NASA Conference Publication 10050 

Part 1 

Airborne 

Wind Shear 

Detection and 

Warning Systems 

Second Corn bined Manufacturers' 

and Technologists' Conference 

Compiled by 

Amos A. Spady, Jr. 

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 Williamsburg, Virginia 

October 18-20, 1988 

U.S. Department of Thinsportation 

Federal Aviation Administration 

July 1990 

National Aeronautics dnd 

Space Adn1fnic +r,it wLangley Research Center 

Hampton, Virginia 23665-5225 
FOREWORD 

i 

4 

The Second Combined Manufacturers' and Technologists' Conference was hosted 

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

Administration (FAA) in Williamsburg, Virginia on October 18-20, 1988. The meeting was 

co-chaired by Dr. Roland Bowles of LaRC and Herbert Schlickenmaier of the FAA. 

Amos Spady of LaRC and the Science and Technology Corporation coordinated the 

meeting. 

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

the second year 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 requested in writing. Questions and 

answers from the floor are included for all sessions. The written questions were presented 

and answered in the final session and are included in the document. Several of the 

speakers did not have vugraphs; their talks were transcribed from the recordings of the 

sessions, edited by the speaker, and are included. Additionally, the opening overview by 

Mr. David Johnson was transcribed and included to provide the reader with an 

understanding of the multiple elements included in the Joint Airborne Wind Shear 

Program. 

1.. 

111 
TABLE OF CONTENTS 

Part 1 

FOREWORD.. ....................................................... iii 

.4 

1. OVERVIEW ....................................................... 1 

Dave Johnson 

2. TECHNICAL PRESENTATIONS - Tuesday, 18 October 1988 

Session I. Airborne-Terms of Reference 

A. Tools for the Trade .............................................. 

B. 

9J 

Wallace M. Gillnian, American Airlines 

Overview of SAE Committee S-7 ARP 4102/11 

“Airborne Wind Shear Systems” ...................................... 35 

Robert L. Ireland, United Airlines 

Steve Morrison, FAA 

Terry Zweifel, HoneywelllSpeny 

C. Wind Shear Regulatory Activities ..................................... 43 

Flight Experience with Wind Shear Detection ............................. 57 d 

J 

D. 

E. Interface Standards for Integrated Forward-Looking Predictive/Reactive 

Wind Shear Systems ............................................... 71 

Mark McGlinchry, HoneywclllSpcny 

Session 11. Airborne-Hazard Definition 

F. Heavy Rain Effects on Airplane Performance ............................. 85 J 

R.E. Dunham, Jr., GM. Bezos, and B.A. Campbell, NASA LaRC, 

WD. Mace, Jr., PRC Kennon, and WE. Melson, Jr., Wallops Flight Facility 

G. A Proposed Definition for a Pitch Attitude Target for the Microburst 

Escape Maneuver ................................................ 103 

11 July 1988 Weather and Rcsulting TDWR Alarms at Denver, Colorado 

Numerical Simulation of the Denver 11 July 1988 Microburst Storm ............. 

Richard S. Bray, NASA ARC 

Wayne Sand NCAR 

Fred Proctor, MESO 

Robert L. Ireland, United Airlines 

H. 

I. 

......... 123 J 

159 

J. 11 July, Denver Wind Shear Encountcrs ................................ 179 

K. Questions and Answcrs for 18 October Sessions I and I1 ..................... 189 

3. TECHNICAL PRESENIATIONS - Wcdncsday, 19 October 1988 

Session I. Airborne-Scnsors 

A. Airborne Doppler Radar Detection of Low Altitude Wind Shear ............... 209 

B. 

J 

E.M. Bracalenre and WR. Jones, NASA LaRC, and Charles L. Britt, RTI 

Analysis of Synthetic Aperature Radar (SAR) Data for Wind Shear Radar 

D. Gineris, ERIM, S. Hnrrah, NASA LaRC, and I/: Dclnore, PRC 

C. L. Britt, RTI, and E. M. Bracalenre, NASA LaRC 

Clutter Modelling ................................................ 225 

C. Preliminary Airborne Wind Shear Detection Radar Assessment Study ............ 243 
D. Clutter Filter Design Considerations for Airborne Doppler Radar 

Detection of Wind Shear ........................................... 

Airborne Radar Scatterometer Design and Flight Test ....................... 

Ramifications of the Recent FAA Rule for Wind Shear Systems 

on the Development of Forward-Looking Systems .......................... 

G. Status of the Delco Systems Operations Forward Looking Wind Shear 

Detection Program ............................................... 

Infrared Thermal Imaging of Atmospheric Turbulence ....................... 

E.G. Baxa, Jr., Clemson University 

WR Jones and C.D. Lytle, NASA LaRC 

E. 

F. 

H. Patrick Adamson, Turbulence Prediction Systems 

Brian Gallagher, Delco Systems 

David Wan, John McHugh, University of New Hampshire, and 

William veil, Kollsman 

Russell Targ Lockheed and Roland Bowles, NASA LaRC 

Mark Stomi, Roland Bowles, and Bruce Conway, NASA LaRC 

H. 

I. 

J. 

Investigation of Airborne Lidar for Avoidance of Wind Shear Hazards ............ 

2 pm Lasers for Wind Shear Detection: A Technology Assessment .............. 

279 

295 

b 

313 v/ 

349 d 

365 

379 

Pnrt 28 

Session 11. Airborne-Flight Management 

K. 

L. 

M. 

N. 

0. 

P. 

Q. 

R. 

S. 

Flight Guidance Research for Recovery From Microburst Wind Shear ............ 

Analysis and Synthesis of a Wind Shear Detection Algorithm .................. 

Analysis of Guidance Law Performance Using Personal Computers .............. 

Crew Interface with Wind Shear Systems ................................. 

393 

417 

469 

485 

511 

545 

563 

591 

639 

David A. Hinton, NASA LaRC 

Kioumars Najmabadi, Boeing 

J. Rene Barrios, HoneywellJSpeny 

Dave Carbaugh, Boeing 

Robert Stengel and Ala Stratton, Princeton University 

Teny Zweifel, HoneywelllSpeny 

Bernard Ades, DGACJSFACTITU-France 

C. Gandolfi, DGACISTNAI3E 

An Expert System for Wind Shear Avoidance ............................. 

The Effect of Wind Shear During Takeoff Roll on Aircraft Stopping Distance ...... 

Wind Shear Wind Model Simulator Analysis Status ......................... 

Wind Shear Predictive Detector Technology,Study Status ..................... 

Questions and Answers for 19 October Sessions I and I1 ..................... 

4. TECHNICAL PRESENTATIONS - Thursday, 20 October 1988 

Session I. Ground Systems 

A. TDWR Program Status ....................... ................. .-. .. 661 

B. Low Level Wind Shear Alert System (LLWAS) ........................... 671 

A.L. Hansen, FAA 

Craig Gof): FAA 

I +Published under separate cover. 

vi 

e 
C. Terminal Doppler Weather Radar 1988 Operational Demonstration 

Stapleton International Airport, Denver, Colorado ......................... 683 

D. A Cursory Study of F-Factor Applied to Doppler Radar ..................... 721 

Wayne Sand, NCAR 

Kimberl), L. Elmore and Wayne R Sand, NCAR 

Mark U! Merritt, MIT Lincoln Laboratory 

E. Summer 1988 TDWR Microburst Analysis ............................... 739 

F. Automatic Detection of' Low Altitude Windshear Due to Gust Fronts in the 

Terminal Doppler Weather Radar Operational Demonstration ................. 753 

Diana Klingle- WIson, MZT Lincoln Laboratory 

Session 11. Perspective 

G. Some Perspective on the Wind Shear Protection Problem .................... 773 

H. LessonsLearned.. ................................................ 785 

I. Wind Shear Procedures and Instrumentation ............................. 797 

J. Airbus Wind Shear Warning and Guidance System ......................... 809 

K. The "Windvan" Pulsed CO, Doppler Lidar Wide-Area Wind Sensor ............. 835 

Sam Saint, Safe Flight 

William Laynor, NTSB 

U! W Melvin, Airline Pilots Association 

J.L. Bonaje, Airbus Indusm'es 

Rhiiian Lawrence, Spectra Technology 

Session 111. Topics 

L. Low-Cost Airborne Lidar for Wind Shear ............................... 843 

M. Questions and Answers for All Sessions ................................. 855 

Loren D. Nelson, OPHIR 

5. APPENDIXES 

Appendix A. Agenda ................................................ 869 

Appendix B. List of Attendees .......................................... 875 

vii 
Overview: Second Combined Manufacturers 

and Technologists Conference 

A 

18 October 1988 

i 

Dave Johnson, Acting Service Director for the Advanced System Design Service. 

Thank you Herb. Good morning and welcome to the Second Combined 

Manufacturers and Technologists Airborne Wind Shear Review Meeting, here in 

beautiful Colonial Williamsburg and I hope you are all appreciating this lovely setting, 

I certainly do. This is going to be an exciting and challenging three days from what 

Herb tells me according to all of the important work you’ve been doing and the 

papers that I’ve seen so far out in the table, there in the adjoining room, and it’s a 

very ambitious schedule, so I know you want to get on with it and I will be brief. 

First, I would like to extend my sincere thanks to the NASA team for giving me the 

opportunity to present the welcoming remarks here this morning and to open the 

conference. The NASA team, with the FAA, industry and academia participating in 

this Wind Shear Program make a really formidable team to take on and try to solve 

this vital, very serious wind shear threat to aviation safety and I think it’s really 

brought home with some of the recent events that we all know about, particularly 

referencing the United experience in Denver, which you will hear more about this 

afternoon from Mr. Ireland. The work that NASA and the FAA and various 

contractor members are performing can only have a major effect in solving the wind 

shear problem if all members of the team share the information, results and the plans, 

and that’s what this conference is all about and I understand it’s an extension from last 

year’s. This very unique: relationship allows all of us to go farther than we could 

individually and produce a lot more results. This information exchange, has a lot of 

the FAA and the NASA Airborne Wind Shear team to focus on the common 

1 
problems and technology, while industry has focused on the means to develop, 

manufacture and obtain the certification for Airborne Wind Shear assistance. This 

conference is very timely, considering the recent announcement by Secretary Bernly, 

conterning the new rule and I quote, “requiring jet airliners to carry equipment that 

will warn pilots when they encounter unexpected low altitude wind shear.” You will 

hear more about this rule from Steve Morrison this morning. But this is only the 

beginning, because we need further research to provide predictive wind shear alert 

technology, not just tell the pilot when he’s already experiencing it, and I’m sure you 

all know that better than I, since I’m relatively new in this game and I’m counting on 

Herb to bring me up to speed and learn a little bit more about wind shear. Also, 

when we speak of technology, let’s not forget the impact on the pilot. The pilot’s vital 

in the system as we all know. And how the technology is provided to the flight crew 

to sensible application of flight management and control concepts is essential to 

successful implementation of the airborne wind shear alerts. Complimentary to the 

Airborne Wind Shear technology are the advances made with ground based wind shear 

systems. I noted the agenda items on Thursday for this important segment of wind 

shear alert systems, and let us all keep the pilots and the controller, and the ground 

and air based systems in perspective. I think that’s really important. It’s a system 

problem and I think it’s important that everyone focus on that, keep their perspective 

and consider the interface and develop the technology such that it does work with the 

complimentary systems. So to get on with the task before us, I think you need to 

remember last year’s successful conference, Herb tells me that you covered quite a bit 

of information and was documented in the January 1988 report where you all 

identified the hazard in aircraft terms, the early results from the sensors technology 

assessment were presented, the plans for managing and displaying airborne wind shear 

information were announced. A discussion was held concerning the draft advisory 

circular the FAA was working on and you were provided with plans and a discussion 

on the TDWR operational demonstration. This year, building on what you all did last 

4 

2 
year, you’ll be relating the hazard and how it relates to the system design concept. 

You’ll be looking at the results of the radar lidar and infrared technology assessment 

and you’ll be looking at the results of the FAA/NASA Flight Management Systems 

efforts and now that the advisory circular is out, there will be further discussion on 

that, and the clock is starting and how it is apt to be implemented and from Herb tells 

me, there’s going to be a review of the Denver operational TDWR system and I think 

that will be very exciting for a lot of folks in this field, and probably what Mr. 

Ireland’s going to talk about. So, without going on too much further, I want to, in 

conclusion say, that I would like to thank you all for your time and effort and for the 

commitment to this very pressing safety issue. To our partners at NASA, thank you 

for the close cooperation and the technical expertise that’s been provided which has 

produced all of the results so far and the agenda is full and I won’t delay with the 

points so let’s get on with it. 

3 
TECHNICAL PRESENTATIONS 

Tuesday, 18 October 1988 

c 
Session 1. Airborne-Terms of Reference 
Session I. Airborne-Terms of Reference 

Tools for the Trade 

Wallace M. Gillman, American Airlines 

9 

PRWEDING PAGE BLANK NOT FILMED 
.. 'INDUSTRY TERMS OF KEFERENCE 

Wallace M. Gillman 

Arne r i c an A i r 1 in e s 

DFW International Airport, Texan, 75261-9617 

ABSTRACT 

'w 

'v 

An alternate title for this presentation is Tools for 

the Trade. A brief review of daily operations j.n the Airline 

business will be made with emphasfs on the decisions made 

by pilots and the information used to make these decisions. 

Various wind shears will be discussed as they affect these 

daily operations. The discussion of tools will focus on 

airborne reactive and predictive systems. The escape maneuver 

used to fly out of a severe windshear wi-3.1 be described from a 

pilot's point of view. 

i 
* 

Session I. Airborne - 'Terms of Reference 

Tools of the Tra de, Wally Gillman, American Airlines 

To all of you here, I would like to say, it's a privilege to be able to talk to you today 

and also very much a challenge. Listening to the previous speakers, I could agree with 

several things that they've said, first of all, Dave Johnson talked about this being a 

system problem. That very much is and that's going to basically be the thrust of my 

presentation, although I say it in different words. Roland said I would have the 

opportunity to articulate operational requirements. I don't even know what articulate 

is, so I'm going to have a difficult time there and Herb talked about this meeting 

being in three phases, hazard characteristics, sensor development, and ground systems, 

and since we're starting off at the beginning, I guess I'm part of the hazard 

characteristics. 

Let me talk a little bit about myself because I will be referring to some personal 

experiences here as I go through. I'm a Captain with American Airlines, been flying 

for over 21 years with American, and about 30 years all together. Seventeen years of 

that flying was on the line, where day after day after day we'd go out and fly in 

various weather conditions. For the last .3 1/2 years, I've been a Manager of Flying 

Engineering for American, which means that my job is to interface with such people 

as yourself to try to define what our needs are, to try to help develop some 

equipment. I do test flights, new equipment and new airplanes and when we have 

certification requirements, then I represent the FAA in certification flights of 

equipment on our airplane. 

Originally, this presentation was supposed to be called Industry: Terms of Reference. 

That was a little scary to me, so I asked if we could change that and actually the title 

13 
now is 'Tools for the Trade." Tools for the Trade, and first of all, before I talk about 

some of these tools, let me talk a little bit about the trade. This viewfoil represents 

the magnitude of the daily operations of commercial airplanes in the United States in 

1987. 6.5 million commercial airline flights. Almost 18,OOO daily flights. A little 

perhaps, personal note, on Sunday the 16th of October, American Airlines flew 231 

million revenue passenger miles. That's an awful lot of operations and an awful lot 

of people travelling an awful lot of miles. I think the point that I would like to make 

here is that we do this daily, every day and we do it in rain or shine, wind shear, 

weather conditions, etc. Now, all of you, in this group, are very familiar with wind 

shears but we tend to focus on microburst quite a bit, but there are all kinds of wind 

shears that we encounter every day. Almost every one of these flights encounters 

some kind of wind shear. And a lot of these types of wind shears have caused 

accidents. A long time ago, an American Airlines airplane hit the dike at La Guardia, 

Runway 31. That shear is probably due to physical obstruction. And, years ago, going 

in the midway airport, we always used to have to be careful of the wind shear because 

of the hangers and the buildings, so those are physical obstructions. We go places 

where we have wind shears continuously, like in Amsterdam. These types of things 

are daily occurrences. They're serious. 

pointed out in his slide, and we have to 

things on a daily basis and we need the 

Some of them can be very serious as Roland 

take them seriously. But we deal with these 

tools to deal with these things. 

If you'll allow me, I'd like to make a few personal references, to talk a little bit about 

some daily decisions because I think it's important that you understand how we use 

these tools in daily operation of 18,000 flights a day. Not long ago, as a matter of fact 

on the 23rd of September, I flew a flight from Chicago to Dusseldorf, Germany, and 

that particular day, there was a line of storms. So I got on the telephone and talked 

to the dispatcher. We agreed on a little different routing, adjusted the fuel, and off 

I went and didn't have any problems. We went through to Dusseldorf with no 

t 

4 

I 

14 
'1, 

ib 

b 

problem. We used satellite weather 

depiction, we used weather reports that we had available. We used some radar 

returns that we had available and we made some decisions. Now, as a result of that 

we had a non-occurrence. That doesn't mean to say that that event wasn't out there. 

I know a lot of people out there are concerned when we talk about forward looking 

sensors, about the fact that by the time you get there the event might not be there, 

it might be related to a false alarm or something like that. Well in this case, there 

was no event that I wasn't concerned about a false alarm, I had a smooth trip. Also, 

about six weeks ago, I flew with a fellow from NASA Langley here, whose name is 

Charlie Knox, I'm sure Roland knows Charlie. Charlie's got a project on data link, 

and so I flew him on a Boeing 767 and we went from Dallas to Dulles and I was 

demonstrating the data link. Now on this particular trip, we rolled out on course and 

The point is, I used some available tools. 

right in front of us was a thunderstorm which was painted on the weather radar. I 

said to Charlie, "Well, we're going to have to deviate around this thing, but let's take 

our time, let's look at what's developing on either side of that storm and beyond that 

storm so we can make our decision in which way to deviate." So we looked at the 

scope, evaluated the radar returns, and eventually I deviated left. We ended up 

deviating for about 250 miles and finally went through the hole and went on to Dulles. 

Again, a smooth ride, a non-event. But I used the tools that were available to make 

that decision. About a month ago, I was flying a Boeing 767 at Moses Lake, 

Washington, on a test flight. Part of that test is to fly autoland approaches. We came 

into Moses Lake and ahead of us was a 747. Now, a 747 is a huge airplane that 

creates a lot of vortices, and sure enough as we got down on final approach, we 

started encountering quite a bit of, what you might term as turbulence. The airplane 

shaking around. We decided to go around rather than continue that approach because 

we didn't feel the automatic system would be able to handle the shear turbulence 

conditions as we were encountering them. So that was a decision based upon actually 

15 
encountering something, not having any idea of the magnitude that was at the front 

of us, but not be willing to continue on into it. 

I 

* 

Now, those are very recent things, but let me talk a little bit more about something 

very pertinent to what we're going to talk about here. About one week after Delta 

191 accident in Dallas, I was taxiing out to take off on Runway 17 right at DFW 

Airport. I 

remember there was some storms coming in from the northwest and we were watching 

it as we were in a line of airplanes waiting to take off. We looked at the wind socks. 

We were listening to the tower reports from the LLWAS system, the winds at various 

portions around the airport. I was number 2 for take off and I said to my co-pilot, 

"I'm not going to go on this runway." But just at that time, the number 1 crew in line, 

Pan Am, said, "I'm not going to go." Then the whole line said, "We're not going to 

go" then the tower taxied us all down the runway, took us about 15 minutes, down to 

the other end. By that time the storm had kind of passed by and we all launched to 

the north. We were using the tools to make those decisions. The tools that we had 

available. That's the kind of thing that goes on daily. One other example where I 

wish I had a tool, this is back in the ~O'S, I was flying co-pilot to Charleston, West 

Virginia. Now that airport sits on top of the mountain and it's kind of a short runway. 

You don't like to land with too much speed because you could run off the far end. 

On the approach, to the runway, you're coming over a great big valley and on that 

approach, I noticed that the power was way back at idle, very much reduced from 

what it normally would be. So we discussed the fact that we must have a tail wind 

at that point, but the tower was reporting a cross wind at the runway. A cross wind 

almost at our maximum for the airplane, which was a Boeing 727, so we discussed the 

fact that we better carry a little extra air speed because we were going to encounter 

a shear. I sure would like to have had a forward looking device so that we could 

have told how big that shear was going to be. But we carried 25 knots extra airspeed, 

4 

a 

Everybody was very conscience of wind shear after that accident. 

16 
I 0 

‘F 

3 

which, when you’re looking at a short runway on the top of a mountain, is an awful 

lot of airspeed to carry. Well we got there, and I would say, it felt like two seconds 

we lost 25 knots. Just like that. I dropped the wing down and just barely saved the 

landing. We had a reasonable landing, rolled out, and went to the terminal. Nobody 

knew anything about it, except the guys in the cockpit. I could have used a forward 

looking sensor for that particular situation. 

I’ve taken quite a bit of time to talk about myself, let’s talk about these tools for the 

trade. I would like to make a little quote from Aeroline, which is a newsletter that’s 

published by ARINC Radio for the AEEC. This is in from the chairman’s corner. 

It says, “We engineers are notorious for becoming entranced with technology for what 

it can do rather than for what we need it to do. And why? Our industry cannot 

afford and will not tolerate such a attitude.” I’m glad an engineer said that rather 

than me, you know. 

We have some valuable tools coming along. The first one is some valuable training 

tools that have been developed over the last couple of years as a result of the FAA 

and industry working on understanding wind shear and particularly microburst. Bob 

Ireland was involved with this group. They came up with a authoritative training aid 

that we have used to make changes in oqr training recently. This is very valuable in 

our ground training. We are much more aware of the conditions that create 

microburst and the things to look for that we might be able to detect it and avoid it. 

In our simulator training, we have microburst models and wind shear models and we 

have our pilots fly through various wind shear scenarios, practicing detection, detecting 

when the wind shear is occurring, and then practicing an escape manuever. Now, we 

talked about having an unstable approach. When you have an unstable approach, it’s 

time to execute an escape manuever. 

17 

! 
Let me tell you folks, this escape manuever is not a very nice thing. So let me talk 

a little bit about escape manuever. It’s something that I don’t want to be in if I can 

avoid it. First of all, when you look at the pilot procedures, they seem pretty straight 

forward. Use maximum power, rotate to 15 degrees at pitch attitude and then control 

the flight path. That doesn’t seem very difficult, but let me tell you, that is an extreme 

manuever from the standpoint of pilot technique. You are operating at a region which 

you normally don’t operate in and it’s not something that I want to get involved with 

if I can avoid it. As far as controlling the flight pass, generally we’re talking about 

stopping a sink so we don’t lose altitude and eventually, if you trade off enough air 

speed in order to stop this sink, you’re going to be approaching the limits or stick 

shaker and you have to respect that and not go into the stick shaker. Well, I would 

like to take a minute to talk about this escape manuever. I don’t know how many 

pilots we have in the audience but I would like to take it out of the airplane 

environment and discuss it from a different perspective. First of all, what is wind 

shear? Wind shear, I have characterized as stepping off a moving sidewalk like at 

DFW airport. What happens is that the top part of the body continues to go forward 

at the same speed but all of a sudden the legs are slowed up because they are no 

longer on the moving sidewalk. So that’s basically the same as wind shear. That’s 

something we can understand and the same affect happens to an airplane. Now, we’re 

dealing with something called angle of attack. -4nd I don’t want to get into 

aerodynamics but, I need to show you what angle attack is before I can continue. 

(Slide of airfoil at high angle of attack) Here we have an airfoil section, a section 

through a wing, which the airplane is pointed horizontally. But the airplane is actually 

going down this path here so that the relative wind is up in that direction. So what 

we have here is the angular difference between the attitude of the airplane and the 

flight path of the airplane, this is the angle of attack at that airfoil. When this angle 

attack exceeds a certain amount, you get over the top surface of the wing instead of * 

getting laminar flow. You lose the lift from the top of the wing and then the airplane 

4 

6 

4 

c 

18 
c 

8 

is going to come down! Plain and simple. Particularly if you’re in the midst of an 

escape manuever in which you already have maximum power. The only way to 

recover is to lower the nose a little bit, reduce the angle of attack, get laminar flow 

over the wing and try to fly out. All right, that’s all I’m going to talk about angle of 

attack. Now let’s go back to my moving sidewalk analogy. We’re going to put a guy 

on a treadmill (Slide of man on treadmill tilted at steep angle with rear (low) end in 

the water and net accross high end) Normally the guy moves right along, and there 

are no problems. He’s got lot’s of treadmill between the bad water down here and 

this bad condition up here (net) which represents stick shaker conditions and the end 

of the treadmill where stall would occur and the guy would fall off. So this guy just 

marches along doing his thing. But now when we get into wind shear and he’s doing 

the escape maneuver, he gets into a very critical situation where he doesn’t have very 

much to play with. (Slide - similar to previous slide except very little distance between 

the water and the net) He is very close to disaster down near the water and disaster 

up near the net and the end of the treadmill. Now we’re going to turn the lights out 

so he can’t see how close he is to this stick shaker (net) because there’s nothing in the 

cockpit of older airplanes that shows you where stick shaker is. So our guy is going 

blindly along hoping that he won’t get into the net and hoping he is doing enough to 

keep from falling into the water. Now, no only am I going to turn the lights out but 

I’m going to simulate up drafts and down drafts by changing the pitch of the treadmill 

up and down. Now our guy is going around in the dark trying to stay in this little bit 

of treadmill while it is pitching up and down. That’s kind of like an escape maneuver. 

It’s not a maneuver I want to have to accomplish. 

Another valuable tool is the airborne reactive wind shear system that has been under 

development for a number of years. Bob Ireland and I have been working on an S7 

committee of SAE, trying to define the operational characteristics of such a system. 

It’s a reactive airborne system like I fly on the Boeing 767 right now. It is a very 

19 
useful tool. We are able to reinforce what we are seeing in the cockpit with this 

detection alerting system. It reinforces the fact that we’re in trouble and that it is due 

to wind shear. You know, a lot of times there can be turbulence and as I said earlier, 

day after day, after day, after day we operate into weather conditions where we have 

shears, we have turbulence, we have deterioration of flight path, and we counter those 

conditions and continue operating. Now all of a sudden, we’ve got a device to help 

us recognize when this shear is beyond the normal limits and annunciates ‘bind shear” 

and provides us with flight director guidance for the escape. This is kind of like 

putting a meter in front of the guy on the treadmill so he can march at the right rate, 

and stay on the treadmill. So far, we’ve been doing a pretty good job with this new 

training program that we’ve got. They do an excellent job of recognizing the different 

tilts of the treadmill and marching at the right pace even without this flight director 

guidance. 

I think in terms of time, the next systems that are going to be operational use will be 

ground based systems. In fact, LLWAS is already in operation. We’re going to have 

some discussions about further development of that tool and development of the 

terminal doppler weather radar later on in this symposium. 

These are exciting tools, but what I would like to focus your attention on is this 

bottom bullet on my viewfoil where I get back to what Dave Johnson said earlier, in 

that it’s a system problem. You’ve got to present information to the crew in such a 

manner that they can utilize the information. When we talk about what happened in 

Denver on July 11, I’d like you to remember this because there was information there 

that the crews did not receive the information in a manner that they could operate 

on it. So if you could just keep this in mind during those presentations, I think that’s 

the kind of thing .. kind of message I’d like to get across. The big thing, as far as I’m 

a 

20 
concerned is that the devices on the ground, ought to be able to give us enough 

information and I can avoid ever getting to that escape manuever. 

The next tools down the line are the tools that are going to come out of all the work 

that’s being done here in airborne sensors. Again this is exciting to have the work 

that’s being done here. We see (we being operational guys in the S7 committee) see 

this falling into two categories. One set of sensors or some early technology might 

give us early detection and early escape and the earlier you escape the more treadmill 

you’ve got to work with, you know, so the less dangerous that escape manuever is. 

Again, though, what we really need to aim at is to have enough information that we 

can avoid the problem. In case I haven’t made my point yet, I just have one viewfoil 

that might emphasize it. (AVOID, AVOID, AVOID IN LARGE LETTERS) That’s 

what I’m aiming at. Now, what are the characteristics of an avoidance tool. 

Remember, this has got to be a systems development. We’ve got to work on these 

tools to present the information so that we can use it. I see them as having some 

kind of a situational display that is easy to interpret. I don’t have to spend a lot of 

heads down time. I don’t h’ave to spend a lot of manipulative time. I don’t have to 

work a lot of dials. It’s a minimum workload. I’m already in an environment during 

take off or during approach where the workload is heavy. I’ve got to have something 

that is very useful for me. I’ve got to have; time or distance (you know we’re travelling 

3 to 4 miles a minute) I’ve got to have time to come to some decision and try to 

coordinate that decision with air traffic control and then I’ve got to have information 

that allows me to pick an avoidance path to get out of this environment so that I can 

avoid it all together. So those are the ingredients I think and characteristics of an 

avoidance tool. 

Thank you very much. 

21 
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34 
Session I. Airborne-Terms of Reference 

Overview of SAE Committee S-7 ARP 4102/11 

"Airborne Wind Shear Systems" Robert L. Ireland, United Airlines 

. 

35 
c 

OVERVIEW OF 

SAE CavIMITTEE S-7 ARF' 4102/11 

"AIRBORNE WINIEHEAR SYSTEMS" 

Robert L. Ireland 

Chairman, S-7 Windshear Subccmmittee 

United Airlines, Inc. 

Denver , Colorado 

ABS- - 

The windshear subcommittee of SAE Committee S-7 (Flight Deck and Handling 

Walitics Standards for Transport Aircraft) has developed an Aerospce 

Recanmended Practice (ARP 4102/11) entitled "Airborne Windshear Systems" 

The subject ARP attempts to cdine the most current knowledge of Wth the 

pilot community as represented by the standinq membership of Qmmittee S-7, 

and the avionics industrq, as represented by consultant members frcm all 

canpnies contemplating windshear device development, in a document to be 

used as a stan&rd for development of windshear avionics. The first 

issuance of the'ARP concentrated on present psition (so-call& "in situ") 

devices, with a mild treatment of lmk-ahead systems. A revision, 

currently being considerd by the votiny membership of the Committee 

revises and clarifys information on "in situ" systems and adds considerable 

detail to the look ahead sections. It is noted that, while the sections 

pertaining to "in situ" systems rely heavily upon knowledge gained in the 

actual development and testing of such system, the portions addressing 

lmk-ahead devices center mre on pilot input of desireable characteristics 

of predictive systems as pre-development input. 

expected to be completed before the next meeting of $7 in Tokyo, durifig 

the week of 0ctc-r 24, 1988. 

Votinq on the revision is 

. 
S.A.E. S-7 

"Airborne Windshear Systems" 

4 

ARP: Aerospace Recommended Practice 

ARP 4109 

- Alerting Systems 

- Detection & Avoidance Systems 

ARP 4109~ ARP ' 4102/11 

I ARP 4102/11 Rev. 1 IN WORK 

- Alerting Systems 

- Detection Systems 

- Avoidance Systems 

38 
SAJ3 -S7 Wind Shear ARP - Bob Ireland, United Airlines 

First of all, I would like to thank Amos, Herb and everyone else who helped put this 

together today and particularly for including on the agenda this year some of us from 

the operational side. I think last year we were just the hecklers. Russell, that’s a 

laser detector wind shear. Just thought I’d get that out of the way. Ok. Before I get 

started I’d like to compliment the FAA and the ATC, yesterday the system of weather 

detection and helping airplanes void was working very well. Is there anyone here in 

the audience who connected through Chicago, yesterday, late afternoon. Just a couple 

of you. Chicago was essentially in what U.S.A. Today this morning called sky locked, 

because there were some thunderstorms in the area, I guess some tornado alerts or 

warnings. It’s an example of the system working right and working together and I 

think although it was inconvenient for some of us to get here for this meeting, as a 

result of it, it’s a very positive sign. Wally alluded to the fact that we have created 

a committee at SAE that speaks towards the needs in the cockpit. That’s what I 

would like to talk about. The committee is called S7 and what the S7 stands for .. 

I’ve never been able to find a person who knows. But the committee itself is known 

as the Handling Qualities and ....... I had it right on the tip of my tongue. It’s such a 

mouthful. Anyway, our committee is composed of representatives from many airlines 

and many manufacturing firms worldwide and our purpose is to write some 

recommended practices. They are called Aerospace Recommended Practices for the 

Society of Automotive Engineers, it’s called an ARP and it’s a tool that manufacturers 

can use to understand what the pilots want to see in the cockpit. In particular in this 

case we formed a subcommittee for the purposes of defining what pilots would like 

to see in the way of wind shear avionics. Being redundant for many of you, I’ve 

coopted so many of you in this room to be part of that committee and so it’s a little 

boring for Sam, Wally, Dave and Sperry folks, there’s a great number of you that are 

already on this committee. We’ve been working together for about three years now 

and created a first document that was called ARP 4109 in the numerical categorization 

39 
of SAE. It contains information on two basic systems. The alerting systems that are 

the focus of the new rule that just came out, those systems which detect wind shear 

only upon entering the phenomenon and providing guidance thereafter and also a 

second group that we lumped together and called it detection and avoidance. These 

% 

were systems as we saw them that would look ahead, would see the phenomenon and s 

we hope give enough warning to allow pilots to deviate around it. As many of you 

are aware, I’m sure, there has been some great discussion about whether it’s practical 

to expect any kind of a device to allow an actual diversion around wind shear as 

opposed to merely beginning a recovery early. We locked in together in that 

particular document. 4109 is on the street. It was issued approximately 1 year ago, 

and the forward looking part of it asks for devices that look ahead 5 miles or more 

and that the display, that it allows the pilots to deviate around. We realize that wasn’t 

necessarily a totally practical approach and 1’11 get to that in a minute. For those of 

you who want to track the documents however, and find out where they’ve ended up, 

Herb quit it. Within the last couple of years, SAE’s been undertaking a rewrite on 

all of it’s S7 documents and renumbering them. Consequently our wind shear ARP 

is going to become an annex of a greater ARP and it will become known as 4102 

Annex 11. And now I get to the current work of our committee. It’s 4102, Annex 

11, Rev. 1, it’s currently in work .. in fact, it is as we are speaking being voted on by 

the members of SAE S7, we’ll know the results of that voting next week when we all 

gather in Tokyo and hopefully it’s been easily approved. So far the voting indicates 

that it will be. What we’ve done in revision 1 is two things. We have expanded the 

alerting systems section. Primarily in recognition in lessons that are being learned in 

the operations of the system and the design of them as more and more of them 

become on the market. Secondly, we have taken the detection and avoidance systems 

and we split them out into two different systems as we saw them. The detection 

system being an intermediate device, if you will, the ones that are primarily being 

focused on for development. Those devices that can give you say 30 seconds to a 

40 
minute of advanced warning, be they IR based or laser based. These would be devices 

that would provide alerting but would not necessarily provide any kind of display 

because in that time frame, it’s probably impractical to try to actually deviate around 

any such phenomenon. We also continue to have our section which some have 

referred to as pie in the sky and that’s what we call avoidance systems. The pilot 

community wants to see a system that can look ahead, far enough to provide a 

geographically based display that can allow aircraft to contact ATC, make 

arrangements to deviate around these hazards. As much as we may say that’s 

impractical today, we’re going to keep pointing in this direction because it is our firm 

belief that the more we say we want it, the sooner it is that you folks are going to 

develop such a system for us. 1’11 hesitate from being too terribly specific on what’s 

in this document because as I said, it is being voted on right now. If people want to 

submit questions on exactly what we’re asking for, I prefer they would just ask me 

privately because I do not want to put it in the public record as that would be 

usurping the authority of the S7 members before it has become a public document. 

Any other questions I would be happy to entertain later and that’s all I’ve got. 

Thanks a lot. 

41 
Session I. Airborne-Terms of Reference 

Wind Shear Regulatory Activities 

Steve Morrison, FAA 

c 
.. 

Part 111 

. 

45 

Department of 

Transportation 

Foderal Avbtion Administration 

14 CFR Part8 121 and 135 

Airborne Low-Altitude Windshear 

Equipment and Training Requiremen% 

Final Rule 
37686 Federal Register / Vol. 53, No. 187 / Tuesday, September 27, 1988 / Rules and Regulations 

DEPARTMENT OF TRANSPORTATION 

Federal Avlatlon AdmlnlrtnUarr 

14 CFR PUtr 121 and 135 

(DOtk.1 WO. 1Bllk kndt NO#. 121-199. 

135271 

Airborne Low-Altitude Wlndrhear 

Equipment and fnlnlng Requtrementr 

AOENCV: Federal Aviation 

Administration (FAA), DOT.' 

ACIIOI(: Final rule. 

~VYYARI: The FAA amend, Part 121 to 

require airborne low-altitude windrhear 

warning and flight guidance equipment 

in airplanes and Part8 121 and 135 to 

require windshear training for fight 

crewmembers. The National 

Transportation Safety Board 

lnvertigationr rhow that low-altitude 

windshear has been a prime wure of air 

tarrier accidentr. This rule ir expected 

to reduce windshear related accidentr 

by training pilotr in avoidance and 

trcape techniques and by providing a 

low-altitude windshear warning system with flight guidance equipment in 

certain airplanes to increase the magin 

of rafety if windshear ir inadvertently 

encountered. 

DAru: Effective Dote: January L 1689. 

Compliance Dotes: 1. Training 

requirements in 00 121..(09.121.419, 

lZl.424, and 121.427; 0 0 135345 and 

135.351. January 2.1891. 

2 Equipment requirement, in 

0 lZl.3581a): January Z 109L den 

certificate holder obtainr M extension 

in accordance with 0 lZ1358(b). 

Gary E Davis. hject Lkvelopment 

Branch (AFS-240). Air Truuportation 

Division, Office of Flight Slandardr, 

Federal Aviation Administration, Ba) 

Independence Avenue SW, 

Warhington. M: 20591; Telephone (202) 

roll CVRTnfR INFORMATION COWACE 

2t37-8096: 

tUCCCfYLWTARY WWlKwt 

Background 

published Notice of Roposed 

Rulemaking (NPRM) 7EbllA proporing 

airborne low-altitude windrhear 

equipment and training requirements. The NPRM war preceded by Advance 

Notice of hpored Rulemaking 

(ANPRM) -11 (44 FR 25867, May 3. 

1e;rS). The ANPRM invited public 

participation in addnrring low-altidude 

windshear in the following wayr: (1) By 

placing windrhear detection equipment 

on the ground and transmitting 

Wonnation to the pilot; and (2) by 

kutalling equipment nbrd the aircraft 

On June 1.1987 (52 FR 20580). tbe FAA 

that would provide the pilot with 

windrhear information in "real time.- 

in the FM'r continuing efforlr to 

combat the windrhear problem A full 

discurnion of rtudier. Adviroy 

Circulars, accident/incident data. and 

"SB recommendationr on windshear 

eppeared in the preamble to NPRM 7% 

31A. The following infonnatim briefly 

rummarizes FAA efforts since 1975. 

In 1975, the National Aeronautia 

rnd Space Administartion [NASA). in 

cooperation with the FAA. instituted the 

Aviation Safety Reporting System 

(ASRS) whereby rafety-related 

Incidentr involving aircraft operation 

nre submitted voluntarily and buttd 

nnonymously to identify rafety 

problems. Windshear ir amoog tbe 

problems identified by reporb Nbmtned 

under thir syrtem. 

In 1977. the FAA conducted a rhdy 

of NTSB reportr on aircrrh acddentr 

and incidents related to lowrhitude 

windrhear that had occurred from 1eaC 

through 1975. 

In May 1977, the PAA amended Put 

121 of the Federal Aviation Regulations 

(FAR) to require air camera to adopt M 

0pproved ryrtcm for obtaining forecasts 

nnd nportr of adverse weatber 

conditions, fncluding low-altihde 

windshear, that could affect the rafety 

of flightr on the router to be flown and 

at airports to be ured. 

The FM hued Advisory Qnular 

(Aq No. IKMOA Low Lave1 wipd 

Shear, to provide guidance in 

recqnizing meteorological conditionr 

&at poduce windrhear phenomena and 

to recommend certain pilot technjquea 

to minimize the effectr of windhear 

when ebcountned during take& or 

The ANPRM and NPRM WM action8 

- landmg. 

The FAA establirhed a rerearch 

mnd development pmgram to ellmine 

tbe hatPrdr waiated with lorrltitpdc 

wfndrhear, develop rolulionr to the 

Viadshear poblcm. and integral. tbow 

rolutiolv into the National Ainp.ce 

Syrtem. 

At 90 major airport8 within &e 

United Stater. the FAA inrtalled a 

ground-bared Low-hvel Winddcm 

Alert Syrtem (LLWAS) capable of 

detecting the pnrence of hazardous 

windrhear in the vicinity of the airport 

at the rurface. The FAA intendr lo 

lnrtall an additional 20 LLWAS'r at 

rirportr acr~ii the nation. In addition, 

the FAA ir working on enhancements to 

the LLWAS and ir cooperating with tk 

National Center for Atmorphelic 

Rerearch on an operational evphtian 

of a Doppler radar windrhear 

forecarting and alerting myrtem. 

Before irruing ANPRM 7gli. (be 

FAA, thhiugh a wries cf sirnula46 

experimentr, Investigated the 

eflectiveners of airborne low-altitude 

windshear ryrtems designed to warn 

pilot, of the exirtence of windrhean 

and to arrirt them in trensiting or 

avoiding such rhears. 

In November 1983, the PM Irmed 

AC No. 1-1, Criteria For Operational 

Approval of Airborne Windrhear 

dating and Flight Guidance Syrtemr, 

to provide indurtry with an acceptable 

means of obtaining operational approval 

far the ure of variour airborne 

windrhear ryrtemr on air carrier 

haft. 

In 1883. in response to Public Law 

97-388. the FAA contracted with the 

National Academy of Science8 (NAS) lo 

rtudy "the state of knowledge, 

alternative approaches and the 

amrequencer of windrhear alert and 

mere weather conditions relating to 

takeoff and landing dearancer for 

commercial and general aviation 

aircraft." The NAS Report, "LowAltitude Windshear and Ita Hazard to 

Aviation." war published in late 1883. 

In 1886. the FAA contracted with a 

conrortium of aviation rpecialirts from 

Tbe Boeing Company, United Airlines. 

McDonneU Douglar, LockheedCalifornia, Aviation Weather 

hociater. md Helliwell, Inc. lo 

produce the Windshear Training Aid 

document and windsheat training 

.idcor The Windshear Training Aid. 

publisbed and dirtributed to industry by 

the FAA provider guidance on 

developing flight crew windshear 

hining curricula. 

In accordance witb FAA rerearch 

findings and the National 

Transportation Safety Board (NTSB) 

mommendations that wen bared on 

widen! investigations, the FAA 

proposed in NPRM 7EllA windshear 

training and airborne equipment 

Wuirements as part of a "ryrtems 

ancept" to rolve the problem of lowaltitude windshear. The concept 

hcluder an improved low-altitude 

windshear weather forecasting 

bcbiqw, ground-baeed windrhear 

dctection equipment airborne 

windshear warning and flight guidance. 

mid improved flight crew training. 

The FAA her decided after thorough 

amsideration of the comments nccived 

m the NPM to proceed with the 

pposed windshear training and 

home equipment requinmentr with 

minor modifications. A detailed 

dbcuuitm of the major irruer mired by 

-tern and the FAA nrponse to 

(bc cbmmentr follows. 
c 

Federal Register / Vol. 53, No. 187 / Tuesday, September 27, 1988 / Rules and Regulations 37689 

Dimmion of Comments 

Twenty-seven comments were 

received on the Notice of Proposed 

Rulemaking. The commentr were 

rubmitted by air camera, airline and 

pilot arsocia tions, manufacturers, 

individualr, and the NTSB. Most 

commentr commended the FAA for 

taking action to reduce the hazardr of 

windshear encounten. However, 

several commenten opposed ertain 

proposed requirementr. Speci Fi c hue8 

that were addressed in the commerntr 

were those on applicability: airborne 

warning devicer; flight guidance 

ayrtemr; training: the compliance date: 

and Advisory Circulan. Several 

comments also addressed the cortl 

benefit aspect8 of the propored rule. A 

few comments recommended entirely 

different approaches to the windrhear 

problem than the one the FAA propored 

Several comments were infonnation on 

airborne low-altitude windrhear 

warning and flight guidance ryrtem. All 

irruer and categories of commenta are 

dircurred below. 

Applicability: Equipment 

The proposed requirement in f 121.358 

for low-altitude windshear equipment 

applied to any turbine-powered airplane 

operated under Part 121 except 

turbopropeller-powered airplanes. The 

FAA arsumes that when commenten 

referred to "turbine-powered airplanes", 

they were using the term as it was 

defined in proposed 0 121.358. The FAA 

did not propose windshear equipment 

requirements for any airplaner operated 

under Parts 91,125, and 135 because 

accident history doer not justify their 

inclusion. 

The Air Line pilots Aerociation 

(ALPA) objected to the exclusion of 

reciprocating engine powered and 

turbopropeller engine powered airplaner 

from equipment requirementr in Part 

121. It slated that the table provided in 

the NPRh4 showed that a sizeable 

percentage of the windshear accidentr 

involved the types of airplanu that the 

propored rule excluded. The comment 

also rtated that the 1987 Annual Report 

by the Regional Airliner hrociation 

estimate6 that by lesf 61 million 

passengera will be carried by memben 

of that Association. Accordmg to ALPA 

there airliner "traditionally use 

reciprocating engine and turbopropeller 

powered aircraft." 

The National Transportation Safety 

Board (NTSB) rtated that the "exclurion 

of reciprocating engine and 

turbopropeller engine airplaner from 

thir (equipment) requirement may be 

reasonable based upon the different 

performance characterirtiu of thore 

I 

- 

airplaner." However, NlsB did "not 

concur with the rationale wed to 

exclude turbine-powered airplanes 

operated under Parte 61, 125. and 135 

from thir equipment re uirement." NTSB 

rtated that it believed tat "the abrence 

of accident data to rupport the need for 

including there operatione may be due 

to the comparatively rmaller population 

of turbine-powered airplaner wed in 

those operationr and in rome carer, an 

inability to evaluate accident 

circumrtancer because of the abrence of 

flight recorder idonnation." The 

Aerospace Industrier Arsociation (AM) 

alro objected to the exclusion of turbinepowered airplanes operated under Part 

135. 

The FAA 'r Response: Although the 

table provided in the NPRM rhowr a 

number of windahear accidentr 

involving reciprocating engine powered 

and turbopropeller ewe powered 

airplanes, the airplane typer involved 

are older airplaner that have been in 

rervice for many yean and that are 

rapidly being retired from Part 121 

operationr. Ae pointed out in the NTSB 

comment, reciprocating engine powered 

airplanes and turbopropeller engine 

powered airplanes currently in 

operation have "different performance 

characterirticr." The FAA agree8 with 

the NTSB that the performance 

characterirticr of these airplanes 

generally make them leer vulnerable in 

the event of inadvertent entrance into 

windshear conditions. 

Turbine-powered airplaner that are 

operated under Parte 61,125, and 135 are 

excluded from the equipment 

requiremenb for several rearom. 

Presently no accident/incident data 

exirtr to rupport requiring windahear 

equipment for there operationr. The 

FAA recently hued a regulation (we 53 

FR 26134. July 11,1988) which raquirer 

flight and voice cecorden in certain 

aircraft where they are not now required when thore aircraft are operated under 

Parte 91.121,125, and 135. After thir rule 

becomer effective, the FAA will be able 

to gather mom complete data and take 

appropriate action. 

At the prerent time only reciprocating 

engine powered and turbopropeller 

engine powered airplaner are being 

operated in commuter operations 

(rcheduled operatiom) under Part 135. 

Ondemand operatiom under Put 135 

and opera tiom under Partr Wl and 125 

are conducted with turbine-powered 

airplaner, but there ut fewer flqhtr and 

these operationr am unscheduled 

operationr and themfore do not have the 

rame degree of exporum to hazardour 

windrhear condition8 or do the 

operations covered by thir final rule. 

Therefore, comirtent with the NPRU 

the final rule excluder reciprocating 

engine powered and turbopropeller 

engine powered airplanes in 4 121.358 

and doer not include qny airplanes 

operated under Parte 61,125, and 135. 

In addition, the FAA har determined 

that a clarification of "hubopropellerpowered airplanes" as wed in propored 4 121.358 ir needed in the final rule and 

har accordingly added the wordr "with 

variable pitch propellerr with constant 

rpeed controls." The addition of there 

wordr clarifier the esrential design 

characteristic of turbopropeller-powered 

airplaner which maker them lerr 

vulnerable to the hazards of inadvertent 

entrance into windshear conditione. The 

FAA wmiden thir addition necessary 

in the event that airplaner are 

manufactured in the future which may 

have rome of the characterirticr of 

turbopropeller-powered airplaner but 

not variable pitch propellen with 

comtant rpeed controls. Any much future 

airplanes would not be excluded from 

the equipment requirements. 

Airborne Low-Altitude Windslrear 

Waming Devices 

Sixteen commentr rpecifically 

mentioned the proposed requirements 

for airborne warning devices. Ten 

favored the requirement, three opposed 

It, and three opposed certain arpects of 

the requirement. Opposition to the 

requirement was primarily directed at 

the need to retrofit existing airplanes. 

Concern8 about the requirement for 

airborne warning devicer were the 

One or more of the predictive 

ryrtem now being developed could be 

kutalled on airplaner and validated for 

far leer coat than present waming 

myrtema. 

No rerearch har been conducted to 

rhow that a warning device system 

would add a rignificant margin of safety 

over training in windshear procedures. 

Airborne warning devicer may be 

counterproductive to training since they 

may encourage a pilot to pursue a 

course that by observation alone he 

would conclude ir dangerous. 

Conditions other than windshear 

may ret off the warning, causing a pilot 

to abort a take-off or landing, thereby 

creating a potential hazard where none 

actually sxirtr. 

Requiring hetallation of warning 

devices may slow development of 

predictive ryrtems. 

Only predictive rystem can 

provide a pilot with information early 

enough to allow arcape. 

following: 

47 
37690 Federal Register / Vol. 53. No. 187 / Tuesday. September 27, 1988 I Rules and Repletions 

- 

The FAA's Response: The FAA does 

not agree with the overall position of 

these comments that requiring an 

airborne warning device ir prematw; 

that the FAA should wait until 

predictive systems are developed and in 

the meantrme rely solely on training in 

windshear recognition and escape 

procedures. The FAA estimates that 

airborne windshear predictive systems 

will not be available for operational use 

for at least another ten years. In the 

meantime training alone is nbbenough. Windshear accidents have continued to 

occur even after windshear training har 

been incorporated into many certificate 

holders' training programs. Since 

windsheer training alone cannot 

guarantee that a pilot will recognize, 

evoid. or ercape windshear conditions. 

the addltion of an airborne warning 

device will provide flightcrcwr with an 

increased margin of safety in 

inadvment encountem with lowaltitude windshear. 

Two systems have already received 

FAA certificetion OS airborne lowaltitude windshear warning and flight 

guidance devices on various airplaner 

In addition, several other manufachven 

have made formal application for a 

Supplemental Type Gertificete (STC) for 

other ryrtem. Any of these syrtem could provide the flghtcrew with 

enough warning and guidance to 

enhance the probabilrty of succersfdjy 

accomplirhing the windshev ucepe procedure for the particular system. One of the low-altitude windshear 

warning systems that has been certified 

and is being used has provided 

operational data. This data indicated 

that the warning system provides a 

signifiurnt benefit to the flight crew of 

the abaft. This data a160 indicsted 

that nuisance and falee alert8 urn 

found to occur at an acceptably low rate 

to maintain flight crew confidenoc in the 

system. (For details we paper titled 

"Flight Experiencc witb Windoh 

Detection", by Terry Zweifel peaented 

to the SAE Aerospace Contrd .ad 

Guidance Systems Committee, March 8- 

11. lssa). 

Becaulre of the reriournns of &e 

windshear problem, a regulatory 

proposal to require implementation of 

an available low-altitude windshear 

warning system that could alleviate the 

problem rhould not be delayed. The 

public must be given the maximum 

available protection from the 

catastrophic accidents which opcrsting 

experience her demonstrated can occur. 

The requirement for airbarn bwaltitude windshear warning systema 

does not mean kt the FAA will duce 

its commitment to ohr whhhear 

equipment development. h rtatcd in 

, 

the NPRM the FAA will amtinut to 

foster rerearch programs to dealgn 

better flight guidance and conml aid8 

which wd improve a pilot's ability to 

avoid an accident in the event of a 

windshear encounter. Future FAA 

action will place emphasis on fotlering 

the development of pndictive 

technology for UBC in syrttmr to detect 

and avoid inadvertent entrance into 

windshear. The FAA will amtinue 

pursuing a "rystems concept" which 

inciudes M improved low-altitude 

windshear weather fomestiag 

technique, ground-based windahear 

detection equipment, airborne 

windshear detection equipment. and 

improved pilot training. 

Flight Cuidonw 

Transportation Safety Board and the Air 

he Pilots Asrociation, virtually all of 

the commenten either opposed or 

expressed rome reservations about the 

proposed requirement lhat the approved 

airborne low-altitude windshear 

warning system be equipped "with night 

guidance." The overall thrust of the 

opposing comments. like the comments 

opposed to installing warning devices. 

was that tbe cost of retrofitting present 

aimaft with a flight guidance system far 

outweighed the potential benefits. ATA 

on behalf of its member airlines asserted 

that "he mounes that would be 

required to install guidance systems 

could better be used for awidance 

systems when they become availablean eventuality not too far in the future, 

rccding to me." 

The FAA 's mpm: The PM dots 

not agree that inmared safety uwuid be 

achieved in a mim cat effective way 

by eliminating the fl& guidance 

mquiremmt and waiting for the 

windbear detection system pnsently 

in development. Ib previovsly stated, 

the FAA does not believe that fully functionel, teeted. and reJieble 

windahear detectim aystemr ere as 

dose at hand a# da merd ammtntua. 

Nor does the PM beliew that a 

wind.hear dccs~tion -em. tf . 

developed. would make a rtnbbaar 

flight guidance +em onncceuary. 

While tk FM agmu that windht 

.voidance is the moa desinrbie rdution 

to the windshear pmbkm, look 

rvddance my never k rcbknbk so 

that an effective flJght guichna ryrtem 

may still be b@y &suable even Ua 

detertion system ir devekipd. The 

awlbenefit rupectr ofthe fight guidanac rsquircmcnt ut dircurred 

der the eamomic evaluation portion 

of lhir preamble. Specific eommQlts 

regarding the night gnidance 

nquircment am dimmed below. 

Except for the National 

48 

Several commenten stated that the 

cost to retrofit existing airvah nilh 

flight guidance syrtems is 

disproportionate to the safety gain, 

especially for aircraft that do not now 

have go-around or takeoff fl@t 

guidance functions in heir fldt dinctor 

ryslems. Some of these commenten 

pointed out that the Windrhear Training 

Aid staler that the manual technique 

(maximum power and establirh a 15 

degree body angle pitch on the attitude 

director indicator) comes within &YO% 

of the potential performance ruing flight 

guidance. One commenter concluded 

that "the difference between manual (no 

guidance) recovery and optimal (but not 

practical) guidance is something at or 

less than 5%!" 

The FAA 'r Response: The coat/benefit 

aspecta of the flight guidance syrtem 

rtquirement are discursed fully ander 

the economic evaluation portion of this 

preamble As more fully explained there, 

tbe FAA believer that flight guidon= 

systems should be quid for turbinepowered airplanes operating under Part 

121. The remaining life span of many 

airplanes already operating under Part 

1n ir sufficiently long to justify tbe 

retrofitting expense of providing lowrltitude windshear flight guidance in the 

event of an inadvertent windshear 

encounter. Tbe Windshear mining Aid 

(WTA) rtatement does not refute this 

amclurion. However, 11 should be noted 

that the conclusions drawn in the WTA 

with respect to comparing the 

performance efficiency of the manual 

(cchnique with flight guidance wee 

based on the amrumption that, for the 

manual technique, the transfer of 

learning effectiveness from the 

dassrwm to &e airplane in la0 percent. 

The mndurion was then drawn that. 

based on the transfer d leanring 

ar~mptioa tbe manual technique 

would be effective Si-95 pacant of the 

time lor hose few windahearn 

encounlcrtd. The behavior pettern 

redtirtg born widahear tminlng using 

vuiour media (ea. classroom 

pdurtr miners rimulaton. dc.) 

may be d-ded over time. 'Zbus. in an 

actual severe bw-altitude winchhesr 

encounter. en individual pilot's reaction 

us- the manual technique most likely 

would not approocb the 

potentiel described in the WTA. 

There is no general industry 

.gwnent on pmmt flight guidance 

4prithmr [that 1.. on just what 

directions the pilot should be givm). 

The FAA% RespoMa. Ont hdd 

perumt agreement on exirtirtg 

aborlthms may not exist: however. 

softwarn har been developed that is 

~~oP~~dtVhhoodcp~~ 

, 
Federal Regimter / Vol. 63, No. 187 / Tuesday, September 27, 1esS / Rules and Regulation8 3769l 

adequate to obtain FAA appnwoL With 

flight @dance provided by thir 

roftwm. a pilot wd have a better 

change of taw action neceuay for 

the aircraft to rwive M inadvertent 

encounter with low~ltitude windshear. 

Adaptation and modification of r older electro-mechanical Wt director 

rystem may affect the latepity of the 

existing ryrtePPr thereby derogaw 

mfety. 

The FM 'r Re8pon8e Modifqtion of 

older flight director ryrtemr rhould not 

approved airborne low-altitude 

windshear ua with night guidance 

rvstem to be inrta "YI ed must have been 

4 affect the integrity of thore ryrtems. Tbe 

&rtificated in accordance with the 

app-te sections of Part 25 of the 

FAR end murt meet the nupective 

almorthineu and operational approval 

criteria addrsreed In AC S12 and AC 

1-1 or their approved uivalent 

This approval mora wo 3 d ensure that 

the integrity $those ryrtems would not 

be compromised. 

guidance systems until it bar completed 

its characterhation of the windahear 

henomenon which b nol echeduled to 

le completed until 1991. 

The FAA 'r Response En 

been leuned about the winds ear 

hazard to pennit the artification of 

rcvml windshear rytems. Ihe part 

8cddent rceaariw m well Undsntood 

and there her been an tmormour amount 

of data generated by the Joint iAirport 

Weather Studiee (JAWS) program. 

While the potential hazards will 

continue to be studied and further 

defined there ir an adequate bare of 

knowledp to derign and CtrLifiCrte a 

be pracrid at thir time datx many of 

the preeent ryrtem =quire me down 

control inpub very dase to the 

Thc FM 'r lkponae: -tau&$ 

guidance d.n only be developed den 

there ir complete knowledge of the 

the aircraft. Optimal flight guidon- la a 

time dopeadent v0ri.k state which 

must conrider a rapidly changing air 

altitude, epeed adition, etc.). In 

the certification procerr the FAA will 

evaluate .li guldanco conmundr, 

including oore dorm wnmrndr, for 

appropriakneu If the optlmrl yidrnca 

rtrategy for a puticul.r windshear 

situation requirarame down umtd 

inputs aocbae totbe mud that It 

would mu10 ooll&foo with tbe Ipound 

tbe guidano etnt.gu would be 

unacceptable rod would not be 

certificated. It ahould be noted that 

"aore down" dom not IWM below the 

FAA 8hOuld not muin wt 

7 

Ch-CkdStiCO Of the OIOBS 6ront d 

mU. U Wd M WCid SihrEthU (k, 

boriron It mmna C bwm &e ma h 

its present qle. 

While tbefliOht guidanoefudm provider a rmd incrmaw la tho 

magaltudo of tb wkrdrheu b which .D 

aircraft can ruccarrfully opcrrto, &at 

incmaae only oocw at very windahear valuer. Therrfoca bacmue of 

the reriour turbulenm wht would be 

encountered, thir unall pin add udy be offset by the pilot'r inability to 

dody follow the mmmmd8 Mn# 

dven. 

The FM 'rhpomwlbe FAA 

recognize# &at ia the wont are# of 

severe windahear ~pe ouy mot be 

possible and, depndipe upon the atme 

of the whbhear w 

guidanoe couund-bo 

readable &caw0 of uvere turbha~ 

However, it Ir 

plutbermors, for thorc wiaddun 6um 

which ercape ir podbb, Wt dam 

Between tbe moderate to eevm Ieveb 

of windshear, flight yldrnoa CUI 

provide a- iu puf7bwiniw 

favored th pmpond hriniple requirenran(r A number of comments 

addrersed rpbcific 

mquirementa. partiaJutv thome 

requireinants concorrriry rimdata &ht 

training. All rpedfic oonuaentr M 

rummarixed below. 

t Safety International dabd 

tar operaton &ouM be 

excluded from the baldq requirements for nrcovery and ucrpe pdurar became not eaotqb data drts to 

develop training in wch pmoedum fa 

belicoptsrs. The FAA 'ORe~paueThe FAA ape8 

with the commenter. The FAA hr 

decided to axduda hallCopterr &om the 

-pYm-bbuu thereare& icieatdataanh~ 

response to windshear amcountem. 

Accordingly I I -a)(7)(ii) ad 

135.345(b)(6)(ii) havo born b 

include the wd "axcept that 

rotorcraft pirots .I, mr8quimd to be 

trained in~tromlow.rkitmda 

windshear." 

Some cummenb hued duaiea 

about tba Inknded moaaing dthe 

propomedbr~nquinnwrntr 

Continrahl Exprrw wu ooacmwd that 

the propeed nrk excluder 

*propakr-powrttd.bpLawin I 12l.Ssa hm bw-rltlrudr uindn&u 

quipmat requhaarnlr WldlouI 

excluding them from the JPSLDC 

windsbtrahiqn 

rubrsquant ~tio~ o tba rula plirht Eagineus'tt.rrutionalAroct(ioo 

dbh b have eevom 

windsbearwi r OutwvembpbuLnOs 

providsrM.ddi~~ 9 dew. 

VirtdyaUdbaolamentrdd 

Ct.innr-- 

rtated that the propored flight tnintng 

enginem and tbat the FAA pro bly intended that they rhould apply to all 

cockpit oranmembers. Apther 

commenter wae concerned that the 

mqulted windshear training -am 

might bave to be 8 reparate and 

therefore cartly training progm. 

The FAA 'a Responsc A8 pmpoeed, 

the language of I 121.Wd) nquim ' 

aimdator windshear flight tnw only if the airplane ir mquired to be equtpped 

with low-.ltitude windaherr quipmeat 

under I IM.358. Therefore, flight tram 

thore turbopropeller powered airp!anea 

excluded Fram the awerage of 8 12I.351). 

In response to the comment from 

Flight Engineers' lntrmationd 

hsociation, *he red amendments 

to Pert 121 inc~uclXpirements for 

Mal, tramition and mcurrent ground 

training in windshear recognition, 

avoidance, and escape prowdurer far 

pilots and Wit engineem but proposed 

requinments for flight training in 

windsheor procedures and equipment 

we were intended only for pilots who 

M at he contmlr of the airplane. 

Currmt i121.125 whlcb covers 

training far fl@ht engineen ir not 

amended by thir rulemaking. Windrhear 

gound tniniog in I121.UQ is applicable 

to dl flight mewmembers while 

windohear flight Wnbg in 8imulaton 

applier only to pilots operating airpleDes 

quipped with lowaltitude windshear 

quipment. If a date holder wishes 

to provide flight hinhq &I windahear 

procedursr and equipment far flight 

cmgineen. It may do ea but the FAA is 

Dot NquiI'iIq 8uch training. 

wncemiq windshear training as a , ar the FAA uplained 

la 8eparats the pmam T le ofthe proposed rule. the 

phrase "an approved bw-dtitude 

windahear ut trainiq~ prolpam" was 

wed to refer to the pmposed uppded 

fli&t training requirements The phraee 

wae not intended b wan that thae 

&odd be a rcpamto 

for than who up1 povlde waltilde 

whdrbecu ut bainhg. wed the 

Lntaotioa ir that the approved bwaltitde uihhear nisbt-be 

inoorporrted into the bdder'r 

.PP-d bw Plognm. 

"he Air Tranrport Matim 

(MA) would Ue to me di&reat 

wording than &at pmpo#d im 

81 12L-d) and in.Uyd) nhiQ 

rtatd thrt a pilot must have ham 

and pmctice in "at hat" and W Irrc 

rll 

and 

Or' be wbxI8bu-p in tbe ~tor'r - 

approved lor*rltltrd, widsbeu flight 

?qUhUd# do Dot apP1Y b Y 

Would be vdd fm PildB flying 

Y ing 

Finally. hm8ponre to lheGamllwlt 

7- 
57692 Federal Register / Vol. 63, No. 187 / Tuesday, September 27, 1988 / Rules and Regulations 

training program. ATA commented that 

if the FAA's intent was to require that 

every pilot receive training in every 

exercise a carrier develops, camen 

might be discouraged from developm 

multiple exercises. 

The FU 'E Response: One means of 

approval of the windshear training 

portion of a certificate holder'r - 

approved training program is the 

Windshear Training Aid developed by 

the FAA and the industry tea led by 

being. In July. 1987. this material was 

widely distributed to all Part In 

operators and to part 135 operaton 

conducting scheduled operationr and 

within the FM. The FAA intends that 

the minimum number of windshear 

ercape maneuvers to be performed in an 

approved airplane simulator for 

approved windshear flight traw 

would include at least the maneuvers 

and procedure8 associated with the four 

basic exercises set forth in the 

Windshear Training Aid. There 

exercises have the pilot encounter a 

windshear situation+) Before 

achieving rotation speed on takeoff; (2) 

during a rotation on takeoff; (3) during 

an initial climb shortly after takeoff; and 

(4) during a precision approach. Each 

certificate holder should develop ruBicient variation in the exercises to 

avoid stereotyping in the training. 

In €0 121.409ld) and 121.424(d)[Z) the 

phrase "at least" is retained. while "all 

of' has been deleted from 

4 12l.424(d)(2). These changes should 

make the FAA intent clear, namely that 

each pilot must receive training in the 

minimum number of windshear escape 

maneuvers and procedures that 

constitute the certificate holder's 

approved low-altitude windshear hght 

training program. The "required' 

training would not include all the 

possible exerciser that an operator 

might develop for its approved lowaltitude windshear training pro While logically most winds ear 

flight training should be conducted in a 

rimulator. rome commenten wanted an 

"escape option" in the event that 

rimulators were not available for 

training. They did not think a pilot'r 

training should be delayed if windshear 

training in a rimulator is temporarily not 

available. If the pilot could substitute 

ruch training in an airplane, at least for 

rome of the training nquiremenb. this 

would be of help. The FAA 'r Response: The FAA 

believes that windshear fight training 

cannot effectively be given in an 

airplane because the total environment 

of a windshear cannot be artificially 

reproduced in an airplane and it would 

be too dangerous. in addition to being 

impractical. to read out actual 

rmwindshear conditions. It ir practice in 

the use of proper procedures and 

techniques under the extreme conditions 

of windshear that must be 

accomplished. This can be done safely 

only in a rhulator. 

To minimize the overall impact of the 

training requirements on simulator time, 

planning will be necessary. Pari In 

certificate holders rhould plan for the 

downtime necessary to modify 

simdatom and the increased tmhiq 

time, and should anticipate usual 

malfunction and maintenance 

downtime. With proper planning the 

training compliance date of two ycan 

after the effective date of the de 

January Z lege should allow for 

modification of simulaton without 

delays in complying with current 

training requirements. Certificate 

holden rhould begin their planning 06 

soon as this de L published. They may 

have to begin their low-altitude 

windshear training as early ar one year 

after the effective date so that they will 

not have to schedule special hhhg for 

recond-incommand pilots whose last 

previous recurrent training occumd lese 

than a year earlier. 

As a practical matter. most certificate 

holden use rimulaton now to meet the 

six-month training and proficiency 

check requirements for a pilot in 

command. The additional fl&t training 

reguired in windshear proceb will 

add approximately 15 minutes of 

rimulator time. Approximately 80 

percent of the pilotr and copilob who 

Wiu be subject to the windshear flight training requirments have at some time 

received some windshear fl&t trapins 

in rimulators. Although cerhficate 

holden will have to rrvise their 

programs to meet the new requinments. 

for most pilots and cepilots actual 

training time will not necessarily be 

rignifcantly increased. Since current 

requirements for remnt training 

allow for a 30-day grace period (14 CFR 

IZl.rol(b)). air camem will have 

flexibility in meeting the recurrent 

windshear training requinmenb. 

Therefore, with proper planning. the 

simulator windshear flight training 

requiremenb rhodd not s@cantly 

affect stmulator use. 

Propored fi 12l.4OQ(d) stated that a 

certilicate holder must ure "an approved 

simulator for each airplane type *." 

Two commenten rtated that if this 

means that each simulator must have 

the rame windshear related avionic8 as 

the aircraft that operator ir LIB-, the 

requirement is too rrrlrictive. They rtate 

there an two dated problems. One, 

rinw simulator time is often leared. 

simulaton that am now being lead by 

rome operatom may not be adapted 

with windshear avionics for the type of 

windshear equipment the operator will 

have installed. Thus the operator may 

have difficulty getting simulator time on 

simulatom with the appropriate 

windshear avionics. Second 

Continental Airlines stated that the 

"escape maneuver rhould be generlc 

and not dependent on the hardware 

installed in the aircraft or rlmulatom." 

The FAA's Response: While the 

responses of most trained pilob to 

windshear are very similar. the 

performance of the aircraft and the 

technical characteristic8 of the 

windshear equipment differ. Therefore, 

a pilot needs to practice in a rimulator 

equipped with the same windshear 

equipment which will be installed in 

airplanes the pilot will fly. This b 

erpecially important since pilot 

responses to windshear must be 

performed wih secondrr. Pilot 

underrtandmg of equfpment differeocer 

and aircraft performance differences 

could be critical. 

The availability of simulator time on 

rimulaton with the appropriate windahear avionics is a factor that a 

certificate holder will need to consider 

and plan for before instalhng windahear 

equipment A certificate holder that u 

leasing simulator time will need to 

determine in advance if that rimulator 

will be updated for the appropriate 

windshear avionic equipmect Also a 

simulator owner who wanto to continue 

leasing will need to plan for certificate 

'holders' new windshear fhght training 

requirrments. Current des for 

rimulator fhght training requirc a 

certificate holder to use an approved simulator for each airplane type. md 

mor! simulaton me capable of being 

adjusted to allow training for different 

windshear systems. Therefore, the FAA 

anticipates that with proper planning 

and coordination the industry will be 

able to provide training on e rimulator 

for each airplane type with the 

appropriate windshear avionics by the 

compliance date. 

ATAs comment maintains that 

mandatory windshear escape training 

and current approach-to-rtall maneuvers 

required in Part 121 may be redundant. 

Both typea of maneuvers involve high 

power, low rpeed conditione, and once 

clear of the windshear. the cleanup 

recovery fmm the windshear escape 

maneuver is identical to the approachto-stall cleanup recovery. 

The FM 's Response: The FAA does 

not agree that these are redundant 

requiremenb. While rome rimilarity of 

maneuvers may exist the situations and 

objectives are different. Windshear 

occurs in a highly unstable environment 

4 

6 

50 
Federal Register / Vol. 53, No. 187 / Tuesday, September 27, 1988 Ruler and Regalatiom 37693 

while skllr can occur at any time. 

Approach-to-stall maneuven are a 

proficiency requirement while 

windshear ercape maneuvers and 

procedures do not have a proficienc 

rformance rtandad In 

%:a$ training the objective b 

to practice windshear ercape 

 procedure^ ln a real the dynamic 

environment, not to train to a 

proficiency rtandard. 

One commenter rupportcd a rixmonth reclvrmt windshear ground 

training requirement but recommended 

only an annual requirement in an 

airplane simulator. The commenter 

stated that "recoverylescape from a low 

level windrhear ir basically a 

mechanical maneuver" and that "as long 

a8 the pilot rememben and underetandr 

the concept of recovery the pmbability of succesr ir greatly inmared." 

Therefore, the commenter maintained 

that "twice annually, monthly, or 

weekly practice of recovery maneuven 

will not ensure one hundred percent" 

ruccerrful recovery. The FAA '0 Response: To darify, a rfxmonth recurrent simulator windshear 

flight training requinment would apply 

only to a pilot in command (1 tnAn(d) 

and S lZl.443(c)(l)(ii.i) and (d)). A 

aecond in command would be rsqutrad 

to have annual recurrent training (1 lZl.M3[c)(l)). Demonrtration of 

proficiency in escaping windrhear ir wt 

the objective of the windshear flight 

training requirement. Adding windsbeu 

rimulator fhgbt training to pilot 

recurrency requiremmtr will prwide the 

pilot with practice in the correct 

procedure8 for M event whicb born a 

rtetirtical rtandpoint will be 

iafraquently encountered but to which a 

pilot ir potentially expond at all timer. 

The FAA believer that practia in 

windshear erccrpe pdurer will 

prepare pilotr to rerpoad immediately 

and appropriately in M inadvertent 

wiadrhear ureounter. 

Effective and Complains htes 

the flight guidance portion af the 

windshear equipment requirement 

rtated that the two-year caqhme 

date war unacceptable for the follow@ 

reasons: 

It would require too much downtime 

for airuaft within a fleet 

It would be impoasible for 

mmufachwr of windrhear equipment 

to rupply the equipment within a twoyear period. 

mere are not enough trained 

mechanics and other rechnicianr to 

accomplish the required work within 

two yearm. and it would be impractical 

to recruit and train perronr for rucb a 

Several commenten who objected to 

developed, and rimulaton would have 

conriderable downtime. Conridering 

how much rimulaton are wed lo pilot 

flight training and recurrent tralning and 

terw the downtime ml&t miourly 

interfere with pilot training. In addition 

at least one commenter questioned 

whether the FAA or ladusby would be 

rerponsible fa development of tbs 

windshear roftware. 

The FM 'r Refpanrr Beuurc of 

the immediacy of the windshear 

problem, the FAA w~tr to enswe hat 

there is no unnecerrary delay in 

providing the traveling public with the 

additional magin of ufety sought by 

there new requirementr However the 

FAA murt allow rd6cient time h the 

rerolution of my technical problems 

with equipment, for production of the 

needed equipment, and iutnllatia~ and 

iwpection on .ircrllk Robably the 

ma rlinu factor,otherth.n 

te&d i3leau ir the availa 

enough trained mechaaicr The FAA racoSfiter that even if it were practical 

b tram more mechaaia to meet 

haeared demand, the nectreuy 

training time would make a twoyear 

compliance date for dl .irplaner 

impractical Therefon, to allow he to 

rsrdve MY technical problem with 

equipment, for equipment manufactun. 

order placement, delivery and 

lortallation of tbe equipment the FAA ir 

permitting a phad complianoc 

mchedule for rstmfit requlremntr unda 

certaio coaditianr. The 6nal de 

(( ma) mquirer Compliane by two 

yean der the effective date for all 

&born equipment nquiramente rrnleu 

UI operator rubmite and obtain8 

a proval for a retmfit ached& that 

rLwr a p~ cow- mer a + 

year period hm the effective date A 

requert for extscuion of the compliance 

date murt be rubmitted no later than 18 

monthr after the effective date Tbe 

phd retrofit compliance dedule 

appliar ody to aer wbore date d 

manufacture WM T fore tbe eHective 

date of tbe rule. For the purpore of thin 

ractim "date of manufacture" mmu 

d 

the date tbc inrpcction aomptance 

reflect that the airplane ir 

complete and meetr the FAA Appmna 

Type Der@ Data. At kt 50 pcrasnt of 

.ucb airphner which are Won the 

certificate holder's maintenam 

operatioar mpecifiutjom 09 the dote of 

rubmirrion murt be retrofitted within 2 

yean after the effective date, at kart I 

pament mom of- .Irplanea with3 

yeam anddl of&& cartificrte hdddm 

51 

affected airplanes within 4 years. Any 

certificate bolder tbat 0bt.fnr a 

compliance date extension mM omply 

witb the rebofit rcbcdule .nd rub& 

oompletion of the rchcdde. 

The ground and fieat tmldq 

provirionr of the hl rule will tah 

effect two yeam after thc effedivr dale 

of the de. To make sure ht a11 

operaton are aware of the compliance 

dater for the training maquirementr. the 

find de lnduder new 8 121.404 and 

revised 4 135.10 that rtrte the axad date 

for compliance. 

For certificate holden to meet the 

two-year compliance date for all of their 

pilotr, most oertificate holden will want 

to have the new windshear training 

program approved one year eukr (Le.. 

not later than one year from the 

effective date). In thir way the 

certificate holder will be able to give 

oeand fn command pilotr their required 

windshear training a8 part of their 

@arIy scheduled annual recurrent 

training. Otherwiee a certificate holder 

will have to rchedule r ecial training for 

previoua ncumnt training occurred leas 

than a year earlier. 

In order lor certificate holden to meet 

thir kind of orderly rcheduling, it is 

important that they begin the .ppnwal 

procerr ar mn ar powiMe 10 that tbey 

will not be faced with last minute 

training and rcheduling problems. 

While the final rule doe8 not contain a 

ape& compliance date for the 

necerrary convenion of rimulaton, it 

can be oeen hom the above dLausioD 

that moet sirnulatom will need to be 

converted within one year .far the finrl 

rule taker effect. 

Although the ha1 de allows for 

phared complipnm for retmfits, tbe 

FAA mer that planning will basin at 

the time of publication of the de.. 

Advko~y Cimulam 

Two commentem ~lrgeerted bat 

advirory msterial kipe &veloped by 

the FAADeedr to be men and 

commented on before the FAA proosedr 

to final rule. One rtated that it war 

diffcull to dircurr the praparl rrlUI opportunity to oomment in parallel 

on the AC dew criteria for approviaS 

airborne low-altitude windshear 

equipment Ibe recond oooParent J.ted 

that the ACrhouAd be parlof tbepabuc 

ncord .ad huld Isceive public input. 

war iuued the FAA developsd d 

Irrued AC OWDk Im Ld 

Windrhear, AC ieMt Cziteria for 

Optra~APgrornlof~rne 

WmrlrbrrAlUtill#dF&htC.Y.EkCi! 

BhtW CVW 8h mtbr Ud 

recond-incommand pi P otr whore last 

rhe FM 'rrsrp0Me: &)ot * NPRM 
37694 Federal Register / Vol. 53, Iso. 187 / Tuesday, September 27, 1988 / Rules and Regulations 

Systems. and the Windshear Training 

Aid previously discussed in this 

preamble. In November 1987, the FAA 

issued AC 25-12. Airworthiness Criteria 

for the Approval of Airborne Windshear 

Warning Systems in Transport Category 

Airplanes. Thus. all of the advisory 

material necessary for manufacturers 

and certificate holders to comply with 

the requirements of this final rule has 

already been published and by the time 

the rule takes effect will have seen 

available for a sufficient length of time 

for all interested persons to be familiar 

with their contents. 

Beyond the Scope 0fhPR.V 

Several comments submitted were 

beyond the scope of this proposed 

rulemaking. The FAA has considered 

these comments as informational and is 

not responding to them. A summary of 

ruch comments follows: 

One comment recommended that 

the proposed rule be withdrawn and "in 

its place a requirement adopted that all 

transport aircreft eventually be 

equipped with an EFlS instrumentation 

system." "EFJS" stands for Electronic 

Flight Information System. This is a 

flight instrumentation system and flight 

guidance system that simplifies the 

integration of information a pilot 

receives from his flight instruments. 

Part 121 aircraft should operate at 

reduced weights by limiting the fuel, 

number of passengers, and baggage and 

cargo anytime that thonderstorms are 

predicted for an amval or departure 

area. According to the comment this 

would provide the Part 

maneuverability closer to that of bar 

jets which have bad relatively few 

windshear accidents. 

Three comments were received 

which the FAA determined were 

primarily Information about predictive 

or night guidance systems that are being 

developed or are currently on the 

market. One recommended that the final 

rule include a requirement for a 

predictive rystem with a compliance 

.date two yearn after approval of ruch a 

rystem. 

One commenter recommended that 

the FAA require a flight procedure 

method for transiting windshears based 

primarily on ainpeedlgoundspeed 

comparison. 

NTSBcomendedtheFAAandthe 

industry. led by the Boeing Company, 

for development of the Windshear 

Training Aid and stated that it hoper the 

Training Aid will be the foundation for 

FAA approval of training cumcula 

implemented by air camere in 

complying with the rule. It recommends 

that an additional training requirement 

One comment recommended that all 

aircraft with 

I 

be added on the use of airborne weather 

radar for thunderstom and convective 

windshear avoidance. It considers this 

valuable equipment for weather 

detection during amval and departure of 

flights. 

One commenter rtated that ground 

training in windshear detection and 

escape maneuvem for Parts 125 and 135 

pilots was not sufficient and that these 

pilots should also receive simulator 

training. 

TWA objected to the requirement to 

have 14 channels of recording 

cdpabilities on flight simulstom. It 

stated that the FAA currently requires 8 

channels for certification of flight 

simulators and that no benefit would be 

derived from having the additional 

capabilities. The FAA has not addressed 

this comment since there Is nothing in 

this rulemaking that states the number 

of channels required in simulators. 

Ecxmomic s:umrIuqy 

The following is I rummary of the 

final cost impact and benefit arsersment 

of a regulation to amend Pd 121 of the 

Federal Aviation Regdatiom FAR) to 

require that certain turbine-powed 

airplanes be equipped with an approved airborne rystem that warn a pilot of the 

presence of hazardous low-altitude 

windshear conditions and if such 

windshear conditions are inadvertently 

encountered. provides flight guidance 

for a missed approach procedure or an 

escape meneuver. In addition, the de 

requires that all Part In operators 

conduct approved low-altitude 

windshear night training in a simulator 

which has installed in it windshear 

equipment needed to conform to the 

airplane type being rimulated. The rule 

further requires that Part In and 135 

certificate holden' training programs be 

required to include training concerning 

fhght crewmember recognition of, and 

escape from. inadvertently encountered 

hazardous low-altitude windshear 

conditions as part of tbeir normal 

ground training. 

The NEB har determined that lowaItitude windshear has been the prime 

cause or a contributing factor in 

numemur air camer rccidents in the 

last 20 years. The objective of these 

der, therefore, is to prevent or reduce 

accidentr attributed to inadvertent 

encounten with low-altitude windahear. 

The methods and arrumptions used to 

prepare the economic impact estimates 

for the various changes to Part 121 have 

been developed by the FAA. The 

estimates of economic impam for the 

final rule revirions bave been 

constructed from unit cost and other 

data obtained from air carriers, industry 

trade associations. and manufacturers. 

information for analysis of benefits was 

obtained from the safety records of the 

NTSB and the FAA. The costs 

calculated for these amendments have 

been projected over the 16year period 

of 1889 to 2004. This analysis compares 

these costs to benefib accruing over the 

isyear span of 1990 to ux)4. The 

purpose of this is to account for the fact 

that in 1989. the first year after the de 

is published. no airplanes equipped with 

the required avionics will be in renrice. 

In 1889. however, impacted entities will 

incur program and planning start-up 

coeb. 

In the Notice of Ropoaed Rulemaking 

(NPRM). the FAA invited public 

comments concerning the technical and 

operational considerations and 

economic impact assumptions ar these 

apply lo 51ghl guidance systems 

equipment modification and 

replacement the frequency and duration 

of Part 121 certrficate holder'r 

windsbear rimulator fLght training, and 

the extent to which Part 135 operators 

provide instruction to their pilots in 

procedures to recognize and escape 

inadvertent encounters wiib lowaltitude windshear. Cammentr OD the 

proposal were submitted by individuals. 

foreign and domestic air camera air 

carrier and airline pilot associations, 

avionics manufacturers, and the 

National Transportation Sefety Board. 

The majority of comments commended 

the FAA for taking action to reduce the 

hazards of windshear encounters. A 

number of commentem, however, 

opposed certain proposed requirements 

and disagreed witb economic impact 

estimates presented in the proposal. The 

FAA bas evaluated the public comments 

and made the fmal determination 

regarding tbeir impact. The comments 

have caused the FAA to revise its 

analysis and increase compliance costs. 

A rubstantial change in the final de 

is the provision of a time-phased retrofit 

schedule for airborne windshear 

equipment requirements. The fmal rule 

requires compliance by 2 years after the 

effective date of the final rule for all 

airborne equipment requirements unless 

an operator rubmitr a rchedule to rhow 

phased compliance over a &year period 

from the effective date of the rule. Under 

0 121.358(b) at least 50 percent of a 

certificate bolder's airplanes that were 

manufactumd before the effective date 

of the rule must be retrofitted within 2 

years, at least 25 percent more within 3 

yearn,. and the remainder of airplaner 

affected within 4 years. The fmal rule 

also established that the ground and 

fl@t training provirions of the rule will 

take effect two years after the effecthe 

date of the rule. The time permitted for 

52 
Federal Register / Vol. 53, Na 187 / Tuesday, September 27, 1988 / Rules and Regulations 37695 

f 

c 

compliance with the ground and flight 

training requirements will allow 

certificate holden rufficient time to 

train flight crews and convert rimulaton 

in advance of the compliance date for 

the required airborne windshear 

warning and flight guidance eqdpment. 

The FAA believer that the time allowed 

for training and equipment inrtallation 

and modification will reduce costa and 

facilitate compliance. 

The FAA finds that with thC exception of new 8 121.358 and the amendmentr to 

58 121.407,121.108.121.424, and 121.427, 

the amendments affecting Part 121 

operators will have a negligible cort or 

no cost impact. The FAA har alro 

determined the cort of compliance with 

the upgraded testing and training 

requirements of the amendmentr to 

S 8 135.293.135.345, and 135.351 to be 

minimal. 

New 8 121.958 and the amendmentr 

80 121.407,121.424, and 121.427 have 

been analyzed independently. For the 

purpose of thir evaluation, however, the 

costa arrociated with there revirione 

have been aggregated. The reason Ir 

that there amendmenta are inextricably 

related and rhare the common objective of improving the rkillr of pilots in 

recognizing and escaping from 

inadvertently encountered low-altitude 

windrhear conditions. 

New 1 121.358 will have an economic 

impact on the approximate 3,800 

airplanes expected to be in rervice in 

1990 and 3.200 airplaner expected to be 

manufactured between 1891 and 2004 

bncaure they would be required to be 

equipped with an FAA-approved ryrtem 

providing airborne windehear warning 

and flight guidance. The ertimated cort 

of thir amendment ir $372.2 million in 

1987 dollan and Sn8.5 million at a 

prerent worth diecount rate of 10 

percent over the ieyear pedod of legg 

to 2004. 

The amendment to 8 121.107 would 

require that air camen inrtall approved 

windehear aerodynamic data prolpamr in their flight rimulaton. The ertbmted 

cost of modifying the 150 flight 

mimulaton currently in ure by Part 121 

certificate holden ir 68.2 million in 1987 

dollars. 

mlmulator utilization har been ertimated 

under 8 121.108 and added to the time 

captainr and fimt officm would rpend in a flight rimulator to comply with the 

windahear rimulator fhght training 

requirement8 of 8) 121.424 and 121.127. 

The FAA ham determined that 

approximately 80 percent of the affected 

certificate holden already provide the 

windrhear flight training required by 88 121.124 and 121.427. Therefore, the 

amendmentr to there rectione would 

The cort per hour of additional 

impact approximately 20 percent of the 

active and future captains and Ant 

officen of the 149 Part 12l GertifiCate 

holden affected by the rule. The 

ertimated coat of compliance with the 

initial, tranrition, and upgrade 

windrhear flight rimulator training 

re uirementr of 8 121.424 would be $13.4 

*!lion in 1987 dollam and $7.1 million 

when dircounted at 10 percent over the 

is-year rpan between iesB and 2001. 

The ertimated cort of requiring the 

affected captains and firat officen to 

undergo windrhear rimulator !light training pureuant to the recurrent 

training requirementr rpecified in 

8 121.427 would be $33.8 million in 1987 

dollan and Sl5.2 million at a pnrent 

worth diecount rate of 10 percent over 

the rame time period. Thir analyrir indicate8 that the total 

cost of compliance with the equipment 

acquirition, inetallation, maintenance 

and flight training requiremenb 

contained in thir rule b ertimated to 

have a prerent value of S246.S million 

over the 16 year-period of 1980 to 2004. 

To ertimate the benefit6 for the 

NPRM, the FAA examined the rafety ncord of Part 121 air caden for the 18 

year period between lm and 1985. At 

the time. thir review indicated that 15 

accidenb attributed to windahear 

phenomena occurred during thir period. 

A more recent review, however, reveals 

that two more accidents attributed to 

windrhear have been added to the 

wfety record by the NlsB for the anme 

15-year period in question. Accordingly, 

the lorrer arrociated with the 17 

accidentr are the barb for the benefita 

of thir rule. Moreover, the analyrir hu 

been advanced to reflect the more 

recent i5-year period of 1872 to 1988. 

To urive at a lore rate indicative of 

the cort of there accidentr, the total 

financial lore of there accidentr war 

divided &to the total number of turbinewend airplane air carrler operationr p" or the we 1b)rear period of 1872 to 

1868. "him calculation ertablirhed a lorr 

rate of $4.34 per turbinepowered air 

unier opera tion over the 16-year period 

of 1872 to 1~6. Similarly, to wtimate the 

future accident prevention value of thir 

'rule, the trtablirhed lor8 rate war 

multiplied by the number of operationr 

forecart for the 16 yeur from lee0 to 

m. Thir calculation mvealr that the 

emtimated potential dircounted benefit 

arrociated with the prevention of 

urualty lore in accidenb atMbuted to 

windrhear to be 8451.6 million. 

The FAA har been unable to 

quantitatively ertimate the accident 

prevention effectivenerr of there 

amendments. The total discounted coat 

of compliance of there amendmentr can 

be fully recovered if the rule ir only bs 

percent effective in reducing future 

carualty 1088. The FAA believer that 

enactment of there amendmentr will 

rignificantly reduce the number of future 

windshear incidenta and accidenta and 

that benefit6 will exceed costa. 

Thir regulatory evaluation focused on 

the rulemeking it rupported There are 

other programs which are alro designed 

to reduce the riek of windehear 

accidents. There other program are 

jurtified partially by benefits included in 

thir analyrir, and additional benefita 

over and above thore necerrary to 

urtify the rulemaking. FAA doer not ba lieve this rulemaking would eliminate 

or reduce the need for other programr 

much ar terminal Doppler weather radar 

md law-lvel Wind Shear Alert 

Syrtemr. 

Regulatw Flexibility Daterminetion 

The Regulatory Flexibility Act of 1980 

requirar a review of ruler to arrero their 

lmpact on amall burinerr. The required 

Part 121 amendmenta will have a 

ripifhnt economic impact on a 

rubrtaatial number of rmall entities. 

However, the FAA bde that there are 

no viable alternatives for amall air 

camen to adopt that would reduce the 

colt of compliance yet achieve the level of protection Bought by thir rulemaking. 

The amendmentr to part 135 have been 

determined to impore only minimal 

cortr. Therefore, Part 135 certificate 

holden would not incur a rignificant 

economic impact ar a rerult of there 

unendmenb. 

lnternrtbDllTt8delmprd8h1.ment 

no impact on trade opportunitiem of 

United Stater firm8 doing burinerr 

oversea8 or for foreign firms doing 

bwinerr In the United Stater. There 

amendmentr apply only to Part 121 and 

Put 135 certificate holdem and arrign 

nrponeibility for the provision of the 

required equipment and windahear 

training program8 specified in the rule to 

the operating certificate holder. Becauee 

mort Part in and Part 135 certificate 

holden compete domertically for 

prrrenger and cog0 revenuer with 

other U.S. operators. thir rule will not 

uure a competitive fare dieadvantage 

for U.S. &en. 

Podemlimn knpliutiollll 

rubrtantial direct effectr on the rtoter. 

on the relatiomhip between the 

National government and the rtater, or 

on the dirtribution of power and 

rsrponribilitier among the variour levels 

of government. Thur, in accordan~e with 

Executive Order 12812 it b determined 

There amendments will have little or 

The mgulatiom herein would not have 

53 
37638 Federal Register 1 Vol. 63,-No. 167 I Tuesday, September 27, 1988 { Rules md Reguletiom 

that these regulations do not bave 

federalism implicetiona r0quirh-q the 

preparation of a Federalism 

Assessment 

P8prWd -0 kl Appo+d 

The recordkeeping and reporting 

requirements contained in this final ruk 

(0 1Zl.358) have been submitted to the 

Office of Management and Budget for 

review since there prOViSiOM were not 

included in the notice of prdpored 

rulemaking. Comments on there 

requirementn rhould be submitted to &e 

Office of Information and Regulatory 

Maim (OMB). New Exelmtive Office 

Building. Room XUl. Washington, DC 

20503. Attention: FAA Desk Officer 

(Telephone MW9!j-;r340) A copy 

should be mbmitted to the FAA docket 

condun'oo 

amendment k not major under 

Executive Order lt291 bat &at it IE 

significant under the Department uf 

Transpmatim Regularmy Pokier md 

Procedm [U FR 11034. Febmmy 28, 

1979). For the rraranr dimrred abwc 

it almo has been determined that the 

amendments to Part 121 will hnve a 

significant ecunomic impact on a 

~bstantial mber of mall entities, but 

that the wendmemtr to part 1s will not 

have a 6ipificant economic impact an 8 

rubstantiel mmbcr of mall entities. 

The FAA has determined that this 

List d sabjacb 

14#%h~t12l 

Air camen. Air transportation, 

Aviation safety. Common cawim, 

Safety, TronsportPtian, WL\rlrhPmr. 

14 cm pbrt I35 

transportation Aviation dty, Safety. 

Windsbear. 

nu Rule 

AircorriernAirtnxiAir 

Accordingly. the Federal Aviation 

Administration lmendr part^ 121 ad 

135 of the Federal Avktian bgdationr 

(14 CFR Porta 121 and US) 86 fobwr: 

OPERATIONS: DOMESTIC, FLU, AND 

SUPPLEMENTAL AIR CARRIERS AWD 

COMMERCIAL OPERATOFIS OF 

URGE AIRCRAm 

continuer op md .I LYm: 

PART 121-c~m~tc~no~ ARD 

1. The authority citation for part 1Zl 

All(bnlm U3.C =(a). 13SS. T354 

1357. IWI. M-¶-. 

USC -1 (Revhi Cub. L n4S. Jmuy 

12 iO(u1. 

2By addq anew flnS56torordar 

fallows: 

I*, md 1502 8 

8 1213s Low-Wtd. whdrh.r 

equlpmnl mqukmnntr 

(a) Exsept RE provided In pgraph 

(b) of thm rectim dtta Jmmrq f 1061. 

no pnon may operate a 

powered .Crplane ulew it k quipped 

with m approved eyetern ppvfduy( 

mihe windshear wpnrirrg 4th flight 

guidance. For the pmpose of thh 

nction, "tnrbincpv~ricrcd atrplam" 

includes. e.g.. turbofen-, turbojet-, 

propfan-, and rrltxa-high bypars fanpowemd sirplaner. The definition 

specificaHy exchder hubopropeDerpowered evplaner with variable pitch 

propellers with faRoland weed urntrdr. 

(b) A certifiite holder xrmy obtain an 

extermion of the compliance dote ia 

paragraph (a) of thir lcctim for 

retdit rcbedrrle. For tk pvportr of 

thir rectios QI rlrphnc k amridcmd 

madm on the& hehspxticm 

rcceptmce @a mkt that the 

airplane ir campieie und lacots tht FAA 

Approved Type Design Datk To obtain 

rppml of a rrrtrofit rcbedule md show 

continued compliance with that ' 

rchedule, P cerbficate holder must do 

tbe following: 

rrtrofit schedulo by jme 1.mte &e 

~tslnn*Divirioab&Mguia 

the region of the certifiite bokimg 

dutrict &e pioal rQpmrd d bc 

pnkd by theDimctarofFiqht 

Standah -1). 

to thio dm &et an! listed in the 

certificste bolder'r maintemrnce 

opmtiona rpcclficutivnm w cbc date 

that the mpest fur extension ia 

wbmfned. that at kast 50% of thore 

&irplmer manufacturrd before Jmuary 

2 m39 will be equipped by January 2 

18BI, rt lesst 25Smare dlhore 

airplaner by jnnunry 2 Iopz. d dl of 

the errtificote holder'r urpLePer 

reguindbbesquippcd inu;cord..ce 

with thir Bectiou by )sruary 4, lsn. 

@)Complyrithnmrrb.QRhh& 

airplane8 mdd Mom jmuq 

% if Oh pP& Uf8 

(I) Submii e req~ut for .pprovd da 

(2) Sbaw, for &ea drpiem rsbiec( 

urd ruW rtrhr rrprb 

idarmation -table tp tbe 

Adminirbntor. The Mthl rspert mwt be 

submitted by ).naery 2, m, ad 

suboeqment reporb mud be mMttd 

every rhr mmth thereafter dl 

ampletion oftbe dduk Tht 

must be rnbmiard to tire FM FIight 

Standah DrstrIct OSR charged witb 

the cmraH inapection drb certifiiurte 

bolder'r opcratio~. 

S.ByrJJiDOanrw 4mADlbnod 

aB fObW8: 

fUl.404 yRnd3rur~compy.na 

dater 

After January 2 1981. EO certificate 

bokler may w a pmon ea a fhght 

mwmrmber deu tbft pereun bar 

completedfa) Windshear ground hntrdng tn 

&mCe vi& t 12um OfdJr pah 

applicable, in accordance with 

0 0 121.m, 121.424. md 121.427 of thin 

Part 

new pmagrapb [a) to mid ar follows: 

alrplrne drnubtan nd .Ow 

d.w 

(b) wmdahtu fllght epinbg. if 

4. By ommding i lf1.107 by adding 8 

i12~7 ~~pr~-=-d 

..e.. 

(d) An airplaDe rimufstor ~ppm~td 

under thir rection murt be used imbed 

of the airplane to satisfy tbe pilot &ght 

train@ ruqrrircxwnta pmcribed in he 

certifiie holder'r approved lowaltit.de windhear net mining 

lvogram ce( forth in 8 mAs(d) d thir 

Pa 

5. By amen- 8121AOB by ad&g a 

LLCW paragraph (d) (0 nsd u followr 

grn.roo Td~colxm8a*.Irphrr 

lJmrktm urd Omu m.d.rlcu 

(a) Each certificate holder rcqvind to 

....a 

comply With 0 121358 Of thi8mrpUrt 

we an approved simulator far each 

airplane type ia e8ch ofi&ppilot treining 

the procrduren ad maneuvem ret forth 

h the certificnte bddcr'r sppnwed bwaltitude vrindrhoar fi&t tsainiq 

progTm. The approved low4titde 

windahear plsht tminhg, It applicable, 

murt be includedm each of tbopilot 

flight hinialg wunwr pnscribtd in 

00 in.uQ(b). =Ala nU4, urd 

121.427 of this pah 

0. By amending 0 121.419 by nvirinp 

panqraph (a)[~)(vi] b read ae dallowr: 

tt21.4M nrOt..ad-.ngirmrr 

m. 

wta*-rdmgand 

~UU?B that provide8 hhl~ hl8t 

ce)*.' 

Crl'" 

(vii Procedures for- 

(A) Recogniziog and a- aevm 

(B] bcaping from &ere W& 

veather utuationr; 

rituationa in uuc d inadvertent 

windshear, and 

IC] Opera!irq in or bear 

tbundentom (includirq bert 

penetrating &tudes), turbulent dr 

bail. d otber potrntiolly h.rprdow 

meteorological csnditiens; 

encountera, ind- hWlc&l#itde 

(inclu~dearritturb~),~ 

e.... 

4 

54 
rt 

I 

Federal Register / Vol. 53, NO. 187 / Tuesday, September 27, 1988 I Rules and Regulations 37697 

7. By amending $ 121.424 by revising 

paragraphs (a). (b), and (d) to read as 

follows: 

8 121.424 Pllotr: In)tkl, tnnrltkn, nd 

upgrrd. fllght tnlnlng. 

(a) Initial, tranrition, and upgrade 

training for pilotr must include flight 

training and practice in the maneuven 

and procedurer set forth in the 

certificate holder'r approved lowaltitude windshear flight train@ 

program and in Appendix E to thio part 

or applicable. 

(b) The maneuvers and procedures 

required by paragraph (a) of thio rection 

must be performed inflight except- 

(I) That windshear maneuven and 

procedures must be performed in a 

simulator in which the maneuven and 

procedures are rpecifically authorized to 

be accom lished and 

(2) To $e extent that certain other 

maneuvers and procedurer may be 

performed in an airplane rimulator, an 

appropriate training device, or a rtatic 

airplane as permitted in Appendix E to 

this part. 

training program include8 a coume of 

training utilizing an airplane rimulator 

under 8 121.m (c] and (d] of this part 

each pilot must ruccessfully complete 

(1) With respect to $ 121.-(c) of thio 

part- [i) Training and practice in the 

aimulator in at least all of the 

mapeuvers and procedurer ret forth in 

Appendix E to this part for initial flight 

training that are capable of being 

performed in an airplane rimulator 

without a visual rystem; and 

(ii) A flight check in the simulator or 

the airplane to the level of proficiency of 

a pilot in command or recond in 

command. as applicable, in at leart the 

maneuvers and procedurer set forth in 

Appendix F to this part that are capable 

of being performed in an airplane 

simulator without a virual rystem. 

(2) With respect to 0 121.109(d) of thio 

part, training and practice in at least the 

maneuvers and procedurer ret forth in . the certificate holder'r approved lowaltitude windshear flight training 

program that are capable of being 

performed in an airplane rimulator in 

which the maneuvers and procedurer 

are specifically authorized. 

8. By amending $ 121.127 by revising 

the introductory text of waph (d)(l) 

to read ar follows: 

8121.427 -(nhlng. 

*e*** 

(d) If the certificate holder'r approved 

.e**. 

(d)' ' 

(1) For pilots, flight training in an 

approved rimulator in mapeuven and 

procedures ret forth in the certificate 

holder'r approved low-altitude 

windshear flight training program and 

flight training in maneuven and 

procedures ret forth in Appendix P to 

thio part, or in a flight training program 

approved by the Administrator, except 

as followe- 

***** 

9. By amending $ lZl.433 by reviring ' 

paragraph (c)(2) and adding a new 

paragraph (e] to read ar followr: 

il2l.W TnWng- **.e* 

(c) 

(2) For pilotr, a proficiency check a8 

provided in $ 121.441 of this part may be 

substituted for the recurrent flight 

training required by thio paragraph and 

the approved rimulator come of 

training under $ lZl.-(b) of thio part 

may be rubstituted for alternate periodr of recurrent flight training required in 

that airplane, except ar provided in 

paragraphs [d) and (e) of thio raction. 

*.*** 

(e) Notwithstanding paragraph8 (c)(2) 

and (d] of this rection, a pmficiency 

check ar provided in $ lZl.441 of this 

part may not be rubstituted for training 

in those maneuvem and procedurer set 

forth in a certificate holder'r approved 

low-altitude windshear flight training 

program when the t program ir included 

in a recurrent flight training coume ar 

required by $ 121.40D(d] of this part. 

10. By amending Part IZl, Appendix E 

by revising the hnt paragraph to read ar 

follows: 

Apl#ndixE--Fl%bt'zhining 

ROqUhUMUItr 

. 

The maneuven and procedures 

required by 0 lZl.424 of this part for 

Llot initial, transition. and upgrade ii ight training meet forth in the 

certificate holder'r approved lowaltitude windrhear hght training 

program and in thio appendix and must 

be performed idght except that 

windrhear maneuven and procedure8 

must be performed in an ahplane 

simulator in which the maneuven and 

rocedurer are rpecifically authorized to 

le accomplished and except to the 

extent that certain other maneuvers and 

procedurer may be performed in an 

airplane rimulator with a virual ryrtem 

(virual rimulator), an airplane rimulator 

without a visual ryrtem (nonvisual 

rimulator), a training device, or a rtatic 

airplane ar indicated by the appropriate 

rymbol in the respective column 

opposite the maneuver or procedure. .**.e 

55 

MRT 135-AIR TAXI OPERATORS 

AND COMMERCIAL OPERATORS 

wntinuer to read as followr: 

through 1431, and 1502: 49 U.S.C. loe(g) 

(Revbed Pub. L 9749. January l2 1883). 

12. By revising 8 135.10 to read 80 

follows: 

9 135.10 compllmnw drtm tor #rbln 

mhs. 

bolder may use a person ar a flight 

crewmember des8 that person has 

completed the windshear pund 

lraining required by $ $ 135.345(b)(6) and 

¶35.351(b)(2) of this part. 

13. By amending $ 135.293 by revising 

paragraph (a)(7) to read a8 followr: 

tls5.283 wtblnd~plot

c.q- 

(a)* 

(7) Rocedurer foe 

(i) Recogniziq and avoiding revere 

weather dtuationr; 

(ii) Eecaping from revere weather 

dtuationr, in care of inadvertent 

encountem, includuq low-altitude 

windshear (except that rotomaft pilots 

art not required to be terted on ercaping 

hm low-altitude windrhear); and 

(iii) Operating in or near 

thundemtormr (includmg best 

penetrating altitudes), turbulent air 

(including clear air turbulence), icing. 

hail, and other potentially hazardous 

meteorological conditions; and 

11. The authority citation for Part 135 

Aulborlty 49 U.S.C. 135h(r). lSS(r). 142l 

After January 21e81, no certificate 

...*e 

14. By amending $135.345 by revising 

paragraph (b)(S) to read a8 follows: 

81S5.345 WdrhJtY-nd 

Ww-QroUndtnwng. 

(b)' (e) Procedures for- 

(i) Recognizing and avoiding revere 

weather situations; 

(ii) Escaping from revere weather 

situations. in case of inadvertent 

encounters, including low-altitude 

windshear (except that rotorcraft pilots 

ut not required to be trained in 

ercaping from low-altitude windshear): 

and 

(iii) Opera- in or near 

thunderstorms (including beet 

penetrating altitudes). turbulent air 

(including clear air turbulence), idng. 

hail, and other potentially hazardous 

meteorological conditions; 

PusIpaph (b)(2) to read ar follows: 

..e.* 

..*** 

15. By amending 8 135.351 by reviring 
376W Federal Rester I Vol. 53, No. 187 / Tuerday, September 27, 1988 / Rdei and Regulations 

4 135.351 Recurrent lmhLnq o.... 

@I' 

(2) Instruction as necesrey in h 

subjects required fa initial pund 

training by this rubpah aa appropriate, 

including low-altitude winbhear 

training as preruibed In I 1,35315 of Lhir 

part and emergency training. 

22.loBa '. ..... 

Issued in Washington. DC. on September 

T. Ahn McMor, 

A dminislmbr. 

[FR Doc 8&22068 Fikd 0-W 49 pnj 

PLUQmMmTtM 

. 

56 
Session I. Airborne-Terms of Reference 

c 

Flight Experience with Wind Shear Detection 

Terry Zweifel, Honeywell/Sperry t I 

57 
NASA 

SECOND COMBINED MANUFACTURERS' AND TECHNOLOGY 

AIRBORNE WINDSHEAR REVIEW MEETING 

OCTOBER 18 - 20, 1988 

WILLIAMSBURG, VIRGINIA 

FLIGHT EXPERIENCE 

WITH WINDSHEAR DETECTION 

PRESENTED BY: 

TERRY ZWEIFEL 

HONEYWELL INC. 

SPERRY COMMERCIAL FLIGHT SYSTEMS GROUP 

PHOENIX, ARIZONA 
FLIGHT EXPERIENCE WITH N91' 11 684 .4 WINDSHEAR DETECTION 

Terry Zweifel 

Honeywell Corporation 

Phoenix, Arizona 

P 

ABSTRACT 

Windshear alerts resulting from the Honeywell Windshear 

Detection and Guidance System are presented based on data from 

approximately 248,000 revenue flights at Piedmont Airlines. 

The data indicate that the detection system provides a 

significant benefit to the flight crew of the aircraft. In 

addition, nuisance and false alerts were found to occur at an 

acceptably low rate to maintain flight crew confidence in the 

system. 

which shows the maximum and minimum windshear magnitudes 

recorded for a representative number of flights in February, 

1987. The effect of the boundary layer of a steady state wind 

is also discussed. 

Data from a digital flight recorder is also presented 

INTRODUCTION 

The Honeywell Corporation has developed a Windshear 

Detection and Guidance System which is currently in use by 

Piedmont Airlines on their Boeing 737-200 aircraft fleet. 

The detection and guidance system consists of air data 

information, inertial sensors, and software algorithms 

resident in Honeywell's Performance Management System. 

Certification of the system by the Federal Aviation 

Administration consisted of two phases. The first phase was 

the certification of the detection portion of the system. 

This was accomplished in November 1985. The second phase was 

certification of the guidance algorithms, and was completed in 

December 1986. The partitioning of the certification was 

deliberate: by getting a detection system out in the field as 

quickly as possible, a substantial amount of data could be 

gathered in parallel with the design and development of the 

guidance control laws. Consequently, modifications and 

refinements to the detection algorithm could be, and were, 

made. 

The improved detection algorithm was released for service 

in September, 1986. Guidance algorithms were included during 

the first part of 1987. This paper presents an analysis of 

the detection algorithm performance during approximately 

248,000 flights. 

METHODS OF DATA GATHERING 

Three separate methods of dat-,a gathering were utilized 

during the evaluation: 

~ 1. Discrete and max/min parameter storage in non-volatile 

memory. 
DIGITAL FLIGHT RECORDER DATA 

2. Digital recording of 26 parameters in real time. 

3. Pilot reporting using a standardized form. 

The Windshear Detection and Guidance System has the 

capability of storing 49 internal parameters in non-volatile 

memory. Periodically, the data were read out by maintenance 

personnel servicing the aircraft. These data were primarily 

used in the early stages of algorithm evaluation to modify and 

refine the detection software. While the data are still 

recorded, it is an overwhelming logistics task to read and 

record data from a fleet of 62 aircraft. The data is also 

necessarily limited to one-time reading of digital data words; 

that is, only parameters for a unique aircraft state can be 

stored with no time variance. This scheme also suffered from 

the possibility of human error in reading and recording the 

data. 

The preferable method of retrieving data is through a 

digital flight recorder capable of recording data at a one 

second rate. This scheme was used on all the certification 

flights, and is currently used aboard one aircraft. A total 

of 26 parameters, including relevant aircraft data such as 

speed, altitude and pitch angle, are recorded during the time 

the Windshear Detection and Guidance System is active 

(takeoff, landing approach, and go around). The data are 

useful in deriving peak g-levels (energy rates) of windshear 

that the aircraft experiences as well as confirming proper 

algorithm performance. Ideally, one would like such a 

recorder on all aircraft. Unfortunately, this is not very 

practical. Aside from the economics of equipping all aircraft 

with such a recorder, the data analysis of a large number of 

flights would tax the resources of even a large engineering 

department. 

The third source of data relies on pilot reporting of 

windshear alerts produced by the system. A sample form is 

shown in Figure 1. While parametric data is not available, it 

has the advantage of being a very direct measure of system 

acceptance by the flight crew. Other useful data includes the 

date and location of the occurrence, general weather 

conditions, and ATC advisories. The location of the 

occurrence is particularly meaningful since certain airports 

are known to have windshears produced by the surrounding 

terrain. Aside from not being able to determine the exact 

magnitude of the encountered windshear, one must also rely on 

a busy flight crew already encumbered by necessary paperwork 

to report system annunciations. 

. 

In order to assess the windshear environment, data from 

the digital flight recorder was compiled for 50 flights that 

occurred in early February, 1987. For each flight regime, i.e, 

62 
c 

A.. 

takeoff and landing approach, the maxima and minima windshear 

magnitudes were recorded. The data are essentially raw data 

with the exception of a one second low pass filter used to 

attenuate noise from the required differentiator. Figures 2 

and 3 illustrate typical time histories. 

experienced a significant windshear event. Even though 

relatively large values of windshear occurred, the windshear 

was not sustained long enough to seriously degrade the 

aircraft's performance and all flights proceeded routinely. 

Figures 4 through 7. Figures 4 and 5 illustrate longitudinal 

windshear magnitudes seen in landing approach and takeoff 

respectively. Figures 6 and 7 illustrate the encountered 

vertical winds measured in feet per second. While the landing 

approach data appears to be fairly Gaussian in nature, an 

examination of the takeoff data indicates a slight positive 

bias. 

A steady state wind will produce a boundary layer near the 

ground. As the magnitude of the wind in the boundary layer is 

a function of altitude, an effective windshear field is 

produced. Any aircraft flying though the boundary layer will 

experience a windshear. The magnitude of the shear 

experienced will be a function of the altitude rate of the 

aircraft. As most takeoffs and landing approaches are made 

into the prevailing wind, an aircraft on takeoff could 

experience a headwind shear while an aircraft on landing 

approach couLd experience a tailwind shear due to the boundary 

layer. Figures 8 and 9 illustrate the actual phenomenon. In 

Figure 8, the aircraft took off into a prevailing headwind 

while in Figure 9 a tailwind was present. In both cases, a 

high sensitivity detection system would have, and did, measure 

a windshear. The effect is most pronounced in takeoff since 

the altitude rate of the aircraft can be large. Most landing 

approaches are dclne at much lower altitude rates, typically 

-10 feet per second (-3 meters/sec). Consequently, one would 

expect the magnitude of the windshear caused by the boundary 

layer to be larger takeoff than in landing approach. It is 

this effect which causes the bias noted in the takeoff data. 

It should be pointed out that none of the flights 

A compendium of the data is presented in histogram form on 

RESULTS OF THE WINDSHEAR EVALUATION FORMS 

As of the time of this writing, approximately 248,000 

revenue flights have been flown with the latest 

configuration of the Honeywell Windshear Detection and 

Guidance System. Twelve Windshear Evaluation Forms indicating 

the occurrence of a windshear alert have been received from 

the flight crews. The results are tabulated in Table 1: 

63 

J 
TABLE 1 

WINDSHEAR ALERT DATA -- 

DATE 

11 Apr 87 

4 May 87 

6 Jun 87 

10 Jun 87 

28 Jun 87 

19 Jul 87 

9 Aug 87 

26 Aug 87 

29 Dec 87 

29 Dec 87 

23 Apr 88 

15 May 88 

AIRPORT 

Fayetteville, NC 

Dayton, OH 

Charleston, WV 

Baltimore, MD 

Charlotte, NC 

Charlotte, NC 

Orlando, FL 

Dallas, TX 

Charlotte, NC 

Roanoke, VA 

Buffalo, NY 

Dayton, OH 

FLIGHT 

REGIME 

Takeoff 

Landing 

Landing 

Landing 

Takeoff 

Landing 

Takeoff 

Takeoff 

Landing 

Landing 

Takeoff 

Landing 

ALERT 

TYPE 

Warning 

Warning 

Caution 

Warning 

Warning 

Warning 

Warning 

Warning 

Warning 

Warning 

Warning 

Warning 

ATC 

ALERT? 

No 

No 

No 

No 

No 

No 

No 

No 

Yes 

Yes 

Yes 

- 

The alert type in the table refers to whether the alert 

was for an increasing headwind or updraft, a caution alert, or 

for a decreasing tailwind or downdraft, a warning alert. The 

ATC alert column indicates whether the flight crew was advised 

by Air Traffic Control of potential windshears at the airport. 

The Federal Aviation Administration has defined windshear 

alerts as falling into three categories. The first is a valid 

alert wherein the windshear has seriously degraded the 

performance capability of the aircraft. The second is a 

nuisance alert where an actual windshear occurs, but its 

magnitude and duration are not sufficient to endanger the 

aircraft. The third category is the false alert where an 

alert occurs in the absence of a windshear condition. 

The alerts of 28 Jul 87 and 9 Aug 87 were false alerts 

caused by an undetected sensor failure and a computer failure 

respectively. Subsequent modifications to the built-in-test 

software should preclude reoccurrence. 

Of the remaining ten reports, six are valid alerts 

substantiated by the flight crew. At least four of these 

are believed to be microburst encounters: 4 May 87, 26 Aug 

87, 23 Apr 88, and 15 May 88. In all cases, the aircraft 

successfully exited the windshear using the Windshear 

Detection and Guidance System. 

The remaining four are classified in the nuisance 

category. Nuisance alerts can occur due to two causes: (a) 

terrain-induced shears, and (b) gusts of sufficient magnitude 

and duration to cause a relatively short-term performance 

loss. Two of the occurrences, 6 Jun 87 and 10 Jun 87 are 

believed to be the result of terrain-induced windshears as the 

airports are known to have such properties. The cause of the 

remaining two is believed to be TiJst-induced. 

Table 2 can be produced: 

Using a base of 248,000 fli?h:s and the data from Table 1, 

64 
c 

TABLE 2 

PROBABILITY OF WINDSHEAR ALERTS 

, L 

. 

I I EVENT PROBABILITY NUMBER IN X FLIGHTS 

(10-5) 

All Alerts 4.8 

Valid Alert 2.4 r Nuisance Alert 1.6 

False Alert 0.8 

1 in 20,667 

1 in 41,333 

1 in 62,000 

1 in 124,000 

Figure 10 illustrates the occurrence of windshears by 

calendar month. The two false alerts have been excluded. With 

the exception of the December data, the occurrence of an alert 

is most probable in the spring and summer months when 

thunderstorms are more prevalent. The data agree in general 

with the data from other microburst windshear studies where 

windshears were found to be most common in warm months. 

CONCLUSIONS 

The Honeywell Windshear Detection and Guidance System 

appears to provide timely windshear detection and, in at least 

two cases, has been credited by the flight crews as being Of 

great benefit in successfully exiting an encountered 

windshear. Overall statistics indicate a windshear alert will 

occur once in 20,667 flights. 

The occurrence of nuisance alerts, while acceptably low, 

is of some technical interest. To reduce nuisance alerts, 

sampling the atmosphere in terms of temperature and pressure 

may be needed. Such a sampling method could be used to compute 

the probability of a microburst and alter the detection 

algorithm threshold sensitivities accordingly. Studies are 

currently underway with both Piedmont and Delta airlines to 

assess the validity of such a method. 

already been accomplished that should reduce the 

probabilities even further. 

The number of false alerts is encouragingly low. Work has 

ACKNOWLEDGEMENTS 

The author would like to thank Piedmont Airlines and in 

particular Mr. Paul Gipson and Captain Jim Sifford for their 

cooperation in the development and testing of the Honeywell 

Windshear Detection and Guidance System and for making the 

data available that formed the basis of this paper. 

65 
This form 

act1 vated automatically. 

be ConQletad any tlm a Wlndshear Cautlon or Warning advisory is 

DATE FLIGHT ACFT. NO. CAPTAIN 

AIRPORTS RUNWAY CLG/VIS / RVR WINOS 2 

TAKEOFF ALTITUDE 

FLAP SETTIN6 

LAND I NG ALTITUDE 

FLAP SETTING 

TYPE OF WARNING: 

CAUTION 

WARN1 NG 

WERE WINOSHEAR CONDITIONS REPORTED 

BY ATC? 

OP IN I ON : 

FALSE NU I SANCE VAL10 

APPROXIMATE LENGTH OF CAUfION/UARNING DURytTION 

_GENERAL WEATHER CONDITIONS: 

. 

MIL TO AVIONICS ENGINEERING - A245 1. 
c 

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0 

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0.1 

8.06 

8 

4.14 

W/S REVENUE SERVICE DATA 

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h 

0 

h 

0 

C 

W/S REVENUE SERVICE DATA 

0 0.1 0.8 0.0 -0.9 4.8 -0.1 

8& 

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W/S REVENUE SERVICE DATA 

U- ~ILNI~~ vma 

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W/S REVENUE SERVICE DATA 

69 
WINDS NEAR THE GROUND 

HEADWIND IN fT/SEC 

neuno 

10 20 30 40 0 

TAILWIND IN FT/SEC 

WINDSHEAR ALERTS BY MONTH 

70 
Session I. Airborne-Terms of Reference 

Interface Standards for Integrated Forward-Looking Predictive/Reactive Wind Shear Systems 

Mark McGlinchey, Honeywell/Sperry 

71 
, NASA 

SECOND COMBINED MANUFACTURERS ' AND TECHNOLOGY 

AIRBORNE WINDSHEAR REVIEW MEETING 

OCTOBER 18 - 20, 1988 

WILLIAMSBURG, VIRGINIA 

INTERFACE STANDARDS FOR INTEGRATED 

WINDSHEAR SYSTEMS 

FORWARD- LOOK1 NG/PREDI CTIVE/REACTIVE 

PRESENTED BY: 

MARK M. MCGLINCHEY 

HONEYWELL INC. 

SPERRY COMMERCIAL FLIGHT SYSTEMS GROUP 

PHOENIX, ARIZONA 

SLIDE NO. 1 
INTERFACE STANDARDS FOR INTEGRATED 

YINDSHEAR SYSTEMS 

FORUARD- LOOKING/PREDI CTIVE/REACT IVE 

J 

P9 

Forward-looking windshear systems are developing to a point (particularly the 

infrared sensors) where their interface with the cockpit and reactive windshear 

systems needs to be defined. As airlines retrofit their aircraft with reactive 

windshear systems, it is important that we recognize that onboard windshear systems 

of the future will be a combination of both forward-looking and reactive elements. 

Today's reactive systems need to be built with the capability to interface to the 

forward-looking systems of tomorrow. This presentation is a first step at looking 

at the requirements and defining interface standards for integrated forward-looking 

and reactive windshear systems. Undoubtedly the requirements for interfacing these 

types of windshear systems will change as the technology changes. 

2.0 PFFINITIONS 

It is important that we comunicate from a c0rmK)n baseline. Therefore, 

definitions shown on Slide No. 2 will be used throughout this presentation. 

important points to remember are: 

the 

he 

1) Each type of windshear system performs a different task. 

1 ookina svste ms are different from predictive svste mq which are different from 

react ive svstemi. 

Therefore, forward2) The caution and warning alerts are always controlled by the reactive system. 

Looking at the best failure modes for the total (forward-looking, predictive, 

and reactive) system, the forward or predictive systems should not operate 

without a reactive system. Yet, the reactive system must operate without the 

fornard or predictive systems. 

3.0 BLOC K DIAGRAM 

What discussion of interfaces would be complete without the block diagram. As 

can be seen in Slide No. 3, the predictive and reactive systems can be combined into 

one LRU. Predictive elements (sensors and algorithms) can be readily incorporated 

into the reactive systems without the need for separate dedicated sensors or LRUs. 

The fomard-looking and reactive/predictive systems will comnunicate over standard 

ARINC 429 data busses. The reactive/predictive system will supply the forwardlooking system with data to help it perform it's function. The forward-looking 

system will then supply the reactive/predictive system with data to activate the 

alerts or perform some precise threshold adjustment. 

allows the flight crew to see the position of the event relative to the aircraft 

position or to display additional data (winds) concerning the event. It is foreseen 

that this would only be used by the flight crew when the aircraft was not in takeoff 

roll , takeoff, approach, or go-around. 

The forward-looking system will interface to a situational display which 

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The dedicated digital flight recorder is shown to emphasize the need for a 

recorder interface which will be used in the certification of any of the three 

(reactive, predictive, or forward-looking) windshear systems. 

as part of the development process and flight test of the forward-looking system 

would be used to demonstrate the nuisance characteristics and possibly the 

determination of Val id windshear detections. 

Data that is gathered 

1 4.0 ANNUNCIATION OPTIONS 

Now that we have integrated the systems in the aircraft we need to define and 

provide the proper annunciations to the flight crew. Current reactive annunciations 

(as defined in AC25-12) are indicated on Slide No. 4. If we extend this philosophy 

of flashing amber meaning headwind or updraft (unstable air), then a steady (steady because it's predictive) amber could also wan a detected unstable aimass. Note 

that this is only valid in approach and although the annunciation activation occurs 

once a minimum landing configuration is selected, the predictive system is gathering 

data throughout the entire descent profile. 

only the cold downflow (decreasing performance), while the DOPPLER or LIDAR can 

detect only the outflows (increasing and decreasing performance) we can simplify and 

determine that if any type of forward-looking system has detected a decreasing 

performance shear and the aircraft is in a potentially low energy state (takeoff 

roll, takeoff, approach, or go-around) then the action is the same as if the 

reactive system had detected the shear, ie., activate the flashing red warning lamps 

along with the windshear aural warning annunciation. 

Fomard-looking systems are a bit harder to categorize. Since the IR detects 

It is recognized that other options are open. The type of information 

displayed on a situational display when the aircraft is outside of the low energy 

state, such as outside the outer marker or as a clear air turbulence indication are 

examples. These displays are separate and independent of the interface to the 

reactive system. 

I 5.0 DATA BUS PARAMETERS 

Slide No. 5 defines the types of data the reactive system has access to and 

should be sent to the forward-looking system to simplify its interface to the 

aircraft. The forward-looking system would use these inputs to perform scanning 

stabilization, sensor cross check, and mode transition, thereby allowing the two 

systems to work together. 

Slide No. 6 defines the typical data that is available from a fomard-looking 

system that could be sent to the reactive system. 

level would be used to activate the red warning alert. 

The hazard index or intensity . 

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Session II. Airborne-Hazard Definition 
Session 11. Airborne-Hazard Definition 

c 

b 

Heavy Rain Effects on Air lane Performance 

R. E. Dunham, Jr., G. M. % ezos, and B. A. Campbell, NASA LaRC 

W. D. Mace, Jr., PRCKentron Inc. 

W. E. Melson, Jr., Wallops Flight Facility 
d HEAVY RAIN EFFECTS ON AIRPLANE PERFORMANCE 

R. E. Dunham. Jr., G. M. Bezos, and B. A. Campbell 

NASA Langley Research Center 

Hampton, VA 23665 

W. D. Mace, Jr. 

PRC/Kentron Inc. 

Hampton, VA 23665 

and 

W. E. Melson, Jr. 

Wallops Flight Facility 

Wallops Island, VA 23337 

ABSTRACT 

The objective of this activity is to determine if the aerodynamic 

characteristics of an airplane are altered while flying in the rain. 

Wind-tunnel tests conducted at the NASA Langley Research Center 

(LaRC) have shown losses in maximum lift, reduction in stall angle, 

and increases in drag when a wing is placed in a simulated rain 

spray. For these tests the water spray concentration used 

represented a very heavy rainfall. 

laws for aerodynamic testing in a two-phase, two-component flow 

makes interpolation of the wind-tunnel test uncertain. 

The large-scale wing is mounted on top of the Aircraft Landing 

Dynamics Facility (ALDF) carriage. This carriage (which is 70-foot 

long, 30-foot wide, and 30-foot high) is propelled with the wing 

model attached down a 3000-foot long test track by a water jet at 

speeds of up to 170 knots. A simulated rain spray system has been 

installed along 500 foot of the tests track and can simulate rain falls 

from 2 to 40 inches/hour. Operational checks are underway and the 

initial tests should be completed by the Fall of 1989. 

A lack of definition of the scaling 

Tests of a large-scale wing are to be conducted at the LaRC. 
88 

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101 
c 

Session 11. Airborne-Hazard Definition 

A Proposed Definition for a Pitch Attitude Target €or the Microburst 

Escape Maneuver 

Richard S. Bray, NASA ARC 
c 

N9 1-11 687 J 

A PROPOSED DEFINITION FOR A PITCH ATlTI'UDE TARGET 

FOR THE MICROBURST ESCAPE MANEUVER 

Richard S Bray 

NASA Ames Research Center 

Moffett Field, California 

SUMMARY 

The Windshear Training Aid promulgated by the FAA defines the practical recovery 

maneuver following a microburst encounter as application of maximum thrust accompanied 

by rotation to an aircraft-specific target pitch attitude. In search of a simple method of 

determining this target, appropriate to a variety of aircraft types, a computer simulation was 

used to explore the suitability of a pitch target equal in numerical value to that of the angle of 

attack associated with stall warning. For the configurations and critical microburst shears 

simulated, this pitch target was demonstrated to be close to optimum. 

BACKGROUND 

In January , 1987, the FAA released the Windshear Training Aid (reference l), a package of 

documentation and visual materials defining procedures and contents of a recommended 

training course for pilots on the subject of microburst wind shear. The primary target of this 

effort was the civil air-transport community, and the material was derived and presented in 

the context of the operation of large jet transport aircraft. While most of the extensive 

educational material contained in the documents was not aircraft-specific in nature, those 

sections dealing with escape from microburst encounters, and especially the simulator 

training programs, specifically considered the B-727 aircraft. 

It is recommended in Reference 1 that, upon recognition of encounter with a severe wind 

shear, the pilot should command full thrust and mate the aimaft to a specified target pitch 

attitude. In the supporting documentation, the procedure used in defining this pitch target for 

the B-727 is described. The process consisted of determining the attitude that resulted in 

survival in the strongest shear, with a minimum exposure to a stall-warning angle-of-attack 

condition. This was accomplished with the use of a mathematical model of the aircraft in 

computations of trajectories resulting from various pitch attitudes. The selected value, 15 

degrees, was not described as related to any other aircraft-specific measure. More recently, 

Lockheed, using a similar approach, developed the recommendation that a pitch target of 17 

degrees be used in the case of the LlOl 1 aircraft. The documents imply that this same 

procedure be used for developing escape procedures for each aircraft type and model. The 

following paragraphs propose and discuss examination of a simpler pitch target definition 

that might be applied to my aircraft configuration. 

THE PREMISE 

It is noted that the pitch targets chosen for the B-727 and the LlOl 1 crudely approximate the 

numerical values of the angles-of-attack associated with the activation of their stick-shaker 

stall warning systems. It is also noted that if it can be assumed that extended areas of strong 

downdraft cannot exist near the ground, even in a microburst, an aircraft cannot descend 

rapidly into the ground before experiencing stall warning if its pitch attitude is at or above the 

numerical value of stall-warning angle of attack. (Flight path angle = pitch angle minus angle 
of attack). This paper reports an examination of the premise that a pitch target, effective for 

a range of aircraft characteristics, is represented by the numerical value of the stall-warning 

angle of attack. 

PROCEDURE 

The dynamic performance characteristics of three generic aircraft were defined for take-off 

and approach configurations in terms of wing loading, W/S, thrust-to-mass, T/m, and lift 

and drag. After establishing initial conditions, and defining pitch attitude and thrust for the 

recovery maneuver, the models were "flown" through a modelled microburst wind field 

using various pitch attitude targets in a procedure similar to that used in support of the 

Windshear Training Aid. When stall-warning angle of attack was encountered, pitch was 

reduced to avoid significant increase of angle of attack beyond that value. Details of the 

method of trajectory computation are included in Reference 2. 

For each configuration, a microburst intensity was chosen that resulted in a marginal 

recoveiy using the "stall-warning angle of attack" pitch target. In the same microburst, 

trajectories were computed for lesser and greater recovery pitch attitudes, and the relative 

success, in terms of ground clearance and time near stall, were noted. 

AIRCRAFT CONFIGURATIONS 

Chosen for study were generic configurations representative of three categories of aircraft; a 

large, high-wing-loading jet transport incorporating high-lift leading edge slats; a jet-powered 

configuration of lower wing loading without leading-edge devices, and a turboprop-powered 

configuration, also without leading-edge devices. These latter two might be considered 

representative of some business jets and turboprop commuter aircraft respectively. The three 

aircraft were assumed to be twin-engined configurations, and they were not considered to be 

operating at full maximum gross weight; thus, they possessed large performance margins to 

help them recover from shear encounters. No special effort was made to exactly match the 

performance margins of these models because (1) they represented categories of aircraft that 

experience quite different operational situations, and (2) it was not the primary intent of this 

work to study their relative performance in wind shear. The three aircraft will be referred to 

as heavy jet (HJ), light jet (LJ), and turboprop (TP). The aircraft are described in Table 1, 

and the maximum thrust characteristics, which vary with speed, are defined in Figure 1. 

MICROBURST MODEL 

The wind fields were defined by the computational microburst model described in 

Reference 2. The model describes an axially symmetric downdraft column that is 

converted to a radially divergent outflow near the ground plane. Below a specified altitude 

at which divergence begins, vertical velocity reduces exponentially to zero at ground level. 

Considering volumetric continuity, the resultant peak horizontal divergence velocities (near 

the circumference of the downdraft column) increase linearly with altitude increment below 

the specified altitude; thus,.the maximurndivergence of the winds, and the maximum shear 

gradient, occurs near the ground. No specific vortex flow is defined, and no smaller scale 

turbulence is included. The amplitude of the divergence can be increased by either 

increasing the diameter of the micoburst (holding gradient constant), or increasing the 

downdraft velocity (increasing gradient). For this work, the aircraft experiences winds as 

if it had flown directly through the center of the microburst. Basic characteristics of the 

microburst winds encountered by the models in this exercise are listed in Table 2. 

106 

. 
INITIAL CONDITIONS 

The initial conditions for the start of the trajectory computations were somewhat arbitrarily 

chosen, as was the relative position of the modelled microburst. For take-off, the aircraft 

was assumed to be at 50 feet established in normal climb at a speed of V2+10 knots and just 

RESULTS AND DISCUSSICIN 

The results of a typical trajectory computations are shown for a take-off shear encounter with 

the HJ model in Figure 2, and for a discontinued approach with the same model in Figure 3, 

in which the important variables are plotted versus horizontal distance. Note that the data 

points represent one-second intervals. 

At the’initiation of the take-off calculations (Figure 2), the aircraft is assumed to be entering 

the microburst shear at its trimmed climb attitude of 22 degrees. After a four-second delay, 

in which a loss of 15 knots of airspeed occurs, pitch attitude is reduced to the pitch target of 

18 degrees. In the large shear gradient, speed continues to decay, and climb rate reduces to 

zero at an altitude of 335 ft. At this point, the aircraft is flying in a downdraft of 23 ft/sec. 

With continuing reduction in airspeed, angle of attack increases until stall warning is 

indicated at a value of 18 degrees. In response, pitch attitude is reduced to prevent angle of 

attack from increasing. After 4 seconds, the shear and downdraft end, and a rapid increase in 

airspeed begins. Over the next 6 seconds, recovery is made at a very low altitude at high 

angle of attack. As indicated earlier, the microburst severity was chosen to produce a 

marginal recovery with this pitch attitude target. 

Similar events are seen in the approach case illustrated in Figure 3. The recognition delay, 

together with delay in thrust response, result in only a temporary delay in further descent, 

and recovery again occurs as the shear ends lifter the aircraft has suffered a period of about 

six seconds at stall-warning angle of attack. 

Take-off trajectories: 

The take-off trajectories for the three configurations, at various pitch attitudes, are shown in 

figures 4 through 6. The behavior of the HJ configuration is shown in figure 4. For this 

case, the breadth of the microburst shear was set at 4200 feet, and the higher altitude 

downdraft velocity was set at 60 feevsecond. As was seen in Figure 2, for the pitch target of 

18 degrees, the total horizontal shear experienced was 145 fdsec (86 knots), and the 

the same microburst model configuration. It is seen that as the pitch target is increased to 21 

degrees, nearly the same recovery altitude results. A slightly higher peak altitude is reached, 

but the time at limit angle of attack, the pitch down and peak descent rate are greater. Data 

not included in the figure indicate that further increases in pitch target produce even less 

favorable results. As illustrated in the figure, reducing the pitch target to 15 degrees 

* maximum downdraft encountered was 23 ft/sec. The other trajectories reflect the effects of 

107 
produces the favorable effects of lower airspeed loss and less time at limit angle of attack, but 

the recovery altitude is lower. Further reduction of target attitude results in ground contact. 

The results for the W configuration a.6 shown in figure 5. In this case, stall-warning occurs 

at 12 degrees, and the operational pitch attitudes are generally lower than in the,previous 

model. Increasing the pitch target to 15 degrees results in an increase of 15 ft in recovery 

altitude, but at the expense of a considerably greater time at limit angle of attack, and a larger 

pitch-down to avoid stall. A pitch target of 9 degrees results in a recovery very close to the 

ground. 

The performances of the TP configuration are shown in figure 6. The stall warning is 

assumed to occur at 11 degrees. The microburst intensity is approximately the same as for 

the previous configurations. Speeds and peak altitudes reflect the lower operational speed of 

this lighter wing-loading aircraft. Again, varying the pitch target above or below 11 degrees 

does not result in a net improvement in recovery performance. 

Discontinued approach trajectories: 

The discontinued approach trajectories for the three configurations, at various pitch attitudes, 

are shown in ‘figures 7 through 9. The behavior of the HJ configuration is shown in figure 

7. For this case, the breadth of the microburst shear was set at 4400 feet, and the higher 

altitude downdraft velocity was again set at 60 ft/sec. As was seen in Figure 3, for the pitch 

target of 18 degrees, the total horizontal shear experienced was 135 ft/sec (80 knots), and the 

maximum downdraft encountered was 22 ft/sec. The other trajectories reflect the effects of 

the same microburst model configuration., An increase of the pitch target from 18 to 22 

degrees resulted in a failure to recover, while a decrease to 14 degrees produced a recovery 

altitude only slightly lower than that seen at 18 degrees while only approaching limit angle of 

attack. 

The performances of the W configuration, in the same winds, are shown in Figure 8. The 

effects of varying target pitch attitude are seen to be very much as those seen with the 

previous configuration. 

Performances for the TP configuration are shown in Figure 9. In this case, the stall-warning 

angle of attack is assumed to be 10 degrees. It is seen that reducing the pitch target to 8 

degrees results in about the same recovery altitude as produced by an attitude of 10 degrees, 

and again with slightly more favorable angle of attack and speed histories. On the other 

hand, increasing the attitude target to 13 degrees results in more adverse performance in all 

respects. 

The less adverse sensitivity to reduced pitch attitudes in the approach case is a result of the 

opportunity for the aircraft to exchange altitude for airspeed. It apparently does this more 

efficiently at slightly reduced attitudes As the encounter altitude is lowered, it is expected that 

the results would more resemble those of the take-off case, which exhibited reduced adverse 

sensitivity to increased pitch attitudes. 

CONCLUDING REMARKS 

In search of a simple method of determining a wind-shear recovery pitch-attitude target, 

appropriate to a variety of aircraft types, a computer simulation was used to explore the 

suitability of a pitch target equal in numerical value to that of the angle of attack associated 

108 
1 

I 

3 

with stall warning. In the case of encounter shortly after lift-off, recovery success was not 

adversely sensitive to small increases in target attitude above that proposed, but reductions in 

pitch target produced less than successful results. In the approach encounters, it was seen 

that the reverse trend prevailed. For the three aircraft configurations and the critical 

microburst shears simulated, the proposed pitch target was demonstrated to be close to 

optimum for both take-off and low-approach encounters. 

REFERENCES 

1. 

2. 

Windshear Training Aid, Federal Aviation Administration, Washington, D. C., 1987 

Bray, Richard S.: Aircraft Performance and Control in Downburst Wind Shear, 

Paper No. 861 698, SAE Aerospace Technology Conference, Long Beach, California, 

1986. 

1 09 
Table 1: Aircraft characteristics 

Pefini tions; 

A Angle-of-attack, deg 

CL Lift coefficient 

CD Drag coefficient 

UD Liftldrag ratio 

VREF 1.3*stall speed, knots 

v2 

WIS Wing loading, lb/ft2 

Minimum speed, second-segment climb, knots 

.. Charactenstics; 

H J: 

w: 

TP: 

HJ: 

LJ: 

TP: 

CL = CLo + 0.095*A - 0.000025*A3 

CD = cL/m 

LID = LID0 + 0.9*A - 0.055*A2 + 0.0007*A3 

LID = LIDO + 0.9*A - 0.07*A2 + 0.0005*A3P 

CL = Cb + O.lO*A - 0.000025*A3 

CD = CDO + O.O54*(CL - DELCLP + FCLT*(T/m) 

Take-off ADDroach 

0.25 0.50 

6.0 3.0 

CLO 

m0 w/s 110 90 

v2 152 

VREF 136 

Stall warning A = 18 deg 

0.25 0.50 

3.0 

CLO 

m0 6.0 

WIS 79 65 

v2 152 

VREF 136 

Stall warning A = 12 deg 

CLO 

CDO 

w/s 

v2 

VREF 

Stall warning A 

DELCL 

FCLT 

0.3 0.7 

0.05 0.14 

40 40 

110 

11 10 

110 

0.3 0.5 

0.02 0.03 

110 
Table 2: ,Microburst characteristics (based on model of reference 2) 

Diameter, 

' ft 

1J and LJ: 

Take-off 4200 

Approach 4400 

Take-off 4000 

TP: 

Approach 4000 

11 

10 

9 

8 

7 

6 

5 

Tlm.9 

FT/S EC/S EC 

Downdraft, Max. divergence, 

(above 1500') 

ft/sec knots 

I 

60 86 

60 80 

62.5 87 

60 74 

70 80 90 100 110 120 130 140 150 

AIRSPEED, KNOTS 

Figure 1. Variation with airspeed of acceleration due to thrust. 
PITCH 

ATTITUDE, 

ffi 

ANGLE 

CF 

ATTACK, 

ffi 

WIND 

VELOCITY, 

FT/SEC 

22 

20 

18 

16 

14 

12 

10 

20 

18 

16 

14 

12 

10 

8 

80 

60 

40 

20 

0 

-20 

-40 

-60 

-80 

. 

0 1 2 3 4 5 6 

DISTANCE, FT/lOOO 

7 8 

Figure 2. Performance of the HJ configuration in a take-off 

microburst encounter using a pitch target of 18 degrees. 

112 
180 

170 

160 

AIRSPEED, 5o 

140 

130 

120 

KNOTS 

ALTlTU D E, 

Fr 

350 

300 

250 

200 

150 

100 

50 

I I I I I I I I 

0 1 2 3 4 5 6 

DISTANCE, FT/lOOO 

7 8 

. 

Figure 2. -continued. 

113 
1 

1 

PITCH 

ATTITUDE, 1 

E1 

20 

18 

16 

14 

12 

10 

8 

6 

4 

ANGLE 

CF 

ATTACK, 

E33 

80 

60 

40 

20 

0 

-20 

-40 

-60 

-80 

1 I I I I 

WIND 

VELOCITY, 

FT/SEC 

0 1 2 3 4 5 

DISTANCE, FT/lOOO 

6 7 

Figure 3. Performance of the HJ configuration in a landing 

approach microburst encounter using a pitch attitude 

target of 18 degrees. 

. 

114 
I' 

T/m 

Fr/sEC/SEC 

IL 

AIRSPEED, 

m 

12 

10 

8 

6 

4 

2 

160 

150 

140 

130 

120 

110 

100 

400 

350 

' . 300 

ALTITUDEl 2 5 0 

200 

150 

100 

50 

0 1 2 3 4 5 6 7 

DISTANCE, FTAOOO 

Figure 3. -continued. 

115 
PITCH 

ATTITUDE, 

c%3 

ANGLE 

CF 

ATTACK, 

CBS 

AIRSPEED, 

K"Is 

22 

20 

18 

16 

14 

12 

10 

8 

6 

200 

180 

160 

140 

120 

100 

400 

350 

300 

250 

150 

ALTITUDE, 

100 

50 

0 

0 1 2 3 4 5 6 

DISTANCE, FT/lOOO 

7 8 

Figure 4. Performance of the HJ configuration in take-off 

micro bu rst encounters. 

116 
PITCH 

ATTITUDE, 

ffi 

ANGLE 

CF 

ATTACK, 

CEIj 

I I I I I I I I 

200 

190 

180 

170 

AIRSPEED, 160 

KNcns 150 

140 

130 

120 

1101 I I I 1 I I I I I 

ALTITUDE, 

FT 

8 

350 

300 

250 

200 

150 

100 

50 

0 

0 1 2 3 4 5 6 7 8 9 

DISTANCE, FTAOOO 

Figure 5. Performance of the LJ configuration in take-off 

microburst encounters. 

117 
PITCH 

ATTITUDE, 

ffi 

ANGLE 

CF 

ATTACK, 

OEIj 

AIRSPEED, 

KNOTS 

14 

1 3!.......!.......!.......-I 

> 

2’ I I I I I I 

12 

11 

10 

9 

8 

0 1 2 3 4 

DISTANCE, FT/lOOO 

5 6 

e 

Figure 6. Performance of the TP configuration in take-off 

microburst encounters. 

118 
PITCH 

ATTITUDE, 

cB(j 

ANGLE 

CF 

ATTACK, 

cB(j 

AIRSPEED, 

KNcrrs 

ALTITUDE, 

FT 

22 

20 

18 

16 

14 

12 

10 

8 

6 

44 I I I I I I I 

160 

150 

140 

130 

120 

110 

100 

90 

400 

300 

200 

100 

0 

I I I I I I I 

1 I - .--- HI 

'H-H-H * 

0 1 2 3 4 5 6 7 

DISTANCE. FT/lOOO 

Figure 7. Performance ot the HJ configuration in landing 

appoach microburst encounters. 

119 
PITCH 

ATTITUDE, 

ffi 

ANGLE 

CF 

AlTACK, 

ffi 

160 

150 

140 

AIRSPEED, 130 

KNOTS 120 

110 

100 

90 

ALTlTU DE, 

FT 

400 

350 

300 

250 

200 

150 

100 

50 

0 

0 1 2 3 4 5 6 7 

DISTANCE, FT/lOOO 

. 

. 

Figure 8. Performance of the LJ configuration in landing 

approach microburst encounters. 

120 
PITCH 

ATTITUDE, 

CEljl 

ANGLE 

CF 

ATTACK, 

cB3 

AIRSPEED, 

KN(TTs 

ALTITUDE, 

Fr 

I I I 

12 

10 

8 

6 

4 

2 

0 

TI 1 

400 

350 

300 

250 

200 

150 

100 

50 

0 

0 1 2 3 4 5 6 

DISTANCE, FT/lOOO 

Figure 9 Performance of the TP configuration in landing 

approach microburst encounters. 

121 
Session 11, Airborne-Hazard Definition 

11 July 1988 Weather and Resulting TDWR Alarms at Denver, Colorado 

Wayne Sand, NCAR 
11 July 1988 Weather and 

Resulting TD WR Alarms 

at Denver, Colorado 

Wayne Sand 

Research Applications Program 

National Center for Atmospheric Research 

Presented at: 

W illiamsburg, Virgina 

18-20 October 1988 
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11July 1988 Weather and 

TDWR Alarm Summary 

* This was a typical microburst day 

* Microburst possibilities were forecast 

* Sounding supported microburst potential 

1 Weak radar e.chos were present, about 35 dBZ at the 

start of the event 

I * Very light rain at the airport, dry microburst 

* Extremely strong event, both AV and divergence 

I * Event built rapidly, 0-80 kts in 6 minutes, normal 

for microbursts 

* All pilots were aware of microburst potential 

* All pilots were given microburst alarms 

* Alphanumeric alarms contained all the pertinent data, 

TDWR successfully detected the event in a timely manner 

* Geographic Situation Display very comprehensible and 

representative of complex data 

c 

, 

* GSD primarily available to supervisors \ 

158 
Session 11. Airborne-Hazard Definition 

Numerical Simulation of the Denver 11 July 1988 Microburst Storm 

Fred Proctor, MESO 

159 
W 

IL 

0 - 

Ia 

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177 
Session 11. Airborne-Hazard Definition 

J 

11 July, Denver Wind Shear Encounters 

Robert L. Ireland, United Arlines 
1 

Robert L. Ireland 

Unitd Airlines, Inc. 

Iknver, (30 80207 

On July 11, 1988, btwen 2207 and 2213 u1y: (16:07-16:13 MIX), four successive 

Unit4 flights had inadvertent encounters with microburst wi-rdshear conditions 

while on final apprcxiCi.1 to knver Stapleton Airport (DEN), wch rcsultirig in a 

rnissed approach, subsequent delay, and uneventful arrival. 4 fifth flight 

executed a miss4 app-oach without encountering the phenomena. 

damage to aircraft and no pssenqer injuries were incurrd. 

"inadvertent" is used within United Airlines' windshear training mterials and 

the FAA Windshear Training Aid to mnndte an encounter with windshear after 

vigilance and cautionary practices fail to identify and afford cmplete 

avoidance of the hazardous area. 

comprehensive investigation for scientific purposes in the study of windshear 

phenamenon is bei:ig conductel sepemtely under the guidance of the FAA with 

involvement and cooperation from United, NTSB, lrbtional Center for Atmspheric 

Research (NCAR), &PA, APA, Boeing, Buglas, and NASA. 

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c 

Questions and Answers for 18 October Sessions I and I1 
Questions and Answers 18 October 1988 

Mark, a question or two. One nice thing about questions at least you know the 

people were awake when they listened to you. Mr. Biake, I hope I pronounced that 

correctly, just a point of clarification you state that Doppler or Lidar can only detect 

out flows. This is not correct. Lidar systems, unlike Doppler systems which make 

* 

/?/Oil clutter can be used in an up and down angle pointing mode to resolve ’the 

vertical wind velocity component. So, with that, we go to Rev. A. Vertical wind. 

That’s what really what this was intending to do, was to promote discussion like that. 

Second question from Howard Long at Delta. Q: Should the warning from TDWR 

systems be transmitted to the cockpit and displayed through on board feactive systems? 

A: Currently, there is nothing defined to do that, capability exists in ACAR systems 

or possibly with TCAS COM CMCOM D, to do that type of work. You’d have to .. 

if you wanted to light the red light determine what magnitude, I guess of a detection 

that TDWR picked up to illuminate the red light. Maybe if we get into providing 

GSD type displays in the cockpit, this might be a subset of that, whereas the GSD, 

which is like the situational display would display the airport area and the events 

surrounding it, however, once it reached a certain magnitude, like the light in the 

cockpit, which would mandate a go around, that’s a possibility. Does that answer your 

question? Anything else? 

.? Earl Dunham, NASA LaRC. 

I have seven question, some of them have more than one part to them and I looked 

these questions over and I said they’re very good. There’s a couple of them I wish 
I knew the answer to. But let’s start with them and go through them as they come 

UP* 

-1 - Wayne Sand and he asked the question, “How about some of the other 

questions addressed by Jim Loors, such as the weight of water and the physics of why 

CL is decreased, are these valid questions.” Yes, they are valid questions as a way of 

background information, I’m sure you’re aware of it because you used Mr. Loors 

name. About 8 years ago, NASA had a contract with Jim Loors at the University of 

Dayton Research Institute and once he did a little analysis that said that if he 

considers all of the physics that he can think about and how rain would interact with 

an airplane light, it increases the weight of the airplane because there’s a water film 

on it. It increases the surface roughness which increases the skin friction on the 

airplane, changes the drag characteristics and he made his hypothesis that there were 

probably also some associated changes in lift performance. Well, his initial analysis 

is what started us down as an experimental program because we looked at what he 

did and says his argument are good, there may be something there, but there is no 

data available to us and so that’s what was the genesis of what we’re involved in right 

now, so yes, he did ask good questions. 

Ouestion 2 - Question by Joe Yasafi, Whqt is the expected affect of the inplate on the 

test result, that is the drainage of the surface in water turbulence and what have you? 

A It turns out that we have run wind tunnel tests on complete wing configurations 

if you like, finite aspect ratio air pull, we’ve run wind tunnel tests with inplates on the 

air pull and the particular test that we’re running on the large scale carriage, does 

have inplates on it. There’s one of these difficulties that there’s only a finite size 

structure you can place on this carriage and hope to run it down the track and not fly 

the carriage off of the track. The purpose of the inplate is to minimize the effects 

that we have by not using a full span wing. It’s an attempt by channeling the flow 

C 

192 
nice and straight down this little segment of wing that we have and basically, what you 

wind up doing is generating an affective larger aspect ratio wing. So, even though the 

wing span between those inplates is only about 14 feet, the wing cord is about 10 

feet, it effectively in terms of aspect ratio, looks like it’s a much bigger wing. The test 

criteria for doing this says we will have low wind conditions or we will attempt to 

make measurements in low wind conditions, I could share some of your concerns about 

the influence of water on the inplates itself. Most of these affects I think are going 

to be very near the end of the year for and not impact a major portion of the lift 

taking through the, say 80 or 90% of the span of this model that we have. It turns 

out, that what you would really like to have done was to put a 737 wing on top of this 

carriage and shoot it down. You get rid of all the problems of having to do this kind 

of modeling. Anyway I think it’s a pretty good aerodynamic approach to the situation. 

Any more comments about it? 

* 

3 

Question 3 - The question was asked about the mass flow of water coming down 

simulating rain, does it drag air with it and make a significant down flow velocity. It 

turns out that what we have tried to do in one little series of tests was to put an 

anemometer on the top of the spray rig and look at air being entrained as it came 

down and I hate to add, the anemometer didn’t even spin as I recall. There was no 

measurable affect. 

Question 4 - Jim Bull, Can you give the equivalence of rain water concentration, rain 

fall rate and millimeters an hour? For example, what did that number of 46 grams 

per cubic meter come out to in millimeters an hour? It’s about 1,000 millimeters an 

hour. It turns out that the meteorologist do have an equivalency between liquid water 

content and expected rain fall rate. It’s known as the Marshall-PaImer rain drop 

distribution that relates liquid water concentration to rainfall rate. It’s fairly standard 

and accepted especially amongst the meteorology community and the radar community 

.? 

193 
because radars are somewhat calibrated against liquid water concentration. It’s about 

this 46 grams per cubit meter. Now, there’s a problem when I make that statement. 

1) The Marshall Palmer rain drop distribution was developed in the 40’s and it has 

since been tested and reevaluated but most of the time, that measurement is made for 

fairly low rainfall environments and it sort of gets extrapolated up to high liquid water 

concentrations such as this, but using that standard, you would get about 1,000 

millimeters per hour. Is that really what you wanted to know? 

Q: I’m Jim Bull and I’d like to add the question have any standards been set as far 

as what aircraft can operate in as far as rain fall rate. A: Well that’s so to speak 

the final outcome of our program experiments and what have you. We don’t know. 

Q: Greg Solatola - MTSB. Earl, there’s kind of a rule of thumb relating rainfall rate 

to liquid water content, approximately your rainfall rate in inches per hour equals your 

liquid water content, For instance, 4 inches per hour equals 4 grams per cubic meter. 

40 inches per hour equal approximately 40 grams per cubic meter. 

A That’s true following the Marshall Palmer distribution which is really developed 

the rainfall rate and liquid water concentrations down around the 1 to 2 inch per hour 

stuff. You just extrapolate it on up and say well it applies on up here when it’s really 

hasn’t been established that it does. 

r“ 

194 
You ought to point out the difference between rates averaged over time as opposed 

to instantaneous rates. You might relate that little effort, that storm that came 

through the peninsula where you had your load cells operating. 

+ 

Ok, well, it gets us involved in another issue of the probability of occurrence of a given 

rain fall rate of occurring and exactly what are world record rain fall rates, the 

established world record is like 79 inches an hour. It’s an enormous rain fall rate and 

the statement that I usually make is you don’t expect that to last very long and it 

didn’t last very long. What you concern yourself with for our stuff and for the 

aerodynamics is the concentration of liquid water and the air mass that we’re flying 

through. Now, there is a relationship that you can relate that to rain fall rate but, I’m 

talking about a concentrated region in a storm where there might be divergence of 

water so that the water gets concentrated in one spot. It may not deposit that 

particular concentration on the ground. We have measured during a thunderstorm, 

rain fall rates in the neighborhood of 17-18 inches an hour, but that’s not what’s 

accumulated on the ground because that only occurred over about a 15 - 20 second 

increment. As a matter of fact, it got measured by the same calibration technique that 

I showed earlier, not the coffee can, which I found out was sweet potato cans, I don’t 

know how we got them, or where they came from, but anyway, it was measured with 

the little box that’s just time derivative of accumulation of water. 

. 

Norm Gable - Aerospace Consultants - Q: Earl, what are your drop size distributions 

look like and how do they compare with natural rain? A: Ok, what do you want to 

talk, wind tunnel or this thing? The car wash. Alright, the car wash. We are in the 

process of measuring those drop size distributions. We have done some photographic 

measurements of them and they basically look like natural rain at that rain fall rate. 

We’ve got large drops on them following the same sort of distribution. We got at 

least two more. 

1 

I 

195 
Greg Solatela - Q: Following the Southern 242 accident at New Hogue, Georgia in 

the late ~O’S, the NTSB recommended that the affects of rain on weather radar ray 

domes be determined. Has this been done? 

A Well, what we did was we stuck a ray dome in the wind tunnel, and we measured 

.. let me backtrack a little bit, the questions relates to is there enough of a water film 

and mass of water on a ray dome since that the weather radar doesn’t really penetrate 

out and see the hazards that are in front of it. With this particular accident, I think 

that they are suggesting that maybe the pilot didn’t see how severe the weather was 

a mile or so ahead of them because he had such intense water on the ray dome. OK, 

what we did do at NASA LaRC was to do a small experiment in which we took a ray 

dome, placed it in the wind tunnel in that spray environment that we did tests on 

wings, aerodynamic testing on wings, tried to measure the water film thickness on that 

ray dome and that very intense rainfall rate. Well, the test was somewhat inconclusive, 

the results indicated some very small water film thickness. There was some discussion 

about the size of the water drops that we were using, even though we had the right 

concentration of water, whether it really would have sheeted up on the ray dome in 

the proper fashion because we didn’t have the right size drops, because we used the 

full scale ray dome on them. We used the ray dome off of a T39 I think it was. So 

there were some questions about the way we scaled those tests in that result and then 

we saw some things in the testing that would lead us to believe that there’s .. the rain 

drops as they hit the ray dome splatter back out and there’s a certain mass of them 

that come up and get swept back in the boundary there and there’s sort of a fog layer 

standing off of the ray dome and the question was asked how does the radar 

propagate through that because it’s obviously had a very high concentration of water 

and even though the water film on the ray dome was small. We had decided at that 

time that what we really needed to do was a better job of scaling rain and the way 

r 

196 
we’re doing it is with an outdoor facility, and downstream in our test program is 

putting some sort of a ray dome on this test sled, doing some sort of a test that’s not 

clearly defined yet but it hasn’t been dropped and it is still being worked. 

* 

I’ve got four of them from Greg Ifel from Boeing - some of these are the easy ones. 

Q: How is speed measured on the sled? A Well that one’s pretty easy, all of our 

data are TM backed to a control room and part of the TM is just speed right off the 

carriages, just a tick every ten feet down the track. Just a magnetic pickup and every 

ten feet down the track there’s a little piece of metal and it’s ticking it off, coming 

back with a function of time and that gives you velocity. 

v 

Q: Is local area ambient wind measured and considered? 

A: And of course it is because we really want to get back from basic force 

measurements to aerodynamic lift and drag coefficients measurements, so we’re 

operating in an environment in which the wind is blowing so we do have to consider 

that. It does get cranked in to it, whenever we calculate the lift coefficient. For lots 

of reasons we said we want to do most of our testing at low wind conditions, pointly 

because of variability in wind, even if you take it into account. You’d have to measure 

all the way down the track on the carriage. 

Q: Am I checking the effect on air speed and angle of attack measuring systems. A: 

We did a series of tests, actually, Jim Lewis at University of Dayton Research Institute, 

did a series of tests in a little wind tunnel type facility that he had. There’s a report 

available on what he did in the use of standard .. there’s two types of angle of attack 

sensors in the industry. There’s a little turbo driven pressure nulling and there’s the 

flow vein. He used the flow vein, didn’t look at the pressure nulling device but on the 

197 
flow vein, he saw very little effects and angle of attack. Most of the operational air 

speed heads that you use are set up for water drainage and seem to have little effect 

on those. 

Q: Since the sled starts at 0 air speed with the wing at a fined angle of attack, how 

are aerodynamics hysteresis to be accounted for? 

A I would like to talk to you a little bit more about that particular question. I’m not 

so sure I really fully understand it. My impression was that for this type of air flow, 

the hysteresis is very small, really only near CL mac and we probably wouldn’t see it 

in the type of testing that we’re doing. I’m aware of some work that was done by Dr. 

Jim Marchman at DTI, when he was looking at the hysteresis effect in and out of rain 

on an air flow, but he was looking at a laminar air flow, which has a pretty large 

aerodynamics hysteresis in it. I wasn’t aware with a leading edge slap, pretty turbulent 

flow air foil that I would need to consider that type but maybe you and I ought to talk 

about that a little bit later. 

Q: If you’ll consider the problem analogous to say the gust, indicial gust response, 

who was the guy that asked the question, if you consider the problem similar to that 

of a indicial response of an air foil that is starting out at 0 angle of attack, you look 

at the classic solutions by cord lengths. You’re practically up 90 percent of steady 

state. You go to 10 cord lengths, you know it is very close to steady state. So how 

many cord of lengths do you run before you hit the rain, Earl? A: 40 or 50. Q: 

Now, how long is your run through the shower? A: It’s 500 ft. Q: So there are a 

considerable number of cord lengths elapsed. It’s not an exact answer because nobody 

really knows what the hysteresis is on this thing, but we talked about this and thought 

about this in designing this system and by very crude analogy, it’s 10 times bigger than 

in the drive case, so it should be very close to steady state. It’s the best we can do. 

198 

I 
Yea but ... I need to talk to you because I thought about that too Norman, in light 

of the transient analysis that we had done and looked at and also we’ve done some 

wind tunnel tests where we instantaneously turned the rain on, we instantaneously 

turned it off, looked at that. That’s a time dependent characteristic. Hysteresis is not 

necessarily a time dependant phenomena. It’s going to a state coming back and the 

path you took back. So I am aware of it for laminar flow air foil but one way after 

this, and 1 don’t think really it’s a problem, but you and I, I think should talk about 

this a little bit. 

Don McClear, Boeing - Q: (tape difficulty) .... under a fixed angle of attack, an 

equilibrium lift for example, shoot in the ride. A I have no difficulty with the 

transient effect. I think we’ve got enough run down the track, wet versus dry and 

what we’ve seen in the data, we do have the steady state value. There’s no problem 

with that. That hysteresis one is .. As I understand it, the second question you’re 

asking is if you change the angle of attack in the heavy rain, is that a unique angle of 

attack dependency L, or does it depend on past history. Is there a real issue there? 

I don’t think there is. I think we have enough test track, enough time running in the 

rain that it’s not really a problem. I would worry about it if I had a laminar flow air 

foil, because .. I think I need to Greg a little bit. That’s one of the one’s I had a hard 

time answering. 

Don Bapin - I’d like to expand on that third question up there. Has anyone 

considered the implications on the pilot training aides and so on and also on the 

guidance, if the results from your tests and experiments sort of like the wind tunnel, 

the lift from the drop (tape difficulty, various individuals speaking, not audible) A: 

that’s the purpose of why we’re doing the tests. That’s what the interpretation of the 

wind tunnel results are. That’s the way, if you just look at is and say, hey this is 

what’s going to happen, based on that wind tunnel test. What I tried to allude to, you 
know, is that interpretation is based on some scaling laws that hasn’t been established 

with regard to this type of testing, so we have to do large scale tests. If the large 

scale test comes out like the wind tunnel test, then we have a problem I guess and 

what you tell someone to do in a wind shear environment if he’s getting wet at the 

same time, then the question comes up that like one of the other ones that I’ve got 

on here, how wet is he getting at the time you have to be able you’ll have to be 

telling him that. I’ve got another question .. Say Earl, before you go on, I have one 

more question briefly again. This thing is really intermittent. Q: Maybe I 

misunderstood, are the inplates actually connected to your wing section, A: No, they’re 

free floating. Q: So there not part of your balance measurement. A: No. 

Q: These are the last two questions I had and top one is regarding Delta flight 191 

accident data, a sharp wing drop was recorded at an angle of attack much less than 

stalled, has this event been correlated with the aircraft that gets exposure to heavy 

rain. A I’m going to call a little bit on Dick Gray and I know he worked real closely 

in this particular accident and looking at the record, I looked at them too and I set 

down and I talked with Dick. It turns out that my .. as I recollect, the pilot did not 

stay very long at a very high angle of attack from that data, and I’m not so sure that 

even when he was at the high angle of attack that correlated with the region when 

they said he was in heavy rain. We looked at that data set hoping we could learn 

something from it as a sense of a full scale test and it turns out that the angle of 

attack that he stayed at were very low and remember the curve and data that 1 

showed you, you would not have seen much in effect at the lower angles of attack. 

The wing drop .. Dick do you remember when that occurred with respect with the rain 

and was there something else going on at the same time. The questions that’s being 

asked and let me repeat it for you because I’m sure you can’t see it from the back. 

. 

4 

200 
A 

. It says regarding the Delta flight 191 accident, a sharp wing drop was recorded at an 

angle of attack much less than stalled. Has this event been correlated with the 

aircraft’s exposure to heavy rain. I would say, based on our data, if it were much less 

than stalled, we probably wouldn’t have seen much a change or change in lift in one 

wing or either wing. The question, I guess, if you can help us out was do you recall 

the wing drop, when did it occur? So basically the answer is that they think that most 

of the motions were wind generated. 

-T 

Howard Long ’- Delta Airlines. I’ve looked at that also very closely, and in that area 

and from a pilot point of view, what I see happening right at that point is that the guy 

has encountered the center of a vortex and it’s trying to roll the airplane to the right 

very violently. The control forces that were put in at that point were pull controls to 

the left for 2 full seconds. The effect that you’re doing there is that you have 

destroyed all the lift or as much as you could off the left wing to keep the thing from 

rolling upside down, the right wing is in the down draft part of the microburst or part 

of the vortex, and so you have effectively taken away a lift from both sides of the 

airplane at the same point, thusly, the nose will start to come down. No body thinks 

it was rain related. I think that’s the basic answer to that. And the last one is from 

Bob here is, Q: Can you relate liquid water concentration to radar return, can you 

correlate color weather radar returns with lift loss or reduction in stall speed. A: 

Well, basically, color weather radars do contour which means they are looking at the 

concentration of liquid water in front of them and so yes, color weather radars are 

correlated with liquid water concentration. The purpose of our test for these large 

scale data is to do that correlation between stall speed reduction in lift with liquid 

water concentration. This Q: is just as a matter of reference, the liquid water 

contents that you were using up to 46 grams per cubic meter, are those already a long 

ways into the red region in a color weather radar return or we looking at anything 

20 1 
pilots might be flying into. 

probably folded over a few times so to speak. 

A It would definitely be well into the red region, 

Bill Briar Q: Can you put the picture of the sled back, please for just a second, I 

have a dumb question to ask. Is there leading edge equipment on that wing? A It’s 

a fallot double slotted flap. As I said, if you just cut a section right out of the L 1011 

wing, it looks a lot like it. 

f 

First question from Wayne Sands, Q: Do you see any evidence of pulsing of the 

microburst velocities in the model? A: No, I have not. I guess I would like to ask 

Wayne, what if he has seen this on what scales would you usually see this. What’s the 

horizontal scales. The reason I would ask this, is because with this model that I am 

using, this particular run, we used a grid size of 200 meters meaning that in order to 

resolve the pulsing if it existed, it would have to be on a scale of at least 400 meters 

or more, so do you have any ideas? 

Q: The different microburst are not visible in plain view? Can you point them out? 

You are referring to the simulated microburst. A: First, at 47 minutes there was 

some smaller weaker microburst, I think you can see it up in this region and this was 

prior to the very intense ones, and somewhat latter, at a later time, you can, of course 

this was the more intense one in the simulation, there was also another one here and 

there was one beginning to form in this region. Actually these two here, coalesce 

together and about four minutes later, you get something that looks like this because 

they expand into macroburst. So Wayne, does that answer your question? 

A 

202 
Q: Also by Wayne Sands. The dual doppler plot of the Denver micro burst seemed 

more asymmetrical than the wind fields generated by the model. Please discuss. Q: 

Well first, I would start off asking the question to Wayne, what elevation are you 

looking at and what’s your beam width at that particular point. A: We’re just looking 

at the low level tilt and it’s a one degree beam width, it’s a few hundred meters off 

the ground like 300 or thereabout, I might defer to Jim Evans for the number, but 

that’s the right order. So, you would say somewhere from 200 to 300 meters. Well, 

the reason I ask that is because as you go up in elevation, not only in this case but 

in other cases that I have seen, the flow tends to become more asymmetric. The 

microburst from other simulation that I’ve seen also appear to have the most 

symmetrical qualities at my lowest level, and this level as you can see is 80 meters 

off the ground. But, as you were to go up in elevation, it would appear more 

asymmetrical, part of that being due to the depths of the out flow are somewhat 

deeper in certain areas and the veIocities may be more intense on certain sides so you 

will see this. Unfortunately, I don’t have any plots with me of the outflow at 200 and 

300 meters but there are differences. Too, I’ll point out this is the elevation where 

we do tend to see the most intense out flow speed anywhere in between say, 50 

meters off the ground to about 100 meters above the ground for microburst. 

D 

# 

A 

Q: Question from an unknown author. There were a number of microburst in the 

area, prior to and following the simulation. These did not show surface winds greater 

than 20 meters per second, yet presumably, had the same sounding environment. Q: 

How would this difference between microburst emerge from the simulation? A Well 

first of all, I would say, there probably is a lot of differences in the environment as 

you would go across the area. Now, what I have used to initialize my simulation was 

a modification of the 202 Denver sounding, I modified it to agree in the barrender 

layer with the observed 222 Denver temperature or temperature just prior to 222 it 

was about that time. Now, I haven’t done any kind of sensitivities studies on say, what 

203 
would happen if the temperature or the moisture in the boundary layer was a little bit 

different. Now, that could certainly affect the intensity of the storm, or the structure 

of the storm. And when I did run this simulation, I was a bit concerned also with 

using the winds from the 202 sounding which was 2 hours prior to the event. In other 

words, if there were some slight changes in the winds, they certainly could have 

affected the structure of the actual storm, versus that of the simulated storm. But, I 

think you have to keep in mind that this is not a replication of an observed event, 

although, I think we’re simulating a lot of the features very well. Don’t look at it as 

an embedded mesh forecast of the Denver area. I think that may have answered the 

second question. Oh, the second question, how have you compared the simulation 

results with radar measurements. Today, was the first day that I’ve seen any of the 

observations so I haven’t compared anything yet. Does anyone have anything else? 

Meeting concluded 113 Oct 88. 

204 
TECHNICAL PRESENTATIONS 

Wednesday, 19 October 1988 

. 

PReEDING PAGE BLANK NOT FILMED 
, 

4 

Session I. Airborne-Sensors 
Session I. Airborne-Sensors 

Airborne Doppler Radar Detection of Low Altitude Wind Shear 

E. M. Bracalente and W. R. Jones, NASA LaRC 

Charles L. Britt, RTI 
AIRBORN3 DOPPLER RADAR 

DETECTION OF LOW ALTITUDE 

WINDS HE^ 

Emedio M. Bracalente, William R. Jones 

NASA Langley Research Center 

Hampton, Va. 23665 

And 

Charles L. Britt 

Research Triangle Institute 

Hampton, Va. 23665 

Paper presented at The 

AlAA Conference on Sensor ti Measurement Techniques 

for Aeronautical Application 

September 7-9, 1988 

Atlanta, Ga. 780507003002 

21 1 
c c 

AIRBORNE DOPPLER RADAR DETECTION OF 

LOW ALTITUDE WINDSHEAR 

1 

E.M. BRACALENTE, C.L. BRITT', W.R. JONES 

NASA LANGLEY RESEARCH CENTER, HAMPTON, VA. 

r" 3- 

23665 Y e --.. 

Abstract 

N9 1 - I1 689 4 

As part of an integrated vindshear program, the 

Federal Aviation Administration, jointly with NASA, 

is sponsoring a research effort to develop airborne 

sensor technology for the detection of low altitude 

vindshear during aircraft take-off and landing. One 

sensor being considered is microvave Doppler radar 

operating at X-band or above. Using a Microburst/ 

Clutter/Radar simulation program, a preliminary 

feasibility study was conducted to assess the performance of Doppler radars for this application. 

Preliminary results from this study are presented. 

Analysis show, that using bin-to-bin ACC, clutter 

filtering, limited detection range, and suitable 

antenna tilt management, vindshear from a "vet" 

microburst can be accurately detected 10 to 65 seconds (.75 to 5 Km) in front of the aircraft. 

Although a performance improvement can be obtained 

at higher frequency, the baseline X-band system 

simulated detected the presence of a vindshear 

hazard for the "dry" microburst. Although this 

study indicates the feasibility of using an airborne Doppler radar to detect low altitude microburst windshear. further detailed studies --including future flight experiments -- will be required 

to completely characterize the capabilities and 

limitations. 

Key Words 

Aviation safety, vindshear detection and avoidance, vindshear hazard index. airborne remote sensor technology, microvave Doppler radar. 

Nomenclature 

A/D 

A/C 

AGC 

C 

CSD 

CSR 

D 

dB 

dBv 

dBz 

F 

8 

G 

I&Q 

k 

b 

FR 

Analog to Digital 

Automatic Gain Control 

Aircraft 

Speed of light, m/s 

Clutter Spectral Density 

Clutter-to-Signal ratio 

Rain drop diameter, mm 

Decibels 

Decibels relative rn 1 vatt 

Reflectivity factor in Decibels 

Hazard factor 

Radial component of hazard factor 

Acceleration of gravity, m/s2 

Peak antenna gain 

In-phase and Quadrature 

Boltzmann's constant, Joules/Kelvin 

Refractive index factor for rain 

*Affiliation: Research Triangle Inst., 

Hampton. VA 

1 

n 

NRCS 

Pn 

PS 

pt 

PRF 

Rg 

RT 

SAR 

SCR 

SNR 

TS 

Tilt 

V 

"C 

wh 

WX 

ze 

9 

A 

I 

One-vay rain attenuation loss 

Receiver bandvidth lots factor 

Natural log (to the base e) 

Total raln reflectivity per unit volume 

Normalized Radar Cross Section 

System noise power. vatts 

Reflected signal pover, vatts 

Peak transmitter pover, vatts 

Pulse Repetition Frequency 

Range bin distance from A/C, m 

Range to target, ukters 

Synthetic Aperture Radar 

Signal-to-Clutter ratio 

Signal-to-noise ratio 

System Noise Temperature, deg. Kelvin 

Antenna angle measured from A/C glide-slope 

Aircraft airspeed, m/s 

Cell volume of rain target, m3 

Vertical component of inertial wind, m/s 

Horizontal component of inertial wind, m/s 

Reflectivity factor, mm6/m3 

TransGMer pulse duration. sec. 

Antenna 3 dB beamwidth, radians 

Wavelength, meters 

I. Introduction 

Thls paper Is declared a work of the U. S. Government 

and Is not subject to copyright protection in the United States 213 

Low altitude microburst vindshear is recognized 

as a major hazard during takeoff and landing of 

aircraft. Microbursts are relatively small, 

intense dovndrafts vhich spread out in all directions upon striking the ground. 

shear is encountered at low altitudes during landing or takeoff, the pilot has little time to react 

correctly to maintain safe flight (Fig. 1). In the 

United States during the period 1964 to 1985. there vere 26 major civil transport aircraft accidents 

and four incidents involving 626 fatalities and 

over 200 injuries for vhich vindshear vas a direct 

cause or a contributing factor. As part of its 

integrated vindshear program, the Federal Aviation 

Administration (FAA) jointly with NASA, is sponsoring a research effort to develop airborne sensor 

technology for detection of low altitude windshear 

during A/C takeoff or landing. A primary requirement for an airborne forvard-looking sensor or system of sensors is to be capable of detecting both 

heavy ("vet") and light ("dry") precipitation 

mf-robursts. One sensor being considered for this 

application is microwave Doppler radar operating at 

X-band or higher frequency. Since absolutely clear 

air produces no radar return at microvave frequencies except very slight scattering from gradients 

in the index of refraction on the scale of the r.f. 

wavelength, the emphasis in the present research is 

on those microburst containing at least some liquid 

water. 

When such wind- 
Previous experiments1 and studies have demonstrated, in a limited way, the capability of airborne Doppler radars to detect the presence of 

windshear. However. for A/C landing and take-off 

applications, the problems of severe ground clutter, rain attenuation, and low reflectivity levels 

must be solved. To consider these problems, a 

Microburst/Clutter/Radar simulation program has 

been developed to aid in ?he evaluation and develi 

opment of Doppler radar concepts. 

program incorporates windfield and reflectivity 

databases derived from a high resolution numerical 

windshear model2, clutter maps derived from airborne Synthetic Aperture Radar (SAR) backscatter 

data, and various airborne Doppler radar configurations and signal processing concepts. The program 

simulates the operation of a Doppler radar located 

in an A/C approaching a runway, sensing signal 

returns from a windshear microburst and an airport 

clutter environment. 

burst/Clutter/Radar sirnulation program is presented 

along with examples of simulation outputs. 

Using this program, a preliminary tradeoff and 

assessment study was conducted to evaluate the performance of Doppler radars to detect windshear during A/C landing. Case study results for a strawman design are presented, illustrating airborne 

Doppler radar capabilities. Results for both a 

"wet" and "dry" microburst are included. This preliminary study shows the feasibility of using airborne Doppler radars to detect windshear; however, 

further detailed studies will be required, fncluding future flight experiments, to completely characterize their capabilities and limitations. 

The simulation 

A description of the Micro- 

$1. DODDIer Ra dar Desinn Reauand Performance TradeA preliminary set of perfoknce requirements3 

Preliminarv Desinn Reauirement 

has been established for design of forward-looking 

windshear detection sensors. The sensors' primary 

requirement is to detect severe microburst windshear during final approach to landing (Fig. 1) or 

during takeoff, and to provide as a minimum, 15 to 

40 seconds (approximately 1 to 3 km) warning to the 

pilot. 

tions 50 to 100 seconds (4 to 8 km) in front of the 

A/C is also desired. The sensor or sensor system 

must be able to detect windshyr caused by both 

heavy and light precipitation microbursts. The 

sensor must measure mean horizontal wind speeds 

every 150 to 300 meters out to a range of 6 to 8 km 

along the flight path and a small sector (approx. 

20 deg.) on either side of the A/C, with approximately 1 m/e accuracy. These primary requirements 

have been established as minimum guidelines for 

developing sensor design requirements and evaluating potential concepts. The requirements to provide other information and capabilities, such as 

vertioal wind speeds, rain reflectivity, wind turbulence, microburst signature recognition, and various display capabilities have not been established. Guidelines for these requirements are being 

developed. 

Advisory information on vindshear condiA major area of radar design that requires 

extensive development is the radar signal processing technique, which will suppress clutter interference and provide maximum windshear detection 

accuracy. 

and evaluated, radar parameters must be choseit a, 

evaluated. The radar parameters chosen by the 

radar designer are those which go in the radar 

equation to compute Signal-to-Noise Ratio (SNR) 

performance. 

distant rain cell target is approximated by the 

following equations :4 

Before these techniques can be developed 

The SNR for a signal reflected from a 

P, 

Pn 21n(2)(4f13 k Ts RT4 

pt ~2 12 1, A* n vCr 

SNR -- - 

where : 

Pn - k Ts/r 

n - (7r5/A4) lk,,I2 2, 

T 

As seen from these equations a large number of 

parameters affect the performance of the radar. 

The designer, hovever, has control over only a few 

of them, mainly transmitter power. antenna gain, 

frequency of operation, pulse duration, and to a 

minor degree, target range. There is. for airborne 

operation, a number of factors which limits the 

choice of values for these parameters. The use of 

higher operating frequencies rovides greater sensitivity to rain reflectivityy3) and higher resoluti~n(~), but is subject to greater attenuation by 

rain. 

operate at frequencies of S-band (1-3 CHz). C-band 

(3-8 CHz), and X-band (8-12 GHz.). Although neglfgible attenuation occurs at S-band, the increase in 

sensitivity and smaller cell resolution at X-band 

outweighs the small increase in attenuation (2-5dB) 

experienced for "wet" mfcrobursts. 

rnicrobursts, frequencies in the Ku-band (12-18 Chz) 

region could be considered since attenuation would 

remain low. 

both "wet" and "dry" microbursts could utilize dual 

frequency operation. but practical considerations 

make it desirable to find one frequency that can 

provide acceptable performance for all microbursts. 

Most operational Doppler weather radars 

For "dry" 

Windshear detection capability for 

L 

2 14 
Airborne veather radars, operate in an allocated 

frequency band around 9.3 GHz and utilize solid 

state transmitters of about 100 vatts. They are 

presently in use to display rain reflectivity and 

vind turbulence advisory information to the pilot. 

Therefore, it is of interest to assess airborne 

Doppler radar concepts for vindshear detection 

operating in this frequency band utilizing relatively low povers. Space limitation in the nose radome of passenger A/C limit the maximum antenna 

size to about 30-36 inches (.76-.91 m) in larger 

A/C and about 18-20 inch in smaller A/C. 

makes it more important, from a resolution and sensitivity standpoint, to operate at the higher 

frequencies. It is desirable to keep transmitter 

pover requirements lov SO that solid state transmitters can be considered. 

such as pulse repetition frequency (PRF). and pulse 

bidth are chosen to minimize velocity and range 

foldover problems and to provide acceptable range 

resolution. 

ameter values being considered in the feasibility 

study, and vhich represent state-of-the-art airborne Doppler radar hardvare implementation capability. Also listed is a baseline set of values 

used in the initial radar simulation case studies. 

This 

Other radar parameters c 

Table 1 lists the range of radar parTable 1 Wind shear Doppler radar parameter values 

Parameter 

Pulse repitition freq. (PRF') 

Pulse width (TAU) u-sac.---- 

Max. det. range, km -------- Range gate resolution, m --- Range sampling window, km -- Max. unambiguous YO, m/sec.- 

Wind speed accuracy, m/sec. 

Operating frequency, GHz --- 

Antenna diameter, m -------- Antenna gain, dB ----------- Antenna beamwidth, deg.----- 

Sidelobe level, dB ------- Antenna polarization ------- Ant. tilt angle range, deg. 

Azimuth angle range, dag. -- 

Minimum det. signal, dBZ --- Transmitter peak pover, Irv - 

System noise figure, dB ---- 

Return sig. dynam. range ,dB 

Receiver dynamic range, dB - Xmit/rec. phase jitter,d.rms 

Number of A/D conv. bits---- 

Clutter filter type -------- 

Processing technique ------- 

---_-----_____--_---________ 

. 

1.0 

10 

150 

1-9 

24 

1.0 

9.3 

.76 

35.5 

3 

< -25 

LINEAR n 

0 to 2 

+OR- 21 

0 

2 

4 

70 

50 

.5 

' 12 

2 pole 

PP 

1.0 -3.0 

5 TO 10 

150 TO 450 

1-10 

24 TO 45 

.5 TO 2 

9.3 - 15 

.46-.91 

31 TO 40 

.a TO 5 

-20 TO -35 

DUAL POL 

0 to 20 

+OR- 45 

-15 TO 10 

.2 to 10 

3 TO 6 

45 TO 55 

.1 TO 2 

10 TO 14 

TBD 

FFT, PP 

60 - a0 

SNR Performance 

Using selected values of parameters found in 

table I, a set of SNR performance curves vere computed using (1). Sample plots of these SNR curves 

are shown in figures 2 61 3. The SNR is computed in 

a bandvidth equal to 1/T. A SNR in this bandvidth 

of greater than unity (0 dB) is generally required 

to obtain adequate Doppler processing performance. 

These curves show that SNR performance exceeding 0 

dB can be obtained for relatively lov reflectivity 

levels (0 to 10 dBz) for ranges out to 10 km. 

Reflectivity values range from 60 dBz in the core 

of "wet" microbursts. to 10 to 40 dBz in the outflov region. The performance curves for both the 

9.3 CHz (fig. 2) and 15 CHz (fig. 3) show more than 

sufficient SNR performance for these ranges of 

reflectivities. For "dry" microbursts the core 

reflectivity can be in the range of 20 to 30 dBz 

range, falling to -20 to +5 dBz in the outflow 

region. The 9.3 and 15 CHz performance for a -10 

dBz reflectivity falls below 0 dB SNR at about 3 km 

and 6 km respectively, which are still acceptable 

ranges for this application. An increase in transmitter pover vould be required to operate down to 

the -20 dBz level. 

Clutter Performance 

The X and Ku-band SNR performance vas shown in 

the previous section to be more than sufficient to 

allow adequate Doppler processing. Hovever, one of 

the major problems associated with the sensing of 

microburst using an airborne Doppler radar is the 

presence' of ground clutter. To assess the magnitude of this problem, an analysis of clutter spectra and clutter-to-signal (CSR) ratios vas conducted, using ground clutter maps derived from 

well-calibrated SAR Normalized Radar Cross Section 

(NRCS) data as described in section 111. A set of 

clutter maps has been produced for a number of different airports from existing sets of SAR data. 

Figures 4 h 5 show sample clutter-to-signal (CSR) 

ratio results, assuming a 10 dBz rain reflectivity 

signal level, for a few sample radar configurations 

approaching Willow Run airport. Plots are shown 

for a 5 km A/C range from touchdown, antenna tilt 

angles of Oo and 2O (antenna angle measured up from 

the A/C glide-slope of -3O). and antenna azimuth 

angles of Oo and loo. 

parameters used in these analyses. Figure 6 shows a histogram plot of the range of NRCS levels which 

exist in the clutter map used. The NRCS levels 

larger than -10 dB come primarily from urban areas 

and high level discrete targets. 

Table 2 lists the radar 

Table 2 Radar parameters used in clutter analysis 

A/C range from runvay -- A/C ground velocity ---- A/C glide slope -------- 

Antenna Dia. ----------- Antenna edge illum. ---- 

Rain Reflectivity ------ 

pRf _____________-______ Ant. tilt angle -------- Ant. azimuth angle ----- 

Frequency -_--__---_____ 

Pulse Width ------------ 

567km 

77 m/s 

30 

9.3 CHz 

.76 m (30 in.) 

10 dBz 

1 u-sac. 

5000 

0 61 2 deg. 

0 h 10 deg. 

-10 dB 

215 
The results of this preliminary clutter analysis 

show that the highest clutter levels (CSR of 30-60 

dB) occur where the pulse in the main beam intersects the ground, from the urban areas, and for 

antenna tilt angle of oo. 

are shown by these analyses, which can be utilized 

to greatly reduce the effects of clutter. First, 

lower CSR values occur at short ranges in front of 

the A/C, at range gates where the pulse in the main 

beam has not touched the ground. At these ranges 

the clutter is coming primarily from aidelobes, 

which if sufficiently low will suppress the clutter 

signals. For a 3O beamvidth antenna pointed down 

at a Oo tilt angle and a 5 km A/C range, the -3 dB 

point of the main beam first touches the ground at 

about 3.5 km. and the first sidelobe null point at 

about 2.7 km (a point about 35 seconds ahead of the 

aircraft). For a 2O tilt these points are about 6 

and 4.3 km respectively. Note in figure 4 the 

increase in CSR at a range of 2.5 km. This point 

corresponds to NRCS levels of -5 to 0 dB from a 

residential area about 2.5 to 3 km from the runway. 

The clutter level would have been much higher had 

the main beam been viewing this area rather than 

the beam sidelobes. 

TWO significant results 

A second fact that is very evident in the data 

is the significant reduction in clutter that occurs 

when the antenna is tilted up from Oo to 2O. Thus, 

by limiting the range of data processing and 

employing proper antenna tilt control, CSR levels 

can be kept below 40 dB (well within the dynamic 

range capabilities of present day Doppler radar 

receiver design technology). Clutter suppression 

techniques can then be employed to reduce clutter 

to acceptable levels. Figure 7 shows a sample 

clutter spectral density plot for the 2.5 km range 

gates of figure 4 (ant. Tilt=2O, Arido, A/C at 5 

km). The density levels are plotted against velocity relative to the A/C*s ground velocity. 

the most significant clutter spectrum energy levels 

contained between zero and about 4 m/s, a high pass 

filter with maximum attenuation at zero velocity 

can be employed to significantly reduce the clutter 

levels. The CSR shown in figure 7 will be reduced 

by over 25 dB if the energy below 3 m/s is filtered 

out. Since the most severe wind velocities of 

interest exist at much higher speed6 (5-30 rn/s), 

this filter will have little effect on the wind 

speed velocity estimation. Studies are underway to 

evaluate filter processing techniques which can 

provide optimum results. Section IV presents sample 

case study results of windshear detection performance, using the radar simulation program. 

With 

X-N 

General Description 

calculation of the expected output of an sirborne 

coherent pulsed Doppler radar system viewing a lowlevel microburst along or near the approach path of 

the aircraft. Figure 8 is a block diagram shoving 

the major features of the simulation ITrputz 

the program include the radar system paradeters ai.' 

large data files that contain the characteristics 

of the ground clutter and the microburst. The 

ground clutter data file consists of high-resolution (20m) calibrated Synthetic Aperture Radar 

(SAR) data of selected airport areas. The microburst data files provide reflectivity factors, 

x,y,z wind velocity components, and other meteorological parameters with a resolution of 40 meters. 

This database is genekated by a numerical convective cloud model2 driven by experimentally-determined initial conditions, and represents selected 

time periods of the microburst development. 

The radar simulation program is a comprehensive 

For each range bin, the simulation calculates 

the received signal amplitude level by integrating 

the product of the antenna gain pattern and scattering source amplitude and phase over a sphericalshell volume segment defined by the pulse width. 

radar range and ground plane intersection. The 

amplitude of the return from each incremental scatterer in the volume segment is proportional to 

either the square root of the normalized cross-section of th.e ground clutter (from the clutter map) or the square root of the reflectivity factor of 

the water droplets in the microburst (from the 

microburst data base). The phase of each incremental scatterm-4s the sum of a uniformly distributed 

(0 - 2719 random phase term, a phase term due to 

relative aircraft-scatterer radial velocity, and 

normally-distributed random phase terms representing transmitter/receiver phase jitter and ground 

clutter random motion. The random phase terms simulating phase jitter and ground clutter motion are 

updated for each transmizted pulse, while the uniformly-distributed phase terms are updated for each 

sequence of pulses in a range bin. The phase terms 

representing aircraft-scatterer relative motion are 

linear functions of time. 

Path attenuation for each incremental scatterer 

is determined by integrating the path losses over 

the transmission path. 

\isad to determine the incremental path losses from 

the liquid water content of the microburst. Aircraft ground velocity is assumed to be known accurately so that derived Doppler frequencies can be 

referenced to a value of zero corresponding to that 

velocity. 

Empirical formulas4 are 

Antenna patterns simulated include a generic 

parabolic antenna with size and aperture illuminatton taper specified by input data, and a flatplate array antenna with a pattern similar to that 

found in the current generation of X-band airborne 

veather radars. 

216 

. 

. 
In the simulation. a sequence of N pulses of inphase (I) and quadrature (Q) signal amplitudes are 

calculated for each range bin as discussed above 

and subjected to ACC amplification and A/D quantization. A simulated fast-acting ACC is used to 

adjust the gain of the system on a bin-by-bin basis 

to achieve a wide dynamic range and to prevent signal saturation (due to clutter) prior to and during 

A/D conversion. The I and Q pulse stream is then 

digitally filtered to suppress ground clutter near 

zero Doppler frequencies and processed using both 

conventional pulse-pair and spectral averaging 

algorithms to derive the average velocity and spectral width of the scatterers in the range bin. 

Further processing of the velocity data provides 

information on windshear and aircraft hazard factor. 

I 

.- 

Provision is made in the simulation to generate 

returns from a specified number of range bins over 

a specified azimuth scan so that simulated color 

displays of reflectivity, velocity, windshear, 

spectral width, etc.. can be examined. Other outputs of the simulation include plots of pover levels, velocity, spectral width, windshear hazard 

factor, and ACC levels vs. radar range. Doppler 

spectra of ground clutter and moisture as derived 

from the I and Q signals from each simulated range 

bin are also plotted. 

Ucroburst Model 

As mentioned above. the microburat model is a 

detailed numerical convective cloud and storm model 

that calculates the time history of the development 

of a microburst. The model uses a nonhydrostatic. 

compressible and unsteady set of governing equations which are solved on a three-dimensional staggered grid. The computation can be initiatcd from 

observed data and generates realistic wind fields 

that compare favorably with observed data such as 

that obtained in the JAWS study5. 

simulations to date, a 4x4 km lattice of 40x40 

meter grid spacing increments (tvo-dimensional axisymmetric version) has been generated at selected 

time periods. Output parameters include the radar 

reflectivity factor (dBz), vind velocity components, temperature, equivalent potential ternperature. pressure and moisture content (water vapor, 

ice, cloud droplets, rain, snow and hail/graupel). 

The model developed under NASA sponsorship is 

described in detail in references 2 and 5. 

For the radar 

For the radar simulation cases discussed in this 

paper, a typical "wet" microburst and a typical 

"dry" microburst were selected and used to investigate radar performance at a particular instant of 

time. 

velocity field of the axisymmetric "wet" microburst 

used in the radar simulation. The "dry" microburst 

is similar in form but with smaller dimensions, 

lower wind speeds, and much lower reflectivity lev- , els. The "wet" microburst data are taken at 11 

minutes after initiation of the microburst calculation and the "dry" microburst data are 23 minutes 

after initiation. The "wet" microburst resembles 

sn axisymmetric version of the 2 August, 1985, Dallas-Ft. Worth storm6 and the "dry" microburst is 

based on soundings taken on 14 July, 1982, within 

the JAWS network near Denver. 

Figure 9 shows the reflectivity factors and 

cThe ground clutter model used for the present 

simulation cases is a high-resolution X-band SAR 

map of the Willow Run, Uichigan, airport area provided by the Environmental Research Institute of 

Michigan (ERII). 

The SAR image files produced by ERIN provide 

calibrated NRCS data with a resolution of 20m. 

Figure 10 shows a high resolution (3m) SAR image of 

Willow Run airport from which this data was derived 

and the runway (9R) used in the simulation runs. 

In the simulations, the aircraft is positioned at a 

selected distance from the runway touchdown point 

on a three-degree glide slope. 

A problem with the use of existing SAR data is 

associated with the vhiation of cross section with 

depression angle. These data were taken at depression angles ranging from approximately 18 to 50 

degrees, whereas for the operational qirborne radar 

simulated the depression angles of interest are 

approximately 1 to 20 degrees, 

account for this difference, ERIU supplied an 

empirical depression-angle correction function that 

corrects the NRCS to the angle seen by the airborne 

radar. Since clutter sources from urban areas have 

cross sections that do not decrease significantly 

with depression angles in the ranges of interest. 

urban areas of the clutter map are excluded from 

this depression angle correction and the originally 

measured cross-section values are used in the simulation. Also, areas of the map with NRCS values 

equal to or greater than 5 dB are not corrected. 

To partially 

The corrections for depression angle are not 

entirely satisfactory,, and cause an uncertainty in 

the clutter calculations of the preliminary cases 

discussed in this paper. Flight experiments using 

the ERIM SAR instrument will be flown in the summer. 

and fall of 1988 to collect more representative 

airport clutter data with depression angles corresponding to those that would be seen by an airborne 

radar on the approach path. 

vide better information of depression angle rariation of NRCS for urban environments as well as 

other surfaces. 

These data will pro217 
IV. SIMlTUTED RADAR PERPORHANC& 

"Wet" Microburst 

To examine the expected radar performance in 

specific situations, several cases have been simulated, as illustrated in figure I, using the baseline system parameters given in table 1 and the 

ground clutter map from the Willow Run airport 

area. Figure 11 plots the SNR and SCR vs. radar 

range for a "wet" microburst that would be seen by 

the radar at a distance of 7 km from the runway 

touchdown point vith the antenna tilted up 2 deg 

from the projected aircraft path. 

axis is located on the projected path 2 km from the 

touchdovn point. The calculated reflectivity factor of the vater droplets along a line corresponding to the projected aircraft path is also plotted 

in figure 11 for comparison to the simulated radar 

measurements. For this case, the SNR and SCR are 

high over the entire region of the microburst, vith 

a minimum value of SCR (lOdB) occurring at approximately 3 km from touchdown. This minimum value is 

due to high clutter power from an urban area at 

this location. The SNR exceeds 20 dB over the 

range, with approximately 18 dB difference between 

the near side and far side of the microburst due to 

path attenuation and geometrical factors (in this 

plqt, the pover levels are not corrected for the 

Figure 12 shows the calculation of the radial 

component of vind velocity derived from both pulsepair and spectral averaging algorithms operating on 

128 simulated I and Q pulses from the radar. This 

figure also plots, for comparison, the "trua" wind 

speed, defined as the velocity component along the 

center line of the antenna beam. It should be 

noted that the true velocity, as defined, will 

always differ somewhat from the radar-measured 

velocity because the true velocity is measured 

along a line (the antenna center line), whereas the 

radar system measures a weighted (by reflectivity 

and antenna pattern) average of the velocity over a 

finite volume of the microburst. 

The microburst 

RT loss). 

A two-pole high-pass Buttervorth filter vas used 

to filter the I and Q pulses to suppress ground 

clutter. The 6 dB frequency response cutoff point 

is located at a Doppler frequency --relative to the 

A/C ground valocity-- corresponding to a radial 

component of wind velocity of 3 m/s, and the filter 

has two zeros at zero Doppler frequency. The 

effect of the clutter filter can be seen in figure 

13. which is a plot of the Doppler spectrum in a 

range bin 4 km from the radar calculated vith and 

without the clutter filter. For simulated velocity 

measurements, a processing threshold of 4 dB is 

used (i.e., the pulse-pair and spectral averaged 

velocities are set to zero if the radar received 

power is less than 4 dB greater than the noise 

threshold). 

The simulated velocity measurements are within 2 

m/s of the "true" velocity for velocities greater 

than 5 m/s and indicate clearly the potentially 

hazardous windshear associated with the microburst. 

To more closely indicate the windshear hazard tn 

the aircraft, a measure called the F-factor or 

hazard index has been defined by Bo~les.~ 

index.is defined by the equation: 

This 

g V 

where Wx is the rate of change of the component 

of wind velocity alopg the aircraft path, g is the 

acceleration of gravity, Wh is the vertical component of wind velocity and V is the aircraft velocity. Values of F greater than 0.1 to 0.15 are 

considered hazardous to jet transport aircraft, 

considering aircraft type, configuration, and range 

of gross weight^.^ 

Although a forvard-looking radar sensor cannot 

directly measure the vertical wind component, the 

radial velocity component is measured directly. 

The first term in the equation for the F-factor can 

be derived from radar measurements of radial velocity as follows: 

where : 

dWx - change in radial velocity between adjacent 

6Rg - distance between range bins 

FR - the radial component of the hazard index 

This radial term is calculated in the simulation 

range bins 

from the velocity measurements as shown in figure 

12 by averaging velocity differences over 5 range 

bins, and results in outputs as shown in figure 14. 

The radial term of the hazard factor reaches a maximum value of 0.1 for this microburst. and both 

pulse-pair and spectral averaging algorithms give 

good measurements of the factor. 

218 
"Drv" Microburst 

vere also made vith the "dry" microburst discussed 

previously. Figure 15.shovs the hazard index 

derived by these runs using the baseline system 

parameters operating at 9.3 CHz. The figure indicates that although the vindshear vas detected, the 

velocity measurement vith the baseline set of system parameters vas somevhat noisy. 

Simulation runs similar to those discussed above 

To improve the performance on the "dry" microburst, several system parameters can be changed. 

These trade-off studies have just been initiated. 

For example, to illustrate the radar performance at 

Ku-band, the dry microburst case discussed above 

vas simulated using the same set of baseline parameters, except the operating frequency vas changed 

to 15 CHz and the PRF vas changed to 4878 pulses 

per second. Results for the Ku-band system vith the 

dry microburst are shpwn in figures 16, 17, and 18. 

As may be seen, even though the SNR and SCR values 

are much lover than those vith the vet microburst. 

the vind velocity vas successfully measured over 

the hazardous part of the microburst. 

factor calculation clearly indicates the vindshear 

hazard associated vith this microburst. 

Simulated Disulavs 

The radar simulation program provides for an 

azimuth scan mode and the generation of simulated 

displays of several variables of interest. Figure 

19 shows a black and vhite copy of a simulated 

(color) display of radial vind velocity for the 

%etn microburst vith the baseline set of radar 

parameters. Figure 20 is a aimulated plot of the 

radial term of the F-factor and clearly indicates 

that a potential vindshear hazard lies on the aircraft path. These displays should not be interpreted as recommended displays for the aircrev. 

since the specific method of alerting the crew to a 

hazard requires extensive study, vhich is presently 

under way, and will most likely consist of a warning light or alarm which may be supplemented by 

displays of additional information to aid the aircrew's decision-making process. 

Future Simulation Develoumenc 

The simulation program will be improved in the 

near future by incorporating more sophisticated 

signal processing techniques, models to represent 

moving ground clutter, and techniques for estimating true, nuisance. and missed hazard alarms. Considerable effort is planned to incorporate and 

investigate a full range of microburst/clutter 

environments, provide improved displays of simulation output data for evaluating performance, and to 

conduct extensive tradeoff and optimization 

studies 

The hazard 

V. Concludinn Remarks 

A preliminary tradeoff and assessment study vas 

conducted to evaluate the performance of airborne 

Doppler radar sensors to detect hazardous microburst vindshear during A/C landing. Using a preliminary set of performance requirements for the 

design of foward-looking sensors, a baseline set 

of radar parameters vas developed for use in 

assessing vindshear detection performance using a 

radar simulation program. 

of the simulation program, vhich includes excellent 

models of microburst vind fields, realistic clutter 

maps of airports, and accurate models of Doppler 

radar operation and signal processing. 

A description vas given 

For the baseline Doppler radar sensor configurations modeled, prelialnary analyses of the computer 

simulation case studies shov that vindshear can be 

accurately detected 10 to 65 seconds in front of 

the aircraft approaching a hazardous microburst 

positioned in the flight path of landing aircraft . This vas accomplished using a bin-to-bin ACC. clutter filtering, limited detection range, and suitable tilt management. The sensor is highly effective for the "vet" microburst vhere very high SNR 

and SCR are obtainable due to large reflectivity 

levels. For the "dry" microburst. vith low reflectivity levels, vindshear vas detected, hovever. 

more tradeoff analyses and signal processing 

studies are needed before the performance for the 

"dry" microburst case can be fully assessed. 

Initial simulations vere conducted vith a specific airport, selected microburst time instants. 

and the base-line radar parameters. These simulations clearly-;hov that in realistic situations, 

downward-looking airborne radar sensors have the 

potential to detect vindshear and provide information to the aircrev that will permit escape or 

avoidance of hazardous shear situations. Plans are 

underway to investigate a full range of microburst/clutter environments, conduct extensive tradeoff and optimization studies, and investigate 

various signal processing and clutter filtering 

concepts vhich can provide reliable windshear 

detect ion capability . 

The initial simulation studies vere confined to 

the landing approach, since it presents the.most 

severe signal-to-clutter situation. Studies of the 

takeoff case are planned. Since the antenna can be 

tilted up, therefore providing high signal-toclutter ratios, acceptable detection performance is 

anticipated for this case. 

4 

219 
Although hazardous windshear can be detected by 

Doppler radar, the pilot must be alerted in a 

timely manner to avoid the hazard. A hazard index 

has been developed) vhich establishes when a threat 

to the performance of the A/C exists. The simulation studies shoved that a Doppler radar sensor can 

detect the horizontal component of this index with 

sufficient accuracy to indicate in a timely manner 

that a threat exists. Further studies using this 

index vi11 be conducted for various microburst 

types and locations relative to the A/C to assess 

the missed and nuisance alarm rate. Displays of 

additional advisory information for the aircrev 

will probably be required, and are under study. 

Output display examples from the simulation studies 

represent scne of the information that could be 

provided. 

The present and future simulation studies vi11 

provide a good foundation to determine the capabilities and limitations of Doppler radar concepts for 

the detection of microburst vindshear. 

experiments are needed to evaluate the simulation 

modeling and performance estimates. 

experiment program is planned for the 1990-91 time 

period. The first phase of flights vi11 involve 

measuring the clutter environment from selected 

airports during landing approaches. These data vi11 

be used to evaluate the clutter map models derived 

from the SAR data. A second phase of flights will 

collect data from severe convective storms at altitudes above 2000 feet. These data will be combined 

with the clutter data to be used to evaluate the 

performance of various signal processing concepts. 

Flight tests for candidate concept evaluation and 

demonstration would follow. 

Flight 

A flight 

VI. References 

1. Staton, L. D.: "Airborne Doppler Radar For Wind 

Shear Detection." In workshop proceedings, 

"Windshear/Turbulence Inputs to Plight Simulation 6 Systems Certification." NASA CP 2474, 

July 1987. 

2. Proctor, F. W.: "The Terminal Are6 Simulation 

System Vol. I: Theoretical Formulation." 

NASA CR 4046: DOT/FM/Pn-86/50, I. April 1987 

3. Bovles, R. L.; and Targ, R.: "Windshear Detection and Avoidance: Airborne Systems Perspective." Presented at 16th Congress of the ICAS 

Aug 28-Sept 2, 1988, Jerusa~em. Israel. 

4. Doviak, R. J.; and Zrnic, D. S.: "Doppler Radar 

and Weather Observations." Acadamic Press Inc. 

1984. 

5. Proctor, F. H.: "The Terminal Area SFmulation 

System Vol. 11: Verification Cares." 

NASA CR 4047: DOT/FM/PM-86/50, 11. April 1987 

6. Bovles, R. L.; "Windshear Modeling: DFW Case 

Study", presented at conference "Windshear 

Detection Forvard-Looking Sensor Technology", 

NASA CP 10004: DOT/PM/PS-87/2. Oct. 1987 

ESC"7 

Fig. 1 Sketch illushating the microburst vindshear hazard for an approaching A/C, being 

probed by a radar beam. Potential impact 

path is shovn if escape or avoidance 

maneuver is not activated. 

- 10dBz 

20 

-1 0 

-20 IIIIIIIIIIIII 

123456789101112 

RADAR RANGE, km 

Fig. 2 Signal-to-Noise performance for different 

reflectivity levels, A/C 10 km from touchdown, 9.3 CHz, Py2 kv,r-l US, Ant. 

Dia.930 in., Tilt-OO 

40 r 

30 

20 

% 

a' 10 2 

UJ 

0 

t 

-1 0 

-20 

12 3 45 6 7 8 9101112 

RADAR RANGE, km 

Fig. 3 Signal-to-Noise performance for for 15 CHz. 

All other conditions the same as in Fig. 2. 

220 
- Ant. Tilt Angle - 0' 

..... .. Ant. Tilt Angle - 1 

50 4 E 

, '. . 

~~ 

1 2 3 4 5 6 7 8 

RADAR RANGE, km 

Fig. 4 Clutter-to-Signal (CSR) vs range from A/C, 

using Willow Run clutter map. A/C 5 km from 

touchdovn;Ant. Az angle-OO, Ze-10 dBz. See 

table 2 for other parameter values. 

.20 -lo* 1 2 3 4 5 6 7 8 

RADAR RANGE, km 

Fig. 5 Clutter-to-Signal (CSR) vs range from A/C 

for same conditions as fig. 4 except Ant. 

Az angle - loo 

"r Urban Tamots 

f7 

w !: 

P4 2 

B2 

$1 

g3 

0 

-34.31 -28 -25 -22 -19 -16 -13-10 -7 -4 -1 2 5 8 11 14 

. \.' NRCS. d0 

Fig. 6 :.Histogram plot of range of NRCS levels contained in the Willov Run Airport clutter 

map. 

20 30 k- CSA - 18.2 dB 

m 

9 10 

a 

B 

!lo 

.10 

-200 -1 -2 3 4 -5 d -7 8 -9 -10 

VELOCIPI. m/s 

Fig. 7 Normalized clutter spectral density plot 

for 2.5 km ralrge bin. A/C 5 km from touchdon, Ant. Tilt-Z', Az-0'. Ze-10 dBz 

Radar Parameters 

Antenna Patterns 

A/C Pos., Microburst Pos. 

L 

Add System 

Noise & Jitter 

Calculate 

Range Bin 

L 

Simulated AGC 8 

Processing 

Signal Levels 

Clutter Levels 

Derived Velocity 

Shear Hazard Index 

Turbulence 

Doppler Spectra 

FIB. 0 Block diagram of the radar simulation program shoving the major features of the simulat ion. 

22 1 
Fig. 9 Reflectivity co:itours and velocity field 

for the axfs:,m:Jetric "vet" microburst model 

used for initial radar performance simulations studies. 

Fig. 10 High resolution SAR image of the Willow 

Run, MI airpoLt area. NRCS map, produced 

from this image data base, is used to calculate the ground clutter return in the 

radar sfnulation program. 

6o r . .L\, I 

40- 

N 

B 

B: 

$ 0' 

d 

L 20 - 

-20 .-- . . . . .. , 5CR. rlt 

. SNR, dtj 

----. Refledivty, d8r 

0 2 4 

1 1 - - .E. -4 2 -60 " 

aAWE To TOUCI-IDOWN. km 

Pig. 11 Plot of caiculated SNR, SCR and reflectivity factor vs range to touchdown for the 

"vet" microburst. Aircraft located -7h 

from touchdsvn on 3O glide slope, radar 

antenna tilt = ZO, microburst centered on 

projected flight path -2h from the touchdown point, freq - 9.3 CHz. 

- PULSE-PAIR 

.._._ -. SPECTRAL AVR. m301 ---. TRUE 

20 

. 

E. 10 

u 

SO > 

-1 0 

.l n 7 4 -20 -0 -4 -c " - 

RANGE TO TOUCHDOWN.^^ 

Fig. 12 Radar wind velocity measurement vs range to 

touchdown; same conditions as in figure 11. 

In this plot, positive velocities represent 

headwinds. 

.90 

I 

. T 

-140 ' 

-20 -15 -10 -5 0 5 10 15 20 

VELOCIM. d9 

Fig. 13 Plot of Doppler spectrum from radar range 

bin 4km from touchdown, prior to wind velocity estimation, showing effect of 2-pole 

filter used to suppress ground clutter. 

.3 '4 F - PulssPair 

..__.... Spectral Avr. 

-.-- TNO 

.2 k 

3 I -.l F 

-.2 -.3 t br 

-.4 

-6 -4 -2 0 2 4 

RANGE TO TOUCHDOWN. km 

Fig. 14 Hazard index vs. range to touchdown derived 

from the velocities shown in figure 12. 

Index is calculated from average velocity 

differences over 5 range cells (750m). 

c 

222 
- Pulse-Pair 

---._._. Spectral Avr. 

---- True 

.1 

0 

rO z 

f -.1 

-.2 

-3 1 I 

-.4 

-6 -4 -2 0 2 4 

RANGE TO TOUCHDOWN, km 

Fig. 15 Hazard index vs. range to touchdovn derived 

from the "dry" microburst velocities using 

the baseline parameters, and conditions 

listed in fig. 11, freq. - 9.3 CHz. 

T 40 

-6 .4 -2 

RANGE TO TOUCH1 

2 4 

IWN. km 

' Fig. 16 Plot of calculated SNR, SCR and reflectivity factor vs range to touchdown for the 

"dry" rnicrobyrst, and conditions listed in 

fig. 11, except freq. - 15 CHz. 

- PULSE-PAIR 

....... SPECTRAL AVA. 

30 r ---. TRUE 

-I0 t 

-70 -- -6 ' 

-4 -2 0 2 4 

RANGE TO TOUCHDOWN, krn 

Fig. 17 Radar wind velocity measurement vs range to 

touchdown under same conditions as those of 

figure 16. The noise spikes are due to low 

SCR from urban clutter (-3km), and other 

clutter sources (+3km) where reflectivity 

levels are low. 

- Pulse-Pair 

_.._.... Spectral Avr. 

-.-. TN~ 

-3 -'2 L 

-.4 

-6 

- 

-4 -2 0 2 4 

RANGE TO TOUCHDOWN, km 

Fig. 18 Hazard index vs. range to touchdovn derived 

from the "dry" microburst velocittes shown 

in figure 17. 

223 
2 lo 0 

-2 1 

1k- .---+v / \ 

\ \ -*- / 

a 

Range (km) 

X" 

lis9 

Wind Speed 

0 (m/d 

-1 2 

= -1 5 -18 

.03 

0.0 

-.03 

-.OS 

-.08 

- . in ." 

-.13 

-.15 

-.18 

12 

Fig. 19 Range-azimuth display of wind velocity contours for the "wet" mfcroburst, baseline 

radar parameters, and conditions listed in 

fig. 11. 

and wind direction change is clearly shown. 

The large head to tail velocity 

0 

-2 1 21 

F-f act or 

? 

Pig. 20 Range-azimuth display of hazard index 

(P-factor) contours for the "wet" microburst, same conditions as fig. 19. The 

potential shear hazard area is clearly 

shown. 

224 
. 

Session I. Airborne-Sensors 

Analysis of Synthetic Aperture Radar (SAR) Data for Wind Shear Radar 

Clutter Modelling D. Gineris, ERIM 

S. Harrah, NASA LaRC 

V. Delnore, PRC .. . ' 

225 
ANALYSIS OF 

RADAR (SAR) 

SYNTHETIC APERTURE 

DATA FOR WINDSHEAR 

RADAR CLUlTER MODELLING 

D. Gineris, ERlM 

S. Harrah, NASA 

V. Delnore, PRC 

221 



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232 
Analysis of Specific Areas 

Input: 

specific areas in the image which can be classified 

are located and extracted from the image 

Process: 

statistical analysis of each image 'dump' are 

performed. This analysis calculates the mean, 

skew, and kurtosis of the 'dumped' area. A 

probability density function is fit to the data. 

output: 

statistical summaries of each particular clutter 

group in the image. 

bar charts of the statistical data 

histograms of each type of clutter group in the 

image 

233 

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231 
. 

'. 

Probability Density Function 

of Building Clutter Areas 

-60 -40 -30 -20 -10 0 10 20 30 

Sigma0 (dB) 

Minimum: -45.81 

Maximum: 24.01 

I 

238 
Probability Density Function 

of Urban Clutter Areas 

I 

-60 -40 -30 -20 -10 0 10 20 30 

Sigma0 (dB) 

Minimum: -46.14 

Maximum: 27.22 

239 
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240 
Results of Inter-Image Analysis 

similar clutter areas in all images have similar 

clutter characteristics; mean values may change 

from image to image because of differences in 

incidence angle, but the probability density 

functions which describe a particular type of clutter 

are similar from image to image. 

point target clutter does not seem to change over 

the range of incidence angles present in the 

I mag es. 

24 1 
Results of Intra4mage Analysis 

> 

-- 

the majority of the clutter areas with returns greater 

than -5 dB are located around the airports and in near 

range. Roughly 2% to 3% of the image has returns 

greater than 0 dB. The areas of lowest return (other 

than water) are also located at the airport. 

and urban areas rarely have a mean 0;' greater than 

* 

distributed targets such as forests, fields, runways, 

-5 dB. 

urban areas and forested areas have similar clutter 

characteristics. The percentage of point targets in an . urban area is only about 5% to 10% of the total area. 

242 
Session I. Airborne-Sensors 

Preliminary Airborne Wind Shear Detection Radar .Assessment Study C. L. Britt, RTI 

E. M. Bracalente, NASA LaRC 

. 

. 

243 
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277 
, 

1 Session I. Airborne-Sensors 

Clutter Filter Desi n Considerations for Airborne Doppler Radar Detection of Wind Shear 

E. G. Baa, Jr., di emson University 
Second Combined Manufacturer's and Technology Airborne Wind Shear Review Meeting 

October 18-20, 1988 

CLUTTER FILTER DESIGN CONSIDERATIONS 

FOR 

AIRBORNE DOPPLER RADAR DETECTION OF WINDSHEAR 

E. G. f3axa, Jr. 

Cle mson U n iversit y 

28 1 
N91-11690 J 

CLUTTER FILTER DESIGN CONSIDERATIONS 

r 30 

FOR 

AIRBORNE DOPPLER RADAR DETECTION OF WINDSHEAR 

Ernest G. Baxa. Jr. 

Clemson University 

Clemson, SC 29634-0915 

ABSTRACT 

The problem of clutter rejection when processing down-looking 

Doppler radar returns from a low altitude airborne platform is a 

paramount problem. 

and predicting windshear in the vicinity of an urban airport, 

dynamic range requirements can exceed 50 dB because of high 

clutter to signal ratios. This presentation describes signal 

processing considerations in the presence of distributed and/or 

discrete clutter interference. Previous analyses have considered 

conventional range cell processing of radar returns from a rigidly 

mounted radar platform using either the Fourier or the pulse-pair 

method to estimate average windspeed and windspeed variation 

within a cell. Clutter rejection has been based largely upon 

analyzing a particular environment in the vicinity of the radar 

and employing a variety of techniques to reduce interference 

effects including notch filtering, Fourier domain line editing, 

and use of clutter maps. For the airborne environment the clutter 

characteristics may be somewhat different. Conventional clutter 

rejection methods may have to be changed and new methods will 

probably be required to provide useful signal to noise ratios. 

Various considerations are described. A major thrust has been to 

evaluate the effect of clutter rejection filtering upon the 

ability to derive useful information from the post filter radar 

data. This analysis software is briefly described. Finally, some 

ideas for future analysis are considered including the use of 

adaptive filtering for clutter rejection and the estimation of 

windspeed spatial gradient directly from radar returns as a means 

Of reducing the effects of clutter on the determination of a 

windshear hazard. 

With radar as a remote sensor for detecting 

283 
CLUTTER FILTER DESIGN CONSIDERATIONS 

FOR 

AIRBORNE DOPPLER RADAR DETECTION OF WINDSHEAR 

Ernest G. Baxa, Jr. 

Clemson University 

Clemson, SC 29634-0915 

OUTLINE 

I. The Clutter Problem 

A. Radar antenna sidelobes causes high clutter levels 

B. Moving radar platform influences spectrum widths 

C. Discrete clutter sources in the urban environment 

11. Review of Past Clutter Rejection Research 

A. Notch filtering at zero Doppler 

B. Fourier line editing 

C. Geographical clutter maps 

111. Clutter Rejection for Airbourne Radar 

1. zero gain at zero Doppler 

2. transient response short 

3. notch width considerations 

4. dynamic range requirements 

5. non-stationarity 

1. mid-band discrete clutter 

2. computational load 

C. Geographical clutter maps 

1. poor repeatability 

D. Antenna Steering 

E. Adaptive Filters 

F. Non-conventional Signal Processing 

A. Notch filter requirements . 

B. Fourier line editing 

1. estimating windspeed gradient directly 

2. hazard detection and estimation 

IV. Effects of Clutter Rejection On Signal Parameter Estimation 

A. Computer software development 

1. filtering in time or frequency domain 

2. repeated trials 

3. simulated or real data 

1. ideal notch filter 

2. simple IIR filters 

3. phase response constraints 

4. the pulse canceller 

B. Pulse-pair estimation of spectral parameters 

V. Summary and Conclusions 

284 

. 
r 

Clutter Filter Design Considerations For 

Airborne Doppler Radar Detection of Windshear 

October 19, 1988 

Clutter Filter Design Considerations 

for 

Airdrne Doppler Radar Detection of Windsrear 

E.G. Baa. Jr. 

Clemson University 

OUTLI NE 

u 

Radar Svtenr Laboratory 

Clerron Unirerricy 2nd MAW Klectrical aad CorpUter Knglncering oct. 19, lgee 

Q II 

The Clutter Problem 

Review of Past Clutter Rejection 

Research 

Clutter Rejection for Airborne Radar 

Effects of Clutter Rejection On 

Signal Parameter Estimation 

Summary and Conclusions 

0 

... 285 
0 

68- 

Clutter Filter Design Considerations For 

Airborne Doppler Radar Detection of Windshear 

October 19, 1988 

I 

The Clutter Problem 

88- 

moving 

p/atlbm, r) 

I 1 1 

discfete 

soums 

low 

kbht 

TD 

Si m u I ated Spectra 

-24.4 -18.3 -12.2 -6.1 0.0 6.1 12.2 18.3 24.4 

Windspeed mkec 

Padu Syxtenr Laboratory 

CIemron Unirorriti znd MAW -ing Electrical and Computer Engineering Oct. 1s. lses E 

4 lr 

. 

286 0 
. 

FFT EDIT 

0 

. FFT -’ 

Clutter Filter Design Considerations For 

Airborne Doppler Radar Detection of Windshear 

October 19, 1988 

0 

l! DISCRETE CLUTTER 

DFT of 512 Samples of Radar IQ Data DB 

-24.4 -18.3 -12.2 -6.1 0.0 6.1 12.2 18.3 24.4 

discrete Windspeed rn/sec 

clutter 

Conventional CI utter Rejection 

Notch Filter 

Fourier Line 

Editing 

2nd ~AW meeting 

~.du STXIOMS Laborator7 

Electrical and Computer Engineering 

Clemxon University oct. 1% 1m 

t IL 

287 
I1 

RIM Appu@mhw Q@ auIwsr wog~e@>w 

- I ti' 

Steering 

Adaptive I Filtering 

Estimate 

Windspeed 

Spatial I Gradient 

Hazard 

Detection and 

Estimation 

Y - 

I 

CI utter Reject ion Eva1 uat io n 

'adar -1 Rejection IQ Data 

Weather 

Spectrum 

Parameter 

Estimates 

II 

0

288 
0 

ZJ 

29 

2) 

2 a: 19 

10 

1 .I' 

14 

Clutter Filter Design Considerations For 

Airborne Doppler Radar Detection of Windshear 

October 19, 1988 

. 

.--,. 

0 

. 

c 

It. PULSE-PAIR MEAN ESTIMATE t! 

. .~.............. ......... 0 12 3 4 5 6 7 8 9 101112I3 

NYOUIST BW - f 244 m/s 

TRUE WIDTH SIGMA = 2 0333 rn/s 

Radar Svtenr Laboratory 

Electrical and Computer Inginenring 

Clemron Uniwrsit~ 2nd mAW meeting at. 19, lgea 

e 

tl ti 

PULSE-PAIR WIDTH ESTIMATE 

Width Bstimate vamu Rue Yem 

:[- ,. , . , . , -, . , . ,. ,. ,. , _, . , 

1 

0 12 3 4 5 6 7 8 9 101112 

NYQUIST BW - t 24 4 m/s 

TRUE WIDTH SIGMA = 20333 m/s 

0 289 
0 

48 

3. 

2 

Clutter Filter Design Considerations For 

Airborne Doppler Radar Detection of Windshear 

October 19, 1988 

' l! PULSE-PAIR MEAN WITH IDEAL NOTCH FILTER 

4 ..-. -...-.-.-.-.-.-.- .... 0 12 3 4 5 6 7 8 9 1011121 

NYOUIST BW = 2 244 m/s 

TRUE WIDTH SIGMA = 20x3 m/s 

IDEAL FILTER NOTCH BW = 244 m/s 

!t PULSE-PAIR WIDTH WITH IDEAL NOTCH FILTER 

11 

IL 

mt.b Edhnala -BUR "rue 

. 

.. 

. 

290 0 
0 Clutter Filter Design Considerations For 

Airborne Doppler Radar Detection of Windshear 

October 19, 1988 

Nean Eetimate vwme Rue Mean 

1: 0 12 3 4 5 6 7 8 9 101112 

NYOUIST BW - t244 m/s 

TRUE WIDTH SIGMA = 2 0333 m/s 

IDEAL FILTER NOTCH BW = 488 m/s 

Padu SI.cerr Lsbormcory 

Electrical Md Corputer Lngineerin~ 

C1er;on Wnivurslty 2nd ~AW mwing oct. 1s. 1988 

I 

IL PULSE PAIR WIDTH WITH 4 m/s IDEAL NOTCH 

Width Bntlmate verrrue True Mean 

0-t .... -.-.-.- ....... ~ ...... 1 0 12 3 4 5 6 7 8 9 10111213 

NYOUIST BW = f 24 4 m/s 

TRUE WIDTH SIGMA = 20333 m/s 

IDEAL FILTER NOTCH 0W - 488 rn/s 

0 29 1 
Clutter Filter Design Considerations For 

Airborne Doppler Radar Detection of Windshear .. October 19, 1988 

!.I PULSE-PAIR MEAN 

WITH BUTERWORTH NOTCH FILTER 

Mean Entimate vemn True Mean 

0 12 3 4 5 6 7 8 9 101112 

NYOUIST BW - f 24 4 m/5 

TRUE WIDTH SIGMA = 20333 m/s 

y(n) = 05 * y(n - 1) + x(n) - x(n - I) 

PULSE-PAIR WIDTH 

WITH BUTTERWORTH NOTCH FILTER 

Width Butimate vcm True Yearn 

11 0 12 3 4 5 6 'I 8 9 10111213 

NYOUIST BW i 244 m/S 

TRUE WIDTH 

y(n) = 05 * y(n - I ) + x(n) - x(n - 1) 

SlGHA = 2 0333 rn/s 

0 

(0 292 
0 

H It' 

Clutter Filter Design Considerations For 

Airborne Doppler Radar Detection of Windshear 

October 19, 1988 

PULSE-PAIR MEAN WITH PULSE CANCELLER t! 

Mean Estimate vemp Rus Mean 

.. 

NYOUIST BW - f 244m/s 

TRUE WIDTH SIGMA = 20333 m/s 

y(n) = x(n) - x(n - I) 

u u 

PULSE-PAIR WIDTH WITH PULSE CANCELLER 

00 0 12 3 4 5 6 7 8 9 10111213 

NYOUIST BW - f 24 4 m/s 

TRUE WIDTH SIGMA = 20333 m/s 

y(n) = x(n) - x(n - I) 

Radar Slrtenr Laboratot~ 

Clerion Unlwriity 2nd ~AW ,,,aing Electrical Md Computer Engineering at. 1% 1988 

e 

293 0 
I 0 Clutter Filter Design Considerations For 

Airborne Doppler Radar Detection of Windshear 

October 19, 1988 

~ 

SUMMARY 

Airborne Environment Has Unique Problems 

large clutter to signal ratios 

dynamic range requirements 

non-stationarities 

lack of repeatability 

0 Optimized Signal Processing Schemes are 

Needed and are Feasible 

294 
. 

Session I. Airborne-Sensors 

Airborne Radar Scatterometer Desi n & Flight Test 

W. R. Jones and C. D. Lytle, NAS A L.aRC 

295 

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Session I. Airborne-Sensors 

Ramifications of the Recent FAA Rule for Wind Shear Systems on the 

Development of Forward-Looking Systems H. Patrick Adamson, TPS 

.. 
A. 

4 

. 

N9 1- 11 69 1 J 

RAMIFICATIONS OF THE RECENT F.4A RULE 

FOR WINDSHEAR SYSTEMS 

ON THE 

DEVELOPMENT OF FORWARD-LOOK1 NG SYSTEPIS 

€4 *-_.Patrick Aclams.9n 

Turbulence Prediction Systems 

Boulder, Colorado 80301 

ABSTRACT 

r"'+ 

The recent FAA rule requiring windshear systems with f'l ight 

guidance may have severe ramifications for the development of 

Infrared and other forward-looking systems. The industry needs 

to have and can have a more cost effective option through t.he 

use of a forward-looking system with a reactive backup instead 

of a reactive system with flight guidance. However, because 

of the short time for compliance with the new FAA rule, it is 

possible that existing transport aircraft will be in full 

compliance before a comprehensive investigation of all forwardlooking systems can be completed. If this occurs, it is possible 

that the market for forward looking systems will be severely 

reduced, thereby eliminating the economic incentive to develop 

these much needed systems. Thus, t,o assure that this option 

is available for the airlines, it behooves the industry to 

immediately support an in-service evaluation of all available 

forward-look ing sys terns. 

315 
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COST BENEFIT OF OPTIONS 

Option A Alrborne reactive Low Level Wind Shear system with f light 

Opti& B Alrborne reactive LOW Level Wind Shear system and 

Turbulence Precicrlon Systems' Airborne predictive Low 

Level Wind Sheer and Clear Air Turbulef,ce system 

guidance or 

COST 

Equ i pme n t 

Reactive System 

F 11 ght Guidance 

Pred:ctive Systerr, 

Miscellaneous Materials 

Instal lation 

Reactive System 125 hrs § 250/hr 

Flight Guidance 125 hrs t $SO/hr 

Predictive System 125 hrs § $50/hr 

Re-Certify 

Flight Guidance 20 ttrs 5 $100/hr 

T rai ni ng 

Simulator Modifications 

Flight Guidance 4 hrs/perso!: 

x 2 peop:e/crew 

ODtion A ODtlon 

s 25,000. $ 25,000. 

50,000. 

10,000. 15,000. 

10,003. 

6,250. 6,250. 

6,250. 

€l,25Cm. 

2,000. c.. 

x 5 crews/aircrhft 

x $500 per hour s 20.000. 

Total pirrct C9st per aircraft 1st yr f go coo 4. 

Down Time 

Reactive System 125 hrs § S500/hr 62,500. 

Flight Guidance ;2f hrs 0 $SGO/'hr 62,500. 

Preaictive System 125 hrs § f503/hr 

Total Indirect .€mL per aircraft 1st yr )125.000. 

Total Ccst per aircraft 1st year $224.500, 

ANNUAL SAVINGS DUE TO CAT AVOIDANCE 

* Cost of CAT t6.00/flight expressed in 1964 dollars "Report of 

the National Committee For Clear Air Turbulence..; U.S. 

Department of Commerce; @ecember 1966, pp 37. 

320 
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323 
AIAA-88-4659 

Airborne Passive Infrared System for 

the Advance Warning of Low-Level 

Windshear and Clear Air Turbulence: 

1988 In-Service and Theoretical 

Work 

H. Patrick Adamson, Turbulence 

Prediction Systems, Boulder, CO 

AIAA/NASA/AFWAL Conference on 

Sensors and Measurements 

Techniques for Aeronautical 

Applications 

September 7-9, 1988/Atlanta, Georgia 

For pemissllon to copy or republish, contact the American Institute of Aeronrutlu and Astronautics 

370 L'Enhd Promenade, S.W., Washington, D.C. zooZ4 

324 
AIRBORNE PASSIVE INFRARED SYSTEM FOR THE 

ADVANCE WARNING OF LOW-LEVEL WINDSHEAR AND CLEAR AIR TURBULENCE: 

1988 IN-SERVICE AND THEORETICAL WORK 

H. PATRICK ADAMSON' 

TURBULENCE PREDICTION SYSTEMS 

BOULDER. COLORADO 

Abstract 

Air turbulence is the leading cause of weather-related fatalities for 

commercial airlines. Air turbulence 

is classified as either Clear Air 

Turbulence (CAT) (high altitude) or LowLevel Wind Shear (LLWS) (low-altitude), 

which is the most dangerous. Currently, 

there is no method available to provide 

sufficient advance warning to the 

flight crew of either impending CAT or LLWS. Flight research, supported later 

by laboratory research and computer 

simulation, indicates that a microprocessor based passive infrared system 

could provide an adequate advance 

warning for both CAT and LLWS. 

The effectiveness of this infrared 

system will be determined during an inservice evaluation on a commercial airline(s). This evaluation is scheduled 

to begin in September 1988 and to 

continue for up to 12 months. At that 

time, the system is expected to be 

certified by the Federal Aviation 

Administration and made available to the 

aviation industry. This system coupled 

with present avionic aids and pilot 

training will substantially reduce the 

probability of an accident due to air 

turbulence. 

Introduction 

As the leading cause of weather 

related air carrier accidents in the 

United States, air turbulence has been 

recognized as a national problem.' 

Consequently in 1987, the US government 

instituted an Integrated Wind Shear 

Program administered by the Federal 

Aviation Administration (FAA).¶ The 

airborne sensor segment of this program 

is jointly administered by FAA and 

NASA. The focus of this paper is to 

describe our work in assessing the 

effectiveness of an Infrared Remote 

Sensing System (Infrared) as a viable 

airborne sensor within this program. 

Air Turbulence 

Air turbulence ircp defined as the 

rapid change in the air/wind speed 

and/or direction that can have a dynamic 

*Principal Investigator 

Copyright c 1988 by H. Patrick Adamson. Published 

by the American Institute of Aeronautics and 

Astronautics, Inc. with permission. 

effect on the performance of an aircraft. 

Such turbulence has been classified as 

either Low-Level Wind Shear (LLWS) or 

Clear Air Turbulence (CAT), with LLWS 

presenting the most serious threat to 

aircraft and passenger safety. 

Low-Level Windh~ear - 

Low-Level wind shear is defined as air 

turbulence occurring between 1500 feet 

above ground level (AGL) and the surface. 

These events may be from 7 - 8 kilometers 

to 25 or 30 kilometers wide to thousands 

of meters higha3 

"The meteorologlcal phenomenon producing low-level windshear are, primarily, 

thunderstorms, gust fronts, fast-moving 

frontal zones, and less frequently, 

low-level inversions. "3 "The most 

threatening types of wind shears are 

downbursts, or microbursts - descending 

shafts of air.. . "4 Yicroburst 

lifecycles are typically 10 - 15 minutes. 

Clear Air Turbulence - 

"Clear air turbulence, often termed 

CAT, is a region of high turbulence 

encountered by an aircraft without visual or radar warning. CAT includes all forms 

of turbulence occurring in clear air 

which does not involve convective 

forces. "5 

"Two separate conditions are known 

which result in CAT. The first condition 

is created by a standing wave found in 

the lee of a mountain barrier which 

occurs when statically stable air is 

carried over the mountains. The second 

condition results from waves formed in 

statically stable layers in the atmosphere that are subjected to sufficiently 

strong vertical wind gradient (8hear)"s 

Airborne Sensors/Systems - LLWS 

There are two basic types of 

airborne sensors/systems used for 

detecting impending LLWS; they are reactive and predictive. To ascertain 

the danger to the aircraft from air 

turbulence, a number of factors must be 

considered. Since these factors can occur in different combinations, a hazard 

ORIGINAL PAGE IS 

OF POOR QUALlrV 

325 
index is used to ascertain the extent of 

the danger to the aircraft. Both 

systems need to characterize the hazard 

to the aircraft. One accepted formula 

to calculate this hazard is: 

W>/g - V/AS = Hazard Index 

A positive (+I number represents a 

hazard. 

WX is the rate of change in horizontal winds in knots per second and 

a positive (+) number indicates a 

tai lw ind. 

g equals the gravitational constant. 

of 19.04 knots per second. 

V equals vertical wind velocity in 

knots and a minus (-) number indicates a downdraft. 

AS equals airspeed in knots. 

Reactive (In-Situ) Sypts~ - 

These systems utilize the aircraft as 

the sensor to ascertain when the 

aircraft is entering wind shear. At 

this point, immediate action is required 

by the flight crew to escape the event. 

Predictive Lerward Looking) Systems, 

LLws - 

These systems are comprised of any 

sensor(s) that would provide advance 

warning to the flight crew of impending 

windshear. If the warning is provided 

more than five miles (approximately 1.5 

minutes) before the aircraft would 

encounter the LLWS, the warning is 

classified as "advisory". Less than 

five miles, it is an "executive" 

warning. An executive warning indicates 

that immediate action must be taken by 

the flight crew to avoid encountering 

LLWS . 

Airborne microwave doppler, laser 

doppler (LIDAR) and infrared techniques 

have been and are currently being tested 

to ascertain their effectiveness in 

providing advance warning of impending 

LLWS . 

Airborne Sensors/Systems - CAT 

Since encountering CAT has not 

traditionally been considered a crisis 

event, no effort has been conducted to 

develop a reactive CAT system. However, 

because of the inconvenience 6nd cost 

associated with CAT, various techniques 

have been tested for the purpose of 

providing advance warning of impending 

CAT. Other than Infrared, none have 

been considered successful. 

rn_t-rar_d_.;?p~lication - LLWS 

The application of Infrared to 

provide advance warning of air turbulence is based upon meteoroloRica1 

dynamics which causes the event. Based 

on meteorological research conducted by 

Bpers and Brahame 1 n t tiei r 'i'hiindcri t orrn 

Fawbush and Miller' 5;h:r.h drrnoristlatP11 

that down drafts (microbursts) were 

colder than the surrounding air, Drs. 

Peter Kuhn and Fernando Caracenas 

concluded that infrared technology could 

be used to detect these cold downbursts. 

Project and research conducted by '* 

. This hypothesis was subsequently 

substantiated by airborne research 

conducted by Dr. Kuhn in the Joint 

Airport Weather Study (JAWS).a 

During the study, 42 microbursts were 

penetrated at altitudes of 300 - 800 

feet AGL with 100% success in advance 

identification of these events. Later 

flights proved that infrared will 

function properly in light rain and dry 

air.9 

An analysis of this research and 

other studies enable us to ascertain, 

from perceived temperatures, an estimation of the wind velocities that the 

aircraft is expected to encounter. 

Thus, the extent of the impending danger 

to the aircraft can be estimated through 

the use of infrared technology. 

Infrared ADDlication - CAE 

Although others had, with limited 

success, used infrared to detect CAT, 

Dr. Kuhn conducted the most extensive 

and successful program from 1978 through 

1982. In approximately 700 flight 

hours, he obtained a 98% success rate in 

detecting CAT with advance warning 

ranging from 2 to 9 minutes.10 

Infrared-Cuyrent Status 

As an extension of the instrument 

design and development work conducted at 

the Instrument Development Laboratory at 

the University of Colorado, we have 

developed an airborne passive infrared 

system that provides advance warning of 

both LLWS and CAT. This system is now 

in the pre-production phase ready for 

aircraft installation. The system 

meets military specifications. It 

weighs approximately 30 pounds and the 

dimensions are 11 1/4" X .8 1/2" X 6 

1/2". The production model, on which 

construction has begun, is approximately 4 

2/3 of the weight and size of the preproduction model. 

I 

326 
To validate the performance 

pre-production instrument, the are in progress: 

1) Laboratory simulations 

2) Computer simulation 

3) In-service evaluation 

of the 

f ol lowing 

Laboratory-Simulation - LLJS 

The purpose of the laboratory 

simulation is to establish the accuracy, 

sensitivity and reliability of the 

instrument. To accomplish this, a test 

facility has been constructed to 

simulate atmospheric conditions. This 

facility allows for the calibration and 

the testing of the instrument at various 

temperatures to detect varying temperatures at both near and far distances. 

These tests assess the system's capacity 

to detect small change in temperatures 

at various distances and to reliably 

repeat these tests. 

Since the functions of the optical 

and mechanical components are controlled 

by a microprocessor, the software must 

also be tested for accuracy and reliability. In addition, the instrument 

must be tested for suitability in an aircraft environment. 

Laboratory Simulation - CAT 

Based on the in-flight research 

conducted by Dr. Kuhn, we do not 

anticipate that CAT simulation will be 

necessary. However, depending on the 

results obtained in the in-service 

evaluation phase, CAT simulation could 

be conducted later. 

Computer Simulation - LLWS 

The purpose of these simulations is 

to simulate flying our instrument 

through NASA generated microburst 

weather models. This involves selecting 

1) an atmospheric model, 2) a particular 

look distance (calculate infrared 

transmittance), and 3) a flight path 

(landing or takeoff). These parameters are used to calculate the expected 

hazard index. 

.* 

These atmospheric models include a complete thermodynamic profile of the 

event in the spatial realm of five 

kilometers on either aide of the event 

and four kilometers in altitude. That 

is, the model provides temperatures, 

pressure, rain, water vapor, snow, and 

vertical/horizontal wind profiles.11 

NASA has generated two models that 

they consider represent the conditions 

contained in a microburat. These are 

the "Wet" and "Dry" models. 

These axisymmetric models, by design, 

include the most extreme atmospheric 

conditions that an aircraft could be 

expected to encounter. That is, they 

range from the wettest to the driest 

microburst with cold or warm downdrafts. 

The Wet model includes rainfall of 

approximately 4.5 inches per hour at the 

center of the microburst and has a 

decreasing temperature profile, i.e. a cold downdraft relative to the ambient 

air. The rain rate and temperature 

profile approximate the conditions 

encountered by Delta 191 at Dallas in 

1985. This model appears to accurately 

represent meteorological conditions as observed by in-flight researchers as 

well as reported by aircraft digital 

flight data recorders. 

The Dry model does not include any 

precipitation and has a cold downdraft 

that becomes warmer near ground level. 

While some ground based research indicates neutral or positive temperatures 

for the radial winds associated with 

microbursts, empirical airborne research 

data supports only decreasing temperature profiles. For example, in JAWS 

only decreasing temperatures were 

recorded in all 42 microbursts that were penetrated at 300' to 800' AGL.0 

Furthermore, almost all of these were 

dry microbursts. To our knowledge, the only 

increasing temperatures recorded to 

date in a microburst were from ground 

measurements.lz* 13 The problem ~ith 

ground based data, however, is the 

measurement can be affected by the warm 

air next to the ground. 

Computer Simulation Procedures - LLWS 

Infrared Transmittance Calculations - 

To calculate the effective look 

distance of the instrument, transmittance of infrared power in the 

atmospheric conditions presented in the 

model must be calculated. The LOWTRAN 6 

computer program is used for this 

purpose. This program was developed by 

the Air Force Geophysics Lab (AFGL) and 

is the standard used by the infrared 

indus try. 1 4 

Aircraft Flight Path - 

The model assumes a normal landing 

and takeoff pattern for a typical air 

transport. For each simulation, the 

flight profile is determined first. For 

landing, the aircraft flies horizontally 

from lOkm to within 3.6km of the microburst's axis at an altitude of 300 

meters ACL. At this point, which is the 

327 
outer edge of the microburst, the 

aircraft descends at a 3 degree glide 

slope through the microburst and lands 

2 km beyond the microburst axis. 

For takeoff, the aircraft remains on 

the ground during the simulation with 

the planned rotation point located at 

the near edge of the microburst. 

After the flight pattern is 

established, the next step is to determine the hazard by establishing the 

vertical and radial winds that will be 

encountered. 

Hazard Index - 

Two separate hazard indices are 

calculated. One is the hazard index 

computed by the system (system's index) 

using proprietary algorithms and the 

other is the hazard index computed using 

inertial data (inertial index). By 

including data from the inertial index, 

it is possible to assess the accuracy of 

the system. 

The system index is computed by using 

LOWTRAN 6 to calculate the transmission 

of infrared power along the proposed 

flight path. The power is calculated on the spatial grid by an analytic 

expression. Once the total power is 

computed, the perceived temperature can 

be calculated. Assuming an air speed 

and knowing the change in perceived 

temperature, vertical and horizontal 

winds can be inferred and thus, the 

hazard index is determined. 

The inertial index is computed from 

inertial data experienced by the aircraft. That is, the rate of change in 

horizontal winds, vertical winds and air 

speed. The formula to calculate this 

index is: 

0 

WX/g - V/AS = hazard index. 

The process of calculating both the . 

system index and the inertial index 

involves flying a normal takeoff or landing profile into a specific microburst model and then calculating, at one 

second intervals, the specific hazard 

index. By time tagging each index 

(system and inertial) the system index 

at a given point in time can be compared 

to the inertial index that the aircraft 

would encounter seconds later. This 

comparison provides the opportunity to 

assess the accuracy of the system index. 

Computer Simulation Result8 - LLWS 

Wet Cold Microburst - 

index alert of 0.15, would have provided 

a warning 33 seconds prior to that 

provided by the inertial index. That 

is, the inertial index exceeded 0.15 

alert level, approximately 33 seconds 

after the system index exceeded 0.15. 

At .I25 the warning would have been 

approximately 40 seconds. 

Warning time can be determined by 

counting the number of boxes that occur 

after the instrument line crosses the 

alert line (0.15) to the point where the 

pluses (+'SI cross the alert line 

(0.15). Each box or plus (+) equals one 

second. The selection of 0.15 for an 

alert level is based on assumed levels 

of aircraft performance. The level 

could be set either higher or lower. 

The problem with high settings is the. 

danger of encountering a dangerous 

microburst without providing a warning. 

A low setting however, may result in a 

warning when the air turbulence is not 

dangerous (nuisance alert). This is one 

of the answers the in-service evaluation 

will provide. 

* 

-0.. 

! -0s -l 

Figure 1 

In the takeoff profile, depicted in 

Figure 2, the system, using an alert 

level of 0.15, would not have provided 

an advance warning, but at .125 it would 

have provided a warning approximately 13 

seconds prior to that provided by the 

inertial index. 

c 

In the landing profile, depicted in 

Figure 1, the aystem, using a hazard 

328 

ORIGINAL PAGE I: 

OF POOR QuALrn 
c 

When it is determined, by all parties 

involved, that the system is operating 

properly, two more systems will be 

installed and evaluated by all parties 

for up to 12 months. The FAA has 

expressed an interest in the analysis of 

this data and it is anticipated that the 

data obtained from this in-service 

evaluation will be a significant factor 

in obtaining FAA certification. 

Conclusion 

Assuming the successful completion of 

the in-service evaluation, we expect 

that this AWS will be available to the 

aviation industry by the later part of 

1989. With the availability of an 

advance warning system coupled with a 

reactive system and continued pilot 

training, the probability of avoiding a 

LLWS accident is almost 100%. 

We are looking forward to making 

continued progress in assisting the 

aviation industry in increasing aviation 

safety. 

REFERENCES 

lAirLine Pilot (Technical Talk), 

Vol. 46, April 1977, pg. 38. 

"Integrated FAA Wind Shear Program 

Plan," United States Department of 

Transportation, DOT/FAA/DL-87/s, April 

1987. 

'Federal Aviation \dministratlon, 

aKuhn, P. M., R.L. Iiurkowski, F. 

Caracena, "Airborne Operation of an 

Infrared Low-Level Wind Shear Prediction 

System," Journal of Aircraft, Volume 20, 

Number 2, February 1983, pp. 170-173. 

'Richmond, .Jeff, "Taking The Wind 

Out of Wind Shear," Hinh Technolony, 

May 1986, p. 62. 

'Kuhn, Peter ?I., Invmtor, "Yethod 

and Apparatus for Detecting Clear Air 

Turbulence"; United States Patent; 

4,266,130, May 5, 1981, p. 1. 

'Bpers, H.R. and R.R. Braham, 

Jr . , "The Thunderstorm" ; Report of the 

Thunderstorm Project, U. 9. Weather 

Bureau, Washington, D.C., June 1949. 

'Fewbush, E. J. and R. C. Mi1ler;"A 

Basis for Forecasting Peak Wind Gusts in 

Non-Frontal Thunderstorms," Bulletin of 

- the American Meteorological Society, 

Vol. 35, No. 1, January 1954, pp. 14-19. 

aKi11in. P. If., '1nnIir.ttion of 

Infrared Radiometers for Airborne 

Detection of Clear Air Turbulence and 

Low-Level Wind Shear," Final Report NASA 

ARC Contract (NAS2-10592), March 1985. 

9a-~~~~~111~~, F. inti P. :\rthn, 'Forward 

Looking Airborne Infrared Wind Shear 

Sensor Operations in Precipitation," 

Paper NOAA #43-RANR-5-03966, October 

1987. 

loSt+ai.n%, I.. .~nd \'. \.()<a\-, 'FlnaI 

Statistical Report on Aviation Safety 

Technology (In-Flight Detection and 

Prediction of Clear Air Turbulence," 

NASA, Ames Research Center, RTOP 505-08- 

11, RNA-43115-B, December 1979. 

*~PI,K~I,~, L.., S. (.liinr?g, J.k. Lank. 

M.L. Kaplan, and F. Proctor, "A Numerical Weather Prediction System Designed. 

to Simulate Atmospheric Downburst 

Phenomena." AIAA-84-0352. 

IaBedard, I. ~nd LeFeb!ir?, 'Surfsce 

Measurements of Gust Fronts and Microbursts During the JAWS Project: Statistical Results and Implications for Wind 

Shear Detection, Prediction, and Modelling," NOAA ERL WPL-135, April 1986. 

IaFu.jita, I., The Downbur&t-::-Mlcroburst and Macroburst, MesometeoroloEY 

Research Project, SMRP Dept. of Geophysic Sciences, University of Chicago, 

1985. 

14hneizys, F.X., et.al, "Atmospheric 

Transmittance/Radiance: Computer Code 

LOWTRAN 6," Air Force Geophysics Laboratory, AFCL-TR-83-0187, August 1983. 

329 
Drv Hot Microburst - 

In this NASA provided model, in 

neither the landing nor takeoff profile 

did the system index provide a warning 

earlier than the inertial index. This 

would always be the situation because 

the system index is based on encountering a cold downburst in either the wet 

or dry microburst. 

DzCold Microburst - 

In order to assess the accuracy of 

the instrument in the dry microburst 

model, we combined the Dry microburst 

model with the cold temperature profile 

(decreasing temperature) of the wet 

microburst model. This temperature 

profile is representative of the 

airborne temperature changes recorded 

for the dry microbursts encountered in 

the JAWS program. 

In the landing profile, depicted in 

Figure 3, the system index, using an 

alert level of 0.15, would have provided 

a warning approximately 27 seconds prior 

to that provided by the inertial index. 

DRY MICROBURST RUN #24 TIME 24.00 MIN -. IM L m LOO.. 111 nu 

In the takeoff profile, depicted in 

Figure 4, the system index, using an 

alert level of 0.15, would have provided 

a warning approximately 39 seconds prior 

to that provided by the inertial index. 

il 

Figure 4 

Actual Flight Data - 

While computer simulations and 

modelling are excellent analytical 

tools, it is desirable to use real data 

whenever possible. Consequently, we 

have taken the actual flight data from 

several flights: Delta 191, Iberia 933 

(Logan) and an incident occurring over 

Atlanta, and simulated what warning, if 

any, the system index would provide at 

an alert level of 0.15. In each 

situation, the actual hazard encountered 

coincided closely with the system hazard 

index. For example, in the Delta 191 

accident the system index set at 0.15 

alert level would have provided a 30 

second advance warning in the landing 

profile. 

In-Service Evaluation - 

In conjunction with Sperry Commercial 

Flight Systems, a division of Honeywell, 

Inc., we will conduct an in-service 

evaluation of our system for advance 

warning of CAT and LLWS. This advance 

warning system (AWS) will be installed 

with a dedicated flight recorder and a 

Honeywell reactive system. 

This evaluation will be conducted in 

two phases. The first phase, involving 

one system, will be flown either on a 

commercial airline or a corporate 

aircraft for a period of at least 30 

days. 

BRIQfNAb PAGE IS 

OF POOR QUALrrV 

3 30 
Session I. Airborne-Sensors 

Status of the Delco Systems Operations Forward Looking Wind Shear 

Detection Program Brian Gallagher, Delco Systems 

33 1 
’r 

J STATUSOFTHEDELCOSYSTEMSOPERATIONS 

FORWARD LOOKING WINDSHEAR DETECTION PROGRAM 

Brian J. Gallaaher 

Delco Systems Operations 

Milwaukee, Wisconsin 53201 

ABSTRACT 

I -7 

Y 

Delco Systems Operations, a division of General Motors Hughes Electronics 

Corporation, is developing a Forward Looking Windshear Detection System based 

on the integration of infrared remote sensing and accelerometer reactive 

sensing technologies. The IR sensor is a multi-spectral, scanning radiometer 

operating in the 8 to 14 micron region. A 2 x 5 detector array with parallelserial scanning produces 60 degrees horizontal and 10 degrees vertical-fields 

of view. Using multiple wavelength signals, azimuth temperature gradients 

are analysed for characteristic signatures of thermally induced windshear 

phenomena. Elevation temperature gradients are processed through an atmosphere 

model to continuously compute a stability index for arming microburst 

detection criteria. The atmosphere model and proprietary computer processing 

algorithms combine to generate coarse estimates of disturbance ranges based on 

multiple wavelength radiance data with different extinction coefficients. 

Computer outputs of atmospheric stability, disturbance intensity, and azimuth 

and range information provide a situation display capability. A ground 

operated, experimental radiometer has been developed and is being used to 

verify our detection and discrimination concepts at an atmospheric and 

simulated rain test facility in Milwaukee. A prototype airborne radiometer is 

being developed for flight test evaluation during the summer of 1989. 

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cr! 

e 

Session I. Airborne-Sensors 

Infrared Thermal Ima ing of Atmospheric Turbulence David Watt and John%cHugh, University of New Hampshire William Pfeil, Kollsman 

. 

349 
N9 I- 11 69 3 

INFRARED THERMAL IMAGING OF ATMOSPHERIC TUBULENCE 

David Watt and John McHugh 

University of New Hampshire 

Durham, NH 03824 

William Pfeil 

Kol lsman 

Merrimack, NH 03054 

ABSTRACT 

A technique for analyzing infrared atmoshperic images to 

obtain cross-wind measurements is presented. The technique is 

based on Taylor's forzen turbulence hypothesis and uses crosscorrelation of successive images to obtain a measure of the 

cross-wind velocity in a localized focal region. The technique 

is appealing because it can possibly be combined with other IR 

forward look capabilities and may provide information about 

turbulence intensity. The paper describes the current research 

effort, its theoretical basis, and its applicability to wind 

shear detection. 

35 1 
Image Cross-Corelation for 

Atmospheric Wind Measurement: 

Review of Work in Progress 

David Watt 

John McHugh 

Department of Mechanical Engineering 

The University of New Hampshire 

~ 

Durham, N.H. 

William Pfeil 

Merrimack, N. H. 

Kollsman Instrument Co. 

r. 

t 

A 

352 
GOALS . 

* P,rimary goal is to develop a 

predictive on-board windshear 

detection device 

The desired specifications of a 

future detection system include 

I. 

2. 

3. 

Capable of detecting 1-2 

kilometers ahead of plane 

Capable of obtaining some 

measure of the NASA/FAA 

hazard index. 

Monitor crosswind by 

image anaylsis. 

353 
APPROACH 

lmaae Cross-correlation Velocimetrv 

Quasi -steady/ 

Flow Image 

W 

\ Detector 

Taylor's "Frozen Turbulence" Assumption: 

1) Flow image moves at dominant velocity scale. 

2) Fine scales change slowly, Flow image steady 

0 Velocity determined comparing two successive 

images within short time interval. 

Comparison mechanism is cross correlation 

function. 

Continuously monitor cross-wind velocity. 

. a Images generated by various optical phenomena. 

354 
Quasi-Steady Turbulence Generated Images 

Laser Speckle 

Gated 

- laser 

I 

* Speckle is coherence artifact 

* Steady Scattering and Refractive Index Field 

* Requires laser & gated detector for ranging 

4 

* 

* 

Ranging by time of flight during gating interval 

Could be integrated with lidar 

4 

355 
Quasi-Steadv Turbulence Generated lmaaes (cont'd) 

t 

FLlR 

- 

-Passive Detection 

-IR intensity variation driven 

I by temperature fluctuations 

-Images may provide other relevant information: 

Turbulence Intensity 

Temperature gradient 

-Compatible with other aircraft 

forward-look needs l 

-Signal strength to be evaluated in detection region 

356 
Passive IR Imaging In 

Absorbing-Emitting Media . 

di do 

b 

0 

Intermediate 

Afocal region 

field 

Focal region 1 

Need to Isolate Focal Region 

Far-field signal attenuated by atmospheric absorbtion 

1 Signal from intermediate range is defocused. 

357 
Imaging Model 

Radiative Transfer Ea u at' ion 

vz 0 

B(a,T) = Emitted and incident radiation 

ow = Spectral transmittance of lens. 

3 T(V,Z) = Differential transmittance of 

az 

- atmosphere. 

a = Solid angle 

N = Radiant flux onto detector pupil 

Model lmaaina Equation 

i(x,y)= h(x,y,z)* (€e (x,y,z)exp(= az)) dxdy dz 

0 (x,y ,z 1 

Model RTE 

h - point spread function 

E - pointwise emissivity 

e - spectral emissive power 

.o(x,y)-aperture solid angle 

b,h 

. 

I 

* -convolution 

358 
Emittance Calculation 

Wavelength (pm) .. 

(d) Transmittance of hformly mixed gases (CO2. N20, CO, CH,, 02) 

(4.5 to 19.0 Nm). ** 

Transmittance-Beer's Law 

T~(z)= exp (- a z h) 

Absorptance -emittance 

359 

Local Emissivity 

E =I-exp(-a &) 

3 t5z = volume of resolution cell 
Imaae Localization bv Defocussinq 

Incoherent Imaging MTF, with atmospheric absorbtion I 

Target Distance- 1000m, 50cm f.l., f/l.O 

Ranae 

Og5-1/ 500 750m 

/,lo00 m 

MTF 

0.0 

1250 m 

1500 m 

FLlR limit 

0.2 0.4 0.6 0.8 1 .o 

0 Normalized Spatial Frequency, f / 2 f 

-At higher spatial frequencies, focal 

region contains most signal energy 

-By high-pass spatial filtering 

signal can isolate focal region 

-Upper limit imposed by sensitivity, 

spatial resolution of FLlR 

360 
lmaaina Simulations 

i I I f t 1 I f I f f f 1 I 1 4 I 1 I I I f I 1 1 1 1 1 1 ! HI 1 ! 1 1 1 1 f 1 1 t 1 1 ! I f 1 1 : 1 1 f 1 I f f 1 1 ! +!!I I"""""""""""""""""""""""""""' 

4;xI II II I I I II I I IIItII I I I I I I I1 I I1 I I! I I I I I I I I I IIII I I I I I I; I I 

Model Features 

0-2-D Fractally Generated Temperature Field 

. --2 x 1 kilometers deep (1024 x 512 nodes) 

--Uniform Emissivity and Absorptivity 

--Intensity variation due to 

temperature fluctuation only 

0-50 cm f.l., f /1.0 lens 

-- Separate MTF calculated for each z location 

-- Convection by rigid motion of all or part of 

36 1 
Y 

cd 

a 

Q 

c 

0 

cd 

.- 

CI 

- 

a 

0 

0 

L 

L 

ic 

E 

a 

0 

cd 

a. 

cn 

a 

0 

m 

c 

0 

0 

a 

> 

c 

0 

.- 

c, 

0 

I 

)5 

tn 

v) 

a 

0 

a 

c 

2 

gcn 

a 

cd 

cn 

U 

0 

cn 

a 

c, .- 

.I 

e- 

.- 

L 

c 

.- cn 

Q>tn cnv) 

- 

I 

362 
Future Work 

-- Assess the effects of refractive turbulence 

-- Adapt TASS Model for Imaging Simulation 

--Develop Model of sub-grid temp. fluctuation 

--Use standardized radiation model (HITRAN) to 

Account for precip. broad spectra. 

--Several Flight Paths 

-- Obtain experimental FLlR images to assess 

suitability for this application. 

-- Simulate laser speckle imaging 

363 
Session I. Airborne-Sensors 

Avoidance of Wind Shear Hazards 

.. 
3 

INVESTIGATION OF AIRBORNE LIDAR 

FOR AVOIDANCE OF WINDSHEAR HAZARDS 

Russell Targ 

Lockheed Missiles & Space Company, Inc. 

Research & Development Division 

Palo Alto, California ' 94304 

and 

Roland L. Bowles 

NASA Langley Research Center 

Hampton, Virginia 23665-5225 

i Presented at the 

Second Combined Manufacturers' and Technology 

Airborne Windshear Review Meeting 

Williamsburg, Virginia 

October 18-20, 1988 

367 
-. ., I~ESlIGATION OF AIRBORNE LIDAR 

FOR AYOIDANCE OF IYINDSHEAR HAZAIZDS 

I~usscll Targ 

Lockhecd hlissiles & Space Company. Inc. 

Research & Development Division 

Palo Alto, California 94304 

and 

Roland L. Bowles 

NASA Langley Research Center 

Hampton, Virginia 23665-5225 

Abstract 

A generalized windshear hazard index is defined, which 

is derived from considerations of wind conditions at the 

present position of an aircraft and from remotely sensed 

information along the extended flight path. Candidate 

airborne sensor technologies based on microwave 

Doppler radar, Doppler lidar, and infrared radiometric 

techniques are discussed in the context of overall system 

functional requirements. Initial results of a performance 

and technology assessment study for competing lidars 

are presented. Based on a systems approach to the 

windshear threat, lidar appears to be a viable technology 

for windshear detection and avoidance, even in conditions of moderately heavy precipitation. The proposed 

airborne CO2 and Ho:YAG lidar windshear-detection 

systems analyzed in this paper can give the pilot 

information about the line-of-sight component of 

windshear threat from his present position to a region 

extending 1 to 3 km in front of the aircraft. This 

constitutes a warning time of 15 to 45 seconds. The 

technology necessary to design, build, and test such a 

brassboard 10.6-pm COz lidar is now available. However, for 2-pm systems, additional analytical and 

laboratory investigations are needed to arrive at optimum 

2-pm rare-earth-based laser crystals. 

B= 

d= 

D= 

E= 

F= 

g= 

h, = 

h= 

LR= 

T= 

v= 

w= 

K(R) = 

w, = 

w, I 

P= 

Nomenclature 

system bandwidth 

telescope diameter 

aircraft drag force 

total aircraft energy (or laser pulse energy) 

aircraft specific hazard index 

(nondimensional) 

acceleration of gravity 

aircraft potential altitude (energy height) 

aircraft altitude 

round-trip extinction for range R 

distance between adjacent range gates 

range of return 

aircraft thrust force 

aircraft airspeed 

aircraft weight 

vertical component of inertial wind 

horizontal component of inertial wind 

backscatter cross section 

This paper is declared a work of the U S. Government and IS not 

subject to copyright protecuon in the United Stales. 

369 

P3Y 

y = flight path angle relative to air mass 

A = laser wavelength 

q = detection and mixing efficiency 

7 = forward-look alert time 

v = gradient operator 

1. Backeround and Introduction 

Low-altitude windshear is recognized by the commercial 

aviation industry as a major hazard. In the United 

States, during the period 1964 to 1985. windshear has 

been a contributing factor in at least 26 civil transport 

accidents and 3 incidents involving 500 fatalities and over 200 injuries. Numerous methods of reducing the 

low-altitude windshear hazard have been proposed by the 

airlines, airframe manufacturers, and the Government. 

The Federal Aviation Administration (FAA), as lead 

agency for civil aviation safety, has established an 

integrated windshear program plan which addresses the 

windshear problem through focused research and 

development efforts over a 5-year period. The National 

Aeronautics and Space Administration (NASA) has 

responded by signing a memorandum of agreement with 

the FAA (July 1986) to pursue a cooperative research 

program which addresses technical factors related to 

airborne detection, avoidance, and survivability of severe 

windshear atmospheric conditions. Key elements of the 

NASA research effort include characterization of 

windshear phenomena in the aviation context, airborne 

remote-sensor technology that provides forward-looking 

avoidance capability, and flight-management system 

concepts that promote risk-reduction piloting through 

timely and accurate transfer of information to flight 

crews. The NASA research thrust is directed at developing system concepts which embrace forward-looking 

sensor technology, thereby providing the flight crew with 

awareness of the presence of windshear with enough 

time to avoid the affected area and escape from the 

encounter. 

This paper emphasizes the analysis of competing lidars 

for use in an airborne forward-looking system, to enable 

aircraft to avoid the hazards of low-altitude windshear. 

The analysis includes a definition of lidar sensor 

requirements, the formulation of a system to meet these 

requirements, and an investigation and simulation of the 

capabilities and limitations of such a system, together 

with recommendations identifying the most feasible and 

cost-effective laser for use in a lidar system for 

windshear detection and avoidance. 
The rno lidar s!'srems ini,estigated. solid-state Ho:\'AG 

31 2 1 pm and CO2 at 10 6 bm. appear able to meet the 

windshear warning requirements as determined by 

computer simulations of the 19S5 DallasiFort Worth 

microburst event. The performance of Ho Y.AG is 

potentially superior io that of the C02 lidar. but 

Ho.YAG is far from being a\ai!able at this time. On the 

orher hand, the CO2 technolog is quite mature. and has 

been tested extensively in both airborne and groundbased uind-field mapping applications. 

7 The Tb;ear FTT \\'indqhear 

Sational attention has focused on the critical problem of 

detecting and avoiding windshear since the crash on 

.August 2, 1985. of Delta Air Lines Flight 191. a Lockheed L-1011. at the Dallas/Fort IVorth International 

.Airport. Other crashes and near misses caused by 

windshear have occurred almost annually. 

The hazard of windshear arises principally from its 

deceptive nature: In a u-indshear situation, from a 

microburst or any other source, the pilot is confronted 

with a performance-increasing headwind, followed a few 

seconds later by a powerful. performance-decreasing 

tailwind. To cope with the headwind. the pilot may take 

actions to prevent the plane from climbing. These 

actions are then compounded by the lack of lift caused 

by the tailwind and downdraft, so that it may be 

impossible to keep the plane in the air. The downburst 

shown in Fig. 1 can be entirely invisible to the pilot and 

the ground controllers. and it need not be associated 

with any rain on the ground. In a NASA/FAA study of 

186 windshear occurrences in 1983, the average change 

in wind speed was approximately 40 knots.' 

The NASMAA Joint Airport Weather Study (JAWS)i 

observed and measured windshears at the Denver/ 

Stapleton Airport over a 3-month period. The principal 

finding confirmed that I* ... low-altitude wind variability 

(or windshear) presents an infrequent but highly significant hazard to aircraft landing or taking off." From 

analysis of aircraft accidents where low-altitude 

windshear was a factor, it appears that the greatest 

hazards are caused by downdrafts and outflows produced 

by convective storms. 

* 

Pilors now recei\ e inconsistent windshear Lvarnings that 

are of questionable reliability. The ground-based data 

from anemorncters must first be interpreted by trained 

meteorologists. The tower attempted to warn Flight 191 

of \<indshesr a full 2 min after it crashed. The 

I+'incsnt-ar Trcining .4id2 produced by the SAS?.iF.LU 

Integrated Program in 19S6 carries the warning. "Maximum \rindshear capability of jet transpons at heavy 

\\eizht. for a uindshear encounter at a cri~kal location. 

is 40 IO 50 knots wind-speed change. Sone windshears 

cannot be escaped successfully [once they are actually 

en:ered]!" For this reason it is essential to emphasize 

ai oidance ra:her than recovery. .4n onboard forwardlookng \vindshear-avoidance system can warn the pilot. 

at the location marked "tvindshear enir)" in Fig. 1. that 

he IS approaching a \rind hazard. When the plane is at 

the Iccation "recover or crash." it can be too late to 

inform the piiot that he is 

3 Renuirerrenrs for an Airborne U'indshear Dercctioq 

S\ ctem 

windshear. 

The fundamental requirement for a forward-looking. 

airboine windshear detection system is realtime remote 

sensing. This implies the ability to reliably measure 

line-of-sight and vertical components of wind velocity 

and to alen the crew when they are approaching a 

windshear hazard. The system should monitor the 

approach path, the runway, and the takeoff path. in both 

rain and clear-air conditions. This alert should be 

provided with enough warning time to allow the pilot to 

increase the energy of the plane and safely transit or 

avoid the microburst. The quantitative technical rtquircments are given in Table 1. 

Table 1. Quantitative Technical Requirements 

~ 

Minimum sensing range lto3km 

Advance warning time 

Range resolution 0.3 km 

Velocity resolution Approximately 1 m/s 

15 to 40 s 

Fig. 1. The windshear problem. 

370 
i 

t 

There are additional functional requirements for any 

airborne system: It must not interfere aith other 

instruments on the aircraft; it should be as SmJll as 

possible; it should operate reliably in an aircraft emiron. 

ment for 2000 hours ulth little or no maintenance; and 

it should not require any expendable supplies that would 

have to be replenished. All these factors should work 

together to make a system that is almost free from false 

or nuisance alarms. The first specific hazard that should 

trigger a windshear alarm is a performance-decreasing 

wind (tailwind) which increases its velocity at a rate’of 

2 knows in the direction of travel of the aircrafr. A 

second threatening condition is the downburst, which is 

considered a hazard when the vertical velocity reaches 

1500 ft‘min. A numerical hazard index “F” has been 

derived by NASA using both these factors, where 

F > 0.1 is considered a potential aircraft hazard. 

4. Definition of Hazard lndex 

The key to the development of airborne windshear 

detection. warning, and avoidance systems is the 

identification of a hazard index. This index should 

exhibit a functional dependence on atmospheric states 

that can be reliably sensed, and scale with available 

aircraft performance in such a way that the index . predicts impending flight-path deterioration. The hazard 

index must also account for factors such as the statistical nature of the windshear threat, fusion of present 

position and “forward-looking” sensor capabilities, and 

the development of objective methods for determining 

system warning thresholds which consider the potential 

for nuisance alerts. A hazard index which has the above 

properties and is based on accepted fundamentals of 

flight mechanics and current state of knowledge of 

windshear phenomena has been derived. 

.An analysis was conducted which revealed the importance of aircraft energy balance for flight in spatially 

and temporally varying windfields. This energy-state 

analysis showed that aircraft motions khould be referenced to the accelerated and nonhomogenous airmass 

which typifies windshear phenomena. The concepts of 

airplane total energy and rate of change of total energy 

are useful in interpreting the impact of windshear on 

aircraft performance. The airplane total energy is 

defined as the sum of the air-mass relative kinetic 

energy and the inertial potential energy. Air-mass kinetic 

energy is used since only airspeed, not ground speed, 

describes the airplane’s ability to climb or maintain 

altitude. Inertial potential energy is likewise used since it 

is altitude above the ground that is useful to the airplane. 

Therefore, airplane total specific energy (energy per unit 

weight), or porenrial altitude, is defined as: 

where V is airspeed, 

aircraft altitude. The rate of change of specific energyalso defined as the potential rate of climb of the 

airplane, assuming negligible energy loss when trading 

airspeed for climb rate-is given by: 

is aircraft weight, and h is 

CVhen combined tvith appropriate aircrat’t quat:onj of 

motion.’ the potential rate of climb given by Eq. (2) 

reduces to: 

IVISDSHEAR “HIT” 

= - E = (+- TD - [Los y + --,n y - - 

W 8 Y 

where (T - D)/W is the ratio of aircraft thrust minus 

drag to weight, W, and W,, are the horizontal and 

vertical wind velocity components. respecriLeIy. and y is 

the flight-path angle relative to airmass. 

The dot notation in Eq. (3) indicates the substantial 

derivative with respect to time, since the wind velocity 

components depend explicitly on aircraft position. 

For representative numerical values of windshear 

gradients, and for flight-path angles compatible Bith 

stabilized flight. i.e.. for y - 0. the hazard index labeled 

as windshear “hit” in Eq. (3) is accurately approsimaed 

as 

and Eq. (3) takes the approximate form: 

h‘ = - Le = [-i.- T- D -+. 

pw 

Equations (4) and (5) explicitly define the qumitative 

impact of windshear on aircraft energy state and the 

rate-of-climb capability. The analysis reveals that the rate 

of change of specific energy (potential climb rate) 

depends linearly on a nondimensional parameter F. 

which contains only information regarding air mass 

movement. Further analysis indicates that the subject 

parameter can be physically interpreted as the loss or 

gain in available excess thrust-to-weight ratio due to 

downdrafts, updrafts, and horizontal windshear. thus 

providing an aircraft-specific index on which to base 

annunciated warnings. 

The derived hazard index given by Eq. (1). referred to 

as the F-factor. exhibits the following properties: 

1. It scales with available aircraft performance in such 

a way as to predict impending flight-path deterioration. 

2. It shows a Functional dependence on atmospheric 

states that can be reliably sensed. 

3. It is applicable to both in-situ and remotely sensed 

windshear information. 

4. It is compatible with stringent nuisance-alarm 

requirements. 

Positive values of F indicate a performance-decreasing 

situation for the aircraft, whereas negative values 

indicate a performance-increasing condition due to 

atmospheric disturbance. Considering jet transports in 

take-off configuration and the current state of kno\c ledge 

regarding windshear phenomena, typical numerical 

37 1 
\slues for the terms under hazardous conditions maling 

up the F-factor are 

hote that a head\\ind loss of (V, = 0 1 J (2 Anots/s) 

has the same impact on aircraft performance (F value) 

as a doundratt \Vh = -15 hots (-1500 fvmin). considering a reference airspeed of 150 hots Figure 2 sho*s 

the ”safe operations” conditions as a function of the 

F-factor Larisblcs 

I W,, . TOTAL DERIVATIVE OF HORIZONTAL E’ 

. WINO COMPONENT 

w, = VERTICAL WIND COMPONENT 

- fi\ 

1 TAIL- HEAD 

Fig. 2 Definition F-factor hazard index. 

A possible airborne windshear detection, warning, and 

avoidance system architecture, which flows from the 

application of the F-factor concept, is shown in Fig. 3. 

The proposed architecture is compatible with a single-tier 

warning system (no amber caution) and provides for 

fusion of “present position” information, F(t). with 

“forward look” information, F(t + T). The prediction 

interval T is determined by a preselected and interrogated range gate divided by current aircraft ground 

speed. A preset hazard threshold Fo, is incorporated. 

which. when exceeded below a specified aircraft altitude, 

provides an alert to the flight crew. Any combination of 

horizontal windshear and/or vertical wind that results in 

F less than the threshold value indicates safe aircraft 

, W.19 In0?.120UTALI ~ , FLICHT CUIOIUCE 

-------- 

WhlV - (VERTICAL1 *Gzkzl 

REMOTE SENSOR1 SITUATIOU I PROCESSIUC 

Fig. 3 Fusion of present-position and predictive information. 

operation in relation to ava:Iable excess thrust-to-ireight 

ratio for that aircraft. A threshold exceedance that 

persists for a sufficient period of time warrants the 

annunciation of a uindshear warning. uhich indicates IO 

the crew that the affected area should be avoided or an escape maneuver should be initiated. The alen and 

uarning threshold is dererniined by considerins the 

maximum permissible F in relation to available aircratt 

performance capability u hile minimizing potential for 

nuisance warnings. Research indicates that threshold 

values for F between 0.1 and 0.15 are representative for 

landing and rake-off phases of flight for jer rransport 

aircraft, considering factors such as aircraft type. 

configuration. and range of gross weights. Figure 1 

illustrates average values for Lvindshear F-factors derived 

from five airzraft accidents. The data presented indicate 

that. in all cases. the average F-factor exceeded the 

ability of the airplane at maximum \\eight to acceler’x 

in level flight. 

- AIRPLANE LEVEL.FLICHT 

, ACCELERATION CAPABILITY 

, ATMAX WEIGHT 04- 

- 

I 

I 

i K 03- 

YI 

U LL 02- i 

I 

01- I 

II /I 

DENVER NEW CHICAGO DENVER DFW 

I ORLEANS I1 

ACCIDENTS 

Fig. 4 Accident windshear F-factors compared to 

airplane capabiiiries. 

The F-factor concept can be extended to forward-looking 

sensors through utilization of spatial wind measurements 

along a given line-of-sight direction, a characteristic 

which is typical for pulsed-Doppler detection and ransing 

systems. The substantial derivation expressed in Eq. (4). 

assuming a “frozen wind field” hypothesis, can be 

approximated as: 

aw, aw, 

at ax w, = v w, . v, + - = - v 

where V, is the inertial velocity vector of the aircraft. If 

Eq. (6) is substituted into Eq. (4) and the result 

linearized about the ith. range gate along a ray of the 

forward-look sensor, one obtains the recursion 

W, (i+ 1) 

V - 2Wx (i+ 1) + W, (i)] - 

The quantity L is defined as the distance between any 

two adjacent range gates along a line-of-sight ray of the 

i 

372 
c 

3 

Lactive sensor. Typical values for L are between 150 m 

and 500 m, depending on sensor pulse width. The 

realtime calculation of Eq. (7) predicts the distribution 

of hazard index based on absolute wind measurements 

at predetermined range gates. Sote that F(0). 

Wh (0). uhich can be determined from present position 

in situ measurements, are required to initiJlize the 

iteration. Application of the algorithm described above. 

in a variety of simulation studies. has demonstrated the 

need for presmoothing the spatial wind measurements in 

order to suppress small-eddy turbulence, otherwise an unacceptable incidence of nuismce warnings may occur. 

(0). m 

5 Amroaches to Airborne \Vindshear Detection 

5.1 Lidar Systems 

For more than two decades, optical heterodyne detection 

has been successfully used to measure the frequency of 

Doppler-shifted laser light scattered from moving 

aerosols. This technique has been pioneered by many 

researchers, including those working with both NASA 

and NOAX. Although wind-velocity measurements are 

routinely made with good accuracy to ranges of more 

than 10 km in clear air, the range is seriously degraded 

by rain. The attenuation from radiation in the infrared is 

approximately 9 dB/km per inch of rain per hour.J 

Thus, a moderate-size airborne lidar system, which may 

have 3- to 5-km range in clear air. will have its range 

reduced to 1 km in a rain of 3 in./h, such as one might 

find in the core of a wet microburst. However, even 

under these severe conditions, 14 s of advance warning 

can be provided. 

Although the subject of this paper is the analysis of lidar 

approaches to windshear detection, it is useful to put 

lidar into context with two other candidate systems 

which are presently under active development to meet 

this goal. 

j.2 Microwave SvstemS 

High-power ground-based Doppler radars operating at 

C-band and X-band are able to measure wind velocity at 

ranges of 10 to 20 km by measuring the scattered 

radiation primarily from precipitation, ice crystals, or 

other debris in the air. Microwave systems receive only 

minimal returns from dry air. Although windshear is 

usually associated with violent thunderstorms in the 

southern United States, 80 percent of the observed 

windshear events in the Denver study (JAWS) were dry 

at ground level. If the wind data for the flight paths 

could be rapidly updated and made available to the 

pilots, flight safety could be greatly improved. A major 

problem with on-airport radars-and to an even greater 

extent airborne radars-is the appearance of ground 

clutter. For the airborne system, the clutter return from 

the moving terrain along the flight path has a much 

greater amplitude (approximately +60 dB) than, and a 

frequency in the same band as, the hoped-for Doppler 

return from the wind. In comparing airborne radars with 

the ground-based systems such as those participating in 

the successful JAWS measurements, one must take into 

account the reduction in transmitter power that such an 

airborne system will have available, as well as the 

reduced antenna aperture, leading to a beam divergence 

of several degrees. All these factors have a significant 

impact on the ultimate achievable signal-to-noise ratio 

(SNR) (-30 to -40 dB as compared with a ground-based 

system), Details regarding the NASA airborne windshear 

radar research efforts are found in Ref. 5. 

T.2 Radiometer 

hleasurements indicate that there is il temperature 

gradient associated with the formation of a windshear. It 

appears that this gradient can be measured by an 

airborne infrared radiometer. The radiometers u hiih 

have been used for this purpose measure emission from 

the 14-pn band of atmospheric C02. The technique 

compares emission from COz in the immediate neighborhood of the aircraft to the emissions from the C02 in 

the air 2 or 3 km away. It is conjectured that the more 

negative this temperature gradient, the steeper the gust 

front causing it. Although it appears that radiometers of 

this type can detect temperature gradients associated 

with microbursts under favorable conditions, the question 

of nuisance alarms has not been addressed. since it has 

not yet been determined what other types of atmospheric 

phenomena cause similar gradients. Indusrry initiatives to 

exploit infrared technology for airborne windshear 

detection are discussed in Ref. 6. 

6. S ti cce ss f ti I Lid a r W i nd -\'e I os i t v Mea s ti rc ni c n : 5 

Since early work in the 1970's, there have been many 

advances in airborne laser velocimetry. James Bilbro. dt 

NASA's Marshall Space Flight Center, has successfully 

measured wind velocity from an aircraft using a modulated CO2 continuous wave (cw) laser followed by a 

large high-power amplifier that produced 10 mJ at 

10.6 J.L~.' Bilbro's Doppler lidar operates in clear air 

and has a range of more than 5 kni. A compact and 

reliable laser system has been flight-tested for several 

years by J. Michael Vaughan of the Royal Signals and 

Radar Establishment.a His lidar used a cw C02 laser 

focused 300 m in front of the airplane to measure 

backscatter coefficients at many European and American 

test sites and airports. Vaughan also uses optical 

heterodyne detection to determine the plane's velocity 

from the Doppler shift in the radiation scattered from 

the aerosols illuminated by the laser. Because it is a cw 

focused system, rather than pulsed, it is difficult to 

extract range information, and its look-ahead is limited 

to a warning of only a few seconds. In recent years, 

pulsed transversely excited atmospheric pressure (TEA) 

C02 lasers have been made increasingly reliable for 

long-term operation. Such a system has been used with 

good success by R. Michael Hardesty at NOAA to 

measure wind velocity and map wind fields over a 20-krn 

range with a lidar system located in a vam9 From these 

studies it is clear that similar systems using smaller 

lasers can be developed for airborne applications. 

7. Simulation and Performance Anal vsis of thC 

Ho:YAG and co? 1.' idars 

The approach simulated in our study is that of a pulsed 

laser which is focused 3 km in front of the aircraft and 

is then coherently detected to yield the Doppler shift in 

the light scattered back to the aircraft. A typical optical 

heterodyne transceiver is shown in Fig. 5. More than 100 

lidar simulation runs have been made for NASA by 

Coherent Technologies, Inc.. computing end-to-end 

signal-to-noise ratios and velocity errors for two candidate lidars as a function of distance from the ;ore of :!x 

DallasiFort Worth microburst. A simplified form of tix 

373 
Fig. 5 Typicai optical hererod) ne transceiver 

lidar equat:on used for these ca!culations is sho\vn 

below. 

where 

&= 

D= 

P= 

A= 

11= 

K(R) = 

R= 

B= 

hS 

N SRZ Bh 

XED' /7 1 71 K (R) -= 

laser pulse energy 

telescope diameter 

backscatter cross section 

laser wavelength 

detection and mixing efficiency 

round-trip extinction for range R 

range of return 

system bandwidth 

Planck's constant 

Representative results from these analyses are presented 

by Huffaker.lO A conclusion of this work is that, in 

order to demonstrate a windshear threat, it is sufficient 

for a sensor system to determine that there is a performance-increasing wind followed spatially by a performance-decreasing wind, where these changes are of the 

order of 10 to 20 knots per half kilometer. An initial 

assumption has been that 30 s of warning time was a 

requirement of an airborne windshear-detection system. 

Using the Ho:YAG or C02 lidars examined in this 

study, this warning time is achievable in most, but not 

all, microburst situations. In the DallasPon Worth 

microburst, the peak rain rate was 3.85 in./h at the core. 

The starting parameters for the two lidars are shown in 

Table 2. 

Table 2. Base-Case Lidar Parameters ~~ 

Lidar System 

Ho:YAG(Z I pn) C0,(10.6 m) 

Parameten 

~~ ~ 

5OO.m Backscaner 1.28 x 5 x 10-8 

Efficiency ( qf 6 ll q ) 0.1 0.1 

Coeff. (I/(m-sr)) 

ocq 

ARCnUtiOn (dB/km) 01 10 

Pulse Energy (d) 5 5 

Bandwdth (MHz) 10 10 

Pulse LcnOh (1s) 0,s 1 .o 

Mirror Diameter (cm) 1s 15 

Usins the lidar equation to calcuhte SSRs. \\e find thJt 

a 5-mJ C02 lidar on board 2n aircratt 4 Im from the 

core cenier \rill be able to penerrax approsimatei) 

250 n into the core This lidar 11111 :ompletely sense the 

~erformance-increasmg portion sf the \I inds. but on!) 

the stan of the perfor~ance-de~reasinS \rinds in the 

l~S5 DLIiaj Fort \\'or:!i example 

If an aircraft is 3 km from the microburst core center. 

the COz lidar can penetrate approximately 700 m into 

the core of the microburst. This increase in penetramn 

aIlo\vs the lidar to show clearly a significant portion of 

the performance-decreasing Lvinds. Reducing the lookahead disiance from 4 km to 2 km reduces the \rarn;ng 

time to -12 s before the aircraft reaches the near 

"edge" of the microburst. \Ve have examined what 

energy-increasing strategies a pilot can erploy. for 

example. in a Boeing 72: with 12 s in \\h;:h to prepare 

for an encounter with a microburst. 11 the pilot has 

confidence in the warning he receives from the 1:darbased \+indshear alarm, he can initiate a "go-around" 

procedure with the aircraft throttle settin: advanced to 

full thrust and a pitch attitude of 15' at a rate ot 4';s. 

It is then possible for him to gain 500 ft of altitude 

within the available 12 s. If the go-around was initiated 

at an altitude of 400 ft the microburst transit would be 

accomplished safely. b'ith a warning representative of 

that which might be obtained with an in ~L~IJ reactive 

system, the aircraft would not achieve any altitude 

margin prior to windshear encounter. All of these data sere obtained from a simulation carried out on a 727-2A 

flight simulator; for a plane with gear down and 30" 

flaps. 

Figure 6 shows the signal-to-noise ratio (SNR) as a 

function of range from the DallasFort Wonh microburst 

for a 5-mJ CO2 lidar for two aircraft locations. It also 

shows the radial wind velocity profile associated with 

this microburst. The Ho:YAG system has a reduced 

atmospheric attenuation of approximately 0.1 dBkm as 

compared with 1.0 dBlh for C02, as a result of this 

initially greater SNR. and it has somewhat superior 

penetration into the rain-filled core of the microburst as 

compared with C02. This performance is shown in 

- -10 : 

- E 

< 

- -1s 

.20 0 -1 -1 -1 -. RANGE FROM MICROBURST CENTER (knl 

Fig. 6 CO2 lidar signal-to-noise ratio and true wind 

velociry versus distance from the microburst core 

for two aircraft positions, 2 and 4 h from the 

microburst center. 

374 
% 

I.. 

J 

Fig. 7. The effect of differing SNRs of the 10-pn7 sqbtzni 

is again apparent tvhen we calculate veiocit!. error as J 

function of range. This calculdtion is plotted in Fig. 8 

for dry-air conditions. The velocity error ut\.) is based 

on Zrnic's analyses as recently described b!. Kane. I' 

I\ 

- 52 co. -iG 

--- UO.YAG 

01 I 

0 05 1 li 2 2a 3 

RAIN RATE (in. h; 

Fig. 9 Rdnge in rain for unity SNR 5-mJ CO2 Jnd 

Ho:YhG lidars. 

even in a homogeneous rain field of 3 in.;h. the basecase lidars <an measure wind velocity a hilonietrr in 

front of the aircraft. It should be noticed that for 

moderately heavy rain (2 in.ih) both lidar systems have 

approximately the same penetration capability. 2 km. 

This is because the attenuation in rain is very large as 

compared with the differences in the two lidars. At rf 

rain rate of 3 in./h, the round-trip attenuation is -4s dBi 

km. 

I I ' 3210 121, 20 

HAhCE FROh4 \IICROBURST CENTER ikml 

Fig. 7 Ho:YAG lidar signal-to-noise ratio and true wind 

velocity versus distance from the microburst core 

for three aircraft positions. 

The performance degradation of lidars in rain raises 

several important questions, key among them being, 

what range of forward-look alert times is required to 

assure aircraft survivability and flight-crew acceptance of 

the attendant windshear cockpit automation? A definitive 

answer to this question is not available at this time, 

because of the complex issues involving human factors 

and piloting technique. flight guidance and windshear 

information display, and considerations of aircraft 

performance capabilities. Figure 10 shows the change in 

aircraft energy height accrued from the time of annuncixed warzing to &.ear exit. as a function of fxuard-lcmk 

0.0' 1 I I 1 I I I 1 I1 0 12 3 4 5 6 7 8 9 10 

RANGE [km) 

Fig. 8 Comparison of velocity errors for 2.1-juri and 

10.6-~m lidars. 

8. Lidar Ranee in Rain and Minimum Reaui r eQ 

Advance Warnine Time 

It is well known that lidar has the potential for measuring wind velocity in clear air. One of the overriding 

concerns of the NASA program has been to determine 

the performance of lidar systems under conditions of 

precipitation, both light and heavy. We have made use 

of the measurements of attenuation in rain by Chu and 

Hogg4 and the backscatter measurements of Rensch and 

Longll to calculate the range in rain for unity SNR of 

our base-case lidar as a function of rain rate. Unity SNR 

is chosen because the system still has a satisfactory 

velocity error for that SNR. The data in Fig. 9 show that 

375 

1500 - 

- 

..- - 

- 1000 

!2 

- t 

I 

-20 0 20 40 90 

ALERT TIME T (s) 

Fig. 10 Change in energy height JS J funaion ii: 

torward-look alert time. 
alen time, for several values of hazard indes F. Segative values of 7 represent reactive windshear alerting 

systems (or no alen at all), whereas positive values of 7 

represent advanced \Laming times achievable \rith 

remote sensing of atmospheric windshear conditions. 

Figure 10 clearly demonsrrates the benefits and payoff 

attendant ro iorwrd-look \\ indshear detection and 

warning system concepts. The aircraft selecred for this 

analysis is typical of a modern, medium-range tir-in 

:urbojet trinspon. Prior to \I indshear encounter. rhe 

aircraft \\.as assumed to be in approach configuration 

\vith a rkroburst windshear located bet\veen the 

aircraft's Zurrent position and the run\vay threshold. 

Sinpiifying assumptions used in the calculations \\.ere 

constax F-factor once the shear is encountered, no 

change of aircraft configuration. and inclusion of 

representative latency for engine spool-up characteristics 

once the crew has elected to execute a windshear escape 

maneuver. Comparison of Figs. 9 and 10 suggests that 

lidar performance in moderate to heavy rain is adequate 

to significantly enhance aircraft survivability. although 

for short ioruard-look alert times. complete avoidance of 

microburst windshear may not be possible. Preliminary 

results of piloted simulation studies, jointly conducted by 

Boeing and SAS.4. tend to confirm the data presented in 

Fig. 10. Tentative results of the simulator study indicate 

that short alert times (15 to 30 s) can enable aircraft to 

amain safe altitude prior to shear entry, and are assessed 

as timely by the simulator test subjects. 

2 SNR FOR CO2 UDAR I I I 

DRY MICROBURST 35 -/--. - \.A, 

Performance of the Ho:YAG and C02 lidar systems has also been evaluated for thc "dry" microburst case, of the 

type typically encountered at DenverIStapleton Airport. 

Such a case might include virga. but no rain reaching 

the ground. Figure 11 shows the SNR for the two lidars, 

as a function of aircraft distance from the core of the 

microburst. The true wind velocities are also shown. The 

velocity error for each system is less than 1 m/s for 

ranges out to 7 km in front of the aircraft. 

15 

- 

5- 

I 

1 MICROBURST I CORE I 

I I 

- .IS 

I I I I I 

Fig. 11 Signal-to-noise ratio and true wind velocity 

versus distance from core of a dry microburst. 

9. Lidar Hardware Evaluation 

One of the goals of the program was to evaluate the 

state of the art with regard to laser performance and 

reliability. Together with our subcontractors, Spectra 

Technology of Seattle, Washington. and Lightwave 

Electronics of Mountain View, California. we have made 

detailed performance estimates for CO2 and Ho.\'.AG 

lasers. Both laser systems appear :o have the capability IO meet the program objectives. \rith the CO2 laser 

having a significant advantage in technical maturity. .A 

5-mJ radiofrequency pumped waveguide CO2 laser 

represents the state 'of the an for compact. reliable COz 

lijcrs 2nd. in the Q-s\\itchcd mode of oprr3tion. appeJrs 

(3 be a very lo\c-risk Solution to our system requirements. This type of compact, long-lived laser has already 

demonstrated adequate frequency s:abilic). in airborne 

applications. \\:e have carried out a schematic optomechanical design of an airborne COS lidar using this 

laser and other commercially available components. The 

resulting op;ical package, including laser :;ansminer, 

local oscillator, detector. and -beam scanner, has a 

volume of approsimately 5 ft'. 

The theoretical performance of the 2-pm lidar appears 

superior to that of the IO-pm lidar; however. only very 

low laser output efficiency has been seen to date for 

room-temperature. Q-switched. 2-pm lasers. There are 

also several remaining scientific and technologi;aI 

questions for the solid-state 2-pm lidar: (1) \\'111 

single-mode oscillation be possible? (2) Will efficient 

Q-jwitching be possible? (3) Will practical detectors \vith 

adequate frequency response reach the market? (4) \\'ill 

purnp diodes meet their projected lifetime? Efforts weie 

made to identify the potential 2-prn system components 

together with their likelihood of success. using inputs 

from the several researchers. Unlike the C02 situation, 

there are no Ho:YAG vendors. only researchers. Therefore, if we had to. select which laser sysrem should be 

incorporated into the windshear lidar today, we would 

have no choice but to select the 10-pm system. A 

conceptual design layout for the optical head of an 

airborne windshear is shown in Fig. 12. 

10. Conclusions 

Lidar appears to be a viable approach to windshear 

detection and avoidance, even in conditions of moderately heavy precipitation. The technology necessary to 

design, build, and test a brassboard IO-pm CO2 lidar is 

available. The airborne lidar windshear-detection systems 

analyzed in this program can give the pilot information 

about the line-of-sight component of windshear threat 

from his present position to a region extending 2 to 

3 h in front of the aircraft. Techniques to measure and 

display vertical wind components and spatial distribution 

are a significant part of the windshear problem, and will 

be addressed in our continuing investigation. Although 

an eye-safe lidar at 2 

advantages, the lasers and detectors for such a lidar 

have not yet been sufficiently developed to support their 

use in a near-term system: In the long term, diodepumped solid-state lidars could well supplant COz. 

Although both C02 and Ho:YAG systems are shown 

feasible for airborne windshear detection in this study, 

several important questions remain to be answered 

before final decisions on development are made. 

Specifically. additional simulation studies are needed to 

investigate techniques to measure both the radial 

(line-of-sight) and vertical winds. A "dry" microburst 

case will be examined in the same way the present 

"wet" microburst was analyzed. Lidar scanning techniques will be investigated to allow modeling of the 

spatial extent of the threat, as well as radial and vert;:al 

components. The signal-processing algorithms to define 

enjoys some performance 

e 

376 
a 

TRANSMllTER 

Fig. 12 Conceptual design of an airborne CO2 laser radar. 

the windshear threat must be examined along with 

recent advances in lidar signal processing. Developments 

in Cop and solid-state technology should continue to be 

monitored. A more fully developed windshear hazard 

analysis and warning criterion should be developed and 

incorporated into the computer simulation. 

Finally, some of these questions can be answered 

definitively only through an airborne sensor-validation 

program. Such a program would be aimed at determining lidar performance against a windshear threat, 

characterizing that threat, examining lidar system 

performance in turbulent flows, and collecting valuable 

data on windshear phenomenology. 

11. References 

1. Wilson, J. W., et al., “Microburst Wind Structure 

and Evaluation of Doppler Radar For Airport 

Windshear Detection,” prepared for the Joint Airport 

Weather Studies Project. National Center for Atmospheric Research, Boulder, Colorado. NCAR report 

JAWS, January 1984. 

2. Federal Aviation Administration, “Windshear 

Training Aid,” example windshear training program, 

November 1986. 

3. Bowles, R. L., and Frost, W., WindshearlTurbulence 

Inputs to Flight Simulation and Systems CertiJcation. 

NASA-CP-2474, July 1987. 

4. Chu, T. S., and Hogg, D. C.. “Effects of Precipitation at 0.63, 3.5. and 10.6 Microns,” The Bell Systems 

Technical Journal, May-June 1968. 

5. Airborne Windshear Detection and Warning Systems. 

First Combined Manufacturers’ and Technologists’ 

371 

Conference, NASA-CP-10006. FAWPS-E%/7. January 

1988. 

6. Kuhn, P. M., Kurkoski. R. L.. and Carasina, F., 

“Airborne Operation of an Infrared Low-Level 

Windshear Protection System,” Journal of Aircraft. 

Vol. 20, No. 2, February 1983. 

7. Bilbro, J. W., “Atmospheric Laser Doppler 

Velocimetry: An Overview,” Optical Engineering, 

VOI. 19, NO. 4, July-August 1980. 

8. Vaughan, J. M., et al.. Atmospheric Backscatter at 

10.6 Microns, a compendium of measurements made 

outside the United Kingdom by the Airborne WTAS 

Coherent Laser Radar Velocimeter. Procurement 

Ministry of Defense, RSRE, Malvern Worchestershire. May 1987. 

9. Hardesty, R. M., et al., “Ground-Based Coherent 

Lidar Measurement of Tropospheric and Stratospheric Parameters,” SHE. Vol. 415, Coherent 

Infrared Radar Systems and Applications II, 1983. 

10. Huffaker, R. M., et al.. “Performance Analysis and 

Technical Assessment of Coherent Lidar Systems for 

Airborne Wind Shear Detection,” SPIE Paper 889-1 1. 

January 1988. 

11. Kane, T. J.. Zhou, B.. and Byer, R, “Potential for 

Coherent Wind Velocity Lidar Using Neodymium 

Lasers,” Applied Optics, Vol. 23. No. 15. AuSust 

1984. 

12. Rensch, D. B.. and Long, R. K., “Comparative 

Studies of Extinction and Backscattering by Aerosols. 

Fog, and Rain at 10.6 p and 0.63 k,” Applied Optics. 

Vol. 9, No. 7, July 1970. 
Session I. Airborne-Sensors 

2 pm Lasers for Wind Shear Detection: A Technalo Assessment 

Mark Storm, Roland Bowles, and Bruce Conway, NA !? A LaRC 
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1. Repon No. 2. Government Accession No. 

NASA CP-10050, Part 1 I 

4. Titie and Subtitle I 5. Report Oats 

3. Recrprent's Catalog No. 

Airborne Wind Shear Detection and Warning Systems - 

Second Combined Manufacturers' and Technologists* 

Conference 

July 1990 

7. AuthorW 8. Performing Organization Repon No. 

Amos A. Spady, Jr., Roland L. Bowles, 

9. 

NASA 

and Herbert Schlickenmaier, 

Performing 

Langley 

Organization 

Research Center 

Name and Address 

compilers 

+ 

Hampton, VA 23665-5225 

2. Sponsoring Agency Name and Address 

c 10. Wok Unit No. 

505-67-41-54 

- 

11. Contract or Grant No. 

13. Type of Repon and Period Covered 

Conference Publication 

17. Key Words lSuggested by Authorlsl) 

Hicrobursts Doppler Radar 

Wind Shear Infrared 

iircraft Hazards LIDAR 

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

18. Distribution Statement 

Unclassified - Unlimited 

Subject Category 03 

14. Sponsoring 4gency Code 

9. Security Classif 20 Securicy Classif lot this pagel 21 No of pages (of this repon) 

Unclassified Unclassified 397 

I 

5. Supplementary Notes 

Amos A. Spady, Jr. and Roland L. Bowles: Langley Research Center, Hampton, Virginia 

Herbert Schlickemaier: Federal Aviation Administration, Washington, D.C. 

22. Price 

A1 7 

6. Abstract 

The Second Combined Manufacturers' and Technologists ' Conference 

hosted jointly by NASA Langley (LaRC) and the Federal Aviation Administration (FAA) 

in Williamsburg, Virginia, on October 18-20, 1988. The meeting was co-chaired by Dr 

Roland Bowles of LaRC and Herbert Schlickenmaier of the FAA. The purpose of the 

meeting was to transfer significant, ongoing results gained during the second year c 

the joint NASAIFAA Airborne Wind Shear Ptogram to the technical industry and to pose 

problems of current concern to the combined group. 

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 discussion which followed the session. 

It also provided a forum for 

NASA 1626 ocT 86 For sale by the National Technical Information Service, Springfield, Virginia 22161-2171