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The Mirror Effect

From Issue 3/75

"Runway Lights in Sight..."

Last year 97 people were killed when a 707 entered a particularly steep rate of descent in the last 20 seconds of an instrument approach. As the runway became visible the first officer called "you're a little high", so the captain increased his rate of descent from 690 fpm to 1470 fpm. This excessive descent continued until the aircraft crashed.

Why? The captain had relied primarily on visual clues. The heavy rain on the windshield may have caused the runway lights to appear larger, thereby convincing the pilot he was cioser to the runway than he reallv was.

"Runway lights in sight..." is a reassuring call from the first officer but it means you're entering a critical phase of flight. That transition from instruments to the visual part of the landing requires more than just a casual check of the flight instruments. Your instrument scan should continue, adding to it visual clues (such as VASI) as they appear. This way, during transition you'll detect any deviations from the glidepath and desired rate of descent.

Having some visual clues may tempt you to abandon your instrument scan early but rain on the windshield changes the perception of distance on the approach. It can make lights appear larger which may convince you the runway is closer than it really is. With this iilusion it's easy to convince yourself to increase the rate of descent or descend prematurely. Or rain may cause runway lights to appear less intense by diffusing their glow. This would probably lead you to think that the lights are farther away than they actually are.

Don't fall into the visual trap. Maintain a good scan of your flight instruments as you transition from instrument phase to the visual approach and landing.

The Mirror Effect

Have you ever looked into a wall-to-wall mirror and wondered exactly where the surface was? Hard to tell, isn't it? It's the same thing when taking off or landing on glassy water.

Ask any experienced float pilot - glassy water operations are tricky and you need to be extra alert. Here's an example. After refuelling on shore, a chopper pilot moved to a hover over a glassy lake surface. As he began h is transition to forward flight the skids struck the water surface causing the chopper to tumble into the water. Fortunately the crevv escaped uninjured as the chopper was sinking.

The pilot said he had never been instructed on the hazards associated with glassy water operations. Have you? There is more information on this subject in Part 4 of the Flight Information Manual (FIM).

Originally Published: ASL 1/1998
Original Article: From Issue 3/75 - "Runway Lights in Sight..."; The Mirror Effect