Deep inside the inner ear is a tiny, complex organ called the labyrinth that looks like a cross between a tuba and a toy gyroscope. The portion of this organ that we’re concerned with is a set of three bony loops called the semicircular canals.
One loop of the semicircular canals is horizontal, lying flat like a bicycle inner tube on the driveway. The other two canals stand upright at right angles to each other. All three are connected in a structure called the vestibule.
Inside the bony exterior of the semicircular canals is a fleshy lining of hairlike fibers bathed in fluid. When you turn your head, the bony structure and the tiny hairs inside it turn with it, only the fluid is slower to accelerate. It’s just like rotating the outside of a glass filled with an icy drink. The glass rotates in your hands, but the icy liquid inside begins to move only very slowly, creating a difference in velocity between the rim of the glass and the liquid just inside.
There are a couple of other boy organs that contribute to equilibrium. Cristao have tiny jellylike blobs that sense rotation, and maculae are bundles of nerves on a stem that tips downward when you bend down Like the semicircular canals, both of these organs can be easily fooled in an airplane at a high altitude unless your eyes arc working well.
The tiny hairs in the semicircular canals are forced to sway in one direction or another from the difference in speed between the fluid and the bony structure, and nerves beneath each hair detect the degree of swaying. In our brains, this is transformed into a sensation of movement.
Without visual cues to help make sense of some of the sensations coming out of the semicircular canals, the vestibular system can relay completely inaccurate messages to the brain.
Let’s imagine a pilot flying in complete darkness. If he enters a right – hand bank very gradually, the hairy fibers in the semicircular canals may not be sensitive enough to detect the movement of the fluid. Although JFK Jr.’s airplane was gradually entering a right turn, his vestibular system wouldn’t have known it.
Now let’s imagine that the pilot glances at his flight instruments. He’d at least see a right bank indication on his attitude indicator and his turn indicator—two gyroscopic instruments. Surprised, he might move the aileron controls abruptly to the left to level the wings again. Now, that rapid control movement to the left would certainly create enough of a jolt to the hairy fibers to send a signal to the brain: We’re turning left.
That left-turn signal is wrong in this case. The pilot is actually moving from a right bank to level flight. But because the semicircular canals didn’t pick up the right bank and only noticed the left-hand movement of the ailerons to level the wings, the brain perceives a left turn.
The power of these sensations is hard to describe. In the scenario we’ve just described, the pilot might find the sensation of turning left so powerful that almost nothing would convince him he had done otherwise. He would be very likely to respond with rightaileron control to correct what his senses tell him was a left turn, even though his eyes told him a moment ago that he was correcting a mistaken right turn.
One of the most dangerous things a pilot can do when flying in instrument conditions or in very dark skies like John Kennedy Jr. experienced is to make any rapid movement of the head, The jostling to the semicircular canals can set up a host of conflicting, and inaccurate, sensations of movement
By the Book
Spatial disorientation is the
catch-all term used to describe any situation in which a pilot isn’t certain of the attitude of his airplane relative to the horizon.
The power of these illusions was brought home to me some years ago during a training session on the topic of spatial disorientation.
I was placed in a contraption consisting of a simple chair mounted on a swivel. After an instructor told me to buckle myself into the seat (I thought this was an overprecaution), he had me lay my head on its side with my eyes closed. He rotated the chair with me in it, accelerating it so gradually that I had only a slight sensation of movement. In reality it was spinning quite fast at the end.
After about a minute of this, he gave me a signal to sit upright and open my eyes, while he simultaneously stopped the chair’s rotation. What I felt was an overwhelming sensation of falling forward toward the floor. The feeling was so powerful that I yelled—an expletive, if I recall—and put my hands out in front of me to stop myself from falling on my face. What others in the room saw was a confused pilot sitting in a still chair, in the grip of a powerful balance illusion of falling that lasted for about a minute, and, I confess, turned my stomach.
Had I been in an airplane when this situation occurred—as when a pilot bends down to search for a flashlight or pencil on the floor while the airplane is turning—I believe
that no amount of discipline and attention to my instruments would have prevented me from pulling the airplane into a steep climb. The illusion I experienced, called the Coriolis illusion, surpassed reason and went straight to the level of instinct and fear.
In this case, and in other balance illusions, the solution lies in prevention. Pilots must understand how these illusions are created and learn to avoid them. In the case of John F. Kennedy Jr., it’s unlikely that his brief flying experience would have equipped him to prevent balance illusions or to correct them if they occurred.
Because the accident occurred in total isolation from air traffic control, and because human factors leave behind no evidence that can be examined in a lab, the cause of the crash that killed John F. Kennedy Jr. and his wife and sister-in-law will never be known with any certainty. Still, the sparse evidence we have of its last few minutes leaves us with a powerful lesson—that every pilot is subject to the same destructive attitudes and is saddled with the same unreliable senses. If any good comes out of John Jr.’s death, it will be a heightened focus on safety among general aviation pilots for decades to come.