What is spatial disorientation? How does it affect pilots and how can it be prevented?

Statistics show that between 5% and 10% of all general aviation accidents can be attributed to spatial disorientation-90% of which are fatal. A study conducted concerning spatial disorientation concluded that “if a pilot flies long enough, there is no chance that he/she will escape experiencing at least one episode of spatial disorientation”.

Representative | AOPA

In other words, pilots can be categorized into two:

  • those who have been disorientated, and
  • those who will be

So, what is spatial disorientation?

Spatial disorientation

Representative | ETC Aircrew Training Systems

The inability of a person (or an aviator in this case), to determine his/her true body position, motion, and altitude relative to the earth or his surroundings is defined as “spatial disorientation”.

Genetically, we humans are designed to maintain spatial orientation on the ground. The three-dimensional environment of flight, which is unfamiliar to the human body, creates sensory conflicts and illusions that complicate spatial orientation, and are sometimes difficult to achieve.

Banks and turns often create false sensations and these illusions can lure pilots into making poor decisions or improper control inputs.

Types of spatial disorientation

Disorientation experienced in space may be broadly divided into the following six:

1. “The Leans”

Code 7700

This is generally caused by level flight after a rapid roll- wherein the inertia of the roll causes the body to lean in a direction opposite to the direction of turning even after the motion of the roll has been stopped. The best way to prevent such an effect would be to avoid super-slow turns in the clouds.

2. Coriolis illusion

Code 7700

This happens when the pilot rapidly looks downward while turning. The plane feels as though it is descending and hence the immediate reaction of the pilot is to pull back on the stick to raise the plane.

When the fluid in the ears stops moving, our brain is tricked into thinking the flight is ‘straight-and-level’, while it may not. This can lead to performing dangerous manoeuvres, like putting the plane in a dangerous attitude.

This can often be prevented by focussing on instrument scan patterns and thereby bringing the airplane back to straight-and-level flight.

3. The Graveyard Spiral and Graveyard Spin

Representative | The Aerobatics School

The cause of both can be attributed to the acclimation of the semicircular canals to prolonged rotation.

If a “spin” is continued long enough, it creates an illusion of non-motion. Hence when the pilot corrects the spin, he has the feeling of spinning in the opposite direction, and his natural reaction is to counter his corrective measures and go back into the original spinning pattern. This phenomenon is known as the “graveyard spin.”

Losing the sensation of turning in a banked turn is what results in a “graveyard spiral”.

The pilot may not recognize the illusion before the aircraft loses too much altitude, resulting in a collision with terrain or the G-forces on the aircraft may exceed the structural strength of the airframe, resulting in catastrophic failure. The crash involving John F Kennedy Jr in 1999 is a prime example.

4. Somatogravic illusion

FL360aero

The tendency to incorrectly perceive acceleration as an increase in pitch attitude in the absence of visual references results in somatogravic illusion. This may lead pilots to instinctively make nose-down inputs even if the aircraft is flying level. The opposite holds for rapid deceleration as well.

This may be typically prevented by avoiding rapid acceleration and deceleration in the clouds.

5. Inversion illusion

Representative | Aero Corner

This involves a steep ascent (forward linear acceleration) in a high-performance aircraft, followed
by a sudden return to level flight. When the pilot levels off, the aircraft’s speed is relatively higher. This combination of accelerations produces an illusion that the aircraft is in an inverted flight. Naturally, the pilot’s instinctive response is to then lower the nose of the aircraft.

6. Elevator illusion

Representative | Code 7700

Elevator illusion happens when an updraft is hit, causing an abrupt upward vertical acceleration. This can stimulate the otolith organs to create the illusion of being on a climb resulting in the disoriented pilot pushing the aircraft into a nose-low attitude.

An abrupt downward vertical acceleration, usually in a downdraft, has the opposite effect, with the disoriented pilot pulling the aircraft into a nose-up attitude.

How to prevent spatial disorientation?

Thorough training and instrumentation are the best measures that can prevent spatial disorientation, although the following may also help:

  • Flight instruments to be relied on at night, or with reduced visibility
  • Spatial disorientation(s) may be simulated and experienced in a Barany chair, a Vertigon, a GYRO or a Virtual Reality Spatial Disorientation Demonstrator
  • VFR flights may be avoided when there is a possibility of getting trapped in deteriorating weather
  • In the likely event of experiencing a visual illusion (most pilots do at one point or another), the focus is to be placed on instruments and all conflicting bodily signals are to be avoided
  • If one of the flight crew experiences a visual illusion, the control of the aircraft may be transferred to the other crew member as two pilots seldom experience visual illusions at the same time

A GH-200 Spatial Disorientation Trainer | ETC Aircrew Training Systems

Even with good visibility, misleading visual inputs such as sloping cloud decks, unfamiliar runway grades, or false horizons can also form optical illusions- resulting in the pilot misjudging the vertical orientation.

SOURCE(s)

COVER: Aviation Oil Outlet

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