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11.7.11 Vision, Disorientation, Illusion

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Disorientation

Many different illusions can be experienced in flight. Some can lead to spatial disorientation. Others can lead to landing errors. Illusions rank among the most common factors cited as contributing to fatal aircraft accidents.

Illusions of attitude and motion result in spatial disorientation and have been shown to contribute substantially to the frequency of accidents in aviation. Such illusions are normal responses to particular situations, and they involve both ocular and labyrinthine mechanisms, especially the latter. Because they are normal reactions, thorough indoctrination is needed to convince the pilot that proprioceptive sensations are totally unreliable.

Careful training is needed to induce the proper reliance on flight instruments. Even so, an overcomplicated cockpit layout, extremely high speed, bad weather, and difficult tactical conditions have frequently resulted in rejection of the instrument information by the pilot and have rendered him even more susceptible to disorienting sensations.

Increased effort should be exerted to deal appropriately with all factors in human physiology and in aircraft design that contribute to spatial disorientation as a hazard of flight.

Overcome Sensory Illusions

Use instrumentation that work in the environmental conditions flown:

  • Quality of displays.
  • Instruments which can be read quickly and un-ambiguously by night and day.
  • Instruments adequate for manoeuvres and conditions expected.
  • Reliability.
  • Clear malfunction indication.
  • Use of head up displays to assist transfer from external to internal cues and reduce head movements.
  • Display should reduce perceptual conflict when external cues are uncertain.

Flightdeck:

  • Position ancillary instruments and controls so that head movements are reduced during critical flight phases.
  • Configuration - a lack of well-defined aircraft frame of reference, contributes to break-off and leans.
  • Presence of sloping edge of canopy and instrument panel not aligned with transverse axis of aircraft, does not assist pilot to maintain level attitude when flying on external visual references.
Operational Factors

Recognise manoeuvres and flight environments which carry a high disorientation risk. Flight crew should fly only those aircraft, those manoeuvres and in those flight conditions which are commensurate with training, experience and proficiency.

Flightcrew Factors

Training and experience are of paramount importance:

  • Selection: This is important because of the large difference between individuals in apparent susceptibility to disorientation in flight.
  • Health: Disorders affecting vestibular and visual systems should result in grounding.
  • Drugs: Susceptibility to disorientation increases when drugs are used eg hypnotics (sleeping pills) and especially barbiturates, anti-histamines (for hay fever), anti-motion sickness tablets (hyoscine) and alcohol. Many stay in the body for more than 24 hours.
Practical Advice to Flight Crew

Preventative Advice:

  • You cannot fly by the seat of your pants.
  • Don't allow control of the aircraft to be based at any time on seat of your pants sensations, especially when deprived temporarily of visual cues.
  • Do not mix instrument flying with flying by external visual cues unnecessarily.
  • Make an early transition to instruments in poor visibility. Once on instruments, stay on instruments, until external cues are unambiguous.
  • Maintain a high proficiency at flight in IMC.
  • Be particularly vigilant in high risk situations - night, poor visibility, etc.

Do Not Fly:

  • With an upper respiratory tract infection (common cold, ear or sinus infection).
  • Under the influence of drugs or alcohol.
  • When mentally or physically debilitated for any reason.

Make your first flight after a period off flying a simple VMC sortie. Experience does not make you immune.

CROSS CHECK YOUR INSTRUMENTS AND TRUST THEM, THEY CANNOT ALL BE WRONG...

Coping with Spatial Disorientation
  • You can dispel persistent minor illusions (eg leans) by redirecting attention to other aspects of flying.
  • When suddenly confronted with strong illusory sensations:
    • Get on instruments.
    • Maintain instrument reference and correct scan pattern.
    • Control aircraft to make instruments display desired flight pattern.
    • Don't mix external visual and instrument references.
    • Seek help if disorientation persists, from co-pilot, ground control, etc.
  • Finally, remember that disorientation is a normal response to the unnatural environment of flight.