AlitaliaORD
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Windshere:What Is It, And Your Expiriences

Tue Apr 20, 2004 10:11 am

What is windshere, I know it causes the plane to drop significantly, is there anyway of telling you will encounter windshere.......and who has had expirience?
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KAUSpilot
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RE: Windshere:What Is It, And Your Expiriences

Tue Apr 20, 2004 10:27 am

Most modern airports with airline service have a low level windshear advisory system installed (LLWAS). It detects windshear by comparing the winds at various locations around the airport. For instance, if the winds on the south side of the airport are coming out the west at 15 knots, and on the north side of the airport, they're coming out of the east at 30 knots, the system will report a 45 knot windshear for the airport. This alert will be included in the ATIS broadcast and the controllers may periodically advice pilots of it. The METAR text weather report will also indicate windshear if it is observed.

Pireps (pilot reports) are probably the most accurate means of determining if windshear exists in an area. Of course, with this method, someone has to be the guinea pig to report the windshear in the first place....

As far as forecasting windshear: frontal passage will always be accompanied by a change in wind, so a pilot should be vigilant for windshear when flying near frontal zones. A temperature inversion is also an indicator of possible windshear, so if you see that the outside air temperature is increasing as you climb, you should be vigilant for winshear. Weather forecasters will include winshear in terminal aerodome forecasts if they feel it may occur at some point in the next 24 hours.

Windshear is most probably most frequently encountered in and around thunderstorms. Within 20NM of thunderstorm activity, horizontal and/or vertical windshear is common. This is one of many reasons why pilots try to stay far away from thunderstorm activity, especially in small aircraft.

I have been fortunate enough to avoid windshear so far in my career, but it has the potential to ruin any pilot's day in a hurry.....

 
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delyan
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RE: Windshere:What Is It, And Your Expiriences

Tue Apr 20, 2004 10:33 am

Windsheer is a big air mass going downwards. When the aircraft enters this air mass, it start moving downwards together with the air mass. It is dangerous because on final approach the aircraft is moving slowly and there is little lift from the wings. Basically, there is very little time to do something because the ground is very close and you need some speed in order to climb back up. I am not a pilot, but I know that it case of windsheer, you have to rev up the engines to the max in order to gain some speed and lift from the wings. I think some of the airport have windsheer radars.
I have never experienced it and I don't want to....
 
KAUSpilot
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RE: Windshere:What Is It, And Your Expiriences

Tue Apr 20, 2004 11:03 am

Windshear is not necessarily associated with an airmass moving downwards. Windshear can occur at any altitude in any direction.

Horizontal windshear is usually broken down into the following two scenarios:

1) A headwind suddenly becomes a tailwind, the airplane will experience a sudden loss of airspeed which may cause it to sink and stall. The pilot must increase engine power to recover from this situation.

2) A tailwind suddenly becomes a headwind, the airplane will experience a sudden surge in airspeed which may cause it to climb and/or exceed it's structural limitations. The pilot should reduce engine power to recover.

Vertical windshear can be divided into updrats and downdrafts. Their effects are pretty obvious. An updraft will lift you higher and a downdraft will push you toward the ground. This is common in and around thunderstorms, or on hot days when hot air from the surface is rising to higher altitudes.

Weather phenomenon such as microbursts may contain both vertical and horizontal windshear.
 
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delyan
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RE: Windshere:What Is It, And Your Expiriences

Tue Apr 20, 2004 11:17 am

KAUSpilot explained it all!
 
NW747-400
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RE: Windshere:What Is It, And Your Expiriences

Tue Apr 20, 2004 12:06 pm

I believe that you are referring to a microburst Delyan, of which a side effect is windshear.

I experienced a microburst once on approach to DFW in one of AA's 757s. On short final over the fence, I could actually hear the automated cockpit recording "WINDSHEAR!! WINDSHEAR!!" Nearly instantaneously the engines began spolling up as we stalled and slammed into the runway pretty hard. It was one of the most horrific experiences I have ever been in.
 
pr1268
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RE: Windshere:What Is It, And Your Expiriences

Tue Apr 20, 2004 1:01 pm

I remember landing at CO / KMCO), USA - Florida">MCO in 1988 in a CO 737-200 (Actually one of those bright red New York Air hand-me-downs) during a 4:00 pm summer thunderstorm. You can almost literally synchronize your wrist watch to these storms!

The approach seemed unusually fast, even the engines seemed to continue to produce cruise thrust or more with flaps-10 and gear extended. Certainly the pilots were hot-rodding the a/c to accommodate for possible wind shear. I suspect we traveled through at least two microbursts during the approach.

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