds at each position.
Observer
FOCAL POINTS
10°
10°
X 10° X 10°
Figure 12-4. Off-center vision technique.
an instantaneous field of view, which is oval and typically
measures 120° vertically by 150° horizontally. When both
eyes are used for viewing, the overall field of vision measures
about 120° vertically by 200° horizontally.
The Eye
Vision is primarily the result of light striking a photosensitive
layer, called the retina, at the back of the eye. The retina is
composed of light-sensitive cones and rods. The cones in the
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.
Cones
Cones are concentrated around the center of the retina. They
gradually diminish in number as the distance from the center
increases. Cones allow color perception 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. The best vision
in daylight is obtained by looking directly at the object.
This focuses the image on the fovea, where detail is best
seen. The cones, however, do not function well in darkness,
which explains why color is not seen as vividly at night as
it is during the day.
Rods
Concentrated outside the fovea area, the rods are the dim
light and night receptors. 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 most 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 rod receptors.
In low light, the cones lose much of their function, while
rods become more receptive. The eye sacrifices sharpness for
sensitivity. The ability to see an object directly in front of you is
reduced, and much depth perception is lost, as well as judgment
of size. The concentration of cones in the fovea can make a
night blindspot at the center of vision. How well a person sees
at night is determined by the rods in the eyes, as well as by the
amount of light allowed into the eyes. At night, the wider the
pupil is open at night, the better night vision becomes.
Night Vision
Diet and general physical health have an impact on how well
a person can see in the dark. Deficiencies in vitamins A and C
have been shown to reduce night acuity. Other factors, such
as carbon monoxide poisoning, smoking, alcohol, and certain
drugs can greatly decrease night vision. Lack of oxygen can
also decrease night vision as the eye requires more oxygen
per unit weight than any other part of the body.
Night Scanning
Good night visual acuity is needed for collision avoidance.
Night scanning, like day scanning, uses a series of short,
regularly spaced eye movements in 10° sectors. Unlike day
scanning, however, off-center viewing is used to focus objects
on the rods rather than the fovea blindspot. [Figure 12-4] When
looking at an object, avoid staring at it too long. If staring
at an object without moving the 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. Also, move the eyes more slowly from
sector to sector than during the day to prevent blurring.
During daylight, objects can be perceived at a great distance
with good detail. At night, range is limited, and detail is poor.
Objects along the flight path can be more readily identified at
night, by using the proper techniques to scan the terrain. To
10°
6 seconds
6 seconds
6 seconds
6 seconds
6 seconds 3 seconds
3 seconds 3 seconds 3 seconds
3 seconds 3 seconds
4 seconds 4 seconds
4 seconds
4 seconds
Figure 12-5. Scanning pattern.
Figure 12-6. Night vision.
scan effectively, pilots look from side to side. They should
begin scanning at the greatest distance at which an object
can be perceived high on the horizon, thence moving inward
toward the position of the aircraft. Figure 12-5 shows this
scanning pattern. Because the light-sensitive elements of
the retina are unable to perceive images that are in motion, a
stop-turn-stop-turn motion should be used. For each stop, an
area about 30 degrees wide should be scanned. This viewing
angle includes an area about 250 meters wide at a distance of
500 meters. The duration of each stop is based on the degree
of detail that is required, but no stop should last more than
two or three seconds. When moving from one viewing point
to the next, pilots should overlap the previous field of view
by 10 degrees. This scanning technique allows greater clarity
in observing the periphery. Other scanning techniques, as
illustrated in Figure 12-6, may be developed to fit the situation.
Obstruction Detection
Obstructions having poor reflective surfaces, such as wires
and small tree limbs, are difficult to detect. The best way to
Figure 12-7. Aircraft position lights.
locate wires is by looking for the support structures. However,
pilots should review the most current hazard maps with
known wire locations before night flights.
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 definition of night flight in accordance with
14 CFR part 91, currency requirements, fuel reserves, and
necessary electrical systems.
Position lights enable a pilot to locate another aircraft, as
well as help 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 all flights, if equipped on the aircraft and in an operable
condition (in accordance with 14 CFR Section 91.209(b),
which aids in the identification during night conditions).
These flashing lights can be in a number of locations but are
most commonly found on the top and bottom of the cabin.
Figure 12-7 shows examples of aircraft lighting. By
interpreting the position lights on other aircraft, the pilot in
aircraft 3 can determine whether the aircraft is flying in the
opposite direction or is on a collision course. If a red position
light is seen to the right of a green light, such as shown by
aircraft 1, it is flying toward aircraft 3. A pilot should watch
this aircraft closely and be ready to change course. Aircraft 2,
on the other hand, is flying away from aircraft 3, as indicated
by the white position light.
Visual Illusions
Illusions give false impressions or misconceptions of actual
conditions; therefore, pilots must understand the type of
illusions that can occur and the resulting disorientation.
Although the eye is the most reliable of the senses, some
illusions can result from misinterpreting what is seen; what
is perceived is not always accurate. Even with the references
outside the cockpit and the display of instruments inside,
pilots must be on guard to interpret information correctly.
Relative-Motion Illusion
Relative motion is the falsely perceived self-motion in
relation to the motion of another object. The most common
example is as follows. An individual in a car is stopped at a
traffic light and another car pulls alongside. The individual
who was stopped at the light perceives the forward motion
of the second car as his or her own motion rearward. This
results in the individual applying more pressure to the brakes
unnecessarily. This illusion can be encountered during flight
in situations such as formation flight, hover taxi, or hovering
over water or tall grass.
Confusion with Ground Lights
Confusion with ground lights occurs when a pilot mistakes
ground lights for stars. The pilot can place the helicopter
in an extremely dangerous flight attitude if he or she aligns
it with the wrong lights. In Figure 12-8A, the helicopter is
aligned with a road and not with the horizon. Isolated ground
lights can appear as stars and could lead to the illusion that
the helicopter is in a nose-high attitude.
When no stars are visible because of overcast conditions,
unlighted areas of terrain can blend with the dark overcast to
create the illusion that the unlighted terrain is part of the sky
in Figure 12-8B. 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.” This illusion can be avoided by
referencing the flight instruments and establishing a true
horizon and attitude.
Reversible Perspective Illusion
At night, an aircraft or helicopter may appear to be moving
away when it is actually approaching. If the pilot of each
aircraft has the same assumption, and the rate of closure
is significant, by the time each pilot realizes his or her
own error in assumption, it may be too late to avoid a
mishap. This illusion is called reversible perspective and
is often experienced when a pilot observes another aircraft
Perceived Horizon
(ground lights)
Actual Horizon
A O M
CLUTCH MR
TEMP
MR
CHIP
STARTER
ON
TR
CHIP
lOW
FUEL
LOW
RPM
GS
VERTICAL SPEED
100 FEET PER MINUTE
UP
DOWN
2I
I2 6
2 MIN TURN
DC ELEC
L R
30.0
29.929.8
I00 FEET
CALIBRATED
TO
20,000 FEET
ALT
20 20
I0 I0
I0 I0
20 20
TESTSTBY PWR
IN Hg
ALg.
MANFOLD
PRESS
20 30
0 10
MPH
KNOTS
90 80 70
E R
%RPM
20 20
I0 I0
I0 I0
20 20
TESTSTBY PWR
Perceived Horizon
(shore line)
Actual Horizon
(overcast sky)
A O M
CLUTCH MR
TEMP
MR
CHIP
STARTER
ON
TR
CHIP
lOW
FUEL
LOW
RPM
GS
VERTICAL SPEED
100 FEET PER MINUTE
UP
DOWN
2I
I2 6
2 MIN TURN
DC ELEC
L R
30.0
29.929.8
I00 FEET
CALIBRATED
TO
20,000 FEET
ALT
20 20
I0 I0
I0 I0
20 20
TESTSTBY PWR
IN Hg
ALg.
MANFOLD
PRESS
20 30
0 10
MPH
KNOTS
90 80 70
E R
%RPM
20 20
I0 I0
I0 I0
20 20
TESTSTBY PWR
Figure 12-8. At night, the horizon may be hard to discern due to dark terrain and misleading light patterns on the ground.
or helicopter flying an approaching, parallel course. To
determine the direction of flight, the pilot should observe the
other aircraft’s position lights. Remember the following: red
on right returning; that is, if an aircraft is seen with the red
position light on the right and the green position light on the
left, the observed aircraft is traveling in the opposite direction.
Flicker Vertigo
Flicker vertigo is technically not an illusion; however, as
most people are aware from personal experience, viewing
a flickering light can be both distracting and annoying.
Flicker vertigo may be created by helicopter rotor blades or
airplane propellers interrupting direct sunlight at a rate of 4
to 20 cycles per second. Flashing anticollision strobe lights,
especially while the aircraft is in the clouds, can also produce
this effect. One should also be aware that photic stimuli at
certain frequencies could produce seizures in those rare
individuals who are susceptible to flicker-induced epilepsy.
Night Flight
The night flying environment and the techniques used when
flying at night depend on outside conditions. Flying on a
bright, clear, moonlit evening when the visibility is good, and
the wind is calm is not much different from flying during the
day. However, if flying on an overcast night over a sparsely
populated area, with few or no outside lights on the ground,
the situation is quite different. Visibility is restricted, so be
more alert in steering clear of obstructions and low clouds.
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, rely more heavily on the aircraft
systems, such as lights, flight instruments, and navigation
equipment. As a precaution, if visibility is limited or outside
references are inadequate, strongly consider delaying the
flight until conditions improve, unless proper instrument
flight training has been received and the helicopter has the
appropriate instrumentation and equipment.
Preflight
Aircraft preflight inspection is a critical aspect of flight
safety. It must comply with the appropriate rotorcraft flight
manual (RFM). Preflight should be scheduled as early as
possible in the flight planning sequence, preferably during
daylight hours, allowing time for maintenance assistance and
correction. If a night preflight is necessary, a flashlight with
an unfiltered lens (white light) should be used to supplement
lighting. Oil and hydraulic fluid levels and leaks are difficult
to detect with a blue-green or red lens. Windscreens should
be checked to ensure they are clean and relatively free of
scratches. Slight scratches are acceptable for day flight but
may not be for night flight. The search light or landing light
should be positioned for the best possible illumination during
an emergency descent.
Careful attention must be paid to the aircraft electrical system.
In helicopters equipped with fuses, a spare set is required
by regulation, and by common sense, so make sure they are
on board. 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 and should
be left for maintenance to troubleshoot before flying.
All aircraft operating between sunset and sunrise are required
to have operable navigation (position) lights. Turn these lights
on during the preflight to inspect them visually for proper
operation. Between sunset and sunrise, these lights must be
on any time the helicopter is operating.
All recently manufactured aircraft certificated 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
visual flight rules (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 to
become thoroughly familiar with the helicopter’s cockpit,
instrumentation, and control layout. It is recommended that
a pilot 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 difficult
to read at night, be able to locate and use these devices, and
read the markings in poor light conditions. Before starting
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.
Cockpit Lights
Check all interior lights with special attention to the instrument
and panel lights. The panel lighting can usually be controlled
with a rheostat or dimmer switch, allowing the pilot to adjust
the intensity. If a particular light is too bright or causes
reflection or glare off the windshield, it should be adjusted or
turned off. As ambient light level decreases from twilight to
darkness, intensity of the cockpit lights is reduced to a low,
usable intensity level that reduces any glare or reflection off
the windshield. The light level should be adjusted to as close
to the ambient light level as possible. A flashlight, with red or
blue-green lens filter, or map light can supplement the available
light in the cockpit. Always carry a flashlight with fresh
batteries to provide an alternate source of light if the interior
lights malfunction. If an existing map/utility light is used, it
should be hand-held or remounted to a convenient location.
In order to retain night adaptation, use low level light when
using your checklist. Brief your passengers on the importance
of light discipline during night flight so the pilot is not blinded,
causing loss of dark adaptation.
Engine Starting and Rotor Engagement
Use extra caution when starting the engine and engaging 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 conditions permit, also turn the
landing light on momentarily to help warn others that the
engine is about to start 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, slow the 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, ask for
instructions or advice concerning local conditions, so as to
avoid taxiing into areas of construction, or unlighted, unmarked
obstructions. Ground controllers or UNICOM operators are
usually cooperative in furnishing this type of information.
Night Traffic Patterns
Traffic patterns are covered in Chapter 9, Basic Flight
Maneuvers, but the following additional considerations
should be taken into account when flying a helicopter in a
night traffic pattern:
1. The minimum recommended pattern height at night
is 1,000 feet when able.
2. If possible, consider taking the right hand night pattern
with fixed wing in the left hand pattern for extra
separation, but if needed, conform and integrate with
the fixed wing using the same pattern height.
3. Be extra vigilant on abiding with noise abatement
procedures at night.
4. Always plan to use the lit runway at night for
unaided (no night vision equipment) approaches and
departures.
5. Avoid downwind and crosswind approaches at night
when able.
Takeoff
Before takeoff, make sure that there is a clear, unobstructed
takeoff path. At airports, this is accomplished by taking
off over a runway or taxi way, however, if operating off-
airport, pay more attention to the surroundings. Obstructions
may also be difficult to see if taking off from an unlighted
area. Once a suitable takeoff path is chosen, select a point
down the takeoff path to use for directional reference. The
landing light should be positioned in order to illuminate
the tallest obstacles in the takeoff path. During a night
takeoff, notice a lack of reliable outside visual references
after becoming 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 altimeter and the airspeed indicator to verify the
proper climb attitude. An attitude indicator, if installed, can
enhance attitude reference.
The first 500 feet of altitude after takeoff is considered to be
the most critical period in transitioning from the comparatively
well-lit airport or heliport into what sometimes appears to be
total darkness. A takeoff at night is usually an “altitude over
airspeed” maneuver, meaning a pilot most likely performs
a nearly maximum performance takeoff. This improves the
chances for obstacle clearance and enhances safety.
En Route Procedures
In order to provide a higher margin of safety, it is
recommended that a cruising altitude somewhat higher than
normal be selected. There are three reasons for this. First,
a higher altitude gives more clearance between obstacles,
especially those that are difficult to see at night, such as high-
tension wires and unlighted towers. Second, in the event of
an engine failure, there is more time to set up for a landing
and the greater gliding distance gives more options for a safe
landing. Third, radio reception is improved, particularly if
using radio aids for navigation.
During preflight planning, when possible, it is recommended
that a route of flight be selected that is within reach of an
airport, or any safe landing site. It is also recommended
that pilots 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 zigzags to stay close to suitable landing sites and
well-lit areas, only adds a little more time and distance to an
otherwise straight course.
In the event of a forced landing at night, use the same
procedure recommended for day time emergency landings.
If available, turn on the landing light during the final descent
to help in avoiding obstacles along the approach path.
Collision Avoidance at Night
Because the quantity and quality of outside visual references
are greatly reduced, a pilot tends to focus on a single point
or instrument, making him or her less aware of the other
traffic around. Make a special effort to devote enough time
to scan for traffic. As discussed previously in this chapter,
effective scanning is accomplished with a series of short,
regularly spaced eye movements that bring successive
areas of the sky into the central visual field. Contrary to
the 30-degree scan used to view the ground in the case of
scanning for other aircraft, each movement in this case
should not exceed 10 degrees, and each area should be
observed for at least 1 second to enable detection. If the
pilot detects a dimly lit object in a certain direction, the
pilot should not look directly at the object, but scan the area
adjacent to it, called off-center viewing. This will decrease
the chances of fixating on the light and allow focusing more
on the objects (e.g., tower, aircraft, ground lights). Short
stops of a few seconds in duration in each scan will help to
detect the light and its movement. A pilot can determine
another aircraft’s direction of flight by interpreting the
position and anticollision lights, as previously described.
When scanning, pilots should also remember to move their
heads, not just their eyes. Ground obstructions can cover
a considerable amount of sky, and the area can easily be
uncovered by a small head movement.
Approach and Landing
Night approaches and landings do have some advantages 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 landing at night, especially at an unfamiliar
airport, make the approach to a lighted runway and then use
the taxiways 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 there is a greater chance
of hitting an obstacle, such as an overhead wire or fence, that is
difficult to see. It is good practice to make steeper approaches at
night, increasing the probability of clearing obstacles. Monitor
altitude and rate of descent using the altimeter.
Another pilot tendency during night flight is to focus too
much on the landing area and not pay enough attention to
airspeed. If too much airspeed is lost, a vortex ring state
condition may result. Maintain the proper attitude during
the approach, and ensure that you keep some forward
airspeed and movement until close to the ground. Outside
visual references for airspeed and rate of closure may not be
available, especially when landing in an unlit area, so pay
special attention to the airspeed indicator.
Although the landing light is a helpful aid when making
night approaches, there is an inherent disadvantage. The
portion of the landing area illuminated by the landing light
seems higher than the dark area surrounding it. This effect
can cause a pilot to terminate the approach at an altitude that
is too high, which may result in a vortex ring state condition
and a hard landing.
Illusions Leading to Landing Errors
Various surface features and atmospheric conditions
encountered in night landing can create illusions of incorrect
height above and distance from the runway threshold.
Landing errors from these illusions can be prevented by
anticipating them during approaches, conducting an aerial
visual inspection of unfamiliar airports before landing, using
electronic glideslope or VASI systems when available, and
maintaining optimum proficiency in landing procedures.
Featureless Terrain Illusion
An absence of ground features, as when landing over water,
darkened areas, and terrain made featureless by snow, can
create the illusion that the aircraft is at a higher altitude than
it actually is. The pilot who does not recognize this illusion
will fly a lower approach.
Atmospheric Illusions
Rain on the windscreen can create the illusion of greater
height, and atmospheric haze can create the illusion of being
at a greater distance from the runway. The pilot who does not
recognize these illusions flies a higher approach. Penetration
of fog can create the illusion of pitching up. The pilot who
does not recognize this illusion steepens the approach, often
quite abruptly.
Ground Lighting Illusions
Lights along a straight path can be mistaken for runway
and approach lights. This might include street lights along a
roadside or even the internal lights of a moving train. Another
illusion may occur with very intense runway and approach
lighting. Due to the relative brightness of these lights, the
pilot may perceive them to be closer than they really are.
Assuming that the lights are as close as they appear, the
pilot may attempt an approach that is actually lower than
glideslope. Conversely, the pilot flying over terrain with few
lights may make a lower than normal approach.
Helicopter Night VFR Operations
While ceiling and visibility significantly affect safety in night
VFR operations, lighting conditions also have a profound
effect on safety. Even in conditions in which visibility and
ceiling are determined to be visual meteorological conditions,
the ability to discern unlit or low contrast objects and terrain
at night may be compromised. The ability to discern these
objects and terrain is referred to as the “seeing condition,”
and is related to the amount of natural and man-made
lighting available, and the contrast, reflectivity, and texture
of surface terrain and obstruction features. In order to conduct
operations safely, seeing conditions must be accounted for in
the planning and execution of night VFR operations.
Night VFR seeing conditions can be described by identifying
high lighting conditions and low lighting conditions.
High lighting conditions exist when one of two sets of
conditions are present:
1. The sky cover is less than broken (less than 5⁄8 cloud
cover), the time is between the local moon rise and
moon set, and the lunar disk is at least 50 percent
illuminated; or
2. The aircraft is operated over surface lighting that, at
least, provides lighting of prominent obstacles, the
identification of terrain features (shorelines, valleys,
hills, mountains, slopes) and a horizontal reference
by which the pilot may control the helicopter. For
example, this surface lighting may be the result of:
a. Extensive cultural lighting (manmade, such as a
built-up area of a city),
b. Significant reflected cultural lighting (such as the
illumination caused by the reflection of a major
metropolitan area’s lighting reflecting off a cloud
ceiling), or
c. Limited cultural lighting combined with a
high level of natural reflectivity of celestial
illumination, such as that provided by a surface
covered by snow or a desert surface.
Low lighting conditions are those that do not meet the high
lighting conditions requirements.
Some areas may be considered a high lighting environment
only in specific circumstances. For example, some surfaces,
such as a forest with limited cultural lighting, normally
have little reflectivity, requiring dependence on significant
moonlight to achieve a high lighting condition. However,
when that same forest is covered with snow, its reflectivity
may support a high lighting condition based only on starlight.
Similarly, a desolate area, with little cultural lighting, such as
a desert, may have such inherent natural reflectivity that it
may be considered a high lighting conditions area regardless
of season, provided the cloud cover does not prevent starlight
from being reflected from the surface. Other surfaces, such
as areas of open water, may never have enough reflectivity or
cultural lighting to ever be characterized as a high lighting area.
Through the accumulation of night flying experience in a
particular area, the pilot develops the ability to determine,
prior to departure, which areas can be considered supporting
high or low lighting conditions. Without that pilot experience,
low lighting considerations should be applied by pilots for
both preflight planning and operations until high lighting
conditions are observed or determined to be regularly
available. Even if the aircraft is certified for day and night
VFR conditions, night flight should only be conducted if
adequate celestial illumination is assured during the entirety
of the flight.
Chapter Summary
Knowledge of the basic anatomy and physiology of the eye
is helpful in the study of helicopter night operations. Adding
to that knowledge a study of visual illusions gives the pilot
ways to overcome those illusions. Techniques for preflight,
engine start-up, collision avoidance, and night approach and
landings help teach the pilot safer ways to conduct flight at
night. More detailed information on the subjects discussed
in this chapter is available in the Aeronautical Information
Manual (AIM) and online at www.faa.gov.