Cemetery spiral
In aviation , the graveyard spiral is a type of dangerous downward flight movement that is accidentally initiated by a pilot who is not trained to fly under instrument meteorological conditions (IMC) or in instrument flight . Other names for this phenomenon are suicide spiral, fatal spiral, death spiral, and devil's spiral.
Cemetery spirals are most common in nighttime or poor weather conditions where there is no horizon to provide visual correction for misleading signals from the inner ear. Cemetery spirals are the result of several sensory illusions that can occur in the actual or simulated IMC when the pilot experiences spatial disorientation and loses awareness of the aircraft's location. In other words, the pilot loses the ability to judge the orientation of his aircraft due to the misperception of spatial cues by the brain.
The cemetery spiral consists of both physiological and physical components. Mechanical failure is often a result, but usually not a causal factor, as it is the pilot's sense of balance that leads to the spiral descent. Flying with the Popometer and failing to detect and / or react to instrument readings is the most common source of controlled flight into terrain where the fully controllable aircraft hits the ground.
physics
The pilot mistakenly believes that he is flying at the level of the wings, only in a descent shown on the altimeter and ascender . This usually results in the pilot trying to climb by pulling the control horn . In a banked curve, however, the aircraft is at an angle and will describe a large circle in the sky. Pulling back the control horn has the effect of tapering that circle and causing the aircraft to lose altitude with increasing speed, like water swirling in a drain or funnel. An increasing component of the lift created by the wings is directed laterally through the bank angle, not only to push the aircraft "up" into the turn, but to reduce the amount of lift that is holding the aircraft up. At this point, the plane describes a descending circle, or spiral, with a trajectory that in turn resembles a funnel. In the increasingly narrow, descending spiral, the aircraft eventually leaves the base of the clouds and / or hits the ground.
In order to defuse this situation, a trainee pilot or pilot practices by using a view barrier to learn the skills of instrument flight under the supervision of a flight instructor. Instrument pilots also use vision restriction devices monitored by an instructor or a safety pilot to practice instrument flight and to maintain instrument flight skills.
Vestibular Aspects
The inner ear contains the vestibular system, which is also known as the organ of equilibrium . On the size of a pencil eraser, the vestibular system contains two different structures: the semicircular canals which detect changes in the angular acceleration, and the Otolithorgane (saccule and utricle), the changes in the linear acceleration and gravity recognize. Both the semicircular canals and the otolith organs give the brain information about the position and movement of the body. A connection between the vestibular system and the eyes helps maintain balance and focus the eyes on an object while the head is moving or while the body is rotating.
The semicircular canals are three semicircular, interconnected tubes located in each ear and correspond to three gyroscopes located in three planes perpendicular (at right angles) to each other. Each plane corresponds to the rolling, pitching or yawing movements of an aircraft. Each channel is filled with a fluid called an endolymph and contains a motion sensor with hair-like protrusions , the ends of which are embedded in a gelatinous structure called a cupula. The cupules and hairs move as the fluid moves within the canal in response to angular acceleration.
The movement of the hair is similar to the movement of algae caused by ocean currents or wheat fields moved by gusts of wind. When the head is at rest and the plane is straight and level, the fluid in the channels does not move and the hairs stand straight up, which indicates to the brain that there is no rotational acceleration (a twist). When you turn either your plane or your head, the channel moves with your head, but the fluid inside doesn't move because of its inertia. As the channel moves, the hairs inside move with it and are bent in the opposite direction of acceleration by the stationary fluid. This hair movement sends a signal to the brain to indicate that the head has turned. The problem starts when you spin your aircraft at constant speed (like in a coordinated turn) for more than 20 seconds.
In this type of rotation, the liquid in the channel first begins to move, then the friction causes it to catch up with the walls of the rotating channel. When this happens, the hairs in the canal return to their straight position, sending a false signal to the brain that the curve is ending - while in fact the curve is going on.
Then when you begin to roll out of the turn to return to level flight, the fluid in the canal will keep moving (because of its inertia) and the hair will now move in the opposite direction, sending a false signal to the brain that suggests that you are turning in the opposite direction when you are actually decelerating from the original curve.
However, entering the cemetery spiral is a gradual event that allows the pilot to mentally adjust to an incorrect degree of feeling level. Without external cues, a pilot who does not rely on altitude instruments will believe that the wings are level because the vestibular organ falsely reports that gravity is evenly acting on the pilot's head.
The cemetery spiral is associated with a return to level flight after an intentional or unintentional banked turn. For example, a pilot entering a banked turn to the left will initially feel like a turn is in the same direction. If the left turn continues (about 20 seconds or more), the pilot will experience the feeling that the aircraft is no longer turning to the left. At this point, when the pilot attempts to level the wings, that action will create a sensation that the aircraft is turning and banking in the opposite direction (to the right), a sensation commonly known as The Leans . If the pilot believes the illusion of a right turn (which can be very compelling), he / she will re-enter the original left turn in order to counteract the feeling of a right turn. If the pilot does not see the illusion and does not level the wings, the aircraft will continue to turn to the left and lose altitude. Since an aircraft has a tendency to lose altitude when turning, unless the pilot compensates for the loss in lift, the pilot may experience a loss of altitude. The lack of a sense of turning creates the illusion of being on a descent. The pilot can pull the control horn back in an attempt to climb or to complete the descent. This action tightens the IUD and increases the loss of altitude.
The solution, of course, is for the pilot to consciously override the brain's imperative to judge physical altitude based on signals from the balance organ and rely solely on the visual cues from the horizon or the altitude instruments in the aircraft until the brain settles readjusts and the vestibular sensory input matches the visual input.
See also
Individual evidence
- ↑ a b Federal Aviation Administration. 2016. Aeromedical Factors. Pilot's Handbook of Aeronautical Knowledge . p 16-6 Oklahoma City, OK: FAA Flight Standards Service.
- ↑ Soderlind, Paul A. The Deadly Spiral. AVWeb.com, May 11, 2000. http://www.avweb.com/news/airman/184306-1.html retrieved March 24, 2013.
- ↑ 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.
- ↑ Melchor Antunano: Medical Facts for Pilots . In: Federal Aviation Administration . Retrieved December 10, 2013.
- ↑ Pilot Handbook. FAA. https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/
- ^ Vestibular Illusions . Flight learnings. Retrieved December 10, 2013.