NASA CR 178032

Performance of a Commercial

Transport

Under Typical MLS Noise

Environment

Final Report

John K. Ho

Boeing Commercial Airplane Company

Seattle, Washington

Prepared Under Contract NAS1-17635

February 1986

I I/L%A

Nal_onat Aeronautics and

Space Administration
TABLE OF CONTENTS

Page

LIST OF FIGURES ............................................................. ii

LIST OF TABLES ............................................................... iii

1.0 SUMMARY .............................................................. 1

2.0 INTRODUCTION ......................................................... 2

3.0 SYMBOLS AND ABBREVIATIONS ......................................... 3

4.0 RESULTS FROM EARLIER STUDY ......................................... 4

5.0 AIRPLANE SIMULATION ................................................. 5

5.1 Nonlinear Simulation ..................................................... 5

5.1.1 Airplane Model and Configuration ........................................... 5

5.1.2 Automatic Flight Control Laws ............................................. 6

5.1.3 MLS Error Model ......................................................... 6

5.1.4 MLS Simulation Results ................................................... 7

5.1.5 ILS Simulation Results .................................................... 7

5.1.6 Acceptability Criteria ..................................................... 8

5.1.7 Analysis of Results ........................................................ 8

5.2 Linear Covariance Analysis ................................................ 9

5.2.1 Linearized Control Laws ................................................... 9

5.2.2 Results of Linear Covariance Analysis ....................................... 9

6.0 CONCLUSIONS .......................................................... 10

7.0 RECOMMENDATIONS .................................................... 11

REFERENCES ................................................................. 12
LIST OF FIGURES

Page

1 MLS Curved Path Segmented Approach ........................................ 13

2 MLS Transmitter Antenna Arrangement and Axis System ........................ 14

3 Longitudinal Autopilot (Altitude Hold and Glide Slope Control Modes) ............... 15

4 Lateral Autopilot (Altitude Hold and Glide Slope Control Modes) ................... 16

5 Typical MLS Noise Outputs .................................................. 17

6 X Trajectory (Run No. 3, Straight-In Approach) .................................. 18

7 Y Trajectory (Run No. 3, Straight-In Approach) .................................. 18

8 Altitude (Run No. 3, Straight-In Approach) ...................................... 19

9 Pitch Angle (Run No. 3, Straight-In Approach) ................................... 19

10 Angle of Attack (Run No. 3, Straight-In Approach) ............................... 20

11 Roll Angle (Run No. 3, Straight-In Approach) .................................... 20

12 Heading Angle (Run No. 3, Straight-In Approach) ................................ 21

13 Vertical Speed (Run No. 3, Straight-In Approach) ................................. 21

14 Calibrated Airspeed (Run No. 3, Straight-In Approach) ............................ 22

15 Ground Speed (Run No. 3, Straight-In Approach) ................................. 22

16 Normal Acceleration (Run No. 3, Straight-In Approach) ........................... 23

17 Lateral Acceleration (Run No. 3, Straight-In Approach) ........................... 23

18 Contaminated Glide Slope Error (Run No. 3, Straight-In Approach) ................. 24

19 Contaminated Localizer Angle (Run No. 3, Straight-In Approach) ................... 24

20 Elevator Activity (Run No. 3, Straight-In Approach) .............................. 25

21 Aileron Deflection (Run No. 3, Straight-In Approach) ............................. 25

22 Upper Rudder Deflection (Run No. 3, Straight-In Approach) ........................ 26

23 Lower Rudder Deflection (Run No. 3, Straight-In Approach) ........................ 26

24 Roll Rate (Run No. 3, Straight-In Approach) ..................................... 27

25 Pitch Rate (Run No. 3, Straight-In Approach) .................................... 27

26 Yaw Rate (Run No. 3, Straight-In Approach) ..................................... 28

27 Beam Angle Error (Run No. 3, Straight-In Approach) ............................. 28

28 MLS Azimuth Signal (Run No. 3, Straight-In Approach) ........................... 29

29 MLS Elevation Signal (Run No. 3, Straight-In Approach) .......................... 29

30 DME Signal (Run No. 3, Straight-In Approach) .................................. 30

31 Linearized Longitudinal Autopilot (Altitude Hold and Glide Slope Control Modes) ..... 31

ii
LIST OF TABLES

Page

1 Speed and Flap Setting at Different Distance From Threshold ...................... 32

2 Configuration and Initial Condition for MLS Simulations .......................... 33

3 LaRC Recommended MLS Parameter Values .................................... 34

4 Simulation Output Variables ................................................. 35

5 Results of Run No. 1 (Perpendicular to Extended Runway Centerline Approach) ....... 35

6 Results of Run No. 2 (Perpendicular to Extended Runway Centerline Approach) ....... 36

7 Results of Run No. 3 (ILS Type Straight-In Approach) ............................. 37

8 Results of Run No. 4 (ILS Type Straight-In Approach) ............................. 38

9 Results of Run No. 5 (ILS Type Straight-In Approach) ............................. 39

10 Results of Run No. 6 (Offset Straight-In Approach) ............................... 40

11 Results of Run No. 7 (Offset Straight-In Approach) ............................... 41

12 Results of Run No. 8 (Slant Approach) .......................................... 42

13 Results of Run No. 9 (Slant Approach) .......................................... 43

14 Results of Run No. 10 (Glide Slope Control With MLS Noise) ....................... 44

15 Results of Run No. 11 (Glide Slope Control With ILS Noise) ........................ 46

16 Comparison Between Linear Covariance Analysis and Nonlinear Simulation (Altitude

Hold) ..................................................................... 48

17 Comparison Between Linear Covariance Analysis and Nonlinear Simulation (MLS Glide

Slope) ..................................................................... 49

18 Comparison Between Linear Covariance Analysis and Nonlinear Simulation (ILS Glide

Slope) ..................................................................... 49

iii

1.0 SUMMARY

The purpose of this report is to evaluate the performance of a 747-200 automatic flight control

system (AFCS) subjected to typical Microwave Landing System (MLS) noise. The results are compared with those in an earlier study which had the AFCS subjected to International Civil Aviation

Organization (ICAO) MLS standards and recommended practices (SARPS) maximum allowable

guidance error. It was found that the operable range of altitude and distance from threshold a 747

could fly under the typical MLS noise is two to three times better than with the maximum SARPS

allowable noise.

In this report, the AFCS was slightly modified to allow other types of landing approaches besides

Instrument Landing System (ILS) type straight-in approach. Results showed that under the altitude hold mode, acceptable longitudinal guidance under typical MLS noise was found from threshold to 77,000 ft (13 nmi) out and up to 110,000 ft (18 nmi) out for lateral guidance. For the glide

slope control mode, acceptable longitudinal guidance was found at an altitude of 1,300 ft or below,

and good lateral performance was found at an altitude of 4,000 ft or below. However, when the

control surface activity requirement is relaxed from 1-deg rms to 2-deg rms, the airplane performed

satisfactorily throughout the whole MLS coverage zone (20 nmi from threshold).

A case with typical ILS noise was also carried out and was found to have control surface activities

three to four times higher than with typical MLS noise. Finally a linear covariance analysis on the

longitudinal guidance is presented to compare with the nonlinear simulation.
2.0 INTRODUCTION

The purpose of this task is to evaluate the performance of a 747-200 automatic flight control

system (AFCS) subjected to typical MLS noise. In 1981, a NASA contract (NASl-16300 Task Requirement B-8) was conducted by the Boeing Flight Control Research Group. It was found that

when a B747 airplane was subjected to the International Civil Aviation Organization (ICAO) MLS

standards and recommended practices (SARPS) maximum allowable guidance errors, the performance was unacceptable. These ICAO SARPS guidance errors caused unacceptable deviations

from 18,000 ft and beyond for longitudinal performance, and 27,000 ft and beyond for lateral performance (ref. 1). Since then, research and operational test results showed that typical MLS equipment has a noise level relatively lower than the SARPS maximum allowable noise. Therefore, the

purpose of this task is to repeat some of the runs that were done in 1981, with the airplane subjected to typical MLS noise, and determine the improvement in performance of the airplane. In

order to review the whole MLS coverage zone, besides the ILS type straight-in approach, some

curved path segmented approach cases were examined. A comparison between the MLS and ILS

performances is also included in this report. Furthermore, a linear covariance analysis on the longitudinal guidance is presented to show a cost efficient way of doing the analysis.
3.0 SYMBOLS AND ABBREVIATIONS

a

AFCS

Alt Hold

AYACEL

AZACEL

DME

GSE2

G/S

H

HIC

HR

ICAO

ILS

LaRC

Local2

MLS

P

q

r

rms

SARPS

VCAS

X,Y,H

X,

Y,

¢

¢

T

0

0 x

Oy

t_

tPGT

Filter Parameter

Automatic Flight Control System

Altitude Hold

Lateral Acceleration

Normal Acceleration

Distance Measuring Equipment

Contaminated Glide Slope Error

Glide Slope

Vertical Speed

Holding Altitude

Radio Altitude

International Civil Aviation Organization

Instrument Landing System

Langley Research Center

Contaminated Localizer Angle

Microwave Landing System

Roll Rate

Pitch Rate

Yaw Rate

Root Mean Square

Standards and Recommended Practices

Calibrated Airspeed

Rectangular Coordinates With Origin at Threshold of Runway

nth Sample From a White, Gaussian, Random Sequence

nth Sample of MLS Noise

Angle of Attack

Bank Angle

Roll Rate

Correlation Time for Filter

Pitch Angle

Standard Deviation of X,

Standard Deviation of Y,

Heading Angle

Ground Track Angle
4.0 RESULTS FROM EARLIER STUDY

An evaluation of the performance of a 747 automatic flight control system under the maximum allowable MLS guidance errors was conducted by the Boeing Flight Control Research Group

in 1981. These MLS guidance errors used the maximum errors that are allowed by the ICAO MLS

SARPS. Out of the three cases conducted in 1981, two of them were ILS type straight-in approaches, and the third case was a curved path segmented approach. For the two ILS type straightin approach cases, the altitude hold mode used the barometric H as the input signal. The MLS

SARPS noises were included in the guidance signals only when the airplane was on the glide slope

control mode. Hence, only the glide slope portion was used in the analysis. Results showed that for

distances beyond 18,000 ft from threshold, the guidance errors caused unacceptable altitude deviation, as well as pitch angle and elevator perturbations. Also, from 27,000 ft and beyond, the roll

angle and aileron deflection were found to be unsatisfactory.

For the curved path segmented approach case, the initial crosstrack position was 50,000 ft from the

extended runway centerline with the interception point 100,000 ft from the threshold. The airplane then flew perpendicular to the extended runway centerline and executed a 90-deg turn to

capture the extended runway centerline. The altitude signal was generated by the MLS elevation

and DME. However, the control law used in the report was not suitable for curved path operation,

hence only the portion of the perpendicular approach was analyzed. It was found at this distance

out, both longitudinal and lateral guidance caused unacceptable control surface activity as well as

altitude and attitude deviations.
5.0 AIRPLANE SIMULATION

This section evaluates the performance of a 747-200 automatic flight control system (AFCS)

subjected to typical MLS guidance errors. Different landing approach paths were simulated within

the MLS coverage zone, each with the MLS guidance errors used as the input to the AFCS. The

response of the airplane was then analyzed to determine if the performance was acceptable for

each of the approach paths based on the following requirements: passenger comfort, path tracking

accuracy, and control surfaces activity.

Four different types of landing approach paths were used in the simulation. The first type was a

perpendicular to extended runway centerline approach, in which the airplane flew perpendicular

to the extended runway centerline and then executed a 90-deg turn to capture the extended runway centerline. The second type was an equivalent ILS type approach path, in which the airplane

flew straight-in towards the runway. The third type was an offset straight-in approach, in which

the airplane flew parallel to the extended runway centerline and then maneuvered to capture the

centerline. The fourth type was a slant approach which intercepted the extended runway centerline at an angle. Figure 1 shows the four types of landing approaches. A total of 11 runs were

simulated.

The rest of the section describes the airplane model, its automatic flight control laws, and the MLS

error model used in this simulation. It also includes both ILS and MLS glide slope control simulation results, the acceptability criteria, and the analysis of the results.

5.1 NONLINEAR SIMULATION

The Boeing Flight Simulation Laboratory, with its multiprocessor Harris computer system, was

used for this MLS/airplane simulation. The simulation program includes the nonlinear characteristics of the airplane.

5.1.1 Airplane Model and Configuration

As the 747-200 airplane is the most common type of 747 flying today, the 747-200 AFCS was used

as the basis of the simulation. A medium weight of 560,000 lb was chosen. Different speeds, ranging from 148 kn to 238 kn, along with different flap settings were used depending on the approach

position. Since there is no general guideline in how a pilot should fly within the MLS coverage

zone, Table 1 was used as a baseline to determine the speeds and configurations for the different

simulation runs. Table 2 shows the initial conditions for each run. Some of the starting positions

were intentionally displaced by a small amount from the selected course in order to eliminate initial transients due to the bias on the MLS noise.

The MLS ground transmitter antenna arrangement and the definition of the axis system used in

this report can be found in Figure 2. During simulation, no antenna switching on the airplane is

performed. The antenna for both the MLS angular data and DME is assumed to be colocated with

the ILS glide slope antenna at the nose section.
5.1.2 Automatic Flight Control Laws

For the longitudinal guidance, two modes were simulated: altitude hold and glide slope control.

The altitude hold mode used an MLS derived altitude signal as the input to the control system.

This MLS derived altitude input was calculated by the distance measuring equipment (DME) signal and the two MLS angular data (i.e., the elevation and the azimuth angles) all with noises

according to Table 3. For the glide slope control mode, the contaminated glide slope angle error was

used for the longitudinal guidance.

For the lateral guidance, the contaminated track angle error was used as an input to the control

system. The reference point of this track angle error for ILS type straight-in approach was the

threshold of the runway, and the contaminated localizer angle was used as the track angle error.

For other types of landing approach simulated in this study, the reference point was the point of

turn of the approach paths. Hence by converting the position of the airplane calculated by the

contaminated MLS signals from the reference point to the selected course into an equivalent localizer angle error, it was used as an input to the lateral control law.

The longitudinal autopilot chosen for this study was the Sperry 247 computer with the Sperry 308

computer selected as the lateral autopilot. These two computers are commonly used on the 747-200

airplanes that are flying today with a fail passive system. Detailed information about the autopilots can be found in Reference 2. The altitude hold and glide slope portions of the control laws can

be found in Figures 3 and 4.

For landing, these autopilots are designed for ILS type straight-in landing approach only. Under

this MLS study, the control laws were modified slightly to allow the other types of landing approaches in order to investigate the MLS characteristic throughout the whole MLS coverage zone.

Therefore, the results from the perpendicular to extended runway centerline, offset straight-in,

and the slant approaches may not be the optimal performances of the airplane.

5.1.3 MLS Error Model

Many factors contribute to the lateral and longitudinal dispersion of the airplane from its selected

course. These factors include wind gusts, sensor noises, and MLS signal error. In this report, the

only error being considered is the MLS signal error which is the difference between the MLS receiver position outputs and the actual position of the MLS equipped airplane in space. This error is

due to the inherent noise of the transmitter and receiver, equipment misalignment, and signal

strength variations. NASA Langley Research Center (LaRC) has provided a MLS error model

which is based on some flight test results of the Bendix MLS facility at Wallops Flight Center. This

error model generates MLS noise errors by passing a white, Gaussian, random sequence through a

low-pass, digital filter as described by the following equation:

where

Y, = (l-a) Y_.I + aX_

Y, = nth sample of MLS noise

X, = nth sample from a Gaussian random number generator with standard deviation

% and zero mean.

a = filter parameter chosen to adjust the correlation time

= 1-exp(-ST)

T
where AT = sample rate

= correlation time

The variance of Y_ is then:

(%)2 = a (o×)2

2-a

where % = standard deviation of Y_

ox = standard deviation of X_

Table 3 shows the recommended parameter values for the LaRC MLS noise model. For the simulation runs done at the Boeing Flight Simulation Laboratory, a sample rate of 50 ms was used. Typical noise models, generated by different white, Gaussian, random sequences, scaled according to

Table 3, are shown in Figure 5.

5.1.4 MLS Simulation Results

Four types of landing approaches, a total of 10 MLS runs, were simulated on the Harris computer

with the AFCS subjected to typical MLS noise. Table 2 shows the initial positions, configurations,

types of landing approach, and other information of each run. The time history of 28 variables were

recorded and plotted for each run. Table 4 lists the 28 variables. Figures 6 through 30 show the

typical responses of the 747-200 due to the MLS noise.

To interpret the simulation data, the mean and standard deviation were calculated for every thousand samples to compare with the acceptability criteria. However, the first several hundred samples of each run are left out in the analysis to enable initial transients to be ignored.

Statistics of the output variables for each of the 10 MLS runs are shown in Tables 5 through 14.

Each column in the table gives the statistics of the variables for a thousand data points or 50 sec of

simulation time. Some cases were run for a longer period of time than others.

5.1.5 ILS Simulation Results

The Instrument Landing System (ILS) has been used for landing guidance for the last 40 years.

Over the years, it has undergone a number of improvements to increase its performance and reliability. However, due to increasing activity in the terminal area and the restricted operation possible with ILS, the International Civil Aviation Organization has decided to replace the ILS with the

MLS within the next decade. Therefore, it is useful to compare the performances of the two

systems.

The ILS noise model is generated by passing a white, Gaussian sequence through a low-pass, digital filter with a 0.5-sec correlation time, and then scaled with a standard deviation of 0.0443 deg

and 0.0633 deg for localizer and glide slope error respectively. No bias is included in either of the

noise models. The simulation results can be found in Table 15. These results, when compared with

the MLS results in Table 14, show three or four times higher in magnitude.
5.1.6 Acceptability Criteria

The acceptability criteria are considered from three different aspects: path tracking accuracy, passenger comfort, and control sm_face activity. With the output variables roughly categorized into

positions, airplane attitude angles, lateral and normal accelerations, vertical and longitudinal

speeds, control surfaces activity, MLS noises, and receiver signals; all aspects of the acceptability

requirements could be addressed.

In order to be consistent with the work done earlier (ref. 1), similar acceptability criteria are being

used in this report. Throughout the MLS coverage zone, the MLS guidance errors have to satisfy

the following requirements:

. With

a.

b.

C.

d.

regard to path tracking accuracy

Altitude variation shall not exceed 25-ft rms

Vertical guidance error shall not induce speed variation greater than 2-kn rms

On the glide slope, at 700-ft altitude, the airplane shall not deviate from the glide path

12 ft or more

The lateral tracking error is allowed to degrade with distance, at 300-ft altitude, the

lateral tracking error allowed is 40 ft, and at 1300 ft altitude, the allowable error is 98 ft

. With regard to passenger comfort

a. Normal and lateral accelerations shall not exceed 0.05-g n rms (1.61-ft/sec 2 rms)

b. Sink rate variation shall not be greater than 20% of nominal rate

c. Airplane attitude variation shall not be greater than 1-deg rms

3. With regard to control surface activity, the deflections shall not exceed 1-deg rms

5.1.7 Analysis of Results

The results which are presented in Sections 5.1.4 and 5.1.5 were compared with the acceptability

criteria given in the previous section. Of all the nine altitude hold runs, Run No. 2, which is a

perpendicular to extended runway centerline approach, has a 2.128-kn rms of speed variation at

about 89,000 ft (15 nmi) out and a 1.636-ft/sec rms variation in normal acceleration at about 80,000

ft (13 nmi) out. Run No. 6, which is an offset straight-in approach, has a 1.095-deg rms variation in

the bank angle at about 113,000 ft (19 nmi) from the threshold. These dispersions could be due to

the fact that the autopilots were not designed for landing approaches other than ILS type straightin approach. Nevertheless, they could still be considered to be marginally acceptable. The rest of

the altitude hold runs show all variables have standard deviation well within the acceptable

region.

On the glide slope control run (Run No. 10), the elevator has activities greater than the 1-deg rms

requirement from altitude 1,300 ft and up, this variation ranges from 1.001-deg rms to 1.312-deg

rms. All other variables are well within the requirements.

Run No. 11, which is a glide slope control run with typical ILS noise, when compared with Run No.

10 which is with MLS noise, was found to have variations in its variables three to four times

higher than the MLS run.
5.2 LINEAR COVARIANCE ANALYSIS

The objective of the linear covariance analysis is to demonstrate a cost efficient way of determining

the covariance response of the airplane due to MLS/ILS noise. MPAC, which is a program for analysis and synthesis of linear time-invariant control system, was used for this purpose. The program

calculates the steady state covariance coefficient matrix of the variables in the system. These coefficients include the standard deviations of the variables and hence could be used to compare with

the results from the nonlinear simulation.

5.2.1 Linearized Control Laws

Some of the gains in the AFCS are functions of position and speed of the airplane. In order to

linearize the control laws, these gains are assigned with some constant values depending on the

mean position and nominal speed being simulated.

Figure 30 is a linearized version of the longitudinal autopilot. In it, F1CAS and F3CAS are functions of speed. With a nominal speed of 148 kn, F1CAS and F3CAS are 1 and 0.704 respectively.

GKV1 is a function of radio altitude. For the glide slope control run, GKV1 is 0.58 at 650-ft altitude. GR1 and GR2 are functions of the distance from the threshold. At 45,000 ft from the threshold, GR1 and GR2 are 0.0012 and 803.0 respectively. For the glide slope run, GR1 is 0.0046 at

650-ft altitude.

For altitude hold mode, GR1 and GR2 are reciprocals of each other. They will cancel each other in

the H loop, leaving the GR2 gain directly affecting the input magnitude of the elevation noise.

Since GR2 is a linear function of distance, this implies the result of one run could be scaled proportionally for other runs at different distances from the threshold.

For the glide slope control mode, the gains that are functions of distance are the GR1 and GKV1

gains. Notice that both of the gains are inside the H loop, also the aerodynamics data varies with

altitude. Hence, the linear generalization that was applied to the altitude hold mode cannot be

applied here.

The MLS derived altitude used in the linear covariance analysis was calculated by the noisy elevation angle together with the distance from the transmitter. The azimuth and DME noise were not

included in the calculation as they are in the nonlinear simulation. This is considered acceptable

because the contaminated elevation angle is the major contribution to the longitudinal guidance

error.

5.2.2 Results From Linear Covariance Analysis

Three runs were analyzed with MPAC. One was the low-speed ILS type straight-in altitude hold

mode at 45,000 ft from the threshold of the runway and using MLS elevation noise. The other two

runs were both glide slope control mode at altitude 650 ft; one using MLS noise, and one with ILS

noise. These results are then compared with the Harris nonlinear simulation Runs 5, 10, and 11

respectively. The comparison can be found in Tables 16 thru 18.

The differences between the results of the two analyses are all within 25c_, except that the difference in the elevator activity is as high as 37%. This could be due to the use of a very simplified

model of the actuator servo system of the elevator in the linear covariance analysis. Nevertheless,

the results from the linear covariance analysis should give a good indication of the airplane performance under the influence of MLS/ILS noise. Also, a cost saving of roughly 50% could be achieved

by using the linear covariance analysis to calculate the performance.

9
6.0 CONCLUSIONS

The simulation runs under NASl-16300 Task B-8 have been repeated under this study using

the typical MLS noise level together with the error model described in Paragraph 4.1.3. With the

existing AFCS slightly modified, other approach runs which cover the whole MLS coverage zone

have also been carried out. A glide slope run with typical ILS noise level is included for comparison

purpose. It is concluded that:

1. The operable range of altitude and distance from threshold which the airplane could fly under

typical MLS noise was two to three times better than with maximum SARPS allowable noise.

. For altitude hold mode, with a slightly modified AFCS,

a. Acceptable longitudinal guidance was found from threshold to 77,000 ft out (13 nmi).

The criteria setting this limit is the MLS noise-induced variations in speed and normal

acceleration.

b. Acceptable lateral guidance was found from threshold to 110,000 ft out (18 nmi). The

criteria setting this limit is the MLS noise-induced deviation in bank angle.

. For glide slope mode,

a. Acceptable longitudinal guidance was found below 1,300 ft. The criteria setting this

limit is the MLS noise-induced elevator perturbation.

b. Acceptable lateral guidance was found below 4,000 ft. The criteria setting this limit is

that 4,000 ft was the maximum height being simulated in this study.

4. The ILS noise causes control surface activities three to four times higher than the MLS noise

would.

10
7.0 RECOMMENDATIONS

The preceding sections clearly show the performance of a 747-200, with its modified AFCS,

under the given MLS noise model, cannot satisfy the acceptability criteria throughout the whole

MLS coverage zone. It is therefore recommended that:

1. Once a curved path approach control law is designed, the simulation should be carried out

once again to examine the improvement in both longitudinal and lateral performance for

these different types of curved path approach.

. By relaxing the control surface activity requirement from 1- to 2-deg rms, the airplane could

perform satisfactorily throughout the whole MLS coverage zone which is 20 nmi from the

threshold.

. When more data on the MLS noise are collected, the simulation should be carried out again

using the new error model.

. This nonlinear simulation should be carried out on other airplanes so as to get a better understanding of the MLS characteristics on a variety of airplanes.

. For cost saving purpose, linear covariance analysis could be used as a good approximation of

the airplane performance due to MLS noise.

. The possibilities of developing guidance noise filters to make automatic flight control system

more noise tolerant be investigated.

11
REFERENCES

.

"MLS/Airplane System Design--RF Component Design and MLS/Flight Control System Error Evaluation" Boeing Report D6-51280, December 14, 1981.

"Description of RFSC Simulation Software for 747 Autopilots" Boeing Report BCS-G1751,

November 3, 1983.

12
1. Perpendicular to extended runway centerline

2. ILS type straight-in

3. Offset straight-in

4. Slant

/

/

/

/

/

/

/

/

40 deg

MLS datum

point

40 deg \

\

\

\

Threshold \

\

/

/

\

/

/

/

\

\

\

/

\

\

\

\

C/L

Approach

direction

Figure 1. MLS Curved Path Segmented Approach

13
tO

Q..

Q.

<

tO

.m

(3

N

Y

Threshold /

1,000 ft_

I '---- Elevation

antenna

10,000 ft

t

1,000 ft

I

I

I

I

I

1'

X

Azimuth and

DME antennas

Figure 2. MLS Transmitter Antenna Arrangement and Axis System

14
0

0 u3

,_-

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mA VI_A A

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10 20 30 40 50 60 70

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A

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Z

tO

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0.045-

0.035

0.025

0.015

0.005

-0.005

-0.015

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0 10 20 30 40 50 60 70

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Figure 5. Typical MLS Noise Outputs

17
-102,000

-106,000.

-110,000.

-114,000

x

-118,000

-122,000

-126,000

-130,000

0 10 20 30 40 50 60 70

Time (sec)

Figure 6. X Trajectory (Run No. 3, Straight-In Approach)

v

>-

36

34

32

30

28

26

24

22

20

18

16

14

12

0

i I ' ' I' ' I ,h I' ' I ,i 'I ' ' i I

10 20 30 40 50 60 70

Time (sec)

Figure 7. Y Trajectory (Run No. 3, Straight-In Approach)

18
-1-

3170

3150

3130

3110

3090

3070

3050

3030

3010

2990

0

i (, i ' ' 4 '

10 20

' I , i . . l i .). i

3O 4O 5O

Time (sec)

Figure 8. Altitude (Run No. 3, Straight-In Approach)

I , i , , t

60 70

O_

7.0'

6.6

6.2

5.8

5.4

5.0

4.6

4.2

3.8

3.4

0

I I I B

10 20 30 4O 50 60 70

Time (sec)

Figure 9. Pitch Angle (Run No. 3, Straight-In Approach)

19
"t3

8.0"

5.8

5.6

5.4-

5.2.

5.0-

4.8

4.6-

4.4-

4.2-

4.0-

3.8

3.6

0

' t _ I ' I ' I _ I ' _ t .... h ' I

10 20 30 40 50 60 70

Time (sec)

Figure 10. Angle of Attack (Run No. 3, Straight-In Approach)

°6t

0.5

0.4

0.3

0.2

0.1

0.0

-0.1

-0.2 "

-0.3 -

-0.4

0

I ' i ' I ' I ' 1 i I ' I

10 20 30 40 50 60 70

Time (sec)

Figure 11. Roll Angle (Run No. 3, Straight-In Approach)

2O
(_

9-

0.24

0.20

0.16

0.12

0.08

0.04

0.00

-0.04

-0.08

-0.12 I I _ I 1 I _ I _ I

10 20 30 40 50 60 70

Figure 12.

Time (sec)

Heading Angle (Run No. 3, Straight-In Approach)

.-1-

18

16

14

12

10

8

6

4

2

0

-2

-4

-6

10

I _ q ' I _ I ' I ' I

20 30 40 50 60 70

Time (sec)

Figure 13. Vertical Speed (Run No. 3, Straight-In Approach)

21
E"

Go

<

o

>

240.0

239.0

238.0

237.0

236.0

235.0 i l i l J I _ ' I ' i ! i I i I

0 10 20 30 40 50 60 70

Time (sec)

Figure 14. Calibrated Airspeed (Run No. 3, Straight-In Approach)

"O

(3.

Or)

"t3

t-

£

(.9

251.0

250.0

249.0

248.0

247.0

246.0

245.0

0

i p i ) i I i I ' I i I i I

10 20 30 40 50 60 70

Time (sec)

Figure 15. Ground Speed (Run No. 3, Straight-In Approach)

22
-J

LU

0

<

.

8

7.

6

5

4.

3

2

1.

0

--1'

--2'

-3

0

I I ' I ' t I ' I I

10 20 30 40 50 60 70

Time (sec)

Figure 16. Normal Acceleration (Run No. 3, Straight-In Approach)

0.020

0.010

0.000

o

-0.010

-0.020.

-0.030.

I I ' 3 ' I ' I

0 10 20 30 40 50

Time (sec)

Figure 1 7. Lateral Acceleration (Run No. 3, Straight-In Approach)

I I

60 70

23
(3}

"0

v

UJ

(/3

(.9

1.80

1.70

1.60

1.50

1.40

1.30

' ' l ' I' ' ' l " ' I ' I , ', I , _ I

0 10 20 30 40 50 60 70

Time (sec)

Figure 18. Contaminated Glide Slope Error (Run No. 3, Straight-In Approach)

{33

04

0

0

-J

0.050

O.O40

0.030

0.020

0.010

0.000

-0.010

-0.020

-0.030

Vv'

0 10 20 3O 4O 50

Time (sec)

' I I

60 70

Figure 19. Contaminated Localizer Angle (Run No. 3, Straight-In Approach)

24
0.0

-1.0

"_ -2.0

v

-3.0

"4,,--*

--_ -4.0

I.LI

-5.0

-6.0

0

I I t I ' I ' I

10 20 30 40 50 60

Time (sec)

Figure 20. Elevator Activity (Run No. 3, Straight-In Approach)

1

7O

¢,-

o

.<

0.5

0.4

0.3

0.2

0.1

0.0

-0.1

-0.2

-0.3

-0.4

-0.5

-0.6

IA t

0

I I I I 1 ' I

10 20 30 40 50 60

Time (sec)

Figure 21. Aileron Deflection (Run No. 3, Straight-In Approach)

I

70

25
0.10

0,08

0.06"

0.04

0.02

"0

-I

n- 0.00

$ -0.02

{3.

Q.

-0.04

-0.06

-0.08

-0.10

0 10 20 30

Time (sec)

40 50 6O

Figure 22. Upper Rudder Deflection (Run No. 3, Straight-In Approach)

I

7O

0.10

0.08

0.06

0.04

0.02

$ o.oo

n=" -0.02

$ -0.04

o_ -0.06

..J

-0.08

-0.10 I I

0 10 20 30 40 50 60 7O

Time (sec)

Figure 23. Lower Rudder Deflection (Run No. 3, Straight-In Approach)

26
0.0040

0.0030

0.0020

0.0010

0.0000

-0.0010

-0.0020

-0.0030

-0.0040

0 10 20 30 40 50 60

Time (sec)

Figure 24. Roll Rate (Run No. 3, Straight-In Approach)

/

I

70

O3

0.040

0.030

0.020

0.010

0.000

-0.010

0 10 20 30 40 50 60 70

Time (sec)

Figure 25. Pitch Rate (Run No. 3, Straight-In Approach)

2?
O)

13

0.0014

0.0012

0.0010

0.0008

0.0006

0.0004

0.0002

0.0000

-0.0002

-0.OO04

-0.0006

-0.0008

0

I I ' I ' I ' I ' I '

10 20 30 40 50 60 70

Time (sec)

Figure 26. Yaw Rate (Run No. 3, Straight-In Approach)

"O

v

UJ

¢-

<

(8

#-

0.050

0.040

0.030

0.020

0.010

0.000

-0.010

-0.020

-0.030

rV /VVv

I I '

10 20

I ' I _ t _ I _ I

30 40 50 60 70

Time (sec)

Figure 27. Beam Angle Error (Run No. 3, Straight-In Approach)

28
0.050

0.040

0.030

0.020

o_ 0.010

= 0.000

"5

E_ -o.olo

N

<

-0.020

-0.030 I ' I ' I I b I _ I ' I

0 10 20 30 40 50 60 70

Time (sec)

Figure 28. MLS Azimuth Signal Run (Run No. 3, Straight-In Approach)

O_

Q)

c-

.o

Q)

UJ

1.70

1.60

1.50

1.40

1.30

1.20

0 10 20 30 40 50 60 70

Time (sec)

Figure 29. MLS Elevation Signal (Run No. 3, Straight-In Approach)

29
142,000

138,000

134,000

130,000

_-_126,000

uJ

122,000 a

118,000

114,000

11O,000

0

l ' _' ' I _ I _ I i I _ I n I

10 20 30 40 50 60 70

Time (sec)

Figure 30. DME Signal (Run No. 3, Straight-In Approach)

3O
cO

A

_A

A_

p_

¢D

O

+

rr

"I"

(3")

O

O

O " "

_O

II

V

(.9

O

t_

TAI

Vl> A A

,fJL_ _ _J

CM

o >

O

d o

I O

00LO

O¢'M CM OI

_ 0_ 0

It II

CO CO

0 0

,7 U.m

OI

"1:3

.E

(/)

c"

oc_ E

rn6 _

ea

II

;_]

II

I

/\

k/

o

31
Table 1. Speed and Flap Setting at Different Distance From Threshold

MODE DISTANCE FROM THRESHOLD SPEED FLAPS

Altitude hold

Altitude hold

Altitude hold

Altitude hold

Glide slope

20 nmi

15 nmi

10 nmi

5 nmi

All

238 kn

200 kn

178 kn

148 kn

148 kn

1 deg

5 deg

10 deg

30 deg

30 deg

32
2

t_

._E

_0

09

_J

0

0

2

0

0

oj

_D

.Q

0

Z

LAJ

mm

i,i

0

mm

ILl

C__

CO

<_

_J

ILl

CO

0

t_

Z

0

O9

0

O_

C__

Z

_x

cO

O_

c_g_--

zzn

Z_

_0

._JaZ

O_

Oz o

u'_ _ I_- CO _ 0

I T T I T T

< < < < < <

T

_0

I I 0_ 00

< < (D 0

_- _- _- Q- 0 Q- Q- Q. r_ 0 0

_-- 0 _- 0 0 I"-

• • • • •

"0 "0 "0 "_ "0

uO _ UD 0 0

O0 CO

_Z t" t-- c" t- t" e- C t" t"

LO CO _ 0 CO I.O 0 UD 0 O0 O0

0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

0 0 0 _0 UD 0 _ UD U'_ 0 0

UD CO CO _ ,_- OD ',- T- ,- _" 'm"

Q. t',

0 0 _O _0 UD u_ 0 UD 0 0 0

0 0 eq _- _- _ OJ _ _q _

0 0 0 0 0 0

0 0 _ 0 0 tt'_ tl_ _

0 0

0 0 0 0 0 0 0 _ 0 0'_ 0'_

CO CO 0 0 0 0 0 r-.- _c, _

0'_ 0'_ 0 0 _D 0 0 0'_ _" OD CO

oo _ CO I'-- u'D co 0 _ I'_

' ' T ' ' T T ' ' _-=oo

0 0 t-- t-- c-- t'- t- t-- t--

"T "-- "T "T

s_ m N N N 0"_ O_ 00 m N N

0

o

0

0

"0

0

.m "l_

<0

_f

0

0

---06

0_0_

t_00.

e9

_ r'-

c- 0 _-

010.--

33
O9

,,,,.,,.

I,,.,.

q)

CLEO

_)

q)

C.)

,..j

e_

.Q

E

.o

a.__.

co

o_ r...

Z,,- m

r-

._o

Z_

._j_o

Q --

"o_

.13

m_

e-_ ,,.- m

oo

b,- o

_ Vlo

_-o

_v8

vl_A

rr_rrI

rr

co

"13 "-"I I..I')

',-- O,I_

o. od

ooi

ii m

34
Table 4. Simulation Output Variables

1 X

2 Y

3 Barometric altitude

4 8

5 cr

6

7 _u

8 H

9 VCAS

10 Ground speed

11 AZAC EL

12 AYACEL

13 GSE2

14 LOCAL2

15 Elevator

16 Aileron

17 Rudder (upper)

18 Rudder (lower)

19 p

20 q

21 r

22 Beam angle error

23 Azimuth noise

24 Elevation noise

25 DME noise

26 MLS measured azimuth angle

27 MLS measured elevation angle

28 MLS measured DME distance

Table 5. Results of Run No. 1 (Perpendicular to Extended Runway Centerline Approach)

H (ft)

(ft/s).

AZ (if/s')

VCAs (kn)

e (deg)

(deg)

Elevator (deg)

GSE2 (deg)

X (ft)

Y (ft)

AY (ft/s 2)

(deg)

(deg)

Aileron (deg)

Rudder (deg)

Beam error (deg)

Local2 (deg)

AVERAGE STANDARD

DEVIATION

5153

238.3

-89972

70551

7.995

2.002

1.079

1.030

0.3292

0.2188

0.4364

5.496

0.01479

0.2501

0.07567

0.1930

0.04485

0.01512

35
£

Q_

Q_

(O

Q:

(D

O

O_

d

Q=

O

co

Q)

Q=

co

-.,,..

.Q

Z o _ _ _ _ o

c0

o 09 o o_ -w

o c5 o c5 o o

LU

_D

,_ o¢o ,-

o_ D..

ZO

7-- o co co co _- o_

-ILl 0,I 04 QD O0 D,- _" 0")

oa c6 _ ,-.-. o d d 6

(.o

o

i<

',- 00 co

(xl (D ',- I'_

O 04 OO O'_ _O ",'-

O CO _-- OJ O O

oo6ooo

UJ

(D

<

Z

con

LIJ

(D

<

LID

s b.. u_

CO b..

O_ CO

O_ O_

•-- cO _O b.. ¢O O _t"

O 0_ O_ _ b.. _-- _ O')

O') .,- T- ,r- _.Q _- 00 D.-

d N ,- e,i o d o

O4

co _ ho

o I_- o _

I_ uo o uo

0 t.O ,eO 04 _-- 04 O O

o o d o o o

i..o

_._ _ v. "o "o "o "1o _ ,.,-"-' _ "o "o "o "o "1o "o

v v

-- _ _ "_ _ 0

36
Table 7. Results of Run No. 3 (ILS Type Straight-In Approach)

H (ft)

H (ft/s)

AZ (ft/s 2)

VCAs (kn)

e (deg)

o_ (deg)

Elevator (deg)

GSE2 (deg)

X (ft)

Y (ft)

AY (ft/s 2)

(deg)

qu (deg)

Aileron (deg)

Rudder (deg)

Beam error (deg)

Local2 (deg)

AVERAGE STANDARD

DEVIATION

3152

238.0

9.915

1.946

1.035

1.030

0.3212

0.2110

0.4299

-111120

20.80 r 7.639

0.01377

0.2189

0.08935

0.1802

0.04182

0.01326

37
Table 8. Results of Run No. 4 (ILS Type Straight-In Approach)

H (ft)

ILl (ft/s)

AZ (ft/s 2)

VCAs (kn)

e (deg)

(deg)

Elevator (deg)

GSE2 (deg)

X (ft)

Y (ft)

AY (ft/s 2)

(deg)

(deg)

Aileron (deg)

Rudder (deg)

Beam error (deg)

Local2 (deg)

AVERAGE STANDARD

DEVIATION

1577

-55707

183.3

12.10

19.26

1.339

0.7359

1.911

0.3915

0.2873

0.5317

4.058

0.00545

0.1870

0.08302

0.2256

0.05099

0.01318

38
Table 9. Results of Run No. 5 (ILS Type Straight-In Approach)

H (ft)

(if/s)

AZ (ft/s 2)

VCAs (kn)

e (deg)

(deg)

Elevator (deg)

GSE2 (deg)

Ix (ft)

Y (ft)

AY (ft/s 2)

(deg)

(deg)

Aileron (deg)

Rudder (deg)

Beam error (deg)

Local2 (deg)

AVERAGE STANDARD AVERAGE STANDARD

DEVIATION DEVIATION

1562 1538

149.6

-49320

16.75

5.399

1.427

0.7902

0.3754

0.4497

0.3001

0.7209

4.611

0.02565

0.3447

0.1731

0.3547

0.08211

0.02198

149.7

-36417

14.01

14.67

1.371

0.6857

0.3623

0.4339

0.2695

0.5843

6.729

0.02061

0.2311

0.1242

0.2845

0.07537

0.01852

39
Table 10. Results of Run No. 6 (Offset Straight-In Approach)

H (ft)

(ft/s)

AZ (ft/s 2)

VCAs (kn)

e (deg)

(deg)

Elevator (deg)

GSE2 (deg)

X (ft)

Y (ft)

AY (ft/s 2)

(deg)

(deg)

Aileron (deg)

Rudder (deg)

Beam error (deg)

Local2 (deg)

AVERAGE STANDARD

DEVIATION

3155

-111120

25029

10.10

1.987

1.061

1.023

0.3273

0.2158

0.4344

20.64

238.0

0.06471

[1.095]

0.4473

0.7072

0.1961

0.06812

40
Table 11. Results of Run No. 7 (Offset Straight-In Approach)

H (ft)

ICl (ft/s)

AZ (ft/s 2)

VCAs (kn)

e (deg)

(deg)

Elevator (deg)

GSE2 (deg)

X (ft)

Y (ft)

AY (ft/s 2)

ft, (deg)

(deg)

Aileron (deg)

Rudder (deg)

Beam error (deg)

Local2 (deg)

I

AVERAGE STANDARD

DEVIATION

1634

203.7

-84166

50016

17.81

2.161

1.250

1.534

0.46O7

0.3056

0.6578

11.80

0.01796

0.6133

0.2708

0.5910

0.1329

0.04260

41
Table 12. Results of Run No. 8 (Slant Approach)

H (ft)

ILl (ft/s)

AZ (ft/s 2)

VCAs (kn)

e (deg)

(deg)

Elevator (deg)

GSE2 (deg)

X (ft)

Y (ft)

AY (ft/s 2)

(deg)

(deg)

Aileron (deg)

Rudder (deg)

Beam error (deg)

Local2 (deg)

AVERAGE STANDARD

DEVIATION

1628

237.7

-86890

36993

8.478

1.646

0.8752

1.056

0.2759

0.1820

0.3889

0.02547

0.3640

0.1576

0.3458

0.08108

Q02613

42
Table 13. Results of Run No. 9 (Slant Approach)

H (ft)

(ft/s)

AZ (ft/s 2)

VCAs (kn)

e (deg)

(deg)

Elevator (deg)

GSE2 (deg)

X (ft)

Y (ft)

AY (ft/s 2)

+ (deg)

t_ (deg)

Aileron (deg)

Rudder (deg)

Beam error (deg)

Local2 (deg)

AVERAGE STANDARD

DEVIATION

1589

203.6

-63750

13844

15.39

1.458

0.8340

1.519

0.3196

0.2214

0.4496

0.02098

0.6887

0.3114

0.6289

0.1407

0.05286

,13
03

....j

O

O

CO

(1)

C3..

O

"t3

L9

C3

d

c:::

::3

O

::3

r_

n

L

ew-

_L J

A

/ --

i-.- u,.,i

_a

Lid

(D

m

IJ.I

,cl --

A

v

LU

r,D

n"

LU

aZ

rr O

Z--

03Q

Ill

(.9

'<

n"

iii

<>

_ 0 0 0 _ 0 _ 0 0 0 0 0

CO

0

0 CO

_0 _" ¢0 _ _" _- _

CO ',- LO _ _ ",--" O

C'G ,-: O C50 ,-': O

O'_ (O

I"-. O O,I 0 O0

OO O CO _ CO

I..O _ CO CO r-.. I'_

.,- o c_ _ o,i o

_ o o d o o

tO

¢O

O

O

I..O

I"-

C6 C_

cO

LO

O_ 0

0

0

0

u?

_0

to 00 co _ I'--

co to o_1 _ 00 _ o'_

o ,,- co _ 00 o 03

_ 00 I'-. _ o,.I o

c_ .,- o 6 o ,,- o

o

tO _ 00 O,.I 00

O _ (3') _ t.O

O,.I _ O_ O QD tO

O'_ O T- ",-- _ O

c6 o c_c5 o o

tO

00

O

o_ oJ

o Lo T- _ 00

co co

co __ _LU o E _

44
Table 14. Results of Run No. 10 (Continued)

H

f4

AZ

VCAS

e

O/

Elevator

GSE2

X

Y

AY

+

tp

Aileron

Rudder

Beam error

Local2

(ft)

(ft/s)

(ft/s 2)

(kn)

(deg)

(deg)

(deg)

(deg)

(ft)

(ft)

(ft/s 2)

(deg)

(deg)

(deg)

(deg)

(deg)

(deg)

AVERAGE STANDARD AVERAGE STANDARD

DEVIATION DEVIATION

-24035

1322

-13.64

149.6

11.04

1.538

1.114

0.3333

0.5388

0.4207

[1.001]

0.01886

4.494

0.02671

0.3712

0.2054

0.3520

0.07725

0.02427

642.1

-13.42

149.6

-11258

5.091

1.063

0.7008

0.2605

0.3582

0.2661

O.646O

0.02242

4.202

0.01685

0.1793

0.0995

0.2085

0.05805

0.01839

45
O

O

L)

d

O

_S

_Zl

Z

00m i

W

Z

o3

W

rr

W

Z

o

Z--

con

W

o _ o

_ _ _ _ _ o

T--

'_" 0 _ 04 '_" 0_1

o_ d d o ,- o

o

o

o

co

o_ 7"

o

I'_

00

e0 _o

v.

0D

O4

_D ,_" _" _ O_ O_

Co _ _- o_ O o_ O

O I'_ 03 O _D I'_

O _ CO 0_ _I

O_ O O O _-- O

_D

LO

O

O

L_

LO

QD

CO

Ob

_D

To

co

00 o u_ I_ 0_ ,_- o_ 00 o ,-- _ _ o

I_ I'_ 04 _ o _ 04 _- co o_ 04 o

_o uo ,- ai ai uo o co o o o ,- o

co

_.o

_-

o

o

O4

CO _-

_ o _

o_,

co ' ',- 04

_ __ _ = e e m • _ _-_ e e m e • e

= _ £ E -- I _ > W

,

i "r .7- _ _ _LU C.O X >-. -e- _ =,,_ n'- r,n j

46
Table 15. Results of Run No. 11 (Continued)

H

AZ

VCAS

e

Ot

Elevator

GSE2

X

Y

AY

+

Aileron

Rudder

Beam error

Local2

(ft)

(ft/s)

(ft/s 2)

(kn)

(deg)

(deg)

(deg)

(deg)

(ft)

(ft)

(ft/s 2)

(deg)

(deg)

(deg)

(deg)

(deg)

(deg)

AVERAGE STANDARD AVERAGE STANDARD

DEVIATION DEVIATION

1324

-13.52

149.1

-24216

5.031

6.820

6.439

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1. Report No 2. Government Accession No. 3.

NASA CR-178032

4. Title and Subtitle 5.

Performance of a Commercial Transport under Typical MLS

Noise Environment 6

7. Author(s) 8.

John K. Ho

9. Performing Organizat,on Name and Address 10.

Boeing Commercial Airplane Company

P.O. Box 3707

Seattle, Washington 98124

12. Sponsoring Agency Name and Address

National Aeronautics and Space Administration

Washington, DC 20546

Recipient's Catalog No.

Report Date

January, 1986

Performing Organization Code

Performing Organization Report No.

D6-52712

Work Unit No.

11 Contract or Grant No.

NAS1-17635

13. Type of Report and Period Covered

Contractor Report

14. Sponsoring Agency Code

505-45-33-56

15. Supplementary Notes Langley Technical monitor:

Carey R. Spitzer

ATOPS Program Office

NASA Langley Research Center

Hampton, VA 23665-5225

16. Abstract

William F. White APM 430

Federal Aviation Administration

800 Independence Ave. SW

Washington, D.C. 20591

This document reports the performance of a 747-200 automatic flight control system (AFCS)

subjected to typical Microwave Landing System (MLS) noise. The performance was then

compared with the results from a previous study which had a B747 AFCS subjected to the

MLS standards and recommended practices (SARPS) maximum allowable noise. A glide slope

control run with Instrument Landing System (ILS) noise was also conducted. Finally, a linear

covariance analysis is presented.

17. Key Words (Suggested by Author(s))

Microwave landing system (MLS)

Automatic flight control system (AFCS)

Instrument landing system {ILSI

18. Distribution Statement

Unclassified--Unlimited

Subject Category 04

19 Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

62

22. Price

FORM 0005 For sale by the National Technical Informalion Service, Springfield, Virginia 22161