Visual Illusions Awareness
Page 2
AIRBUS INDUSTRIE
Flight Operations Support
. Uphill or downhill terrain before the runway threshold:
. An uphill slope in the approach zone or a drop-off of terrain at the approach end of the runway creates an illusion of being too high (i.e., impression of a steep glide path, as shown on Figure 1), thus:
°. possibly inducing a correction (increasing the rate of descent) that places the aircraft below the intended glide path; or,
°. preventing the flight crew from detecting a too shallow flight path.
Getting to Grips with Approach-and-Landing Accidents Reduction
Runway environment:
. Runway dimensions / aspect ratio (Figure 3):
. the runway aspect ratio (i.e., its length relative to its width) affects the crew visual perspective view of the runway:
°. a large or short runway (low aspect ratio) creates an impression of being too low; and,
°. a narrow or long runway (high aspect ratio) creates an impression of being too high.
. A downhill slope in the approach zone creates an illusion of being too low (i.e., impression of a shallow glide path, as shown on Figure 2), thus:
°. possibly inducing a correction placing the aircraft above the intended glide path; or,
°. preventing the flight crew from detecting a too steep flight path.
Figure 3
Photo - LFBO 15 R ( 3500 m x 45 m ) 3-degree glide slope / 200 ft RA
. Runway uphill or downhill slope:
. An uphill slope creates an illusion of being too high (impression of a steep glide path); and,
. A downhill slope creates an illusion of being too low (impression of a shallow glide path).
. Approach and runway lighting:
. The approach and runway lighting (including the touchdown zone lighting ) affects the dept perception as a function of:
°. The lighting intensity;
°. The daytime or night time conditions; and,
°. The weather conditions.
Visual Illusions Awareness
Page 3
. Bright runway-lights create the impression of being closer to the runway (hence on a steeper glide path);
. Low intensity lights create the impression of being farther away (hence on a shallower glide path);
. A non-standard spacing of runway lights also modifies the pilot’s perception of the runway distance and glide path; and,
. If runway lighting is partially visible (e.g., during the downwind leg or during the base leg of a visual or circling approach), the runway may appear being farther away or at a different angle (i.e., the intercept angle is perceived as smaller than actual).
Runway approach aids:
The following runway approach-aids and conditions may increase the crew exposure to visual illusions:
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