Wednesday, April 13, 2016

How spatial disorientation can trap pilots

A pilot must learn, under actual threat of death, that it is impossible to maintain an airplane in controlled flight without visual reference to the horizon, even if that horizon is an artificial one.
Loss of control accidents caused by spatial disorientation continue to regularly claim the lives of pilots and passengers in spite of required training and the best efforts of instructors to instill the importance of non-instrument rated pilots recognizing and avoiding instrument flying conditions.

There are many ordinary circumstances in flying that can result in a pilot inadvertently encountering instrument flying conditions where there is no effective natural horizon:
  • Flying over water on a clear moonless night can easily result in disorientation, intense vertigo, and a loss of control.
  • Flying under the same conditions over land in sparsely populated areas has the same effect.
  • Flying on top of a horizon-to-horizon seemingly flat deck of solid cloud that is not aligned with respect to the real (invisible) horizon below, can be disconcerting to the point of serious nausea and worse.
  • Clouds are easy to inadvertently enter when flying at night, even over a large city.
  • In addition to acting alone, haze, smoke, and fog exacerbate the above conditions.
It is almost impossible to imagine the difficulty or impossibility of controlling an airplane under these seemingly ordinary circumstances without actually experiencing the conditions. It’s not stubbornness or lack of training that causes the continuing occurrence of this type of accident; it’s our anatomy that confronts a pilot with often insurmountable problems.
We maintain the position of our head in space using a combination of sensory inputs, obviously including vision, but less obvious and equally important are the effects of gravity and inertia on our muscles and on the fluid in the semi-circular canals in our inner ears. Even so, most of us can walk, swim or run with our eyes closed.
Speaking of the inner ear, we have three semi-circular canals (tubes, really) partially filled with fluid, in each ear. There is one tube in each of our ears for the three dimensions of angular rotation that we must learn to contend with when learning to walk:
  • The pitch axis – head tilt forward and back (nose up or down in an aircraft, controlled by the elevator).
  • The roll axis – head tilt left and right (wings banked, controlled by the ailerons, if you are in flight).
  • The yaw or vertical axis – think figure skater in a spin (controlled by the rudder pedals in an aircraft).
That last one is not always as useful as the other two axes in controlling an aircraft, but it is still critically important, as it is good at adding to the confusion that often results in disorientation and vertigo.
Our brain processes these hundreds, if not thousands, of simultaneous sensory inputs and directs the rest of the body to position the head accordingly.
Inner ear diagram
The system works really well… until it doesn’t.
By the time we decide to learn to fly, the portion of our brain which is responsible for balance and spatial orientation – our position in space – is thoroughly convinced that it knows best. It is more than a little difficult to convince it that it still has more to learn, despite the fact that the logical portion of the brain has been studying, and is insisting otherwise.
If we allow it, its survival instincts are strong enough to kill us.
Centrifugal, centripetal and inertial forces in flight mimic the effects of gravity and, in combination with the actual effects of gravity, just confuse the hell out of the brain. Without sufficient study, re-training, practice and experience, it reacts, often inappropriately, when it becomes disoriented.
I observed all this in action with my buddy Max.
My student Max, like many before and after him, could just not bring himself to believe that he could not fly the airplane by the seat of his pants without visual references outside the cockpit in spite of instruction and all the materials he had read about spatial disorientation and vertigo.
One evening we flew to a grass strip about fifty miles south of the city in the middle of sparsely populated farm country, where an old Piper Cub was being restored in the proverbial barn. We had a great time hangar flying with the owner and when it was finally time to leave and actually go flying, it was pitch black outside. It was a beautiful night, perfectly clear, no moon – you could see a hundred miles if you were high enough.
Max was shocked. “There are no runway lights, what do we do now?” He had never been allowed to use the “landing light” during night flights at our lighted home field – that’s another story – but I explained that it was actually not a bad takeoff light. “We’ll just taxi the length of the runway to make sure there are no deer eating it, and it’ll be just like driving your car,” I told him.“Cool,” said Max.
Max took off and we began to climb. A couple of hundred feet from the ground, I asked how he liked flying from a grass strip. He was having a ball. Not long thereafter Max, the airplane, and I were in a ten-degree bank to the left. “How are we doing Max?” Max was ecstatic. This was fun! At 400 feet, and now in a 30-degree bank, I asked how the attitude indicator looked. It must have looked a little funny, because Max allowed that it must be “a little off.” At around 600 feet, we had pretty much stopped climbing, and the attitude indicator was telling us that we were in a sixty-degree bank. Max was perplexed, but insisted that the instrument must be failing. He was finding it difficult to believe that we were anything but wings level.
When we were well past ninety degrees of bank, I said to Max “I have the airplane” and, as he had been trained to do, he immediately removed his left hand from the control wheel, his right hand from the throttle, and pulled his feet well back from the rudder pedals, positively relinquishing control of the airplane to me. No big deal, just routine until I rolled the airplane back to wings level. His reaction was involuntary and violent as he crashed into the pilot’s door as the recalcitrant portion of his brain fought to remain “upright.”
Given the subdued light in the cockpit, and our less than perfect visual night adaptation, there were just enough bright stars in the sky to match the scattered barn lights on the ground. There was no visible horizon on that beautiful, clear night.
Max became a true believer at that point and at last check, he was still alive and flying.