Once an aircraft enters conditions under which the pilot cannot see a distinct visual horizon, the drift in the inner ear continues uncorrected. Errors in the perceived rate of turn about any axis can build up at a rate of 0.2 to 0.3 degrees per second[
citation needed]. If the pilot is not proficient in the use of gyroscopic flight instruments, these errors will build up to a point that control of the aircraft is lost, usually in a steep, diving turn known as a
graveyard spiral. During the entire time, leading up to and well into the maneuver, the pilot remains unaware that he is turning, believing that he is maintaining straight flight. One of the most famous mishaps in aviation history involving the graveyard spiral is
the crash involving John F. Kennedy Jr. in 1999.
[5]
The graveyard spiral usually terminates when the
g-forces on the aircraft build up to and exceed the structural strength of the
airframe, resulting in catastrophic failure, or when the aircraft contacts the ground. In a 1954 study (180 – Degree Turn Experiment), the University of Illinois Institute of Aviation
[6] found that 19 out of 20 non-instrument-rated subject pilots went into a graveyard spiral soon after entering simulated instrument conditions. The 20th pilot also lost control of his aircraft, but in another maneuver. The average time between onset of instrument conditions and loss of control was 178 seconds.
Spatial disorientation can also affect
instrument-rated pilots in certain conditions. A powerful tumbling sensation (
vertigo) can be set up if the pilot moves his or her head too much during instrument flight. This is called the
Coriolis illusion.[
citation needed] Pilots are also susceptible to spatial disorientation during night flight over featureless terrain
Spatial disorientation,
spatial unawareness, or "Spatial-D" is the inability to determine one's position, location, and motion relative to their environment.
[1] This phenomenon most commonly affects
aircraft pilots and
underwater divers,
[2] but also can be induced in normal conditions—or reproduced in the lab with instruments such as the
Barany Chair. In aviation, the term means the inability to correctly interpret aircraft attitude, altitude or airspeed, in relation to the ground or point of reference. This most commonly occurs after a reference point (
e.g., the horizon) has been lost. Spatial disorientation, often referred to as 'Spatial-D' by aviators occurs when aircrew's sensory interpretation of their position or motion conflicts with reality. Spatial disorientation is often separated into 3 main categories by mishap investigators:
https://en.wikipedia.org/wiki/Spatial_disorientation