Night Vision: Rods and Cones

Night Vision: Light-Sensitive Cells

• Two types of light-sensitive cells are located in the retina: rods and cones.
• Cones are concentrated in the macula, specifically the fovea, and are used for day or high-intensity light vision.
• Cones are involved with central vision, enabling the detection of detail, color perception, and identification of distant objects.
• Rods are located mainly in the periphery of the retina, an area about 10,000 times more sensitive to light than the fovea.
• Rods are used for low light intensity or night vision, providing peripheral vision for position references.
• Rods detect objects in shades of gray but cannot detect detail or color, and they make night vision possible.

Dark Adaptation

• Cones adapt to darkness in approximately 5 to 10 minutes.
• Rods require a longer adaptation time, about 30 minutes, to adjust to darkness.
• Pilots should allow sufficient time for eye adaptation to low light levels and avoid exposure to bright light to prevent temporary blindness.

Night Blind Spot

• The night blind spot results from the absence of rods in the fovea.
• It affects the central 5 to 10 degrees of the visual field under low ambient illumination.
• This can cause objects viewed directly at night to go undetected or fade away.

False Horizon Illusion

• Flying at night under clear skies with ground lights makes it difficult to distinguish ground lights from stars.
• Geometric patterns of ground lights can provide inaccurate visual information, making it difficult to align the aircraft with the actual horizon.

Autokinesis

• In the dark, a stationary light can appear to move when stared at for many seconds, which is known as Autokinesis.
• A disoriented pilot could lose control of the aircraft when trying to align with the perceived movement of this light.

Featureless Terrain Illusion

• The featureless terrain illusion, or black-hole approach, occurs when landing is made over water or non-lighted terrain, with runway lights as the only source of light.
• Without peripheral visual cues, orientation is difficult, and the runway may seem out of position, potentially causing the pilot to land short of the runway.

Runway and Approach Lighting Illusions

• Bright runway/approach lighting, especially with few surrounding lights, creates the illusion of being lower or closer to the runway, causing pilots to fly a higher approach.
• Conversely, terrain with few lights can make the runway appear farther away, causing pilots to fly a lower-than-normal approach.

Ground Lighting Illusions

• Lights along a straight path, such as roads or moving trains, can be mistaken for runway and approach lights.
• Bright runway and approach lighting, with few surrounding lights, may create the illusion of less distance to the runway, causing pilots to fly a higher approach.

Preventing Optical Illusions at Night

• Anticipate visual illusions during approaches to unfamiliar airports, especially at night or in adverse weather conditions.
• Use airport diagrams and Chart Supplements for runway slope, terrain, and lighting information.
• Make frequent reference to the altimeter during all approaches, day or night.
• If possible, conduct an aerial visual inspection of unfamiliar airports before landing.
• Use VASI or PAPI systems or an electronic glideslope for visual reference when available.
• Utilize the visual descent point (VDP) on non-precision instrument approach procedure charts.
• Recognize that the chances of an approach accident increase when an emergency or other activity distracts from normal procedures and maintain proficiency in night landing procedures.

Maintaining Good Eyesight

• Good eyesight depends on physical condition, and fatigue, colds, vitamin deficiency, alcohol, stimulants, smoking, or medication can seriously impair vision.

Self-Imposed Stresses that Impair Vision

• Self-imposed stresses such as self-medication, alcohol consumption, tobacco use, hypoglycemia, sleep deprivation/fatigue, and extreme emotional upset can seriously impair vision.

Hypoxia and Visual Performance

• Unaided night vision depends on the function and sensitivity of retinal rods.
• Hypoxia significantly reduces rod sensitivity, and sharp vision requires adequate oxygen, especially at night.
• Night vision declines measurably above 4,000 feet without supplemental oxygen.

Airport Lighting: REILs

• Runway End Identifier Lights (REILs) are installed at many airfields for rapid and positive identification of the approach end of a particular runway.
• REILs consist of a pair of synchronized flashing lights located laterally on each side of the runway threshold and may be omnidirectional or unidirectional facing the approach area.

Runway Edge Lights

• Runway edge lights outline runway edges during darkness or reduced visibility conditions and are white, except on instrument runways.
• On instrument runways, yellow replaces white on the last 2,000 feet or half the runway length, whichever is less, to form a caution zone for landings.
• Lights marking runway ends emit red light toward the runway for departing aircraft and green outward to indicate the threshold to landing aircraft.
• Light systems are classified by intensity or brightness: High Intensity (HIRL), Medium Intensity (MIRL), and Low Intensity (LIRL).

Runway Centerline Lighting System (RCLS)

• RCLS are installed on some precision approach runways to facilitate landing in adverse visibility.
• Lights are located along the runway centerline, spaced at 50-foot intervals, and appear white from the landing threshold until the last 3,000 feet.
• The white lights alternate with red for the next 2,000 feet, and for the last 1,000 feet of the runway, all centerline lights are red.

Touchdown Zone Lights (TDZLs)

• TDZLs consist of two rows of transverse light bars disposed symmetrically about the runway centerline.
• The system consists of steady-burning white lights starting 100 feet beyond the landing threshold and extending to 3,000 feet beyond the threshold or to the midpoint of the runway, whichever is less.

Taxiway Lighting

• Taxiway edge lights outline taxiway edges and consist of blue lights.
• Taxiway centerline lights assist ground traffic in low visibility and consist of steady-burning green lights.
• Clearance bar lights are installed at holding positions on taxiways and consist of three in-pavement steady-burning yellow lights.
• Runway guard lights are installed at taxiway/runway intersections and consist of either a pair of elevated flashing lights or in-pavement yellow lights across the taxiway.
• Stop bar lights are used to confirm ATC clearance to enter or cross an active runway in low visibility.

Rotating Beacons to Identify Airports

• White and green signifies a lighted land airport.
• Green alone signifies a lighted land airport.
• White and yellow signifies a lighted water airport.
• Yellow alone signifies a lighted water airport.
• Green, yellow, and white signifies a lighted heliport.
• White (dual peaked) and green signifies a lighted military airport.
• Green alone or yellow alone is used only in connection with a white and green or white and yellow beacon display, respectively.

Visual Approach Slope Indicator (VASI)

• VASI is a system of lights arranged to provide visual descent guidance information during the approach to a runway.
• It uses color differential between red and white, with each light projecting a beam having a white segment in the upper half and a red segment in the lower half.
• For a two-bar VASI: red over red is below the glide path, red over white is on the glide path, and white over white is above the glide path.

Precision Approach Path Indicator (PAPI)

• PAPI uses light units similar to VASI but are installed in a single row of either two- or four-light units and have an effective visual range of about 5 miles during the day and up to 20 miles at night.
• Four white lights indicate a high position (more than 3.5 degrees), three white one red indicate slightly high (3.2 degrees), two white two red indicate on the glide path (3 degrees), one white three red indicate slightly low (2.8 degrees), and four red lights indicate a low position (less than 2.5 degrees).

Obstruction Lighting

• Aviation red obstruction lights include flashing aviation red beacons and steady-burning aviation red lights for nighttime operations.
• Medium and high-intensity white obstruction lights may be used during daytime and twilight with reduced intensity for nighttime operation and are not normally installed on structures less than 200 feet.
• Dual lighting combines flashing aviation red beacons and steady-burning aviation red lights for nighttime operations and flashing high-intensity white lights for daytime operation.
• Catenary lighting includes medium and high-intensity flashing white markers for high voltage transmission lines and support structures.

Determining the Status of a Light System

• Pilots determine the status of a light system by checking the Chart Supplement U.S. and any Notices to Airmen (NOTAMs) for available lighting systems, light intensities, and radio-controlled light system frequencies.

Activating Radio-Controlled Runway Lights

• Pilots activate radio-controlled lights by keying the microphone on a specified frequency.
• On initial arrival, key the microphone seven times to turn the lights on and achieve maximum brightness.
• If the runway lights are already on, repeat the above sequence to ensure a full 15 minutes of lighting.
• The intensity of the lights can be adjusted by keying the microphone seven, five, or three times within 5 seconds.

Airplane Equipment required for VFR Night Flight

• Required instruments and equipment include all equipment for VFR day flight, plus:
• Fuses: one spare set or three of each kind required accessible to the pilot.
• Landing light if operated for hire.
• Anticollision light system: approved aviation red or white.
• Position lights: navigation lights.
• An adequate source of electrical energy for all installed electrical and radio equipment.

Aircraft Position lights

• A red light is positioned on the left wingtip, a green light on the right wingtip, and a white light on the tail.
• If both a red and green light of another aircraft are observed, and the red light is on the left and the green to the right, the airplane is flying in the same direction.
• If red were on the right and green to the left, the airplane could be on a collision course.

Position Light Operation Times

• Position lights are required from sunset to sunrise.

Aircraft Operation in a Night Operations Area

• Aircraft must be clearly illuminated, have lighted position lights, or be in an area marked by obstruction lights.

Mitigating Risk During Engine Start at Night

• Before entering the airplane, clear the area around the airplane.
• Inform ramp personnel and others of the intention to start.
• Switch on the NAV lights and rotating beacon prior to start.
• Carefully scan the area around the aircraft.
• If all is clear, announce "clear prop," pause and listen, clear the area again, then start the engine.
• While on the ramp, remain alert for activity outside the aircraft.
• Always be ready for an immediate engine shutdown.

Aircraft Anticollision Lights

• Anticollision lights are required to be on during night flight operations.
• The pilot-in-command can determine that turning the lights off is in the interest of safety due to operating conditions.

Definitions of Night

• FAA definition in 14 CFR $1.1: The time between the end of evening civil twilight and the beginning of morning civil twilight.
• FAA definition in 14 CFR $61.57: The period beginning one hour after sunset and ending one hour before sunrise.
• FAA definition in 14 CFR $91.209: The period from sunset to sunrise.

Pilot Equipment for Night Flight Operations

• At least one reliable flashlight (incandescent or LED dimmable, white/red light) and a spare set of batteries.

Recommended Light Color for Night Operations

• White light is used for preflight visual inspections, red light is used for flight deck operations, and dim white light may be used for chart reading.

Effect of Red-Light Illumination on Aeronautical Charts

• Red light distorts colors such that magenta and yellow pigments appear as red, and cyan pigment appears black.

Other Important Items

• Aeronautical charts and spare batteries for the flashlight.

Electronic Flight Bags

• An unadjusted EFB can reduce night vision.
• Device brightness should be adjusted as to not impair night vision.

Night Flight Equipment Checks

• Personal equipment such as flashlights, EFBs, and portable transceivers.
• Spare batteries charged and available.
• Proper functionality of the aircraft's position lights, landing light, and rotating beacon.

First Indication of Flying into Restricted Visibility

• The gradual disappearance of lights on the ground.
• To avoid disorientation, if the lights appear surrounded by a halo or glow.

Hazards of Crossing Large Bodies of Water

• The pilot may be forced to ditch the airplane in the water in case of engine failure.
• Limited or no lighting makes the horizon blend with the water.
• Poor visibility conditions can lead to a loss of orientation.
• Star reflections on the water surface may appear as a continuous array of lights.

Attention to Weather Reports

• Special attention should be given to temperature/dewpoint spreads to detect possible fog formation.

Determining Wind Directions and Speeds

• Accurate calculations are necessary to counteract inaccurate drift perception at night.

Preparing Aeronautical Charts for Night Flight

• Study the planned route thoroughly, marking lighted checkpoints clearly and obtaining charts for the route and any adjacent charts.
• Airport diagrams should be available.

Radio Navigational Aids or GPS

• Review all radio navigation aids for correct frequencies and availability.
• Ensure the GPS is working properly before the flight and that all the necessary waypoints are properly programmed.

Risk Factors

• Pilot-Fatigue, night flying currency and proficiency, deficiencies in night vision, optical illusions.
• Aircraft—Airworthiness, inoperative lighting, lack of proper equipment.
• Environment-Weather, situational awareness, terrain, obstacles, CFIT, airport lighting familiarity.
• External pressures-Need to get there, pressure from passengers, someone waiting.