WINDSHEAR Lt Col Wally Emerson 15 April 2007. WHY STUDY WINDSHEAR? 744 Dead 287 Injured CONUS Only...

WINDSHEAR

Lt Col Wally Emerson 15 April 2007Lt Col Wally Emerson 15 April 2007

WHY STUDY WINDSHEAR?

744 Dead744 Dead287 Injured287 Injured

CONUS OnlySince 1964

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.

OVERVIEW

1) Windshear weather, particularly microbursts, and clues which may indicate its presence,2) Effects of windshear on airplanes3) Windshear recognition cockpit, and avoidance,4) Precautions to take when windshear is suspected,5) Standard operating techniques related to windshear6) Recovery techniques to an inadvertent windshearencounter.

WINDSHEARDefinitions

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.

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.

WINDSHEAR

WIND SHEAR AC 00-54

Severe Windshear - A rapid change inwind direction or velocity causing

airspeed changes greater than 15 knotsor vertical speed changes greater than

500 feet per minute.

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.

WINDSHEARWeather to look out for

WINDSHEARDuring 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.

WINDSHEAROnce 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.

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.

WINDSHEARThe 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.

WINDSHEARAs 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.

WINDSHEARAnother 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

MICROBURSTS

“The Granddaddy of all Windshears”

Microbursts: Dry or Wet Wet microbursts are more common in Wet microbursts are more common in

places like the Mississippi valley where places like the Mississippi valley where thunderstorm bases tend to be much lower.thunderstorm bases tend to be much lower.

Dry microbursts occur primarily in the high Dry microbursts occur primarily in the high plains/intermountain's where the plains/intermountain's where the temperature/dew point spread is wide (30° temperature/dew point spread is wide (30° to 50°)to 50°)

Downburst/Microburst Definition

A downburst is HEAVY COLD/MOIST air dropping A downburst is HEAVY COLD/MOIST air dropping spilling out producing horizontal shears along a damage spilling out producing horizontal shears along a damage path of 1-5 miles .path of 1-5 miles .

A microburst is a downburst that covers an area less than A microburst is a downburst that covers an area less than 3 miles with peak winds that last 2–5 minutes.3 miles with peak winds that last 2–5 minutes.

Why are they important? Eastern Airlines Flight 66 crashed 24 June 1975Eastern Airlines Flight 66 crashed 24 June 1975

August 1983 near miss at Andrews AFBAugust 1983 near miss at Andrews AFB

Fast winds with rapidly shifting directions are bad for Fast winds with rapidly shifting directions are bad for planes trying to take off or landplanes trying to take off or land

There are typically 50–100 downbursts each year during There are typically 50–100 downbursts each year during the convective seasonthe convective season

Downdraft FormationTwo main mechanisms:Two main mechanisms:

– EvaporationEvaporation Cools the air; cold air sinksCools the air; cold air sinks Rain that evaporates before reaching the ground is called Rain that evaporates before reaching the ground is called

virgavirga Cold air can descend as fast as 40–60 m.p.h.Cold air can descend as fast as 40–60 m.p.h.

– Drag forceDrag force Falling precipitation drags air down with it, creating fast Falling precipitation drags air down with it, creating fast

descending airdescending air One raindrop is inconsequential but many drops have a One raindrop is inconsequential but many drops have a

large effect on air flowlarge effect on air flow

Downburst/Microburst Structure

Weak environmental wind fieldWeak environmental wind field– Downburst is symmetricalDownburst is symmetrical

– Equal speed/damage on all sidesEqual speed/damage on all sides

Weak environmental wind field or more stationary the frontWeak environmental wind field or more stationary the front

Aircraft will experience equal headwinds and tailwindsAircraft will experience equal headwinds and tailwinds

Downburst/Microburst Structure

Strong environmental wind fieldStrong environmental wind field– AsymmetricalAsymmetrical

– Strongest wind is downwind of Strongest wind is downwind of stagnation conestagnation cone

– May produce a well-defined “foot” May produce a well-defined “foot” shape to precipitationshape to precipitation

Strong environmental wind field or fast moving frontStrong environmental wind field or fast moving front

Aircraft will experience bigger kick on the backsideAircraft will experience bigger kick on the backside

Vortex Ring

WINDSHEAREvolution of a microburst. Microburst winds intensify for about 5 min after ground contact and typically dissipate about 10 to 20 min after ground contact.

DRY MICROBURST

In this example, air below a cloud base (up to approximately 15,000 feetAGL) is very dry. Precipitation from higher convective clouds falls intolow 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.

WINDSHEARGreatest danger: Takeoff and landingGreatest danger: Takeoff and landing

1.1. During landing, the pilot has already reduced During landing, the pilot has already reduced engine power and may not have time to increase engine power and may not have time to increase speedspeed

2.2. During takeoff, an aircraft is near stall speedDuring takeoff, an aircraft is near stall speed

General

Windshear, particularly low altitude windshear encounters, are Windshear, particularly low altitude windshear encounters, are of significant importance because it can place the flight crew in of significant importance because it can place the flight crew in a situation where the a situation where the maximum performance capability of the maximum performance capability of the aircraft is requiredaircraft is required. Windshear encounters . Windshear encounters below 500ft are the below 500ft are the most threateningmost threatening because there is very little time or altitude to because there is very little time or altitude to respond and recover from an inadvertent encounter.respond and recover from an inadvertent encounter.

General

Knowledge of how windshear affects performance can be Knowledge of how windshear affects performance can be essential to a successful recovery maneuver following an essential to a successful recovery maneuver following an inadvertent windshear encounter.inadvertent windshear encounter.

General

Windshear that improves performance will be first indicated in Windshear that improves performance will be first indicated in the cockpit by an increased airspeed. Pilot reaction – reduce the cockpit by an increased airspeed. Pilot reaction – reduce thrust.thrust.

With power back you experience a shear in the With power back you experience a shear in the reversereverse sense sense that will decrease airspeed and degrade vertical flight path that will decrease airspeed and degrade vertical flight path performance.performance.

General

The magnitude of the pitch change is a function of the followingThe magnitude of the pitch change is a function of the following

- Aircraft configuration - Aircraft configuration - Weight - Weight - Speed - Speed - C of G - C of G - Thrust - Thrust - Severity of airspeed change - Severity of airspeed change

General

If an attempt is made to regain lost speed by lowering the nose, If an attempt is made to regain lost speed by lowering the nose, the combination of decreasing airspeed and decreasing pitch the combination of decreasing airspeed and decreasing pitch attitude produces a high rate of descent. In some circumstances attitude produces a high rate of descent. In some circumstances as little as 5 seconds may be availableas little as 5 seconds may be available to recognize and react to to recognize and react to a degrading vertical flight path.a degrading vertical flight path.

General

INDICATORS OF WINDSHEAR:INDICATORS OF WINDSHEAR:

•SIGMETSSIGMETS

•Visual signs (T-storms, black wall of death, tornados etc..)Visual signs (T-storms, black wall of death, tornados etc..)

•Unusual control forces required Unusual control forces required

•Significant changes in airspeed occurSignificant changes in airspeed occur

•PIREPSPIREPS

General

Crew Actions - Take-off Windshear PrecautionsCrew Actions - Take-off Windshear Precautions

Maximum thrust should be usedMaximum thrust should be used

If practical the longest suitable runway available should be If practical the longest suitable runway available should be used, provided it is clear of areas of known windshear.used, provided it is clear of areas of known windshear.

The flight director should not be relied upon during take-off in The flight director should not be relied upon during take-off in suspected windshear conditions. The attitude director is the suspected windshear conditions. The attitude director is the primary reference for pitch attitude.primary reference for pitch attitude.

General


Crews should be alert for airspeed fluctuations during take-off Crews should be alert for airspeed fluctuations during take-off and initial climb. Such fluctuations may be the first indication and initial climb. Such fluctuations may be the first indication of windshear. Control forces may be different from those of windshear. Control forces may be different from those expected, especially if airspeed is below the in-trim speed.expected, especially if airspeed is below the in-trim speed.

General


Crew co-ordination and awareness are very important. Close Crew co-ordination and awareness are very important. Close monitoring of the flight instruments is imperative, and the non-monitoring of the flight instruments is imperative, and the non-handling pilot should be especially aware of these and call out handling pilot should be especially aware of these and call out any deviations from normal values.any deviations from normal values.

General


The stick shaker must be respected at all times. If it is activated, The stick shaker must be respected at all times. If it is activated, pitch attitude should be reduced just enough to stop the stick pitch attitude should be reduced just enough to stop the stick shaker. Flight with intermittent stick shaker operation may be shaker. Flight with intermittent stick shaker operation may be required to maintain a positive rate of climb during a windshear required to maintain a positive rate of climb during a windshear encounter.encounter.

MAX PERFORMANCE – just in and out of stick shakerMAX PERFORMANCE – just in and out of stick shaker

Effect on AirplanesWindshear encounter during takeoff after liftoff.

(1) Takeoff initially appears normal.

(2) Windshear encountered just after liftoff.

(3) Airspeed decrease resulted in pitch attitude reduction.

(4) Aircraft crashed off departure end of runway 20 set after liftoff.

Effect on AirplanesWindshear encounter during takeoff on runway.

1. Takeoff initially appeared normal.

2. Airspeed buildup slowed due to windshear.

3. Airplane reached VR near end of runway, lifted off but failed to climb.

4. Airplane contacted obstacle off departure end of runway.

General

Crew Actions - Approach and Landing Windshear Crew Actions - Approach and Landing Windshear

Large thrust reductions or trim changes in response to a sudden Large thrust reductions or trim changes in response to a sudden airspeed increase should be avoided as these may be followed airspeed increase should be avoided as these may be followed by a decrease in airspeed.by a decrease in airspeed.

General

Crew Actions - Approach and Landing Windshear Crew Actions - Approach and Landing Windshear

In windshear conditions flight director commands should be In windshear conditions flight director commands should be checked against ADI, and altimeters. These instruments are the checked against ADI, and altimeters. These instruments are the primary references for vertical flight path control.primary references for vertical flight path control.

Effect on AirplanesWindshear encounter during approach.

1. Approach initially appeared normal.

2. Increasing downdraft and tailwind encountered at transition.

3. Airspeed decrease combined with reduced visual cues resulted in pitch attitude reduction.

4. Airplane crashed short of approach end of runway.

GeneralCrew Actions - Windshear Recovery ManeuverCrew Actions - Windshear Recovery Maneuver

As a guide, marginal flight path control may be indicated by As a guide, marginal flight path control may be indicated by uncontrolled changes from the normal steady state flight uncontrolled changes from the normal steady state flight conditions in excess of:conditions in excess of:

- 15 knots indicated airspeed - 15 knots indicated airspeed - 500 fpm vertical speed - 500 fpm vertical speed - 5 degrees pitch attitude - 5 degrees pitch attitude - 1 dot glideslope displacement - 1 dot glideslope displacement

General

Crew Actions - Windshear Recovery ManeuverCrew Actions - Windshear Recovery Maneuver

Whenever flight path control becomes marginal below 500ft Whenever flight path control becomes marginal below 500ft AGL, or when the "WINDSHEAR" or "PULL UP" warning AGL, or when the "WINDSHEAR" or "PULL UP" warning occurs, simultaneously:-occurs, simultaneously:-

- Call "Windshear Go-around" - Call "Windshear Go-around" - Complete the rest of "Windshear" recall items (QRH)- Complete the rest of "Windshear" recall items (QRH)

General


The call of "Windshear Go-around will advise the non-handling The call of "Windshear Go-around will advise the non-handling pilot that the usual go-around procedure does not apply and that pilot that the usual go-around procedure does not apply and that speeds and pitch attitudes may not be normal for a go-around.speeds and pitch attitudes may not be normal for a go-around.

General

Crew Actions – Crew Actions –

Windshears which exceed the performance capabilities of both Windshears which exceed the performance capabilities of both small and large aircraft have and will occur below 500ft. The small and large aircraft have and will occur below 500ft. The flight crew should search for any clues to the presence of flight crew should search for any clues to the presence of windshear along the intended flight path.windshear along the intended flight path.

General

Crews should carefully review all available information such as Crews should carefully review all available information such as pilot reports of windshear or turbulence, low level windshear pilot reports of windshear or turbulence, low level windshear reports and weather reports - especially thunderstorms and reports and weather reports - especially thunderstorms and 'virga'.'virga'.

General

Windshear that produces uncommanded airspeed changes of 15 Windshear that produces uncommanded airspeed changes of 15 knots or more is regarded as knots or more is regarded as severesevere.. Areas of known windshear Areas of known windshear should be avoided and pilots should delay take-off or should be avoided and pilots should delay take-off or discontinue an approach until conditions have improved discontinue an approach until conditions have improved wherever necessary.wherever necessary.

General

Windshear encounters should be reported precisely and Windshear encounters should be reported precisely and promptly to assist other pilots. Accurate pilot reports of promptly to assist other pilots. Accurate pilot reports of windshear can be a valuable clue as to the presence and severity windshear can be a valuable clue as to the presence and severity of windshear conditions.of windshear conditions.

General

Windshear Effects on SystemsWindshear Effects on Systems

AltimetersAltimetersDuring callouts and instrument scan in a windshear, use During callouts and instrument scan in a windshear, use

of radio and/or barometric altimeters must be tempered by the of radio and/or barometric altimeters must be tempered by the characteristics of each. Since radio altitude is subject to terrain characteristics of each. Since radio altitude is subject to terrain contours, the indicator may show a climb or descent due to contours, the indicator may show a climb or descent due to falling or rising terrain, respectively. The barometric altimeter falling or rising terrain, respectively. The barometric altimeter may also provide distorted indications due to pressure variations may also provide distorted indications due to pressure variations within the microburst.within the microburst.

General


Vertical Speed IndicatorsVertical Speed IndicatorsThe vertical speed indicator (VSI) should not be solely The vertical speed indicator (VSI) should not be solely

relied upon to provide accurate vertical speed information. Due relied upon to provide accurate vertical speed information. Due to instrument lags, indications may be several seconds behind to instrument lags, indications may be several seconds behind actual airplane rate-of-climb/descent and, in some situations, actual airplane rate-of-climb/descent and, in some situations, may indicate a climb after the airplane has started descending. may indicate a climb after the airplane has started descending. Vertical speed indicators driven by an Inertial Reference Unit Vertical speed indicators driven by an Inertial Reference Unit (IRU) show significant improvement over other type (IRU) show significant improvement over other type instruments but still have some lag.instruments but still have some lag.

General


Vertical Speed IndicatorsVertical Speed IndicatorsIn addition, gust induced pitot static pressure In addition, gust induced pitot static pressure

variations within the microburst may introduce further VSI variations within the microburst may introduce further VSI inaccuracies. Due to such lags and errors, all vertical flight path inaccuracies. Due to such lags and errors, all vertical flight path instruments should be cross-checked to verify climb/descent instruments should be cross-checked to verify climb/descent trends. trends.

General


C-21 Windshear RecoveryC-21 Windshear Recovery

ThrustAggressively apply necessary thrust (not less than go-aroundthrust) 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.

General


C-21 Windshear RecoveryC-21 Windshear RecoveryPitchFor 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.

General


C-21 Windshear RecoveryC-21 Windshear RecoveryPitchThe 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.

General


C-21 Windshear RecoveryC-21 Windshear RecoveryPitchIn 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.

General


C-21 Windshear RecoveryC-21 Windshear RecoveryPitchRapidly 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/undershoot of the desired attitude. Once the airplane is climbing, and ground contact is no longer an immediate concern, airspeed should be increased by cautiousreductions in pitch attitude.

General


C-21 Windshear RecoveryC-21 Windshear RecoveryConfigurationDo 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.

General


C-21 Windshear RecoveryC-21 Windshear RecoveryConfigurationExtending 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.

Quick reviewQuick review

1-3 miles in width1-3 miles in width

Downdraft shaft 1 Downdraft shaft 1 mile diametermile diameter

Downdraft up to 6000 feet/minuteDowndraft up to 6000 feet/minute

Up to 90 knots horizontal shearUp to 90 knots horizontal shear

Downdraft up to 6000 feet/minuteDowndraft up to 6000 feet/minute

Up to 90 knots horizontal shearUp to 90 knots horizontal shear

Duration 15 minutes or less…but once microburst activity starts Duration 15 minutes or less…but once microburst activity starts not uncommon for multiple microburst'snot uncommon for multiple microburst's

Downbursts

Approach to PreventionApproach to Prevention

Headwind increases – Headwind increases – experience increased experience increased performance/pitches upperformance/pitches up

Headwind decreases until Headwind decreases until downdraft – experience downdraft – experience decreased decreased performance/pitches downperformance/pitches down

Initiate go-around – experiencing Initiate go-around – experiencing increasing tail wind and decreasing increasing tail wind and decreasing performanceperformance

- 15 knots indicated airspeed - 15 knots indicated airspeed - 500 fpm vertical speed - 500 fpm vertical speed - 5 degrees pitch attitude - 5 degrees pitch attitude - 1 dot glideslope displacement - 1 dot glideslope displacement

SOLUTION

Detection EquipmentDetection Equipment

–Ground-BasedGround-Based

–AirborneAirborne EducationEducation

Ground-Based Detection (NEXRAD) Doppler Radar(NEXRAD) Doppler Radar(6 Min)(6 Min)

(LLWAS) Low Level Windshear (LLWAS) Low Level Windshear Alerting SystemAlerting System– Barometric Pressure Jump IndicatorsBarometric Pressure Jump Indicators

(TDWR) Terminal Doppler (TDWR) Terminal Doppler Weather Radar Weather Radar (2 Min)(2 Min)

AIRBORNE DETECTION

PredictivePredictive– Alerts Crew Prior to EntryAlerts Crew Prior to Entry

Non-PredictiveNon-Predictive– Alerts Crew That Windshear Has Been EnteredAlerts Crew That Windshear Has Been Entered– ““Test Probe”Test Probe”

AIRBORNE DETECTION

PredictivePredictive– Alerts Crew Prior to EntryAlerts Crew Prior to Entry– KC-135 (WXR-700X)KC-135 (WXR-700X)

PWS (in auto) – automatic during T/O & Land PWS (in auto) – automatic during T/O & Land – +- 60*, 5 miles in front (microburst windshear detection)+- 60*, 5 miles in front (microburst windshear detection)

– Gives warning, caution or advisoryGives warning, caution or advisory

WARNINGWARNING

If a windshear warning alert occurs during final approach, If a windshear warning alert occurs during final approach, pilots should consider executing go-around procedurespilots should consider executing go-around procedures

AIRBORNE DETECTION

Non-PredictiveNon-Predictive– Alerts Crew That Windshear Has Been EnteredAlerts Crew That Windshear Has Been Entered– ““Test Probe”Test Probe”

AIRBORNE DETECTION

SIGMETSSIGMETS VISUAL CLUESVISUAL CLUES PIREPSPIREPS

What Do We Have?

EDUCATION!

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.

Months & Time of Day

WEATHER FACTORS

Convective65%

Convective65%

Fronts15%

Fronts15%

Other20%

Other20%

If you avoid any precipitation and If you avoid any precipitation and fronts, you avoid fronts, you avoid 80%80% of the threat! of the threat!

Watch Out for Fronts If . . .

The temperature differential exceeds The temperature differential exceeds 10 degrees Fahrenheit10 degrees Fahrenheit

The front is moving faster than 30 The front is moving faster than 30 knotsknots

Cold Fronts

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

Warm Fronts

Be alert for windshear below 1,000 Be alert for windshear below 1,000 feet AGL six to twelve hours feet AGL six to twelve hours priorprior to to frontal passagefrontal passage

Warm front shears tend to be more Warm front shears tend to be more severesevere

Microburst Producers

High-Based ThunderstormsHigh-Based Thunderstorms Small Rapidly-Developing CellsSmall Rapidly-Developing Cells Anything that Produces ConvectionAnything that Produces Convection

– Convection is Responsible for 90% Convection is Responsible for 90% of Windshear-Related Accidentsof Windshear-Related Accidents

Microbursts: Dry or Wet Dry microbursts occur primarily in the high Dry microbursts occur primarily in the high

plains/intermountains where the plains/intermountains where the temperature/dew point spread is wide (30° temperature/dew point spread is wide (30° to 50°)to 50°)

Wet microbursts are more common in Wet microbursts are more common in places like the Mississippi valley where places like the Mississippi valley where thunderstorm bases tend to be much lower.thunderstorm bases tend to be much lower.

A

B

Can you see Can you see the micro the micro burst?burst?

C

D


E

F


http://www.cimms.ou.edu/~doswell/microbursts/Figure_17b.JPG

F


http://www.cimms.ou.edu/~doswell/microbursts/Figure_13.JPG

B


Microburst About 5% of all thunderstorms produce About 5% of all thunderstorms produce

microburstsmicrobursts WetWet

– Places like the Mississippi River ValleyPlaces like the Mississippi River Valley Convective activity with low basesConvective activity with low bases Heavy rainHeavy rain

Dry Microbursts

Microburst DryDry

– High plains/interior mountainsHigh plains/interior mountains Convective activity forms at higher levelsConvective activity forms at higher levels

– Thunderstorm base 10,000 - 15,000 MSLThunderstorm base 10,000 - 15,000 MSL Dry surface conditionsDry surface conditions Surface Temperature of 80+ degrees FSurface Temperature of 80+ degrees F Wide temp/dew point spreadWide temp/dew point spread

– 30 - 50 degrees F30 - 50 degrees F VirgaVirga

Visual Identification (Dry)

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

- Blowing dust/dust rings at surface- Blowing dust/dust rings at surface

Dry MicroburstsThe microburst is rendered visible by an expanding ring of dust The microburst is rendered visible by an expanding ring of dust under a virga shaft descending from a high-based cumulonimbus. under a virga shaft descending from a high-based cumulonimbus. The precipitation largely evaporates before reaching the surface, The precipitation largely evaporates before reaching the surface, so the surface rainfall is probably no more than a trace. As the so the surface rainfall is probably no more than a trace. As the microburst pictured in the previous developed, the ring of dust microburst pictured in the previous developed, the ring of dust spread out over the surfacespread out over the surface

Here is a time lapse of a dry microburstNote the difference in wind speed and direction

Visual Identification (Wet)

Heavy precipHeavy precip Rain foot (Huh?)Rain foot (Huh?)

http://www.cimms.ou.edu/~doswell/chasesums/chase97_18.JPG

MICROBURST WINDSHEAR PROBABILITY GUIDELINESOBSERVATION PROBABILITY

OF WINDSHEARPRESENCE OF CONVECTIVE WEATHERNEAR INTENDED FLIGHT PATH:

With localized strong winds (Tower reports orobserved blowing dust, rings of dust,tornado-like features, etc. ) ………………………………..HIGHWith heavy precipitation (Observed or radarindications of contour, red or attenuation shadow) ………..HIGHWith rainshower ……………………………………………MEDIUMWith lightning………………………………………………MEDIUMWith virga…………………………………………………..MEDIUMWith moderate or greater turbulence (reported orradar indications)……………………………………………MEDIUMWith temperature/dew point spread between30 and 50 degrees Fahrenheit……………………………….MEDIUM


OF WINDSHEARPRESENCE OF CONVECTIVE WEATHER NEAR INTENDED FLIGHT PATH:

ONBOARD WINDSHEAR DETECTION SYSTEM ALERT (Reportedor observed)………………………………………………….HIGHPIREP 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


OF WINDSHEAR

NOTE: These guidelines apply to operations in the airport vicinity (within3 miles of the point of takeoff or landing along the intended flightpath 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.

WINDSHEARThere I was

Close Call for Reagan!

Strongest microburst ever recorded Strongest microburst ever recorded occurred at Andrews AFB on 1 Aug occurred at Andrews AFB on 1 Aug 83, at 1410. 83, at 1410.

Air Force One had landed at 1404. Air Force One had landed at 1404. The wind difference between front and The wind difference between front and

back exceeded 214 knots!back exceeded 214 knots!

Brush up timeTest

Brush up timeWinds. 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 isrepresented 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 totrue north.

1 Aug 83

300/015300/015

330/065330/065

300/110300/110

““The Devil and Delta 191:The Devil and Delta 191:It Was No Act of God”It Was No Act of God”

by J. Mac McClellanby J. Mac McClellan

Flying MagazineFlying MagazineJanuary 1987January 1987

CVR from Delta 191 (DFW)

CP says “There’s lightning comin’ out CP says “There’s lightning comin’ out of that one.” (6:04:18)of that one.” (6:04:18)

Captain is more concerned about his Captain is more concerned about his malfunctioning DME (6:04:40)malfunctioning DME (6:04:40)


Capt says “Watch your speed.” CP Capt says “Watch your speed.” CP replies, “I’ve got ‘em in idle!” replies, “I’ve got ‘em in idle!” (06:05:18) (06:05:18)

Speed had increased from 150 KIAS Speed had increased from 150 KIAS up to 173 KIASup to 173 KIAS


Capt anticipates the windshear: Capt anticipates the windshear: “You’re gonna lose it all of a sudden; “You’re gonna lose it all of a sudden; there it is.” (6:05:22) there it is.” (6:05:22)

Speed dropped from 173 KIAS to 129 Speed dropped from 173 KIAS to 129 KIAS; Vref = 137 knotsKIAS; Vref = 137 knots


Capt says, “Push it up; push it way up. Capt says, “Push it up; push it way up. Way up. Way up--that’s it.” (6:05:24) Way up. Way up--that’s it.” (6:05:24)

Sound of fans spooling up, then being Sound of fans spooling up, then being pulled back again (6:05:31)pulled back again (6:05:31)

AOA goes from 6 to 23 within 1 AOA goes from 6 to 23 within 1 second; pitch +15.7 to - 8.5; over 5000 second; pitch +15.7 to - 8.5; over 5000 fpm VVI; 2Gs to -0.3Gsfpm VVI; 2Gs to -0.3Gs


GPWS begins to sound (6:05:43)GPWS begins to sound (6:05:43) Capt commands “TOGO!” (6:05:45)Capt commands “TOGO!” (6:05:45) CP says “Push it way up!” (6:05:47)CP says “Push it way up!” (6:05:47) ““Oh, #%$!” (6:05:53)Oh, #%$!” (6:05:53) Hit the water tanks doing 200 KIASHit the water tanks doing 200 KIAS

AIRCREW ACTIONS

AVOID!AVOID! Analyze the weatherAnalyze the weather Select the most appropriate runwaySelect the most appropriate runway Use the appropriate flap settingUse the appropriate flap setting Consider using max powerConsider using max power Be ready to use the escape maneuverBe ready to use the escape maneuver

Consider a Go-Around . . .

+/- 15 KIAS+/- 15 KIAS +/- 500 fpm VVI+/- 500 fpm VVI +/- 5 degrees of pitch+/- 5 degrees of pitch +/- one dot on glide slope+/- one dot on glide slope Unusual throttle position for Unusual throttle position for

an extended period of timean extended period of time

Critiques

WINDSHEAR Lt Col Wally Emerson 15 April 2007. WHY STUDY WINDSHEAR? 744 Dead 287 Injured CONUS Only...

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Transcript of WINDSHEAR Lt Col Wally Emerson 15 April 2007. WHY STUDY WINDSHEAR? 744 Dead 287 Injured CONUS Only...