Per the regulations, "night" is defined as the time between the end of evening civil twilight and the beginning of morning civil twilight (14 CFR 1.1, "Definitions and Abbreviations"). Morning civil twilight begins when the geometric center of the sun is 6° below the horizon, ending at sunrise. Evening civil twilight begins at sunset, ending when the geometric center of the sun reaches 6° below the horizon.
For flight operations, "night" refers to the time period starting one (1) hour after sunset and ending one (1) hour before sunrise (14 CFR part 61). No person may act as pilot in command (PIC) of an aircraft carrying passengers, within the preceding 90 days, unless that person has made at least three takeoffs and three landings to a full stop during this night period.
During the period from sunset to sunrise, operating aircraft are required to have a functioning anti-collision light system, including a flashing or rotating beacon and position lights.
The Pilot's Handbook of Aeronautical Knowledge is one of the reference texts for this task. Chapter 17, "Aeromedical Factors," includes information on vision, dark adaptation, and night illusions.
Chapter 10 of the Airplane Flying Handbook, "Night Operations," also covers aeromedical content, along with the practical components of this task.
Factors related to night vision
There are two types of light-sensitive nerves within the retina: Cones and rods. Both the cones and the rods are used for vision during daylight and moonlight. In the absence of normal light, the process of night vision is placed almost entirely on the rods, which make night vision possible.
To see an object clearly at night, pilots should looking 5° to 10° off center of the object. During daylight, an object can be seen best by looking directly at it. At night, there is a night blind spot in the center of the field of vision. Any object is in this area may not be perceived by the optic nerve.
During the dark adaptation process, the pupils immediately enlarge to receive as much available light as possible. Within five to ten minutes, the cones adjust to the limited amount of light. After this, the eyes are approximately 100 times more sensitive to light than they were before the dark room was entered.
It takes about about 30 minutes for the rods to adjust to darkness. This is due to the central location of cones in the eye. A night blind spot in the center of the field of vision can develop.
If a night flight is scheduled, pilots and crew members should wear sunglasses when exposed to bright sunlight.
Lack of oxygen to the rods (hypoxia) significantly reduces their sensitivity. Supplemental oxygen is recommended above 5,000 MSL.
Disorientation and night optical illusions
Autokinesis is caused by staring at a single point of light against a dark background for more than a few seconds. The light will appear to move on its own in about 8 to 10 seconds. This illusion can be eliminated or reduced by visual scanning, by increasing the number of lights, or by varying the light intensity.
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. It can also occur while 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 mistaken for stars in the sky.
Dark nights tend to eliminate reference to a visual horizon.
A reversible perspective illusion may make an aircraft appear to be moving away from a second aircraft when it is, in fact, approaching a second aircraft. This illusion often occurs when an aircraft is flying parallel to another's course. To determine the direction of flight, pilots should observe aircraft lights and their relative position to the horizon. If the intensity of the lights increases, the aircraft is approaching. If the lights dim, the aircraft is moving away.
A size-distance illusion results from viewing a source of light that is increasing or decreasing in brightness (luminance). Pilots may interpret the light as approaching or retreating.
Fascination, also called "fixation," occurs when pilots ignore orientation cues and fix their attention on a goal or an object, such as when they are concentrating on aircraft instruments, or when attempting to land. This can be especially dangerous at night because aircraft ground-closure rates are difficult to determine.
Flicker vertigo is caused by a light flickering at a rate between 4 and 20 cycles per second, which can produce nausea, vomiting, and vertigo. Convulsions and unconsciousness are possible. Proper scanning techniques at night can prevent flicker vertigo.
On a clear night, distant stationary lights can be mistaken for stars or other aircraft.
Geometrical patterns of ground lights can cause confusion.
A black-hole approach an make the runway can seem out of position, with either a down-sloping or up-sloping aspect. It can be caused when the runway lights are the only source of light.
Proper adjustment of interior lights
Flight deck lighting should be kept as low as possible. During an adjustment period after departure, night vision should continue to improve until optimum night adaptation is achieved.
Importance of having a flashlight with a red lens
A light-emitting diode (LED) flashlight or penlight that produces red or blue light is ideal for cockpit use. The red or blue light will not interfere with night vision, while a white light will disrupt night adaptation. This light can be used for reading checklists and charts, and it's commonly worn on a lanyard around the pilot's neck. Note that any chart details in red/blue ink will not be legible under a red/blue light.
Night preflight inspection
14 CFR 91.205 includes a list of required equipment for VFR flight. Little of it is surprising, and it would take some effort to memorize. Key points include:
Preflight aircraft inspection should be done with a flashlight. (Note that this may reset dark adaptation, so preflight may need to be complete 30 minutes before departure.)
Parking ramps should be checked with a flashlight prior to entering the airplane to ensure that items and debris easily seen during the day are not overlooked.
Engine starting procedures, including use of position and anti-collision lights prior to start.
Be extra-certain that the area is clear before starting the engine at night.
After starting the engine and when ready to taxi, turn the taxi or landing light on. Because the airplane taxis at low RPM, the landing light may create a drain on the battery. This should be monitored. Overheating of an incandescent landing light also is possible when the aircraft is stationary or taxiing.
Taxiing and orientation on an airport
Be certain to taxi with the aircraft centered on any taxi lines that are painted on the ramp or taxiway.
During the run-up checklist, be alert for any forward movement, which is less obvious at night than during the day.
Anti-collision/strobe lights and a taxi/landing light may be turned off at certain points as a courtesy to other pilots in the movement area.
Takeoff and climb-out
Check the flight instruments frequently during the takeoff to ensure the proper pitch attitude, heading, and airspeed are being attained. Refer to both outside visual references, such as lights, and to the flight instruments.
After becoming airborne, the darkness of night often makes it difficult to sense the airplane's relationship with the surface. To ensure the airplane continues in a positive climb, be sure a climb is indicated on the attitude indicator, vertical speed indicator (VSI), and altimeter. Maintain best-rate-of-climb speed (Vy).
The landing light can cause distortion when it is reflected by haze, smoke, or clouds that might exist in the climb. The pilot may want to turn off the landing light in these conditions. However, it is recommended that the landing light remain in use for collision avoidance when operating below 10,000 feet. Therefore, the landing light should be re-activated if smoke, haze, and clouds are no longer a factor.
When flying at night under visual flight rules (VFR), pilots must exercise caution to avoid flying into clouds, which can be difficult to see in the dark. Typically, the first indication of flying into restricted visibility conditions is the gradual disappearance of lights on the ground.
If lights on the ground begin to take on an appearance of being surrounded by a halo or glow, use caution in attempting further flight in that same direction. Such a halo or glow around lights on the ground is indicative of ground fog.
Crossing large bodies of water at night in single-engine airplanes could be potentially hazardous. During poor visibility conditions over water, the horizon becomes obscure and may result in a loss of orientation.
Importance of verifying the airplane's attitude by reference to flight instruments.
Learning to safely fly at night requires time and experience. Pilots should practice straight-and-level flight, climbs and descents, level turns, climbing and descending turns, and steep turns. Practicing recovery from unusual attitudes should only be done with a flight instructor.
Under no circumstances should a VFR night flight be made during poor or marginal weather conditions unless both the pilot and aircraft are certificated and equipped for flight under instrument flight rules (IFR).
Night emergencies procedures
In the event of an engine failure, the emergency checklist should be followed. This checklist does not change for night operations.
Consider an emergency landing area close to public access if possible. This may facilitate rescue or help, if needed.
If the condition of the nearby terrain is known and is suitable for a forced landing, turn towards an unlighted portion of the area and plan an emergency forced landing to an unlighted portion.
If the landing lights are unusable and outside visual references are not available, the airplane should be held in level-landing attitude until the ground is contacted.
When approaching the airport to enter the traffic pattern and land, it is important that the runway lights and other airport lighting be identified as early as possible.
Fly toward the rotating beacon until the lights outlining the runway are distinguishable. The runway threshold and runway-edge lights must be positively identified in order to fly a traffic pattern of proper size and direction.
More dependence must be placed on flight instruments, particularly the altimeter and the airspeed indicator. This is due to deceptive perceptions of distance can be created by the lack of intervening references on the ground.
At night, the judgment of height, speed, and sink rate during landing is impaired by the scarcity of observable objects in the landing area. Inexperienced pilots tend to round out too high until attaining familiarity with the proper height for the correct round-out.
Approaches and landings with and without landing lights
Rely on the flight instruments and make a landing as it would be done during daylight hours.
A VASI/PAPI, if available, will assist with obstruction clearance and maintaining the glideslope.
Blackout landings should always be included in night pilot training as an emergency procedure. During landings without the use of landing lights, the round out may be started when the runway lights at the far end of the runway first appear to be rising higher than the nose of the airplane.
When landing at night, if either the runway or altitude is in doubt, execute a go-around.
Practical Test Standards: Flight Instructor
II. Technical Subject Areas
Task H: Night Operations
Objective: To determine that the applicant exhibits instructional knowledge of the elements of night operations by describing:
Flight Instructor Test Questions
Powered aircraft on VFR night flights must have an anti-collision light system.
If not equipped with position lights, an aircraft must terminate flight at sunset.
— Position lights are required from sunset to sunrise.
An aircraft to the right will have right-of-way, and will see the green starboard light on another airplane's wing when that airplane is to the left. When overtaking, an aircraft should pass on the right.
If on a night flight, the pilot of aircraft A observes only the green navigation light of aircraft B, and the aircraft are converging, which aircraft has the right-of-way? Aircraft A; it is to the right of aircraft B.
— Answer with some caution: Aircraft A is to the right of aircraft B; however, Aircraft B is to Aircraft A's left.
Oral Exam Questions