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If you fly at night or in instrument conditions, it's important to understand somatogravic illusion and how to overcome it.

What Is Somatogravic Illusion?

Somatogravic illusions occur during rapid acceleration and deceleration in flight. This illusion usually happens when there's limited exterior visibility, and you react to body senses over actual flight instrument readings.

As you accelerate, your body senses a pitch-up motion, so your natural reaction is to pitch down. The reverse is true for deceleration, where deceleration is felt as a pitch-down motion and your reaction is to pull back on the yoke to pitch up.

While the illusion can happen during deceleration, one of the most common examples of this illusion is from the rapid acceleration during a go-around while flying through reduced visibility or night-time conditions.

Imagine you're flying an instrument approach. As you reach decision altitude, the runway is nowhere in sight. As you add power to go around, you rapidly transition from a slow approach to an accelerating climb-out. You look down in the cockpit to change power, flaps, and landing gear settings. In the back of your mind, you sense that you're pitching up more than you need to, so you correct by pitching down, all without actually looking at your attitude indicator. And seconds later, you're nose low, descending toward the ground.

So how could your body trick you into making such a grave mistake so easily? It all comes down to how your inner-ear works.

Inner-Ear Sensations

Sensory information about motion, equilibrium, and spatial orientation is provided by the vestibular system and its associated parts in and around the ears.

Inside the utricle of the inner ear, there are little hairs that, as your body moves, senses motion by bending forward and backward. As you can see in the diagram below, the tilting motions of these hairs during acceleration and deceleration are the same as when you tilt your head forward or backward. That's why when you accelerate and decelerate in the plane, your vestibular system tells your brain you've entered a false flight attitude.

The Solution

To counter the effects of somatogravic illusions, remember to check your instrumentation before reacting to a perceived flight attitude, especially during high workload and reduced visibility. Use your instrument scan pattern to keep your plane in a safe flight attitude, and avoid making large, quick movements with your head.

What your body tells you to do isn't always accurate, and the sensation of somatogravic illusion can feel overwhelming at times. The term 'trust your instruments' can feel cliche to say, but it's the best tool you have to overcome this in-flight illusion.

Have you ever encountered spatial disorientation in your own flying? Tell us about your experience in the comments below.

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