One of the leading causes of general aviation accidents is continuing VFR flight into instrument meteorological conditions (IMC). When pilots lose their outside visual references, they can lose their spatial orientation – what’s up, down, left, right, and what’s straight and level. This happens because the human senses of position are easily fooled. Spatial disorientation, also known as vertigo, can quickly lead to losing control of the aircraft.

Basically, we use three senses to understand where we are. Vision is the first of these, and it’s straightforward. We see and recognize what is up, down, left, right, and what comprises a horizon. Our second orientation sense is “proprioception” – the “seat of the pants sensation.” In reality, we have nerve receptors in all the muscles of the body, but the most important ones are in the neck and the knee joints. They detect position in the body and the reaction of muscles to their location.

Third is the vestibular sense, which is the other half of our sense of hearing. Deep within the inner ear, adjacent to the organ of hearing, or cochlea, is our organ of balance – the vestibular apparatus. It is divided into two parts – the three semicircular canals and the two otoliths.

The three semicircular canals are oriented 90 degrees to one another. They are angular accelerometers that detect pitch, roll, and yaw. Adjacent to them are two otoliths – linear accelerometers that detect motion to the front, back, left, and right. They also sense the earth’s gravity.