Spatial Orientation

Question 1

Vestibular Aspects

Answer 1

● The inner ear contains the vestibular system, which is also known as the organ of equilibrium.
● The vestibular system contains two distinct structures:
○ Semicircular canals, which detect changes in angular acceleration.
○ Otolith organs, which detect changes in linear acceleration and gravity.

Question 2

The Semicircular Canals

Answer 2

● The semicircular canals are three half-circular, interconnected tubes located inside each ear.
● Each corresponds to the aircraft movements of:
○ Rolling.
○ Pitching.
○ Yawing

● If you turn either your aircraft or your head, the canal moves with your head, but the fluid inside does not move because of its inertia
● As the canal moves, the hairs inside also move with it and are bent in the opposite direction of the acceleration by the stationary fluid .
● This hair movement sends a signal to the brain to indicate that the head has turned.
● The problem starts when you continue turning your aircraft at a constant rate (as in a coordinated turn) for more than 20 seconds

● When this happens, the hairs inside the canal will return to their straight up position, sending an erroneous signal to the brain that the turn has stopped–when, in fact, the turn continues

● If you then start rolling out of the turn to go back to level flight, the fluid inside the canal will continue to move (because of its inertia), and the hairs will now move in the opposite direction.
● This sends an erroneous signal to the brain indicating that you are turning in the opposite direction, when in fact, you are actually slowing down from the original turn

Question 3

Vestibular Illusions

Answer 3

● Illusions involving the semicircular canals of the vestibular system occur primarily under conditions of unreliable or unavailable external visuals and result in false sensations of rotation.
● These include the:
○ Leans.
○ Graveyard Spin.
○ Spiral.
○ Coriolis Illusion

Vestibular Illusions: Leans
● Most common illusion during flight.
● Caused by a sudden return to level flight following a gradual and prolonged turn that went unnoticed by the pilot.
● The reason a pilot can be unaware is below the detection threshold of the semicircular canals

● Levelling the wings after such a turn may cause an illusion that the aircraft is banking in the opposite direction.
● In response a pilot may lean in the direction of the original turn in a corrective attempt to regain the perception of a correct vertical posture

Question 4

Vestibular Illusions: Graveyard Spin

Answer 4

● An illusion that can occur to a pilot who intentionally or unintentionally enters a spin.
● For example, a pilot who enters a spin to the left will initially have a sensation of spinning in the same direction.
● However, if the left spin continues the pilot will have the sensation that the spin is progressively decreasing

● At this point, if the pilot applies right rudder to stop the left spin, the pilot will suddenly sense a spin in the opposite direction (to the right).
● If the pilot believes that the airplane is spinning to the right, the response will be to apply left rudder to counteract the sensation of a right spin

Question 5

Graveyard Spiral

Answer 5

● Graveyard Spiral is more common than the Graveyard Spin.
● Associated with a return to level flight following an intentional or unintentional prolonged bank turn
● For example, a pilot who enters a banking turn to the left will initially have a sensation of a turn in the same direction.
● If the left turn continues (~20 seconds or more), the pilot will experience the sensation that the airplane is no longer turning to the left

● At this point, if the pilot attempts to level the wings this action will produce a sensation that the airplane is turning and banking in the opposite direction (to the right).
● If the pilot believes the illusion of a right turn (which can be very compelling), he/she will re-enter the original left turn in an attempt to counteract the sensation of a right turn

Question 6

Coriolis Illusion

Answer 6

● Coriolis Illusion involves the simultaneous stimulation of two semicircular canals and is associated with a sudden tilting (forward or backwards) of the pilot’s head while the aircraft is turning.
● This can occur when you tilt your head down (to look at an approach chart or to write a note on your knee pad), or tilt it up or tilt it sideways

● This produces an almost unbearable sensation that the aircraft is rolling, pitching, and yawing all at the same time, which can be compared with the sensation of rolling down on a hillside.
● This illusion can make the pilot quickly become disoriented