Spatial Disorientation - Attitude Illusions
Spatial disorientation occurs when your orientation differs with regard to the actual position, attitude, or movement of your airplane in space.
Your body uses three systems, working together, to ascertain orientation and movement in space. They are, respectively:
• Vestibular system—organs found in the inner ear that sense your position by the way you are balanced.
• Somatosensory system—the nerves in your skin, muscles, and joints, which, along with hearing, sense position based on gravity, feeling, and sound.
• Visual system—your eyes, which sense position based on what you see.
All this information comes together in the brain and, most of the time, the three streams of information give you a clear idea of where and how your body is moving.
Flying may cause these systems to supply conflicting information to your brain, which can lead to disorientation.
During flight in VFR conditions, your eyes are the major orientation source and usually take preference over false sensations from your other sensory systems. When these visual cues are removed, as they are in instrument conditions, false sensations can cause you to quickly become disoriented.
The vestibular system in the inner ear allows you to sense movement and determine orientation in the surrounding environment. It is like a gyroscope in the way it maintains it's orientation.
In both the left and right inner ear, three semicircular canals are positioned at approximate right angles to each other.
Each canal is filled with fluid and has a section full of fine hairs. Accelerated motion of the inner ear in any direction causes the tiny hairs to deflect, which in turn stimulates nerve impulses, sending messages to the brain. The vestibular nerve transmits the impulses from the utricle, saccule, and semicircular canals to the brain to interpret motion.
The somatosensory system sends signals from the skin, joints, and muscles to the brain that you interpret in relation to the Earth’s gravitational pull. These signals determine your posture.
Inputs from each movement update your body’s position to the brain on a constant basis. “Seat of the pants” flying is largely dependent upon these signals. Used in conjunction with visual and vestibular clues, these sensations can be fairly reliable.
However, your body cannot distinguish between acceleration forces due to gravity and those resulting from maneuvering the aircraft which leads you to to sensory illusions and false impressions of an aircraft’s actual orientation and movement.
Under normal flight conditions, when there is a visual reference to the horizon and ground, the sensory system in the inner ear helps you to identify the pitch, roll, and yaw movements of the aircraft. Think of how the walls of a room and the ceiling meet at a specific corner of the room. The two walls are pitch and roll. The ceiling represents the yaw.
When you lose visual contact with the horizon , your vestibular system becomes unreliable. Without visual references outside the aircraft, there are many situations in which combinations of normal motions and forces create convincing illusions that you find difficult to overcome.
Prevention is usually the best remedy for spatial disorientation. Unless you have many hours of training in instrument flight, flight should be avoided in reduced visibility or at night when the horizon is not visible.
You can reduce susceptibility to disorienting illusions through training and awareness. Instrument training is the key to avoid the temptations offered by illusions. You learn to rely totally on flight instruments.
