UNIVERSITY DAILY KANSAN
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Wednesday, April 5, 1995
9A
'Elevator illusion,' microburst may have caused crash
The Associated Press
WASHINGTON — A sensory illusion that makes people think they are tilting backward may have caused the July USAir DC-9 crash during a violent storm in Charlotte, N.C., federal safety officials were told Monday.
The plane crashed while attempting to pull out of an unsuccessful landing. Thirty-seven people died, and 20 survived.
The National Transportation Safety Board studied several factors in the accident, including severe weather, the crew's actions and what information air traffic controllers had given the crew.
As the plane tried to land it encountered a severe windstorm and rain, and the crew tried to pull away from the runway by increasing speed and raising the nose of the craft to 15 degrees above level, board investigators said.
The captain called out "Down, push it down," and the plane's nose lowered. Moments later, it crashed.
Renee Mills of the board staff said that the captain might have been affected by "elevator illusion."
When a plane accelerates as it climbs, the two movements can combine to make a person feel as if they are being tilted onto their back, she said.
The normal reaction is to tilt the
How a microburst causes dangerous wind shear
Investigators suspect a microburst caused Saturday's airliner crash in Charlotte, N.C. Microbursts are small, intense downdrafts that spread outward when they reach the ground. They can be hazardous to aircraft, especially at low altitudes.
Facts about microbursts
What is wind shear? Winds moving past each other in opposite directions, horizontally or vertically. Microbursts can cause wind shear.
Size: Typically less than a mile across. Spreads to about 2.5 miles across near the ground.
SOURCE: Airman's Information Manual/Federal Adoption Regulations 1994
■ When they occur: Usually in a thunderstorm producing heavy rain. Weaker storms with little or no rain also can cause them.
Intensity: Downdrafts can be as strong as 6,000 feet per minute. Horizontal winds of more than 100 mph can occur within a few hundred feet of the ground.
plane's nose down.
Duration: Microbursts rarely last more than 15 minutes after striking the ground. The horizontal winds increase in intensity for the first 5 minutes, with the strongest winds lasting 2 to 4 minutes.
Both the pilot and co-pilot said that they did not remember deciding to lower the nose of the plane.
Board investigators said that in the attempt to pull out of the landing, the plane first encountered a headwind of 40 miles per hour, then a sudden burst of wind moving vertically downward, called a microburst, and then a tailwind just before the plane crashed.
Knight-Ridder Tribune/BRENDA PINNB
The board also heard reports that a wind shear warning and lightning warning were not passed along and that a ground instrument to measure runway visibility was not turned on.
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