Spatial Disorientation and Motion Sickness
Types of spatial disorientation
Spatial disorientation is a failure to perceive correctly position or motion relative to the earth. Type I is unrecognised, the most dangerous; Type II is recognised but the pilot cannot correct it; Type III is recognised and corrected. The common illusions include the leans, somatogravic illusion, somatogyral illusion, Coriolis illusion, graveyard spiral and black-hole approach.
Causes and countermeasures
The vestibular system is the main culprit: it senses acceleration, not attitude. Visual illusions (black-hole approach, sloping runway, false horizon) add to the problem. Countermeasures are instrument cross-check, trusting the instruments, avoiding abrupt head movements in turns, and training. Motion sickness arises from conflicting sensory signals; it is reduced by looking at a distant point, fresh air, avoiding head movement and, where appropriate, medication - but medication can cause drowsiness.
Traps in questions
A classic trap is asking whether to trust sensations or instruments: always instruments in instrument conditions. Another is confusing the somatogravic illusion (acceleration feels like climb) with the somatogyral illusion (false rotation). Also remember that the leans are corrected by reference to the attitude indicator, not by 'seat of the pants'.
Worked example
On a dark night after take-off, a pilot accelerates and feels the aircraft pitching up, so pushes forward. This is the somatogravic illusion and can lead to a descent into terrain. Rule of thumb: at night or in cloud, fly the instruments and cross-check the attitude indicator.