Microburst and Windshear


#1

I’m listening to Orlando now and they have a 50 knot Microburst alert and 35 knot windshear alert. How does this rank on severity?


#2

Enough for ATC to put a hold on inbounds and outbounds usually. They take this kind of stuff very seriously these days. There were a few high profile accidents over the years attributed to the then-underappreciated windshear/microburst phenomenon.


#3

isnt the microbursts the worst type of windshear you can get? im sure i read that somewhere


#4

The nasty part about microbursts (as far as aviation is concerned anyway) is that they blow down, leaving little course of action for an approaching or departing aircraft to take. I’m no pilot, so I couldn’t begin to tell you how to react to one or if they’re in fact the worst, but I’d have trouble naming something worse, other than maybe trying to land into the vortex of an F5 tornado.
Microbursts are tricky since they tend to “show up” so quickly. It’s basically just air that’s being displaced at the leading edge of a heavy t-storm by the high volume of rain or hail that’s falling. I’ve experienced heavy damage to my old house from a microburst; it’s a pretty scary event, albeit a quick one. Couldn’t imagine trying to fly through that.

If I’m not mistaken, it was a microburst that took a Delta L-1011 down at DFW around 1984 or so.


#5

As the image above shows, the winds blow down until they hit the ground, then the winds blow outward. An approaching aircraft will first encounter a sudden strong headwind which causes a sudden increase in airspeed. The pilot’s first reaction is to reduce power. Then the headwind suddenly becomes a very strong downdraft. IF the plane is still airborne after the downdraft, it will fly into a very strong tailwind which produces a sudden decrease in airspeed which would inevitably result in a stall.

It was indeed a microburst that brought the Delta L-1011 down. That crash triggered research in windshear and microburst phenomena which spawned the detection and warning systems in place today.

DELTA FLIGHT 191 CVR TRANSCRIPT.


#6

Point of Information, do you mean a headwind would decrease airspeed and a tailwind would increase airspeed? Other than that, good info.


#7

Nope, I think Needle has it correct. A headwind would increase airspeed, but decrease groundspeed. Opposite for a tailwind.


#8

Good point. The airspeed/groundspeed didn’t fully process…

It’s Monday, and my brain got fried in 100+ degrees in McAllen, TX this weekend…


#9

Hopefully get this correct :smiley:

If you hit wind shear, you would get an increase of IAS (indicated air speed) followed by the decrease on the down draft.

Your GROUND speed would decrease resultant to the windshear, but your AIR speed would drastically go up due to the extra air now running through your pitot static system on the initial onslaught of air rushing toward you.

Hit the downdraft, you now lose that extra air that your airspeed indicator had going for you, and you lose that lift that you thought you had.

All the airplane cares about is IAS.

Also note, windshear can be encountered at any level of the atmosphere. A sudden change of direction in wind is considered windshear.

See casa.gov.au/fsa/2004/aug/quiz.pdf for a helpful guide on microburst and windshear.

Allen