North America:1 (800) 942-7767 International:+1 (937) 778-4200

Woman and man pilot looking at camera, showing thumb up, preparing for flying

Staying Safe in the Clouds: How to Prevent Vestibular Illusions

Date: September 16, 2019 Category: Blog Tags: , , , ,
Print Friendly, PDF & Email

When you’re flying, your eyes are your primary sensory input. You depend on visual cues to let you know where you are in relation to the earth. But when you’re flying in the clouds, your visual references are limited at best. Without visual cues, your eyes and ears may start to disagree about which way is up. These sensory conflicts are known as vestibular (ear) illusions.

The phenomenon known as spatial disorientation is often caused by vestibular illusions. According to FAA statistics, between 5 to 10% of all general aviation accidents can be attributed to spatial disorientation. Of these, 90% are fatal.

Why do vestibular (ear) illusions occur?

The vestibular system includes three fluid-filled canals in your inner ear which help you determine your body’s position relative to the earth. Working together with your eyes, the vestibular system helps you maintain balance and keep your eyes focused on an object while your head or body is in motion. When flying in conditions where visual references (like the horizon) are unreliable or unavailable, your senses may send your brain unreliable signals about your position in three-dimensional space, leading to spatial disorientation.

Vestibular illusions to know:

“The Leans”

This common illusion can result after intentially or unintentionally entering a slow and prolonged turn. The banked attitude is too gradual to disrupt the fluid in the inner ear, so your brain thinks you’re still flying straight and level. Once you notice that you’re turning and quickly level the wings, you experience the sensation that the airplane is now banking in the opposite direction. In response, you might lean your body in the other direction to feel like you’re sitting in an upright position.

How you can avoid it:

Don’t make extremely slow turns, especially when you’re in the clouds.

The Coriolis Illusion

When you’re in a constant turn for a long period of time, the fluid in your ears will stop moving, tricking your brain into believing that you’re flying straight and level. But if you suddenly tilt your head up, down, or sideways, it will set the fluid into motion and create the sensation that the airplane is rolling, pitching, and yawing all at the same time. The FAA states that the Coriolis illusion “can be compared with the sensation of rolling down a hillside.” As you can imagine, experiencing this illusion is extremely disorienting and may result in loss of control. 

How you can avoid it:

Avoid moving your head too quickly. For example, if you drop something in the cockpit, use minimal head movement when retrieving it. If you feel disoriented, focus on your instrument scan and return to straight and level flight.

The Graveyard Spiral

With the word “graveyard” in its name, it’s clear that you don’t want to experience this illusion in flight. Like the other vestibular illusions mentioned, a graveyard spiral happens when you stay in a bank turn for so long that the fluid in your inner ear stops moving, producing the sensation that you’re no longer turning at all. When you attempt to level the wings, it suddenly feels like the aircraft is turning and banking in the opposite direction. To counteract this sensation, you reenter the original turn. But all the while, the airplane has still been turning in the same direction and descending. If you believe that you’re in a wings-level descent and pull back on the yoke, it will only tighten the turn and increase the descent rate. If this mistake is not corrected, the airplane will continue spiraling and losing altitude until it impacts the ground.

How you can avoid it:

Trust your instruments over your senses. Keep your instrument scan strong and try not to fixate on any one instrument. 

The Inversion Illusion

Pitching down too quickly when returning to level flight after a steep ascent can lead to the sensation that the airplane is tumbling backward in inverted flight. Your instinct may be to lower the nose of the aircraft, but doing so puts the airplane in a dive attitude and can intensify the inversion illusion even further.

How you can avoid it:

Use control when returning to level flight after a rapid ascent and don’t rush.

The Elevator Illusion

If you catch an updraft in turbulence, your plane may be abruptly accelerated vertically, creating the illusion that you’re in a climb. To counteract the sensation, you might feel the need to push the aircraft nose forward, but this puts you into a nose-dive position. With downdrafts, this illusion has the opposite effect, creating the illusion of a descent.

How you can avoid it:

Always keep your instrument scan pattern moving. On turbulent days with strong updrafts and downdrafts, rely on your attitude indicator to keep the wings straight and level.

The Head-Up and Head-Down Illusion

A rapid forward linear acceleration during level flight can cause the sensation that the nose of the aircraft is pitching up. This is called the head-up illusion. In response to the sensation of pitching up, you might feel compelled to push the aircraft into a nose-low attitude. The head-up sensation may also occur as a result of a “black hole illusion,” which can happen when taking off from a well-lit airport into a totally dark sky. An opposite effect can occur with a sudden linear deceleration in level flight, prompting you to pitch the aircraft up into a nose-high attitude.

How you can avoid it:

Again, fly by reference to your instruments, not your sensory perceptions. When flying in the clouds, try to avoid rapidly accelerating or decelerating.

Final Thoughts

The dangers of vestibular illusions are very real, but they can be avoided. Perhaps the single best way to prevent loss of control due to spatial disorientation is to obtain and maintain your instrument rating. While ignoring your sensory perceptions is easier said than done, being able to interpret flight instruments and control the aircraft accordingly will help keep you safer in the skies.

Stay tuned for next week, when we’ll discuss some of the most common visual and night flying illusions.

Hartzell Propeller