Spiral Turn Illusion

The spiral turn illusion occurs to a pilot who enters a turn to the left or right inadvertently while on instruments .

For example, a pilot who enters a turn to the left will initially have a sensation of turning in the same direction. Without a visual horizon to verify what is happening the pilot will have the sensation that the turn is progressively decreasing. At this point, if the pilot applies right rudder to stop the left turn, the pilot will suddenly sense a turn in the opposite direction (to the right).

If the pilot believes that the airplane is turning to the right, the response will be to apply left rudder to stop the sensation of a right turn. However, by applying left rudder the pilot will unknowingly re-enter the original left turn. If the pilot cross-checks the turn indicator, he would see the turn needle indicating a left turn while he senses a right turn. This creates a sensory conflict between what the pilot sees on the instruments and what the pilot feels.

The whole purpose of instrument flight instruction is to believe what your instruments tell you about the position of your plane with respect to the surface of the earth without seeing the horizon. 

If the pilot believes the body sensations instead of trusting the instruments, the left turn will continue and it may deepen into a tight spiral turn that will result in altitude loss and forces may build up that results in structural damage to the plane and/or the loss of wings from the plane. If enough altitude is lost before the pilot recognizes this illusion a crash with the ground will result.

Visual illusions can kill. Fly aware and safely,

Jim