Saturday, July 6, 2013

What is a Microburst? What Do They Look Like?

The speculation the Asiana crash was caused by wind shear or a microburst (a particularly dangerous type of wind shear) continues. Here is just one of the articles sent to me:
That is just one of many. Because the last wind shear airline accident in the U.S. was 19 years ago (July 2, 1994, USAir 1016 in Charlotte) many in the media -- and, maybe the airline industry -- have forgotten some of the fundamentals.

This is what a wet microburst looks like:

There are dry microbursts (at the ground) but they always start with rain falling. Here is a photo from 1982 of a dry microburst near Denver. You can see the rain falling from the clouds on the left half of the photo but the rain evaporated before it reached the ground.

Now, contrast these photos with the photo taken immediately after the Asiana crash.
There are no thunderstorms or thunderstorm-like clouds for hundreds of miles!

A microburst, because of the extremely rapid changes in wind speed and direction, is an extreme hazard to aviation. This is a schematic diagram. A microburst (a small downburst) is a hazard only on landing and takeoff.

It is literally impossible there was a microburst in the area of San Francisco International Airport and the airport weather observations (see posting below) do not indicate any other form of wind shear.

Naturally, people want to know what went wrong so it can be fixed. Unfortunately, these investigations (I have been part of several of them) take months or, sometimes, more than a year. But, we can check "microburst" off the list of possible causes.

1 comment:

  1. Well, the CNN story says the flight was approaching the airport "...on a clear summer day." That sure eliminates the shear as you have stated several times.