Vision - Is it Reliable

Down here in sunny South Carolina there are many trails that folks walk to just relax and get away from it all. If you regularly hike these trails the odds are you actually stepped over a Copperhead. No warning from these creatures. Their coloration pattern allows them to blend perfectly with the leaves and debris along a wooded nature trail. Sometimes you step on them and their bites account for the majority of bites treated in local hospitals. Very shy and difficult to provoke a strike but, thankfully, the venom is not life threatening but very painful. Visual Illusions abound in nature.

Another is a spotted fawn and other animals. If they remain motionless they are very difficult to spot.

In flight, camouflage used during wartime, protected important targets from discovery. What you see is not what is actually there. Entire encampments were disguised as serene villages when seen from the air.

For you and I visual illusions, especially under stress, can happen while flying. This is especially true in night flights. The "familiar" suddenly becomes the "unfamiliar."

Your instructor can provide other examples in Ground School.

The Leans

There are several ways you can experience the “Leans”. Some may be perceptual, others may effect the vestibular apparatus which is part of your inner ear.

This is the most common illusion during flight, and is caused by a sudden return to level flight following a gradual and prolonged turn that went unnoticed by the pilot. The reason a pilot can be unaware of such a gradual turn is that after twenty seconds a standard rate turn of two degrees per second falls below the detection threshold level of the semicircular canals. 

When you level the wings of your plane after such a turn it may cause an illusion that the plane is banking in the opposite direction. In response, a pilot may lean in the direction of the original turn in a corrective attempt to regain the appearance of normal straight and level flight.

From a playground setting , after riding a merry-go-round slowly and then jump off, you attempt to lean in the opposite direction from the spin of the merry-go-round. Hey, whats the matter, you got a case “of the leans?”

In instrument conditions this may lead to the "death spiral" if the pilot does't have a instrument rating. It is extremely difficult to recover from this illusion if you don't believe your instruments or rely on flying by the "seat of your pants."

If you have regular instrument conditions for flying where you live, think about instruction leading to a instrument rating.

Spiral Turn Illusion

The spiral turn illusion occurs to a pilot who enters a turn to the left or right inadvertently while on instruments .

For example, a pilot who enters a turn to the left will initially have a sensation of turning in the same direction. Without a visual horizon to verify what is happening the pilot will have the sensation that the turn is progressively decreasing. At this point, if the pilot applies right rudder to stop the left turn, the pilot will suddenly sense a turn in the opposite direction (to the right).

If the pilot believes that the airplane is turning to the right, the response will be to apply left rudder to stop the sensation of a right turn. However, by applying left rudder the pilot will unknowingly re-enter the original left turn. If the pilot cross-checks the turn indicator, he would see the turn needle indicating a left turn while he senses a right turn. This creates a sensory conflict between what the pilot sees on the instruments and what the pilot feels.

The whole purpose of instrument flight instruction is to believe what your instruments tell you about the position of your plane with respect to the surface of the earth without seeing the horizon. 

If the pilot believes the body sensations instead of trusting the instruments, the left turn will continue and it may deepen into a tight spiral turn that will result in altitude loss and forces may build up that results in structural damage to the plane and/or the loss of wings from the plane. If enough altitude is lost before the pilot recognizes this illusion a crash with the ground will result.

Visual illusions can kill. Fly aware and safely,

Jim

Coriolis Effect - Introduction

This illusion occurs when you stimulate two semicircular canals simultaneously. If you remember, in instrument flight training, when you were flying “under the hood” straight and level, your instructor dropped a object at your feet. Distraction while flying can precipitate this sensation.

As you leaned down to pick it up the instructor took over the controls and put the plane into a steep climbing turn to the right. You all know what the experience was like. Immediate nausea and the illusion that you were tumbling out of control. It is a very dangerous condition for a human being when flying a plane.

My instructor gave the control of the plane back to me and told me to land. I didn’t think I could I was so sick. But, land I did! He let me have a few minutes to get my “bearings” and ordered me to take-off and experience it again. By the way, the airport was a small grass strip with no communication facilities. A great spot to torture instrument flight students.

Net effect this can produce an overpowering sensation that the plane is rolling, pitching, and yawing all at the same time, which compares with the sensation of rolling down a hillside. This illusion can make the pilot quickly become disoriented and lose control of the plane. This introductory article is teaching you what not to do while on instruments. Know the attitude of your plane at all times.

The Dangers of Landing Behind Large Aircraft

Heavy planes, like airliners, produce vortexes at their wingtips. These twin tornados can flip a small plane over if the pilot doesn’t understand the hidden danger on the runway.

You must ask the control tower to lengthen your approach to give the ground turbulence time to dissipate before you touch down. If a slight cross-wind is present you should check the wind sock to see direction and possible velocity of the cross-wind.

The cross-wind may place one of the vortexes right on the runway just as you land. It is your responsibility to avoid that from happening.

You can ask for a go-around if you are unsure. That may save you from experiencing a bad day.

Ask your flight instructor at you local fixed-base operation to detail, for you, other precautions involved in mixed aircraft landings and takeoffs.