Wind Shear
As I posted on my previous post, weather is perpetual
in the state of the atmosphere to all Pilots, remember that all flying takes
place in the atmosphere, so flying and weather are inseparable.
Why accidents happen, and why is a good
question that every pilot has to learn to appreciate and understand what that
means a good or bad weather, to recognize and respect marginal or hazardous weather,
and to avoid violent weather when the atmosphere is on its most difficult behavior.
So, for your Safety and the Safety of those
with you, always learn to recognize potential trouble and make a comprehensive flight
decision before it is too late.
Wind Shear generates eddies between two wind
currents of differing velocities. The difference may be in wind speed, wind
direction, or in both. Wind Shear may be associated with either a wind shift or
a wind speed gradient at any level in the atmosphere. There are three conditions
of special interest to know, Wind Shear with a low level temperature inversion,
Wind Shear in a frontal zone, and Clear Air Turbulence (CAT) at high levels
associated with a Jet Stream or Strong Circulation.
So, let’s review Wind Shear with a low level temperature
inversion: A temperature inversion forms near the surface on a clear night with
calm or light surface wind. Wind just above the inversion may be relatively
strong. Wind Shear zone develops between the calm and the stronger winds above.
Eddies in the Shear Zone cause airspeed fluctuation
as an aircraft climbs or descends through the inversion. An aircraft most
likely is either climbing for takeoff or approaching to land when passing
through the inversion, so airspeed is low, only a few knots greater than stall
speed.
The fluctuation in Air Speed can induce a stall
dangerously close to the ground.
Since surface Wind is calm or very light,
takeoff or landing can be in any direction.
Takeoff may be in the direction of the wind
above the inversion.
If so, the aircraft encounters a sudden
tailwind and a corresponding loss of Air Speed when climbing through the
inversion. Stall is possible. If the approach is into Wind above the inversion,
the headwind is suddenly lost when descending through the inversion. Again the
sudden loss in Air Speed may induce a stall.
When taking off or landing in Calm Wind under
clear skies within a few hours before or after sunrise, be prepared for a temperature
inversion near the ground. So, you as a Safety Pilot can relatively certain of
a shear zone in the inversion if you know the Wind at 2.000 to 4.000 feet is 25
knots or more. The important thing is to allow a margin of airspeed above
normal climb or approach speed to alleviate danger of stall in event of
turbulence or sudden change in Wind Velocity.
Now, let’s review Wind Shear in a frontal zone:
As you have learned as a Pilot when you study the concept of meteorological conditions,
so far a front contains many hazards. However, a front can be between two dry
stable airmasses and can be devoid of clouds. Even so, wind changes abruptly in
the frontal zone and can induce Wind Shear turbulence. The degree of turbulence
depends on the magnitude of the Wind Shear. When turbulence is expected in a
frontal zone, follow turbulence penetration procedures recommended in your
aircraft manual. (SOP)
It seems the term Wind Shear have been in a
Pilots vocabulary for many years, lessons learned from accidents ,so the key it
is to stay away from incidents and accidents,
always try to recognize on time the clues , listen to pilots reports of Wind
Shear, ATC advisories , onboard radars returns , forecast and observation. Don’t
become complacent; you might have successfully flown near thunderstorm activity
hundreds of times before. The most important always takes the clues seriously,
update your personal weather knowledge, and make a point to seek out the latest
information to make a Safe Landing.
Fly Safely all the time, Safety is First.
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