Page:NTSB Report, Paul Kelly Flying Service crash.pdf/16

Rh In view of the foregoing the Board believes that spatial disorientation is the more probable reason for the loss of control. Spatial disorientation is the inability of the pilot to determine his position relative to his environment. It is triggered by conflicting information from the physio- logical sensing elements of the body. Among the many factors which produce this phenomenon, two are of paramount importance in this instance:

(1) Inadequate stimuli - the absence of visual reference, or even the reduction in quality, creates false sensations. This is particularly hazardous over snow, water, or other barren areas. (2) Division of attention - failure to establish a continuous source of attitude reference, either visual or instrument, increases the opportunity for conflict between the two.

The evidence shows that the flight was turning in darkness away from any populated area toward dark, cloud-shrouded, mountainous terrain when control was lost. Any drizzle or rain accumulation on the windscreen would have further reduced or possibly negated the usefulness of the few visual cues which were available. Paradoxically the aforementioned circumstances, which establish the prudence of flight by reference to instruments, also dictate the need for continuous lookout. The flight was restricted by topography and cloud cover to operation within the confines of a relatively small air— space. It is not known whether the pilot was aware of exactly how many other aircraft were in the vicinity, but he must have known there were