Human Factors - 2
Human Factors - 2
Orientation and sensing motion
There are three main ways to sense motion and maintain balance:
1. Visual — with our eyes
2. Vestibular — with our inner ears
3. Kinesthetics — pressure felt by muscles and bones
Human Eye
Light reflected from an object enters the eye through the cornea where it is bent to help the focusing process. The light continues through to the pupil.
The pupil regulates the amount of light entering the eye. When light is bright. the pupil contracts to protect the inner eye.
Step 2
Next the light travels through the lens which changes shape to focus light on the retina.
Light is processed by photoreceptor cells, known as rods and cones. located in the retina which carry the information via electrical pulses down the optic nerve to
the brain.
Rods and Cones
Located in the retina.
The ratio of rods to cones in the retina is approximately 17:1.
A small area in the center of the retina, called the fovea, is made completely of cones. From the fovea to the edge of the retina the number of cones will decrease, and the number of rods will increase. At the edge, or periphery, of the retina there are only rods.
Rods and cones have very different characteristics.
Cones
Provide us with superior detail and color perception as well as some motion perception
Requires a lot of light to function properly
Responsible for photopic vision (the center of your vision)
Rods
Poorer quality of vision but better motion perception
Not sensitive to color
Functions well in in low light conditions
Responsible for scotopic vision (peripheral vision)
Visual scanning techniques
Depending on the amount of light available we will need to change our traffic scanning technique.
During the day, we can effectively scan and identify traffic by looking directly at it.
However, during low light conditions objects in the center of our vision may disappear if there is not enough light for the cones to function.
At night, you may have difficulty focusing on your traffic or other obstacles in the center of your vision.
To complete an effective scan at night, yo iwill need to look at least 10° to the side of an object.
Sloping runways
Sloping runways will give an illusion of being too high or low relative to the runway.
On approach to a downsloping runway. the pilot will think they are low on approach. If they take action to correct the illusion, they will end up too high and overshoot the runway.
On approach to an upsloping runway, the pilot will think they are high on approach. If they take action to correct the illusion, they will end up too low and undershoot the runway.
Terrain effect
Terrain surrounding a runway in a valley or on a mountain can also cause illusions of being too high or low on approach.
When the runway is in a valley you will feel too close to surrounding terrain and think you are low on approach. If you correct for the illusion. you will become too high.
When the runway is on a bill you will feel too far from the surrounding terrain and think you are high on approach. If you correct for the illusion, you will become too low.
Wide/Narrow runways
Runway width will give illusions of being too high or low on approach but more importantly will affect flare height tendencies because we train ourselves to use visual cues when landing.
Wider runways gives the illusion that you are low causing pilots to flare early/ high and drop heavily onto the runway.
A narrow runway gives the illusion that you are high, causing pilots to flare too late/low resulting in a flat landing, a bounced landing, or in the worst case a propeller strike.
Rain on windshield
Rain on the windshield causes distortion due to water's ability to refract light.
Rain causes objects in front ofyou to appear angled underneath you while also being magnified.
ln flight, objects or terrain may appear to be lower and closer than they actually are.
Black hole illusion
When on an approach over water or an unlighted area, the absence of visible ground features reduces the pilot's ability tojudge their approach angle.
There are no visual indications of height above ground or distance from the runway.
This often results in a curved approach path with the aircraft undershooting the runway.
Good visibility
Good visibility can lead a pilot to think they are too low because land features are very clear and distinct.
This may cause an untrained pilot to climb and fly too high. This can be particularly hazardous when trying to maintain vertical separation from other aircraft.
Poor visibility
Flying in low visibility conditions may result in the illusion of being too high because landmarks and objects are obscured.
An untrained pilot may descend to bring things into focus, but this can be dangerous if there are obstacles or areas of high elevation.
Some causes of low visibility are:
Rain
Fog
Haze
Smoke
Glare from the sun
Twilight or approaching darkness
Autokinetic phenomena
When a stationary object appears to be moving. In the case of flying at night, a single fixed light in a largely unlit area may appear to move. Pilots can confuse
the apparent moving light with potential aircraft traffic.
Empty field myopia
The eye lens is responsible for focusing light on the retina, but it requires an image with contrast to focus properly.
When flying in a clear blue sky or at night with few lights, images may lack contrast and the lens will go into a passive resting state resulting in myopia (near-sightedness) that focuses about 5 ft away. This will make spotting and tracking traffic difficult.
To prevent empty field myopia, it is recommended to exercise your eyes by focusing on distant objects/terrain.
If there are no distinct features to stimulate your eyes, focus on your own craft’s wingtips
The ear
Outer, middle, inner parts of the ear
Outer
Main parts
the Auricle,
the Ear Canal,
the Tympanic Membrane (eardrum)
Middle
Main parts
the Ossicles
the Eustachian Tube
Inner
Main parts
the Cochlea
the Semi-circular Canals
the Otoliths
Hearing
Sound travels down the external canal to the eardrum causing it to vibrate back and forth.
Three tiny bones behind the ear drum, called the ossicles, transfer the sound waves to the cochlea which is a fluid filled organ containing thousands of sound receptors.
The receptors in the cochlea send electrical impulses down the auditory nerve for recognition and processing.
Impairments
Outer ear
If the ear canal is obstructed sound waves can not move freely.
A common obstruction is ear wax.
The external ear may also be obstructed by infections that cause swelling.
Middle ear
Infection can cause the middle ear to fill with fluid which will dampen the vibrations from the eardrum.
The eustachian tube is responsible for equalizing pressure between the middle ear and the outside environment.
Pressure imbalance and blockage can result from altitude changes, water immersion, and sickness. This can sometimes be fixed using the valsalva technique.
With age the joints between the ossicles start to stiffen causing less energy to be transmitted to the cochlea.
Inner ear
Loud noise can damage the inner ear receptors and they may have difficulty recovering.
Steady or too loud noise can cause permanent damage.
It is recommended to limit noise exposure to 8 hours at 90dB.
Orientation/Disorientation
Semicircular canals
Fluid filled canals responsible for our sense of angular motion.
They are our personal gyro for sensing roll, pitch, and yaw.
Each canal is lined with hairs that move in the fluid. When you turn your head, the canal moves but the fluid does not due to its inertia. This causes the hairs to bend which sends a signal to your brain about the movement.
2 types of illusions from semicircular canals
The leans
The leans is an illusion caused by the semicircular canals while in a prolonged turn.
In a prolonged turn the friction between the fluid, canal, and hairs will stir the fluid causing it to move. If the fluid moves at the same rate as the hairs, the hairs will not bend; therefore, they won't send a signal to your brain.
This gives the illusion of feeling straight and level even though you are in a turn.
When you level your wings, the inertia of the fluid will cause it to continue moving.
The movement of the fluid will bend the hair sensors in the opposite direction.
This will give a second illusion of banking, or leaning, in the opposite direction.
Coriolis illusion
Another illusion caused by the semicircular. It is considered the most dangerous.
While in a turn, if you turn your head in the opposite direction of the turn it forces the fluid of another canal into motion and severely confuses your senses.
It will make you feel like you are violently tumbling and make you unable to focus your eyes.
Otoliths
The otoliths are tiny organs that sense linear motion.
The otoliths have little hairs tipped with calcium stones that project into a fluid.
As you tip your head back the weight of the stones will cause the hairs to bend.
As the hairs bend they send a signal to your brain.
False pitch illusions
The otoliths can be tricked into thinking you have moved your head by acceleration and deceleration.
If you accelerate but hold your head straight, the weight of the stones will cause the hairs to bend indicating to your brain that you are now looking up (pitched up).
This can be especially dangerous during take-off at night or in IMC conditions when we cannot visually confirm if we are climbing. IMC = instrument meteorological conditions.
As you accelerate on the take-off roll, your brain thinks you are already pitched up. When you actually pitch-up to climb out, your brain is now indicating you are pitched too nose high.
As pilots we are trained to recognize excessive nose high attitudes as a symptom of stall.
Our natural reaction would be to pitch down but this would force the aircraft into level flight or, worse, to crash back onto the runway.
To prevent this from happening we must confirm "two positive rates" using our altimeter and vertical speed indicator.
False pitch illusions can also be experienced during acceleration or deceleration in cruise flight or in prolonged climbs and descents.
While in a prolonged descent, the otoliths might stabilize and when you return to a cruise attitude, the cruise attitude feels like a climb or vice versa.
* Special note: the false pitch illusion is caused by a combination of vestibular and kinesthetic
sensors. The pressure we feel as we are pushed into our seat upon acceleration makes the illusion feel worse.