The Eyes of Death by John Albrecht
Type II Disorientation - Recognized

Type II or recognized spatial disorientation is most often associated with the accidents that inevitably occur when the VFR pilot pushes his luck into the subtle but deadly I.F.R. environment. The pilot is disoriented and aware of the fact, but for reason of lack of instrument proficiency or vestibular (inner ear) or proprioceptive (seat of the pants) illusions is unable to believe the attitude instruments. Loss of control is inevitable. - 178 seconds and counting!

The non-aviator may have experienced similar sensations while driving a vehicle in heavy drifting snow or operating a boat in fog. Time and distance are distorted. There is the option of stopping at the curb or dropping the anchor to await improving weather conditions. The aviation equivalents include cloud, fog, starless night, whiteout or grayout - unfortunately there is no easy out other than a personal or ballistic parachute and often insufficient time or presence of mind to activate the device.

Once in instrument conditions the VFR pilot does not have the training or discipline to cope with loss of the natural horizon. Smooth transition to instrument flight is most unlikely. Visual input is rapidly overcome by illusions of vestibular or proprioceptive organs. A gentle yaw or roll below the threshold of these organs leads to an unperceived bank and an insidious spiral dive develops. Back pressure on the control column mimics gravity in the pilot’s buttocks. His brain interprets an illusion of pitching up the nose in relation to the natural horizon. Reality is steepening of the spiral with rapid progression to inverted flight and vertical descent!

It is difficult to accept that without visual reference to the natural or instrument horizon, the other two senses cannot be trusted to maintain orientation. Acceleration without monitoring the attitude instruments gives an illusion of the nose pitching up. The pilot compensates by pitching the nose down. - a dangerous reaction when taking off on a dark featureless night. The end result is an unexplained accident with the aircraft impacting terrain on take-off. With deceleration the process is reversed with the illusion of the nose pitching down and the pilot reacting by raising the nose of an already slowing aircraft. A setup for a stall and spin in IMC.

The proprioception and vestibular organs are sensitive to initial linear acceleration or deceleration and angular acceleration (turning).For example, they would be stimulated with the spin entry. However, once a stabilized state is established in the spin after several rotations they signal the brain that all is well. - i.e. straight and level flight. This is hard to believe but air transport pilots have spun into the ground while debating instrument discrepancies. To convince yourself, try this with another pilot flying at a safe altitude. Look down at the floor prior to spin entry or close your eyes. After several revolutions you will have no sensation of spinning. It can be quite shocking when you look up or open your eyes. Have a barf bag ready just in case! When descending out of a cloud in a spin, the visual shock may be overpowering and prevent the pilot from regaining control of the aircraft.

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