Somatogravic Illusion - a devillish Spatial disorientation , Pilots need to keep under check !

Why are we talking about Somatogravic Illusion ?

Yes , We have Limitations ! Humans have sensory systems well suited for moving on the surface of the earth but poorly suited for flying. In flight, humans have many difficulties in orientation, particularly if the input to the primary sense, vision, is degraded or removed.

What is it ?

Somatogravic Illusion is a Spatial disorientation that occurs when there are difficulties in orientation, or there is a mismatch between the real world and what is sensed.

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What is the aviation connection ?

Somatogravic Illusion (SI) is a spatial disorientation phenomena which is caused by a mismatch between different signals from our senses and the brain. It is generated by a strong longitudinal acceleration or deceleration.

The brain interprets acceleration as a pitch up and this may lead to inappropriate pitch down command, in other words, a False Climb illusion prevailed here.

How Important is it for pilots ?

Pilots can be susceptible to SI, especially when performing a go-around at night or in poor visual conditions. The strong longitudinal accelerations combined with a lack of visual references lead to the mistaken perception of excessive pitch up.

                                                                                                                           Picture Source : Airbus 

How the Somatogravic Illusion (SI) develops ?

• ✈ Acceleration in one direction , let's say for around 20 seconds, a perception will develop that the acceleration has stopped.
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• ✈ Very slow change in motion / movement - take the case of roll at a rate of less than approximately 2° per second or so.
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• ✈ Two different planes - In case of angular motion of the aircraft, sensory stimulation from the of the head and of the aircraft occur simultaneously in two different planes - illusion creeps in interrupting looking ahead to look up to an overhead panel, when the aircraft is also in angular motion.

The Risk Factor out of  Somatogravic Illusion :

Loss of control (LOC) and Controlled Flight Into Terrain (CFIT ) are among the most risks involved in Somatogravic Illusion. When there are positive changes in acceleration, illusion may take place when combined with ambient conditions.

While Pilot act on the initiation of a go around or  the transition to initial climb after take off, the resultant illusion can rapidly lead to CFIT or  LOC based on 'early condition recognition' and 'recovery handling' .

What can Pilots do about it ?

• ✈ Accept it First , accept the human Limitations , you will make the life of flight smooth.
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• ✈ External visual references available - Learn the risk in SI operating conditions , make use of the references.
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• ✈ External visual references unavailable (insufficient) - Believe your Flight instruments, they won't lie, Control the aircraft flight path using flight instruments, keep an eye on the Flight director.
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• ✈ Help Pilot Flying (PF) , in case of erronous flight control inputs to avoid a CFIT.
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• ✈ Anticipation helps !  A pitch up illusion while in acceleration or a pitch down illusion in case of deceleration should be expected, keeping reference on instruments. 

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Display Picture Source :  Airbus.