Every night flight or breath for that matter involves a risk on some level. What we do can be evaluated and delineated as to the mathematical risk factor it presents to us. Every night flight decision we make holds consequences. Not making decisions also holds consequences. The ideal would be that we be able to have the foresight to see living and night flying in terms of future consequences. We can't, so we do what we can to face the risks.

Fact is that we do have this predictive capability if we but know HOW to use it. The chances we take in life can be measured and controlled by the way we handle future events. Mathematicians and thinkers since 1654 have provided the probability theory needed to place a degree of certainty into our uncertainty, risk taking and decision making. A pilot must accept the presence of risk and the existence of fear. Both are present and accepted as part of the process. Being afraid makes you more careful. As time fades memory, we are apt to once again approach the risk fear situation but this time you will probably have more awareness and respect for the possible negative outcomes. Your fears are instance policies

Night flight risk analysis begins with finding causes that are influenced by indirect and subtle correlative events or conditions. The relationships are usually not clearly defined but more often summarized as being present. Whenever a kind of relationship does exist we have a correlation. If night accidents are caused by darkness, then primary correlative elements would be amount of natural and man created light. Additional correlative elements of area familiarity, experience, maintenance, equipment, weather and interior lighting come immediately to mind.

The FAA, NTSB, AOPA, and insurance companies have gathered and maintained the data base of night flying statistics compared to day flying statistics. The data, through statistical inference points to causality. Modern computers can crunch the numbers to find future probability. Without this gathering of data there would be no prediction of probability. Enough samples of night flying accidents with selected correlative elements gives us probability.

The ability to make a prediction of accident probability for a given night flight resulting in an accident results in a number. The number is a percentage that gives the probability of an accident occurring. With sufficient data transposed into percentages a person is able to compare, decide, and fly at night in given conditions with some assurance of a non-accident flight. It is a gamble on the odds of event probability. A pilots decision for making any flight, day or night, has to be based upon this theory of decision making because there is no certainty as to what will happen. This is a process that every pilot partakes from for every flight, night or otherwise.

We use risk analysis to evaluate the consequences of starting the engine, taking off, flight altitude, direction, and landing. To do otherwise is to be oblivious of probability as it can and does affect all our lives. Don't say that you don't gamble, take chances, and challenge probability. You do and it makes your life more worth living because certainty will destroy incentive, interest and curiosity.

40% of all night takeoff accidents have non-instrument pilots. Of all night accidents the darkness of the night was listed as a factor in 54%. 26% were judged to be caused by spatial disorientation. Most of the takeoff accidents occurred with in 3 miles and one minute of takeoff. More often than not the pilot was unaware of his unusual attitude. The darker the night the more important is instrument flight capability.

Hundreds of pilots before you have made the risk decision in favor of taking night flight. In the proper moonlight conditions you can see well enough to see clouds, water, some terrain and many lighted areas. A flight over familiar areas at night is a thing of beauty. Other aircraft can be detected far beyond daytime sighting distances. Night landings are acts of faith. You must believe that the lighting and surface delineate the airport and a safe place to touch the earth. Oddly, taxiing at night is a very difficult process. Many aircraft lights do not light your way. Flying at night is like the risks you take with a beautiful woman. You could wind up married (buried).

FAA 'Examiner Update'
Pilot operation 9 (FAR 61.107) Pilot must have SOME night instruction before being qualified to be eligible to take flight test. To be fully certified for night flight a student must have at least three hours of instruction at night with ten full-stop landings.

Night flight requires a more proficient instrument crosscheck than does day. In making maneuvers the horizon may be lost and spatial disorientation can occur. Night flight has more inherent dangers and potential problems. The obstacle you don't know about will kill you at night. More than ever, altitude at night is insurance. Your policy is an accurate altimeter set.

Physiology of Night
Read up on the physiology of night vision to better understand the operation of the eye. Over age 40, fatigue, and smoking affect visual acuity and adaptation to darkness. Do not look directly at an object at night because the optic nerve location may not let you see it. The decrease in oxygen above 4000' decreases visual efficiency. Air Force requires full oxygen from the surface at night. The light smoker is physiologically at 3000' before he gets into the plane. Above 8000' at night it is a good idea to have oxygen. Since we don't see as well as might be desired at night we must compensate using experience (brains) and technology.

The human eye performs poorly at night.Fatigue has greater influence on pilot skills at night. The retina is the first and fastest part of the body to react to reduction of blood oxygen. Cigarette smokers start out with an immediate night vision problem. Night vision can be improved by the use of oxygen. Night flying errors happen because of human lack of capability. Night vision is the key limiting factor. Without surface lights, it is hard to know your altitude above the ground, with surface lights it is difficult to locate the airport beacon.

Most night accidents occur on 'dark night' flights. Fatigue makes all of the safety factors involved to be more likely misjudged. Raise you personal safety parameters at night and raise them even more when fatigued. Skillful night flying is fragile, unused night flying skills must be polished regularly or they will be lost quickly.The eye is much like a video camera. A view is focused on the retina, converted electrically to data sent to the brain. Rods and cones make the visual to electrical conversion. Cones, near the focal center give colors, brightness and sharpness when light is good. Rods are the night-vision part of seeing. The peripheral region of the retina is rod territory. Rods make it so we can see at night but not in color. Complete night adaptation of the eye to darkness can take over 30 minutes and be destroyed in seconds.

The human eye is a dual system devoted to day vision or night vision. The duality has inherited abilities that vary with the individual. Some pilots just see better, day or night. Some eyes have retinal structure and nerve elements that are visually more efficient. Pigment and other factors such as pupil size allow eyes to respond to weak stimulus. Age affects the pupil's ability to change size. The wider the pupil the better the night vision. A pilot's ability to adjust to darkness deteriorates with age.

The rods and cones adapt to night conditions. The cones are centered in the eye but are slow to adapt and then only by a factor of x 100. Rods spread to the sides in the back of the eye. They are more sensitive at night by a factor of x 100,000. Rods take 30 minutes to recover from a bright light shock.

--There is an oval shaped region of the retina known as the blind spot. It cannot see light.
--Binocular vision compensates for this in daytime.
--At night we often are unable to see objects if we look directly at them.
-- To see at night we cannot look directly at what we want to see.
--Your central vision is inoperative at night..
--Looking off center at night uses peripheral vision.
--Peripheral vision is 100,000 times more sensitive than central vision at night.
--Your eyes can be adapted to night vision by wearing red glasses, patching one eye and using dimmed lighting.
--No matter how well you do this one flash of a strobe taxiing out destroys it all.
--It the lighted airports of today I prefer to work in a lighted cockpit.
--I like to see my strange charts clearly with all obstacle heights known and avoided.
--90% of our orientation is visual even in the cockpit.
--NASA has proven that there is less oxygen at night than during the day.
--The eye is quite susceptible to oxygen deficiency.
--Vision at night at 9000' gives the visual acuity that you would have at 15000' during the day.

Your visual adaptability to light/darkness is reduced 50% every eleven years of your life. Experience and frequency of night flight is the best compensation for this loss. Any bright light effectively reduces night vision. You might try protecting one eye from light until airborne. Try wearing sunglasses at dusk.

The use of colors other than red in the cockpit has become more common in the 1990's. Light-emitting diodes are more efficient than other systems and will be in all cockpits of the future. Blue lighting such as is common in military aircraft requires much more lighting than white lighting. Vitamin A is a vital element for night vision and adaptation. Vitamin A deficiency will make a significant difference in night vision. However excessive intake of Vitamin A will not give an apparent improvement.

Ample oxygen is necessary for adequate night vision more so than day vision. Above 4000 feet supplemental oxygen will improve night vision. There will be an initial decrease of 5% in night vision and the deficiency is accumulative over time. At 8000 feet the initial effect is about 15% and will become worse with time. The most dangerous aspect of this is that the pilot has no way of knowing that he is not seeing as well.

The wearing of sunglasses during the day is one way to improve your night vision. Neutral gray glasses seem best in their ability to absorb ultraviolet light. At night, red lenses will absorb blue light and aid dark adaptation. Limit your use of bright lights at night since even a momentary flash can destroy your night vision.

Should blur interfere with the things you see at night, it may be indicative of night myopia. Squinting will help some or the use of glasses. If the eye is unable to focus on anything at a distance at night it may be having space myopia. Keeping the eyes moving can help limit these effects that are made worse by staring.

Objects are harder to see at night just because they are less well defined around the edges. This makes things appear farther away than they actually are. The requirement for glasses at night is much greater than during daylight.

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