AVIATION SAFETY NEWSLETTER

www.faa.gov/fsdo/stlfsdo

Thought for the month.....
A little learning is dangerous but a lot of ignorance is worse.

Whoa. Which way is up?.... Humans have been walking a lot longer than we have been flying. Over the centuries we have developed some pretty extraordinary equipment that permits us to perform many foot-borne activities like dancing, surfing, skiing and skating. Our body's ability to sense and interpret our relationship to the earth and maintain our balance is truly remarkable. Unfortunately, it doesn't work when we're flying.

Earthbound, we utilize several systems to figure out what's going on. Proprioceptors are the name of the sensory receptors in our muscles, skin, tendons and joints. These send messages to our brain letting us know when we are standing, sitting, reclining, etc. The term "seat of the pants flying" refers to the most basic type of aviating, where we respond to the various pressures we perceive sitting in the aircraft. It is a muscle sense of equilibrium, but it works primarily in the vertical plane and cannot do much to ensure we are upright.

The vestibular organs are situated in our inner ear and are comprised of three semicircular, liquid filled, canals. They are aligned in three dimensions, pitch, yaw, and roll. When we move in any of these directions, the fluid has a tendency to remain stationary while the structure of the canal moves around it. The best visualization I can provide is a glass of water with an ice cube in it. If we turn the glass, the water remains stationary. The ice cube doesn't turn. If you can imagine hair-like receptors attached to the glass, the stationary water would displace them as the glass is turned. In the vestibular organs, these receptors send a message to the brain indicating movement in that plane.

If we continue to spin the glass however, the fluid will begin to move with it. Eventually, the fluid and the ice cube will be turning at the same rate as the glass. The receptors would no longer detect any relative motion since the fluid and the container are both moving at the same speed. If we stop the glass at this point, the fluid will remain in motion for a time. During this period, the receptors will be displaced in the opposite direction because the container is stationary but the fluid is not. This would be interpreted as a turn in the opposite direction even though the glass is not moving.

Since this condition can occur in any one of the three canals, it can also occur in two of them simultaneously. When it happens it is called the coriolis effect, and it can be very disorienting. This is often created at picnics or school outings where contestants in a race are required to place their foreheads on a baseball bat and spin around it for several seconds before the race starts. This activates the fluid in two canals and when the contestants raise their heads to begin the race, the false indications caused by the residual fluid motion causes disorientation and most of the racers are unable to track a straight line and often lose their balance and fall down. It's funny on the playing field, but not nearly so hilarious if it occurs in flight which might happen if a pilot looks down while the aircraft is in a prolonged turn.

Because we rely so much on our eyesight, we can often correct these confounders of equilibrium. The "eyes" have it when it comes to orientation as long as we have reliable visual clues. Obviously in flight, all of these sensors are going to be active often giving us incorrect information. By looking outside the aircraft we are able to properly orient ourselves and continue to control the aircraft. If we lose visual references outside the aircraft, our only salvation is to refer to our attitude instruments in the cockpit.

Anything that can interfere with our ability to maintain visual references is a hazard, as well as anything that can interfere with our ability to properly interpret those visual clues or make us more susceptible to disorientation such as illness, medication, fatigue, and hypoxia. Good risk management demands that we address these concerns in our planning. Pilots who fly aircraft with instruments installed should maintain some level of proficiency at flying only by reference to them. It won't make you an instrument pilot, but ignorance in this area could be deadly.

Upcoming Events

April 29th
Ups and Downs of Takeoffs and Landings
AOPA Air Safety Foundation
Florissant Valley College
7 to 9 PM

May 7th
Working CFI Seminar
Maryland Heights Centre
2344 McKelvy Road
Maryland Hghts
8:30 AM to 1:00 PM

May 10th
Collision Avoidance
Mid America Airport Terminal
Mascoutah, IL
1 to 4 PM

June 12th
Spatial Disorientation
Catfish Wharf Restaurant
Kennett, MO
7 to 9 PM

June 21st
Giving and Getting a Good Flight Review
Skyline Aeronautics
Spirit of St. Louis Airport
9 to 11 AM

LET'S NOT MEET BY ACCIDENT
FRED P. HARMS
Operations Safety Program Manager
1-800-322-8876 extension 4835
Fred.Harms@faa.gov