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This Illusion Can Easily Lead To A Crash

Spatial disorientation is the lead killer of pilots. More than mechanical failures, fires, and medical emergencies. If you fly at night or in instrument conditions, it's especially important to know about the somatogravic illusion. It's caused crashes of naval aviators and airline pilots alike, so regardless of what you fly, this illusion is critical to understand.

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When It Happens

Somatogravic illusions occur during rapid acceleration and deceleration flight movements. Specifically, this illusion usually happens when there's limited exterior visibility and a pilot reacts to body senses over actual flight path and instrument readings. As you accelerate, your body senses a pitch up motion, so your natural reaction will be 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, the most common example of this illusion is from the rapid acceleration during a go-around while flying through reduced visibility like instrument meteorological conditions (IMC) or night time conditions. Imagine you're flying an instrument approach to a runway and as you hit your minimum 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 to a dangerous angle of attack, so you correct by pitching down, all without actually looking at your attitude indicator. And seconds later, your airplane impacts the ground.

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Because you were going around at a low altitude, you only had a few seconds to remember to check your attitude indicator and realize your mistake before the imminent crash. So how could your body trick you into making such a grave mistake so easily? It all comes down to how the inner-ear works.

Inner-Ear Sensations

Sensory information about motion, equilibrium, and spatial orientation are 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 our bodies move, sense motion by bending forward and backward. As you'll notice 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 essentially tricks your brain into thinking you've entered a false flight attitude.

It Affects Naval Aviators And Piper Warrior Pilots Alike

Before we get started, take a look at the video below.

Did you notice that the pilot was catapulted off the carrier with his hands off of the flight controls? Only after the plane was in-flight did his hand switch from a hand-hold to the control stick between his legs. One reason for this hands-off takeoff is so that the pilot doesn't react to the acceleration somatogravic illusion. Pilots naturally feel the fighter entering a high angle of attack while accelerating on the catapult from 0 to over 160 knots in less than 3 seconds. Before takeoff, the airplane is trimmed slightly nose-up so that it flies naturally off the carrier deck. Over time, the navy has lost many airplanes to pilots reacting to somatogravic illusions by diving the airplane directly into the ocean after taking off (especially during nighttime catapult launches). A hands-off takeoff is one way to solve the problem.

Wikimedia

It's Caused Airline Crashes Too

Illusions like this have caused a number of fatal crashes. One, in particular, that of Gulf Air Flight 72, is an example of a somatogravic illusion affecting something as large as a commercial airliner.

Wikimedia

The A320 with 143 passengers and crew on board approached to landing in Bahrain at higher speeds than normal and carried out an unusual low altitude orbit in an attempt to correct the approach. The orbit was unsuccessful and a go around was attempted. While carrying out a turning climb, the aircraft entered a descent at 15 degrees nose down. The aircrew did not respond to repeated ground proximity warning systems (GPWS) warnings. Approximately one minute after starting the go-around, the aircraft disappeared from radar screens. There were no survivors.

The accident investigation concluded that the primary cause of the crash was "spatial disorientation related pilot error."

Wikimedia

The Solution

To best counter the effects of somatogravic illusions, remember to check your instrumentation before reacting to a perceived flight attitude, especially when in times of reduced visibility. What your body tells you to do isn't always accurate. If you choose to react to sensations in the cockpit without taking in all flight information first, you may end up in a pretty bad spot.

Swayne Martin

Have you ever encountered spatial disorientation in your own flying?

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and an Embraer 145 First Officer for a regional airline. He graduated as an aviation major from the University of North Dakota in 2018, holds a PIC Type Rating for Cessna Citation Jets (CE-525), and is a former pilot for Mokulele Airlines. He's the author of articles, quizzes and lists on Boldmethod every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures on his YouTube Channel.

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