WINDSHEAR

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WINDSHEAR
Lt Col Wally Emerson 15 April 2007
2
WHY STUDY WINDSHEAR?
744 Dead 287 Injured
CONUS Only Since 1964
3
OBJECTIVE
Emphasize that the best defense against the
hazards of low altitude windshear is avoidance.
Give you key information to assist in
recognizing and avoiding windshear. Discuss
some precautions and techniques for improving
chances of surviving an inadvertent windshear
encounter.
4
OBJECTIVE
Emphasize that the best defense against the
hazards of low altitude windshear is avoidance.
Give you key information to assist in
recognizing and avoiding windshear. Discuss
some precautions and techniques for improving
chances of surviving an inadvertent windshear
encounter.
5
OBJECTIVE
Emphasize that the best defense against the
hazards of low altitude windshear is avoidance.
Give you key information to assist in
recognizing and avoiding windshear. Discuss
some precautions and techniques for improving
chances of surviving an inadvertent windshear
encounter.
6
OVERVIEW
1) Windshear weather, particularly microbursts,
and clues which may indicate its presence, 2)
Effects of windshear on airplanes 3) Windshear
recognition cockpit, and avoidance, 4)
Precautions to take when windshear is
suspected, 5) Standard operating techniques
related to windshear 6) Recovery techniques to an
inadvertent windshear encounter.
7
OVERVIEW
1) Windshear weather, particularly microbursts,
and clues which may indicate its presence, 2)
Effects of windshear on airplanes 3) Windshear
recognition cockpit, and avoidance, 4)
Precautions to take when windshear is
suspected, 5) Standard operating techniques
related to windshear 6) Recovery techniques to an
inadvertent windshear encounter.
8
OVERVIEW
1) Windshear weather, particularly microbursts,
and clues which may indicate its presence, 2)
Effects of windshear on airplanes 3) Windshear
recognition cockpit, and avoidance, 4)
Precautions to take when windshear is
suspected, 5) Standard operating techniques
related to windshear 6) Recovery techniques to an
inadvertent windshear encounter.
9
OVERVIEW
1) Windshear weather, particularly microbursts,
and clues which may indicate its presence, 2)
Effects of windshear on airplanes 3) Windshear
recognition cockpit, and avoidance, 4)
Precautions to take when windshear is
suspected, 5) Standard operating techniques
related to windshear 6) Recovery techniques to an
inadvertent windshear encounter.
10
OVERVIEW
1) Windshear weather, particularly microbursts,
and clues which may indicate its presence, 2)
Effects of windshear on airplanes 3) Windshear
recognition cockpit, and avoidance, 4)
Precautions to take when windshear is
suspected, 5) Standard operating techniques
related to windshear 6) Recovery techniques to an
inadvertent windshear encounter.
11
OVERVIEW
1) Windshear weather, particularly microbursts,
and clues which may indicate its presence, 2)
Effects of windshear on airplanes 3) Windshear
recognition cockpit, and avoidance, 4)
Precautions to take when windshear is
suspected, 5) Standard operating techniques
related to windshear 6) Recovery techniques to an
inadvertent windshear encounter.
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WINDSHEARDefinitions
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WINDSHEAR
Windshear is a generic term referring to any
rapidly changing wind currents.
GP WIND SHEAR - A change in wind speed and/or
wind direction in a short distance, resulting in
a tearing or shearing effect. It can exist in a
horizontal or vertical direction and occasionally
in both.
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WINDSHEAR
WIND SHEAR Vertical wind shear is the rate of
change of the wind with respect to altitude.
Horizontal wind shear is the rate of change on
a horizontal plane.
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WINDSHEAR
WIND SHEAR AC 00-54 Severe Windshear - A rapid
change in wind direction or velocity
causing airspeed changes greater than 15 knots or
vertical speed changes greater than 500 feet per
minute.
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WINDSHEAR
Wind shear can be encountered when flying through
a temperature inversion layer. However, the
dangerous wind shear we're interested in is
generally associated with a frontal system,
especially one which includes a thunderstorm.
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WINDSHEARWeather to look out for
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WINDSHEAR
During a thunderstorm, a large column of cold,
dense air rapidly descends to the surface of the
earth. This fast moving column can be described
as a downburst. Once the downburst reaches the
surface of the earth, it expands horizontally in
all directions.
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WINDSHEAR
Once the downburts spreads out horizontally, it
undercuts the warmer air outside the storm. This
mixing of air produces a rolling vortex of wind.
The vortex then causes high velocity winds to
surge in opposing directions. These strong winds
which makes up the gust front are also known as
horizontal wind shear.
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WINDSHEAR
"Valley wind shear" is a name for another natural
cause of wind shear which results from a
temperature inversion. This phenomena begins by
the cooling of the air in a valley. This cooling
results in a stable air mass on the valley floor.
The wind blowing across the top of the mountain
pushes air down the mountain slope.
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WINDSHEAR
The wind blowing across the top of the mountain
pushes air down the mountain slope. The air
experiences heating during this descent. However,
when this air encounters the stable air mass on
the valley floor, it cannot penetrate it and
flows over top of it. This results in a layer of
warmer air being pushed out over a layer of
colder air, a temperature inversion. Thus a wind
shear is developed due to the air flowing over
the inversion, and stable air below it.
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WINDSHEAR
As the valley floor air is warmed the next
morning, it begins to rise weakly. Air begins
moving down the slope of the mountain downwind to
replace this rising air. As this continues and
increases in strength, it results in a rotary
motion. This rotary motion is another form of
wind shear.
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WINDSHEAR
Another way that mountains can create wind shear
is by turbulence. As the wind blows up one side
of a mountain and reaches the top, it can begin
to mix turbulently. This turbulence on the lee
(downwind) side of the mountain is a form of wind
shear. The same effect takes place around the
sides of buildings
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MICROBURSTS

• The Granddaddy of all Windshears

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Microbursts Dry or Wet

• Wet microbursts are more common in places like
  the Mississippi valley where thunderstorm bases
  tend to be much lower.
• Dry microbursts occur primarily in the high
  plains/intermountain's where the temperature/dew
  point spread is wide (30 to 50)

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Downburst/Microburst Definition

• A downburst is HEAVY COLD/MOIST air dropping
  spilling out producing horizontal shears along a
  damage path of 1-5 miles .
• A microburst is a downburst that covers an area
  less than 3 miles with peak winds that last 25
  minutes.

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Why are they important?

• Eastern Airlines Flight 66 crashed 24 June 1975
• August 1983 near miss at Andrews AFB
• Fast winds with rapidly shifting directions are
  bad for planes trying to take off or land
• There are typically 50100 downbursts each year
  during the convective season

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Downdraft Formation

• Two main mechanisms
• Evaporation
• Cools the air cold air sinks
• Rain that evaporates before reaching the ground
  is called virga
• Cold air can descend as fast as 4060 m.p.h.
• Drag force
• Falling precipitation drags air down with it,
  creating fast descending air
• One raindrop is inconsequential but many drops
  have a large effect on air flow

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Downburst/Microburst Structure

• Weak environmental wind field
• Downburst is symmetrical
• Equal speed/damage on all sides

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Weak environmental wind field or more stationary
the front Aircraft will experience equal
headwinds and tailwinds
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Downburst/Microburst Structure

• Strong environmental wind field
• Asymmetrical
• Strongest wind is downwind of stagnation cone
• May produce a well-defined foot shape to
  precipitation

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Strong environmental wind field or fast moving
front Aircraft will experience bigger kick on
the backside
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Vortex Ring
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WINDSHEAR
Evolution of a microburst. Microburst winds
intensify for about 5 min after ground contact
and typically dissipate about 10 to 20 min after
ground contact.
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DRY MICROBURST
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In this example, air below a cloud base (up to
approximately 15,000 feet AGL) is very dry.
Precipitation from higher convective clouds falls
into low humidity air and evaporates. This
evaporative cooling causes the air to plunge
downward. As the evaporative cooling process
continues, the downdraft accelerates. Pilots are
therefore cautioned not to fly beneath convective
clouds producing virga conditions.
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WINDSHEAR

• Greatest danger Takeoff and landing
• During landing, the pilot has already reduced
  engine power and may not have time to increase
  speed
• During takeoff, an aircraft is near stall speed

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General
Windshear, particularly low altitude windshear
encounters, are of significant importance because
it can place the flight crew in a situation where
the maximum performance capability of the
aircraft is required. Windshear encounters below
500ft are the most threatening because there is
very little time or altitude to respond and
recover from an inadvertent encounter.
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General
Knowledge of how windshear affects performance
can be essential to a successful recovery
maneuver following an inadvertent windshear
encounter.
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General
Windshear that improves performance will be first
indicated in the cockpit by an increased
airspeed. Pilot reaction reduce thrust. With
power back you experience a shear in the reverse
sense that will decrease airspeed and degrade
vertical flight path performance.
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General
The magnitude of the pitch change is a function
of the following  - Aircraft configuration   -
Weight   - Speed   - C of G   - Thrust   -
Severity of airspeed change
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General
If an attempt is made to regain lost speed by
lowering the nose, the combination of decreasing
airspeed and decreasing pitch attitude produces a
high rate of descent. In some circumstances as
little as 5 seconds may be available to recognize
and react to a degrading vertical flight path.
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General

• INDICATORS OF WINDSHEAR
• SIGMETS
• Visual signs (T-storms, black wall of death,
  tornados etc..)
• Unusual control forces required
• Significant changes in airspeed occur
• PIREPS

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General
Crew Actions - Take-off Windshear Precautions
Maximum thrust should be used If practical the
longest suitable runway available should be used,
provided it is clear of areas of known
windshear.The flight director should not be
relied upon during take-off in suspected
windshear conditions. The attitude director is
the primary reference for pitch attitude.
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General
Crew Actions - Take-off Windshear Precautions
Crews should be alert for airspeed fluctuations
during take-off and initial climb. Such
fluctuations may be the first indication of
windshear. Control forces may be different from
those expected, especially if airspeed is below
the in-trim speed.
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General
Crew Actions - Take-off Windshear Precautions
Crew co-ordination and awareness are very
important. Close monitoring of the flight
instruments is imperative, and the non-handling
pilot should be especially aware of these and
call out any deviations from normal values.
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General
Crew Actions - Take-off Windshear Precautions
The stick shaker must be respected at all times.
If it is activated, pitch attitude should be
reduced just enough to stop the stick shaker.
Flight with intermittent stick shaker operation
may be required to maintain a positive rate of
climb during a windshear encounter.
MAX PERFORMANCE just in and out of stick shaker
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Effect on Airplanes

• Windshear encounter during takeoff after liftoff.
  
• Takeoff initially appears normal.
• Windshear encountered just after liftoff.
• Airspeed decrease resulted in pitch attitude
  reduction.
• Aircraft crashed off departure end of runway 20
  set after liftoff.

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Effect on Airplanes

• Windshear encounter during takeoff on runway.
• Takeoff initially appeared normal.
• Airspeed buildup slowed due to windshear.
• Airplane reached VR near end of runway, lifted
  off but failed to climb.
• Airplane contacted obstacle off departure end of
  runway.

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General
Crew Actions - Approach and Landing Windshear
Large thrust reductions or trim changes in
response to a sudden airspeed increase should be
avoided as these may be followed by a decrease in
airspeed.
51
General
Crew Actions - Approach and Landing Windshear In
windshear conditions flight director commands
should be checked against ADI, and altimeters.
These instruments are the primary references for
vertical flight path control.
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Effect on Airplanes

• Windshear encounter during approach.
• Approach initially appeared normal.
• Increasing downdraft and tailwind encountered at
  transition.
• Airspeed decrease combined with reduced visual
  cues resulted in pitch attitude reduction.
• Airplane crashed short of approach end of runway.

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General
Crew Actions - Windshear Recovery Maneuver As a
guide, marginal flight path control may be
indicated by uncontrolled changes from the normal
steady state flight conditions in excess of -
15 knots indicated airspeed   - 500 fpm vertical
speed   - 5 degrees pitch attitude   - 1 dot
glideslope displacement
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General
Crew Actions - Windshear Recovery Maneuver
Whenever flight path control becomes marginal
below 500ft AGL, or when the "WINDSHEAR" or "PULL
UP" warning occurs, simultaneously-- Call
"Windshear Go-around" - Complete the rest of
"Windshear" recall items (QRH)
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General
Crew Actions - Windshear Recovery Maneuver The
call of "Windshear Go-around will advise the
non-handling pilot that the usual go-around
procedure does not apply and that speeds and
pitch attitudes may not be normal for a
go-around.
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General
Crew Actions Windshears which exceed the
performance capabilities of both small and large
aircraft have and will occur below 500ft. The
flight crew should search for any clues to the
presence of windshear along the intended flight
path.
57
General
Crews should carefully review all available
information such as pilot reports of windshear or
turbulence, low level windshear reports and
weather reports - especially thunderstorms and
'virga'.
58
General
Windshear that produces uncommanded airspeed
changes of 15 knots or more is regarded as
severe. Areas of known windshear should be
avoided and pilots should delay take-off or
discontinue an approach until conditions have
improved wherever necessary.
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General
Windshear encounters should be reported precisely
and promptly to assist other pilots. Accurate
pilot reports of windshear can be a valuable clue
as to the presence and severity of windshear
conditions.
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General
Windshear Effects on Systems Altimeters During
callouts and instrument scan in a windshear, use
of radio and/or barometric altimeters must be
tempered by the characteristics of each. Since
radio altitude is subject to terrain contours,
the indicator may show a climb or descent due to
falling or rising terrain, respectively. The
barometric altimeter may also provide distorted
indications due to pressure variations within the
microburst.
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General
Windshear Effects on Systems Vertical Speed
Indicators The vertical speed indicator (VSI)
should not be solely relied upon to provide
accurate vertical speed information. Due to
instrument lags, indications may be several
seconds behind actual airplane rate-of-climb/desce
nt and, in some situations, may indicate a climb
after the airplane has started descending.
Vertical speed indicators driven by an Inertial
Reference Unit (IRU) show significant improvement
over other type instruments but still have some
lag.
62
General
Windshear Effects on Systems Vertical Speed
Indicators In addition, gust induced pitot
static pressure variations within the microburst
may introduce further VSI inaccuracies. Due to
such lags and errors, all vertical flight path
instruments should be cross-checked to verify
climb/descent trends.
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General
Crew Actions - Windshear Recovery Maneuver C-21
Windshear Recovery Thrust Aggressively apply
necessary thrust (not less than go-around thrust)
to ensure adequate airplane performance. Avoid
engine over boost unless necessary to avoid
ground contact. When airplane safety has been
ensured, adjust to maintain engine parameters
within specific limits.
64
General
Crew Actions - Windshear Recovery Maneuver C-21
Windshear Recovery Pitch For a windshear
encounter after liftoff or on approach, increase
or decrease pitch attitude as necessary, at a
normal pitch rate, toward an initial target
attitude of 15 degrees.
65
General
Crew Actions - Windshear Recovery Maneuver C-21
Windshear Recovery Pitch The all-engine pitch
attitude may be maintained until either the shear
has been exited or stick shaker is encountered.
Always respect stick shaker. Use intermittent
stick shaker as the upper limit for pitch
attitude.
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General
Crew Actions - Windshear Recovery Maneuver C-21
Windshear Recovery Pitch In a severe shear, stick
shaker may occur below 10 degrees pitch attitude.
Rapidly changing vertical winds can also cause
momentary stick shaker at any attitude.
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General
Crew Actions - Windshear Recovery Maneuver C-21
Windshear Recovery Pitch Rapidly changing winds
may cause rapid excursions in pitch and roll with
little or no pilot input. Control pitch in a
smooth, steady manner (approximately 2 degree
increments) to avoid excessive overshoot/undershoo
t of the desired attitude. Once the airplane is
climbing, and ground contact is no longer an
immediate concern, airspeed should be increased
by cautious reductions in pitch attitude.
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General
Crew Actions - Windshear Recovery Maneuver C-21
Windshear Recovery Configuration Do not change
flap, gear, or trim position until terrain
contact is no longer a factor. However,
stabilizer trim may be used to trim out stick
force due to thrust application. Although a small
performance increase is available after landing
gear retraction, initial performance degradation
may occur when the landing gear doors open for
retraction.
69
General
Crew Actions - Windshear Recovery Maneuver C-21
Windshear Recovery Configuration Extending flaps
during a recovery after liftoff is not
recommended since the risk of moving the flaps in
the wrong direction or amount is considered a
greater risk than encountering a shear so great
that a flap change is needed for recovery.
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Quick review
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(No Transcript)
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Duration 15 minutes or lessbut once microburst
activity starts not uncommon for multiple
microburst's
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Downbursts
Approach to Prevention
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(No Transcript)
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Headwind increases experience increased
performance/pitches up
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Headwind decreases until downdraft experience
decreased performance/pitches down
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Initiate go-around experiencing increasing tail
wind and decreasing performance - 15 knots
indicated airspeed   - 500 fpm vertical speed
  - 5 degrees pitch attitude   - 1 dot
glideslope displacement
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SOLUTION

• Detection Equipment
• Ground-Based
• Airborne
• Education

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Ground-Based Detection

• (NEXRAD) Doppler Radar(6 Min)
• (LLWAS) Low Level Windshear Alerting System
• Barometric Pressure Jump Indicators
• (TDWR) Terminal Doppler Weather Radar (2 Min)

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AIRBORNE DETECTION

• Predictive
• Alerts Crew Prior to Entry
• Non-Predictive
• Alerts Crew That Windshear Has Been Entered
• Test Probe

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AIRBORNE DETECTION

• Predictive
• Alerts Crew Prior to Entry
• KC-135 (WXR-700X)
• PWS (in auto) automatic during T/O Land
• - 60, 5 miles in front (microburst windshear
  detection)
• Gives warning, caution or advisory

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AIRBORNE DETECTION

• Non-Predictive
• Alerts Crew That Windshear Has Been Entered
• Test Probe

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AIRBORNE DETECTION

• SIGMETS
• VISUAL CLUES
• PIREPS

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What Do We Have?

• EDUCATION!

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Examination of the worldwide windshear associated
accidents and incidents has shown that the
majority of these have occurred in the United
States. The greater number of accidents results
from the combination of high convective activity
and high air traffic density. Many more windshear
associated accidents and incidents have probably
occurred worldwide but have not been recorded as
such.
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Months Time of Day
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WEATHER FACTORS
If you avoid any precipitation and fronts, you
avoid 80 of the threat!
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Watch Out for Fronts If . . .

• The temperature differential exceeds 10 degrees
  Fahrenheit
• The front is moving faster than 30 knots

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Cold Fronts

• Be alert for windshear below 1,000 feet AGL 30
  minutes to an hour after frontal passage

90
Warm Fronts

• Be alert for windshear below 1,000 feet AGL six
  to twelve hours prior to frontal passage
• Warm front shears tend to be more severe

91
Microburst Producers

• High-Based Thunderstorms
• Small Rapidly-Developing Cells
• Anything that Produces Convection
• Convection is Responsible for 90 of
  Windshear-Related Accidents

92
Microbursts Dry or Wet

• Dry microbursts occur primarily in the high
  plains/intermountains where the temperature/dew
  point spread is wide (30 to 50)
• Wet microbursts are more common in places like
  the Mississippi valley where thunderstorm bases
  tend to be much lower.

93
A
Can you see the micro burst?
B
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D
Can you see the micro burst?
C
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E
Can you see the micro burst?
F
96
F
Can you see the micro burst?
http//www.cimms.ou.edu/doswell/microbursts/Figur
e_17b.JPG
97
Can you see the micro burst?
B
http//www.cimms.ou.edu/doswell/microbursts/Figur
e_13.JPG
98
Microburst

• About 5 of all thunderstorms produce microbursts
• Wet
• Places like the Mississippi River Valley
• Convective activity with low bases
• Heavy rain

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Microburst
Here is a time lapse of a wet microburst Note the
ensuing outflows
A
D
B
E
C
F
100
Dry Microbursts
101
Microburst

• Dry
• High plains/interior mountains
• Convective activity forms at higher levels
• Thunderstorm base 10,000 - 15,000 MSL
• Dry surface conditions
• Surface Temperature of 80 degrees F
• Wide temp/dew point spread
• 30 - 50 degrees F
• Virga

102
Visual Identification (Dry)

• - Virga wisps or streaks of water or ice
  particles falling out of a cloud but evaporating
  before reaching the earth's surface as
  precipitation. (NOAA 2001)
• - Blowing dust/dust rings at surface

103
Dry Microbursts
The microburst is rendered visible by an
expanding ring of dust under a virga shaft
descending from a high-based cumulonimbus. The
precipitation largely evaporates before reaching
the surface, so the surface rainfall is probably
no more than a trace. As the microburst pictured
in the previous developed, the ring of dust
spread out over the surface
104
Here is a time lapse of a dry microburst Note the
difference in wind speed and direction
105
(No Transcript)
106
Visual Identification (Wet)

• Heavy precip
• Rain foot (Huh?)

http//www.cimms.ou.edu/doswell/chasesums/chase97
_18.JPG
107
C
108
MICROBURST WINDSHEAR PROBABILITY
GUIDELINES OBSERVATION PROBABILITY OF
WINDSHEAR PRESENCE OF CONVECTIVE WEATHER NEAR
INTENDED FLIGHT PATH With localized strong
winds (Tower reports or observed blowing dust,
rings of dust, tornado-like features, etc. )
..HIGH With heavy precipitation
(Observed or radar indications of contour, red or
attenuation shadow) ..HIGH With rainshower
MEDIUM With lightning
MEDIUM With virga..MEDIUM
With moderate or greater turbulence (reported
or radar indications)MEDIUM With
temperature/dew point spread between 30 and 50
degrees Fahrenheit.MEDIUM
109
MICROBURST WINDSHEAR PROBABILITY
GUIDELINES OBSERVATION PROBABILITY OF
WINDSHEAR PRESENCE OF CONVECTIVE WEATHER NEAR
INTENDED FLIGHT PATH With localized strong
winds (Tower reports or observed blowing dust,
rings of dust, tornado-like features, etc. )
..HIGH With heavy precipitation
(Observed or radar indications of contour, red or
attenuation shadow) ..HIGH With rainshower
MEDIUM With lightning
MEDIUM With virga..MEDIUM
With moderate or greater turbulence (reported
or radar indications)MEDIUM With
temperature/dew point spread between 30 and 50
degrees Fahrenheit.MEDIUM
110
MICROBURST WINDSHEAR PROBABILITY
GUIDELINES OBSERVATION PROBABILITY OF
WINDSHEAR PRESENCE OF CONVECTIVE WEATHER NEAR
INTENDED FLIGHT PATH With localized strong
winds (Tower reports or observed blowing dust,
rings of dust, tornado-like features, etc. )
..HIGH With heavy precipitation
(Observed or radar indications of contour, red or
attenuation shadow) ..HIGH With rainshower
MEDIUM With lightning
MEDIUM With virga..MEDIUM
With moderate or greater turbulence (reported
or radar indications)MEDIUM With
temperature/dew point spread between 30 and 50
degrees Fahrenheit.MEDIUM
111
MICROBURST WINDSHEAR PROBABILITY
GUIDELINES OBSERVATION PROBABILITY OF
WINDSHEAR PRESENCE OF CONVECTIVE WEATHER NEAR
INTENDED FLIGHT PATH With localized strong
winds (Tower reports or observed blowing dust,
rings of dust, tornado-like features, etc. )
..HIGH With heavy precipitation
(Observed or radar indications of contour, red or
attenuation shadow) ..HIGH With rainshower
MEDIUM With lightning
MEDIUM With virga..MEDIUM
With moderate or greater turbulence (reported
or radar indications)MEDIUM With
temperature/dew point spread between 30 and 50
degrees Fahrenheit.MEDIUM
112
MICROBURST WINDSHEAR PROBABILITY
GUIDELINES OBSERVATION PROBABILITY OF
WINDSHEAR PRESENCE OF CONVECTIVE WEATHER NEAR
INTENDED FLIGHT PATH With localized strong
winds (Tower reports or observed blowing dust,
rings of dust, tornado-like features, etc. )
..HIGH With heavy precipitation
(Observed or radar indications of contour, red or
attenuation shadow) ..HIGH With rainshower
MEDIUM With lightning
MEDIUM With virga..MEDIUM
With moderate or greater turbulence (reported
or radar indications)MEDIUM With
temperature/dew point spread between 30 and 50
degrees Fahrenheit.MEDIUM
113
MICROBURST WINDSHEAR PROBABILITY
GUIDELINES OBSERVATION PROBABILITY OF
WINDSHEAR PRESENCE OF CONVECTIVE WEATHER NEAR
INTENDED FLIGHT PATH With localized strong
winds (Tower reports or observed blowing dust,
rings of dust, tornado-like features, etc. )
..HIGH With heavy precipitation
(Observed or radar indications of contour, red or
attenuation shadow) ..HIGH With rainshower
MEDIUM With lightning
MEDIUM With virga..MEDIUM
With moderate or greater turbulence (reported
or radar indications)MEDIUM With
temperature/dew point spread between 30 and 50
degrees Fahrenheit.MEDIUM
114
MICROBURST WINDSHEAR PROBABILITY
GUIDELINES OBSERVATION PROBABILITY OF
WINDSHEAR PRESENCE OF CONVECTIVE WEATHER NEAR
INTENDED FLIGHT PATH With localized strong
winds (Tower reports or observed blowing dust,
rings of dust, tornado-like features, etc. )
..HIGH With heavy precipitation
(Observed or radar indications of contour, red or
attenuation shadow) ..HIGH With rainshower
MEDIUM With lightning
MEDIUM With virga..MEDIUM
With moderate or greater turbulence (reported
or radar indications)MEDIUM With
temperature/dew point spread between 30 and 50
degrees Fahrenheit.MEDIUM
115

• MICROBURST WINDSHEAR PROBABILITY GUIDELINES
• OBSERVATION PROBABILITY
• OF WINDSHEAR
• PRESENCE OF CONVECTIVE WEATHER
• NEAR INTENDED FLIGHT PATH
• ONBOARD WINDSHEAR DETECTION SYSTEM ALERT
  (Reported
• or observed).HIGH
• PIREP OF AIRSPEED LOSS OR GAIN
• 15 knots or greater..HIGH
• Less than 15 knots .MEDIUM
• LLWAS ALERT/WIND VELOCITY CHANGE
• - 20 knots or greater HIGH
• - Less than 20 knots MEDIUM
• FORECAST OF CONVECTIVE WEEATHER ..LOW

116

• MICROBURST WINDSHEAR PROBABILITY GUIDELINES
• OBSERVATION PROBABILITY
• OF WINDSHEAR
• PRESENCE OF CONVECTIVE WEATHER
• NEAR INTENDED FLIGHT PATH
• ONBOARD WINDSHEAR DETECTION SYSTEM ALERT
  (Reported
• or observed).HIGH
• PIREP OF AIRSPEED LOSS OR GAIN
• 15 knots or greater..HIGH
• Less than 15 knots .MEDIUM
• LLWAS ALERT/WIND VELOCITY CHANGE
• - 20 knots or greater HIGH
• - Less than 20 knots MEDIUM
• FORECAST OF CONVECTIVE WEEATHER ..LOW

117

• MICROBURST WINDSHEAR PROBABILITY GUIDELINES
• OBSERVATION PROBABILITY
• OF WINDSHEAR
• PRESENCE OF CONVECTIVE WEATHER
• NEAR INTENDED FLIGHT PATH
• ONBOARD WINDSHEAR DETECTION SYSTEM ALERT
  (Reported
• or observed).HIGH
• PIREP OF AIRSPEED LOSS OR GAIN
• 15 knots or greater..HIGH
• Less than 15 knots .MEDIUM
• LLWAS ALERT/WIND VELOCITY CHANGE
• - 20 knots or greater HIGH
• - Less than 20 knots MEDIUM
• FORECAST OF CONVECTIVE WEEATHER ..LOW

118

• MICROBURST WINDSHEAR PROBABILITY GUIDELINES
• OBSERVATION PROBABILITY
• OF WINDSHEAR
• PRESENCE OF CONVECTIVE WEATHER
• NEAR INTENDED FLIGHT PATH
• ONBOARD WINDSHEAR DETECTION SYSTEM ALERT
  (Reported
• or observed).HIGH
• PIREP OF AIRSPEED LOSS OR GAIN
• 15 knots or greater..HIGH
• Less than 15 knots .MEDIUM
• LLWAS ALERT/WIND VELOCITY CHANGE
• - 20 knots or greater HIGH
• - Less than 20 knots MEDIUM
• FORECAST OF CONVECTIVE WEEATHER ..LOW

119

• MICROBURST WINDSHEAR PROBABILITY GUIDELINES
• OBSERVATION PROBABILITY
• OF WINDSHEAR
• PRESENCE OF CONVECTIVE WEATHER
• NEAR INTENDED FLIGHT PATH
• ONBOARD WINDSHEAR DETECTION SYSTEM ALERT
  (Reported
• or observed).HIGH
• PIREP OF AIRSPEED LOSS OR GAIN
• 15 knots or greater..HIGH
• Less than 15 knots .MEDIUM
• LLWAS ALERT/WIND VELOCITY CHANGE
• - 20 knots or greater HIGH
• - Less than 20 knots MEDIUM
• FORECAST OF CONVECTIVE WEEATHER ..LOW

120

• MICROBURST WINDSHEAR PROBABILITY GUIDELINES
• OBSERVATION PROBABILITY
• OF WINDSHEAR
• PRESENCE OF CONVECTIVE WEATHER
• NEAR INTENDED FLIGHT PATH
• ONBOARD WINDSHEAR DETECTION SYSTEM ALERT
  (Reported
• or observed).HIGH
• PIREP OF AIRSPEED LOSS OR GAIN
• 15 knots or greater..HIGH
• Less than 15 knots .MEDIUM
• LLWAS ALERT/WIND VELOCITY CHANGE
• - 20 knots or greater HIGH
• - Less than 20 knots MEDIUM
• FORECAST OF CONVECTIVE WEEATHER ..LOW

121
MICROBURST WINDSHEAR PROBABILITY
GUIDELINES OBSERVATION PROBABILITY OF
WINDSHEAR NOTE These guidelines apply to
operations in the airport vicinity (within 3
miles of the point of takeoff or landing along
the intended flight path and below 1000 feet
AGL). The clues should be considered
cumulative. If more than one is observed the
probability weighting should be increased, The
hazard increases with proximity to the convective
weather, Weather assessment should be made
continuously. CAUTION CURRENTLY NO QUANTITATIVE
MEANS EXISTS FOR DETERMINING THE PRESENCE OR
INTENSITY OF MICROBURST WINDSHEAR, PILOTS ARE
URGED TO EXERCISE CAUTION IN DETERMINING A COURSE
OF ACTION.
122
WINDSHEARThere I was
123
Close Call for Reagan!

• Strongest microburst ever recorded occurred at
  Andrews AFB on 1 Aug 83, at 1410.
• Air Force One had landed at 1404.
• The wind difference between front and back
  exceeded 214 knots!

124
Brush up time
Test
125
Brush up time
Winds. Wind information plotted uses the
Shaft-Barb-Pennant method The FROM direction
which the wind is blowing is represented by the
shaft or a line. The wind speed is represented
by the barb or pennant. A short barb represents 5
knots and a long barb represents 10 knots.
Pennants are 50-knot winds. Wind directions are
plotted to the nearest 10 degrees relative
to true north.
126
1 Aug 83
127
300/015
330/065
300/110
128
The Devil and Delta 191 It Was No Act of
God by J. Mac McClellan Flying
Magazine January 1987
129
CVR from Delta 191 (DFW)

• CP says Theres lightning comin out of that
  one. (60418)
• Captain is more concerned about his
  malfunctioning DME (60440)

130
CVR from Delta 191 (DFW)

• Capt says Watch your speed. CP replies, Ive
  got em in idle! (060518)
• Speed had increased from 150 KIAS up to 173 KIAS

131
CVR from Delta 191 (DFW)

• Capt anticipates the windshear Youre gonna
  lose it all of a sudden there it is. (60522)
• Speed dropped from 173 KIAS to 129 KIAS Vref
  137 knots

132
CVR from Delta 191 (DFW)

• Capt says, Push it up push it way up. Way up.
  Way up--thats it. (60524)
• Sound of fans spooling up, then being pulled back
  again (60531)
• AOA goes from 6 to 23 within 1 second pitch
  15.7 to - 8.5 over 5000 fpm VVI 2Gs to -0.3Gs

133
CVR from Delta 191 (DFW)

• GPWS begins to sound (60543)
• Capt commands TOGO! (60545)
• CP says Push it way up! (60547)
• Oh, ! (60553)
• Hit the water tanks doing 200 KIAS

134
AIRCREW ACTIONS

• AVOID!
• Analyze the weather
• Select the most appropriate runway
• Use the appropriate flap setting
• Consider using max power
• Be ready to use the escape maneuver

135
Consider a Go-Around . . .

• /- 15 KIAS
• /- 500 fpm VVI
• /- 5 degrees of pitch
• /- one dot on glide slope
• Unusual throttle position for an extended period
  of time

136
Critiques
137
REVIEW

• 1. Micro bursts have a total horizontal extent
  of LESS THAN 2.5 NM
• 2. Microbursts reach maximum intensity 5
  MINUTES AFTER GROUND CONTACT
• 3. Frontal shears can occur 30 - 60 MINUTES
  AFTER PASSAGE OF A COLD FRONT AND 6 - 12 HOURS
  PRIOR TO PASSAGE OF A WARM FRONT

138
REVIEW CONTINUED

• 4. The major causes of windshear are frontal
  passages, convective activity, and mountain wave
  turbulence. FALSE
• 5. The two weather phenomena that are prime
  producers of microbursts are high based
  thunderstorms and small, rapidly developing
  cells. TRUE

139
REVIEW CONTINUED

• 6. Shears produced by a WARM FRONT are more
  severe than those produced by a COLD FRONT.