Probable Cause #44: Dark Departure
This article originally appeared in Aviation Safety, Sept. 2005.Night flying can be one of the most enjoyable ways a pilot can exercise his or her flight privileges. The air is generally smoother, there usually is less traffic (unless you're flying near Memphis or Louisville) and any traffic will be easier to spot. Too, clear nights away from city lights afford pilots a much clearer view of the moon and stars, which always seem closer. But night flying brings not only change, but challenge. The same dark conditions that make it easier to spot an illuminated object or aircraft can make it impossible to identify something without lights. That lack of light wreaks havoc on the human eye's ability to detect objects, literally lending motion to fixed objects, changing their color and, at even moderate altitudes, severely limiting our ability to acquire distant or dimly lit objects. The eye's limitations can be especially insidious when we consider that we need light in the cockpit to read and understand our instruments and charts. Then, we want to minimize that illumination when trying to look outside. When we consider that the human eye can require as much as 30 minutes to become fully adapted to low-light or nighttime conditions, poorly designed cockpit lighting, bright ramp and terminal illumination, and reflections all work against pilots flying at night. That's especially true for pilots unable or unwilling to control the aircraft by referring to instruments, and who may find themselves unable to identify a natural horizon. The lack of available references a pilot needs to orient himself and the aircraft can be fatal. As the AOPA's Air Safety Foundation (ASF) says, "Humans are VFR-only creatures. The senses we use to maintain our balance and know 'which end is up' are completely unreliable when our bodies are in motion without visual reference to the world around us. Pilots deprived of visual references while flying can quickly lose control of the aircraft and succumb to one of general aviation's killers: spatial disorientation." The ASF goes on to define spatial disorientation as the "mistaken perception of one's position and motion relative to the earth" and notes that "Any condition that deprives the pilot of natural, visual references to maintain orientation, such as ... sky backgrounds with indistinct contrast (such as arctic whiteout or clear, moonless skies over water) can rapidly cause spatial disorientation. Pilots can compensate by learning to fly by reference to their instruments." Spatial disorientation in so-called "white out" and "black hole" conditions has figured prominently in highly publicized fatal accidents, involving both personal aircraft and transport-category jets.