Spatial disorientation

040 Human PerformanceChapter 5

When visual and vestibular cues conflict, pilots experience spatial disorientation — a major cause of controlled flight into terrain in IMC.

Schematic

Semicircular canals sense angular acceleration; otoliths (utricle/saccule) sense gravity and linear acceleration.

Vestibular system

Key fact

Semicircular canals (3) — detect angular acceleration (roll, pitch, yaw). Utricle & saccule (otoliths) — gravity and linear acceleration. System senses rate of change, not sustained constant motion.

Key fact

Seat-of-the-pants — proprioceptors in muscles, tendons, joints report body position. Unreliable in flight — trust instruments.

Dangerous illusions

Illusion	Mechanism	Risk
Somatogravic	Forward linear acceleration	Illusion of pitch-up → pilot pitches down (head-up illusion)
Head-down	Sudden deceleration	Pitch up
Somatogyral / leans	Return to level after unnoticed turn	Feels like entering turn → re-bank wrong way
Graveyard spin	Adaptation to spin	Recovery feels like new spin → re-enter spin
Graveyard spiral	Prolonged undetected bank	Spiral dive
Coriolis	Head movement during turn	Most dangerous vestibular illusion — multiple canals stimulated
Vertigo	Visual vs vestibular mismatch	Disorientation

Exam trap

Leans — after prolonged undetected turn, levelling wings feels like banking the opposite way. Pilot may re-enter the original bank.

G-forces

Key fact

+Gz (head-to-foot): blood drains from brain → grey-out ~+3G, blackout ~+4.5G, G-LOC ~+5G. Factors: hypoxia, low blood sugar, obesity.

Key fact

+Gx forward acceleration — oculogravic/somatogravic illusions. +Gy lateral — not normally significant in fixed-wing ops.

Motion sickness

Key fact

Systems involved: vestibular, vision, proprioceptive, gastro-intestinal. Vibration 1–100 Hz affects organs at resonant frequencies (e.g. head 10–30 Hz, vestibular 0.1–2 Hz).

Runway & approach illusions (summary)

See Vision & hearing for runway width/slope, black hole, fog, and rain illusions. At night with no visual aids, pilots tend to fly lower than intended.

Key fact

Approaches at night without landing aids — pilot feels higher than actual → risk landing short. Countermeasure: use approach aids and standard procedures.