The leans is the most common type of spatial disorientation for

aviator An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its Aircraft flight control system, directional flight controls. Some other aircrew, aircrew members, such as navigators or flight engineers, are al ...

s. Through stabilization of the fluid in the

semicircular canal In mathematics (and more specifically geometry), a semicircle is a one-dimensional locus of points that forms half of a circle. The full arc of a semicircle always measures 180° (equivalently, radians, or a half-turn). It has only one line o ...

s, a pilot may perceive straight and level flight while actually in a

banked turn A banked turn (or banking turn) is a turn or change of direction in which the vehicle banks or inclines, usually towards the inside of the turn. For a road or railroad this is usually due to the roadbed having a transverse down-slope towards the ...

. This is caused by a quick return to level flight after a gradual, prolonged turn that the pilot failed to notice. The phenomenon consists of a false perception of angular displacement about the roll axis and therefore becomes an illusion of bank. This illusion is often associated with a vestibulospinal reflex that results in the pilot actually leaning in the direction of the falsely perceived vertical. Other common explanations of the leans are due to deficiencies of both otolith-organ and semicircular-duct sensory mechanisms.

Physiology

The leans is a type of vestibular illusion in flight which causes spatial disorientation. The process involves the semicircular canals of the

vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...

. The semicircular canals detect angular acceleration. In total, there are three

s: the anterior, posterior, and

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...

canals. Each canal is filled with a fluid called

endolymph Endolymph is the fluid contained in the membranous labyrinth of the inner ear. The major cation in endolymph is potassium, with the values of sodium and potassium concentration in the endolymph being 0.91 mM and 154 mM, respectively. I ...

and each canal arises from a small bag-like structure called a utricle. At the ends of each duct, there is a saclike portion called the

ampulla An ampulla (; ) was, in Ancient Rome, a small round vessel, usually made of glass and with two handles, used for sacred purposes. The word is used of these in archaeology, and of later flasks, often handle-less and much flatter, for holy water or ...

. Inside are

hair cell Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment. ...

s and supporting cells known as the

crista ampullaris The crista ampullaris is the sensory organ of rotation. They are found in the ampullae of each of the semicircular canals of the inner ear, meaning that there are three pairs in total. The function of the crista ampullaris is to sense angular acc ...

. Changing a person's orientation will cause specific ducts to be stimulated due to these hair cells. When the head turns, the canals move but because of its inertia, the endolymph fluid tends to lag and thereby stimulates the hair cells. This stimulation results in awareness of angular acceleration in that plane. After approximately 10–20 seconds, the endolymph velocity matches that of the canal, which stops stimulation of the hair cells, and the person's awareness of rotation is reduced or stopped. In addition, the canals cannot detect rotational acceleration of approximately 2 degrees per second or lower; this is the detection threshold of the semicircular canals. Therefore, a pilot may not notice a slow turn or a bank if entered gradually and maintained long enough. If the pilot then exits the turn or bank and levels the wings, the endolymph fluid continues to move, re-stimulating the hair cells and producing the illusion that the plane is banking too much in the opposite direction, due to the input lag. As a response, the pilot often leans in the direction of the original turn to attempt to correct and regain his/her perception of the correct vertical position. The leans may also be caused by peripheral visual orientation cues that become misled.

Danger and risk

If a pilot does not notice the disorientation and continues to lean, the plane may over bank in the wrong direction and cause rolling. This is the most common spatial disorientation for pilots. In all cases of spatial orientation, pilots must be able to rely on their flight instruments when making control inputs to override false sensations. The

Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...

warns pilots qualified solely under

visual flight rules In aviation, visual flight rules (VFR) are a set of regulations under which a pilot operates an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better ...

to avoid situations "when there is a possibility of getting trapped in deteriorating weather."

References

{{DEFAULTSORT:Leans Aviation risks Proprioception Illusions

Physiology

Danger and risk

See also

References