It is getting towards evening and you are almost home. The Birddog has done well today. The weather isn't the best, but it’s the "mandatory" "1000 and 3." The weather has a few problems, but you should be able to thread through any of the weather to make it home.

It is getting a little darker, but there is no worry. You look over your right shoulder and check the fuel. It is time to change tanks. Recheck the VOR.....OK now, fuel pump on. Look up over your left shoulder and check the fuel and switch tanks. Check the transponder.......Oh, dog breath....you dropped your pencil.......head down and a quick look at the floor......it will have to wait, you have another pencil........head up........OH CRAP, YOU'RE IN THE CLOUDS! .WHAT'S GOING ON!!!!!!!!!.................YOU'RE IN A LEFT BANK AND DIVING!!!!!!......... WAIT A MINUTE, THE ATTITUDE INDICATOR INDICATES WINGS LEVEL!!!!!!!!!!!....THAT INSTRUMENT HAS TO BE WRONG!!!!!!

You have just experienced SPATIAL DISORIENTATION! The definition of spatial disorientation is "the lack of appreciation for one's position in reference to the earth's surface." For all of you Birddog pilots.....it means that you don't know which end is up...

The body has three means by which the Birddog pilot can sense postion:

In flight, ONLY YOUR EYES GIVE CAN YOU RELIABLE SENSORY INPUT! This input can be the ground, stars, other aircraft, instruments, etc. The inner ear and proprioceptors give you false information and cannot be believed. Disorientation, due to believing the wrong sensory input can cause unusual attitudes and uncontrolable conditions.

The most common type of disorientation occurs in weather or at night. Anytime you can not see the horizon, you are at risk. Over water is another good example. Make sure that your instruments work and then believe in them! This includes those who are flying in VFR conditions.

Types of Spatial Disorientation:

1. The Leans - This is a very common form of spatial disorientation This can result from unperceived rolls. If you fly for some time with one wing high, your "false sense of balance" will call that normal. When you "see" the mistake and correct the wings to level, your senses tell you that your are incorrect, with the other wing down.

2. Somatogyral Illusion - That is a real mouth full. This means that a sensation of rotation is in the direction different that that of the actual motion that is occurring. I am a simple person. I take this as one step farther than the "leans." A pilot has gone into an unknown, gentle spin. His ears (vestibular apparatus) and propioceptors equilibrate and make this spin "normal and level." The pilot finally "senses" a problem and tries to correct the problem. This causes him to "sense" the wrong correction and he turns back into the spin. This is called the "graveyard spin or spiral."

3. Oculogyral Illusion - Where do they come up with these names? This is the apparent movement of a viewed object, such as the instrument panel, occurring in the response to stimulation of the semicircular canals (inner ear). This can happen if you are turning your head or doing maneuvers. You have just made a rocket run and you are pulling out and looking over your shoulder at the ground. When you look at the instruments, it takes time to focus.

This article will continue in Part 2. The point of all types of disorientation is the same. YOU CAN ONLY BELIEVE YOUR EYES and Spatial Disorientation can happen at any time. It is most common in weather, at night and when you can't see the horizon! Don't believe your ears or seat. Know you instruments.

Have a safe flight!
REX 79


Written for Birddog owners by Dr. Steve Frushour, IBDA Aero-Medical Officer