The 3 canals arranged at approximately right angles to each other detect the roll, pitch and yaw axis
In the center of the canal is the cupola, a gelatinous structure that rests upon sensory hairs located at the end of the vestibular nerves
It is the movement of these hairs within the fluid which causes sensations of motion [Figure 2]
Because of the friction between the fluid and the canal, it may take about 15-20 seconds for the fluid in the ear canal to reach the same speed as the canal's motion
Mismatch between what the fluid/hairs are telling your body and what is actually happening can lead to disorientation
To illustrate what happens during a turn, visualize the aircraft in straight and level flight
With no acceleration of the aircraft, the hair cells are upright and the body senses that no turn has occurred
Placing the aircraft into a turn puts the semicircular canal and its fluid into motion, with the fluid within the semicircular canal lagging behind the accelerated canal walls [Figure 3]
This lag creates a relative movement of the fluid within the canal
The canal wall and the cupula move in the opposite direction from the motion of the fluid
The brain interprets the movement of the hairs to be a turn in the same direction as the canal wall
The body correctly senses that a turn is being made
If the turn continues at a constant rate for several seconds or longer, the motion of the fluid in the canals catches up with the canal walls
The hairs are no longer bent, and the brain receives the false impression that turning has stopped
Thus, the position of the hair cells and the resulting sensation during a prolonged, constant turn in either direction will result in the false sensation of no turn which can result in illusions such as the graveyard spiral
When the aircraft returns to straight-and-level flight, the fluid in the canal moves briefly in the opposite direction
This sends a signal to the brain that is falsely interpreted as movement in the opposite direction
In an attempt to correct the falsely perceived turn, the pilot may reenter the turn placing the aircraft in an out of control situation, a condition called the Coriolis illusion
The otolith organs detect linear acceleration and gravity in a similar way
Instead of being filled with a fluid, a gelatinous membrane containing chalk-like crystals covers the sensory hairs
When the pilot tilts his or her head, the weight of these crystals causes this membrane to shift due to gravity and the sensory hairs detect this shift
The brain orients this new position to what it perceives as vertical
Acceleration and deceleration also cause the membrane to shift in a similar manner
Forward acceleration gives the illusion of the head tilting backward
As a result, during takeoff and while accelerating, the pilot may sense a steeper than normal climb resulting in a tendency to nose-down, also called the somatogravic illusion
Figure 3: Instrument Flying Handbook, Linear AccelerationFigure 3: Instrument Flying Handbook, Linear Acceleration
Ear Block:
Causes:
As the aircraft cabin pressure decreases during ascent, the expanding air in the middle ear pushes the eustachian tube open, and by escaping down it to the nasal passages, equalizes in pressure with the cabin pressure
During a climb, middle ear air pressure may exceed the pressure of the air in the external ear canal, causing the eardrum to bulge outward and the Eustachian tube to bulge outward
Therefore during climbs and descents a pilot must periodically open the Eustachian tube by swallowing, yawning, tensing muscles in the throat or the Valsalva maneuver
Descents can be more difficult to relieve due to the fact that the partial vacuum tends to constrict the walls of the Eustachian tube
To remedy this often painful condition, which also causes a temporary reduction in hearing sensitivity, pinch the nostrils shut, close the mouth and lips, and blow slowly and gently in the mouth and nose
During descent, the pilot must periodically open the eustachian tube to equalize pressure
This can be accomplished by swallowing, yawning, tensing muscles in the throat, or if these do not work, by a combination of closing the mouth, pinching the nose closed, and attempting to blow through the nostrils (Valsalva maneuver)
Either an upper respiratory infection, such as a cold or sore throat, or a nasal allergic condition can produce enough congestion around the eustachian tube to make equalization difficult
Consequently, the difference in pressure between the middle ear and aircraft cabin can build up to a level that will hold the eustachian tube closed, making equalization difficult if not impossible
The problem is commonly referred to as an "ear block"
Effects:
An ear block produces severe ear pain and loss of hearing that can last from several hours to several days
Rupture of the ear drum can occur in flight or after landing. Fluid can accumulate in the middle ear and become infected
Prevention:
An ear block is prevented by not flying with an upper respiratory infection or nasal allergic condition
Adequate protection is usually not provided by decongestant sprays or drops to reduce congestion around the eustachian tubes
Oral decongestants have side effects that can significantly impair pilot performance
Conclusion:
A physician should be consulted if any problems occur and as always remember the IMSAFE checklist for medications to see that you're fit to fly
