PPRuNe Forums - somatogravic illusion

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somatogravic illusion

There are several references to somatogravic illusion on the threads on R&N re the Gulf Air, A320 accident.

Could someone please explain what a somatogravic illusion is?

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bottums up !

See http://john.berkeley.edu/Projects/SGIllusion.html

Bettr yet http://www.ozemail.com.au/~dxw/dnt.html

[This message has been edited by forget (edited 09 September 2000).]

A quick summary...

The 3 semicircular canals in the human ear cannot differentiate between acceleration in the forward plane and a pitch upwards with no visual input. (this is how flight sims work). Think about it - the fluids slosh rearwards (to the back of the head) in both instances.

After takeoff on a dark night for example, you start to accelerate away from ground effect, or lowering the nose to a climbing speed. This speed increase may be percieved as a pitch up without any external visual cues (and without an instrument scan).

The pilot's natural fear of stalling leads him or her to pitch down, further increasing the speed and the pitch up perception, so push the stick forward etc etc until impact.

It is important to note that a lack of visual cues (and often a lightly loaded aircraft which will perform well) are essential to this illusion...dark night bush takeoffs are a prime candidate.

BASI did an excellent report 8? years ago on a KingAir which smacked in 6ish nm from the runway under full power one dark night somewhere in Queensland. Maybe others can enlighten us to the occurrence report.

By God I actually remember something useful from ATPL! :)

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Those who restrain desire do so because theirs is weak enough to be restrained.
William Blake

Thanks for your input folks.

This now explains why I sensed a much higher pitch attitude (felt almost vertical) on a couple of recent over water take-offs, than the 12 deg NU I had.

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bottums up !

Also known as the false climb illusion, I nearly pushed a Westwind into the desert due to this.

When you think about it, possibly the most scary aspect of this illusion is that it is "self reinforcing" ie the very effect amplifies itself when you lower the nose a bit to ease the "high" attitude it feels worse.