Shedding Light On Night Flying

I still remember my first flight at night. I felt deeply attracted and interested in experiencing the flight when darkness enveloped the small airport where it was my flight school. I used to hear stories from other pilots who would tell me that after the rotation all the real world ended and all that counted were my flight instruments.  Night flying has magic and beauty, there’s usually less air traffic and controllers are more helpful. However, the limitations that darkness puts in human vision, the effect of daily fatigue and time changes increase the risks of night flying.

In this post I would like to cover the issues involved in flying at night: The vision limitations at night, night scanning, night illusions, aircraft lightning, night operations, regulations and tips to make your night flight more comfortable and safe.

After sunset, our perception of real world changes completely, depth perceptions are severely altered and visual acuity diminishes.

Visual Limitations at Night – Pilots rely more on vision than on any other sense to orient themselves in flight. The following visual factors contribute to flying performance: good depth perception for safe landings, good visual acuity to identify terrain features and obstacles in the flight path and good color vision. Although vision is the most accurate and reliable sense, at night visual cues can be misleading, contributing to incidents occurring within the flight environment. Pilots must be aware of and know how to compensate effectively for the following:

– Physical deficiency or self-imposed stress, such as smoking, which limits night-vision capability
– Visual cue deficiencies
– Limitations in visual acuity, dark adaptation, and color and depth perception.

Even pilots with perfect vision find that image sharpness decreases as pupil diameter increases. These factors become important when pilots rely on terrain features during unaided night flights. Practicing good light discipline is very important and helps pilots to retain their night adaptation. Keeping the cockpit lighting on dim allows the pilot to better identify outside details, unmarked hazards such as towers less than 200′ AGL, and unimproved landing sites with no hazard lighting.
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 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 automatically adjusts for the light level experienced. During night flight, the cockpit and instrument lights should be as dim as possible. The eye can then adjust for the outside lighting conditions (ambient lighting) to see outside. The dimmer the inside lighting is, the better you can see outside.

Effects of cockpit light dimming at night flying.

Effects of cockpit light dimming at night flying.

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 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. 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 when pilots use the proper techniques to scan the terrain. To scan effectively, pilots look from right to left or left to right. They should begin scanning at the greatest distance at which an object can be perceived (top) and move inward toward the position of the aircraft (bottom).

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 visual system is the most reliable of the senses, some illusions can result from misinterpreting what is seen; what is perceived is not always accurate.

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 that 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. 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 this illusion, the shoreline is mistaken for the horizon. This illusion can be avoided by referencing the flight instruments and establishing a true horizon and attitude.

Reversible Perspective Illusion – At night, an aircraft 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 flying a 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.

At night, the horizon may be hard to discern due to dark terrain and misleading light patterns on the ground.

At night, the horizon may be hard to discern due to dark terrain and misleading light patterns on the ground.

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. Flashing anticollision strobe lights, especially while the aircraft is in the clouds, can produce this effect.

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 lower 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, such as a road, and even lights on moving trains can be mistaken for runway and approach lights. Bright runway and approach lighting systems, especially where few lights illuminate the surrounding terrain, may create the illusion of less distance to the runway. The pilot who does not recognize this illusion flies a higher approach. Conversely, the pilot overflying terrain which has few lights to provide height cues may make a lower than normal approach.

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.

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. 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 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.

Aircraft Position Lights

Aircraft Position Lights

Here we have an example 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.

Preflight – Aircraft preflight inspection is a critical aspect of flight safety. During night preflight we should use a flashlight with an unfiltered lens (white light) to supplement lighting. Windscreens are checked ensuring they are clean and relatively free of scratches. Slight scratches are acceptable for day flight but may not be for night flight. Careful attention must be paid to the aircraft electrical system. A tripped circuit breaker may be an indication of an equipment malfunction and should be left for maintenance to troubleshoot.
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.

One of the first steps in preparation for night flight is becoming thoroughly familiar with the 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.
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 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 you passengers in the importance of light discipline during night flight so the pilot is not blinded and loses dark adaptation.

Taxi Technique – Taxi slowly at night, especially in congested ramp and parking areas. 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.

Takeoff – Once you are ready and cleared for takeoff, select a point down the takeoff path to use for directional reference. During a night takeoff, notice a lack of reliable outside visual references after becoming airborne. To compensate for the lack of outside references, use the available flight instruments as an aid. Establish a climb attitude on the attitude indicator, check the altimeter and the airspeed indicator to verify the proper climb attitude. The first 500 feet of altitude after takeoff is considered to be the most critical.

En Route – During preflight planning, it is recommended that a route of flight that is within reach of an airport, or any safe landing site, be selected when possible. 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. 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.

Approach and Landing – 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 settling-with-power 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 settling-with-power condition and a hard landing.

Regulations:
Night Flying Currency – 14 CFR section 61.57, Recent Flight Experience Pilot In Command, in order to carry passengers, “during the period beginning one hour after sunset and ending one hour before sunrise,” the pilot in command must have made at least three takeoffs and three landings to a full stop, between the hours of one hour after sunset to one hour before sunrise, within the preceding 90 days.

Title 14 Code of Federal Regulations (14 CFR) part 1 “Night means the time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the American Air Almanac, converted to local time.”

– Aircraft Lights – 14 CFR section 91.209 “No person may: (a) during the period from sunset to sunrise… (1) Operate an aircraft unless it has lighted position lights.”

 

For More Information

– Risk Management for VFR Flight at Night

– “N.I.G.H.T.” FAA Aviation News,

– AOPA Air Safety Foundation’s Night VFR Checkup

 

Sources:

– FAA Night Vision & Night Operations – Chapt. 13.

– FAA Night Flight Safety.

– Illustrations & Pics:  FAA

Capt. Ivan

 

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