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- • Explain how various sensory systems contribute to spatial orientation.
- • Describe the vestibular and proprioceptive systems in terms of:anatomy,function,limitations
- • Categorise the types of vestibular and central illusions.
- • Recommend strategies for the prevention of disorientation.
- • Recommend strategies for overcoming disorientation in flight.
- • Identify vestibular illusions experienced or observed using the Barany Chair.
- • Describe situations in which aircrew can suffer spatial disorientation.
- • Discuss the role of vestibular physiology in the genesis, prevention and management of disorientating vestibular illusions in flight.
Spatial Disorientation SENSING ORIENTATION?
- Eyes 80%
- Proprioceptors 10%
- Vestibular 10%
- Integration and Interpretation
- Perception of orientation
- Peripheral Vestibular System
- • Mechanoreceptive sensory hair cells
- • Afferent traffic via the vestibuloacoustic nerve (CN VIII)
- • 3 ampullary nerves
- • 2 saccular nerves
- • 1 utricular nerve
- • Nerve cell bodies lie in Scarpa’s ganglion in internal auditory meatus
- • 3 in each ear at right angles to each other
- • Angular accelerometers
- • Stimulation threshold of 2o/sec2
- • Prolonged rolls and turns reach steady state –no further acceleration
- • Cupula returns to resting position
- • Subsequent change in angular acceleration (eg cease turn, move head) sensed as a NEW movement
- • Acceleration less than 2deg/sec not sensed at all
- • Basis for SOMATOGYRAL, CORIOLIS, LEANS
- • Medial longitudinal fasciculus
- • Extraocular muscles linked to vestibular system
- • The vestibulo-ocular reflex (VOR): stabilisation of retinal image
- • Conjugate eye movements coordinated with head movements
- • Prevents smearing of visual image
- 1. Detection of rotation
- 2. inhibition of extraocular muscles on one Side.
- 2 Excitation of extraocular
- 3. Compensating eye movement
- • 2 in each ear - utricle and saccule
- • Aligned in horizontal and vertical plane
- • Linear accelerometers
- • Vertical organ senses gravity under normal conditions
Sensing linear acceleration?
- • Deceleration and tilting head down give the same movement of the otolith membrane
- • Confused messages basis of the SOMATOGRAVIC ILLUSION
Semicircular canals Respond to?
- Angular acceleration
- Visual stability
- Sense of turning/rotation.
Otolith Organs Respond to?
- •Linear acceleration
- ` Functions
- Tilt sensation
- External force sensor.
SPATIAL DISORIENTATION (SD)?
The failure to correctly sense the position, motion or attitude of yourself, or your aircraft, in relation to gravity and the Earth’s surface.
• 90% of SD related accidents are fatal.
High risk flight environments?
- • Flight in IMC Night
- • High altitude
- • Featureless terrain
- • Prolonged accelerations
- • Prolonged angular motion
- • Subthreshold attitude changes
- • High workload
- • Cloud penetration
- Low altitude in helicopters
Experience does not confer immunity?
Types of Disorientation?
- • Unrecognised
- • Recognised
- • Incapacitating
- Type 1
- Type 2
- Type 3
- Incorrect perception
- Correct perception
- Conflict not resolved
Somatogravic Illusion Caused by?
- -Linear acceleration
- -Otoliths and proprioceptors
- -Poor visual cues
- -False sensation of pitch (up or down)
- -Dark Night Takeoff Illusion”
- -Missed Approach
- -Catapult launch
Somatogravic Illusion Prevention?
- -Stay on instruments
- -May be accompanied by the oculogravic illusion 223 kt, 15CO fl
Somatogyral Illusion Caused by?
- • False sensation of rotation
- • Semi-circular canals
- • Graveyard spin or spiral
- • Accompanied by the oculogyral illusion
Somatogyral Illusion occurs When?
- • Spin recovery
- • Extended turns
- • Poor visual cues
Somatogyral Illusion Prevention?
- • Avoid prolonged spinning
- • Trust your instruments.
G-excess Illusion Caused by?
- • False sensation of rolling off bank during a turn
- • Pulling G during a level, banked turn and looking into the turn.
G-excess Illusion Prevention?
- • Don’t look into turn
- • ‘Snapshot view’ only.
- • A false sensation of roll attitude when flying level
- • Pilots can lean in order to dispel the sensation
- • Not usually dangerous
- • The most common illusion of all
Coriolis Illusion Caused by?
- • Tilting one’s head out of the plane of angular motion,
- • ‘cross-coupling’ that transfers the motion percept from one semicircular canal to another
Coriolis Illusion Result in ?
- • Strong, unpleasant sensation of tumbling
- • Nausea is common
Coriolis Illusion Prevention?
• Minimise head movements when turning
- • Rotating or flickering light
- • False sense of rotation in a direction opposite to the moving light.
- • Spinning sensation caused by a difference in pressure between the left and right middle ear “Central” Errors
- • Break-off phenomenon - feelings of detachment, isolation or physical separation while flying
- • Variations:
- • Knife edge - increased awareness of aircraft movement
- • Giant hand - inability to make control inputs
PREVENTION OF SPATIAL DISORIENTATION?
early use of instruments don’t lie
What can AVMOs do?
- • Assess fitness to fly
- • Subtle symptoms and signs cause significant SD risk
- • Advise aircrew
- • Medications, conditions, alcohol, fatigue, operational factors
- • Advise Command
- • Awareness of increased risk of SD in operations helps determine risk
What can be done pre-flight?
- • Pre-flight preparation
- • SD Training
- • Awareness of mission and flight conditions
- • Recognise a problem early and take immediate action
- • Maintain proficiency in instrument flying
- • Don’t fly by ‘seat of the pants’
- • Early and clear transition to instruments
- • Fly only if physically & mentally fit
- • Avoid alcohol and self-medication
If disorientation occurs?
- 1.Recognise the problem early
- • Take immediate action
- • Defer non-essential tasks
- 2.Re-establish visual dominance
- • Get on instruments, make them “read right”
- • Avoid unnecessary head movements
- 3.Beware of persistent symptoms
- • Maintain straight & level flight
- • Advise ATC
- • Declare emergency
- 4.Try to resolve sensory conflicts
- • Inability to resolve may lead to panic and psychological incapacitation
- • Abandon aircraft
- 5.Transfer aircraft control
- • Co-pilot
- • Autopilot.
- Make the instruments “read right”
Quiz question 14?
- • The semicircular canals detect:
- a. Angular acceleration
- b. Linear acceleration
- c. Movement of the eyes
- d. Acceleration due to gravity
Quiz question 15?
- A somatogravic illusion generally produces a false sense of:
- a. Roll attitude
- b. Yaw attitude
- c. Pitch attitude
- d. Rotation
- • All major Aviation Medicine reference texts categorise Somatogyral Illusion and The Leans as separate entities.
- • Semantics in terminology is not important, but understanding what it feels like is essential.
- • “…a false sensation of rotation (or absence of rotation) that results from misperceiving the magnitude and direction of an actual rotation…result from an inability of the semicircular canals to register accurately a prolonged rotation.”
- • Examples:
- • Graveyard spin
- • Graveyard spiral
- • Gillingham illusion
- • :…a false percept of angular displacement about the roll axis…often associated with a vestibulospinal reflex appropriate to the false percept..”
- • Caused by subthreshold rolls or prolonged bank
- • Involves both otoliths and semicircular canals in prolonged turns
- • Feeling banked turn dissipates (somatogyral)
- • G vector gives false vertical cue (somatogravic)