Do you remember the flight training exercise where the instructor asks you to close your eyes while she/he places the aircraft in a nose low or nose high attitude in a shallow turn? It is a hard exercise to simulate as the necessary power changes give us clues as to what is happening.
When asked to recover from whatever unusual attitude we find ourselves in, we are supposed to rely solely on what the instruments are telling us. In fact we use the engine sounds and our senses to help.
In a real disorientation situation the engine sounds are not likely to change much and we really cannot rely on our senses. In practice, the instructor may try to throw the aircraft around some to disorient you, but you can usually feel what is happening.
In real life, the aircraft attitude may change so gradually that you are not able to sense changes in pitch and roll. All you have is the instruments to maintain control of the aircraft and you must believe them. This is not easy.
All of your senses may be screaming that the instruments cannot possibly be correct. Confusion will result, which may lead to outright terror. It will take all of your concentration to overcome your senses. It will be a fight for your life.
A newly instrument rated Cirrus SR 22 pilot with 483 hours was in instrument conditions when he became disoriented. Radar showed that the aircraft climbed on a northwest heading to 1,600 feet, then started a right turn toward the northeast and climbed to 1,800 feet. The aircraft continued the turn to a southeast heading and descended to 1,000. The aircraft turned left toward the northeast and climbed to 1,900 feet. It then turned right toward the south and descended to 400 feet in 12 seconds. It then climbed to 1,400 feet in 12 seconds. The aircraft then turned left through north descending through 1,100 feet, and continued the descent into the ground.
A radar controller tried several times to give headings and altitude information to the pilot. The pilot sometimes responded and sometimes did not. A few of the responses were, "I’m hearin’ ya. I’m hearin’ ya. I’m, I’m, I gotta get my act together here. I hear you, but I’ve got, I’ve got problems, I’ve got avionics problems. I’m trying to get the plane, ah, level. The wings are level." The last transmission, "I’m losin’, I’m losin’ it again here."
Based on the aircraft logs and on the recovered instruments, there was not likely any avionics failures. Even if there were, there were sufficient back up instruments available.
Disorientation can be caused by both visual and vestibular (inner ear) illusions.
Clouds are never absolutely flat on the bottom. When entering cloud, you may lose sight of the ground on one side of the aircraft before the other. This may create the illusion that you are in a turn in the direction you last saw the ground.
Seeing a flash of ground on one side of the aircraft while in cloud may create the same illusion. The feeling of being in a turn, or climbing or descending, when you are not, is also called vertigo.
Vertigo can also be caused by vestibular illusions. Your sense of balance is based on fluid movement in the inner ear. If the fluid is forced to move suddenly, you may feel you are in a turn, or a climb or descent when you are not.
Turbulence, positive or negative G caused by rapid acceleration or deceleration, or just sudden head movement can cause fluid movement in the inner ear sufficient to cause severe disorientation.
The leans may occur when a pilot in IMC does not notice a gradual roll rate of up to 3 degrees per second. When she/he becomes aware that some roll has occurred she/he tends to roll abruptly back to level flight. This disturbs the fluid in the inner ear and gives the illusion that she/he is in a turn in the opposite direction. The pilot knows the instruments are correct, but she/he has an overpowering urge to lean away from the imagined turn.
A turning illusion occurs when a pilot in IMC rolls into a turn and remains in the turn for awhile (10 to 30 seconds). The pilot begins to feel she/he is in straight and level flight. The pilot may have a tendency to roll to a steeper angle of bank to be able feel the turn. Even if this tendency is controlled, the roll out to level flight may cause the feeling that she/he is now in a turn to the other side.
An addition of power causing acceleration in IMC may give a sense of pitching up. A sudden deceleration in IMC may cause a sense of pitching down.
As can be seen from the scenario above, vertigo or severe disorientation may result in the loss of control of an aircraft. You must concentrate on, and believe in, your instruments until the disorientation disappears.
You may say that you will never get yourself into this situation, but it is easier than you think. You do not have to actually enter cloud. Virga hanging down obscuring the horizon to one side may cause you to lower a wing gradually to feel wings level.
Dusk or night with a cloud cover may cause the horizon to become obscured. Low light conditions over snow covered terrain may result in the loss of the horizon. Any time you lose the horizon, you are in danger of becoming disoriented if you do not immediately focus on and believe your instruments.
The disagreement between your senses and the instruments may happen slowly or rapidly. You don’t immediately understand what is happening which causes confusion. You may think your training has prepared you for this and that you would immediately go on instruments. I have news for you. I’ve been there and I was confused. I chased the aircraft up and down and around for a bit before I could force myself to focus solely on the instruments. I can identify with the fellow in the SR 22. I won the battle with myself, he didn’t.
Dale Nielsen is an ex-Armed Forces pilot and aerial photography pilot. He lives in Abbotsford, B.C., and currently flies air charters. He still freelances as a flying instructor and seminar facilitator. Nielsen is also the author of seven flight training manuals published by Canuck West Holdings.
Got an aviation safety story to tell? Dale Nielsen would like to hear from pilots who have educational aviation experiences to relate. Excerpts from these stories will be used in upcoming safety articles. Dale can be contacted via e-mail: firstname.lastname@example.org