Night VFR

Aims and Objectives

Aims

• to review general human factors as they apply to flight
• to learn about vision and visual factors that apply to night flight
• to learn about hearing and balance and related factors that apply to night flight

Aims and Objectives

Objectives

• understand decision-making and associated processes and stressors that affect flight
• understand vision and visual illusions
• understand decisions and actions to mitigate the effect of visual illusions
• understand the inner ear, vestibular system, proprioceptive system and how these sense may produce orientation illusions
• understand decisions and actions to mitigate the effect of orientation illusions

Human Factors

Review

• Piloting an aeroplane is more than physical skill and coordination
• Manipulating flight controls to achieve a desired performance is important
• However, the pilot must
  • assemble information
  • interpret data
  • assess its importance
  • make decisions
  • act
  • communicate
  • continually reassess
• This complete process is called piloting

Human Factors

Decision Making

• The fundamental and essential role of the pilot is to make reliable, safe and timely decisions
• Emotions can play a significant, even dominant, role in the decision-making process
• We may be cautious, ambitious, confident or diffident
• We must be survival-oriented rather than goal or success oriented

Human Factors

Internal Stressors

• Indecision may cause internal stress
• While deciding under pressure, the level of stress may become unreasonable
• Avoiding decisions also creates further internal stress
• The solution is to make a decision and commit to it
• Internal stress is relieved by action
• “It is better to have a bad plan than no plan” — Garry Kasparov, World Chess Champion 1985-2000

Human Factors

External Stressors

• External pressures can have a significant effect on decision-making
• An objective decision is made in isolation to these external pressures
• Such a decision can often only be made retrospectively

Human Factors

Personality, Hazardous Attitude

• Some personalities are prone to taking greater risks than others
• A common conviction being, “it won’t happen to me”
• Five hazardous attitudes that contribute to poor judgement have been identified:
  1. Anti-authoritarianism (don’t tell me)
  2. Impulsivity (do something quickly)
  3. Invulnerability (it won’t happen to me)
  4. Machismo (I can do it)
  5. Resignation (what’s the point)

Vision

The Eye

• The eye collects light reflected from an object, using the lens to focus the light into an image on the retina
• The image is converted into electrical signals and sent to the brain via the optic nerve
• This is how we see
• The brain matches the image to previously stored data so an object can be recognised
• This is how we perceive
• The optic nerve is so close and integral and functionally dominant that the eys may be considered an extension of the brain

Vision

Structure of the Eye

• The main components of the eye are
  • cornea
  • lens
  • retina
  • optic nerve

Vision

Structure of the Eye — Cones

• Cones are concentrated around the central section of the retina
• The area of the retina directly opposite the lens is highly concentrated, known as the foveal region
• Cones are sensitive to colour, details and distant objects
• Cones are most effective in daylight
• Objects focussed on the foveal region in dim light will not stimulate the cones to transmit a message on the optic nerve — the image will not be seen

Vision

Structure of the Eye — Rods

• Rods are concentrated in a band outside the central foveal region
• Rods are sensitive to movement but not detail or colour
• Rods are effective in both daylight and darkness
• Rods are responsible for peripheral vision, which helps orientation and night vision
• Therefore, objects in dim light are most easily noticed when the image falls on the peripheral area of the retina

Vision

Empty Field Myopia

• When the eye is not focussed on any specific object e.g. gazing out the windscreen at an empty blue sky, the natural tendency for the eyes is to focus in a range of 1-2 metres
• This condition is known as empty field myopia
• A pilot flying visually must continually scan for other aircraft and obstacles and focus on any observations
• In an empty sky, it requires a conscious effort to focus on distant objects

Vision

Vision Limitations

• Rods and cones form the endings of the optic nerve
• They will be affected by anything that affects the brain e.g. oxygen supply
• A shortage of oxygen (hypoxia) can be caused by:
  • high altitude
  • high-G manoeuvres
  • medication
  • alcohol
  • smoking
  • other drugs

Vision

Colour Vision

• Colours are detected in the central foveal region of the retina by cone receptors
• When these receptors are insensitive to certain shades of light, colour blindness results
• Typically, colour blindness is difficulty distinguishing between red and green
• Colour blindness may cause problems with night flying, and in poor visibility

Vision

Night Vision

• Special considerations of vision are required for night flight
• Attention will be both inside and outside the cockpit and light intensity will vary
• It takes several minutes for vision to adapt to a dark environment
• Night vision is susceptible to hypoxia at altitudes above 4000ft
• Use a red headlamp with low intensity inside the cockpit for viewing charts, etc
• Note: red lines on charts will not be visible under red light

Vision

Visual Scanning at Night

• Since the foveal region is not sensitive to low levels of light, there is an area of reduced visual sensivity in the central vision
• Peripheral vision is more effective at approximately 10-20 degrees
• The most effective way to use your eyes is to scan small sectors slower than you would in daylight

Vision

Visual Scanning at Night

• Sighting traffic at night relies on the aircraft’s lighting system
• The colour of the lights is used to determine the direction of travel of other aircraft

Visual Illusions

• Vision is our dominant sense
• However, sometimes what we think we see is not actually there
• Images sent from our eyes can be misinterpreted by our brain

Visual Illusions

Relative Movement

• We are familiar with the effect that a moving vehicle has on the occupants of an adjacent stationary vehicle
• The effect is the perception that the stationary vehicle is moving
• Similarly, an aircraft entering an air bridge may feel as if it has sped up if an adjacent aircraft is pushed back
• This effect is relative movement

Visual Illusions

Autokinesis

• The illusion of autokinesis can occur at night by staring continuously at a single light against a dark background
• The light will appear to move, perhaps oscillate, after a few seconds of staring
• Spatial disorientation may result by using a single light as a sole point of reference
• Autokinesis can be avoided by maintaining normal eye movement, scanning and frequent instrument monitoring

Visual Illusions

Judgement of Distance and Angles

• From our experience, we assume that light travels in a straight line
• However, this is not always true e.g. as light travels through water, then through air, it refracts
• An aircraft on approach through heavy rain can refract the image of the runway, appear further and lower than actual

Visual Illusions

False Horizons

• Sloping layers of cloud by day can present the illusion of a false horizon
• Similarly at night, angled lines of light can present a false horizon

Visual Illusions

Runway Slope

• Most runways are a standard width with nil slope
• A pilot accustomed to such a runway will develop a habit of expecting visual cues
• A runway that slopes upwards will look longer and feel higher on approach
• This may cause a tendency to descend below a standard flight path angle

Visual Illusions

Runway Size

• A runway that is wider than usual will appear closer than it actually is
• Conversely, a runway that is narrower than usual will appear to be further aware than it actually is
• A wide runway can also cause the illusion of being too low, resulting in a flare too high as a result
• Similarly, a narrow runway may cause the illusion of being too high, delaying the flare

Visual Illusions

Black Hole Approach

• Flying an approach to a runway with no other visual references such as town or street lights is called the black hole approach
• A black hole approach can create the illusion that the aircraft is higher than is actual
• This may cause a tendency to descend below a standard flight path angle
• To alleviate this illusion, use all available aids such as instruments (e.g. VSI), runway lighting, VASI or PAPI systems

Hearing and Balance

• The ears provide two senses
  • Hearing
  • Balance
• Hearing allows us to perceive sound and interpret them
• Balance allows us to interpret which way is up and acceleration/deceleration

Hearing and Balance

Structure of the Ear

• The ear is comprised of three parts
  • outer ear
  • middle ear
  • inner ear

Hearing and Balance

Structure of the Ear — Outer Ear

• The outer ear is comprised of
  • the external ear (pinna), used to gather sound signals
  • the ear canal through which pressure waves pass
  • the eardrum which is vibrated in harmony with pressure waves

Hearing and Balance

Structure of the Ear — Middle Ear

• The middle ear is an air-filled cavity containing three small bones called ossicles
• The ossicles are forced to move by the vibrating eardrum, converting pressure wave energy into mechanical motion
• Air in the middle ear is maintained at ambient atmospheric pressure by the eustachian tube

Hearing and Balance

Structure of the Ear — Middle Ear

• An obstructed eustachian tube by mucous, swelling or inflammation, can prevent pressure from equalising e.g. during a climb or descent
• This condition, called barotrauma, can be extremely painful and incapacitating

Hearing and Balance

Structure of the Ear — Inner Ear

• The inner ear is comprised of:
  • the cochlea, converting mechanical energy from the ossicles into electrical signals for the auditory nerve
  • the vestibular apparatus, consisting of three fluid-filled semicircular canals that sense angular acceleration through a cluster of small hairs
  • the otolithic organs which detect linear acceleration using fluid in the cochlea to cause movement on small hairs

Hearing and Balance

Balance

• Balance allows us to remain upright
• The dominant sense of balance is the visual channel
• When standing on one leg with eyes closed, other sensory mechanisms become dominant
• These secondary mechanisms are designed for detecting orientation, not motion or acceleration
• In an aircraft, with no visual horizon, orientation signals are craved and these secondary senses take over

Hearing and Balance

Spatial Orientation

• Orientation is achieved by:
  • vision
  • balance
  • proprioception
• Our brain assembles all this information to achieve orientation
• If there is conflicting information, vision is given priority
• Unawareness of aircraft attitude in relation to the horizon is called spatial disorientation
• When denied vision, you need to rely entirely on flight instruments, scanning regularly

Hearing and Balance

Human Balance Mechanism

• The balance mechanism is called the the vestibular apparatus
• It is designed to keep us upright while standing or moving
• In the absence of visual references, the inner ear can sense what is perceived as verticality by sensing a tilt angle

Hearing and Balance

Sensing Gravity

• Sensing gravity, or verticality, is detected by the sensory hairs in the otolithic organs
• The otolithic organs have a resting position when our head is upright
• The brain interprets the message sent from the sensory hairs as “up” — a direct downward force of 1G
• If the head is tilted, the otoliths move and take up a new position
• This then bends the hairs, which send a different signal to the brain

Hearing and Balance

Sensing Gravity

• The otolithic organs can detect the direction of g-force
• However, they cannot distinguish the origin of the force
• It could be the force of gravity, or centripetal force in a turn
• In a turn, the otolithic organs will detect a false vertical

Hearing and Balance

Sensing Linear Acceleration

• When our body tilts or accelerates, we naturally lean to avoid falling over
• In the absense of a visual reference, our body cannot distinguish between tilting and accelerating
• Our corrections to this sensation may not be appropriate

Hearing and Balance

Sensing Angular Movement

• The three semicircular canals of the inner ear contain fluid
• The canals are at right angles to each other
• Therefore, they can detect angular acceleration in all three axes

Hearing and Balance

Sensing Angular Movement

• The semicircular canals are not designed to detect linear changes in motion or linear acceleration
• The upper and lower volumes of fluid are self-cancelling
• During acceleration, the fluid at the top and bottom of the semicircular canal moves rearward, and the hairs remain upright

Disorientation and Illusions

The Leans

• When combining a false sense of vertical with the sensation of rolling, the brain can become confused
• This condition is called the leans

Disorientation and Illusions

The Leans

• Perception of rapid roll rates can produce strong sensations of disorientation
• The leans may be perceived during a turn entry or exit
• We mitigate this during night flight by:
  • relying on instrument scan if a reliable visual horizon or reference is not detected
  • trusting the instrument scan over our sensations
  • applying smooth control movements into and out of turns

Disorientation and Illusions

The Leans

• Failure to mitigate this illusion can result in the pilot sensing wings-level when the aircraft is rolled
• When the pilot applies inappropriate flight inputs in response to the illusion, the aircraft enters the graveyard spiral

Disorientation and Illusions

Nose-Up Pitch Illusion of Linear Acceleration

• When tilting our head forward or backward, the hairs in the otolithic organs signal to our brain that the vertical axis has inclined
• The same sensation is caused by linear acceleration
• This false sensation under linear acceleration is called the somatogravic illusion
• We are prone to the somatogravic illusion when:
  • absence of a reliable visual reference
  • high-powered aircraft under rapid acceleration e.g. during take-off

Disorientation and Illusions

Nose-Up Pitch Illusion of Linear Acceleration

• The somatogravic illusion can cause the pilot to believe the aircraft is pitched nose-up when it is level
• An inappropriate response of the pilot is to push the nose forward

Disorientation and Illusions

Nose-Up Pitch Illusion of Linear Acceleration

• In the event of a loss of visual reference, we mitigate this illusion by:
  • Relying on our instruments, particularly the attitude indicator
  • Trusting the instruments over any perceived sensations
  • Maintaining our posture and head tilt position during climb

FlyDubai 981 (2016)

Quiz on Objectives

• Which part of the eye is responsible for detail and colour during day flight?
• Which part of the eye is responsible for orientation and night vision?
• What are some reasons that our night vision may be deteriorated?
• You see an aircraft ahead with green on the left and red on the right — is this a risk?
• What are some illusions caused by our eyesight and how do we overcome them?
• Which apparatus is responsible for balance?
• What are some illusions caused by our balance mechanism and how do we overcome them?