Graveyard spiral
In aviation, a graveyard spiral is a dangerous spiral dive entered into accidentally by a pilot who is not trained or not proficient in instrument flight when flying in instrument meteorological conditions (IMC).[1]
Graveyard spirals are most common in nighttime or poor weather conditions where no horizon exists to provide visual correction for misleading inner-ear cues.[2] Graveyard spirals are the result of several sensory illusions in aviation which may occur in actual or simulated IMC, when the pilot loses awareness of the aircraft's attitude. In other words, the pilot loses the ability to judge the orientation of his aircraft due to the brain’s misperception of spatial cues.
The graveyard spiral consists of both physiological and physical components. Mechanical failure is often a result but generally not a causal factor, as it is the pilot’s sense of equilibrium which leads to the spiral dive. Flying by “the seat of the pants,” and failing to recognize and/or respond to instrument readings is the most common source of what is referred to, in U.S. Air Force parlance, as controlled flight into terrain, or abrupt, violent collision with the earth.[2]
[edit] Physics of the Graveyard Spiral
The impression given by the senses in that situation would be level flight, with a descent indicated on the altimeter and vertical speed indicator. This usually leads to the pilot "pulling up" or attempting to climb by pulling back on the control yoke. In a banking turn, however, the plane is at an angle and will be describing a large circle in the sky. Pulling back on the control yoke has the effect of tightening that circle and causing the plane to lose altitude at an increasing rate. An increasing component of the lift being generated by the wings is directed sideways by the bank angle. At that point the aircraft is describing a descending circle or spiral. In the ever-tightening, descending spiral the aircraft eventually exits the base of the clouds and/or impacts the ground.[1]
To avoid this situation, a student pilot or a pilot under instruction uses a view limiting device to learn instrument flying proficiency under the supervision of a flight instructor. Instrument-rated pilots also use view-limiting devices supervised by an instructor or a safety pilot to practice instrument flight and maintain instrument flying proficiency.[2]
[edit] References
- ^ a b Federal Aviation Administration. 2008. Aeromedical Factors. Pilot's Handbook of Aeronautical Knowledge. Oklahoma City, OK: FAA Flight Standards Service.
- ^ a b c Naval Air Training Command. 2002. Joint Aerospace Physiology Student Guide: Spatial Disorientation. Corpus Christi, TX: AETC/BUMED Joint Specialized Undergraduate Pilot Training.
