Technical Program Evaluation and Co-ordination
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Slide 1
Hazards Associated With Flying at Night
Presented by
Name
Transport Canada, System Safety
Speaker's Notes
Even though most of the hazards associated with flying at night have been known in the aviation industry for many years, these types of accidents continue to occur, which would indicate that pilots’ knowledge or awareness of these hazards is still very low.
In this presentation, we hope to address some of the hazards that cause accidents during night operations. As you probably already know, most of the cause factors are a result of the short comings we have as humans.
Night-flying has always been, and continues to be, more dangerous than flying during the day. This is, for the most part, because of a lack of visual cues and our vulnerability as humans to be affected by illusions.
Historical accident data indicates that not only does the risk of specific types of accidents increase at night (in the form of dark-night takeoffs, inadvertent VFR-into-IMC, CFIT, black-hole illusion), but also that these accidents are usually fatal.
Slide 2
Main Causes of Night Accidents
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VFR-into-IMC
- CFIT
Speaker's Notes
Because we are all humans, we are all affected by the increased risk when flying at night—it doesn’t matter whether you are a low-time recreational pilot or a 20,000-hr. airline captain. In January 1999, a DC-3 was en route from Vancouver to Victoria, B.C., on a night VFR flight when it collided with trees on Mayne Island at about 900 ft AGL. The aircraft then fell into a valley, where a post-crash fire erupted. The two occupants of the aircraft sustained fatal injuries, and the aircraft was destroyed (TSB Final Report A99P0006). This CFIT accident occurred even though there were almost 30,000 hr. flight experience between the two pilots!
Slide 3
CARs
-
CAR 602.115 three mile visibility for night VFR
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CAR 703.27 prohibits en route night VFR at less than 1000 ft above the highest obstacle along specific routes
Speaker's Notes
CAR 602.115 requires a visibility of three miles for night VFR flight, but remember: this is a minimum.
For commercial operators, CAR 703.27(a) prohibits en route night VFR at less than 1000 ft above the highest obstacle. In addition, flights must be conducted along air routes or routes specifically established by the air operator and designed in accordance with section 723.34 of the Commercial Air Service Standards (CASS).
CAR 605.16 requires the pilot-in-command to have a number of spare fuses that is equal to at least 50% of the total number of installed fuses of that rating accessible to him/her during flight.
Slide 4
The Eye
Speaker's Notes
Rods and cones - When light strikes the retina, it activates two types of light sensitive receptor cells called rods and cones. As light strikes, the rods and cones undergo chemical changes creating electrical impulses to the optic nerve.
Of the millions of rods and cones in the retina, the rods outnumber the cones by a ratio of approximately seventeen to one (17:1). A small area in the centre of the retina (called the fovea) is covered entirely by cones. From the centre to the edge of the retina, the number of cones decreases and the density of rods increases. At the edge, or periphery, of the retina there are only rods.
Rods and cones have very different characteristics. When we look directly at something, light falls mostly on cones, which provide us with superior detail, colour, and motion perception. However, they require relatively high illumination levels to function properly. On the other. hand, rods require considerably less light and are most useful in low light conditions. Because there are more rods at the edge of the retina, they also provide the majority of information about objects in our peripheral vision.
Unfortunately the rods provide a poorer quality of vision. For example, they are largely insensitive to colour, which is why everything starts losing the vibrancy of its colour as dusk approaches. Although we know that flowers and leaves are not really turning grey as the light diminishes, they do appear to be losing their colour because it is then that our visual information is being gathered increasingly by the rods.
Therefore, in the absence of bright daylight or moonlight, the process of vision depends mostly upon the rods.
Slide 5
Factors that Affect our Night Vision
- Night vision
- Two blind spots
- Lack of colour
- vision
- Reduced acuity
- Reduced depth
- perception
- Night myopia
- Visual hypoxia
- Night blindness
- Effects of aging
- Carbon monoxide, alcohol, drugs, fatigue, smoking
Slide 6
Night Vision
- Process requires about 30 min
- Rods become adjusted to darkness
- Off-centre viewing important during night flights
- Smoking, carbon monoxide, hypoxia, certain drugs adversly affect night vision
- Avoid bright lights to preserve night vision
- Red light preserves night vision but severley distorts colours
Speaker's Notes
Dark-adaptation: dual receptor system for day and night vision; adaptation time approximately is 30 min—it may be longer if you are older, smoke, or have been in the sun all day; avoid bright lights to attain and preserve dark-adaptation. The use of red light preserves dark-adaptation but creates other problems.
Slide 7
Two Blind Spots
- Physiological blind spot
- Central blind Spot
- Use an off-centre scanning technique
Speaker's Notes
Physiological Blind Spot: Inside each eye is an oval-shaped area of blindness. If an object is imaged within this region, it will not be seen. We do not normally notice this because our other eye will compensate. (Windshield post may create monocular vision.)
Central Blind Spot: No rods in the fovea—you need to look approximately 15° off a faint light source.
Slide 8
Lack of Colour Vision
- Rod vision is unable to discriminate colours
Slide 9
Reduced Acuity
- Central vision blindness at night
- High rod-to-optic nerve fiber ratio reduces acuity
Slide 10
Reduced Depth Perception
- Rod vision and pupil dilation reduces depth perception
Slide 11
Night Myopia
- Shortsightedness occurs during dark focus
- Periodically change focus distance
Slide 12
Visual Hypoxia
- The retina of the eye is more sensitive to hypoxia than any part of our body
- One of the first symptoms of hypoxia is a decrease in night vision
- Effects most noticeable starting at 5000’ above ground level to which you are acclimated
- Smokers are much more susceptible to hypoxia due to the build-up of carbon monoxide in their blood
Speaker's Notes
Visual Hypoxia - supplemental O2 recommended above 5,000’ MSL - O2 demands of retina and corneal hypoxia reduce acuity, brightness, and peripheral vision. One of the first symptoms of hypoxia is a decrease in night vision.
Slide 13
Night Blindness
- Functionally blind due to pigment deficiency in rods
- Night blindness induced within 60 days on diet lacking vitamin A
Slide 14
Effects of Aging
- Pupil size decreases
- Range of eye focus is reduced
- Visual acuity is reduced
- Colour discrimination becomes more difficult
- It takes longer to process visual information in general
- Sensitivity to glare increases
- Takes longer to read under dim light conditions
Slide 15
Night Illusions & Limitations
Illusions
- Autokinesis (objects appear to shift)
- False reference (stars or lights near horizon)
- Venus and sirius (false aircraft)
- Night myopia (dilation, inability to focus)
- Somatogravic (acceleration with pitch) Limitations
Limitations
- Night blind spot (rods & cones, stars, etc)
- Light to dark adaptation (2 hours)
Speaker's Notes
Somatogravic Illusion
Piper Chieftain, Pelee Island Airport (Ont.), June 24, 1989 (TSB Final Report A8900280)
Skylink Airlines at Terrace, 1989
Over a 15-year period, the Transportation Safety Board of Canada (TSB) found that 78% of night take-off accidents occurred in dark-night conditions (“Pitch Up, Pitch Down, Pitch Black” Aviation Safety Reflections Vol. 4, Dec. 1993). One of the contributing factors to these types of accidents is called the somatogravic illusion. When our body is accelerated, our inner ear senses two forces: acceleration and gravity. The brain resolves these two forces as a single resultant force acting downward and backward. We tend to interpret this force as the head being tilted backward, so the pilot feels as if the nose of the aircraft were pitching up. In normal conditions, outside visual cues correct this false sensation. However, during a takeoff at night from a well-lit field into a black hole, it is a difficult sensation to ignore. A common reaction to the somatogravic, or pitch-up, illusion is to push forward on the controls.
On January 10, 1996, a Cessna T210 Centurion departed Flin Flon, Manitoba, on a night VFR flight to Lynn Lake, Manitoba. The pilot advised the FSS that he was ready to taxi for takeoff and indicated that he would call airborne after takeoff. There was no further communication with the pilot. The aircraft was later located approximately one and a half miles from the end of the runway on the surface of a frozen lake; the pilot was fatally injured.
The TSB (TSB Final Report A96C002) reported the following: “The pilot likely lost situational awareness and inadvertently flew the aircraft into the ice surface while in controlled flight because of the combined effects of the lack of external visual references and his weak instrument flying skills. The effects of somatogravic illusion may have contributed to the pilot’s disorientation.”
Slide 16
Focused Scan Problems: Night
- Night blind spot (A.I.P. AIR 3.7)
- centre portion of eye is blind at night
- Night Scan
- look 10-15° away from what you try to see
- night vision is affected by altitude
- drugs, alcohol, smoking and fatigue adversely affect night and day vision
Slide 17
Pre-Flight Planning
- Route Study
- Weather Conditions
- Equipment
- Alternate Plan
Speaker's Notes
Pre-flight planning is extremely important, especially at night. As it is difficult to see weather at night, you need to review the weather conditions that you may encounter. Pay particular attention to the temperature-dew point spread. Be very cautious when the spread is less than 5°C.
A thorough route study is required to identify any hazards or obstructions along the way. As ground features may be very difficult to see, identify any NAVAIDs that you can use along the way.
In the planning stages, be on the look out for the possibility of dark-night conditions. Dark-night conditions normally occur when there is very little or no celestial lighting or when this lighting is obscured by an overcast layer of cloud. Most night accidents happen in these conditions because of the lack of visual cues available to the pilot even in VMC.
Ensure you have a serviceable flashlight and carry extra batteries and a spare bulb. Better yet, carry a spare flashlight. The last thing to check before going for a flight is your aircraft. Are all the lights working? Check your navigation lights, anti-collision, landing and taxi light(s), and don’t forget to check all the interior lights, such as the instrument panel, overhead and cabin lights.
Always have an alternate plan. For example, what are you going to do if you get to your destination and the runway lights are not working? If you do not hold an instrument rating, or you are not current, it would be a good idea to get some basic instrument training. You should at least be capable of making a 180° level turn solely on the flight instruments. This will be your “out” if you inadvertently enter cloud.
As it is difficult to visually detect and stay clear of terrain and obstacles, make sure you plan and fly at a safe altitude. When selecting an altitude, keep in mind that the retina is more sensitive to hypoxia than any part of your body.
Slide 18
Ground Operations
- Taxi speed illusion
- Geographic disorientation
- Risk of collision
Speaker's Notes
Because of the restricted visibility, you should taxi at a reduced speed, particularly in the vicinity of other aircraft and obstacles. Keep in mind that speed is deceptive at night, and there is a tendency to taxi too fast. One reason for this is the lack of customary visible ground objects that make speed apparent during the day. At night, stationary lights are nearer than they appear to be, which makes judging distance difficult. Also, our depth perception is reduced in dark conditions, so give yourself a little extra room while manoeuvring.
Some aircraft do not have a taxi light, so the landing light could be used. Keep in mind that at the slower speeds the landing light may overheat and fail. Also keep in mind that other pilots may be trying to adapt to night vision and would not appreciate your landing or taxi light illuminating their immediate surroundings. It is also more difficult to detect movement at night; therefore, when parked with the engine running or doing your run-up, make sure you have the brakes firmly applied and be on the look-out for any movement that may occur.
Slide 19
Take off and Climb
- Lining up
- Take off into the black-hole
- Somatogravic illusion
Speaker's Notes
One of the high accident-rate areas at night occurs during the take-off and climb phases of flight. According to information from the FAA, you are more than five times as likely to have an accident during this phase of flight at night. Before takeoff, adjust your cockpit lighting so that the brightness does not interfere with your night-adapted eyes or reflect off the windows to the point of distraction, but keep it bright enough to clearly read the instruments.
It may take some time to find the correct level of lighting for the given situation.The correct level will change as your eyes adapt to the darkness, which will take about 30 min.
Takeoff into black hole
Most take-off accidents at night occur in pitch-black conditions. During a 15-year period, the TSB found that 83% of night take-off accidents occurred in dark-night conditions.
In a recent accident, a Piper PA-31 with nine occupants on board departed Rainbow Lake, Alta., westbound at night and collided with trees and terrain approximately 3000 ft west of the departure end of the runway. The sky was clear with unrestricted visibility and light winds. The ambient lighting conditions were described as dark, with no moon, little illumination from the night sky and no lights to the west of the airport—basically, dark-night conditions. The TSB determined that the aircraft was inadvertently flown into trees and the ground in controlled flight because a positive rate-of-climb was not maintained after takeoff.
The pilot’s night departure technique was considered to be the active failure in this accident. Night departures in dark conditions require full use of the aircraft flight instruments, and it is essential that the pilot achieve and maintain a positive rate-of-climb. In the absence of outside visual cues, the pilot must rely on aircraft instruments to maintain airspeed and attitude to overcome any false sensations of a climb. In this case, the pilot was either relying on outside visual cues during the initial climb and/or using only a partial instrument panel scan while being influenced by a somatogravic illusion. (TSB Final Report A98W0009)
At night, a reduction of external visual references caused by inadequate ground and sky illumination, coupled with the requirement to use cockpit lighting to illuminate the instrument panel, will increase the difficulty of the departure procedure. Such a lack of external visual reference could have adversely affected the pilot’s ability to maintain required visual reference with the ground during the initial climb or to see and avoid obstacles. Somatogravic illusion may have adversely affected the pilot’s performance during the acceleration stages of the takeoff and initial climb.”
Slide 20
Cruise
- Ability to detect and monitor weather
- Terrain detection
- Geographic disoriention
Speaker's Notes
The most significant problem that occurs while flying en route at night is flying into weather that you are unable to see and, therefore, avoid. Approximately 10% of all accidents in Canada occurs during the hours of darkness, which parallels estimates of the general level of night flying activity (also 10%). However, VFR-into-IMC accidents occurring during the hours of darkness accounted for almost 30% of the total accidents. (TSB Report No. 90-SP002. 1990)
The consequences of flying in reduced visibility are exacerbated when operating at night, in light conditions that do not permit sufficient warning for the pilot to see and avoid worsening weather conditions. In reviewing accident reports of this nature, the typical scenario is the pilot inadvertently enters cloud, becomes disorientated and loses control of the aircraft, or continues under controlled flight into terrain.
Examples of night CFIT accidents include the DC-3 crash, at Mayne Island, British Columbia, in January 1999; the December 1972 crash of an Easter Airlines L-1011 in the Florida Everglades, when pilots became distracted with a minor problem; the December 1995 navigational error by an American Airlines crew and subsequent loss of a Boeing 757 near Cali Columbia.
Navigation Errors
Night VFR navigation becomes more difficult when trying to use ground features. In order to navigate accurately, we need to use all available sources of information such as VORs, NDBs and GPS, especially in sparsely settled areas.
Slide 21
VMC into IMC Conditions
178 Seconds
Speaker's Notes
The non-instrument rated pilot of the C150 was on a night VFR flight from Spirit River, Alberta, to St. Paul. The aircraft had crashed about 2 1/2 hours after take-off and was found the next day in a farmer’s field. The pilot was fatally injured. Weather conditions were good when the pilot departed Spirit River, but deteriorated as the pilot proceeded along his route as he approached a cold front. The pilot encountered low cloud and reduced visibility in fog and rain. Being over a sparsely populated area at night, surface references and the natural horizon would have become obscured. The report indicates the cause of the accident as “The pilot continued flight into deteriorating weather conditions, probably became disorientated, and lost control of the aircraft. The aircraft entered a spiral dive from which the pilot did not recover”. (TSB Report # A96W0178)
Researchers at the University of Illinois studied how long a pilot who has no instrument training can expect to live after he/she flies into bad weather and loses visual contact. Twenty student “guinea pigs” flew into simulated instrument weather, and all went into graveyard spirals or roller-coasters. The outcome differed in only one respect; the time required until control was lost. The average time was 178 seconds! (TP 2228E) Once again, this emphasizes the importance of having some basic instrument flying skills.
Constantly monitor the weather and look for changes. You can usually detect low cloud or fog forming if there are lights on the ground by halo or glow around them. This would be a good time to consider your alternate plan of action. Always be prepared to do a 180 turn in the event you enter cloud or deteriorating weather. Remember, you will probably have to do this on instruments and to have the skill, it will take training and practice.
Slide 22
Approach and Landing
- Runway detection
- Black-hole approach
- Effects of runway slope
- Runway dimensions
- Atmospheric conditions
- Runway lighting
Speaker's Notes
Even when your trip is almost complete, do not allow yourself to become complacent. Adherence to procedures and safe altitudes is very important for minimizing the effects caused by illusions at night and the reduced depth perception that is experienced.
In April 1990, a C99 airliner was on a night instrument approach to Moosonee, Ontario. During the approach, the crew began a descent to 440 ft, the minimum altitude allowed for this instrument approach procedure. As the aircraft descended through 900 ft, it broke out of cloud about nine miles from the airport. Both pilots could see the runway lights at this point, so the captain decided to change to a visual approach and proceed inbound at 700 ft ASL. Shortly after advising the co-pilot of his intentions, the pilot-in-command initiated the “before landing” cockpit check and selected the landing gear lever to the “down” position. Immediately thereafter, the aircraft struck trees and crashed seven miles east-northeast of the Moosonee Airport, killing one crew member and seriously injuring everyone else on board. The TSB indicated the black-hole illusion as one of the contributing factors in this accident.
Black Hole
- Approach occurs at night with little or no surrounding surface lights
- results in low approach and premature ground contact short of runway—deadly!
- flight instructor explaining the illusion to student when they flew into trees
Slope
- upsloping runway (and/or terrain) gives illusion of being too high resulting lower approach and hard landing/crash short of runway
Runway Dimensions
- a greater length-to-width (L/W) ratio than the pilot is accustomed to (narrower and /or longer) gives the illusion of being too high, resulting in a lower approach and a hard landing/crash short of runway.
- “relative size” depth perception cue.
- smaller runways (same L/W ratio ) than the pilot is accustomed to lead to late flare and hard landings.
Atmospheric Conditions
- “aerial perspective” cue—extremely clear air (usually dry) creates the illusion of being closer than you actually are, which could lead to premature descent and a subsequent low approach.
Runway Lighting
- “relative brightness” cue—brighter than normal runway lights give illusion of being closer than actual, which could lead to premature descent and subsequent low approach.
- Knowledge on how to operate ARCAL (what to do if system is American).
Slide 23
Black-hole Diagram
Speaker's Notes
The black-hole illusion is one of the most insidious illusions in flying. This illusion was a contributing factor when a Canadian Forces Hercules struck the terrain short of Canadian Forces Station Alert while conducting a visual approach on a clear night in 1991 and when the crew of a Learjet did not detect the altimeter error and unknowingly flew the aircraft into the water while on approach to Masset, B.C., in 1995.
There is no amount of training or practice that will make this illusion go away. A human factors engineer with Boeing, Dr. Conrad Kraft, observed similarities among these accidents, in that all of them involved an aircraft that landed short of the runway at night in clear visual conditions after an approach made over water or dark ground. Dr. Kraft’s subsequent studies showed that even experienced pilots overestimate their altitude on such approaches and tend, therefore, to fly a lower approach path. If the pilot does not become aware of this error (by reference to the altimeter or an approach slope indicator, such as VASI or PAPI), the flight path may take the aircraft into the ground or water short of the runway.
In the Moosonee accident, the TSB had determined that the pilot-in-command was unaware of the black-hole illusion and that neither the pilot-in-command nor the co-pilot had received training in aviation medicine or aviation psychology. In fact, the pilot-in-command, who survived the accident, reported that “he was completely surprised when the aircraft struck the trees; so surprised, in fact, that he did not react at all.”
One method for reducing the black-hole illusion is to avoid long, straight-in approaches in darkness without some type of glideslope guidance. Other things you can do to reduce the risk of becoming adversely affected by this illusion include the following:
- Maintain a safe altitude until the airport and associated lighting are clearly visible and identifiable
- Cross-check flight instruments frequently, in particular airspeed, altitude, and rate-of-descent. An unusually high rate-of-descent may indicate an unusually steep descent profile.
- Use distance-measuring equipment to help establish a safe descent profile in VMC. A pilot can fly a three-degree profile by remaining 300 ft above the ground for each nautical mile.
- Make use of any approach aid available, such as an ILS, PAPI or VASI.
Slide 24
Be alert for the black-hole illusion if you observe these conditions
- An airport that is on the near side of a brightly lit city with few or no terrain features or lights between you and the airport
- An airport that is on the coast or lake shore
- An airport in a very sparsely settled areas
Slide 25
Fatigue Induces Human Error
Speaker's Notes
In addition to other human factor influences, fatigue plays a large roll for obvious reasons.
As with most accidents today, the cause factors can be traced back to the human factor. Because our body normally wants to be asleep during the hours of darkness, fatigue is present in most night-flying operations. Fatigue slows reaction time, reduces concentration and affects our decision-making skills. Pilots should be aware of the subtle effects that acute or chronic fatigue can have on motor skills and judgment. Fatigue also makes you more susceptible to illusions like the black-hole illusion, which can prove to be a deadly trap when night flying.
Discuss effects and ways to minimize fatigue.
Slide 26
Preventative Measures
- Recognize normal human visual limitations involved know what they are and circumstances they are most likely to occur
- Learn which airports are conducive to visual illusions at night and use the Canada Flight Supplement (CFS) for more information and restrictions during hours of darkness
- Use flight instruments for approaches especially those that provide glide path information (i.e., ILS, DME readouts and altimeter)
- Use airport aids to vision (i.e., VASIS, T-VASIS)
Slide 27
More Preventative Measures
- Avoid visual long straight-in approaches (overfly airport if necessary)
- For geographic disorientation use radio navigation and GPS if fitted
- Pay attention to alert devices (radio, altimeter, GPWS)
- Double check your own expectations and perceptions
- Ensure adequate sleep and nutrition
Speaker's Notes
Night VFR can be enjoyable, and it can be an option if you are unable to proceed IFR. Because of the increased risk, thorough pre-flight planning and awareness of the hazards will minimize this risk and contribute to conducting night flying operations safely. The two main hazards to be concerned with are deteriorating weather and the black-hole illusion.
If ever in doubt, climb to a safe altitude and cross-check your instruments frequently. I can’t emphasize enough the importance of getting some instrument training if you are not qualified. For those of you who do have an instrument rating, use it; it is your best defense for the hazards of night-flying. Contact your RASO for more information on this or any other safety-related topic.