Number of accidents have occurred around the world due to Spatial Disorientation.
Tests conducted with qualified instrument pilots indicate that it can take as much as 35 seconds to establish full control by instruments after the loss of visual reference with the surface.
Five most common illusions reported were:
60 percent had a sensation that one wing was low although wings were level.
45 percent had, on levelling after banking, tended to bank in opposite direction.
39 percent had felt as if straight and level when in a turn.
34 percent had become confused in attempting to mix “Contact” and instrument cues.
29 percent had, after recovery from steep climbing turn, felt to be turning in opposite direction,
Surface references and the natural horizon may at times become obscured, although visibility may be above visual flight rule minimums.
Lack of natural horizon or surface reference is common on overwater flights, at night, and especially at night in extremely sparsely populated areas, or in low visibility conditions.
A sloping cloud formation.
An obscured horizon.
A “White-out” condition caused by fog, haze, or falling snow blending with the snow-covered earth surface.
A dark scene spread with ground lights and stars.
And certain geometric patterns of ground lights can provide inaccurate visual information for aligning the aircraft correctly with the actual horizon.
Other factors which contribute to disorientation are:
Reflections from outside lights.
Sunlight shining through clouds.
Reflected light from the anti-collision rotating beacon, Flashing Lights, Nav Lights and Rotor Tip Lights.
All these factors may obscure outside references leading to a disoriented pilot who may place the aircraft in a dangerous attitude as a consequence of sensory illusions.
VESTIBULAR ASPECTS OF SPATIAL ORIENTATION:
The inner ear contains the vestibular system, which is also known as the organ of equilibrium.
About the size of a pencil eraser, the vestibular system contains two distinct structures:
The semi-circular canals, which detect changes in angular acceleration.
And the otolith organs (the utricle and the saccule), which detect changes in linear acceleration and gravity.
Both the semi-circular canals and the otolith organs provide information to the brain regarding our body’s position and movement.
A connection between the vestibular system and the eyes helps to maintain balance and keep the eyes focused on an object while the head is moving or while the body is rotating.
THE SEMICIRCULAR CANALS.
The semi-circular canals are three half-circular, interconnected tubes located inside each ear that are the equivalent of three gyroscopes located in three planes perpendicular (at right angles) to each other.
Each plane corresponds to the rolling, pitching, or yawing motions of an aircraft.
Each canal is filled with a fluid called endolymph and contains a motion sensor with little hairs whose ends are embedded in a gelatinous structure called the cupula.
The cupula and the hairs move as the fluid moves inside the canal in response to an angular acceleration.
The movement of the hairs is similar to the movement of seaweed caused by ocean currents or that of wheat fields moved by wind gusts.
When the head is still and the airplane is straight and level, the fluid in the canals does not move and the hairs stand straight up, indicating to the brain that there is no rotational acceleration (a turn).
If you turn either your aircraft or your head, the canal moves with your head, but the fluid inside does not move because of its inertia.
As the canal moves, the hairs inside also move with it and are bent in the opposite direction of the 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 continue turning your aircraft at a constant rate (as in a coordinated turn) for more than 20 seconds.
In this kind of turn, the fluid inside the canal starts moving initially, and then friction causes it to catch up with the walls of the rotating canal.
When this happens, the hairs inside the canal will return to their straight up position, sending an erroneous signal to the brain that the turn has stopped– when, in fact, the turn continues.
If you then start rolling out of the turn to go back to level flight, the fluid inside the canal will continue to move (because of its inertia), and the hairs will now move in the opposite direction .
Sending an erroneous signal to the brain indicating that you are turning in the opposite direction, when in fact, you are actually slowing down from the original turn.
VESTIBULAR ILLUSIONS (SOMATOGYRAL – Semi-circular Canals)
Illusions involving the semi-circular canals of the vestibular system occur primarily under conditions of unreliable or unavailable external visual references and result in false sensations of rotation.
These include the:
The Graveyard Spin and Spiral.
The Coriolis Illusion.
The Leans is the most common illusion during flight and is caused by a sudden return to level flight following a gradual and prolonged turn that went unnoticed by the pilot.
The reason a pilot can be unaware of such a gradual turn is that human exposure to a rotational acceleration of 2 degrees per second or lower is below the detection threshold of the semi-circular canals.
Levelling the wings after such a turn may cause an illusion that the aircraft is banking in the opposite direction.
In response to such an illusion, a pilot may lean in the direction of the original turn in a corrective attempt to regain the perception of a correct vertical posture.
The Graveyard Spiral is more common than the Graveyard Spin, and it is associated with a return to level flight following an intentional or unintentional prolonged bank turn.
For example, a pilot who enters a banking turn to the left will initially have a sensation of a turn in the same direction. If the left turn continues (~20 seconds or more), the pilot will experience the sensation that the airplane is no longer turning to the left.
At this point, if the pilot attempts to level the wings this action will produce a sensation that the airplane is turning and banking in the opposite direction (to the right).
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 an attempt to counteract the sensation of a right turn.
Unfortunately, while this is happening, the airplane is still turning to the left and losing altitude.
Pulling the control yoke/stick and applying power while turning would not be a good idea–because it would only make the left turn tighter.
If the pilot fails to recognize the illusion and does not level the wings, the airplane will continue turning left and losing altitude until it impacts the ground.
The Coriolis Illusion involves the simultaneous stimulation of two semi-circular canals and is associated with a sudden tilting (forward or backwards) of the pilot’s head while the aircraft is turning.
This can occur when you tilt you head down (to look at an approach chart or to write a note on your knee pad).
Or tilt it up (to look at an overhead instrument or switch) or tilt it sideways.
This produces an almost unbearable sensation that the aircraft is rolling, pitching, and yawing all at the same time, which can be compared with the sensation of rolling down on a hillside.
This illusion can make the pilot quickly become disoriented and lose control of the aircraft.
Non-adherence to standard operating procedures (SOPs).
The captain, as PF, did not follow standard procedures, resulting in:
A higher than standard speed for start of descent and initial approach.
A non-stabilized approach.
The low-altitude orbit as a nonstandard manoeuvre to the runway.
The incorrectly performed go-around.
The first officer did not object or call the captain’s attention to his non adherence to the procedure.
The controller allowed a shortcut — a 360-degree turn above the airport — and did not follow the procedure for the path leading to a stabilized approach from the final fix.
During go-around, the crew apparently experienced spatial disorientation, which may have caused the captain to wrongly think the airplane was pitching up.
Despite the GPWS warnings, the crew did not adequately respond.
Analysis of the cockpit voice recorder (CVR) data showed the crew did not perform as a team, due to inadequate training in crew resource management (CRM), SOPs, controlled flight into terrain (CFIT) and GPWS.
Somatogyral/ Somatogravic illusions.
During the approach in night conditions, the crew had on one side a very bright view of the airport and a landmass and on the other side a completely dark area over the water.
Focusing on the visual approach, the crew may have lost visual cues and may have experienced visual illusions and disorientation when initiating the tight 360- degree turn over water, after the non-stabilized approach.
The first officer, as pilot not flying (PNF), was not monitoring his instruments and did not use proper CRM techniques to gain the captain’s attention.
In addition, TOGA provides constant acceleration.
In the absence of visual cues such as the horizon, this constant longitudinal acceleration fooled the captain’s vestibular system into interpreting this as horizontal flight at constant speed.
Lines of Defence.
The first precaution to avoid an accident is to not put oneself in a nonstandard situation.
The resulting situation may not appear to be risky at the beginning, but, as we know, accidents often result from multiple contributing factors.
Allowing the situation to develop in the first place generates unnecessary risks.
Further, the quality of the approach briefing helps to focus on the following:
Ensuring that one crewmember maintains visual contact with the runway lights.
Task sharing and workload management between the crewmembers.
Effective coordination with the ATC.
Being prepared for a go-around.
Remembering the consequences of visual illusions when there is a mismatch between the real world and what is sensed.
Maintaining continuous instrument monitoring to counter the onset of vestibular system illusions.
When realizing that situational awareness is lost:
Applying strict SOPs such as precise go-around procedures with task sharing.
Speeds, headings and minimum safe altitudes.
This is the principal reason for approved SOPs.
Adherence to SOPs.
Adequate CRM training helps to achieve an effective balance among crewmembers.
Emphasis on cross-checking and clear task sharing provides a basis for sound attitudes.
In our example, the first officer’s task was to monitor the instruments to effectively and adequately inform his captain.
The captain’s role in relation to his first officer was to encourage him to speak.
Quality of briefings:
Operational procedures require a go-around to be flown at constant speed and without any acceleration with one flap retraction.
The acceleration and clean up should be done at a higher altitude.
This is to ensure that a correct go-around is performed and associated procedures follow.
In general, there are no go-around procedures that require a sustained turn because, from a human factors point of view, crews might suffer Somatogyral (Coriolis) disorientation as well as Somatogravic (false climb) disorientation.
Avoiding shortcuts and strict adherence to procedures help to avoid creating risky situations.
Improved training in CRM and visual illusions.
Training to prevent Somatogravic illusion is almost impossible, but information and sensitization can help pilots recognize its onset and prepare to face it.
The only known way to regain proper orientation is to focus on the airplane’s instruments to rebuild a correct mental image of the situation.
The pilot should understand the elements contributing to spatial disorientation so as to prevent loss of aircraft control if these conditions are inadvertently encountered.
The following are certain basic steps which should assist materially in preventing spatial disorientation.
Before flying in less than 5 Kms visibility, obtain training and maintain proficiency in airplane control by reference to instruments.
When flying at night or in reduced visibility, use the flight instruments.
If intending to fly at night, maintain night-flight currency. Include cross country and local operations at different airports.
If only Visual Flight Rules-qualified, do not attempt visual flight when there is a possibility of getting trapped in deteriorating weather.
If you experience a vestibular illusion during flight, trust your instruments and disregard your sensory perceptions.
Study and become familiar with unique geographical conditions in areas proposing to operate.
Check weather forecasts before departure, en route, and at destination.
Be alert for weather deterioration.
Do not attempt visual flight rule flight when there is a possibility of encountering deteriorating weather.
Discipline helps: adherence to SOPs helps improve safety.
In the absence of visual cues, referring to the instruments to get a correct mental image and continuous instrument monitoring may help to counter vestibular disorientation.
Rely on instrument indications unless the natural horizon or surface reference is clearly visible.
Adequate crew communication is a critical contributing factor to risk reduction as well as effective coordination with ATC.
Remain prepared for a go-around while remaining aware of possible visual illusions.