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Airborne

Wind Shear

Detection and

Warning Systems

Third Combined Manufacturers'

and Technologists" Conference

Compiled by

Dan D. Vicmy

and Roland L. Bowles

NASA Langley Research Center

Hampton, Virginia

Herbert Schlickenmaier

Federal Aviation Administration

Washington, D.C.

Proceedings of a conference sponsored by the

National Aeronautics and Space Administration

and the Federal Aviation Administration

and held in Hampton, Virginia

October 16-18, 1990

January 1991

National Aeronautics and

Space Administrahon

Langley Research Center

Hampton, Virginia 23665-5225

FOREWORD

The Third Combined Manufacturers' and Technologists' Conference was hosted

jointly by NASA Langley Research Center (LaRC) and the Federal Aviation Administration

(FAA) in Hampton, Virginia on October 16-18, 1990. The meeting was co-chaired bv

Dr. Roland Bowles of LaRC and Herbert Schlickenmaier of the FAA. Dan Vicroy of

LaRC served as the Technical Program Chairperson and Carol Lighmer of the Bionetics

Corporation was the Administrative Chairperson.

The purpose of the meeting was to transfer significant ongoing results of the

NASA/FAA joint Airborne Wind Shear Program to the technical industry and to pose

problems of current concern to the combined group. It also provided a forum for

manufacturers to review forward-look technology concepts and for technologists to gain an

understanding of the problems encountered by the manufacturers during the development

of airborne equipment and the FAA certification requirements.

The present document has been compiled to record the essence of the technology

updates and discussions which followed each. Updates are represented here through the

unedited duplication of the vugraphs, which were generously provided by the respective

speakers. When time was available questions were taken form the floor; if time was not

available questions were requested in writing. The questions and answers are included at

the end of each presentation. A general question and answer session was conducted at the

end of each day and is included at the end of report along with closing remarks.

TABLE OF CONTENTS

Part 1

FOREWORD ..............................................................................................................

TABLE OF CONTENTS ............................................................................................

SESSION I. -- Terms of Reference

mo

B.

i

iii

Airline Industry Intentions .................................................................................... 3

Frank Tullo, Air Transport Association

Wind Shear Program in France

1) Overview ..................................................................................................... 19

Bernard Ades, DGAC/SFACT

2) LIDAR Studies on Microbursts ........................................................................ 29

Y. Aurenche and J.L. Boulay, ONERA

3) RADAR Performance Experiments ................................................................... 37

C. Le Roux, DGAC/STNA

4) MEGASODAR Experiment ............................................................................ 57

Alain Donzier, REMTECH

SESSION II. -- Case Study

A. Integrated Data Analysis of July 7, 1990 Microburst .................................................. 63

Dave Hinton, NASA Langley

B. Model Comparison of July 7, 1990 Microburst ......................................................... 81

Dr. Fred Proctor, MESO

SESSION III. -- Flight Management

A. Microburst Avoidance Simulation Tests .................................................................. 107

Dr. John Hansman, MIT

B. Wind Shear Training Applications for91/135 ........................................................... 143

Capt. Ed Arbon, Flight Safety Foundation

C. Determining Target Pitch Angle ............................................................................. 153

Herb Schlickenmaier, FAA

D. Probabilistic Reasoning for Wind Shear Avoidance .................................................... 161

Dr. Robert Stengel, Princeton University

Alex Stratton, Princeton University

SESSION IV. -- Sensor Fusion & Flight Evaluation

A. Integration of Weather Sensing Devices ................................................................... 177

Jim Daily, Honeywell Sperry

B. NASA Langley Flight Test Program ....................................................................... 201

Mike Lewis, NASA Langley

SESSION V. -- TDWR Data Link / Display

A. TDWR Information on the Flight Deck ................................................................... 227

Dave Hinton, NASA Langley

B. Orlando Experiment ............................................................................................. 243

Dr. Steve Campbell, MIT Lincoln Laboratory

C. Integration of the TDWR and LLWAS Wind Shear Detection System ........................... 263

Larry Cornman, National Center for Atmospheric Research

o°o

111

PRE'CEDIi'_I P_.IGE BLANK NOT FILMED
D. A Status Report on the TDWR Efforts in the Denver Area .......................................... 299

Wayne Sand. National Center for Atmospheric Research

E. Thermodynamic Alerter for Microbursts ................................................................... 35l

Dr. Peter Eccles, MITRE

SESSION Vl. -- Heavy Rain Aerodynamics

A. Status of Heavy Rain Tests ................................................................................... 367

Gaudy Bezos, NASA Langley

B. Heavy Rain Field Measurements ............................................................................ 395

Ed Melson, NASA Wallops

C. Estimate of Heavy Rain Performance Effect .............................................................. 425

Dan I/icroy, NASA Langley

SESSION VII..- 2nd Generation Reactive Systems

A. Status of Sundstrand Research ................................................................................ 453

Don Bateman, Sundstrand

B. Temperature Lapse Rate as an Adjunct to Wind Shear Detection ................................... 479

Terry Zweifll, Honeywell Sperry

Part 2"

SESSION VIII..- Airborne LIDAR

A. NASA Langley / Lockheed Research Status .............................................................. 509

Russel Targ, Lockheed

B. Continuous Wave Laser ........................................................................................ 527

Dr. Loren Nelson, OPHIR Corporation

C. Status of 2 Micron Laser Technology Program ......................................................... 555

Mark Storm, NASA Langley

D. Avionic Laser Multisensor Program at Litton Aero Products ....................................... 577

Rod Benoist, Litton

SESSION IX. -- Airborne Passive Infrared

A. Status of NASA's IR Wind Shear Detection Research ................................................. 589

Dr. Burnell McKissick, NASA Langley

B. Status of Turbulence Prediction Systems' AWAS III .................................................. 609

Pat Adamson, Turbulence Prediction Systems

C. Status of Colorado State Universities' IR Research .................................................... 637

Dr. Pete Sinclair, Colorado State University

SESSION X. -- Airborne Doppler Radar / Industry

A. Status of General Motors Hughes Electronics Research ............................................... 681

Dr. Brian Gallag her, Delco

Mark Selogie, Hughes

B. Saberliner Flight Test .......................................................................................... 713

Bruce Mathews, Westinghouse

C. Status of Bendix Research ..................................................................................... 755

Daryal Kuntman, Bendix

D. Status of Collins Research .................................................................................... 767

Roy Robertson, Collins

* Published under separate cover.

iv
SESSION XI. -- Airborne Doppler Radar / NASA

A. Clutter Modeling of the Denver Airport and Surrounding Areas .................................... 785

Steve Harrah, NASA Langley

V. Delnore, Lockheed

R. Onstott, ERIM

B. Radar Simulation Program Up-grade & Algorithm Development .................................. 837

Charles Britt, RTI

C. Signal Processing Techniques for Clutter Filtering & Wind Shear Detection ................... 869

Dr. Ernest Baxa, Clemson University

M. Deshpande, VIGYAN Corp.

D. Airborne Radar Simulation Studies of the Denver July 11, 1988 Microburst ................... 913

Charles Britt, RTI

E. M. Bracalente, NASA Langley

E. Description, Characteristics, & Testing of the NASA Airborne Radar ............................ 937

W. R. Jones, NASA Langley

O. Altiz, Rockwell International

P. Schaffner, NASA Langley

J. H. Schrader, RTI

H. J. C. Blume, NASA Langley

GENERAL QUESTIONS AND ANSWERS ..............................................................

CLOSING REMARKS ...............................................................................................

APPENDIX - List of Attendees ................................................................................

981

987

991
vi
Session I. Terms of Reference

l t

Session I. Terms of Reference

Airline Industry Intentions

Frank Tullo, Air Transport Association

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AMERICAN AIRLINES

FORWARD LOOKING INFRARED SENSORS

TURBULENCE PREDICTION SYSTEMS (TPS)

3 MD-80°S RECORDING DATA

TRANSPARENT TO FLIGHT CREWS

SIGNIFICANT EVENT MARKER

5
NORTHWEST AIRLINES

REACTIVE AND FORWARD LOOKING INFRARED

HONEYWELL REACTIVE SYSTEM

INFRARED - TPS

DATA COLLECTOR

PILOT REPORT FOR EVENTS

6
EASTERN AIRLINES

BENDIX DOPPLER RADAR

B-757

FORWARD SWEEP WX

REVERSE SWEEP DOPPLER
CONTINENTAL AIRLINES HAS SIGNED

A MEMORANDUM OF UNDERSTANDING

FOR

DOPPLER RADAR WITH

- BENDIX

- COLLINS

23 AUG 1990

22 JUN 1990

INFRARED WITH

- HONEYWELL- KOLLSMAN

- SUNDSTRAND - COLORADO

STATE UNIVERSITY

20 JUL 1990

22 JUN 1990

THESE MOU'S PROVIDE FOR A FLIGHT EVALUATION

PROGRAM OF BOTH TECHNOLOGIES. AT THE

PRESENT TIME, BOTH APPEAR VIABLE. THEY WILL

FLY COUPLED WITH REACTIVE SYSTEMS WHICH ARE

PRESENTLY CERTIFIED TO FAR 121.358

COMPLIANCE.
HONEYWELL - KOLLSMAN

AIRCRAFT 788, B727-200, WILL RECEIVE AN

INSTALLATION PACKAGE CONSISTING OF:

- HONEYWELL REACTIVE

WIND SHEAR COMPUTER

- KOLLSMAN FLIR SENSOR

- DATA RECORDER

PRESENT SCHEDULE

• APPLICATION FOR STC, 10 SEP 1990

• INSTALLATION AND CERTIFICATION,

NOV - DEC, 1990

• REVENUE FLIGHTS AND DATA COLLECTION,

JAN - DEC 1991

• FINAL REPORT, OCT 1991
SUNDSTRAND - CSU

ONE OF OUR B737-300 AIRCRAFT, WHICH HAS THE

SUNDSTRAND MKV WIND SHEAR SYSTEM (BOEING

ALGORITHM) INSTALLED WILL BE UTILIZED. THE

INSTALLATION PACKAGE WILL CONSIST OF:

- CSU INFRARED SENSOR

- SUNDSTRAND MKV (SUNDSTRAND ALGORITHM)

WIND SHEAR COMPUTER

- OPTICAL DISK RECORDER

PRESENT SCHEDULE:

• COMPLETE CSU SENSOR FLIGHT TRIALS,

NOV 1990

• PRELIMINARY 737-300 SYSTEM INSTALLATION

DESIGN, DEC 1990

• APPLICATION FOR STC, JAN 1991

• COMPLETE FABRICATION, ASSEMBLY, AND TEST

OF SYSTEM COMPONENTS FOR 737-300

INSTALLATION, APR 1991

• 737-300 INSTALLATION BUY-OFF, MAY 1991

• INITIATE 737-300 REVENUE FLIGHTS AND DATA

COLLECTION, JUN 1991

• COMPLETE DATA COLLECTION AND REMOVAL OF

737-300 INSTALLATION, OCT 1991

• FINAL EVALUATION REPORT, NOV 1991

10
COLLINS

ONE OF B737-300 AIRCRAFT, WHICH HAS THE

SUNDSTRAND MKV WIND SHEAR SYSTEM (BOEING

ALGORITHM) WILL BE UTILIZED. DETAILS OF THE

INSTALLATION HAVE NOT BEEN WORKED OUT AS OF

THIS TIME. A PLAN TO UTILIZE THE AIRCRAFT WHICH

HAS THE SUNDSTRAND CSU SYSTEM INSTALLED

FOR THIS EVALUATION ALSO IS BEING PURSUED.

PRESENT PLANS WILL ALLOW FOR SYSTEM

INSTALLATION IN APRIL 1991.

11
BENDIX

ONE OF THE B737-300 AIRCRAFT, WHICH

HAS THE SUNDSTRAND MKV WIND SHEAR

SYSTEM (BOEING ALGORITHM) WILL BE

UTILIZED. THE INSTALLATION PACKAGE

WILL CONSIST OF:

- BENDIX 708 RADAR

- RECORDER - CONTROL SYSTEM

PRESENT SCHEDULE:

• R/T MODIFICATION, MAR 1991

• FLIGHT TESTS (BENDIX), JUN 1991

• INSTALLATION AT CONTINENTAL, JUL 1991

• REVENUE FLIGHTS AND DATA COLLECTION,

JUL- NOV, 1991

• FINAL REPORT, DEC 1991

12
PROBLEM AREAS

INFRARED SENSOR- DE-ICE REQUIREMENTS

DOPPLER RADAR - ARINC 708

• TSO CERTIFICATION

• WEATHER TSO UNCHANGED

• MODIFY DOPPLER FUNCTION ONLY

• CONTROL FROM INSTALLATION PACKAGE

• BLIND TO FLIGHT DECK

° FORWARD SWEEP- WX

° REVERSE SWEEP- DOPPLER W/S

FAA EXEMPTION

DATA- WHO AND WHOM

].3
Airline Industry Intentions - Questions and Answers

Q: ED LOCKE (Thermo Electron Technologies) - Are there any studies that indicate the

degree to which abortive landings impact the finances of the airlines? Pilots that choose to

not make a landing because the conditions are suggestive of wind shear problems and

therefore connections are lost and so on, and so on. Are there any studies that you are

aware of that do put some numbers to that?

A: FRANK TULLO (ATA) - There are none that I'm aware of. There are large economic

consequences of landing at an alternate airfield and subsequent problems of taking care of

the passengers. I don't know of any study.

Q: WALT OVEREND (Delta Airlines) - What are the advantages to those airlines who

have now or whom have applied for exemptions to install predictive systems if the FAA

will not or has stated they will not certify such systems?

A: FRANK TULLO (ATA) - That's an excellent question. I haven't got an answer for that

but you're right, there is no incentive. I'm hoping that this is a typical FAA posturing

where they're holding our feet to the fire and making us prove to the world that a system,

whatever system that is, can stand alone in predicting wind shear. Obviously there is no

economic advantage to this exemption if the end result is that we have to carry both reactive

and predictive. Hopefully we won't have to.

Q: WALT OVEREND (Delta Airlines) - Is there not more positive methods and resultant

better indications of wind shear conditions from ground systems than from those that can

be carried by each aircraft? How long does it take to develop TWDR - Is the program on

schedule?

A: FRANK TULLO (ATA) - I would like to ask that same question. I know that in the

middle '80s the industry decided to embark on a multifaceted attack on wind shear. One

was pilot education and then ground based equipment and then airborne based equipment.

I believe we've done as much as we can possibly do with pilot education. The fact that we

haven't had an accident in 62 or 63 months is indicative of that. I know that there is

terminal Doppler radar available and I know that it has been proven successful. I don't

know where that program stands. Can anybody enlighten us on that?

A: STEVE CAMPBELL (MIT Lincoln Laboratory)- The TDWR program has been going

on since about 1985 or a little bit earlier and it's really been proceeding at a record breaking

rate for an FAA program. It is anticipated that the first TDWRs will be installed at the end

of 1992 and one of the reasons this is likely to happen is that Ratheon has a substantial

incentive to in fact deliver at that time. ff they deliver the first several units in that time

frame they get a substantial financial incentive, so they have quite a bit of incentive to

actually have that happen. It is an accelerated development program and it seems to be

pretty much on track from what we can tell. I should say one other thing about the impact

of microbursts on airport operations, we haven't assessed this in any tremendous detail

except to say that even in a place like Orlando where you have a tremendous number of

events, the number of hours in the year where microbursts actually impact the airport is

rather small, it's only a matter of 10 or 20 hours. I don't have the actual hours at my

fingertips, but in the grand scheme of things it is a very small period of time and so there

may be a transitional impact upon airport operations but it's not one of these things, for

instance when weather comes in and impacts an airport, that lasts for a long time, fog for

example, one foggy day can cause a lot more impact than a whole summer of microbursts.

14
ROLAND BOWLES (NASA Langley) - Walt; the second part of the question you asked,

as I understand it was. What's the trade off between ground detection and information

dissemination and airborne? Why have both? I might point out that after 1975 the FAA put

together a major wind shear program initiative. I think we declared victory in about 1979.

Then came Pan Am at New Orleans and Dallas and other recent near misses or recent

encounters. So the point is that we've got something going here now on the technology

side, let's go ahead and get the problem solved and get it behind us. There are other things

out there to work on. I might point out that the policy has been made. We are going to

have 47 Doppler radars deployed at major TCAs and there is an equipment rule that says if

you're going to operate under 121 rules you're going to have airborne equipment. This

issue is not whether or not you're going to have the equipment, it's what equipment are

you going to have that gives maximum safety per unit dollar.

Q: UNKNOWN - What are the advantages of airborne equipment?

A: FRANK TULLO (ATA) - As a pilot I like to be as autonomous as possible. The

weakest link is the transfer of information and all too often that information is not received

by the pilot or if it is received it's not understood by the pilot. One glance down at a device

that shows me the threat and where it is in relation to me is so much more important that

somebody giving me a subjective view of what they see on an instrument in their suite.

Q: (unable to understand)

A: FRANK TULLO (ATA) - I believe that's why four of the airlines have elected to take a

chance on other technology because we are not quite satisfied with what we have right

now. It is better than nothing, I'll say that. I heard it mentioned a number of times, we've

gotten an awful lot out of our pilot training effort. I think that's reaped a lot of benefits.

SAM SAINT (Safe Flight Instrument Corp.) - I made a careful study of the eight major

accidents from Eastern 66 in '75 to Delta 191 in '85 and the question I was asking when I

went through that was "would it be likely that this accident would have happened if the

airplanes had been equipped with a reactive warning system?" I couldn't find one accident

in that long list that looked like it had even a chance of happening. I delivered a paper that

said this at a meeting in Paris and I still believe it.

15
16
Session I. Terms of Reference

Wind Shear Program in France

Overview

Bernard Ades, DGAC/SFACT

LIDAR Studies on Microbursts

Y. Aurenche and J.L. Boulay, ONERA

RADAR Performance Experiments

C. Le Roux, DGAC/STNA

MEGASODAR Experiment

Alain Donzier, REMTECH

PRT..'CEDII',,;GPAGE BLANK NG$ FILMED 17
18
Wind Shear Program in France

Overview

Bernard Ades, DGAC/SFACT

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WINDSHEAR PHEN_OM IN FRANCE

METEOROLOGICAL DATA ANALYSIS

ACTING METEROLOGICAL OFFICE

150 KF

WORK IN PROGRESS

21
_IFICATION/OPERATIONAL CONFORMITY

WINDMODEL SELECTION

FALSE ALARM CRITERIA

OPERATIONAL IMPACT

ACTING AEROSPATIALE/CEV

1150 KF

WORK PARTLY ACHIEVED

22
WINDSHEAR OPERATIONAL PROCEDURES

MODERN AIRCRAFT

ACTING AEROSPATIALE/AIRBUS

4000 KF

WORK JUST BEGUN

23
LIDAR STUDIES ON MICROBURSTS

AIRBORNE MODELIZATION/DETECTION

PLANE BEHAVI OUR

ACTING ONERA-DGA/DRET

2500 KF

WORK IN PROGRESS

PRESENTATION

* Y. AURENCHE

BY"

(ONERA )

24
LIDAR STUDIES ON MICRO_TS

ELECTRICAL ACTIVITY MEASURES

DOPPLER RADAR MEASURES

ACTING:

* ONERA-DGA/DRET

* LINCOLN LABORATORY

1700 KF ON FRENCH SIDE

WORK IN PROGRESS

PRESENTATION BY :

* JL. BOULAY, P LAROCHE (ONERA)

* M. WEBER (LINCOLN LABORATORY)

25
RADAR PERFOI_MANCE EXPERIMENTS

5 AND 30 CMS RADARS

ACTING CNET/CRPE

2200 KF

WORK IN PROGRESS

PRESENTATION

* C. LEROUX

* F. BERTIN

BY.

(S TNA )

(CNET/CRPE )

26
MEGASODAR __<IMENT

MULTICELLULAR ANTENNA

ACTING REMTECH

875 KF

WORK IN PROGRESS

PRESENTATION

* A. DONZIER

BY"

(REMTECH )

27
28
N91-24167

Wind Shear Program in France

LIDAR Studies on Microbursts

Y. Aurenche and J.L. Boulay, ONERA

29
ONERA's Program about Windshear Studies

Preliminary Analysis of Requirements for Future Airborne Windshear Detection Systems

Y. Aurenche, Binh Dang Vu, D. Guffond

Office National d'Etudes et de Recherches Atrospatiales (ONERA)

Ch_tillon, FRANCE

1. INTRODUCTION

With DGAC and DRET support, ONERA works since 89 on Windshear problems. The

main studies are:

- Hight Mechanics

- Microbursts modeling

- Microburst detection with airborne systems

(LIDAR, radar, passive infrared sensors)

- Microbursts prediction with ground systems

(VI--IF interferometry)

The purpose of this presentation is to give a short overview of theses studies and some

results.

2. FLIGHT MECHANICS

The studies concern the behavior of two airplanes (B727 and A310) equipped with an ILS

and crossing a microburst.

A simulation program has been developed, using for each airplane a classical and simplified

guidance and flying loop; the loop takes into account the flight maneuvering capabilities in

order to realize an automatic approach and to land with a conventional speed.

The principal criteria for a good landing are:

- an angular error with respect to the glide path inferior to 1°

- a vertical impact speed inferior to 7 ft/s

Six windfield models have been considered:

- 3 historical cases; the New York, Dallas, and Atlanta accidents.

- 2 standard FAA cases (AD 120-41); n°6, being the most severe.

- 1 symmetrical RAE model, with the conditions Kr=l, Kx=3, Kz=l, giving a high

Severity Factor equal to 0.8 during about 25 seconds.

For each simulation, the parameters are presented versus time and can be analyzed (Fig. 1):

horizontal and vertical wind speed, thrust, conventional speed, incidence, trim, etc ...

For the New York case, the Fig. 2 shows:

- the fatal flight path

- the glide path

- the simulated flight path

80
Thesimulationconclusionisthat,withanILSandaconventionallandingspeed,thetwo

airplaneshavesufficientperformancesforfollowingtheglidepathandlandingwith

acceptableconditions.In certaincases,theimpactverticalspeedisslightlyoverthe

criterion(8ft/sfor Dallascase).But,for all historicalandFAAmodels,thesimulation

showsthatthelandingispossible.Ontheotherhand,fortheRAEmodel,theILSis

insufficient.

Thenextstudyconsistedinequippingtheairplanewithaforwardlookingsystemgivinga

microburstdetectionatacertainrangeR(Fig.3)andsettingoff anewflying strategy:

thatis tocommandatthistimeaspeedincrementdV infunctionof theSeverityFactor

measured.

A parametricstudyhasbeendevelopedversusR,dV andD,thedistancebetweenthe

microburstcoreandtherunway.TheglobalresultforRAEmodelispresentedonthe

Fig.4. Thespeedincrementis20knots.ThetwoairplanesequippedwithanILSand

usingthisstrategycanlandwithacceptableconditionsonlyif thepredictionrangeis

1.5 Km.

At thepresentime,thepursuitof thisstudyconsistsin simulatingmoreseverecases.

3. MICROBURSTSMODELING

In orderto studyradarandLIDARbeampropagationacrossmicrobursts,amodeling

programhasbeendeveloped.

It simulatesaverticaldryairflowdirectedto thegroundwiththreedimensionalNavier

Stokesequations,in incompressibleandinstationaryform. Thedomainsizesare10by I0

by 5Km (Fig.5). Thespatialresolutionis 200m butmustbereduced.Thevertical

airflowis initializedbyacertainlaw. The Fig. 6 presents a vertical section and give the

speeds and the vortex locations. The Fig. 7 presents the iso-speed profiles.

At present, the task concerns hydrometers introduction in the model by using a regular

raindrops injection in airflow. The problem is to know if the instationary wind action on

the droplets trajectory does not bring them together and does not give over or under

concentration zones.

The calculation hypothesis are:

- the rain drops don't modify the flowfield velocity

- the forces taken into account are gravity and the drag forces produced by drops and air

velocity differences.

The Fig. 8 shows the concentration factor Cf at t=1000s and for a 30 m/s injected airflow

speed. The over-concentration locations do not correspond with maximal speed location

presented on the Fig. 7.

At present, these studies are going on with a smaller spatial resolution.

31
4. AIRBORNEDETECTIONSYSTEMS

Uptonow,theactivitiesonthissubjecthavebeenmainlyfeasibilitystudies;nohardware

hasbeendevelopedyet.

5. GROUND PREDICTION SYSTEMS

An experiment campaign using a VHF interferometer has been realized in August 90 at

Orlando in cooperation with the Lincoln Laboratory using several radars; the first results

are presented in the next paper.

32
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36
N91-24168

Wind Shear Program in France

RADAR Performance Experiments

C. Le Roux, DGAC/STNA

37
EVALUATION OF 30 cm PROUST DOPPLER RADAR

AND 5 cm RONSARD DOPPLER RADAR AT LOW HORIZONTAL

TILT IN CLEAR AIR AND RAIN LOW LEVEL

WIND SHEAR CONDITION

C. LE ROUX (1), F. BERTIN (2) and H. MOUNIR (2)

(1): DGAC/STNA, PARIS

(2) : CNET/CRPE, St MAUR

38
EVALUATIONOFpROUSTDOPPLERRADAR(_=30 CM) ANDRONSARD

DOPPLERRADAR(t_=5 CM ) AT LOWHORIZONTALTILT IN CLEARAIR AND

RAINLOWLEVELWINDSHEARCONDITION.

C.LEROUX(1), F.BERTIN(2) and H. MOUNIR (2)

(1) : DGAC/STNA, PARIS

(2) : CNET/CRPE, SAINT MAUR.

Abstract : Tneoncal stuclles ancl eXl0erimemal results oOtaJnecl ** Coulommlenl lUrpofl llev, shown the capabilitY of Proust

r•¢lar tO clmect winclshel,.'1, in clear air co,'_lalon as well as in ix••ence of cloud• ot rmn. Several examples are present•a:

- In • blocking Nigl_$ $_tuation we c•n clearly clistlnguish an _mospmmc wave system st the 8runt-vmsaJs

frequency.

- In • srtumton of cloudS without ram. we can see easily me limit between cleat mr ancl clouCl$.

- A last example shows • winclghe_ mmocimea witl_ • gust from In rainy con¢Ittlon.

A companion of 30 cm el•st air r_lar Proust and 5 cm whemr_r dop_ ra_u Ronasra will aJlow to seH)ct tl_e

best candid_e for wtndsllear detection, taking into Rccount the low Nmsibility tO ground cluttM of Ronsard racist.

RHun_ : let Mudm tl_loNqu_ It I_ rdmuitm exp4_lrneml_u_ oOUmus sur I'_m)l_)n de Cou_ommNm_ ont rail in 6viOence

I• capacitl ¢lu _ Pfou_ I d0tect_r lu ciuillements de veto. _ _ P_' c_ cmr qu'an pr_lenc• de nuages ou 0•

pluie. Plusieurl i_emple_ sore W/hmflt6_ :

- Dens une situation de bloc_e atmosc_mque on alstlngue claimment un sys_e a'onaes i la frlKluence ae

B_unt-V_asJa.

- Dan• une situ_ion nuageuso s&ns plume,on dm _lment la Umlte entre I*_r c_a# It la muse nusgeuN.

- Un deflrllef exempt• mo_re un clas_ltement (le vent Ill / un front de rlllUe eft I_tulalon de pluie.

une coml:mrW_on du r•d_' IX cmh' 30 cm Prou_ Ill du rlKW aopplef m4k41om_gique Rons4m:l pc_mcmr• O•

sitlctionrtM ie nleilleur cll1(lldll qullll i I• dlteclK)ll d_l C_ de vmlt. compte timu de le mo_ndre sln$ibilitO (_u

r_lar Ronur0 aux _¢N)e de Io_.

ORIGINAL PAGE IS

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39
SUMMARY

I) CONTRACT BETWEEN DGAC AND CNET

II) PROUST AND RONSARD RADAR CHARACTERISTICS

III) RELATIONSHIP BETWEEN CLEAR AIR AND RAIN

REFLECTIVITY

IV) EXPERIMENTAL RESULTS WITH PROUST RADAR

V) CONCLUSION

dO
CONTRACT BETWEEN CNET

AND DGAC

I-PHASE 1

Evaluating performances of "clear air" radars (_= 30 cm) fOr

detection of wind shear to prevent hazardous situations to

aicraft.

Comparison between PROUST (%= 30 cm) and RONSARD (%= 5

cm) radars for different meteorological conditions ( clear air,

convection cells, clouds, rain,...etc).

Application to wind shear detection.

Experimentation : 12/90 ---> 12/91

41
PROUST AND RONSARD

RADAR CHARACTERISTICS

PROUST RONSARD

WAVELENGTH (cm) 30

BEAMWlDTH(°)

5,4

5 0,9

PEAK POWER (KW) 4,5

PRF (khz) 6,4

MAX RANGE (km) 20

RANGE RESOLUTION(m) 600

250

0,75 ; 1,5 ; 3

200 ; 100 ; 50

FFT (polnts)

VELOCITY RANGE(m/s)

INCOHERENT

INTEGRATION

200 ; 100 ; 50

256 64

+/-16

4 to 32

TIME RESOLUTION (s) 5 to 40

-20

MINIMUM

DETECTABILITY (DBZ)

+/-10 ; +/-20 ; +/-40

1 to 128

0,17 to 22(with PRF=3 KHz)

0

42
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44

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NUMERICAL PROCESSING AND CONTROL UNITS OF PROUST

RADAR

45

ORIGINAL PAGE IS

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4.6 m DIAMETER ANTENNA OF PROUST RADAR

IN COULOMMIERS AIRPORT

46

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47

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REFLECTIVITY

ATMOSPHERIC TURBULENCE

T_(_.) = 0.38 C n 2 _.-1/3

Cn 2 (m-2/3)¢turbulence

of refractive index

10-i9m-2/3<Cn2<iO-13m-2/3

turbulence strong

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HYDROMETEORES

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48
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49
EXPERIMENTAL RESULTS

WITH PROUST RADAR

METEOROLOGICAL CONDITIONS

- CLEAR AIR

- CLOUDS

- RAIN

5O
F'C.N.E.T'C.R.P.E jt

, .. . •

C()UI.OMMIERS 05/03/90

Radial distance (Km) RADAR REFLECTIVITY (CN 2)

14,1

t2.9

11.7

le.5

9.3

8.1

6.9

g.7

i?h !!? 1"/!1 17 17h 27

RADIAL VELOCITY (m.s "1)

14,1

12.9

!t .?

18.5

9,3

8.1

6.9

5.7

l?h !17 JTh 17 l?h 2"7

Time

Radar reflectivity and radial velocity measured by

PROUST radar in clear air at Coulommiers airport

51
i

i'I+I'?_1E[IR I}OD()(

R;_Ji;_ldistance IKin) . RAI),_.I_ REFI,F.CTIVITY ((_ 2)

I_ 43

PROUST radar observation of clouds (Cu) The clouds

contours are well defined by the radar reflectivity

52
iic.N__T.c_a--_-.E-

(?() [ "I.()M,_I I1'iR._ !14/I 4,r'l)ll

Radial distance(Km)

lg.2 _:

1?.8

15.8

1'1.6 Z

RADAR REFLECTIVITY (CN 2)

Time

Radar reflectivity measured by PROUST radar in

Coulolnmiers airport during a gust front

53
!IC'.N.E.T'C.R.P.E_ lI

('()I'I,()MM II",RS ll4:' ! 4:9fl

Vi-I.I)('ITY SI'ECTRILM WIDFII {In.s "1)

RADIAL VELOCITY (m.s -I)

Veh)city spectrum width and radial velocity obtained by

PR()UST radar in Coulommier_ airport during a gust front

54
CONCLUSION

Experimental results have shown the capability of 30 cm wavelength

PROUST radar to detect low level wind shears in all meteorological

conditions (from - 20 DBZ clear air echoes to heavy rain).

But there some limitations consisting essentially in the time

resolution which is at least 5 s and the sensibility to ground clutter

limiting the low elevation.

The comparison of its capabilities with those of 5 cm wavelength

RONSARD radar which is less affected by ground clutter echoes will

permit to select the best candidate.

55
56
N91-24169

Wind Shear Program in France

MEGASODAR Experiment

Alain Donzier, REMTECH

57
SODAR APPLICATION TO WIND SHEAR AND

WAKE VORTEX DETECTION

A preliminary experiment supported by the French Civil

Aviation has proven that wlnd measurement at low elevatlon anqles

uslna acoustic remote sensing was feasible. This experiment was

conducted using a 2.4 meters parabolic dish antenna with about 2

watt of acoustic power emitted at 4000 Hz. The elevation anqle

was of 6 degrees.

However a reflector type antenna does not allow the antenna

pattern optimisation that can be achieved on phased array type

antennas. Moreover arraying elements increases the emitted power.

Remtech has recently developped a commercial phased array

Sodar line. A 2 meters by 2 meters 432 elements commercial phased

array system was operated st Roissy International Airport for a

few days. You will find some radial wind data at the end of this

document. Eventhough this system was not optimized for _such

application it showed ranges of about 800 meters for an averaging

time of I0 minutes and an elevation angle of 20 degrees. Some

strong echo regions are present in the data and seem to be

related to wake vortex.

Further developments starting before the end of thls year

include :

- installation of an optimized phased array system at

Roisey International Airport.

- gathering data for wake vortex study

- generalization of the signal coding techniques to reduce

the acquisition time to a few minutes.

- besm steering with simultaneous measurement on 4 beams.

The study will allow the definition of the technical

specificstlons of a system for wind shear and wake vortex

detection having e _ange of at least two miles.

58
Wind Shear Program in France - Questions and Answers

Q: ERIC PALMER (McDonnell Douglas, Long Beach) - Has the DGAC/JAA a plan to

require airborne wind shear systems? If so, what will be required and when?

A: BERNARD ADES (DGAC) - There is no requirement on the operational side yet; still

waiting for more information on the phenomenon (characteristics in France and Europe/. If

a requirement is made, it shall be made in conjunction, in coordination, within a European

Joint Airworthiness Authority rather than DGAC alone. Furthermore this would be made

within the regular consultation, JAA/FAA consulting process.

Q: MARILYN WILSON (MIT Lincoln Laboratory) - Is wind shear a major hazard in

France? Is it common?

A: BERNARD ADES (DGAC) - Not really. We've asked for a meteorological study to

characterize the phenomenon in France. Unfomanately it has been very difficult to get data

from the airport so what we've begun to do is to collect data from the nuclear centers where

there is a strict follow up of the meteorological conditions. But yet we have no result from

this study. We have very particular cases where kinds of wind shears were recorded in

France, particularly south of France around Nice Airport, but it is something very rare.

You see the problem is that our planes are still flying to other parts of Europe and also to

the US.

59
60
Session II. Case Study

PRF.'CEDIIY_ PAGE BLANK NOT FILMED

61
62
Session II. Case Study

N91-24170

Integrated Data Analysis of July 7, 1990 Microburst

Dave Hinton, NASA Langley

63
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73
?4
Integrated Data Analysis of July 7, 1990 Microburst

Questions and Answers

Q: FRED REMER (University of North Dakota) - How would the July 7, 1990 microburst

in Orlando have affected a transport category aircraft on a stabilized approach?

A: DAVE HINTON (NASA Langley) - That microburst would have generated, or should

have generated a valid alert had any transport aircraft flown through it with a reactive

system. The strength of the microburst (with an F-factor of about 0.15 or 0.17, depending

on which measurement you take) indicates that an aircraft could have easily recovered from

it had the pilot initiated a missed approach. Had the pilot attempted to continue through to

landing it would have been somewhat dangerous.

Q: UNKNOWN - You said that it would have generated a light or something from a

reactive system. What reactive system are you talking about?

A: DAVE HINTON (NASA Langley) - I said, had a transport category aircraft penetrated

that microburst and had such an aircraft been equipped with a reactive system it should

have generated a valid alert. This aircraft did not have a reactive system on board.

UNKNOWN - They're not all the same.

DAVE HINTON (NASA Langley) - I realize that; but if they are functioning properly they

should have generated an alert. The event was strong enough that the threshold agreed to

by the industry was exceeded for some 5 or 6 seconds. There should have been an alert

had any system gone through there.

UNKNOWN - I didn't know there was a threshold agreed to by the industry.

DAVE HINTON (NASA Langley) - TSOC117.

UNKNOWN - There are reactive systems out there that were put together long before the

TSO came out.

DAVE HINTON (NASA Langley) - I realize that. The "national speed limit" was an

F-factor of 0.15 some years ago. I believe most systems in the field, even the older ones

are threshold at approximately 0.12 to 0.13, in that bail park. This exceeded that threshold.

ROLAND BOWLES (NASA Langley) - To my knowledge there has never been a case

where a reactive system has been tested in a situation where an alert was given and there

was independent measurement to confirm the validity of that alert. Now, I'm going to

probably start an argument here. There's some people that will probably argue that. The

key point is where an alert occurred with a reactive system for which there was independent

confirmation; a different data measurement. Now we've had a lot of crews say, "yea, that

was about right." But as many of the responses that you get on that side of it, you've got a

lot of crews saying, "no way can I accept the validity of that alert." One of the things that

we want to do at Denver is to test that hypothesis. There are some subtleties involved here.

I'm sure the manufacturers are putting good systems out there, but I know of no program

where an alert has been given by purposely testing it in an environment for which there's

been independent measurement. In the Orlando case, we had an exceedance of 0.1 for 5 or

6 seconds. It is perfectly believable that the gust rejection filtering in a system could knock

that amplitude down and stretch it out in such a way that we may not have gotten an

75
exceedanceof O.1. MaybetheHoneywellpeoplecancommentonthat.It dependson

whosesystemit is.

Q: PETERECCLES(MITRECorp.)- Aircraftconfiguration(engineout,load

distribution,evenpilotexperience)wouldaffectaircraftsurvivability.Givenasmart

computerwhichkeepsaccountof aircraftconfiguration,acombinationof F-factorwith

configurationwouldgiveabetterideaof aprobabilityof survival.Wouldyouagree?

A: DAVEHINTON(NASALangley)- I wouldsayfromatechnicalviewpoint,yes,that

obviouslykeepingtrackof theseparameterswouldgiveabetteridea.I'mnotsurethat

fromanoperationalpointof viewit'srealizableorevendesirable.Onepointofreferenceis

thatTSOC117thereisonlyonethresholdgivenforall aircraftandweknowthatvarious

aircraft,givenall engines,havedifferentrecoveryperformancecharacteristics.

PETERECCLES(MITRECorp.)- We'renotparticularlystuckwiththatTSO,I mean

therecouldbeotherTSOs.

DAVEHINTON(NASALangley)- I assumethat'ssubjectomodification.

Q: BOBROLL(LockheedMissiles& SpaceCo.)- Isthe4 to6"Ctemperaturedrop

uniquetothemicrobursttypesituationordoesthatoccurineverydaysituations,evenin

clearweather?Secondly,istherealwaysatemperaturedropwhenawindshearhazard

(notnecessarilyamicroburst)occurs?

A: DAVEHINTON(NASALangley)- Toanswerthefirstpartabouthetemperaturedrop

occurring,it's notuniquetomicrobursts,wealsoseeatemperaturedropsingustfronts.

Someearlyinfrareddetectionworkwasdealingspecificallywithgustfrontdetection.As

far as those temperature changes occurring in other conditions, i.e., sea breeze fronts,

temperature inversions, that's still an open question. The current research being

conducted, that being the program that Pat Adamson is in with American Airlines on the

MD80s and some of the research we will be conducting on our 737, is designed to answer

that question. The answer to the second part about are we seeing a temperature drop when

a wind shear hazard exists, I suppose I have to ask, how do you define a wind shear

hazard? That is, are we only talking about microbursts, are we also trying to determine or

detect other types of wind shears. If we look only at microbursts there is a very strong

correlation, even a scaling factor between the temperature drop and the strength of the

event. If you start looking at other events, sea breeze fronts, convective turbulence, we

don't expect to see that temperature correlation. It's not clear that we need to detect those

anyway. That's a question industry will have to answer.

MARILYN WILSON (MIT Lincoln Laboratory) - I just want to qualify that a little bit.

Some microbursts are not associated with temperature drops at the surface. It depends on

where in altitude you look. Aloft there may be a temperature drop, and a strong correlation

as you say. But near the surface some microbursts are actually associated with temperature

increases.

DAVE HINTON (NASA Langley) - We've seen that. Fred Proctor's model has been able

to recreate those situations. It's not clear how often those conditions exist and how strong

a microburst tends to be when you get that type of a temperature inversion in stable air.

That is another question that has to be answered.

Q: WAYNE SAND (NCAR) - With 62 events penetrated, can we expect a detailed

functional analysis of a look-ahead system? If so, when? And, do you always see a

temperature deficit in the microburst?

711
A: DAVEHINTON(NASALangley)- I wouldsaythatasfar asthe62eventsare

concernedtheprimaryemphasisof thatstudyisoncorrelationof terminalDopplerweather

radarbasedF-factormeasurementsorestimationswiththeinsitumeasurementsof the

airplaneasit goesthrough.Anotherobjectiveisthecorrelationof theinfraredF. Weplan

tocorrelatethatwhereverit makessenseto doso. WhatI meanbythatis,thereissome

penetrationswheretheaircraftisnotstabilizedfarenoughawayfromtheeventtogivethe

infraredsystemachanceto lookatit, simplybecauseof thenatureof thewaytheairplane

wasflownin thoseevents.Whenwill thatanalysisbecompleted?It'salwaysdangerous

to saywhenananalysisisgoingto becompleted,asyouknow.Thisstudyis being

conductedundercontractbyLincolnLabs.Thecontractwassignedveryshortlybeforethe

datacollectionstarted.So,theywereonlyabletorecentlyhiretheirdataprocessing

person.As soon as they automate that data processing we expect to process all of the

events as quickly as we can. The final report is due, roughly in the early winter, February,

somewhere in that ball park.

Q: JOHN HANSMAN (MIT) - You said that you only have a limited number of cases

where you had enough infrared line up on the thing to make a measurement. Is that an

inherent limitation on infrared in the future?

A: DAVE HINTON (NASA Langley) - I think we're talking about an inherent limitation of

any forward look system. You have to remember these systems are designed to protect

transport category aircraft flying instrument approaches, or perhaps visual approaches. But

this research aircraft is occasionally making radical maneuvers in order to catch a

microburst before it dissipates.

Q: JOHN HANSMAN (MIT) - Does that imply that procedurally, in potential microburst

cases with look ahead systems you're going to have to stabilize on the approach sufficiently

far ahead of the threat region, and is that any further out than the outer marker?

A: DAVE HINTON (NASA Langley) - No, I don't see that as further out than the outer

marker.

A: DAVE HINTON (NASA Langley) - The third part of the question is, "do we always

see the temperature drop?" Again I have to go back to the fact that we haven't seen the data

yet. We haven't had a chance to look at the data from that experiment. I see that Pat would

like to make a comment though.

PAT ADAMSON (Turbulence Prediction Systems) - We haven't actually analyzed the data,

but looking at about 20 encounters on the UND aircraft, through the month of July or so,

all of the downdrafts that we saw were associated with anywhere from about 3 to 7 degree

temperature drops. Now those are all wet microbursts. We haven't reduced the Denver

data and I don't know if we have a dry microburst there. So, we have a partial answer to

your question. One of the things that we do see is a unique signature for a microburst.

That's really where the differentiation comes between a gust front or a sea breeze or

whatever, is in the unique signature of the microburst.

Q: ROB ROSEN (Hughes Aircraft Co.) - How far did the IR sensor see? Was the IR

sensor scanning? Was the IR sensor able to estimate range and how accurately? Was it

able to estimate the size and the slope of wind shear?

A: DAVE HINTON (NASA Langley) - The sensor was looking about 40 seconds ahead,

which is approximately 2 nautical miles at 190 knots. Was the infrared scanning was the

next part of the question. The answer to that is no, it's a fixed look point sensor. It's

77
actually looking at two elevations for various reasons but it's not a scanning in azimuth

type situation. The third part, was the infrared sensor able to estimate range and how

accurately? The answer to that is that the infrared sensor is not a ranging type instrument

and it's not a range gaited instrument. It looks at two points, one very close to the airplane,

the near temperature, and it looks at a second point relatively far, called the far temperature.

It uses the difference in temperature and the rate of change of that difference to estimate an

F-factor. You can call it pseudo ranging if you like because it varies with atmospheric

humidity and rain. Pat would you like to add something to that?

PAT ADAMSON (Turbulence Prediction Systems) - We actually do calculate a look

distance but it's probably only good to about 20% at best.

Q: DAVE HINTON (NASA Langley) - And it's not presented to the pilot?

A: PAT ADAMSON (Turbulence Prediction Systems) - Not at this time, it could be though

but we don't give it out at this time.

A: DAVE HINTON (NASA Langley) - The fourth part of the question, "was it able to

estimate the size and the slope of the wind shear?" The output of the infra.red sensor is an

F-factor estimate based on the scaling laws that have been derived using meteorological

models such as Fred Proctor's and real world observations. Again, not being a ranging

system it cannot estimate the physical extent of the microburst. It cannot tell you that it's a

1 or 2 or 3 kilometer diameter event. It can only tell you it's there, it's going to be

approximately, depending on humidity, 30, 40 seconds in front of the airplane and give

you an estimate of the F-factor based on the temperature change and the rate of change of

that temperature.

Q: UNKNOWN - You mentioned that it gives us a 20 second warning, was there rain

between the aircraft and all the way to 20 seconds in front of the aircraft?

A: DAVE HINTON (NASA Langley) - We're talking about 40 seconds here, not 20. No,

the air was relatively dry and we had a very dense rain shaft. Pat Adamson has a video

tape that I understand he's going to try and show Thursday which shows it very clearly.

There was very good visibility, a good VFR flying day and a very well defined rain shaft

associated with the microburst.

Q: SCOTr GRIFFI'Hq (Allied Pilots Association/American Airlines)- Based on your

event analysis, how well does the Turbulence Prediction Systems' predictive algorithm

work as a reactive system, i.e., does the insitu measurement of delta T correlate well with

the wind shear measurement?

A: DAVE HINTON (NASA Langley) - If I understand your question, is it based on a local

measurement of F as opposed to a global measurement? People have asked us, "would

you expect temperature changes while you're crossing a microburst to correlate to F-factor

instantaneously?" We haven't seen the theoretical analysis of the physics that would

suggest that's the case. We have always said we expect temperature to correlate extremely

well or very well with the total F-factor of the shear but not to necessarily predict the

performance increase going in or moment by moment what the F-factor is going to be.

However, some of the data we've seen shows that there are correlations. I'm not sure

exactly why. You saw in this case there was a performance increase predicted, and a

performance decrease predicted. There were even some peaks in the insitu F-factor that

could be traced to peaks in the temperature profile as the airplane was flying through and

we have seen that in some model cases as well. Pat Adamson has something to add to that.

78
PATADAMSON(TurbulencePredictionSystems)- We'vegotthedatafromtheinfrared

sensorsandtheinsitu.Theinstrumentactuallyreceivestheoutsideairtemperaturefrom

theaircraftpluswehavetwodetectors.Forthosewhowill behereonThursday,I'll be

showingthatdata.Theinsitu(thecalculationof Ffromtheaircraftsensor,theoutsideair

temperature)onthecitationcalculateda0.15F-factorabout15secondspriorto theinsitu

fromthewinds.Sowehave,if youwill, twoinfraredandonelocaltemperaturesensor

andwiththealgorithmsweusetheyall calculatedthehazardindexwithin0.02of that

whichwasexperiencedbythewinds.

DAVEHINTON(NASALangley)- TocorrectsomethingIjustsaid,theinfrareddetected

aperformanceincreasingshearonthefarsideof themicroburst.It didnotdetecthe

performanceincreasingshearpriortogettinginthere.Thereasonis,thereisnowarming

tocorrespondtopredictinganegativeF-factor.Thereiswarmingontheothersideas

you'reexiting.

79
80
Session II. Case Study

N91-24171

Model Comparison of July 7, 1990 Microburst

Dr. Fred Proctor, MESO

81
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92
7 JULY 1990 ORLANT)O MICROBLRST

SIMULATION

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SUMMARY

O WET MICROBURST WITH HAZARDOUS WIND

SHEAR

O GOOD AGREEMENT BETWEEN SIMULATION AND

OBSERVATION OF EVENT

O COMPLEX MICROBURST STRUCTURE:

1. MULTIPLE DOWNDRAFT CENTERS

2. AREAS OF UPWARD MOTION EMBEDDED

WITHIN OUTFLOW

3. NON CLASSIC OUTFLOW AND F-FACTOR

PROFILES

O PEAK AV OF 28.7 M/S ALONG EAST-WEST

SEGMENT VS. 23.6 M/S ALONG NORTH-SOUTH

SEGMENT

O TEMPERATURE DROP OF --6 ° C AT TIME OF

MICROBURST PEAK INTENSITY CONFORMS

WITH PEAK AV OF 28.7 M/S; HOWEVER LARGER

TEMPERATURE DROPS OCCUR NEAR THE

GROUND DURING THE DISSIPATION STAGE

O PEAK VELOCITY CHANGE OCCURS -8

AFTER PRECIPITATION FIRST REACHES

GROUND

MIN

THE

O RAINFALL RATES EXCEED 5 IN/HR AND FFACTORS EXCEED .15

102
Model Comparison of July 7, 1990 Microburst - Questions and Ans_ers

Q: CLEON BITER (NCAR) - Is there a reference that discusses the rule of thumb

relationship that relates microburst velocity change to temperature drop?

A: FRED PROCTOR (MESO) - Yes. Journal of Atmospheric Science, Volume 46, 1989,

Page 2143. This relationship is, the peak velocity change in meters per second is equal to

the 5 times the value of the peak temperature drop in degrees C. Now, note that the peak

velocity change and the temperature drop do not necessarily occupy the same place. In

other words, the velocity change could be at a different elevation and position than the

temperature. But anyway, we conducted a series of experiments with the asymmetric

TASS simulation to examine this relationship and found that it worked very, well in a

number of cases. Although it certainly had several exceptions, those being when there

were stable layers present, or if there were dry microbursts, or microbursts which

originated as sublimating snow. This relationship doesn't tend to hold in decaying

microbursts. In the case of decaying microbursts, you can still maintain some very, cold

temperatures near the ground, especially right along the surface where your getting

evaporation of rain from the wet ground, yet the velocity changes begin to decrease.

Q: PETER ECCLES (MITRE Corp.) - Your model showed a temperature drop of about

10.2" C but your summary slide showed a temperature change of 6" C. Why is there a

difference?

A: FRED PROCTOR (MESO) - The summary slide should read a 6" temperature drop

during the peak intensity of the event and again, just for the reasons I mentioned before, the

temperature at the surface in the simulation tended to decrease as the microburst decayed

due to the evaporation of the wet ground. However, if you were to look up at a slightly

higher elevation, you probably would not see much of a temperature drop.

Q: ED LOCKE (Thermo Electron Technologies): - Would you expect to see as good a

correlation between the model and TDWR data for a dry microburst?

A: FRED PROCTOR (MESO) - Yes, in fact I'll be presenting results next week at the

Severe Storms Conference in which we did a simulation of the Denver 11 July microburst,

which was a borderline dry microburst, it had peak radar reflectivity of about 40 dBZ in the

microburst. We seem to get very good velocity correlation with the TDWR.

Q: FRED REMER (University of North Dakota): - What is the forcing mechanism for the

initiation of the July 7 microburst?

A: FRED PROCTOR (MESO) - I haven't evaluated the mechanisms for the forcing of this

case, but looking at some of the data it certainly appears that loading is a significant factor.

There was about 9 grams per cubic meter of rain water as the microburst came down. The

mass loading from that amount of rain water would be equivalent to the same affect of a

temperature drop of about 3 degrees. Certainly evaporative cooling would still play an

important role as the down draft began to propagate below the cloud base level where the

lapse rates were more or less adiabatic. Since there was little ice in this event I expect that

the effects of melting and sublimation to be almost negligible. Certainly for other cases and

events the mechanisms such as loading and sublimation would have various intensities.

103
104
Session III. Flight Management

105
106
Session IIl. Flight Management

N91-24172

Microburst Avoidance Simulation Tests

Dr. John Hansman, MIT

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139
Microburst Avoidance Simulation Tests - Questions and Answers

Q: SAM SHIRCK (Continental Airlines) - On graphic EHSI presentation can a pilot in a

timely manner pull wind shear information from the EHSI when cluttered with weather

radar returns, TCAS information, way points, etc., etc., etc. I like it, but can and will it

work?

A: JOHN HANSMAN (MIT) - There is basically a problem of EHSI clutter, and as I said

before, EHSI has become the most popular piece of real estate in the cockpit, everybody

wants to put something there. I think it's a matter of good EHSI design. Currently you

can deselect basically any piece of information off the EHSI, so you don't necessarily have

to have the weather radar or the way points. You can deselect those. However, if you're

going to put alert information up there you have to think about whether you're going to

allow the crew to deselect alert information or not, probably not. And you would probably

have to prioritize the alert information.

Q: PAUL KELLY (21st Century Technology) - Given the limitations on ATC voice

communications, how sensible it is to depend on ATC voice for uplinking of hazard alert

information like a TDWR microburst.

A: JOHN HANSMAN (MIT) - Clearly, if you have the equipment, the data link would be

a more desirable system. It reduces the latency lag times inherent in ATC voice

communication and gets rid of the frequency blocking effects. On the other hand, for the

foreseeable future, and also in the third world, for example, you're probably not going to

have data links and you're going to have to depend on voice for a long rime.

Q: MARILYN WOLFSON (MIT Lincoln Laboratory) - You mentioned reduced wind

shear hazard flying through the edge of the microburst versus going through the middle.

Are there any significant known hazards from cross wind or leading vortex on the gust

front?

A: JOHN HANSMAN (MIT) - We did do a study looking at cross wind effects and we

actually found that if you penetrated the microburst just slightly off center, you got an

increased performance loss due to cross wind and basically weather cocking effects and in

fact that control gains required to keep the airplane on the straight trajectory on a slightly off

center microburst were much higher In fact, inordinately high which basically leads to the

question, which we tend to ignore here, of the controllability in turbulence problem.

F-factor is a good measure of the total integrated energy loss but if you look at some of the

accident cases, Delta 191 is a classic example, that airplane hit the ground with a lot of

energy. Some of the issues may be controllability issues which we tend to ignore because

we basically don't have the measurements of the fine structure of the turbulence that's

encountered. That's something to think about when we think about hazard criteria because

it's a problem we wrestle with but nobody has a real clear measure of.

DAN VICROY (NASA Langley) - In regard to your controllability statement, we have

done some work (about two years ago) where we tried to estimate not the performance

impact but what the handling qualities impact of wind shear is. We did a simple analytical

study that showed that when you're in that vortex roll, that can be a considerable handling

qualities problem.

JOHN HANSMAN (MIT) - It should be pointed out that it's likely that the regions of high

turbulence and handling problems probably correlate reasonably well with the areas of high

F-factors. So, using F-factor as the criteria at the current status is probably not a bad idea.

140
UNKNOWN - If I could tell a personal story about running a 727 off the edge of the

runway at Denver during the JAWS project. There was a case where unreported, just after

touchdown, the airplane experienced enough of a cross wind from an associated suspected

downburst that the airplane was blown completely off the dry runway. I've always

contended that on take off and landing roll that the industry needs to take a look at some of

the hazards rather than just figuring that the landing is complete after touch down.

JOHN HANSMAN (MIT) - That's an important point. Most of the analysis has been done

for basically a two dimensional case, looking at the longitudinal dynamics. It's hard to do

the analysis for the three dimensional lateral dynamics but there are cases where that can be

very important. We didn't expect that when you displace the trajectory slightly, only about

I00 or 200 feet off the center axis of the microburst, you actually get a significant increase

in the performance degradation.

ROLAND BOWLES (NASA Langley) - To follow up on his point and what Dan said: with

the question of cross wind and scales of turbulent motion on the order of the mean wing

core and span of the airplane, you get into another problem. You've got to now address

the question of how do you model the distributed aerodynamics of that airplane. You can

have outboard sections on one wing stalling before another and that can be bad news. The

lateral directional problem is very complicated. We found that conventional yaw dampers

on big airplanes may actually, because of some root bifurcations going on in the dynamics,

may actually hurt you rather than help you, You want to stay out of cross winds and scales

of motion, severe ones anyway.

UNKNOWN - Most of the experiences we have with microburst penetrations are not

actually symmetric penetrations, there's some degree of cross wind component. In fact,

July 7 was a unique case because it was lined up on the runway on the center line it

targeted. There was a strong cross wind in that case. Remember real world microbursts

are not nice, perfect, axisymmetric events. Even when you're going through the center line

or the mean center line of the event you can get and do get cross winds.

UNKNOWN - This has some interesting applications with regard to predictive sensors.

With a 40 second warning, if the pilot makes the missed approach at 1000 feet, those

problems are somewhat reduced. We're getting a lot of discussions in committees like the

$7 about what to do if you have an alert with a predictive system. For example, AM539

following 191 got what would be a 28 second warning and went through the same event at

about 3000 feet and 220 knots and didn't have much of a problem. So a lot of those

problems go away if you've got some altitude when you go through the event. It bears on

what predictive systems have to deal with and what people need to do when they get a

predictive alert.

141
142
Session III. Flight Management

N91-24173

Wind Shear Training Applications for 91/135

Capt. Ed Arbon, Flight Safety Foundation

143
Operators

_he r_ for windshear tra/ning of all pilots has been

gra_cally demonstrated too often by the accident statistics of past

years. _lile the tragic accidents suc_ as New Orleans and Dallas

rQceive most of the msdia attention, other a/rcraft operators have

unf_tely experi_ t.be sam results when _ir_ _.

need to expand the W_ Traini_ Aid that was _o_d by a

_ of _ _ _, _O_m/l _uglas Corporation,

Corporation, unitad Airlires, Aviatian Weather Asscciatad,

H/llwal, Inc _ with FAA, NASA and other omWrin_ors to o_her

sagmm_s of aviation _s r_xxgdzed immmliately upan cumpletian of t_

original _je=t.

_ruup devalo_d a classic doo0ma_= that has been used to train

a/rline crebm on the Ipecific airczaft harold in the Windshear Tra/ning

Aid and to _ r_xx9%itiun of the metxEological cond/tiuns that are

canducive to _ and ai_ fcr_atian.

_ aim=am: q:m'a_ in Lq_S, _ to th_ mA's

Aviation Activity and Avion_m Survey, _ over 2O0,000 _ in

usa hy ncm FAR 121.0 n_adulad airlines. _ aircraft flew

a_w/ma_aly 33,600,000 h_x_r_. It would be follow that m of this

flyinq _ _ to the risk of a _ or mi_ __er.

144
In order to verify that the example Wi_ Training Aid informatic_

and guidelines are transferrable to other categories of a/_. FAA,

under the guidance of Cliff Hay and Herb Slickenma/er, develqoed a

project to test the ccr_. The Flight Safety Foundation, after

ccrc/uding a teaming a_ with Flight Safety International,

simuflite and Flight Safety Services Corporatian, r_ to the RFP

and was awarded a contract as the prime _r.

Under the carr_ the group will test the transfer of the "Example

Windshear Train_ Aid" an a sample test group of airplane pilots

certified uiKier 14 (_ Parts 91 and 135. _ e_le is to include a

r_t/ve crcas s_cian of both the _c and __.ana3.

:_m_, air taxi and cr_te tu_jet and tu_ a/_

flight simulators.

_e pr_ is t_ seek to dem_ta the effect of specific tr_

an pilot performance. We are to dmErmtrate that during an

encounter with low alti_ windshear that flight

performanoe can be im_if pilots ar_ trained in the te_miques

outlined in the "W_ Tr_ Aid'. _ principle lasscn is

avo/dancm. _here are 120 crm4 in the _ _ m_o are d/vided

into r_tlve _ labeled A, S and C.

Tra_t_ is b_ 4_re u Zollo_:

A and B rQc_ive the entire W_ Group C anly r_c_/ve the _und

sd_x_ portion oF W_.

145
Group A ar_ tested prior to and a_ after receiving the WI_.

Group B are tested after ounpleting the WI_.

Group C is tested after the ground sd_ol porticm of the WTA.

_be _ in group "A" form a crrfcrol grot_ that receive no training

prior to evaluatian.

Gro._ B receive specific trainirq _ques in the simJlator as

detailed by the WI_ for specific use in low-level _

prior to flying U_ _ profile.

Group c receive only w_ ground sd_ol _ avoidanue and r_covery

training but no simulatmr train_ prior to flying the test profile.

ca_iea to be _ are:

_In:jirw low thrust to w_ht tLn_o-Ja1=

Saab340

Cmm_a__ III

C_mda/r_l

Falom_

146
These _ wer_ felt to rep_ a reasonable _ section of r.he

r_u/zlmmnts and simulators area available in acklition to

adequate supply of _.

q_e project officially began on February 21, 1990 and the _ct te_m

is wall into the t_ phase. The data is beinq evaluated as it is

accumulated. _e first of four _ reviews will be held on

25, 1990 at FAA head_arters at 800 _ Ave. If any

of you wish to attar_ and haven't trace/veal an invitation please see me.

It is anticipated that the WTA will pruve to be a valuable to the

91/135 q_rators as it has been to thcae who use it as guidelines fo_

their tra/ning t_y. I believe _ here would agree that the WTA

phenummla and has a/ded flight _ 4_-_,_ably.

As new teahnol_y is _ _ sUz_ will still be the

for reu_9_tiun and avo_ of _xaV_m.

_he i=_uct of our proJGct, if wm ar_ able to pro_ _e data is

transferrable, will b_ our _mmmple WI_ including the gruund s_ol

umurse - Vldmo and 3_ slidmm, Ig-_ film and a/c for Part 1/135

q_ratimw. _ will b_ hasty a re-ism_ of t_m original W_A.

147

DISCLAIMER AND INDEMNITY NOTICE

This document, Windshear Overview For

Management, and its companion _ocumerits, Pilot Windshear Guide, Example

W!ndshear .Training Program, WinOshear

Substantiatin_ Data, and video presentaticns "A Windshear Avoided" and

"Windshear What the Crew "can Do" were

prepared pursuant to Federal Aviation

Administration Prime Contract DFTAOIB6-C-00005 with The Boeing Company as

a training aid for flight in windshear

conditions. The information contained

herein and in the companion materials

was derived from information originally developed for the Boeing 727, and

provides a base-line training program

with additional recommendations, developed and approved by Boeing, Douglas or Lockheed for their respective

aircraft, regarding how that program

might be adapted for use in specific

commercial transport aircraft manufactured by Boeing [727, 737, 747, 757,

and 767], Douglas [DC-9, MD-80, and

DC-IO] and Lockheed [L-lOll]. ANY USE

OF THIS WINDSHEAR OVERVIEW FOR MANAGEMENT FOR ANY PURPOSE RELATED TO AIRCRAFT OR CONDITIONS OTHER THAN THOSE

SPECIFIED ABOVE IS NOT AUTHORIZED AND

MAY RESULT IN IMPROPER AIRCRAFT OPERATION, LOSS OF AIRCRAFT CONTROL, INJURY

AND LOSS OF AIRCRAFT AND LIFE. ANY

USE, ADAPTATION AND/OR USE AFTER ADAPTATION OF THE MATERIAL IN THIS WINDSHEAR OVERVIEW FOR MANAGEENT BY ANY

ENTITY FOR ANY PURPOSE RELATED TO AIRCRAFT, CONDITIONS OR TO TRAINING PROGRAMS OTHER THAN THOSE SPECIFIED ABOVE

SHALL BE COMPLETELY AT THE RISK OF THE

ENTITY RESPONSIBLE FOR USING, ADAPTING

AND/OR USING THE AI)APTATION OF THIS

WINDSHEAR OVERVIEW FOR NIJ_AG_.MENT,AND

SUCH ENTITY BY SUCH USE, ADAPTATION

AND/OR USE AFTER ADAPTATION ASSUMES

SUCH RISK AND WAIVES AND RELEASES ALL

CLAIMS IT MAY HAVE AGAINST THE BOEING

COMPANY, McDONNELL DOUGLAS CZ£;Z:.zTION, LOCKHEED CORPD_TZC_, .',[TES

AIRLINES, AVIATION WEATHER AS%CCIA-Z3,

HELLIWELL, INC., THEIR D!VZSZCNS, SLESIDIARIES, AFFILIATES AND THSZK _ro

FICERS, DIRECTORS, SUBCONTRACTORS _,_

EMPLOYEES FROM ANY LIABILITY _HATS3-

EVER, WHETHER BASED ON CCNTRACT {INCLUDING BUT NOT LIMITED TO EXPRESS

AND IMPLIED WARRANTY CLAIMS), TORT

(INCLUDING BUT NOT LIMITED TO NEGLIGENCE AND STRICT LIABILITY CLAIMS) CR

OTHERWISE, ARISING FROM SUCH USE,

ADAPTATION AND/OR USE OF SUCH ADAPTATION. ANY SUCH ENTITY (INCLUDING

WITHOUT LIMITATION ANY MANUFACTURER OF

OTHER AIRCRAFT OR OPERATOR WITH

ANOTHER TRAINING PROGRAM BUT NOT THE

UNITED STATES GOVERNMENT) WHICH USES

THIS WINDSHEAR OVERVIEW FOR MANAGEMENT

OR ADAPTS AND/OR USES AN ADAPTATION

THEREOF WITH RESPECT TO SUCH OTHER

AIRCRAFT, CONDITIONS OR TRAINING PROGRAM THEREBY AGREES TO INDEMNIFY AND

HOLD HARMLESS THE BOEING COMPANY,

McDONNELL DOUGLAS CORPORATION, LOCKHEED CORPORATION, UNITED AIRLINES,

AVIATION WEATHER ASSOCIATES, HELLIWELL, INC., THEIR DIVISIONS, SUBSIDIARIES AND AFFILIATES AND THEIR OFFICERS, DIRECTORS, AGENTS, SUBCONTRACTORS AND EMPLOYEES FROM ANY LIABILITY

WHATSOEVER, WHETHER BASED ON CONTRACT,

(INCLUDING BUT NOT LIMITED TO EXPRESS

AND Ii,lPLIED WARRANTY CLAIMS), TORT

(INCLUDING BUT NOT LIMITED TO NEGLIGENCE AND STRICT LIABILITY CLAIMS) OR

OTHERWISE, ARISING FROM SUCH USE,

ADAPTATION AND/OR USE OF SUCH ADAPTATION.

Notwithstanding any other provision of this contract to the contrary, the FAA shall accept the

items delivered hereunder with the

disclaimer affixed by Contractor

and agrees not to remove such disclaimer for any reason whatsoever.

ORIG;NAL PAGE IS

OF POOR QUAIJTY

149
Wind Shear Training Applications for 91/135 - Questions and Answers

Q: WAYNE SAND (NCAR) - Even though we have not had a microburst accident

involving air carriers for over 5 years, we continue to have numerous fatal accidents

involving general aviation aircraft. General aviation includes aircraft less capable than the

four being tested. Why isn't the training aid being adapted for these smaller general

aviation airplanes?

A: HERB SCHLICKENMAIER (FAA) - What we're tryi'ng to put together is an

application of the wind shear training aid for 91 and 135. 91 kind of covers ever-,'thin_. If

there is some particular engineering issues that are unique to, and I'm not picking'on one

manufacturer over another, but are unique to a Cessna 150 that bear no resemblance

whatsoever to operators of the Falcon 50 aircraft then, yes, I think there is an issue for

some point of departure. Some of the hypothesis that the program office is putting together

is that there's a body of knowledge that will transfer, in the model of flight crew action that

starts all the way from wind shear weather evaluations through precaution and eventually to

escape and recovery, if those conditions are met. And, that 91, whether its a 150 or a

Falcon 50 may be able to make use of the wind shear weather evaluation portion regardless

of the airplane type.

UNKNOWN - I think that the Cessna 150 has a lot less in common with the Falcon 50

than the Falcon 50 does with the 727. I mean we're talking about an airplane that has a

very different wing loading, very different thrust to weight ratio, and a very different

airspeed. Consequently, I think there is going to be less surprises with the executive jets in

that study than there are for example for the Saab 340 and I think that what you learned

from the Saab 340 may have more application for the Cessna 150 for example. It's not at

all clear that the same procedures are going to apply for the single GA type aircraft.

Whereas it's very possible that what you do for the Falcon 50 will look rather familiar.

ED ARBON (Flight Saftey International) - The one thing I would like to point out is that

we don't have the opportunity to use the advanced simulators for the other aircraft that we

need to prove any of this hypothesis that we're talking about. So we have to use these

categories. I hope you remember that we're using categories of airplanes that were chosen

for certain specific things, low thrust weight, high thrust weight, three engine and the turbo

prop, which are representative of the commuter industry. The other side of the coin is the

fact that in the Cessna 150 and such ,the most important part of the wind shear training aid

is the avoidance section and the recognition of wind shear conditions. That part we

certainly hope is transferrable as is. But really the point is simply avoid the wind shear.

Q: WAYNE SAND (NCAR) - The GA guys that are out there are still getting killed on a

one to two at a time bases, and on a very regular bases. My question is, if your not going

to say anything to the GA guys, why not? If you are, I'd like you to tell me you are.

A: HERB SCHLICKENMAIER (FAA) - What are the four products we're looking at?

We're looking at an update to advisory circular 0050 "Wind Shear", which is the basic

informational document to everybody. We're looking at a ground school training curricula

for 135 operators. We're looking at developing a 135 simulator training for those 135

operators who wish to use it. And we're talking about putting together a part 91 home

study course with computer aided instruction, with videos, pamphlets, and informational

documents to get the message out on the hazards, the need to avoid, what to do to look for

it, how to coalesce the information and how to make a decision about it. In that regard,

yes, we've got a product, the homestudy course and it is designed directly for

91 operators, not just corporates but for everybody.

150
Q: WAYN% SAND (NCAR) - Based on experience working with the GA community of

flyers of 182's and such, the question has come up, when is something coming out tbr me?

When is the Wind Shear Training Aid going to be adapted so that it really applies to the

class of airplane I fly?

A: HERB SCH.LICKEN_'MAIER (FAA) - December 21, 1991.

PETE SINCLAIR (Colorado State University) - I agree with Wayne, as a GA pilot and

researcher, we use small aircraft and there's really no connection between your simulator

approach which involves stick shaker and all those kinds of things to the GA airplane.

We've flown many microbursts and the GA airplane on penetration has to do something

quite different. You're not going to make the same penetration or have the same

penetration procedure as you have in a Falcon or turbo prop for a GA ai_,ane that has 500

to 700 feet per minute rate of climb capability. It just isn't the same. So you're going to

have to write your manual quite differently and that's why we're still having these

accidents. Wayne's perfectly right, we have these accidents over the mountains where

there's no recovery altitude at all. The GA airplane is at maximum altitude and now it gets

into a microburst from the clouds that are sitting right over the peaks and there is no

capability at all to recover. We can't apply any of the techniques you're talking about here.

[ think that's an important question. A lot of GA accidents are classed as something else

but they're really microburst operations.

HERB SCHLICKENMAIER (FAA) - I won't argue, Peter, with you or with Wayne. This

is an issue we're taking a look at. Whether we will be able through the testing of Group C,

the ground school instruction group, to determine whether there will be that last loop in the

model of flight crew actions that sits down and says "hey guys, when you've made a

decision, this is what the recommendation is." Can we transfer that? That's part of the

testing that Ed and his people on the contract team are trying to come up with. Will we be

able to transfer that part? I don't know. But I've got to kind of think that in the

information on how you evaluate the weather and how you figure what's going on out

there before you get into it, there's got to be something valuable. We think that if it can

transfer we're going to move it into the general aviation community as fast and as hard as

we can.

PETE SINCLAIR (Colorado State University) - I agree with the weather part, but the

procedural part for the pilots has to be quite different, I would think.

AL MATTOX (Airline Pilots Association) - So far we keep talking about wind shear

detection or wind shear this or that or the other and as an operator I get really confused. It

seems to me like we seem to think we've invented wind shear. Wind shear has been here

for a long time in various forms. I submit that the training aide has done a lot for the

community. But, there are different operators that look at that document with varying

levels of enthusiasm. To take that document alone and say that this is the solution to what I

think most of us are talking about, which is a recovery from a microburst, is totally

different than the other piece of the pie. Which is, there has to be an operation philosophy

in the cockpit, there has to be crew coordination, there has to be understanding of basic

cross wind limitations. When I make the approach and I've got 50 knots of wind with

gusts to whatever, I don't make the distinction between that as a wind shear and a

microburst. It all has to be put in the same context. I don't think it's fair to give, as good

as it is, the training aid more credit than it deserves. You've got to have some other stuff to

support it.

C ...... r.,-_ ;-k-"-r" 151
HERBSCHLICKENM.AIER(FAA)- I can'tdisagreewiththata bit. Whatwe'retr?ingto

dois followaphilosophywe'vehadwiththisprogamfromthebeginning,whichisto

provideincrementalsteps.Wethinkthereissometremendousbenefitto begainedby

gettingsomeinformationouttothegeneralaviationcommunity,andtheairtaxicommuter

communityasearlyaspossible.Thereismoretobedoneandyou'reabsolutelyright.

We'vebeenwithwindshearfor alongtime. Whatwe'vegotto dois, stepby step,aswe

learn,putit together.I thinkgettingtheinformationoutto atremendoussideof the

community,isthefirst step.

152
Session lII. Flight Management

Determining Target Pitch Angle

Herb Schlickenmaier, FAA

153
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159
Determining Target Pitch Angle - Questions and Answers

Q: FRANK DREW (Lockheed Ausan Divisionl - Why are we looking for a max

performance pitch angle rather than an angle of attack? It would seem I can get into real

bad trouble by flying to a canned pitch angle if I don't integrate my vertical vector and my

rrucro air mass velocity vector. Am I missing something?

A: HERB SCHLICKENMAIER (FAA) - No. I don't think you are. The question comes

up, how do we get the information out in a general set of techniques that can be applied to

the community? If you take a look at what Don Bateman and his guys at Sundstrand are

doing or Joe Youssefi and the people at Honeywell and the rest of the people around the

world that are building boxes that are taking a look at some sophisticated processing, and

certainly when you get into the guts of what NASA's second generation reactive device are

going to be doing; there's some processing going on there that's going to be incredible.

When you're talking about a pilot who's just realized that they're sitting in the middle of a

microburst, now what's the recommended "Oh gosh, what do I do here?" We're not

asking you to go to a max pitch angle, we're never advocating stick shaker to go to

directly. We're trying to come up with something that's moderating in between that gives

you just a little bit of reserve when you get back down to the bottom. I always recommend

you take a look at the issues appendix in the documented, the substantiated data document.

it kind of references where those decisions were made and that was one of the points that

came up during the training.

CARL YOUNG (Eastern Airlines) - In your presentation you spoke of pitch and power,

not perhaps in those words, but that was the essence of it and no one has touched upon

power so fax and I do not see it on the agenda. My comment is there was one national

resource specialist from the FAA that was quizzing whether using max available power was

a good idea. In interviewing crews that have been through three serious wind shear

incidences, to a man, they all said, we don't think we would have made it without all

available power. Based on full authority digital engine controls and electronic engine

controls and other assets that limit power, do we really think as an industry that that's a

good idea? And I would also like to comment that General Electric, to their great credit, is

the only large engine manufacturer that I know of that published their statistics to max

performance with engine deterioration and that was 1017 degrees based on a 945 degree

max EGT, and this was done for 5- 1/4 minutes. That's a tremendous spread.

HERB SCHLICKENMAIER (FAA) - At one point I had heard there was some discussions

going on, I wasn't quite sure whether it was the NRS propulsion people or whether it was

one of the folks out at one of the aircraft certification offices in propulsion, but the question

came up about multiple near simultaneous failures, i.e., you find yourself in a wind shear,

you go to take all available power and run the engine all the way up. The question as I

recall is: "what happens ff we over temp an engine and now we flame one out?" There

have been some discussions going on with the manufacturers of the engines, the airplanes,

and with the certification people. Quite honestly I don't know what the resolution of that

is. From what we've seen from the case studies in past, as Roland has been aptly quoted,

there is no replacement for excess thrust to weight available to extricate yourself out of a

wind shear. Again, I recommend you take a look at the issues section in the back of the

training aide for the 121 applications on those 9 aircraft. There was some discussion that

went on in the appendix regarding moving the engine throttles all the way up, and I'd be

hard pressed to quote it right now.

160
Session lII. Flight .Management

Probabilistic Reasoning for Wind Shear Avoidance

Dr. Robert Stengel. Princeton University

Alex Stratton, Princeton University

161
L_bor_:,:,r', /;>r C_'or.:r,-Z : _c: .A_:,;._'_a: ,,

Artificial Intelligence Advisory

System for Wind Shear Avoidance

3rd Combined Manufacturers' and Technologists

Airborne Wind Shear Review Meeting

October 16, 1990, Hampton Virginia

Presentation Outline

*An Expert System for Wind Shear Avoidance

• Risk Assessment and Probability Theory

• Probabilistic Model for Wind Shear Avoidance

Princeton University J

162
I

Laboratory for Control and Automation

Avoidance of Severe Wind Shear

• Remote wind shear detection

Airborne doppler radar, lidar, flir

Ground-based, TDWR, LLWAS

• Meteorological environment

NIMROD, JAWS, FLOWS

statistical results

• Flight crew training, guidance and control

F.A.A. Windshear Training Aid (1986)

Example training program

Precautionary, escape procedures

Avoidance guidelines

Princeton University j

163
Le,G_ret,)r',_ ,'_:_r C,:,r" :r,):' ,_.",_1'.4 _._'. " _., -, ..... ", -

Expert System for

Wind Shear Avoidance

[GROUND-BASED

PIREPS

LLWAS

Terminal Doppler

Terminal Forecasts

Visual Observations

COCKPIT AID

KNOWLEDGE

BASE

I

_i

[ ._RC IK@-_T

A_\ D

SYSTEMS

ON-BOARD SENSORS

Wind shear detector_

Forward-looking sensors

Airborne radar

Motion sensors

Visual observations

• Increase crew decision reliability

Monitor sources

Prediction

Apply knowledge, assess risk

Recommend alternatives

• Rule-based implementation

-200 "IF-THEN" rules

Goal-directed, cyclical search

Real-time, translation

Princeton University /
Laboratory for Control and Automation

Probability Theory for

Risk Assessment

• Windshear Training Aid avoidance guidelines

"Low," "Medium," and "High" risk

Avoidance appropriate: "High" risk

"Low + Medium = High"

"Convective weather near flight path"

"Rainshowers" vs. "heavy precipitation"

"Use of [the avoidance guidelines] should

not replace sound judgment."

• Probability theory

Widespread understanding

Meteorological statistics

Detection reliability statistics

Efficient implementation - Bayesian

network

Princeton University J

165
r , . 4 •

Elements of Probability Theory

• Condition probabilities Bayes's rule

H: Hypotheses of wind shear

E 1" Alert of wind shear

Pr{H J El} :

Pr{E11 H}

Pr{E1}

Pr{H}

Prior probability, Pr{H}

Probability of detection, Pr{Ell H}

Probability of false alarm, Pr{E 11-_ H}

• Multiple evidence, structure

Pr{HI El,E2}-

Pr{E 1,E2 i H}

Pr{E1,E2}

Pr{H}

Conditionalindependence assumption:

alerts independent consequents of wind shear

Pr{H[ EI,E2}=

Pr{E2 [H}

Pr{E2 [El}

Pr{HI El}

Princeton University J
Laboratory for Control and Automation

Graphical Representations

of Dependency

(o--

= LINK)

• Graphical representations

Hypotheses, Nodes

Dependencies, Links

Cause-effect, Arrows

• Causal hierarchies

Lightning, precipitation dependent

Independent given convective weather

Princeton University J

167
Probabilistic Reasoning in

Bayesian Networks

• Evidential Reasoning (Effect to Cause _

vectt_e %_

,CW1

Pr{Hi I E-} =

Pr{E-IHi} =

Pr{E-IHi}

DIE-} Pr{Hi I E-}

Pr{E-I LR}Pr{Lk I Hi}

k

Alert (L)

• Causal Reasomng (Cause to Effect)

Pr{Hi I E+} =_

k

Pr{Hi I CWk}Pr{CWk I E+}

168
Laboratory for Control and Automation

Probabilistic Model of Windshear

Training Aid Guidelines

Location

Time of

Convective Weather

Wind Shea:

Detection System

PIREP

• JAWS, NIMROD, FLOWS, LLWAS

• Relevance to terminal operation

• Combined judgments involving uncertainty

Convective weather near flight path

Alerts versus weather features

"rainshowers" vs. "heavy precipitation"

Princeton University J

169
Requirements for Probabilistic

Representation

Wind Shear

LLWAS

Alert

Given the level of wind

shear on flight path is:

Probability of LLWAS

Microburst Advisory. is:

Probability of LLWAS

Wind Shear Advisory is

Probability of no

LLWAS Advisory is:

Severe

0.6_9

0.223

0.128

Moderate Light

0.082 0.026

0.810 0.2z6

0.108 0.728

• Link probabilities

Enhanced LLWAS, wind shear detectors

*Conditional weather and prior probabilities

JAWS, NIMROD, FLOWS

• Uncertain probabilities

Turbulence

Princeton University J

170
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Conclusions

• Bayesian networks assimiIate meteorologacal

knowledge

manages uncertainty

fusion of evidence

stochastic prediction

• Probability provides scientific basis for avoidance guidelines

meaningful summaries

documented experience

•Uncertain probabilities

refinement by component

basis for meteorological studies

Princeton University

I74
Session IV. Sensor Fusion & Flight Evaluation

175
176
Session IV. Sensor Fusion & Flight Evaluation

N91-24174

integration of Weather Sensing Devices

Jim Daily, Honeywell Sperry.

177
INTEGRATION OF WEATHER SENSING DEVICES

JIM DAILY

HONEYWELL, INC.

ABSTRACT

The state of airborne atmospheric sensing is continually evolving as ze,'tet

are developed which Further enhance the detection of meteorologica_ s_e_z-e-_

Assuming that these technologies prove to be feasible, the greatest ic_-te,-

benefit would be attained by effective integration of the various sensors, z

system which could accomplish this goal would conceivably provide ennarces

atmospheric analysis, coherent display capability, and would allow for t_e

development of expert systems to predict weather conditions.

This presentation briefly outlines the existing and developing weather

detection technologies, followed by an overview of what issues must be deait

with in the creation of an integrated system. The presentation concludes wit_

a framework of a basic system which identifies some of the potential

applications that exist.

1T8

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Integration of Weather Sensing Devices - Questions and Answers

Q: BERNARD SILVERMAN (Active EO Systems Analyses) - What is the basis for the

statement that LIDAR is poor in rain? Is there any good data?

A: JLM DAILY (Honeywell Sperry,) - The ranking of LIDAR as "poor" in rain is due to

information based on the Lockheed CO2 laser. The signal is absorbed by rain and therefore

the signal is significantly attenuated. This translates to a loss of range during severe rain

conditions. The majority of data supporting this is as presented in Russel Targ's

presentation. "Poor" only relates to the ability of the LIDAR system to penetrate heavy

rain, not its ability to identify the edge of the hazard.

199
200
Session IV. Sensor Fusion & Flight Evaluation

N91-24175

NASA Langley Flight Test Program

Mike Lewis, NASA Langley

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NASA Langley Flight Test Program - Questions and Answers

Q: WALT OVEREND (Delta Airlines)- How do you judge go, no go decisions on the

airplane before you penetrate a microburst? What parameters are you v, orking from?

A: MIKE LEWIS (NASA Langley) - We establish a reflectivity limit over which we wont

go through and we'll use the standard weather radar for that function. There will be a fairtv

rough reflectivity limit corresponding to the red level on the standard radar which is about

40 to 50 dBZ. For lighming avoidance, in general we're not going to stay away from all

lightning but certainly areas of severe fighting activity we will avoid. For that we will use a

fighting detector storm scope to be installed on the aircraft. We will be operating at

locations covered by TDWR and will be relying on up [inked TDWR information to

determine whether or not the microburst strength is over the penetration threshold. We will

also use their support for hail detection and avoidance in addition to the standard weather

radar for that function. Additionally, we will have a number of wind shear sensors on the

aircraft and to the degree that we have some operational confidence in those sensors we'll

also use those, albeit research pieces of equipment for determining the limits over which we

won't fly through. Lastly, there is pilot's discretion, everything is up to the guy in the

front flying the airplane and anything that he's not comfortable flying through, for

whatever reason, the airplane won't go through.

Q: UNKNOWN - In regard to a lot of the accidents we've seen, the encounters are down

around 500 to 300 feet, as you go on with your test program are you planning on trying to

gather data down there, especially for the radar sensors?

A: MIKE LEWIS (NASA Langley) - Yes. The information I presented as to what our

final altitude limit will be was preliminary. That's still to be determined. We will be

determining that form the piloted simulations through the microburst models which will

show what kind of safety margins we have. However, I think as a general philosophy, we

don't need to be operating exactly on approach in the same configuration that a real

encounter would be. For test purposes, all we need to do is verify the function of the

experimental systems that we have on board. So we want to fly low enough to get a

healthy enough horizontal component of the shear but not necessarily put ourselves in a

situation where we're flying through the maximum of that horizontal component down at

the 200, 300 foot level. So as long as we stay within a band that has enough of the

horizontal exposure and not totally a vertical component of the microburst we believe that

we can evaluate the function of these various instruments.

ROLAND BOWLES (NASA Langley) - We've taken great pains in both of the pulse

Doppler systems to provide pointing capability. When we are at 1500, in that vicinity, our

problem is to keep range gates out of the ground. We are probing all the way down. The

idea is to manage the antenna tilt in such a way as to not process range gates that are

intersecting the ground and picking up clutter, both moving and fixed. The point is the

remote sensors will be able to probe down. We can point the sensors, and we can slew the

sensors. It's not necessarily confined to looking in a very narrow cone in front of the

airplane.

UNKNOWN - I understand the safety constraints on that from the flight test standpoint. I

guess your answer leads to more questions. You say you're already running into range

problems of picking up ground clutter which are obviously going to get worse the closer

along the approach or lower altitude you're at.

222
ROLAND BOWLES (NASA Langley) - That's the key research question we are dealing

with, the whole emphasis in the radar develop program. The key thing is managing

antenna tilt in such a way that along with clutter suppression techniques at the signal

processing we can detect the wind shear, while de-emphasizing the contaminating effects ef

Wound clutter. That's the research question. If we can't solve that problem then radar is

not a suitable solution. We think we can by managing antenna tilt as a function of "altitude.

always keeping the 3 db point of the antenna out of the ground. The trade off is, we don t

want to do that in such a way as to overlook the top of the out/low and therefore

underestimate the threat. That's the trade off. And the best way we get the answer to those

questions is to configure the system, fly and evaluate.

Q: UNKNOWN - Isn't there an obvious advantage to a ground based LLWAS type

approach over the airborne equipment in avoiding the look down clutter problem'?

ROLAND BOWLES (NASA Langley) - I would think so because they're on the ground.

You're at least looking up a bit with your narrow beam antenna. These guys have spent

considerable effort, time, resource, money and agony, no doubt, in solving the cLutter

return question. It's not a question of ground versus air. The policy has been set. There

shall be ,17 radars deployed at major TCAs and there is an airborne equipment rule. The

point is, what is the airborne equipment technology that best does the job for the least

amount of bucks and makes incremental improvements in safety. I don't know what the

answer to that question is but we think we'll have more information to draw inference on it

after we finish our flight program with these three sensors.

UNKNOWN - Again, 750 feet seems a bit high. I'm still concerned about the issue of

where the down flow becomes outflow and to the extent that you are almost at that

transition altitude and that you are looking at pilot technique above and beyond the sensors.

or the pilot's ability to interface with the information in the flight deck. That's been an area

of difficulty, as you know for us, in the development of the wind shear training aid and

pilot technique and so forth, to recognize the safety concerns. But it does seem there is

area below 750 feet that needs exploration.

ROLAND BOWLES (NASA Langley) - In the NASA program we're not looking at pilot

technique. We're using the airplane as a platform to hold the sensors. We're not looking

at recovery techniques or anything like that. Based on the totality of data obtained over the

many years of the test program the maximum outflow is, statistically, somewhere between

80 and 150 meters altitude and the half velocity point is 300 to 400 meters typically. So

there is plenty of signal and outflow aloft based on, I would think now, hundreds of

measurements of microburst.

MIKE LEWIS (NASA Langley) - The preliminary limits that I was showing are only

applied when we've got a microburst out there that's over our threshold limit, the threshold

being around 0.1 or so. We will then impose a minimum altitude constraint. Below that

threshold we'll fly all the way down to touchdown. These sensors will be operational in

the research mode all the way down through touchdown even through microburst or

whatever other weather phenomena below the 0.1 level threshold. So there is still the

opportunity to detect and evaluate the sensor's performance all the way down to touchdown

within the flight test program.

BILL MELVIN (Airline Pilots Association) - rye got to speak to this maximum outflow

issue. This was an idea that was used to perpetuate the ground cushion theory myth of

microburst or downdrafts. That myth was that in a downdraft you didn't have to worry,

about flying under it because it couldn't blow through the ground so there had to be a

OR_C_NAL PAGE IS

OF POOR QUALITY

223
cushion down there. So, over the years people developed this idea that the maximum out

flow' occurred somewhere around 300 feet, it's also called 100 meters. With that kind of

philosophy it means that it gets better below 300 feet. Therefore, the only reason the

airplane would hit the ground was that the pilot didn't fly it right. Albert Bedard and S. J.

Caplan have measured the maximum outflow, it's in AIAA paper, 87-0440, and the',' found

that in the highest velocity downdrafts the maximum outflows occurred at about 10 meters.

roughly 30 feet above the ground.

ROLAND BOWLES (NASA Langley) - I agree with you Bill. I don't know exactly where

it is, but I know one thing, its got to got to go to 0 somewhere down there. It's jusi a

question of how thick the boundary, layer is.

224
Session V. TDWR Data Link / Display

225
226
Session V. TDWR Data Link Display

N91"24176

TDWR Information on the Flight Deck

Dave Hinton, NASA Langley

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TDWR Information on the Flight Deck - Questions and Answers

Q: FRED REMER (University. of North Dakota) - The climatology of F-factor from

JAWS, flows and TDWRs is impressive, but I'm troubled bv some of the assumptions

used to calculate F-factor, such as the downdraft, the true airspeed, etc. Would it make

more sense to use aircraft data?

A: DAVE HINTON tNASA Langley) - Certainly, where it's available we would like to

have aircraft data. The number of cases where an aircraft went through the core of a

microburst while being examined by a radar is very, very small. I don't believe the true

airspeed assumption is invalid, as a matter of fact, it is probably more valid to assume a

typical transport category aircraft approach speed rather than the airspeed that you would go

through in the Citation. You're going through quite a bit faster than a transport would.

The estimation of the downdrafl is obviously an area that needs more research.

Q: FRANK DREW (Lockheed Austin Division) - There is lots of looking at detection,

interpretation, and integration. Basic systems such as LLWAS and TDWRs use different

I/O parameters. Ground people and air crews have varying information needs. Cockpit

real estate is very limited. Pilots must make their own decisions - not react to safety of

flight decisions made from the ground. You say that future work includes display

development. Given the situation the question is: is anyone in charge of developing cockpit

display requirements, specs and standards? Should there be standardized displays? Who

is in charge? What kind of aviator interaction (ALPA, airline operations people, NASA,

DOD, MAC)? What kind of industry interaction? And a timetable for all of the above?

A: DAVE HINTON (NASA Langley)- I think we're getting into the realm here of the $7

committees, the various processes that are used to formulate industry specs, aviation

practices and TSOs. NASA is certainly not in charge of developing display standards for

the flight deck. We can provide guidelines. We can do the research to tell you what the

forward looking systems are capable of doing. We can develop candidate crew procedures

that can be supported by these forward looking systems. We can certainly develop display

concepts and provide all the guidelines we get from research. We as an industry,, again the

$7, the airlines, the airframers and FAA certification, have to get together as a team to iron

out the standards and specs. Timetable? I don't know. We're talking now about the

formulation of an $7 committee on forward looking systems. I don't know of any being

formed on displays. We'll be able to show you what you can do with a forward look

system, but additional work has to be done to integrate this information with the displays

given all the other requirements on the displays, such as ground prox, TCAS, etc., etc.

Q: WALT OVEREND (Delta Airlines) - You mentioned second generation reactive wind

shear systems. What do you see as a better design to achieve a second generation system?

A: DAVE HINTON (NASA Langley) - I believe the current generation systems have two

problems. One is a false alarm problem that can be induced by the turbulence rejection

filtering that must be done, the lack of appropriate filtering or any rnisphasing of the

various aircraft inputs, Secondly, aircraft maneuvering, thrust changes by the pilot, flap,

spoilers, or gear position changes, all tend to ripple through or feed back as an F-factor on

a reactive system. NASA has been involved in some simulation research over the past year

and we're just now moving it into our airplane, to develop a second generation insitu

system to be used as a truth measurement for our combined sensor flight test. The F-factor

equation I showed this morning is a very simplified form of the F-factor and only holds

true while the airplane is flying in the vertical plane. If you bank the airplane and start

241
turning, a lot of other parameters fall into that equation. These parameters have to be

included and we're now doing that.

Q: WALT OVEREND (Delta Airlines) - Do any of the conducted studies look at prevailing

atmospheric and/or geographic formation to be able to predict how rapidly microburst form

and move or decay and dissipate?

A: DAVE HINTON (NASA Langley) - There is a great deal of experience and

documentation on that problem. The JAWS, Flows and CINDE data, similar to what

we've presented today, show the microburst to be a very dynamic event. They can grow

very rapidly from an insignificant event to a full strength microburst in a 3, 4 or 5 minute

period, then they tail off relatively slowly. When do they cease to be a rrucroburst, and

when do you call off the alarm, is another question. As far as one dedicated reference on

that particular topic, I didn't know of any out there. But, the data is buried in a number of

reports; the information is available.

242
Session V. TDWR Data Link / Display

N91-24177

Orlando Experiment

Dr. Steve Campbell, MIT Lincoln Laboratory

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261
Orlando Experiment . Questions and Answers

Q: ED LOCKE (Thermo Electron Technologies) - What is the cost per airport of the

TDWR as projected by Raetheon? How effective is the TDWR in seeing dry. microbursts?

A: STEVE CAMPBELL (MIT Lincoln Laboratory) - I don't have the exact numbers here

but I believe the total cost per airport is something on the order of 6 to 7 million dollars.

On the other question; our feeling is that the TDWR is very effective in detecting dry

microbursts. About the lowest reflectivity you're going to see in an outflow, even in

Denver, is down in the order of -20 to - 10 dBZ. That is well within the sensitivity rating of

the TDWR. For the ASR9 with the wind shear processing you do have a sensitivity

problem in a Denver type environment.

Q: NORMAN CRABILL (Aero Space Consultants) - Have you considered uplinking the

microburst velocity divided by distance or the Bowles' F-factor to the pilot?

A: STEVE CAMPBELL (MIT Lincoln Laboratory) - We in fact did transmit that to the

airplane but we didn't display it. We could have and perhaps should have. It was an

operational decision.

Q: ED LOCKE (Thermo Electron Technologies) - Can you give the characteristics of the

TDWR used in the tests at Orlando?

A: STEVE CAMPBELL (MIT Lincoln Laboratory) - I'll give you the characteristics for the

TDWR as I recall them and our test bed is very similar to these characteristics. The wave

length is 5 cm; the antenna diameter is 27 feet; the PRF is adaptive. We have an adaptive

scheme where we scan at a low PRF of about 350 Htz. That allows us to identify

unambiguously the very long range echoes. We then adaptively select a PRF which

minimizes second trip folding into the first trip. In particular we try to minimize the folding

around the immediate airport region. If there is folding that we can detect it, since we

know unambiguously where all the range echoes are, we can determine from a given PRF

where all the folding is occurring and flag the obscured cells. As a practical matter our

PRF goes from something on the order of 700 Htz up to about 1200 Htz. The pulse

energy of the Raetheon TDWR is a quarter of a gigawatt and the pulse length is one

microsecond. Our pulse length make be a little bit shorter for technical reasons. The

microburst alarms are updated once a minute. Our beam width, both horizontal and vertical

is a half degree, actually TDWR is 0.55 degrees.

262
Session VD TDWR Data Link / Display

N91-24178

Integration of the TDWR and LLWAS Wind Shear Detection System

Larry Cornman, National Center for Atmospheric Research

263
Integration of the TDWR and LLWAS Wind Shear Detection Systems

by

Larry Cornman

National Center for Atmospheric Research*

Research Applications Program

Abstract

Operational demonstrations of a prototype TDWR/LLWAS integrated wind

shear detection system were conducted at Denver's Stapleton International Airport

during the 1989 and 1990 summer seasons. The integration of wind shear detection

systems is needed to provide end-users with a single, consensus source of

information. A properly implemented integrated system provides wind shear

warnings of a higher quality than stand-alone LLWAS or TDWR systems.

The algorithmic concepts used to generate the TDWR/LLWAS integrated

products and several case studies will be discussed, indicating the viability and

potential of integrated wind shear detection systems. Implications for integrating

ground and airborne wind shear detection systems will be briefly examined.

* NCAR is sponsored by the National Science Foundation.

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Integration of the TDWR and LLWAS Wind Shear Detection System

Questions and Answers

Q: WALT OVEREND (Delta Airlines) - Are LLWAS sensors located high enough, that is,

out of ground effect, to be really sensing the relevant air mass or the prevailing air mass as

it effects the runway?

A: LARRY CORNMAN (NCAR) - In a sense there are two parts to that question. One is

the sheltering effects and the other is the accuracy of measurements that are that close to the

ground relative to what a pilot would see along the glide slope. The f'u-st part of the

question in terms of the accuracy of measurements form poor locations is something the

FAA has dealt with and is part of some of the upgrades to the six stations, certainly the

enhance LLWAS system. Sheltering effects are taken care of by either raising the sensors

or moving them. The second part of the problem is very difficult. You can only raise the

pole so high. The sensor close to the runway surface is probably a very good estimate of

what the pilot would see. Out further from the runway, one, two, or three miles, it gets

worse. Again, you're limited by the location and the size of the pole that the sensors are

on.

Q: GREG HAEFFELE (Boeing) - If both systems alert on the same microburst, but at

different intensities, which takes precedence? If detected by both systems, does the

"bandaid" size increase to encompass both areas?

A: LARRY CORNMAN (NCAR) - Basically, it's independent. LLWAS and TDWR both

produce bandaids independently. The technique for issuing an alert is based on the

technique that was developed for TDWR, that is, a bandaid intersecting a runway gives a

magnitude and location. If you add more shapes you add extent and potentially larger

magnitude. The idea is to pick the largest magnitude in the first potential event

encountered.

Q: PAUL ROBINSON (Lockheed) - Complaints from pilots on wind shear reporting have

been largely due to too much information. For example, wind speed and direction at

different points on the airfield. Is this information from the LLWAS? If not, what

information is communicated from ATC to the pilot concerning wind shear on the approach

from LLWAS? If so, can the information be compressed into a more manageable form?

A: LARRY CORNMAN (NCAR) - Basically, that's been done. In phase III the alerts are

runway specific, and that was part of the TDWR / LLWAS user group work that went into

simplifying that data and make it more precise so each runway would have a specific alert.

Q: HERB SCHLICKENMAIER (FAA) - In one of your charts, you showed the productlevel integration tests in '90. In it, you used TDWR precipitation to validate LLWAS

information. Could the ASR-9 precipitation product be introduced in lieu of the TDWR?

A: LARRY CORNMAN (NCAR) - The product level integration technique that I put

together doesn't care what the source is. So, in fact, right now with the wind shear

detection program going on with ASR-9 the product output from that system would look

identical to the TDWR output. Not only could the precipitation product be used in a similar

fashion but the detection of events with a bandaid in a sense would fall through.

297
298
Session V. TDWR Data Link / Display

A Status Report on the TDWR Efforts in the Denver Area

Wayne Sand, National Center for Atmospheric Research

PRECEDIi'_G PAGE BLANK NOT F!LMF_D

299
A Status

TDWR Efforts in

Denver Area

Report on the

the

by

Wayne Sand

Research Applications Program

National Center for Atmospheric

Research

for

17 October 1990

NASA Langley Research Center

Third Combined Manufacturers and

Technologists Airborne Wind

Shear Review Meeting

30O
A Status Report on the TDWR Efforts in the

Denver Area

by

Wayne Sand

t

National Center for Atmospheric Research

Research Applications Program

Abstract

A prototype radar developed by Raytheon as part of the NEXRAD program is

currently being operated in Denver, Colorado, by the National Center for Atmospheric

Research (NCAR). The Federal Aviation Administration has contracted NCAR to use

output from the radar to duplicate the wind shear detection capabilitiy of a a Terminal

Doppler Weather Radar (TDWR) in an effort to continue development of TDWR

algorithms and to protect Stapleton Airport. NCAR's efforts as they relate to the

ground-based wind shear detection program will be summarized. The presentation

will include a discussion relating in-flight microburst encounters to the severity of the

events as detected by the TDWR system. Controllers' and pilots' perceptions of the

system, overall detection and false alarm statistics from the system, and microburst

alarm threshold logic will be discussed.

* NCAR is sponsored by the National Science Foundataion

301
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Denver Terminal Doppler Weather Radar (TDWR)

Geographical Setting

/_ LONGMONT

ARTCC/CWSU

56',,Kb

', RAP TDWR

__PS CENTER /_ -- ,_)- km T-1

Stapleton

New

Denver

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"'_FUTIJRE

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SIrE

Height of MI-IRo5 ° beam over

Stapleton Is 140 m (450 ft)

/x

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,/_ Foothills

303
Project Summary

1990 Denver TDWR

Program

Shakedown Period: 1-31 May

Operational Period: 1 June-7 Sept

Products Delivered:

I1¢ TDWR/LLWAS Integrated

Alarms

Gust front Detection and

Prediction

LLWAS Operational Winds

Precipitation

Storm Motion

(Reflectivity)

Nowcast Product

304
Operational Summary:

Hardware Problems

Two days down due to

Radar hardware failure,

other minor problems due

to hardware and software

Weather events within 5 nm

of the Airport center

> Microburst

95 Events (30-70

17.6 Hours

(50 affected the

airport)

> Wind shear with loss

159 Events (1_5-30

> Wind shear with gain

65 Events (15-45

Kts)

kts)

kts)

305
Performance of the system,

quick look

> Greater than 90% POD

> Less than 5% FAR

306

308

ORIGINAL PAGE IS

OF POOR QUAUTY
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309
1990 OPERATIONAL DEMONSTRATIONS

USER INTERFACE ASPECTS

NOTIFICATION OF, 1990 OPERATIONAL DEMONSTRATIONS

• PRESEASON AIRLINE BRIEFING

• LETTER TO AIRMEN

• NOTAMS

• PILOT QUESTIONNAIRES

• NOTIFICATION ON ATIS

• ATC TRAINING SESSIONS

PILOT REACTIONS

• FEWER OPERATIONS DURING MBAs; HOWEVER SOME STILL

OCCUR

• FEWER TAKEOFFS WITH 15 KT LOSS ALERTS

PILOT QUESTIONNAIRES

• PROVIDES PILOTS A MEANS TO COMMENT ON SYSTEM

• VERY SMALL PERCENTAGE RESPONSE

• PILOTS REPORT "SIGNIFICANT" WIND SHEAR ENCOUNTERS

BEGINNING AT 10 lETS

ANALYSIS EFFORTS TO REDUCE "NUISANCE" ALARMS

• 15 KTALARMS

• MODIFICATIONS TO WIND SHEAR WARNING BOXES

• REDUCTION IN SIZE OF MB SHAPES

310
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322
Summary, 89 and 90

Activities at Denver:

1. Continued development and

improvement of TDWR/LLWAS

Integration

2. Demonstrated Terminal NEXRAD

concept in 1989, program canceled

3. Considerable Interaction with

other groups for a better

understanding of the July 11,

1988 Microburst Case

> Numerous papers in the

literature

> See DOT/FAA/DS-89/19

323
4. Reasonably good agreement of

f-factor calculations from Radar

with those derived from Aircraft

5, Continued development of

Nowcasting and Convective

Initiation

> Primary users at Center and

TRACON

> Prefer Convective Initiation

and Storm Motion Vectors

6, Continued development of

Tornado Detection and Forecasting

324
7. Continued examination of User

Interface issues

Threshold for warnings (15

Kts)

> Size of warning areas (Alarm

boxes and alarm shapes)

> Perceived over warning

> Terminology

8. Reliable operations during

1990

9. System performance statistics

more than acceptable

10. Runway Extension LLWAS is

providing good coverage farther

from the threshold

325
11. Enhanced understanding of the

relationships between ground

based and airborne systems

expected during the 1991 tests

with the NASA Aircraft flying in

the Denver area

326
AL_ERFk, ]L';A.!4

The 11 July 1988 Microburst at

Stapleton International Airport, Denver, Colorado

K. L. glmore, M. K. Politovich, and W. R. Sand

National Center for Atmospheric Research _

P. O. Box 3000

Boulder, Colorado 8030T

I. Introduction

During the earl}' afternoon of 11 July 1988, while

the Terminal Doppler Weather Radar (TDWR) Operational Test and Evaluation (ST&E) wu underway, thund*.rstorms formed over the mountains west of Denver, Colorado, and moved eastward over the plains. By 21302,

several ceils approached the Denver area. One of the more

vigorous of these was located just northwest o[ Stapleton

international Airport. Tt produced the most intense mlcrob,:rst - 35m s -t differential - investigated to date using

d_JabDoppler radar techniques.

The TDWR mlcrob,rst alarm aJerted ,fir _rafflc coatro;brs to _be hazard from 2206--2?48. During this time, 4

commerdal passenger aircran penetrated this rr6cr_bun, t,

fortunately whhout incident.

The r_Jcrobucst reached the ground levers/ km

soothes.st o_"the main precipitation shaft of the storm.

"Fh;s b_hador dlf_ers from that of moat mlcmbarst rue

studies reported prev_oudy (Fu_ta I985). Tile evolution

o( the mlcrobuest will be exaa_ned in this _ody. Details

not contained in this paper m'il be included in the poster

session.

IT. Data _ources

The prlmat 7 data sets used in this study summary

come from 2 Doppler radars operated az part of the TDWR

ST& g. The Mu=achusetts Institute of Technology Lincoln

Laboratory 10-cm wavelength Doppler radar (FL2)

used as the project test-bed instrument. The University of

North Dakota (UND) 5-¢m Doppler radar, located about

21 km north o_ FL2, silo gathered data. Scanning patterns

of the t.m radm _ coordinated to enable dusJ-Doppler

_st-_s/ys_ o._ the alrp_t area (see Fig. I). Coordinated volume _ _ ¢mnpleted every 2.5 rain. The

)owe_t effective elevati_ _ wu 0.2" [rmn. both FL2

a,d U/_D, pladag the beam center, apl_mately 190 m

abo,_ the center of the airport. Over the slrpmt, both

be'am-i mere roughly 150 m in _ameter.

25 '

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o FLOWS

• CLASS/NWS

I ] I I I I i I t I ,

-2S -20 -_S -_0 -5

DISTANCE EAST OF fL2 R_OAR (krn)

figure Captions

FIOURE I, Locaflo_ of mda_',, su/_¢ce ,.e,oaet ,¢=tio,_e and

iltt CLASS launch sale daei,_ _e 1988 TDWR OTO5 at 5in.

pleton lnte_eflon_l Airped, Denser, Colo'_do T_te airp¢,'i

_l_nwa}'s =_ abo s_otcm. _r'_em_cro_wrsi ouL[ioe (rJiverge_ce _>

t0 m e-rover a distance _<4 kin) rear _Ae ..,'f=c_ _t 't_I_ i.

*,,_,am_eseg.

Surface and upper air tt_ermodynam;e and wind

measurements were tl,o used in this study. The

FAA-Lineoln Laboratory Operational Weather Studies

(FLOWS) me=oneS (Wolf=on eL d. 1987), consisting of

22 stations, wM in place in and around the airport area.

This wu supplemented by the I2-etation Low Level Wind

Alert System (LLWAS), which melunu'ed wind,, near the

airport runways. A Cross-chain Loran Sounding System

(CLASS) launch rote was located at the Denver Nations]

We=LEer Service O_ce adjacent to Stapleton Airport.

NCA R is spoas,_d i_ dt¢ Natio,t_l 5clerics Foundalion

All ti,ne_ awe UTC.

327

ORIGINAL PAGE IS

OF POOR QU/_TY
Ill. Meteorological Conditions

The major ,ynoptic scaleweather featureon II July

tgS8 wu a slowly-eaatlvard-_ng shall_ trough over the

western United States. This feature _ barely dlscernable

at 70 kPa and vanished above that level. Winds were generally westerly snd were less than _.0 m s -I at all levels

over C:florado, Wyoming and Utah. This westerly flow

adverted moisture into the Denver area, which increased

in a deep layer extending from just above the surface to

over !2 kmS. A maximum of 1.0,5 cm of total precipitable

water was measured by the National Oceanic and Atmospheric Administration's 6-channel microwave radiometer

at 5tapleton Airport between 2200 and 2230.

Prior to the storm, conditi_ near th,_ Su/-@ace

typical of those accompanying microhunmts observed in the

Intermountsin West (Caracena and Flueck Ig87). The

temperature-dewpoint spres_ at the surface wu 20 - 25°C,

with a nearly dry adiabatic temperature lapse rate from

the surface to 418 km. Above that, a layer of moist sir wan

present. There wu marginal moist convective instability,

with a Lifted Index of -2.

Equivalent potential temperature (#.) is plotted

against height in Fig. 2 for 2 CLASS soundings preceding the storm. Above the moist layer, the atmosphere is

quite dry and 0, deerlemmes. At T.2 km, a sharp abso|ute

minimum #, of 326 K is present in the 2004 sounding, and a

relative minimum exists betw_n 4.8 and 5.0 ks. The minimum e. occurs at the level o( a 2 "C temperature inversion,

the hue of which hu a temperature of - 20"C. Although

saturated parcels originating between 7.4 km and around

4.8 km are potentially cold and will accelerate downward,

the coldest parcels will originate around 7.3 km and just

below 5 ks.

Three buic Itow regimes efist: light and variable

winds from the surfaceup to $ km, westerlywinds between

S and 7 ks, and northwesterly winds above 7 ks.

IV. Analysis

a. Du_l.Oopplee AnalyJb TeekniqueJ

The CEDRIC analysis padmge (Mohr et ill. 1988) is

used foe three-dimenslonal wind field synthesis and analysis. Fourteen volume1 were analysed, from 2148 through

2220. The analysis has 400 m horizontal and 500 m vertical grid spas:inf. The domain extends from 1.8.10.8 km

(0.19 - 9.19 km AGL) vertically, and 2 - 30 km west, I -

23 km north of FL2 hoviaontall7. Stapleton Airport is

roughly centered in this grid; the microburet impacted on

the southeast edge of the airport, well-centered in the analysis domain (see Fig. I).

Raw input Doppler velocities were corrected br a

deduced storm motion o( 10 m s -I from 2T0"; resulting

analyses shows ground-relative winds.

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winds st 0.5 i'm wesoluiion plolled afai_H heigh! _.e_m the ! 700

an/_00( UTC CLASS sova_nCe.

A one-pass Cressman objective analysis scheme was

used (Cressman IgSg) to map radial velocity components

from sphe_eal c_rdinstee lo gHdded Car(g/;ifi space. Before a consistent w component wu calculated, the horizonCat winds were filtered with S pu_.l of a two- dimensional.

three-point smoothe_ (Shaman 1955). The resultin_ an,_,lyses have 2 km horisonial spatial resolution at the hair.

amplitude points.

b. Micrc_ar_t e_olutlou

The mieroburst-produelng complex originated from

two 604- dBZ, eells welsh formed around 2130 over the

mountains :!4 km west of Stapleton. These cells grew and

moved southemumtwsrd.

By 2147, a line o( eonvergtmee alok_ was observed

near B.6 ks, oriented northwcet-southeui and moving to

the southeast. ReAectivlt7 at that level increased just

west of Stspletou Airport at 2133, and shortly afterward_

FL2 detected large-scale cyclouie shear at 4.6 km ove_

the airport. Surface winds during thlm time were north I

northeutes'lyacross the airport with temperatures of 31-

, 32"C across the FLOWS mesonet. The slr seas fairly dry

with 22-25% relative humidity (RH).

As the storm approached Slapleton Airport, ths

highest radar reflectivlty within the storm was above 9.3

km and slightly greater than 40 dBZ,,.

s All _eiekea =re MSL.

328

ORIGINAL PAGE IS

OF POOR QUAL.#Ty
A_. 2158, .3 refleclivity cores can be identified within

oh; analysis domain, shown in Fig 3a. Core A is the westernmost core extending to the surface. Cores 8 and C

are contained in the comma-ghaped region well dolt and

southeast of core A (both cores are contained in an area

of greater than 33 dBZ,). Core C was associated with the

strongest updraft in the analysis doma/u, 21 m s-I, and

w_ responsibleforthe strongestrnlcroburst.The perspec-

',iv,-used forthese figuressomewhat obscures coreC at this

time.

A p(urne of hydrometeors forms a "bridge" of refl,c',ivity which extends downwind (_nds near the radar.

detected storm top are from the northwest) from the 3

cores. The updrafts within the cores appear to have penetrated into the layer of northwesterly winds above 7 km,

carrying the hydrometeors to the southeut.

Altho*,gh no direct measurements of the hydrometeors are available for this storm, previous studies in northeastern CoLorado thunderstorms (e.g., Dye et d. Ig74)

7

FIGURE 3A. TAree.dime_..eion_l eeflectieiLF peeepeeti*as t,iewe of

lhe mic,.obu,#t.p_dacinf J4ac.eael 11 .lady lg@$. '_e miewe.r im

lot, tin 9 touta_t tAs no,Aunt _,_d ie located lO tm wesi and 78

Ira eoutA et FLt and iz lg. 2 Ira MS[,. Tl_e _3 dgZ', ie contoured

at ever T 05 i'm AC_. Av'_ws depicf air paece| tre_ecteeies duein¢ Ihe -_.5 sin _e eolame aaalysis rep_sente..4nalysi_ lime

iscente_'ed at _158 UTC.

-7

FIGURE 3B. Same as Fir. 3a, }at for t2Ot UTC.

FIGURE 3C. Sam; _ FiF So, |ul J'oe _12 UTC,

suggest that they were likel_ graup,-l. The ;ift,,d ._nd.._

sation level from the 2004 sounding has a temp,-ra_,tr" _F

-0.5 *C, and the temperature at the echo t_p )ev,t is _r_,_nd

-20 "C, both typical of clouds in the area in which ;re phue

precipitation processes are dominant.

Core A descended to the surface first, w,.(I w,,t ,_f

the _rport area, and" repre*ents the main preclplta_inn area

of the storm. It produced a weal,, larl_e-_ale o,tflew

By 2202 cores B and C had also extended d,wnward

to the surface (see Fig. 3b). Core B produced _ _mail

outflow region to the southeut of StapLeton Airpert, which

woe first evident a_ a I0 m s-_ wind speed differentlal in

the dual-Doppler analysis at 2203.

By 2205, the reflectlvitybridge, shown in F_g 3b.

filled in and descended. Most of _t appesrs to have emanated from core C, The surfaceoutflow from c_re C first

appeared at 2205. In 7 mln, by 2212, (t had reached its

maximum strength of 32 m s-t By this time the outflow

from core B is no longer evldent.

The FLOWS mesonet station closestto the core C

microb_st exhibited a temperature drop of 6"C (29 t_

23"C), a windspeed increue from 7 to 15 m s -1 , and a

RH incream from 24 to 43% between 220g and 2210.

The msln microburst maintained a wind speed dirferentlal above the TDWR microb_rst criterion (at lewt

15 m a -t over a distance of 4 km orless)until 2241, according to dual Doppler analysis. By 2254 the differentia] had

decreued to less than I0 m s -_, the cfiterlon for TDWR

wind shear regions. Elmore and McCarthy (Ig_9) report

an average lifetime for mlcrobursts in the Denver area of

13 to 14 mln, with a standard deviation of 75 rain. This

microbarst IMted 38 sin.

As the storm collapsed and dls_dpated, the surface outflow became quite complex. A gust front, which

had been slowly approaching from the northwest, began

to interact with the microbunt outflow. Several additional less-lntensedowndraffs merged with the original

main mlcrobur_t, creating a large, complicated multiplemicroburst outflow regdon.

The highest reflectlv'_ties descended tothe Lowest levels of the storm, unlike earlier anaJyses where_ they were

generally well aloft. Core C remains identifiable through

the l_t dual-Doppler analysis time centered st 2220:47.

Temperatures continued to decreue slowly throughout the FLOWS meeonet M the storm outflow covered the

area. The storm complex eventually developed into a weak

line and moved eoutheut.

c. Air Panel _jeetoe T Analltsi_

The history of the mlcrobor_t wM investigated more

thoroughly by computing air parcel trajectories backward

in time, starting at the time of the most intense outflow.

The CEDRIC analysis loft, ware used in the analyses sub.

tracts the fall apeeda of hydrometeors from the calculated

values, estimated u_ing the obee_ved radar reflecti_iti_.

This approximate_ the verticalmotions of air parcels.

329
P_cels within the main mJcroburst at 2212, at an

aP.itude of 2.2 km (400 m AGL), were tracked to the beginning of the analysis period, 2148.

Three.dimenslonal perspective views of resultant

trajectory ribbons are shown in Fig. 4. Each trajectory

terminus is labelled with a vertical bar, snd s short dash

_ndicates where each of those bars intersects the surface.

The hare then continue down_rard until they reach 0 km.

Trajectory ribbons are illustrated such that rotation Mon K

the path is indicated by twisting of the ribbon. Many more

trajectories than those displayed were examined, but these

are representative of most parcels within the mJcrobunt.

FIGURE 4. Ai, parcel |smiecto_iee olfained to'am dual.Do,lee

analysis. The l_jecto_ee a_ mAoum m lhree dimen#ion# _th

proyeetions on a ]_o_so_a] plane indicated. Each tic & mar]l

•lon 9 a leajecto_/ _bl*on indicates ?0 s oi trove|.

Air within the mlcroburst at 2212 originates well

aloft and to the west of the surface outflow. All air parcel

trajectories remain confined to a narrow east-west corridor

between about .5 and 7 km. Early in the analysis period,

there are 2 groups of trajectories: those at mJdle_Is ,Tell

west of the airport and those that are slowly ucendlng

further to the cut. These SrOUl_ merge between 2158 and

2200 at a height of 5 to 7 km, where they interiors the

developing reflectlvity region. By 2202, the air parcel trajectorles are clearly within the region of reflertivlt 7 greater

than 33 dBZo and have begun to descend, u shown in Fig.

3b. AP.er this time, the region of high reFlectlvity rapidly

descends and the downdraft accelerates until it impacts the

surface between 2210 and 2212, creating the microburst.

Other tra_.,,ctories (not shown) indicsteci that none

of the parcels within the main mierohunt originated above

6.25 km, or above the minimum #o level. Further trajectory

analyses, initialed from the first radar volume and calculated forward in time, showed that sir parcels originating

above about 7.2 km did not tend to descend. In general,

it is likely that no _tuld elf parcels originating above the

minimum 0, level deleended to the surface during this microburlt. Yet, it is quite clear that the hydrometeors did

come from above T.2 km.

The region responsible for most of the cooling and

downdraft acceleration is the broad area of low 0a located

between 5 and "/km. It appears that the hydmmeteors

were carried ahead of the re, on of active convection and

into this ttea of low 0., where rapid sublimation and evaporation soused the air within s narrow vertical layer, intensified the downdra_ and created the strong, Iong-lutlng

microburst at the surface. Visual observations confirmed

that the mleroburst appeared to have descended from aloft

and southeut of the main part of the storm, rather than

through the most intense precipitation region.

V. Concluding Remarks

Figure 5 shows a simplified schematic ev,_h,d_n ,,f

the msln mlcrobunt, combining the information gained

by fo)]owing the trajectories at hydrometeors and _f air

parcels, u discussed in the previous section.

ffydrometeors formed and were carried _ipw_rd ;n

several strong convective updrafts that e:usted in a r-li,_n

where environmental *dnde were generally_ighl.Th_ _y

drometeors continued to grow until they became to_ h,,lvv

to be supported by the updrafts and began slowly lattices.

Strong northwesterly winds near the top of the ,lpdraft

carried the hydrometeor plume southeut of the active ,,_nvectlon. Thus, _ they descended, the hydromc_eor_ _,re

carried beyond the main prefipitation area of the _tnrr_

into a level of low O. ,dr. Liquid water evaporat.ed and

froeen hydrometeors sublimated _thin a relatively 4hallow layer, causing the air to become negativety b,_ya_L

whereupon the cooling air accelerated rapidly downward

to produce a microburst at the surface.

Aekneavledgements

This work wu is funded by NCAR, the Natlnnal

Science Foundation, and the FAA (through Interag*nry

Agreement DTFA01-82-Y-10513).

References

Caracena, F., and J. A. FIueck, [988: Forecastingsad ;la,_i_'yir, g

dry mieroburst activity in the Denver ares subjugate, ely and _b.

jectively. PeeprinLe, 251h Ae_._lmce Sciences Meeting, AIA A.,

New York, NY.

Cressmsn, _.P., IgSg: An operational objeeti_e _nal_,,'e ._ste_

Man. Wea. Ree., ST, 367-374.

Dye, J.E., G. Longer, V. Toutenhoofd and T W Csnnr_n, [971

The mechanism of precipitation formation in n,_rth*astern Colorado cumulus: Ill. Coordinated mlcrophysical sad radar obeervationl and summary. J. _|mos. 5Ci , 31, 2152 215g

Elmore, K. L. and J. McCarthy. tggg_ A ,tatistirM chsrac.

terieation of Denver ares mlccobursts. FAA Tech. Report,

U.S. Dept. of "1_'ans., FAA, 84 pp.

Fujita,T. T. , 1985: The Downhucet: Mierohuret and .M,_c

roburst, SMR.P Research paper No. 210 (NTIS No. PB148880), Dept. of Geophysical Sciences, Uni,. of Chicago,

Chicago. IL, 122 pp.

Mohr, C.G., L.J. Miller, R.L. Vaughsn and ]_.W Frank, ]gS_:

Merger of mesoscale data sets into a common Cartesian format

for'el_eient and .y.tematie snaly_. J. Afmos. _nd Oceanic

TeeA., _, 143-161.

Shumsn, F. G., 1955: A method of designing finite.diWer*nt

' smoothing operators to meet specification. Joint Nume_cal

Weather Prediction _nli Tee/,.. /I,fema.,no. T.

Wolfeon, M. M., J.T. DiSkefsno and B. E. Forman, 1987:

The FLOWS (gAA-Lincoln Labo_tory Operational Weather

Studies) automatic weather station network in operation.

Project Report ATC-134, MI_ Lincoln Laboratory, Report NO.

DOT/FAA/PM.g5._7. U.S. DeFt. at "L_'antportstion Federal

Aviation Administration, Wuhlnl;ton , D.C.

330

r'A(./,__ IS
/

/

EAST (x)

340

11 JULY SCHEMATIC TRAJECTORY

331
Controller and Ptiot Decision Maidng

in Transmitting and Receiving Microburst W_nd Shear A;erts

from an Advanced Terminal Wind Shear Detection System

By

John McCarthy and Wayne Sand

National Center for Atmospheric Research (NCAR) 1

Boulder, Colorado 80307

USA

ABSTRACT

Appr(:ximatety 650 air comer passenger P4_i'des caused _y l¢:w-aJtituCe wine

shear have occurred in the United States over _e past fif1:een (15) years. The _cs:

ccmmcn fcrm at lett_al wind s_ear is the micrcburst, a sCong clcwnctraft ancl

hcr_zcntai outflow _at occurs near the earth's surface.

During the past decade, a sal=histicated mi_ol:ur_ cletec_(:n and warning

syEem has _een develcpecl using Doppler weather (wind-measuring) raclar and an

array of surface wind sensors either together or inclependentty. This system is

ca_alcle of measuring _e heac_wind-to-_lwind change that a pene_:'at_ng aircraft is

likely to encounter, and it provides air traffic c_nVollem with a simpte hazard aden

intended for relay to pilots in _e immediate takeoff or al_Pmac,h-to-lancting mote.

The system is intended to induce an earty _voic!ance decision on the part _f _e

flight crew, thus avoiding a potentiaJly catastrophic wind s_ear acci¢ent. The FeCeral

Aviation Administratien (FAA) will place _is system at apl;roxJrnatety 50 major U.S.

airports _at exDedence mic_burst wind sl'tear on a relatively frequent Ioasis.

Opera_onal demonstrations of this detec_on and warning system in the

summers of 198T, 1988 and 198,g at Stapleton Intema_onai Airport, Denver,

Colorado, provided substantial exl_erience regarding air traffic controller and pilot _se

of ff_is new system. This paper c_esc='ibes three severe micr_i=urs't, events r-a_ging in

tota_wind sl:eed c_ange from 35 to 95 knots, headwind-to-taiiwind. Typical airline

policy f(_r fligt_t crews receiving microi=urst aierts was c_ear: make an immediate

avoidance decision.

332

_.NCAR is si:<_nscred by _e National Science Fcunclat_n.

OF PC_R QUAUTY
Air traffic controller reac'_on varfed from a mec_anic_ recitation of the alert

message imlsedded in a routine clearance to land (normal procedure) to an urgent

relay of a muct_ stronger hazard message fctlowecl by a request of the pilot to 'say

intention," rather than saying "cleared to land." Pilot reac'dons varied from an

immediate _ecisicn to aveicl the hazardous event (thus totally missing the micrc_urst)

to a conscious decision to penetrate the microburst in spite of a c_ear

acknowledgment of the aJert.

Human favors related to the ergonomics of these situations are explored, as

well as air _'affic and flight standards policy issues.

333
I. INTRODUCTION

Microi:urst 2 wind shear accidents have been responsible for over 35 air carrier

accidents in the United States since 1964, resulting in over 650 fatalities (I). In the

U.S., the mcst recent such accident was the crash of Delta Flight 191 at Dallas-Ft.

Worth Airport in Texas on 2 August 1985, which resulted in the loss of 137 lives. Cn

3 Septeml3er 1989, Cubana de Aviation Flight 3046 crashed on takeoff from Havar_a,

Cutoa, with the loss of 115 passengers and crew and 24 persons on the graund.

Eviclence strongly suggested that the aircraft encountered a severe thunclerstorminduced microl3urst.

Since the mid-1980s, the FAA, in conjun_on with several research

organiza_ons, including the National Center for Atmospheric Research (NCAR) and

the Massachusetts Institute of Technology (MIT') Lincoln Laboratory, has developect a

wind shear detection and warning system that consists of two separate wind sensor

systems. First developed in 1976, the Low-Level Wind,shear Alert System (LLWAS)

recently has been upgraded to detect microloursts. This new version of LLWAS,

capable of detecting micrcbursts, employs 11 to 16 anemometer and wind vane

wind- measuring sites situated in the runway proximity to detect diverging wind

features near the ground.

More recently, the FAA developed the Terminal Doppler Weather Radar

('r'DWR), which utilizes the wind-measuring capabilities of Doppler radar to dete_

microbursts in the airport terminal vicinity. Complete technical details of these

systems can be found in the references (7,3).

During the summers of 1987, 1988 and 1989, LLWAS and TOWR were tested

operationally at the Stapleton International Airport, Denver, Coleracic. In 1989, the

microOurst detection capability of both systems was integrated in a prototype

development phase to provide air _'afftc contToilers and pilots @ simple,

unambiguous hazard alert messages. The TDWR system can detect microbursts

w_ a high degree of accuracy and with a low false-alarm rate. Specifir._ly, for

microbursts having headwind/tailwind differences greater than 40 knots, the

probability of detection 3 is 98%, while the false aian'n rate 4 is 4%. When a

i

2A microburst is an intense downdraft and associated outflow, located near the

earth's surface, that produces stTong headwind-to-tailwind changes for an aircraft

which penetrates the phenomenon below 1,0GO ft. AGL. It is typically situated within

thunderstorms but can often occur in less intense convective storms, particularly in

dry climates.

3The probability that a valid detection will be made by the system.

334
micrcburst ctetecticn is made, the system automatic_ly generates a micrcl:urst alert.

and provides an alert message to a computer screen situated in frGnt of the air

traffic controller, the controller relays the aJert to potentially affected flight crews in

either _e takeoff ¢r lanc_[ng mode. A typical approach-to-landing alert reads:

UNITED 226, MICROBURST ALERT, EIGHT ZERO (80) KNOT LOSS ONE

MILE FINAL THRESHOLD WIND TWO ONE ZERO AT TWO TWO KNOTS

A typical takeoff alert reads:

AMERICAN 330, MICROBURST ALERT FOUR ZERO (40) KNOT LOSS ON

THE RUNWAY DEPARTURE END WIND THREE THREE ZERO ONE TWO

KNOTS

During the prototype operational tests of the system, air carriers developed

company I_olicy regarding flight crew use of these alerts. In most cases, flight crews

were provided with flight safety bulletins that typically stated:

FLIGHT CREWS SHALL NOT CONDUCT AN APPROACH TO LANDING OR A

TAKEOFF WHILE A MICROSURST ALERT IS IN EFFECT.

In addition, air traffic controllers were instructed to provide all flight crews with

the alert message whenever an aircraft might be affected by the micr_lourst.

However, since inbound flights normally c_ntacted the air traffic controller at cr near

the final approach fix, the microburst alert was most often issued in association with

the landing cJearance. On takeoff, the alert was typically issued at the time cf takeoff

clearance.

These two demonstrations were prototypical, and while air Caffic controllers

and pilots generally were aware of the operational capability and associated

procedures of the system, it was a new, unique system. Consequently, permanent

conclusions about air traffic controller and pilot use of this system are somewhat

speculative.

In this paper, three microburst events in which valid micmburst alerts were

issued by air traffic controllers are examined for the purpose of identifying human

factor ast_ects of these alerts. Conclusions and recommendations for possible

actions are addressed at the end of the paper.

4The probability that an alarm is raise.

335
2. EXAMINATION OF THREE MICRGBURST ALERT INCIDENTS

Three microtcurst incidents are described briefly, followed hy a descri;:dcn cf

_e_ir'ent _uman fact, ors elements:

1_ Jcty _988

At approximately 1600 ho_rs (oil times are local daylight time), a micrci:urs:

developed at 1-mile final to runways 26 Lsft and 26 Right. TCWR was the onJy

operating system; in 1988 the LLWAS anc_ TDWR systems were not yet integrateC.

The event initially was c_etected as a 35-knot loss; it then drifted east and inter_sff_e¢

to an 80-knot loss at a 3-mile final. The Geographic Situation Display (GSD) for this

event is shown in Fig. 1. The situation steaclily intensified for approximately 8

minutes until it began to dissipate. Five air carrier jet transports were in various

approact_ locations at the time, and they received a microlourst alert outside the

outer marker greater than 3 miles from the runway (4). Figure 2 shews the ve_cal

profile of four of these flights during their go-around sequence. The following is a

sequential summary of each flight:

F!ight 862 (B-737-200) made an immeCiate avoidance decision based on 40-

knot loss microl:urst alert. The pilot stated that he did not want to make an

approact_ when a microburst alert was in effect,

Ftight 395 (B-737-200) was given a 40-knot loss microburst alert at a 1.mile

final. The aircraft continued the approach to a missed approach, reaching its

lowest point at 50 ft AGL approximately three-quarters of a mile short of the

runway. This aircraft encountered the most severe wind shear.

Ftight 236 (DC-8) was given a 50-knot microlourst alert and continued the

approact_; _t encountered severe headwind-taJlwind fluctuations as seen in

indicated airspeed. The flight crew executed a missed approach and

descended to near 250 ft AGL

Flight 949 (B-727) c_rrdnued the al=proach but made an early missed

approach after receMng a microl=urst alert of a 70-knot loss 3-mile final.

aircraft dicl not descend below approximately 500 ft AGL

The

Flight 305 (8-727) received a microi_urst alert indicating an 80-knot loss 3-mile

final. The crew elected to miss the approach just inside the outer marker.

336
The following are the pertinent ,'ac't,s asscciated with these air trafff,,c ccntrcile:s

micrcl_urst alert messages:

The ,_rst two fficjP,ts were hand, led by cr, e air traffc controller. All alerts were

given as al_l_rc¢riate, in the vicinity of the cuter marker. In these _wc cases.

the alerts were issued with a clearance to land.

The last three flights were handled _y a second air traffic ccntrctler who

relievec_ the first controller due to a watch change. The third aircraft in

sequence (F_ight 236) was issued an alert along with a clearance to ;aRC.

The fcurth _ircraft (FTight 949) was issued a microL_urst alert in the btind

without a lancting c..Jearance. In this case, the automatic alert a#ceared ¢n t_,e

controller's display, and the controller issued the alert to all aircraft mcnitcrir.g

the frequency, including Flight 949.

The controller issued the most severe microburst alert (80-knot Icss) to F;ight

305, followed _y "say request" rather than "cleared to land."

There were no adct_cnai apl_rcac,hes following these first five aircraft; c_ue to

the microl3urst event, the traffic was diverted from the airport for 30 minutes until the

weather improved.

8 July 1989

TOWR was not operational on this clay. The Enhanced LLWAS system,

utilizing 16 wind-measuring sites, protected Staloleton Airport. This system inctudect

aclditJ_nal sensors sited to protect the final approach corridors out to 3 miles from

the end of the runway. At approximately 1720 hours, a microl_urst occurred at the

north end of the airport on the approach end of runways 17 Left and Right; this

event is illustrated in Fig. 3. The following describes the exl_erience of Flight 531:

After being cleared for a visual approach, the captain heard three microburst

alerts. The first one indicated a 60-knot loss on a ?.-mile final. He continued

the approach. Shortly thereafter, the captain heard a sect_n(:l alert, indicating

a 95-knot loss 3-mile final. They initiated a missed approach at about a 3-mile

final and did not actually experience the event until about a .5-mile final, when

they I_ 50 knots indicated airspeed and also lost 400 feet in aJtitude while

experiencing mcderate turbulence. The missed ar.,proac_ was initiated at

approximately 600 ft AGL; the event was encounterec_ at al:loroximately 1,0O0

337
ftAGL with a subsequent loss of 400 ft5

The air traffic controller/pilot interac'_on can be summarized as fctlcws:

The air traffic controller first hacl an inclica_on of microburst activity: a 35-kr_c,'

loss on a 2-mile final. When he delivered the alert to Flight 531, the c_ptain

asked for substantia_ng pilots' reports from other aircraft operating these

runways. He queried an aircraft that hacl just landed on Runway 18 (located

about 1 mile west); the pilot indicated a 30-knot toss on that approach. This

report was heard by the captain of Flight 531 and apparently was used by

Right 531 to consider a missed approach. The controller continued to

provide microburst reports to Ftight 531 and following aircraft

Approximately 15 aircraft did not land subsequent to the missed approach of

Right 531. Most aircraft landed at Denver following a hold of approximately 20

minutes; one aircraft diverted to another airport located approximately 60 miles to _e

south of Denver.

2 Seoternber 1989

On this day, a microburst was detected by the integrated TDWR/LLWAS

system at 1-mile final to Runways 26 Left and Right. The integrated "I'DWR/LLWAS

system issues consolidated alarms based on products from each independent

system. The following describes the flight sequence for two flights, 914 and 2235:

Right 914, first in line for the approach, received a microburst alert, for 35-

knot loss 1-mile final. The captain elected to continue the approach. The

event reappeared on the controller's display as a 30-knot loss 1-mile final.

The crew continued the approach after a direct question from the air traffic

cona'oller querying whether the flight wished to continue the approach. The

flight landed with major difficulty, experiencing a 5 g landing that caused

structural damage. The captain, upon exiting the active runway, confirmed the

microburst and fur_er recommended closing of the runway due to unsafe

wind shear conditions.

Right 2235 followed Right 914, continued the approach but elected to execute

a missed approach on short final.

5The captain stated in a post-incident debrief that the wind shear equ{pment was

very good and felt that in this event it probably saved his aircraft.

338
The air ITaffic corm'oiler experience is summa.dzed:

The iden_cation of the microburst was c_ear, and all alerts were issued. Th,,e

c_n_ciler, in the case of the first aircraft, queded the flight crew regarding b_eir

landing intentions, conllrming that they wished to land dunng a micrcburst

alert.

3. ANALYSIS

Several analyses have been conducted for these three events, aithcucjh only

the first one (11 July 1988) has undergone extensive analysis (5). NCAR pa_cipateC

in crew debdefings on the 11 July 1988 ancl the 8 July 1989 events. The following

general anatytical comments apply:

_1 July 198_

1. The microburst was accurately detected and alerts were issued by two air _'affic

con=oilers. However, there was a significant difference in the imperative tone

between the first and second controller; the second controller used a more definitive

tone of voice.

2. The second controller, upon recognizing the urgency of the alert information,

used his c_ntroller's discretionary function not to issue a clearance to la_d for the

fourth aircraft (Right 949). He went further for Right 305 and added "say request."

In this case, we believe that the added query was instrumental in the flight crew's

subsequent missed-approach decision.

3. The flight crews typically were unfamiliar with aidine policy for microi_urst

avoidance and with the airline flight bulletin describing the operational demonstration.

In this regard, it must be recognized that this first-of-a-kind operational test cannot

be expected to be well understood by most flight crews. However, the first aircraft

(Flight 862) c_early was familiar with policy and made an early avoidance decision.

4. Several aircraft used microburst wind shear recovery techniques (6) dunng the

missed approaches, indicating the value of these techniques; this might have saved

Flight 395 from disaster.

339
8 JuJy _989

1. The E_t'_anced LLWAS performed flawlessly in this event, detec"dng a very Or

environment micrclourst when there were no visual clues for either the ftights invclvec

or the air traffic tower c_ntrcilers. It should be noted that *..he g5-knct ',css measLr=.c

_y this system was the strongest micrcicurst ever measured _y a_,y micrcburst

Cetec*Jcn system.

2. The controller exercised goocl judgment hy querying adjacent flights for wind

shear ret3orts. His at'dons serve as a model for c_ntroller handling of wind sh,ear

events.

3. The crew of Flight 531 exercised outstanding judgement and used flight deck

crew c._orc_inaticn (as determined in the crew ¢eerief) to make a consensus

avoidance decision upon hearing the 95-knot loss alert.

2 Septeml3er 1989

1. This microicurst event was just at=ove the headwind/tailwind threshold for

declaring a diverging shear microburst. The event was well ¢lere_ed just a_ove _;e

threshold that indicates a severe wind shear condition. This is confirmation that a

30-knot threshold is an appropriate one, given that the landing aircraft experienced

structural damage.

2. The controller strongly suggested, by his queries, that Flight 914 should give

serious consideration to an avoidance action (they did not take the suggestion). It

should be noted that the controller did not state "say request" or "say intention" as

did the controller on 11 July 1988.

3. The crew of Right 914, made a clear choice to land the aircraft contrary to airline

policy and after informal prompting from the corr_oller, The aircraft easily could have

been lost.

4. CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER STUDY

The LLWAS, TDWR and integrated TDWR/LLWAS microburst alert systems are

a technical success. Once a divergent wind shear event reaches the microburst

threshold of an expected 30-knot heac_wind-to-tailwind differential, the systems work

extremely wetl and produce alarms which are accurate and timely.

The human favors aspects are less successful, and it is in this domain that

considerable additional effort is needed. Flight crews continue to need extensive

training regarding the impact of microl_ursts on aircraft and the inadvisat_ility of

34o
penetrating them; standard procedures are needed to reinforcethe training. In

addition,improved airtraffic controllertrainingisnee(ted to standardize controller

response to micro_urst alerts. From the perspective of the scier_sts who have

examined the basic science of microbursts and helped to develcp detection

capa_il_es, air traffic control rules and procedures that dictate avoidance are a

required next step. Such rules should be consistent _ onboard wind shear

avoidance avionics equipment.

Controllers could help sensitize pilots to making time-critical decisions by

using terminology that triggers the need for a pilot derision based on the presence

of a hazardous weather event. The air traffic service should consider testing a

cautionary message of "say request" or "say inter_ons = to encourage s_ongly a flight

crew avoidance decision. This message will need to be examined to see if it adds

to c_ntroller workload or has other deleterious impacts.

F_nally, accurate and timely microlourst wind shear dieing equipment is

becoming operational in the U.S. Its international use at airportswhere microbursts

are common would be criticalto a major mi'dg_don of thishazard worldwide.

5. ACKNOWLEDGMENTS

Cleon Biter, Larry Common, K_m E]more, Bill Mahoney, Marcia Politovich and

Wes Wilson of NCAR's Researc_h Applicetions Program played major roles in

developing the material presented here. Air _'affi¢ specialists at the Stapletcn

International Airport ATC Tower assisted in obtaining understanding of air traffic

control actions and procedures. The flight crews and safety departments of United

Airlines and Continental Airlines who were involved in these incidents provided

valuable information. This work is funded partially by NCAR, the National Science

Foundation and the FAA through Interagency Agreement DTFA01-82-Y.10513.

341
REFERENCES

(1)

(2)

(3)

(4)

(5)

(6)

National Research Council, 1983: Law-Altitude Wind Shear and Its Hazard '.c

Aviation, National Academy Press, Washington, D.C., 161 pp.

McCarthy, J., and P. Clyne, 1987: A Strategy for Avoidance of Hazardous

Convec'_ve Weather in the Airport Terminal Area. Presented at the 40th

International Air Safety Seminar, F]ig_ Safety Foundation, 26 Cmcber,

Tokyo, Japan.

Sand, W., and C. Biter, 1989: TOWR Display Experiences. Prepdnts, AIAA 27th

Aerospace Sciences Meetinq, 9-12 January, RenD, Nevada. Amedcan

Institute of Aeronautics and Astronautics, Washington, D.C. AIAA-89-

0807.

Coppenbarger, R.A. and R.C. Wingrove, 1989: Analysis of Records from Four

A/diners in the Denver Microhurst, July 11, 1988. Prepdn.ts, AIAA

Atmospheric Ftiqht Mechanics' (_onference, 14-16 August, Boston,

Massachusetts. American Institute of Aeronautics and Astronautics,

Washington, D.C. AIAA-89-3354

Etmore, K.L, M.K. Politovich, and W.R. Sand, in press: The 11 July 1988

Microlourst at Stapleton International Airport, Denver, Colorado.

Available from the Research Applications Program, The National Center

for Atmospheric Research, P.O. Box 3000, Boulder, Colorado 80307-

3000.

Federal Aviation Administration, 1987: windshear Traininq Aid, Vol. 1-

Windshear Overview for Management, Pilot windshear Guide, and

Example Windshear Training Program; Vol. 2- Windshear Sut_stantiating

Data. Prepared for the FAA under Contract No. DFTA01-86-C-00005 by

The Boeing Co., Lockheed Corp., McDonnell Douglas Corp., United Air

Lines, Aviation Weather Associates, Inc., and Helliwell, Inc.

Development and Logistics, DOT/FAA, Washington, D.C. 20591.

342
F_g. 1

11 July lg88, 1612 local tlme, geographic event dlsplay of the Stapleton Airpor_

runways with :3 nm extensions off each runway end and micraburst events areas

shown by ellipses. The 80 knot microburst Is shown at Xt's pesk intensity located

off the approach end of runway 26.

343
\

\

!

!

344
1

44

\

5

10_ 10

87 8 7 0

12 10 14 4

11

Fig. 3

...,lulv 1989, 1620 local time, plan view of theofrunwaySthe windandvectorsthreemile_ runwaYthe

8extensions off all runway ends. The origin re,.resent

location of the Enhanced LLWAS sensors, theandarrowSthe numbersSh°wthe,_ tdlrecti°nthet°wardwind

which the wind is blowing and the lengththe to runwayre"resen-17is clearly

velocity in knots. The 95 knot event on approach

shown to the north of the airport.

345
A Status Report on the TDWR Efforts in the Denver Area

Questions and Answers

Q: ANDY PECZALSKI (Honeywell SRC) - What is the percentage of dry/clear air wind

shear and microbursts that are marginally or not detectable by radar at your test site in

summer and in winter? Where could I get this information?

A: WAYNE SAND (NCAR) - Try as we could we couldn't recall the exact number and

I'm not sure that we have an exact reference for you either. As best we can recall the

number is of the order of 5% that were less than - 10 dBZ, which went into some of the

requirements for the sensitivity on the TDWR specification to build the system. That is part

of the answer and some of it is buried away in a lot of different sources that looked at these

kind of events. Of course if there's real low reflectivity and you don't have any other

evidence you're not really sure you missed the thing. You're not even sure it's there. Of

course when you have them right on the airport it's somewhat easier. We have one known

event at the airport in '88 that was dearly missed because of low reflectivity. It was

detected by the LLWAS system and totally missed by the TDWR. A number of people

were standing there watching it, including the chairman of the NTSB. In the TDWR, the

spec as I understand it, is -20 dBZ sensitivity at 30 kilometers. That's how the problem is

being approached.

Q: DAVE HINTON (NASA Langley) - You indicated that pilots were concerned with a 10

to 15 knot airspeed loss. As Professor Hansman pointed out a 10 knot airspeed loss will

require wind divergence of at least 20 knots, more depending on the diameter of the event.

Could you elaborate on how you use pilot comments concerning airspeed loss to establish

TDWR alarm thresholds that are based on wind divergence.

A: WAYNE SAND (NCAR) - Well, fundamentally this is input from the TDWR/LLWAS

user working group which consisted of a number of pilots and controllers and other people

associated with the problem. It was counsel received from airline operations, pilots, all of

those kinds of people that said they wanted to know when the system detected a 15 knot

event. We're still troubling with that threshold value. We're getting feed back from pilots

saying they're experiencing what they consider to be significant wind shear events with a

10 knot change. So it's a debatable issue. We set that threshold based on "professional"

input from people who thought they knew what they wanted. We continue to assess that

threshold.

Q: FRED REMER (University of North Dakota) - I believe that people are avoiding wind

shear at Denver but the problem there has been well publicized. How are they responding

at other locations?

A: WAYNE SAND (NCAR) - Generally, pretty good. What we're getting back on

questionnaires from Orlando this year and from Kansas City last year is generally

favorable. The pilots are reacting to that and we see the curve going in the right direction

there, at least in our opinion. We have more people avoiding things that are called

microbursts everywhere.

Q: FRED REMER (University of North Dakota) - ATC is an active participant in the

Denver TDWR program, how would you qualify their participation?

A: WAYNE SAND (NCAR) - They are very active participants. The people in Denver are

a good group to work with. The air traffic controllers, supervisors, and the center weather

3411
serviceunitpeopleareall veryinterestedin what'sgoingonandtheyall havealot to say.

I'd like tothinkwelistento all thosepeopleandcertainlyconsiderallof theirinput.

Q: FREDREMER(Universityof North Dakota) - What I found in Florida is that they're

not able to handle the situation before a gust front or a microburst occurs. For example, a

gust front comes through and all the airliners that were lined up, taxi down to the other end

of the runway and get ready for departure. Then the shear is gone and we have

environmental conditions again and they taxi back down to the other end of the runway

where they were originally. So the question I was asking is, are they able to accommodate

that? Do they predict that?

A: WAYNE SAND (NCAR) - In a word, yes. In Denver, they've learned how to deal

with that. This 10 and 20 minute wind shift prediction product, which gives them a

velocity vector of the wind to be expected behind the gust front, is used by the supervisors

to decide when to change runways and if runway changes will be required. They in fact

will start taxiing people to different runways. They'll say, hey, we can take airplanes up to

this guy, the rest of you guys go to the other runway, whatever it is. In my view they're

getting very good at using that wind shift prediction product to reconfigure the airport.

Denver, of course, is a little bit different than Orlando, with orthogonal runways.

UNKNOWN - The LLWAS winds are on the GSD for the traffic supervisor at Denver.

They were not put on the GSD in Orlando. So that the display of a wind map from

LLWAS, which makes the runway management more effective, was not available at

Orlando.

WAYNE SAND (NCAR) - Thafs another word to speak for integration at some level.

Putting those wind vectors on the GSD very rapidly builds confidence in the wind shift

algorithm.

STEVE CAMPBELL (MIT Lincoln Laboratory) - We did have the wind shift prediction

product at Orlando this past summer. Part of the problem may be that the people at Orlando

haven't had as much use, or maybe hadn't built up a confidence factor yet, whereas it's

been available in Denver for the past couple of years. It's worth noting, one of the main

economic justifications for TDWR is the ability to predict these wind shifts. It's one of the

things that controllers in general seem very enthusiastic about along with the storm motion.

WAYNE SAND (NCAR) - A lot of these new enhancements that are coming along for the

system are pretty well received. I think from day one at Denver, when we started putting

up wind shift products they were well received. They figured out right away how to use

that. It was very quick. But, as John pointed out, it probably has something to do with the

vectors that are on there from all the LLWAS sites. That gives them a lot of confidence in

what's going on.

Q: ROBERT OTI'O 0_.ozkheed) - It was stated that there is "reasonably" good agreement

between calculations of F-factor from radar and those from aircraft. Please clarify. What

are the quantitative comparison numbers and how are they determined?

A: WAYNE SAND (NCAR) - There is some arm waving that goes into that. You have to

make some assumptions about the vertical motions. What's used to do that is the

continuity equation. It's coming down, it's got to change directions and go the other way.

So it's a continuity argument used to compare between the two terms in that equation, the

horizontal term and the vertical term. There are a number of people who have attacked that

problem. We've done some of that at NCAR, the people here at NASA Langley have done

quite a bit of it, and the people out at NASA Ames, Rod Wingrove, has done some of those

347
kinds of things. There is some literature now that discusses those kinds of things. You

saw a number of those displays yesterday and today where you're looking at radar

computed F-factors versus airplane computed F-factors and generally those track pretty

well. I think that was the basis of my comment.

Q: PAUL ROBINSON (Lockheed) - This question relates to operational procedures

concerning TDWR procedures on the 11 July microburst encounters. My impression is

that the aircraft were only notified about the microburst after being cleared onto the

approach and pilot reports seem to be absent.

A: WAYNE SAND (NCAR) - Absolutely true. They were absent. Bob Ireland is here

and that was one of the issues that came out of the United report. With that is a very strong

encouragement for pilots to give PIREPS. There were none in that event.

Q: PAUL ROBINSON (Lockheed) - Should the shear information have been

communicated to the pilots before being cleared onto the ILS?

A: WAYNE SAND (NCAR) - The answer to that is probably yes. In fact, the way the

system was working then was that the information was available to the final controllers in

the tower and in the TRACON. Those are the people who axe talking to them basically

before the outer marker. So the flight crews didn't have access to talk to somebody who

had the information available right in front of them until they were at the outer marker.

Now, based on that case and some additional effort that's gone on since then, there is a

little more activity in the TRACON with the supervisors now trying to get that information

to controllers. There are more displays of alpha numeric information in the TRACON so

that controllers have an option to look at that. But I don't believe there's still any obligation

to give that information out from the TRACON positions. It still is the responsibility of the

tower controller to give that information to the flight crews once they come over to tower,

which at Denver is typically about the outer marker. Were PIREPS available? No, they

just weren't available.

Q: ROLAND BOWLES (NASA Langley) - What is the termination criteria for TDWR

alerts?

A: WAYNE SAND (NCAR) - It's a relatively simple termination criteria. It's when the

system senses that the total wind change across the detected event goes below 30 knots.

That is when the event terminates. Now the question is much more complex than it sounds

on the surface because by the time it gets to that point the event typically gets somewhat

bigger. The real question is, is that waiting too long because the level of shear hazard at

that point may be small. It's the delta V over delta R that's important to the airplane. The

delta R often times gets quite big. So it's a question of when you cut that off. At the

moment we're cutting it off when the delta V goes below 30 knots. That may or may not

be correct and that may be one of the ways we can also clean up the time that the system is

alarming. It's something that we continue to try and look at and we don't have an answer

for yet.

Q: BOB IRELAND (United) - For use in writing SAE-S7 standards for look-ahead

systems, please define dry conditions, e.g., dry microbursts, both in terms of reflectivity

and other parameters such as relative humidity.

A: WAYNE SAND (NCAR) - I don't know where you draw the line. The ends of the

spectrum are pretty easy but where you draw that line I don't know.

348
UNKNOWN - To call it dry versus wet is arbitrary. You can draw a line anywhere you

want. The fact is, the spectra of microbursts go from very dry to very wet and it's

continuous.

WAYNE SAND (NCAR) - I'd hate to offer an opinion on that. I would refer back to the

analysis of the July 11 case for just a comment. Most of us think of July 11 as being a dry.

microburst, yet it was mining at the airport and there were reflectivities in the high 30s,

which starts to get up to crowding red on an airborne display. In that one we all refer to it

as dry, yet on many radars you'd have seen dots of red in that particular event. So. I

hesitate to draw that line standing up here on the podium. I don't know where it belongs.

BOB IRELAND (United) - That was probably a little unfair to ask you at the last minute. It

just came up last week at the S-7 meeting and we want to say in our document that we want

systems to work in both dry and wet conditions. We didn't feel that we had the collective

knowledge to draw a line, a reasonable line. We need to say that it's got to work from a

certain minimum to a certain maximum.

MARILYN WILSON (MIT Lincoln Laboratory) - The dry microburst was defined as

35 dBZ or lower because we looked at rain gauge measurement in Denver to see when

measurable precip was actually detected. For the drop size distributions found in the

Denver area, 35 dBZ was most commonly the line. ff the reflectivity was lower than that,

the rain gauge at the surface measured no rain. But, on a day like July 11, 1988, there was

measurable rain. So it's not a hard and fast thing. It depends on what that dBZ is giving

you. Those are also surface reflectivities. If you look aloft you could see a higher

reflectivity. That's sort of the maximum reflectivity at the surface. What the minimum

reflectivity at the surface is, no one has really catalogued.

BOB IRELAND (United) - I guess what I'm concerned about is, in the absence of

precipitation, is there still reflectiviry? rm talking about when there is not precipitation but

we have a dry microburst, what can we use as a measurement?

MARILYN WILSON (MIT Lincoln Laboratory) - There is precipitation there and there is

measurable reflectivity there, it's just that there's a few big drops and it skews this Z

number that the radar measures up to a higher reflectivity, like 20 dBZ, even though there

is nothing measurable by a rain gauge. There is rain in the air it's just sparse. There is also

dust in the air.

UNKNOWN - What we were trying to do on the S-7 committee was to define what an

airborne wind shear system must detect. For example, for the IR we picked up some

numbers as to the level of rain through which it must look. We needed the other side of the

equation for what a LIDAR must do and what a radar must do, in terms of what

performance it must meet from an airborne platform to be acceptable. So the question was,

if a number like 5% of microbursts are very, very dry, is that something that an airborne

radar must detect. Equally, must an IR or a LIDAR look through X rain? That's where we

were trying to go with it. We were trying to pick some numbers. Our committee was

concerned about what is it that our system has to do. Let's define some system

requirements. If people are going to be flying into Denver and if they've got an airborne

radar low level wind shear detection system and there are dry microburst, we've got some

specs for people to shoot at.

WAYNE SAND (NCAR) - It's certainly a fair question and I would suggest that that's

something we probably have to get our heads together between NCAR and Lincoln Labs,

at least, and try and provide you with a number. I think it's a matter of, as you say, setting

349
a definition and somebody has to do it. Maybe we have more data than anybody else

between us to try to come up with that number. Let us get back to you for the committee

on that. We'll work the problem and see if we can come up with at least our best estimate.

350
Session V. TDWR Data Link / Display

Thermodynamic Alerter for Microbursts

Dr. Peter Eccles, MITRE

351
N91-24179 I.

Thermodynamic Alerter for

Microbursts (TAMP)

Peter J. Eccles

MrnRE

The MITRE Corporationhas an internal researchand development program,called MITRE Sponsored

Research (MSR), funded directlyand only by MITRE. All MITRE TechnicalStaff are invitedto submt

proposalsannually for competitionfor the funds allocated for MSR and related work.

In the middleof 1986 a Radar MeteorologyConference was held at Snowmass, CO, inwhich severaJ

workers used surface temperaturedepressiondata for confirmationof meteorological radar observationsof

microbursts, h proposalto engineer a fast, inexpensive,comprehensivemeteorological sensor suitablefor

deploymentinarrays, to buildan array system usingthese sensors as buildingblocks,and to analyze the

resultsfrom the systemwas submittedfor considerationby MITRE at the end of 1986.

Subsequentto some immediate and continuingrevision,thisproposalbecame and MSR project,with initial

funding in October, 1987. This talk describesthis project.

352
Background

Microbursts

eulm=

+ other factors

crash aircraft taking off or landing

close runways

cause delays

force alternative airport landings.

• Microburst detection, location and measurement

m will enhance airport usage and safety.

MITRE

Microbursts,streams of rapidlymoving, downwardlydirected air, are a principalcause of wind shear

hazards. The air withina microburstcools rapidlydue to water dropevaporationand meltinghail, both of

which maintain negative buoyancyin the air and propel it to the ground. Microburstsare always associated

with cloudsand principallywith severe convective storms, though microburstshave been observedbeneath

virga-like predpitation. Microburstsare typicallyellipticalinshape and initiaterelativelyhighin the

atmosphere where heavilywater-laden air can have diameters of ten km or more. The negatively-buoyantly

maintained rapid downward accelerationof thiswater-laden air causes a microburst to become narrower as

it approaches the groundso that it may have a diameter of less than a kilometernear the ground. When

the air in a microburst strikesthe ground,itscootsouthorizontallyina divergingpattern from a central point

(or nadir).

Due to the stronglydivergent air, a moving aircraftfirst experiencesa headwind,which increases lift, rapidly

followed by a tailwir¢l,which reduces liftby reducingthe relative speed of the aircraft. A significantloss of

altitudecan occur which, depending on the altitudeof the aircraft,can cause a crash.

353
J • , • • A

AT • _Y vV •

('C) ..... • •

V

• V

T_mp.

•". Eiq"

m. _Jg _ AIm,_ 4 Mtmp&,m 8uc'_'_mn_

• •

g

1- Pint _ 4m_d M Jkqp*da maca,ednu,al. .I, rr

(sin)

n _ ee

e_ , n=. .;

o s _o is _ _ _

_1_ _ (_1)

Ta_ _ m_ _ rex4 Ii_ed an N*_

MITRE

Initial interestinthisresearchstemmed fromthewidespreaduse ofsurfacetemperaturelossdata

(Wolfson)forconfirmationofmeteorological radarobservationsofmicrobursts.Thus,itseems appropriate

tolocatemicroburstsfromtemperaturelossdataalone.Temperaturesurfacearrayshave thepromiseof

beingfarlesscostlythanradars.Radarshave thepropertyofcoveringlargeareas,butthismay be an

inappropriateusewhen thearearequiredtobe protectedismore nearlya point,namelyan airport.Itis

wellknown thatthemilitaryphilosophyforweatherpredictionistoconcentrateon pointprediction(suchas

airfields) and thismind setisalsotheappropriateone formicroburstmeasurement.

Srivastava, Proctorand Wolfsonhave shownthat temperaturedoes notalways decrease. Forsome dry

microburststempa_ture increltseis expected. However, equivalent potential temperature, 0E, another

atmospheric parameter appears to have much morepotentialthan temperatureas a microburstindicator.

0Eis a conservativequantity. If 0E is measured for an isolatedair parcel, it can be tracked much as if it

contained a radioaclJvenuclidesin it,because its0 Edoes not change withtime. Thus if 0 Eis monitored

over a field,and displayed on a PPl-like display,we have an economic method of examiningthe nearsurfaceatmosphere.

3,54
LONG TERM IMPACT

I I L I I II I I

- HIGH CONFIDENCE OF DETECTING, LOCATING ALL MICROBURSTS

- ECONOMIC OBJECTIVE: AFFORDABLE LOW COST

- WORLDWIDE CONSCIOUSNESS OF MITRE'S COMMITTMENT

TO AIRPORT SAFETY

- POTENTIAL SPONSORS

- GOVERNMENT AGENCIES RESPONSIBLE FOR AIRPORT SAFETY

-FAA

-MAJOR AIRPORTS

- MINOR AIRPORTS

- AIRPORT MANAGEMENT, WORLDWIDE

MITRE

Since its formation, the MITRE Corporationhas been associatedwithAir Traffic ContTol(ATC). We are

aware of the absolute requirement for high quality in the reliability, accuracy, ixecision and availabilityof

equipment for ATC in that these provide confidenceto the users: flight specialistsincluding ATC specialists

and air crew. Our objectivewas to showthat both the equipment and the associated algorithms computing

eEhad these properties. The sensors and the equipment would be inexpensive, solidstate, and solar

powered. The equipment, displays and archivingwould be based on standardIBM-compatible personal

computers (PCs). The successof this very simplifiedwind shear detection systemwould affirm the

company's interest in sensible, simplifiedbut confidence-inspiring ATC equipment.

The experimentalL:_n was to deploya tight array of reliable solid-statemeteorological sensors aroundan

airport, to set up a _ligital data recordingsystemand to operate this ina hands-off mode. In this first

instance the data would be analyzed off-line,though it could be usedfor operationalpurposes, given the

appropriate analysis and displaycapabilities.

Other objectivesof this MITRE-funded research were to have a highconfidence of detecting and locating

all microbursts,and to work to deploy operational eE-measuringarrays in places whichthere are no plans

to detect microburstsat this time, suchas secondary,General Aviationand thirdworldairports.

355
APPROACH

° MODELS

° ALGORITHM

° PATrERN RECOGNITION

° DEFINE PROCESSING REQ.

- COMPUTER SURVEY

° DESIGN - PURCHASE -

FABRICATE - TEST

r

o

o

SENSOR SURVEY

DESIGN - PURCHASE - OTS -

FABRICATE BREAD BOARD

- TEST

° BRASS BOARD

- TEST

BEST

NETWORK SIZE,

DENSITY

NEAR

PROGRAM TASKS

DEPLOYMENT, TEST

OPERATION

FALSE

SAFE

MITRE RATES

FALSE

ALARM

RATES

The MITRE approach to thisproblemwas very standard. One of the firstproductswas the development of

a complete systemspecification. The slide is self-explanatory. It sets out the variousmajor objectives

includingthe detailed planning, purchasingand equipmentrefinementfor the development and test of any

large system including this thermodynamic alerterfor microbursts.

3.56
Thermal Alerter for Microbursts Prototype (TAMP)

I EXPANSION RATE I

CLOSED

OPEN

NEW AIR POTENTIAL

TEMPERATURE

DECREASE

INCREASE

TAMP

ALERTS

MICROBURST

PRESENT

OR

CLOSED

- DELAY

- ALTERNATIVE

AIRPORTS

MITRE

WIND

INCREASE

MICROBURST

PRESENT

Since 0 E iSconservative, new air from aloftwill have a different0 Efrom air at the ground. Therefore, a pool

of different(almost invariablylower) eEwill appear as a rapidlyexpandingpoolwithinthe currentlypresent,

nearly uniform,OE._Proctor has shown modelsof near-surfacechanges of thistype due to temperature

alone. - - _

In additJon,-_emovement of the boundariesof the poolyield a measure of shear, microburst strength, or

the so-calle_ maximum expected lossacrossthe microburst. The depth of the change will also give a

measure of the change, much likethe relation given by Proctor of 8v (m/s) = 2.5 6T°C.

35?'
//__- _Pressure

i'/ _. Ap InDut

=l_.Gak_o _ mm_.mor.

The sensor-transmitters(Senstrans)in the array have wind speed sensorssimilarto the Bedard-Fujita

designshown, but modified by MITRE to include direction sensors,which are straingaugesmounted

directlyon the rodwhich holdsthe Bernoullisphere.When the ball moves,the directionis measured by

resistance changes in the straingauges. In the MITRE design,the pressure switchis replacedby a solid

state pressure transducer soldered to the printedcircuitboard (PCB). The wind shear is then potentially

obtainable inthree ways, direct measurement, inferencefrom the temperaturedepression,and

geometrically,fromthe rate of expansion of the poolof new air.

Further,total pressure change, defined as the sum of the scalarpressure change and the dynamic

pressurecomputed from the IdnelJcenergy of the moving air, givesyet a third potentialindicatorof the

presence of_amjcrttburst (Fujita). Changes in the staticpressureover shortperiods of time (infrasound)

have been postulatedby Bedard as indicatorsof the presence of microbursts,but are not a possible output

from the Se_trans array.

358
MITRE

The plan for the operationalair trafficcontroller(ATC) displayis fora simple nested family of nonoverlappingthreat-indicatingellipses. Ellipses are very simplydefined:five bytes completelydescribethe

locationand size of an ellipse. Therefore sixteen bytes completelydescdbe three ellipses, since only one

byteis needed for color. Given this economy of information to be transferred,the innerellipsewouldbe

filledwith red, indicatingthe highestthreat, probablyimpenetrable by any aircrafton landingor departure.

The area between that and the next ellipse, which totallysurroundsthe former, wouldbe amber, indicating

considerable threat, butpossiblysuccessfullypenetrable by a microburst..experiencedpilot. The finally

enclosedarea would be green indicating a moderate threat, but penetrable by all pilotsexceptthosewho

have no wind shear train=ng. There wouldbe noconfusing overlapping of ellipses. However, there might

be a small numberof red ellipses withinone amber ellipse, and there might similarlybe multipleamber

ellipseswithinone green ellipse. However, for transmission to f'_jhtdecks, a simpler,three nested ellipse

family for any one airportwould be generated from the available data.

The advantage of ellipses is that they simplify the overly-complexshape of meteorologicaliso-lines or

contours (suchas radar echoes)which describerandom noise phenomena and are not meaningfulin

detail. Where threats are defined, however, the selected ellipseis guaranteed to be the smallestellipse

which containsthe definedthreat, and does not overlapany inner ellipse.

Sixteen bytesOf_datacan be transmittedin one information packet of Mode S data. In addition,at the low

transmisdoffcate-of 1200 baud, 16 bytes of data can be transmitted anywhere in the world in a tenthof a

second. Thus, the functionai informationof the locationand size of a microburst on an airport can be

transmitted ingraphical form more economicallythan the ASCII format of the current controller verbal

transmissions.

On the flight deck a colordisplay of threats shouldfacilitate pilotintentions, and an appropriate choice. In

addition,a smartflight-deck computercould generate a probabilityof survival number between zero and 1

(1 being survival, 0 being impact) since itcontains the aircraft configurationinformation.

359
Senstrans - Field Equipment

Sensors and their sensitivities

m Temperature sensor: 0.1deg C in 7 s; shelter air limits rate.

Pressure sensor: 0.1 rob, no time limit.

- Will sense pressure changes ahead of descending air.

- AIIcNS estimate of temperature change due to pressure.

-- Wind speed sensor (Bedard-Fujita design, modified): 1 m/s above

5 m/s, no time limits.

- Uses the same sensor as the pressure sensor.

Relative humidity sensor: 3% RH in 5 minutes.

- Water content change will cause temperature change.

- Sensor siow, but look-ahead and nowcasting possible.

q Solar insolation

- "Free": From output voltage of solar power supply.

Adequateaccur.acyisachievedby acceptingsmalllags in severalparametersthatare measured.

Pressureandwinospeedareavailableinstantaneously, sincetheyare measuredon-chipbya sensorwith

a. d,efl.,ectingsiliconmembrane.Winddirectionhassimilarqualities. Temperaturehasa slightlagbecause

orme merrnaJmassofthe sensor.Humidity,witha lagoftheorderofa minute,becauseofthe needfor

waterconcenl_atJonchangeina thinfilm, hasthelongestlagofthe vitalparameters.

Accuraciesandlagsare givenin thefollowingtable:

Parameter Sensor Accuracy Lag Comment

Temperature Thermistor .1°C 7 seconds

Differential Siliconwafer .1 millibar zero wrtPressure

WindSpeed Siliconwafer 1 m/s zero Above5m/s

Relative _ _;Thinfilm

Humidity _

Insolation_ Solararray

3% 5 minutes

zero Accuracy

N/A

Generallythe sensors,themicrocontroller, thetTansmitterare solderedon onetwo-sidedPCB,thus

eliminatingmanycablesandconnectorswhicharethe mosttroublesomeportionofcomplexequipment.

Thisis mountedinsidea standardinstrumentshelterwhichyieldsadequateexposureto thecomponents

withinit. However,thesolarpanel,1hebattery,andthewindsensormustbeelsewhere,sostandard

telephonecableswiththeirgold-platedandsprungconnectorsare usedwhereconnectorsarerequired.

360
SENSTRAN

Pressure

Temperature

Humidity

Battery

Input

DESIGN

FM

I II

T'RAN_R

The microcontroller contains an ND converterand has eight multiplexed analog inputs. These include one

digitalvoltmeterwhich can be attached to any pointon the PCE, and reads remotely. It feeds synthesized

frequency shiftkeyed (FSI0 tones to a 2.0 watt FM transmitter.

Unfortunately,the microcontroller alsocontains a fatal flaw which will not be addressed nor correctedby

the manufacturer. Accordingly,many Senstrans exhibit"graceful failure', a tendency towards sparser

transmission, and incorrect results. This could be detected and correctedby occasionalvisitsto the

various Senstrans. While this is not commonto all microcontrollers,its unadvertised presence in the

chosen chip was discoveredtoo late to alter the design to accommodate some otherchip.

Future Se_trar_ _11be designed around permanently energized low-current microcontrollers to simplify

design and-to ci_cumventa similarfatal flaw should it be present in any of the low-current microcontrollers.

361
TAMP Installation at Stapleton

LLWAS Sensor (FAA)

11011

TAMP

Senscxr/Tmnsmittmr

(Senstran)

Low level

Wind Sheer

Nert

Tow_' (LLWAS)

.,all

'up to 7 km

Spare LLWAS Antenna (F/L_) -D,-p

SocurltyF_ee MITRE

Control Tower I

I

I

I

I.,q

Equipment I

"Room

/

TAMP Data

Acquisition

Processing

Analysis

Display

unit

(DAPAD)

The receivingantenna is a spare LLWASantenna on the roof of the ATC Tower, which feeds a receiverin

the FAAequipmentroom. This is connectedto a standardcommunicationsport on a PC via a 1200 baud

demodulator. The decodingand archivingsoftwareis a Basicprogram.

With permissionof the StapletonFacilitiesSection,each of thirteen Senstrans is mountedon an LLWAS

tower withina few feet of the operationalLLWAS unit,and is up to 7 kmfrom the receiverinthe ATCT. It

has no impact on the operationof LLWAS.

Operation was achieved on June 26, 1990 and continues.

382
DAPAD Software

RECEIVER

DECODER

STATION

EXTRACTION RACXIU[ $ METEOROLOGICAL 1

VARIABLE COMPUTATION

AND PLO"I-FING

DOS

MITRE

The softwarewithinthe data acquisitionprocessing analysis and display unit (a PC) is a simple Basic

language program. The archive is initially the hard-drive in the PC. Files are occasionally written to 3.5"

tloppydisks and are then sent to MITRE.

Results

One comparison has been made with the 11 August 1990 microburst. At this time there were only three

remaining operational Senstrans, but its presence was detected by all of them.

Acknowledgments

The author is particularly grateful for the collaborationof the North West Mountain Region FAA, specifically

the Denver Hub AirportFacilities Sector led by Mr. Jack McCormick.

363
364
Session VI. Heavy Rain Aerodynamics

365
366
Session VI. Heavy Rain Aerodynamics

N91-24180

Status of Heavy Rain Tests

Gaudy Bezos, NASA Langley

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391
Status of Heavy Rain Tests - Questions and Answers

Q: RICHARD DUBINSKY (Sky Council) - What influence and/or relationships do you

expect for extreme ranges of drop size distributions in heavy rain for microburst and

shears, etc.?

A: GAUDY BEZOS (NASA Langley) - I'm not familiar with the drop size distributions

that have been measured inside wind shear environments of severe thunderstorms. If there

is data available it's a very small data base. I can only share with you my experiences in

trying to form droplets in a wind tunnel and at the ALDF facility. In the wind tunnel

environment, we've noticed that the difference between the exit velocity of the water from

the nozzle and the free-stream velocity we wanted to accelerate the drops to, made a great

difference in the shape and size of the drops themselves. Anything larger than 2 mm in size

would actually shatter and form much smaller drops. So the wind tunnel test technique

gave us an average drop size of about 1.5 ram. At ALDF we used commercial nozzles.

The spec sheet on those nozzles says that they produce drops from as small as 1/2 mm in

size to 4 mm in size. It's very difficult to measure drops in an outdoor facility. We used a

sort of a shadow-graph technique. We had a little box with a lens, a camera and a slit in the

top. We let the drops fall through the slit and would take a picture of it. By just looking

qualitatively at what kind of distribution we got, we did see 1/2 mm size drops and we did

see 4 mm size drops and everything in between. The ALDF facility rain system was

purposely designed to allow the droplets of all the different sizes to achieve their terminal

velocity, + or - 10%, which even for the smallest size drops it would take 14 feet. So the

drops did achieve the proper physics involved in forming and falling to the ground. I do

know that if you are in a wind shear situation you'll have down drafts and that may entrap

the rain that is there and actually force it down a lot harder and maybe the drops themselves

will have a different characteristic. There is research, I don't remember the person's name,

which looked at drop size distributions in light showers versus severe thundershowers and

there is a different distribution.

Q: RICHARD DUBINSKY (Sky Council) - How will you generate and measure different

rain drop size distributions for your future wind tunnel experiments?

A: GAUDY BEZOS (NASA Langley) - We'll generate the different drop sizes by varying

the exit nozzle pressure. We are planning to put our rain system in the settling chamber of

our wind tunnel which will minimize the difference between the air stream velocity and the

exit velocity of the drops. We hope to be able to keep in tact the drops, the large size

drops, like 4 mm in size. We plan to measure the drops using two techniques. We'll again

use the shadow-graph photographic technique and we are also developing a laser system

that will basically be an unobtrusive device which will allow the drops to cross the sheet of

light and then determine its size and its velocity by the width of the interference as it crosses

the laser beam.

Q: WALT OVEREND (Delta Airlines) - How, when you conducted rain tests did you

overcome the water effect on your sensors or your sensor systems?

A: GAUDY BEZOS (NASA Langley) - The insmamentation that we used to acquire our

aerodynamic data were strain gauge load ceils and they were unaffected by the rain

environment. They were waterproofed before hand. We were able to measure

aerodynamic lift and the drag seen by the model without any problem. We also had an on

board pitot static system on the carriage to give us true airspeed. That also did not show a

difference in and out of the rain environment But, you have to remember that we were

only in the rain environment for 2 seconds so the probability of a drop hitting the pitot static

392
tube at just the right spot to clog it up is kind of unlikely. In the wind tunnel we tried to

measure the static pressures on the wing surface and we found that we had great difficulties

in doing that because the water would always clog up the line. So we couldn't measure the

pressure on the surface of the wing.

Q: WALT OVEREND (Delta Airlines) - What do you see as a change in effect on a three

dimensional wing, including tip vortices from your 2 dimensional testing?

A: GAUDY BEZOS (NASA Langley) - The first thing I would like to point out is that we

have done some three dimensional testing on very simplistic models. The first one was on

a NACA 0012 airfoil section with a generic fuselage and a simple flap. The other was on a

NACA 23015 airfoil section model which also had a simple flap system on the trailing

edge. The results do indicate there are lift losses and drag increases. The magnitude and

the shape of these curves may differ a little bit but we don't expect to see many great

changes in our 3-D testing in terms of those characteristics. One thing that we will

probably see is an effect of the fuselage and the tail surfaces. We hope to do a section by

section test of a full configuration model starting f'u'st with the swept wing by itself on a

splitter plate, then test the fuselage and tail surfaces, and then put the whole system together

to see if we can isolate which areas contribute to performance losses. I did want to point

out that testing in a wind tunnel environment or at ALDF is not easy. There are a lot of

operational difficulties involved. A wind tunnel wasn't made to have water thrown in it.

All the instrumentation must be waterproofed. Our blades, which are wooden, have to be

protected from the erosion of the water. We can't test in the wind tunnel during the winter

months because whatever residual water is left in the tunnel circuitry actually forms into ice

and then when we initially turn the system on it actually digs holes, pits, into the wooden

blades. The wind tunnel is not the ideal test technique. It really is a lot of work and effort.

At ALDF we've been testing for two years and we've got 36 data points. Now, of those

36 data points we have some repeat points, but it's a very slow process. We are always

fighting nature, bad weather and high winds.

393
394
Session VI. Heavy Rain Aerodynamics

N91-24181

Heavy Rain Field Measurements

Ed Melson, NASA Wallops

395
HEAVY RAIN FIELD MEASUREMENTS

W. EDWARD MELSON, JR.

NASA/GODDARD SPACE FLIGHT CENTER/WALLOPS FLIGHT FACILITY

THIRD COMBINED MANUFACTURERS' AND TECHNOLOGISTS'

AIRBORNE WIND SHEAR REVIEW MEETING

OCTOBER 16-18, 1990

HAMPTON, VIRGINIA

396
HEAVY RAIN FIELD MEASUREMENTS

W. EDWARD MELSON, JR.

NASA/GODDARD SPACE FLIGHT CENTER/WALLOPS FLIGHT FACILITY

ABSTRACT

Tests have shown that the effects of heavy rain on the aerodynamic

performance of a wing produces a degrading influence. These tests

have also shown that the transition from steady-state dry

condition of the wing to a steady-state wet condition takes place

in a matter of seconds. This short transitional period led to a

need for understanding short-duration high-intensity natural

rainfall. The current data base of the National Weather Service

for rainfall is averaged over relative long time constants. This

averaging tends to mask the short-duration, high-intensity

rainfall characteristics.

A weight-measuring rain gauge was developed to collect rain data

and configured to operate at a high sample rate (one sample per

second). Instead of averaging the rain rate in minutes, hours,

and sometimes days as normally performed, the rain data collected

are examined in seconds. The results of six field sites are

compiled. Rain rate levels, duration of downpours, and frequency

of heavy rainfall events are presented.

397
OUTLINE

• HEAVY RAIN

• TRANSITION TIME

• RAINFALL MEASUREMENTS

• DATA REDUCTION

• HEAVY RAINFALL CHARACTERISTICS

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DYNAMIC RESPONSE OF WING IN SIMULATED RAIN

Test set-up in 14-by-22 foot subsonic tunnel

Rain

Simulator

Section

(NACA 23015)

::.....,_,',_. PAGE tS

Normal force.

Ibf

Transition

time

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Time (sec) -_

{Campoelr & Bezos, 1989

402
DYNAMIC RESPONSE OF WING IN SIMULATED RAIN

TEST SET-UP AT THE AIRCRAFT LANDING DYNAMICS FACILITY

Rain

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(NACA 64-21 O)

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(Bezos, Dunham. Campbell, Melson- 1990!

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LOCATIONS

° GSFC/WFF, WALLOPS ISLAND, VA (FEBRUARY 1989)

° LaRC, HAMPTON, VA (JUNE 1989)

° KSC, KENNEDY SPACE CENTER, FL (JUNE 1989)

° NASA/BMRC, DARWIN, AUSTRALIA (NOVEMBER 1989)

° BOEING AIRCRAFT CO., SEATTLE, WA (JANUARY 1990)

° NCAR/NWS, DENVER, CO (FEBRUARY 1990}

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800,

700

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600,

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400

300

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Time (rain)

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Heavy Rain Field Measurements - Questions and Answers

Q: ANDY PECZALSKI (Honeywell) - What are typical velocity values of rain droplets?

Is there any correlation between droplet velocity and rain rate? Where can I find this

information?

A: ED MELSON (NASA Wallops) - I'm going to have to quote that from memory, so it

will be an order of magnitude. A small droplet, say in the order of 1/2 millimeter, would

fall around 2 millimeters per second and a large droplet, in the order of 4 millimeters

diameter, would fall somewhere in the order of 8 millimeters per second. This data was

from Gunn and he related the fall velocity of droplets. The larger droplets he said follow

Newtonian physics, whereas the small droplets with Stokes. The relationship is indirect in

that we are looking at the velocity of droplets. If you want to relate that to rainfall rate, the

Marshall-Palmer Report, relates drop size to rain fall rate, so indirectly you could relate fall

velocity to rain rate. But from the reports I've seen it's mostly drop size distribution related

to rain fall rate.

Q: NORMAN CRABILL (Aero Space Consultants) - Have you correlated any of the rain

rate measurements with radar measurements?

A: ED MELSON (NASA Wallops) - No, I haven't at this time. We do have three of our

gauges in locations within the range of radars. The one at Denver is under radar coverage,

and the one in Florida is also under radar coverage. The one in Darwin is being moved so

it will be in a better position to be under radar coverage. I know that the data at Kennedy is

being evaluated. The data at Darwin is going to be evaluated by the Tropical Rain

Measurement Mission people. The are using a satellite based radar and they are concerned

about the Z versus R curve, so they are using ground point measurement devices to validate

these radars.

Q: CHET EKSTRAND (Boeing) - Field measurements apparently only involve sampling

at a single geographical position at each site. What do we know about the distribution of

rain rates over a large geographical area at a single site? In other words, in an environment

where significant wind shear might occur, how long might an airplane moving at typical

approach speeds be continuously exposed to rain rates which have significant effects on

aircraft climb performance or stall margin? Do you have any plans to do simultaneous

sampling at several geographic positions at a single site?

A: ED MELSON (NASA Wallops) - We're right now purchasing 3 gauges to put in one

single site so we can get an idea of what is the graphical positioning area of some of these

storms. I think some of this work has been done. I know the WMO, which is the World

Meteorological Organization, in their report on the probability of maximum participation

have looked at how large some of these cells are, and I'm sure this group has looked at

how large some of the microburst ceils are also. I don't particularly know how large some

of them axe, nor do I know exactly how long it would take an aircraft to fly through these

cells. But I think that's something that we are going to have to address as soon as we get

most of our information together from some of the tests that we are doing at these sites and

also in the wind tunnel. The question on are we looking at rain data in a microburst, the

site at Darwin, Australia, is particularly being set up to look for some of that type of data

right now. We had a report from Tom Keenan of Australia who indicated that they were

seeing from the Toga radar on the average of five microbursts a week during the transition

from the monsoon season to the convective storm. At this time there is going to be a

weight measure rain gauge, a tipping bucket, and optical gauge and a distrometer to

423
measure drop size, located at a site in which the Toga radar will be able to overlook it. This

is planned to be conducted this winter here, they're summer there.

424
Session VI. Heavy Rain Aerodynamics

N91-24182

Estimate of Heavy Rain Performance Effect

Dan Vicroy, NASA Langley

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Estimate of Heavy Rain Performance Effect - Questions and Answers

Q: JOE YOUSSEFI (Honeywell) - Your data shows that the stall margin is reduced by

approximately 2 degrees at landing flap configurations to levels on the order of 2.5

degrees. Does this represent adequate margin under turbulent conditions?

A: DAN VICROY (NASA Langley) - I can't answer that, I don't know. I would certainly

think that you would raise a caution flag when you're margin has been reduced to about

half. I don't know how the stick shaker angle of attacks are established and whether or not

they account for a margin for turbulence. Like I said, I'd raise a caution flag in any case.

Q: JOE YOUSSEFI (Honeywell) - Should the training aid guidelines be revised relative to

operation at stick shaker prior to accumulation of additional heavy rain data?

A: DAN VICROY (NASA Langley) - I'd have to say no. We just don't know enough yet

to make those kind of changes. When you look at the data base that the training aid was

developed with compared to the data base we've developed in the heavy rain research, we

just do not know enough yet about heavy rain to make those kind of decisions.

450
Session VII. 2nd Generation Reactive Systems

451
452
Session VII. 2nd Generation Reactive Systems

N91-24183

Status of Sundstrand Research

Don Bateman, Sundstrand

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Status of Sundstrand Research - Questions and Answers

Q: JOHN McCARTHY (NCAR) - Are you aware of a Cuban Allusion 62 fatal accident'?

Havana, Cuba, September, 1989. There was 125 killed. Departure profile similar to

Pan Am 759. The Cuban Civil Aviation Authority blamed (1) microburst, (2) crew

training, (3) pilot actions. So the record is not clean since 1985.

A: DON BATEMAN (Sundstrand) - The chart I presented did not include any Soviet

Union, Eastern bloc countries or Cuba. To me, this illustrates that the value of having an

open society of nations where people trade back and forth accident information. As

everyone knows in this room it was very difficult to get any information at that time, back

in the 60s, the cold war, which really meant anything. Obviously if we put the Cuban and

Russian and the other countries on the chart, we would probably have a continuing accident

profile all the way across. Again I say the training programs, the education, avoidance, has

really paid off. It's paying off everywhere in the world and I'm very proud that a lot of it

came from the United States. I should say that since 1988 things are really changing. Mr.

Gorbachev, who got the Nobel Prize yesterday, has really helped change that. Cuba still is

very, very difficult, so close to us, yet so far in communicating with each other. Even Mr.

Gorbachev hasn't been able to convince that openness that we need.

Q: PAUL KELLY (21st Century Technology) - What is the logic behind a wind shear

alerting system that simply tells the crew somewhere in the vicinity is a wind shear?

Without qualitative and quantitative data on the shear characteristics? Is not the only logical

approach to crew alert some format that indicates the nature of the shear, its relevant

position in respect to that aircraft as well as information on advisable maneuvering options?

What's the good of spending money on any alerting system that does not address these

three factors?

A: DON BATEMAN (Sundstrand) - Well, I wish we could give the pilot pictures. I think

the speakers yesterday talking about the TDWR data transmittal to the airplane and

displaying that, that adds another breadth to this, for the pilot to be able to really see what's

going on out there. But this is nothing new. You have to start somewhere. I believe when

a wind shear warning is given, the pilot is not asked what the picture is, or what the

characteristics of the shear are, he is asked to leave. Perhaps with time maybe we'll get the

pictures that the pilot really needs to see to help. I myself believe in not treating the pilot

like a monkey, but to give him some information.

PAUL KELLY (21st Century Technology) - A very relevant adjunct to that question was as

we saw this morning, sometimes a shear or the focal point of a microburst is not lined up

with the longitudinal axis of the aircraft and it can be such that if the aircraft resorts to

standard evasive maneuver by going on to standard missed approach path for that airport, it

could very well end up putting himself into a tail wind, which of course will have the

maximum danger. So, what is so important I believe, is that pilot needs to have some idea

with regard___tothe physical characteristics of the microburst because standard evasive action

could lead to him getting into a more dangerous situation which he would otherwise avoid

if he had some information that made him realize that factor.

TERRY ZWEIFIL (Honeywell Sperry) - Yes, ideally that's what we would have. There

would be some kind of situational display. Unfortunately there is 3000 commercial

airplanes out there who have no capability to do that. The second point is, the reactive type

systems are not predictive. That is, they only detect shears when you axe in them. So it's

going to be almost moot in terms of what part of the shear that you're in. It will either say

you are in a shear or it will not. It's all one red light that comes on and says, "wind shear,

4T6
wind shear, wind shear." The standard guidance procedure, no matter who's system

you're looking at, in terms of roll, is to keep the wings level. Therefore, we are never

instructing the pilot to turn one way or the other where he might in fact turn into the shear.

Actually the real reason we do that is to keep the drag on the airplane down. So unless you

just happen to have a very bad day and you just happened upon the shear just as it moves

across as you're coming into it, you could in fact get into a worse condition. But the

reactive systems, as they're designed today, have no way of anticipating what that is. Like

I say, in the future we hope to change all of that and that's why we have all of these

forward looking guys with the TDWRs and LLWAS and those sort of things. But for right

now, we need to protect the airplane population that's out there without any of these

display capabilities, which even if we could generate the display, we have no where to put

it. So they're kind of at the mercy right now of a simpler system.

477
478
Session VII. 2nd Generation Reactive Systems

N91-24184

Temperature Lapse Rate as an Adjunct to Wind Shear Detection

Terry Zweif'd, Honeywell Sperry

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480
TEMPERATURE LAPSE RATE

AS AN

ADJUNCT TO WlNDSHEAR DETECTION

TERRY ZWEIFEL

HONEYWELL INC.

ABSTRACT

As airborne windshear detection systems evolve, an increasing sophistication is

required to assure more reliable and timely detection of hazardous windshears. As part

of an on-going study by the University of Oklahoma and Honeywell, Inc., several

meteorological parameters are being examined to determine if measurable atmospheric

conditions can improve windshear detection devices.

Lapse rate, the temperature change with altitude, shows promise as being an

important parameter in the prediction of severe windshears. It is easily measured from

existing aircraft instrumentation, and it can be an important indicator of convective

activity including thunderstorms and microbursts. This presentation briefly reviews the

meteorological theory behind lapse rate measurement and describes an FAA certified

system that is currenty implemented in the Honeywell Windshear Detection and

Guidance System.

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Optimal Guidance during a

Windshear Encounter

An aircraft caught in windshear experiences a dangerous

loss of lift. An application of optimal control theory has identified

the best strateg)' for surviving such conditions, a strategy now

implemented in the Honeywell Windshear Computer.

Terry Zweifel

(Sperry Commercial Flight Systems Division)

AZ75-N30D2:602-869-2979

t six o'clock on the evening of August 2, 1985,

Delta Air Lines Flight 191

was on final approach for a

landing at Dallas-Fort Worth International Airport. A thunderstorm was

forming near the north edge of the

field, directly on the approach path to

the active runway. Two other aircraft

landed safely, but by the time Flight

t91 reached the storm cell, it had built

up to a dangerous intensity. Within the

cell, the aircraft entered a region of

severe windshear and began losing

altitude. In spite of the crew's strenuous efforts to maintain control, the

aircraft fell below the prescribed glide

slope and struck the ground more than

a mile short of the runway. The crash

killed 134 people on board the aircraft

as well as the driver of an automobile

on a highway just outside the airport.

The loss of Flight [91 is the most

recent of 28 aircraft accidents since

1964 caused by the meteorological

effect called windshear. The accidents

have resulted in 623 deaths and 237

injuries. In the past decade, about half

of all commercial-aircraft accidents

have been related to windsbear. All of

them have happened during takeoff or

landing maneuvers.

To prevent such accidentsin the

future,the bestpolicyisdoubtlessto

avoidflyingintoregionsofwindsbear.

To thisend, varioussensorsystems,

such as Doppler radars,have been

developedto detectwindshearconditionsnear airports, so that pilots can

be warned to delay takeoffs and landings until the danger passes. But

ground-based detectors can never be

perfectly accurate and reliable. Inevitably, an aircraft will occasionally stray

into a windshear region. The question

then becomes how best to get out of the

predicament.

My colleagues and I at the Sperry

Commercial Flight Systems Division

have approached this question as a

problem in optimal control. In other

words, we have asked what control

strategy should be adopted to maximize the chances of successfully flying

through the windshear. We have

discovered that the optimum strategy

is in fact a simple one, which we have

implemented in the Honeywell Windshear Computer. This instrument is

now capableof detecting the presence

of windshear and then either directing

the pilot or commanding the aircraft's

autopilot to follow the optimum escape

path.

The Wind.shear Hazard

The term windshear refers to any

situation where wind velocity varies

sharply from point to point. Windshears can be caused by a number of

atmospheric phenomena, such as

weather frontal systems, but the most

lethal form of windshear is called a

microburst. Events of this kind, which

are always associated with thunderstorms, were discovered by T. Theodore

Fujita of the University of Chicago. A

microburst is a column of rapidly

Socrlti fie Honcywetlet

descending air, which fans out radi',dh

as it nears the ground, like the stream

from a faucet splashing into a basin

(see upper illustration on page 112).

A typical microburst is less than three

miles across and lasts 15 minutes or

less.

An aircraft attempting to tra%erse a

microburst during takeoff or Landing

usually encounters a headwind first.

followed by a downdraft and finally a

tailwind. Contrary. to what one might

guess, it is not the downdraft that

represents the greatest hazard to

aviation but rather the tailwind. When

the horizontal component of wind

velocity shifts from a headwind to a

strong tmlwind, the effect is to reduce

the craft's air speed; that in turn

reduces lift. Loss of lift, of course.

causes the aircraft to descend.

The corrective for the loss of lift is to

increase the aircraft's angle of attack.

or in other words to pitch the nose

upward relative to the airstream. If the

angle of attack exceeds a limiting

value, however, the aircraft will enter

an aerodynamic stall. The limiting

value is called the "stick-shaker" angle,

because a mechanical vibrator attached to the pilot's control column is

activa'ted at this point to warn of an

impending stall. On a typical commercial jet transport the difference between

normal angle of attack and stickshaker angle is only about six degrees.

Thus the range of control available for

counteracting the effects of wtndshear

is quite limited.

496
THUNDERSTORM CELLslmwns• micn_arst--a descending

column of cold air--near Stapleton international Airport in

Denver. The microtmrst is the dark •re• in the right half of the

photograph. As it flares out in • radial pattern on reaching the

ground, it creates severe windsbear, or in other words • strong

gradient in wind velocity. Windshear conditions encountered

during take•if•rid landingerethe most serious weather hazards to

modern commercial •via•ion. Much effort his been put into

diet•cling and •void_ wtndshear; the CommercialRight S_t_ems

Division has developed tn instrument that implements the

optimum strategy for escaping • windsbeBr. The photograph vm5

made July 8, 1984, by T. Theodore FujJt• of the University of

Chicago and Wendy Schreiber of the National Center for

Atmospheric Research.

Apart from the limited range of

control, the natural dynamics of an

aircraft create further difficulties in

coping with windshear. Speed and

altitude in an aircraft are closely

coupled: If a windshear causes a loss of

air speed, the aircraft naturally tends

to pitch down (that is, decrease its

angle of attack) and regain the speed at

the sacrifice of some altitude. A loss of

altitude, on the other hand, has the

opposite effect: the aircraft tends to

gain air speed as it descends, which

increases lift and causes the aircraft to

climb. The result of this continual

exchange of potential and kinetic

energy is a miler-coaster motion called

a phugoid oscillation, it is an oscillation with a long period (typically 30

seconds), and in most aircraft it is

poorly damped or even divergent (see

lower illustration on page 113).

in normal flight the phugoid oscillation is suppressed by continually

adjusting the angle of attack in order to

maintain a zero rate of change in

altitude or air speed. The adjustments

can be made by the pilot through the

control column or by an automatic

flight-control system. In a windshear

encounter, however, there may not be

sufficient control latitude to arrest the

phugoid motion, since the angle of

attack may be near the stick-shaker

limit. If the phugoid oscillation is not

controlled, the altitude excursions can

grow large enough to cause ground

impact.

Given these aerodynamic constraints, the object of a windshear

guidance law is to make optimum use

of the available range of control and

thereby to maximize the probability of

survival. To achieve this goal, we

Winter 1989

employed the methods of optimal

control theory.

The Best Flight Path

The first and most fundamental rule

for negotiating windshear conditions

during the approach to landing is that

no attempt is made to land the aircraft.

Instead, the pilot initiates a go-around

maneuver, increasing engine thrust to

the maximum and adjusting angle of

attack so as to establish a nonnegative

rate of climb.

To determine the optimal guidance

law for executing such a go-around

maneuver, we simulated an aircraft's

flight in windshear conditions. The

simulation program, which ran on a

personal computer, was adapted from

one written by J. Rend Barrios. The

original version had been used in the

development of the Honeywell Per497
formance Management System to

determine the Mach number that

yields minimum fuel consumption [see

"Optimizing Aircraft Performance."

by Sam Liden, on page I01]. In our

studies of the wtndshear problem we

modified the program to make the

control variable angle of attack rather

than Mach number. At each instant

during a simulation the state of the

aurcraft was defined by tts aitaude, atr

speed and distance tra'.elled and by the

wind vetocit._.

An interesting aspect of the problem

was choosing criteria by _hich to

GO-AROUNO

RUNWAY

MICROBURST i5 a small-scale but intense meteorological

phenom4mon, seen only in conjunction with thunderstorms. The

downdmft in 8 microburst can have a velocity o(40 karts or more.

and the horizomal winds mar the surface are even more violent,

smnetimes exceeding 200 kno(s. The high wind velocities, however.

are not the principal hazard to aviation: the main threat comes

instead from the rapid change in wind speed and direction

experienced by an aircraft traversing the microburst at low

altitude, in the diagram an aircraft encounters severe windshear

on f_l approach to landing. Initially, • headwind augments the

craft's air speed and lift, so that it rises ahove the intended glide

slope. But • steadily increasing t•ilwind then reduces both air

speed and lift. so that the aircraft sinks and strikes the gn)und short

of the runwny. The recommended action in these circumstances is

not to attempt t landing hut rather to initiate a go-around

nmneuver. Optimal comrol theory has idemified the best strategy

for executing I go-around in windshesr.

ANGLE ....._

OF ATTACK VELOCITY

VECTOR

=,...,.-,,-

ANGLE

OF ATTACK _...=¢ :_

ANGLE OF ATTACK is the primary means of controlling an

ailq_41ne's pith _ l WilldshiHlt encounter. The nolle of alLack

isthe angle _¢med between an aircraft'saxisand itsdirectionof

mosiem relativeto the airmass. Increasing the angle of attack

generates grtster lift, but there is a limitint angJe that cannot he

exceeded or the aircraft will enter an aerodynamic stall. The

limiting tngJe of attack is called the stick-shaker angle because t

HORIZON

flbrator attached to the control ye_ is activated at this poim to

warn the pilot of an impending stall. The difference between

nornml anl_e of attack and the slkk-4Amker anlle is only about six

d_ which is aU the latitude available for controlling flight in m

windshear episode. The aim of the optimal comroi law is to make

the most effective use of this limited rante.

Scientific Honeyweller

498
judge candidate control laws. In the

early stages of the investigation we

considered a number of possible criteria. For example, one approach takes

as an ideal the flight path that would

be followed during a go-around in the

absence of windshear then the optimal

control law is the one that minimizes

de,,iations from this path. Other criterm favor control laws that minimize

the cunature of the flight path or the

rate of change in altitude or that

maximize ground clearance. We constructed grading schemes that incorporated various combinations of these

factors. After a multitude of simulation runs, however, the correct criterion

proved to be a simple one. although not

necessarily an obvious one. To understand the motivation for this choice, it

must first be observed that some

wtndshears are so severe that an

aircraft cannot traverse them no matter

what control law it employs. We found

that the optimal control law is the one

that under such extreme conditions

keeps the airplane airborne for the

longest possible time.

What control law provides the maximum time aloft? The answer to this

question also emerged from our simulations. It turns out that the best policy

is to maintain level flight, or in other

words to fly at a constant inertial

altitude. There are two reasons this

strategy works well. First, it maximizes

the time available before the angle of

attack must be increased to the stickshaker limit in order to maintain

altitude. Second. flying a constant

altitude tends to damp the phugoid

oscillation.

Other candidate control laws invariably call for climbing in the presence of

windshear. The weakness of this

strategy is that it diminishes air speed.

and. as noted above, at a lower air

speed angle of attack must be increased to mmntmn lift; thus the angleof-attack margin available for control is

quickly dissipated. Once the stickshaker angle is reached, the aircraft is

essentially uncontrollable. If the angle

of attack is increased further, the

aircraft will stall; conversely, if the

angle of attack is decreased, the

aircraft will rapidly descend. Even

COCKPIT FLIGHT DIRECTOR advises the pilot when windshear conditions have

been detected and provides guidance on the best strategy for recovery. The warning

"WIN D SH R = in t he upper left corner of the display fbudhes rnd to indicate the Werence of

a serious windshear, The large crosshair in the center of the _ comdsts of vertical end

horgtontal cmurnand bars, witich bum_ the pilot on wJ,*t actinn to tahe. At the left ed_

of the display is u scale bounded by the letters "F'(l_r "fiwt ") lind "S" (for _slow"). During

takeoff and landing this scale indicates the aircraft's angle of ettagk, with the "S" mark

repgerenting the stick-sheher angle; thus the instrmnem shows the pilot how much coem_l

is e_tihtble before the aircraft r_,aches the sfiek-shalt_ lisndt.

2,400

2.000

."c,1.600

1,200

8OO

400

0

0 20 40 BO 80

TIME (SECONDS)

PHUGOID OSCILLATION comp4icater the task of flight control in windehear. The

oscillation results from a natural coupling between air speed and altitude: If some

perturbatkm causes am akc_ft to iuse speed, it will also ioee lift and so wilt hegin to _.

The descent, however, incr,-._sesair speed and lift, inducing • climb. In mo_ tircrafl the

pbulogl oscillatina hu a long perlod (30 secondsor mo_e) and is poarly damped or even

diwqgem. In nornml flight it is easily commlled by nmmud or automatic adjustments to

the mtlgle of attack, but in a wlndshesr the angk of attack may tume to be held at the stickslutl_ Umit. in that cirgumstan_ the flugtuatlam in alfltu_ earl grow uut_ the aircraft

stoker the greund. The graph reem_is a dmulatkxt of an _lled mcfllation.

Winter 19S9

499

_'-,, .',AL PAGE

_L,',;_..', ,:_,NO WHITE PHOTOGRAPH I,t

OF POOR (_YdAL|T'/
holding the controls pert¢ctly steady at

the stick-shaker angle ts not an attractive option. With no range of control

motion to damp the phugmd oscillation, the aircraft begins a series of

altitude excursions that inevitably

result tn ground impact.

]-he clear tmperattse emerging from

our simulations was to maximize the

time available before a pilot must

reso_ to stick-shaker angle of attack in

order to keep the airplane aloft.

Actually. the theoretical maximum

time is attained not in level flight but

when the aircraft is 'allowed to descend

slightly, Incorporating this strategy

into a general control law does not seem

prudent, however. After all. a windshear might be encountered at very low

altitude, or features of the surrounding

terrain, such as hills and tall buildings,

might make descent hazardous,

Other m,,esttgators have also explored the question of optimal gutdance in windshear. For example,

Angelo Miele of Rice University has

applied numerical methods to the

problem. Even though the methodo|og.v differs in the _,arious studies, the

conclusion is the same: the optimum

practical guidance strategy for a pilot

caught in windshear is maintaining

level flight.

Simulation Results

The outcome of one series of simulations is shown in the illustration below.

Here a typical commercial jet aircraft

encounte_ a windshear shortly after

takeoff, when it is at a height of

about 200 feet. The taiiwind develops

about five seconds into the simulation

run and increases at a rate of five knots

per second; it ends after 23 seconds,

'._ hen (he total change in v, md ,,..., .c:t',

is 115 knots. Fhts represents a se;ere

windshear episode. In the crash ot

Flight 191, for comparison, the horizontal component of the wind shifted

o'er a period of about 30 seconds from

a 23-knot headv, md to a 49-knot

tailwind.

The simulation examines the effects

of fi,e control laws, each of which has

been ad,,ocated at one time or another

during the past decade as an appropriate response to v, indshear. 7he first

strategy is to regulate angle of attack so

as to maintatn 110 percent of stall

speed. The resuit ts a steep climb.

which cannot be sustained: after just

20 seconds the aircraft plunges back to

earth. Holding the controls at stickshaker angle of attack leads to an e,,en

more dramatic rise--the peak altitude

is greater than 1,000 feet--and an

7--

1.000-

q

800-

400-

200-

0

WlNOSHEAR REGION

0 10 20

CANDI_TE CONTROL LAWS were t_ by _i on •

/__ flve_ _run/_

at • rote of five knott per secm_ tlMn mlng 13 sec_mds/er.

From of the cmmol htwe teaed lind beem ree_ at one _hme

or •i_Ibtl as arltlglu far escspl.all wimlslltml. Flylng It llg

percen! ol' stall speed, holding stick-shlker Ingle of llllek or

Sa_UFT¢Nom'_,,'d_

i t

30 40 50 60

TIME (SECONDS)

miililil8 • clmitint Ilround speed IdJ produce • drim•tie climb

_ by • c=_ pilmle. When tk _ _ I

!_ _ lUllile, it _ aloft sUgllthj km_. The optimal

lirltlq_ oirflying • ¢miiui lnertill •itttude--or in other words i

zero_ flight-pith ingle--is the only One th•t Illowl the

to surlt_e.

SO0
FLIGHT-PATH COMMAND

(ZERO DEGREESi

INERTIAL

REFERENCE

SYSTEM

RATE

NETWORK

RATE

NETWORK

ANGLE-OFATTACKSENSOR

i t__[ c' C°'AT'O ]

POSITION OF STICK-SHAKER

SENSOR ANGLE OF ATTACK

OPTIMAL CONTROL LAW has been implemented in the

Honeywell Windshear Computer. When windsbear is detected,

the s!stem continually regulates angle of attack in order to

maintain level flight (a zero-degree flight-path angle) without

exceeding the stick-shaker angle. The zero-degree commanded

flight-path angle is compared with the actual angle, as messurecl

by an inertial reference system: the ate of change in the angle is

also included in the calculation to help damp fluctuations. The

+

T

FLIGHT

DIRECTOR

AUTOPILOT

differmce between commanded and actual flight-path angle is an

error signal that goes to a flight-director indicator on the pilot's

instrument panel or to an autopiiot that directly controls angle of

attack. If the angle of attack reaches the stick-shaker limit, an

auxiliary control network takes over, m_,intzining this maximum

useful angle of shack (and thus maximum lift) withmzt allowing

the aircraft to stall.

equall_ catastrophic descent. Maintaining ,,era longitudinal acceleration.

or in other words constant ground

speed, keeps the craft airborne a fe_,

seconds longer.

The most effective of the nonoptimal

strategies tested here is flying at a

constant pitch angle of 15 degrees. This

is the escape plan currently recommended by the Federal Aviation Administration for aircraft not equipped

_'lth windshear detection and guidance systems. If the simulated windshear had ended a few seconds sooner,

the aircraft following the 15-degree

strategy would have successfully

crossed the danger zone.

1-he optimal strategy of maintaining

constant altitude is the only plan that

allows the aircraft to survive the

simulated windshear episode. Even in

this case it is not possible to stay aloft

indefinitely. At about 25 seconds into

the simulation run, the angle of attack

has reached the stick-shaker limit and

cannot be increased further; hence the

aircraft begins to sink. If the windshear

had continued a few seconds more. the

aircraft would have crashed.

Impicmmtation

The optimal control law derived from

our simulations and analyses has been

implemented in the Honeywell Windshear Computer, an instrument developed in the early 1980's by the Sperry

Aerospace &Martne Group and certified by the FAA in 1985. In its original

form the windshear computer merely

detected the presence of windshear.

alerted the flight crew and prowded an

angle-of-attack reference the pilot

could use in flying out of the danger

zone. With the optimal control laws the

computer can now offer more specific

guidance to the pilot or can take over

control of the aircraft, guiding it on the

optimum flight path.

The computer detects windshear

conditions by comparing signals from a

number of inertial and air-data sensots. For example, one warning sign is

a change in airspeed (as measured by a

pitot probe in the airstream) that is not

winter 1989

matched by a change m inertial velocity (as determined by integrating the

output of an accelerometer). Going

beyond mere detection to active control

does not require any additional inputs.

In its simplest form the control

mechanism requires only one input: a

signal representing the flight-path

angle, or in other words the aircraft's

rate of climb or descent. If the aircraft

is equipped with an inertial-reference

system, the flight-path angle can be

measured directly by a system of

gyroscopes and accelerometers. Otherwise, the angle of the craft's trajectory.

with respect to the air mass is calculated from air-data sensors and is then

corrected for the effects of vertical and

longitudinal winds. Regardless of the

source of the information, it serves the

same function. When the computer

detects a windshear condition, the

controller commands an inertial flightpath angle of zero degrees and compares this value with the actual angle.

The difference is an error signal that

indicates deviation from the optimum

501
flight-path angle. If the aircraft ts

under manual control, the error s_gnal

_s supplied to the t]ight director, an

instrument that guides the pdot to the

correct control actions. Under autopitot control, the error s_gnal ts translated

dtrect[_ into movements or the ele_,ator

or other aerodynamic control surfaces,

The actual _,indshear control system

ts _omewhat more complicated than

this account might suggest (see illustration onpage 115). In addition to the

flight-path angle, the computer also

considers the rate of change in this

angie: including a rate term in the

feedback loop helps to damp out rapid

fluctuations and makes the aircraft

more "flyable."

Another part of the control system

takes over when level flight can no

longer be sustained. As a rule, the

controller wilt call for steadily increasing angle of attack during a windshear

episode in order to avoid loss of

altitude. This trend cannot be allowed

to continue once the stick-shaker angle

is reached, or the alrcratt v, dl stall. A

separate control loop is therefore

included to monitor angle of attack.

The stick-shaker angle, w htch depends

on the position of the wing flaps, is

conttnuoust,, calculated and compared

with the actual angle of attack. Whenever the actual angle exceeds the upper

limit, the constant-altitude controller is

switched off, and the airplane is held at

stick-shaker angle of attack. Rate of

change in the angle of attack is also

included in the calculation as a damping and anticipatory factor: If t he angle

of attack is increasing rapidly, the rate

term will prevent overshooting and a

possible stall.

The control section of the windshear

computer includes several further

refinements. For example, filters and

variable gain schedules improve flyability, The implementation of the

control laws is now complete, and the

system is operational in the Honeywell

WtndshearComputer indeed. _t has

passed the ultimate test: _t ha,,, pro'._ded guidance to successtul{._ e,,cape a

real m_croburst encounter

Acknowledgement

The author ,,_ishes to acknov, ledge the

considerable contributions ol J Rene

Barrios to the investigation ot the

optimal control law.

Bibliography

A. Miele. T. Wang and W. W Met_in.

"Optimal Take-Off Trajectortes in

the Presence of Windshear,'" Journal of Optimization Theor_ and

,4pplicat:ons, Vol. 49. No. I, Aprd

1986. pp, 1-.45.

Arthur Bryson and Yu-chi Ho. 4pplied Optimal Control. Washington, D.C.: Hemisphere Publishtng.

1975.

T. Theodore Fujita. DFW Microburst

on August 2, 1985, Chicago. II1.:

The University of Chicago. 1987

SC.emificHon_'_,_'t_

502
Reprinted from

Scientific Honeyweller

Winter 1989

pp. 110-116

©1989 by Honeywell Inc.

Honeywell

HELPING YOU CONTROL YOUR WORLD

A_ Tren_ooct5y,_e¢_ Dw_on

PO, Box 21111

Phoe_x. AZ

503
Temperature Lapse Rate as an Adjunct to Wind Shear Detection

Questions and Answers

Q: CARL YOUNG (Eastern Airlines) - How do you tie lapse rate technolo_' with your

zero gamma reactive system?

A: TERRY Z_'EIFIL (Honeywell Sperry) - A quick word on what zero gamma means.

That is really what we do when the shear is detected. We fly what is called an optimal

flight path which we've shown through various studies, us and others, that flying a zero

gamma relative to the earth gives you the optimal flight path. That is, it will keep you in the

air longer than any other strategy. The lapse rate itself has really nothing to do with the

guidance part of it other than sensitizing the system so that it gives you the wind shear

quicker. The way the system works, when it detects a wind shear, says "wind shear, v,ind

shear, wind shear", if you're in take off you automatically get the optimal guidance. If you

are m approach, you do a missed approach technique, either slamming the throttle full

forward or hitting the go around switches, either one will give you the automatic guidance

But the lapse rate itself really doesn't have anything to do at that.

Q: CARL YOUNG (Eastern Airlines) - If we're going to use an accelerometer based

system to trigger a wind shear reactive system, how would you weight that versus lapse

rate technology? Are you tending more to have lapse rate technology be predictive?

A: TERRY ZWEIFIL (Honeywell Sperry)- No, the lapse rate right now is not intelligent

enough to handle the wind shear detection case. The only thing we can use it as is the

probablistic measure of wind shear, really microburst threats. It, in itself, will never

replace the current reactive systems that you see today.

Q: PAUL ROBINSON (Lockheed) - From your presentation I got the impression that it

was of the greatest importance to detect dangerous wind shears from microburst only.

What precautions are taken to insure that dangerous shear from other sources, not

microburst, are not overlooked by the dependents on lapse rate?

A: TERRY ZWEIFIL (Honeywell Sperry) - We never turn the system off with lapse rate

measurements. It's simply an adjunct to what we're doing now. We'll change the

thresholds slightly, not greatly. Without going into a great, elaborate thing to show you

how actually we detect shears it's kind of hard to explain. The lapse rate is primarily used

to sensitize for microbursts and the reason is that most of the wind shear accidents we have

seen axe in fact microburst caused. But we will still detect frontal shears, even terrain

induced shears could set the system off.

Q: BOB OTrO (lockheed) - What is the reduction in alert time when first generation

reactive systems are coupled with temperature lapse rate measurement? That is, if the

reactive system affords t seconds warning, then what increase to t does lapse rate

measurements afford?

A: TERRY ZW IFIL (Honeywell Sperry) - That's going to depend a lot, of course, on

what particular shear model you use and what the lapse rate looks like. Let me give you an

example, from Dallas you will get about 3 - 4 seconds quicker warning that you would

have from a purely reactive system alone. It's of that magnitude. I think Don Bateman

was saying that they also use lapse rate. I don't think ifs quite the same mechanization but

I think he had numbers very much along that line.

504
Q: FRED PROCTOR (MESO) - Low level stable layers can sometimes be present prior

and during microburst events. Could your system function properly in such cases?

A: TERRY ZWEIFIL (Honeywell Sperry) - It depends. If you look at, as an example, the

11 July sounding, and you can see that in fact there was a stable layer. It did drop back

below the unstable measurement of -0.003. In this case the system, by having read the

previous lapse rate values up in here, has already armed. Then it just sits there and waits to

see if the temperature ever swings out the other way, implying that you've flown into the

cold down flow. So, even though this phenomenon occurs, it does not disarm the system.

It says I saw it once, therefore I'm going to maintain this. Actually, that's not quite _"-ue. If

we see it long enough, over about 1000 feet that it has dropped below -0.0025, then it will

reset and say there really wasn't a serious problem here. Surely I could conceive of some

situation when in fact we wouldn't do exactly what we wanted to do. But in the cases that

we have looked at, even with these stable layers, it still performs it's intended function.

Q: WAYNE SAND (NCAR) - Can you tell us more about your chip to measure dew

point? How accurate is it? How much does it cost? How does it interface with existing air

data computers?

A: TERRY ZWEIFIL (Honeywell Sperry) - How accurate is it -- based on our people up

in SRC, I understand that it is something of the order of + or- 5% in measuring relative

humidity. Basically the reason we, Honeywell, designed this was that we built a lot of

systems to monitor computer rooms and keep them at certain relative humidities and certain

temperatures. That's what the chip is built for. It's not in production so I really can't tell

you how much it costs. Hopefully, not much. Does it interface with existing air data

computers -- not yet, though we have looked into it and I am a little concerned about some

of the engineering that goes into that. We certainly have the room to put it inside our

computer. Our wind shear computer, by the way, has a complete air data computer of its

very own, we don't use anybody else's. How we do that -- haven't got that far. It doesn't

seem to me to be an insurmountable problem. It would be a beautiful thing to have. That's

one part we're missing.

Q: TON NIEUWIKX)RT (Fokker Aircraft) - Using a Kalman filter means that the noise

characteristics have to be known. How are these noise characteristics determined?

A: TERRY ZWEIFIL (Honeywell Sperry) - He's exactly right and that puzzled me for

some time, still does for that matter. Basically the way I did it, a brief explanation. To

compute the time constant for a Kalman filter, basically you have to know the variation of

the thing that you are measuring and also your measuring equipment. In this case we're

really not so much concerned about what is the variance of the temperature probe, we

assume that is accurate enough. What we're really trying to do is separate out the lapse

rate, that's the signal, from the noise, which is the garbage you get from little eddy's going

a.round in the amaosphere. Basically what I did was back into it almost like a circular

reasoning type of thing. I figured out what the number had to be to give the quickest

results, to get the filler as fast acting as possible, yet still giving us enough filtering so we

don't just get total noise. I could give you the number but it wouldn't I don't think mean a

beck of a lot.

Q: PETER SINCLAIR (Colorado State University) - How does your temperature lapse

rate sensing device determine what part of the measured temperature change is due to the

horizontal and vertical temperature components?

5O5
A: TERRY ZWEIHL (Honeywell Sperry) - The answer to that one is real simple. It

doesn't. It assumes that the temperature signature that it measures is simply an indication

of a microburst. It does not care whether it's from a vertical or a horizontal sense.

ROLAND BOWLES (NASA Langley) - Isn't that a fairly significant shortfa,i? When we

do soundings we release balloons to get temperature altitude profiles. The idea is that if it

goes miles down range it's beginning to get cluttered up. Here an airplane on approach can

travel several miles with relatively small altitude change. So are we really getting a lapse

rate measurement off that airplane?

TERRY ZWEIFIL (Honeywell Sperry) - Yes, you are. You're not getting a perfectly

vertical measurement of lapse rate but then when you really look at the data we have from

all these accidents, none of those were done right there at the site.

ROLAND BOWLES (NASA Langley) - Understood, but maybe a significant discriminator

is the along-track rate of change of temperature, a thermal plume that's sitting out there and

we encroach upon it and there's rapid variation along-track. Maybe that's the give away.

TERRY ZWEIFIL (Honeywell Sperry) - That's Conceivable. Typically on approach

you've got about a 3 degree gamma so most of your component is along-track. We do

make that tacit assumption that this is not a real small scale type of event. We assume that

the atmosphere in fact looks like this uniformly within the region of interest, whatever that

might be and, you're right, that is a tacit assumption that we do make.

506
Report Documentation Page

1 Report No 2 Government Accession No, 3. RecJp_ent's Catalog No

NASA CP-I0060, Part 1

D OT/FA A/RD-9 t/2-I

4 Title and Subtme

Airborne Wind Shear Detection and Warning Systems -

Third Combined Manufacturers' and Technologists'

Conference

5 RePort Date

January 1991

6. Performing OrganJzat=on Code

7 Author(si

Dan D. Vicroy; Roland L. Bowles; and

Herbert Schlickenmaier, compilers

9 Performing Organizatton Name and Address

NASA Langley Research Center

Hampton, VA 23665-52225

12. Sponsoring Agency Name anO Address

National Aeronautics and Space Administration

Washington, DC 20546

8. Performmg OrgamzatJon Report No

10. Work Unit No.

505-64-12

11. Contract or Grant No.

13. Type of Report and Parred Covere0

Conference Publication

14. Sponsoring Agency CoOe

15. Suptdementarv Notes

Dan D. Vicroy; and Roland L. Bowles: NASA Langley Research Center, Hampton, Virginia

Herbert Schlickenmaier: Federal Aviation Administration, Washington, DC

16. Abstract

The Third Combined Manufacturers' and Technologists' Conference was hosted jointly

by NASA Langley Research Center (LaRC) and the Federal Aviation Administration

(FAA) in Hampton, Virginia, on-October 16-18, 1990. The meeting was co-chaired by

Dr. Roland L. Bowles of LaRC and Herbert Schlickenmaier of the FAA. The purpose

of the meeting was to transfer significant ongoing results of the NASNFAA joint

Airborne Wind Shear Program to the technical industry and to pose problems of current

concern to the combined group. It also provided a forum for manufacturers to review

forward-look technology concepts and for technologists to gain an understanding of the

problems encountered by the manufacturers during the development of airborne

equipment and the FAA certification requirements. The present document has been

compiled to record the essence of the technology updates and discussions which

followed each.

17 Key Wordl (Suggeeted by Authotla))

Microbursts Doppler Radar

Wind Shear Infrared

Aircraft Hazards LIDAR

18. Dmtnbutmn Ststement

Unclassified-Unlimited

Subject Category: 03

19. SacuriW Classit. (of thin report) 20, Security Clessff. (of this I_ge) 2_ No. of pages [ 2.2. Price

Unclassified Unclassified [513tl f A22

NASA FORM 112l OCT 88 For saJe by the Nsr.ionm] TeckmcaJ [a.t'orma¢ion Service, SpringfieLd, Vir_a 22161-2171