\ 

NASA Contractor Report 178312 

Simulation of Automatic Precision Departures 

and Missed Approaches Using the Mickowave 

Landing System 

J. B. Feather 

McDonnel I Douglas Corporation 

Long Beach, California 90846 

Contract NAS1-16202 

July 1987 

(KASA-CR-178312) SIHULALTICI CF AU'FOllATIC I38 7-20 8 9 3 

PRECISIOll DEPABIUEBS AID BISSED ALPP6lOACHES 

tSIY6 TBB IIICQUbAVE LABDING SYSTEH 

BC AGB/H8 A01 CSCL 176 G3/0U 0091304 

4McDonnell-Douglas Corp-) 56 g Avail: ITIS Unclas 

National Aeronautics and 

Space Ad ministration 

Langley Research Center 

Hampton, Virginia 23665-5225 
NASA Contractor Report 178312 

Simulation of Automatic Precision Departures 

and Missed Approaches Using the Microwave 

Landing System 

J. B. Feather 

McDonnell Douglas Corporation 

Long Beach, California 90846 

Contract NASI-16202 

July 1987 

National Aeronautics and 

Space Administration 

Langley Research Center 

Harnpton, Virginia 23665-5225 
TABLE OF CONTENTS 

- PAGE 

LIST OF FIGURES .................. iv 

LIST OF TABLES .................. viii 

LISTOFSYMBOLS .................. ix 

SUMMARY AND INTRODUCTION ............... 

CONCLUSIONS AND RECOMMENDATIONS ............. 

MLSOPERATIONS .................. 

Precision Departure Geometry ............ Missed Approach Geometry ............. 

PRECISION DEPARTURE PATH DESCRIPTION ........... 

Departure Paths ................ Lateral Guidance Concepts ............. 

MISSED APPROACH PATH DESCRIPTION ............ 

Approach Path ................. Lateral and Vertical Guidance Concepts ......... 

i 

4 

5 

6 

7 

7 

8 

9 

9 

10 
TABLE OF CONTENTS 

( continued 1 

PAGE 

SIMULATION RESULTS ................. 

Simulation Description .............. 

Wind and Turbulence Models ........... MLS Noise Models .............. 

Departurecases ................ 

Case 1 . Path 1. no Wind ........... Case 2 . Path 1. Tail and Cross Winds ....... Case 3 . Path 1. Winds and Turbulence ....... Case 4 . Path 1. Tail and Cross Winds ....... Case 5. 6. 7. . Paths 2. 3. and 4 ........ 

Missed Amroach Cases .............. 

11 

11 

11 

11 

12 

12 

13 

14 

14 

15 

16 

Case 8 . No Wind .............. Case 9 . Tail and Cross Winds .......... Case 10 . Winds with Turbulence ......... Case 11 . Pitch Up . No Winds .......... Case 12 . Pitch Up . With Winds ......... Case 13 . Pitch Up . Barometric Altitude ...... 

REFERENCES .................... 

16 

17 

17 

17 

18 

18 

19 

ii 
TABLE OF CONTENTS 

( continued 1 

PAGE 

APPENDIX A: DERIVATION OF BACK AZIMUTH COORDINATES . . . . . . 47 

APPENDIX B: WIND AND TURBULENCE MODELS . . . . . . . . . . 50 

APPENDIX C: MLS ANGLE AND RANGE NOISE MODELS . . . . . . . . 52 
LIST OF FIGURES 

PAGE 

1 . DEPARTURE GEOMETRY . . . . . . 

2 . MISSED APPROACH GEOMETRY ............. 

3 . TYPICAL DEPARTURE PATH FOR SAN FRANCISCO RUNWAY 28R .... 

4 . TYPICAL VERTICAL PATH FOR MISSED APPROACH (GO AROUND) ... 

5 . TYPICAL VERTICAL PATH FOR MISSED APPROACH (PITCH UP) .... 

6 . BANK ANGLE TIME HISTORY FOR PATH 1 (CASE 1 ) ....... 

7 . VELOCITY TIME HISTORY FOR PATH 1 (CASE 1 ) ....... 

8 . LATERAL TRACKING ERROR FOR PATH 1 (CASE 1) ....... 

9 . LATERAL TRACKING ERROR SENSITIVITY ASSUMED IN ...... BACK AZIMUTH COVERAGE 

24 

24 

25 

26 

26 

27 

27 

28 

28 

10 . LATERAL TRACKING IN DOTS FOR PATH 1 (CASE 1) ...... 

11 . GROUND TRACK FOR PATH 1 (CASE 1) .......... 

12 . BANK ANGLE TIME HISTORY FOR PATH 1 (CASE 2) ....... 

13 . VELOCITY TIME HISTORY FOR PATH 1 (CASE 2) ....... 

14 . LATERAL TRACKING ERROR FOR PATH 1 (CASE 2) ....... 

29 

29 

30 

30 

31 

iv 
LIST OF FIGURES 

( continued 1 

- PAGE 

15. LATERAL TRACKING ERROR IN DOTS FOR PATH 1 (CASE 2) . . . . 31 

16. BANK ANGLE TIME HISTORY FOR PATH 1 (CASE 3) . . . . . . . 32 

17. VELOCITY TIME HISTORY FOR PATH 1 (CASE 3) . . . . . . . 32 

18. LATERAL TRACKING ERROR FOR PATH 1 (CASE 3) . . . . . . . 33 

19. LATERAL TRACKING ERROR IN DOTS FOR PATH 1 (CASE 3) . . . . 33 

20. BANK ANGLE TIME HISTORY FOR PATH 1 (CASE 4) . . . . . . . 34 

21. VELOCITY TIME HISTORY FOR PATH 1 (CASE 4) . . . . . . . 34 

22. LATERAL TRACKING ERROR FOR PATH 1 (CASE 4) . . . . . . . 35 

23. LATERAL TRACKING ERROR IN DOTS FOR PATH 1 CASE 4) 35 

24(A).BANK ANGLE TIME HISTORY FOR PATH 2 (CASE 5) . . . . . . . 36 

24(B).BANK ANGLE TIME HISTORY FOR PATH 3 (CASE 6) . . . . . . . 36 

24(C).BANK ANGLE TIME HISTORY FOR PATH 4 (CASE 7) . . . . . . . 37 

25(A).LATERAL TRACKING ERROR FOR PATH 2 (CASE 5) . . . . . . . 37 
LIST OF FIGURES 

(continued) 

- PAGE 

25(B).LATERAL TRACKING ERROR FOR PATH 3 (CASE 6) . . . . . . . . 38 

25( C) .LATERAL TRACKING ERROR FOR PATH 4 (CASE 7) . . . . . . . . 38 

26. GROUND TRACK FOR PATHS 1, 2, 3, AND 4 . . . . . . . . . 39 

27. PITCH ANGLE TIME HISTORY (CASE 8) . . . . . . . . . . . 40 

28. ALTITUDE TIME HISTORY (CASE 8) . . . . . . . . . . . . 40 

29. VERTICAL TRACKING ERROR TIME HISTORY (CASE 8) . . . . . . . 41 

30. VERTICAL TRACKING ERROR RATE (CASE 8) . . . . . . . . . 41 

31. VERTICAL TRACKING ERROR AS A FUNCTION OF DISTANCE TO GO (CASE 8) 42 

32. VERTICAL TRACKING ERROR RATE AS A FUNCTION OF DISTANCE TO GO . . 42 

(CASE 8) 

33. VERTICAL TRACKING ERROR AS A FUNCTION OF DISTANCE TO GO (CASE 9) 43 

34. VERTICAL TRACKING ERROR RATE AS A FUNCTION OF DISTANCE TO GO . . 43 

(CASE 9) 

35. VERTICAL TRACKING ERROR AS A FUNCTION OF DISTANCE TO GO (CASE 10) 44 

36. ALTITUDE TIME HISTORY (CASE 11) . . . . . . . . . 44 
LIST OF FIGURES 

(continued) 

PAGE 

37 . PITCH ANGLE TIME HISTORY (CASE 11) ........... 45 

38 . VERTICAL TRACKING ERROR AS A FUNCTION OF DISTANCE TO GO (CASE 11) 45 

39 . ALTITUDE TIME HISTORY (CASE 12) ........... 46 

40 . ALTITUDE TIME HISTORY (CASE 13) ........... 46 

vi i 
LIST OF TABLES 

. 

PAGE 

1 . SEQUENCE OF EVENTS FOR DEPARTURES .......... 

2 . DEPARTURE WAYPOINT DATA ............. 

3 . DEPARTURECASES ................ 

4 . MISSED APPROACH CASES .............. 

20 

21 

22 

23 

viii 
LIST OF SYMBOLS 

b Factor used in back azimuth coordinate derivation, 

non dimensional (ND) 

C Factor used in back azimuth coordinate derivation 

h A1 ti tude , ft. 

Range from DME/P transmitter to MLS aircraft 

antenna, ft. R~~~ 

sx ,sy 2JZ Wind magnitude at 33 ft. a1 ti tude in earth 

coordi nates , KT 

u ,v YW Turbulence levels along x-y-z axes, KT 999 

W Wind factor as a function of altitude, ND 

WP Waypoint identifier, ND 

wx Y wy 9 wz Wind magnitudes at altitude h in earth coordinates, KT 

w~~ Y~TY~TZ Total winds (including turbulence) , KT 

XYY Yh Coordinates of a given waypoint , ft. 

xr;l YYh Y zr;l Coordinates defining MLS antenna location, ft. 

xm YY, 9 zm Coordinates of CG location, ft. 

Distance from coordinate origin to the DME/P and 

front azimuth transmitters , ft. XB 

Distance from coordinate origin to the back azimuth 

xD transmitter, ft. 

MLS azimuth angle, deg. 'AZ 

MSL back azimuth angle , deg. 'BAZ 

ix 
‘CE 

‘EL 

0 

“REC 

‘WN 

T 

Wh 

WR 

LIST OF SYMBOLS 

(continued) 

Pi tch s teeri ng command, deg . 

MLS elevation angle, deg. 

Standard deviation used in turbulence filter, KT. 

Standard deviation at MLS receiver output, deg 

White noise gain factor, ND 

Time constant, sec. 

Hi gh frequency MLS noi se f i 1 ter parameter , rad/sec 

Low frequency MLS noise filter parameter, rad/sec 

X 
SUMMARY AND INTRODUCTION 

Results of studies in which precision departures and missed approaches were 

simulated using FILS guidance techniques are presented in this report. The 

study was conducted under t-he Terminal Configured Vehicle (TVC) Program, and 

is an extension of a previous NASA Advanced Transport Operating Systems 

(ATOPS) contract, NASl-18028, (Reference 1 ) in which complex approach paths 

were evaluated. 

coverage has provided additional performance data. In addition, missed 

approaches, which include transitioning from front MLS coverage to back 

azimuth operation, have been simulated. 

elevation antenna used for front MLS coverage has been located on the runway 

centerline. In practice, this antenna will be displaced laterally, so the 

resulting equations for the aircraft position coordinates will be somewhat 

more complicated than those assumed in this study. 

Simulation of precision departures using MLS back azimuth 

For purposes of this simulation, the 

As in the previous studies, an MD-80 aircraft was simulated using its present 

roll and pitch autopilot inner loop configurations. 

of inputs from the MLS guidance algorithms that provided the roll and pitch 

steering commands. With only minor changes, these algorithms are the same as 

those previously devel oped (References 1 and 2). This simul ation imp1 emented 

the MLS guidance laws in conjunction with the MD-80 take off and go around 

pitch autopilot modes. 

off mode, whereas the lateral guidance was under MLS curved path control. 

missed approaches, normal MLS vertical and lateral approach guidance was used 

prior to go around initiation. At that time, the pitch autopilot was changed 

to go around mode, and the lateral guidance remained in its approach mode. 

Switching to MLS back azimuth mode occurred when the aircraft first passed 

into back azimuth coverage. 

simulated. 

The outer loops consisted 

For departures, the pitch guidance was the normal take 

For 

For missed approaches, no lateral maneuvers were 

This effort consisted of departures and missed approaches at an airport where 

MLS, when installed, would provide an operational benefit. 

noise abatement take off procedures which otherwise would not be possible due 

to weather constraints. Several noise abatement departure paths were 

simulated and included the effects of MLS noise, winds, and turbulence on 

performance. Two missed approach procedures were simulated to assess the 

vertical and lateral path tracking accuracies of the system. 

MLS would allow 

1 
CONCLUSIONS AND RECOMMENDATIONS 

CON C L U S I ON S 

Generally, the simulated precision departures for the MD-80 provided 

acceptable lateral tracking performance, except in cases where bank angles led 

to operation near autopilot inner loop command limits. 

tracking errors up to 1500 feet occurred, and the lateral guidance system was 

not capable of controlling these errors when tail and crosswinds were 

simulated. 

bank angles of 25-30 degrees may pose a problem. 

In those cases, 

Also, speed reduction during climbout as a result of turning at 

be less 

tracking 

accepta b 

guidance 

guidance 

Results from all the missed approach cases indicate lateral tracking error to 

thin 

in 

han 20 feet for both front and back azimuth coverage. 

errors during the descent part of the missed approach are well w 

e limits. No problems were encountered when simulating a switch 

implementation involving a1 titude. During descent, the vertical 

a1 gori thm used the MLS-deri ved a1 ti tude. Capturing a barometric 

Vertical 

altitude, and switching the guidance algorithm to track this constant 

altitude, occurred without transients or disruption in operation. 

RECOMMENDATIONS 

Several areas of continued analysis and simulation have been identified as a 

direct result of the present study. Additional follow-on tasks are 

recommended that relate to different aspects of MLS operations other than 

departures and missed approaches. 

The tasks recommended as a result of this study are: 

0 Investigate the problems with large bank angles during departures, 

especially with winds. 

2 
Provide for speed control during the precision departures with turns. 

Formulate and analyze other situations involving the switch from MLS 

a1 titude to barometric altitude. 

Establish if there is an optimum time to switch from front azimuth 

coverage to back azimuth, and evaluate performance under these 

conditions. 

Investigate any problems encountered when leaving back azimuth coverage 

and entering en-route navigation. 

Develop algorithms that can cope with leaving back azimuth guidance then 

re-entering front azimuth coverage during a go around. 

Additional follow-on tasks include: 

0 Simulating the conical azimuth and elevation angle scan geometry of the 

MLS with the elevation antenna offset laterally from the runway 

center1 i ne. 

0 Evaluating the tracking performance when enroute navigation errors cause 

initial lateral and vertical offsets at entry to MLS coverage. 

0 Investigating changes to the guidance algorithms when the aircraft is 

ordered to change to another path while making an approach. 

0 Evaluating the lateral and vertical guidance laws using a fixed-base 

simulator with a pilot in the loop. 

3 
MLS OPERAT IONS 

Different modes of operation of the MLS are employed for departure guidance 

and for the missed approach guidance. For departure, precision distance 

measuring equipment (DME/P) is employed for range information, and a back 

azimuth (BAZ) transmitter provides the azimuth angular information. Figure 1 

is a sketch of the departure geometry assumed for the present study. For 

missed approaches, the same DME/P is used with a front azimuth (AZ) 

transmitter and an elevation (EL) transmitter. 

When the aircraft crosses the y-axis, the front azimuth mode is switched to 

the back azimuth mode. 

elevation information available. Consequently, for purposes of the present 

study, it was assumed that altitude would be available to the MLS guidance 

computer. 

determined for back azimuth operation. The following sections describe the 

calculations required to determine the aircraft position for both front and 

back azimuth modes of operation as a function of the angular and range 

information. 

Figure 2 shows this geometry. 

It is noted that back azimuth operation does not have 

In this way, the coordinates of the aircraft can be uniquely 

4 
PRECISION DEPARTURE GEOMETRY 

Position coordinates ($,, 

calculated from the range, back azimuth angle, and the altitude. 

expressions for those coordinates have been derived using the assumed geometry 

of Figure 1. 

complicated because the x-coordinate requi res the sol ution to a quadratic 

equation. This fact necessitates logic to determine the sign on the radical 

in the equation for Xm' to assure the correct solution. In the following' 

equations, the altitude h is assumed available froma source external to the 

MLS. 

locations at the 12000 foot runway at San Francisco. 

yA3 z;) of the aircraft MLS antenna may be 

The 

Although straightforward, these calculations are somewhat 

The values of the distance XB and XD represent the transmitter 

where : 

xB = -1700 FT 

x = 12000 FT D 

5 
Steps in the development of the above equations are given in Appendix A. 

The sign on the radical in Equation (2) depends on the position of the 

aircraft relative to the DME transmitter. This sign reverses when the 

quantity under the radical passes through zero. Logic in the guidance 

computer is used to set and change this sign automatically. 

simulation, the position coordinates of the aircraft CG (Xm, ym, Zm) are 

computed to account for the offset of the aircraft MLS antenna from the CG. 

In the 

FIISSED APPROACH GEOMETRY 

For missed approaches, the position coordinates are computed from the azimuth 

angle, elevation angle, and DME range when the aircraft is in the front 

azimuth sector. 

switching to the departure guidance equations occurs. 

missed 

As the aircraft passes to the back azimuth coverage, 

approach geometry from which the following equations have been derived: 

Figure 2 shows the 

tan eEL 

The distance, RDpp is obtained in both precision departures and missed 

approaches from the same transmitter, which i.s collocated with the front 

azimuth transmitter. The above equations are Val id for the elevation antenna 

located on the runway centerline as shown in Figure 2. Actually, this 

antenna will be displaced laterally, which will result in somewhat more 

complicated equations. 

performance is slight as compared to the results obtained in this study. 

The effect of such a geometry on tracking 

6 
PRECISION DEPARTURE PATH DESCRIPTION 

A specific airport and departure procedure was chosen to illustrate the 

perfe-ance of a precision departure using the NLS. 

was selected and a noise abatement takeoff procedure was employed. 

procedure requires a sharp right turn just after takeoff to avoid terrain. 

Then, a path is flown over a sparsely populated area until over-water flight 

is attained. 

San Francisco runway 28R 

This 

DEPARTURE PATHS 

Waypoints were defined that resulted in lateral paths suitable for #LS 

implementation. 

departure. 

precision departure. 

Three straight legs and two turns were used in the 

Figure 3 depicts a typical ground track for this simulated MLS 

MLS vertical guidance was not used for this departure. Instead, two existing 

MD-80 autopilot modes, takeoff and speed select, were employed. 

the pitch autopilot was set in take-off mode and the gear was down. 

feet altitude, the gear was retracted. 

autopilot was switched to speed select mode where a target speed of 250 KT was 

input. At 165 KT, the flaps were retracted, and at 197 KT the slats were 

retracted. 

At takeoff, 

At 100 

After the first turn, the pitch 

A summary of events for this departure are given in Table 1. 

When flown visually, this departure requires a right turn with a relatively 

large bank angle to be made as soon as feasible. 

mountainous terrain near the airport. 

paths are prescribed circular arcs defined by the ground speed and turn 

radius. 

variations during the turns. 

angles of 15, 20, 25, and 30 degrees. Waypoint data for these four cases are 

shown in Table 2. Results for these cases, under various wind conditions, are 

discussed in detail in later sections. 

This turn is to avoid some 

When flown using the MLS, the departure 

Four paths were simulated to compare tracking accuracy and speed 

These paths resulted in nominal, no-wind bank 

7 
LATERAL GUIDANCE CONCEPTS 

Lateral guidance for precision departure, as well as for back azimuth coverage 

during missed approaches, is identical to the approach guidance as documented 

in Reference 2 (p. 6-12). 

that is input to the roll autopilot inner loop. During turns, this signal is 

based on the nominal bank angle (for a given turn radius and ground speed) and 

on error signals that are functions of lateral tracking error and error rate. 

During straight leg segments, the steering signal is only a function of 

lateral tracking error and error rate. 

The concept used is to generate a steering signal 

The only difference in departure operation lies in the way in which the 

waypoints are defined. 

and WP1 is arbitrarily selected along the desired radial. In this way, the 

roll steering commands can be computed in the same manner as for approaches 

simulated in previous studies (Reference 2). 

For example, Figure 3 shows WP6 to be at the origin, 

8 
MISSED APPROACH PATH DESCRIPTION 

The same runway at San Francisco used for departures was also used for the 

missed approach cases. 

types used MLS lateral guidance throughout, switching to back azimuth when 

appropriate. Vertical MLS guidance was used prior to go around initiation, 

then MD-80 pitch autopilot modes were selected as appropriate. 

Two types of missed approaches were simulated. Both 

APPROACH PATH 

In the first set of cases, the aircraft was descending under lateral and 

vertical MLS guidance. At a specified altitude, a missed approach was 

initiated. At that time, the pitch autopilot was set in go-around mode 

whereas 1 ateral MLS guidance was maintained. 

lateral tracking accuracy during go around in the presence of noise and 

winds. Figure 4 is a sketch of the vertical profile for this set of cases. 

This procedure a1 1 owed study of 

In the second set of cases, pitch up to level flight was initiated at a 

specified altitude. Lateral and vertical guidance during this time was under 

MLS control. 

initiated in the pitch autopilot (Figure 5). 

front azimuth coordinates (Equations (1) - (3) 1, was maintained until passing 

into the back azimuth sector. At that time, lateral guidance was switched and 

the back azimuth coordinates were used (Equations (4) - (6)). 

At a specified distance from the runway, go-around mode was 

Lateral guidance, using the 

9 
LATERAL AND VERTICAL GUIDANCE CONCEPTS 

No changes to the vertical guidance law (as described in Reference 2, p. 13, 

14) were necessary for use in the missed approach studies. 

guidance law also was usable without change. Additional switching logic was 

required to change from front azimuth coordinates to back azimuth 

coordinates. This switching was programmed to occur at the y-axis crossover, 

when the X coordinate changed sign. 

front and back azimuth coverage, so switching could occur anywhere in this 

region. For the present study, switching was chosen to be at the y axis for 

con ve ni e nc e. 

The lateral 

It is noted that the runway is in both 
SI MULAT I ON RESULTS 

SIMULATION DESCRIPTION 

The basic simulation used for these studies is the same MD-80 program as used 

in previous studies (Reference 1 and 2) with only minor modifications for the 

missed approach cases. The existing MD-80 program was developed for landing 

only, and did not have the capability for takeoff when the aircraft was on the 

ground. Consequently, for precision departures, the aircraft was started at a 

low altitude and takeoff continued from that point. 

Lateral and vertical steering signals were generated and input to the 

appropriate autopilot inner loops. 

in the simulation. 

were external to the autopilot. 

No changes to these inner loops were made 

All required calculations, and the waypoint data storage, 

Wind and Turbulence Models 

Winds (simulated as a function of altitude) and turbulence were used in the 

simulation. 

landing studies Appendix B contains the details of these models, (Reference 

2). 

These models are the same as those used in the previous MLS 

MLS Noise Models 

Noise levels used in the departure and missed approach simulations are based 

on the models given in Reference 2. 

elevation and azimuth angles, and for DME range. 

study contained this MLS noise. 

Appendix C shows these models for 

All cases simulated for this 

11 
DEPARTURE CASES 

Seven departure cases have been simulated using the San Francisco airport 

runway 28R. 

departure, the first turn must be executed as soon as feasible after takeoff 

and be tight enough to avoid nearby terrain. 

different wind conditions compare path tracking accuracy. 

cases for different departure paths under the same wind environment were also 

simulated. 

cases. The second turn, after a short straight leg, is not critical and was 

selected to be nominally 15 degrees for all cases. 

In order to realize the noise abatement benefits of this 

Results of four cases under 

Three additional 

Table 3 defines the bank angle and wind conditions for these seven 

Case 1 - Path 1, No Wind 

Shown in Figure 6 is the bank angle time history for Path 1 (a 20 degree 

nominal bank turn). 

due to the tracking error inherent in the aircraft roll response. 

of the first turn, the bank angle tends to zero for the short straight leg. 

Then, the 15 degree bank turn is executed to place the aircraft along the 

desi red radial. 

Some overshoot is experienced in the no-wind case and is 

At the end 

At the end of the first turn (about 70 seconds), the pitch autopilot is 

switched to a speed command mode, where 250 knots is set as the target speed. 

Flaps and slats are retracted as given in the schedule of Table 2. 

resulting speed profile is shown in Figure 7. 

speed varies about 2 to 3 knots from the desired 158 KT, then increases up to 

the 250 KT target speed. This run was terminated arbitrarily at 150 seconds, 

which was before the speed had reached steady state. 

The 

During the first turn, the 

During this entire time, MLS lateral guidance was employed to keep the 

aircraft on the desired lateral path. Figure 8 shows this lateral tracking 

error, both for the turns and for the straight legs. 

straight portion (at about 22 and 36 seconds), there is an abrupt change in 

the error. 

track to a linear track. 

At the transition to the 

This change is due to switching guidance laws from a circular 
This tracking error can be expressed in terms of dots in a similar manner to 

landing approaches. Figure 9 is the assumed lateral tracking error 

sensitivity definition. It 

is defined as a function of along-track distance (i.e., the actual curved path 

the aircraft is flying) as opposed to the straight extended runway centerline 

as used for present ILS approaches. Figure 10 shows the tracking error as a 

function of along-track distance for a full scale of - + 2 dots. At the end of 

the runway, 2 dots represents 350 feet. The sensitivity varies linearily 

along a 3 deg slope, until at about 33000 feet, 2 dots represents 1500 feet. 

At distances greater than this value, the sensitivity remains at 1500 feet. 

As can be seen from Figure 10, tracking for this case is within + 1/4 dot 

during the enti re departure. 

The envelope shown defines the - + 2 dot boundary. 

- 

Shown in Figure 11 is the resulting ground track for case 1. Back azimuth 

coverage is limited to - + 40" from antenna boresight. 

the back azimuth antenna will have to be skewed approximately 20" from the 

runway centerline to provide coverage for the second turn and straight leg. 

For the 28R departure, 

Case 2 - Path 1 with Left Cross wind 

In this case, a tail and cross wind were added as external disturbances (Table 

3). 

to the no-wind case of Figure 6, one sees the increased bank angle response 

due to the wind components. 

angle varies accordingly. The second turn is now at a bank angle of about 18" 

instead of 15". 

Figure 13. A 6 knot decrease in speed occurs near the end of the first turn, 

then the speed increases due to the pitch autopilot switching to a speed hold 

mode. Lateral tracking errors are larger than the no-wind case. Figure 14 

shows peak errors to be within - + 200 feet as compared to the somewhat smaller 

peaks for the no-wind case. This error tends to zero as the second straight 

leg is being tracked (at distances of 35000 feet and greater). 

tracking degradation can also be seen by comparing the error in dots of Figure 

15 with Figure 10. This particular wind condition produces tracking errors on 

the order of - + 1/2 dot. 

The resulting bank angle is given in Figure 12. Comparing this response 

As the aircraft turns in this wind, the bank 

A larger speed variation occurs for this case as shown in 

Lateral 

13 
Case 3 - Path 1 with Wind and Turbulence 

Turbulence, as defined in Appendix B, was added to the steady portion of the 

tail and cross winds for this path. Comparing the bank angle, velocity, and 

tracking error, Figures 16-19 (Case 31, with Figures 12-15 (Case 2) shows only 

a slight increase in activity due to the turbulence. 

analysis was not performed due to time constraints, this is the only case in 

which turbulence was simulated. It was included to give a general idea of 

response in a turbul ent envi ronment 

Since a statistical 

Case 4 - Path 1 with Right Crosswind. 

In this case, the direction of the cross wind is reversed from the wind in the 

previous cases, but has the same tail wind. 

results in a smaller bank angle during the second part of the first turn 

(Figure 20). 

This opposite direction wind 

The second bank angle is also smaller during the first part of the turn. 

Speed variation during the first turn (Figure 21) is somewhat less than Case 2 

(Figure 13). 

Tracking errors (Figures 22 and 23) are on the same order of magnitude as Case 

2 with the left crosswind (Figure 14 and 15). 

of the first turn for the left crosswind is about 150 feet to the left of 

desired track. 

considerations. A right cross wind causes a 100 foot error to the right of 

desired track at the end of the first turn. 

simulated as being the more critical direction in the remaining cases where 

other paths are flown. 

However, the error at the end 

This is a more critical case from terrain avoidance 

The left cross wind will be 

14 
Cases 5, 6, and 7 - Paths 2, 3 and 4 

These three cases are included so a comparison of performance can be made when 

other bank angles are employed for the first turn. The bank angle for Path 2 

(a 15 degree nominal bank) in Figure 24A appears reasonable in the wind 

environment, but Paths 3 and 4 (25 and 30 degree nominal banks), Figures 24 B 

and C, show bank angle responses that are a result of exceeding existing 

command 1 imits in the autopilot. 

large tracking errors for these two cases (Figure 25 B and C). 

visual departure at 28 R are flown at these bank angles, use of the autopilot 

would cause excessive errors. 

angles could be implemented without changing the autopilot inner loop limits 

and possibly some gains. 

the present study. It is noted that results shown for Path 4 did not have the 

tail or crosswinds present. This wind case was simulated, but the wind levels 

were such that the autopilot saturated due to its internal bank command 

limits. Such a turn would not be possible with these assumed winds. 

study of gain and/or limit changes in the autopilot for this case is indicated. 

Consequently, non-1 inear operation causes 

Even though 

It is not considered likely that these large 

No attempt to make such changes was considered in 

Further 

A sketch of the ground tracks during the first turn for the four paths is 

shown in Figure 26. This figure, which is approximately to scale, shows Path 

2 passing over the mountainous terrain. The simulation results for this case 

give the altitude near the end of the first turn to be 2800 feet. It appears 

that Path 1 would result in a departure that avoids the terrain problem with 

reasonable tracking errors. 

MISSED APPROACH CASES 

Six cases were simulated at San Francisco 28R for missed approach conditions 

(Table 4). 

sectors and signal switching occurred between the coverages. I n a l l cases, 

the aircraft was initially descending along a 3" glideslope. 

Guidance for these cases used both front azimuth and back azimuth 

15 
The first three cases simulated a go around at 200 feet altitude. 

time, vertical guidance was switched from MLS control and the pitch autopilot 

was placed in the go around mode (see Figure 4). 

along the extended runway centerline and lateral guidance was under MLS 

control for the entire simulated mi ssed approach. 

At that 

The desired lateral path was 

The second three cases represent a change in the approach procedure as might 

be directed by air traffic control. Level flight is desired at an altitude of 

1000 feet, so a pitch up is initiated at that time. This path is maintained 

until go around is directed at a specified distance from threshold (see Figure 

5). MLS lateral 

guidance is used throughout, with switching to back azimuth coverage when the 

aircraft crosses the y axis. 

Vertical MLS guidance is maintained until go around. 

In all cases simulated for these missed approaches, the bank angle error was 

less than 1". Similarly, the lateral tracking error was always less than 10 

feet. As a result, vertical tracking is of more interest, so the following 

discussions will focus on the vertical errors rather than on lateral 

performance. 

Case 8 - No Wind 

This case contains no external wind disturbances but does contain MLS angle 

and range noise. 

aircraft pitches up to a new attitude near 20" (Figure 27). 

altitude changes are shown in Figure 28. 

were simulated for an arbitrary 100 second period. 

Go around is initiated at a time of 25 seconds, and the 

The corresponding 

This case, and subsequent cases, 

Vertical tracking error is computed and used by the MLS vertical guidance 

algorithm until go around is initiated. At that time, this error is no longer 

updated or used since the pitch autopilot is now in go around mode. Figure 29 

is a plot of the vertical error as a function of time for this case. 

corresponding error rate is shown in Figure 30. The dispersion in these plots 

is due to the MLS noise on the angle and range signals used by the guidance 

a1 gori thm. 

The 

16 
Tracking error and error rate may be plotted also as a function of distance to 

go. This distance is measured along the x axis to the aircraft, and is always 

considered positive. Figures 31 and 32 show the vertical errors as a function 

of the distance to go. For comparison purposes, the remaining missed approach 

cases Will show the tracking error as a function of this distance. 

Case 9 - Tail and Cross winds 

Peak tracking errors for this case with winds increased by about a factor of 2 

over Case 8, whereas the peak error rates remained about the same (Figures 33 

and 34). 

small even in a wind environment. 

This increase is not significant since the tracking errors remain 

Case 10 - Tail and Cross Winds with Turbulence 

Addition of turbulence to the steady winds increased the peak tracking errors 

by another factor of 2, so now the peak is near 25 feet as compared to 14 feet 

for no turbulence and 6 feet with no wind at all. 

the tracking error is about 23 feet (Figure 35). 

At go around initiation, 

Case 11 - Pitch Up - No Wind 

This case represents a procedure as pictured in Figure 5 where pitch up from a 

3" descent is made at 1000 feet altitude. Go around is initiated at a 

specified distance, and the pitch autopilot is engaged at that time. 

resulting altitude is shown in Figure 36. Pitch attitude is given in Figure 

37, and the vertical tracking error (during MLS guidance) is shown in Figure 

38. At a distance to go of about 2000 feet, transition to level flight is 

made as marked by the abrupt change in tracking error. After capture, the 

error is within a few feet until the MLS mode is terminated and go around is 

The 

initiated. 
Case 12 - Pitch Up With Tail and Cross Winds 

Vertical tracking error is somewhat increased for this case, but the altitude 

is nearly the same (Figure 39) in this simulated wind environment as compared 

to the no wind case shown in Figure 36 (Case 11). 

Case 13 - Pitch Up Using Barometric Altitude 

In this case, the MLS-computed altitude is used while descending along the 3" 

glideslope. At the time of pitch up, barometric altitude is used instead of 

the MLS altitude. 

to determine when the transition is made as well as during the altitude hold 

period. 

The barometric altitude is used in both the switching logic 

Figure 40 is a plot of the resulting altitude for this case. 

difference between this trace and the altitude resulting when no switching 

occurred (Figure 39). 

appears switching to barometric altitude at some point in the approach can be 

made smoothly. 

There is little 

No problems were encountered in this case, and it 
E- 

- 

, RE F ERENC ES 

1. J. B. Feather: Guidance Law Simulation Studies for Complex Approaches 

Using the Microwave Landing System (MLS), NASA CR-178182, November 1986. 

2. J. B. Feather: Guidance Studies for Curved, Descending Approaches Using 

the Microwave Landing System (MLS), NASA CR-178030, May 1986. 

19 
1. 

2. 

3. 

4. 

5. 

6. 

7. 

TABLE 1 

SEQUENCE OF EVENTS FOR DEPARTURE 

Initial climb with pitch autopilot in takeoff mode. 

Retract gear at 100 feet altitude. 

Start right turn at end of runway to a 030" heading. 

At end of turn, switch pitch autopilot to speed mode and select 250 KT 

speed. 

Retract flaps at 165 KT, retract slats at 197 KT. 

Make 15" left turn to intercept the radial R-342. 

Return wings level and maintain desired course until end of simulated 

run. 

20 
f 

f *. ddoo 

> 

Io 

a 

3 

0000 

X 

0000 >- 

Ln 

3 

a 

X 

0 

0 

0 

7 

? 

000 

000 

000 

a3 

> v) 

* 

3 

a F 

0 

h * 

c Q 

IQ 

n 

N 

a3 

M 

a3 

c > 

M 

p. 

3 

m e m- coo* 

LnOM Lncob 

X 

I- = 

Q 

a 

w 

n 

N 

0, 

Ln 

co - >- 

N 

3 

a 

x 0 

Ln 

0 

0 

0 

0 

>- 

- 

a 

3 

ru 

h 

M 

Io 

(u 

x 

0 

0 

d 

I' 

CO 

21 
TABLE 3 

DEPARTURE CASES 

CAS E 

NUMBER 

PATH 

NUMBER 

TAIL WIND 

( KNOTS 1 

CROSS WIND 

(KNOTS) TURBULENCE 

NONE 

NONE 

YES 

NONE 

NONE 

NONE 

NONE 

1 1 NONE NONE 

2 1 10 15 

3 10 15 

4 10 -1 5 

5 2 10 15 

6 15 

7 

3 

4 

10 

NONE NONE 

22 
TABLE 4 

MISSED APPROACH CASES 

CASE 1 TAIL WIND 1 CROSS WIND i 

NUMBER I (KNOTS) I (KNOTS) I TURBULENCE I NOTES 

I I I I I 

I I 1 I GO AROUND 

8 I NONE I NONE I NONE I AT 200' ALT 

I I 

I NONE I AT 200' ALT 

1 I 

9 I 10 I 15 

I I AT 200' ALT I I I 

I I I I 

I I I I 

10 I 10 I 15 I YES 

I 11 I NOiJE I NONE I NONE I PITCH UP 

13 I 10 I 15 

I I 

1 

I NONE 

I 

I NONE 

I 

I 

I PITCH UP 

I 

I PITCH UP 

I (BAR0 ALT) 

23 
MLS ANTENNA POSITION 

X 

/ 

Y 

Figure 1. Departure Geometry 

MLS ANTENNA POSITION 

\ \ 

Figure 2. Missed Approach Geometry 

24 
W 

X 

25 
ALT 

Figure 4. Typical Vertical Path for Missed Approach (Go-Around) 

A LT 

- 

Figure 5. Typical Vertical Path for Missed Approach (Altitude Hold - Go-Around) 

26 
Figure 6. Bank Angle Time History for Path 1 (Case 1) 

TIME (SECONDS) 

Figure 7. Velocity Time History for Path 1 (Case 1) 

27 
E 

W 

60 

40 

20 

0 

- 20 

- 40 

- 60 

- 80 

- 100 

- 120 

- 140 

- 160 

- 180 

-200 7.- ....... I. ........ ! ......... !....... r 4- ........ !.I r. *. .-.! -1.. I ..A ..I.. .*.A .I...... !....I ... I ! ...... ..A 

0 5 10 15 20 25 30 35 40 45 50 55 

ALONG TRACK DISTANCE (1,000 FEET) 

Figure 8. Lateral Tracking Error for Path 1 (Case 1) 

1.500 FT 

2-DOT BOUNDARY 

350 FT 

4 

ALONG TRACK 

1,500 FT 

CROSS-TRACK 

DISTANCE 

Figure 9. Lateral Tracking Error Sensitivity Assumed in Back Azimuth Coverage 

28 
0 5 10 15 20 25 

ALONG TRACK DISTANCE (1,000 FEET) 

Figure 10. Lateral Tracking in Dots for Path 1 (Case 1) 

30 

25 

20 

15 

10 

5 

0 1 

0 60 

DOWN-RANGE (1,OOO FEET) 

Figure 11. Ground Track for Path 1 (Case 1) 

29 
l!5lJiE 1 70 80 90 100 1 

3 120 130 140 1 

TIME (SECONDS) 

Figure 12. Bank-Angle Time History for Path 1 (Case 2) 

TIME (SECONDS) 

Figure 13. Velocity Time History for Path 1 (Case 2) 

30 

I 120 130 140 1 
E 

$ 

w 

If 

U 

w 

0 

Y 

0 

I1 

a 

w 

Iz 

a 

a 

a 

4 

Figure 15. Lateral Tracking Error in Dots for Path 1 (Case 2) 

3 :. 
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 

TIME (SECONDS) 

Figure 16. Bank-Angle Time History for Path 1 (Case 3) 

150- 

0 10 20 

f I 

-mmmmTmTT1 40 50 60 70 80 90 100 110 

TIME (SECONDS) 

Figure 17. Velocity Time History for Path 1 (Case 3) 

rmmrr...r...rnrlnr-.l 

0 130 140 1 

3 13 L 

0 
Figure 18. Lateral Tracking Error for Path 1 (Case 3) 

Figure 19. Lateral Tracking Error in Dots for Path 1 (Case 3) 

33 
i? 

s 

W 

n 

0, 

W 

J 

0 

Z 

Y 

Z 

a 

a 

m 

70 80 90 1 

TIME (SECONDS) 

Figure 20. Bank-Angle Time History for Path 1 (Case 4) 

t 

TIME (SECONDS) 

Figure 21. Velocity Time History for Path 1 (Case 4) 

0 
E 

B 

W 

LL 

Y 

a 

U 

W 

c3 

z 

0 

Q 

I1 

U 

w 

I3 

a 

a 

4 

F 

8 

B 

$ 

a 

U 

W 

c3 

0 

a 

IA 

a 

U 

W + 

a 

4 

Figure 22. Lateral Tracking Error for Path 1 (Case 4) 

35 
E 

s 

4 

2 

W 

a: 

e 

W 

-I 

a 

Y 

z 

5 

W 

W 

a: 

s 

0 

W 

-I 

(3 

z 

Y 

z 

a 

2 

TIME (SECONDS) 

Figure 24A. Bank-Angle Time History for Path 2 (Case 5) 

Figure 248. Bank-Angle Time History for Path 3 (Case 6) 

36 
Figure 24C. Bank-Angle Time History for Path 4 (Case 7) 

Figure 25A. Lateral Tracking Error for Path 2 (Case 5) 

37 
€ 

B 

8 

5 

W 

a: 

LL 

c3 

0 

a 

a: 

IJ 

a: 

W 

a 

4 

5 10 15 20 25 30 35 40 45 50 55 I 

ALONG TRACK DISTANCE (1,OOO FEET) 

Figure 25B. Lateral Tracking Error for Path 3 (Case 6) 

ALONG TRACK DISTANCE (1,OOO FEET) 

Figure 25C. Lateral Tracking Error for Path 4 (Case 7) 

38 
39 
Figure 27. Pitch-Angle Time History (Case 8) 

0 10 20 30 40 

TIME (S 

lI 

rrmm 

I 

ZONDS) 

Figure 28. Altitude Time History (Case 8) 

43 
Figure 29. Vertical Tracking Error Time History (Case 8) 

IU 

a 

0 

z 

IL 

Figure 30. Vertical Tracking Error Rate (Case 8) 

41 

0 

0 
6 

P 

W 

n: 

n: 

W 

0 

Z 

Y 

0 

IJ 

k 

- 

a 

a 

a 

0 

In: 

W 

> 

G 

n 

z 

0 

Y 

ti Q 

k 

a 

W 

W 

Ia: 

PI 

n: 

w 

J 

B 

a 

0 

In: 

W 

> 

Figure 32. Vertical Tracking Error Rate as a Function of Distance to Go (Case 8) 

4 2 

0 
5 

P 

W 

!L 

a 

a 

W 

0 

Y 

0 

I- 

-J 

z 

2 

a 

0 + 

a 

W 

> 

DISTANCE TO GO (FEET) 

Figure 33. Vertical Tracking Error as a Function of Distance to Go (Case 9) 

8 

n 

Z 

0 

Q 

!L 

a 

a 

8 

li 

W 

W 

IP 

a 

W 

-J 

a 

0 

lW 

> 

DISTANCE TO GO (FEET) 

Figure 34. Vertical Tracking Error Rate as a Function of Distance to Go (Case 9) 

43 
00 

Figure 35. Vertical Tracking Error as a Function of Distance to Go (Case 10) 

Figure 36. Altitude Time History (Case 11) 

44 
TIME (SECONDS) 

Figure 37. Pitch-Angle Time History (Case 11) 

......... 

30 

Figure 38. Vertical Tracking Error as a Function of Distance to Go (Case 11) 

2,400 

45 
Figure 39. Altitude Time History (Case 12) 

1,700 

1,600 

1,500 

900 ,.... ................................ 0 10 20 30 40 ' ' .' ' 50 70 80 

TIME (SECONDS) 

Figure 40. Altitude Time History (Case 13) 

46 

0 
t 

I 

APPENDIX A - DERIVATION OF BACK AZIMUTH COORDINATES 

, 

From the geometry of Figure 1, one may write the following expression for the 

tangent of the azimuth angle, 8BAZ: 

An expression containing the DME range is obtained from the triangle 

containing RDME and z;: 

2 '2 = yC2 + (xo - x;) 2 

R~~~ - 'rn 

47 
Solve both (Al) and (A21 for YA2 and equate the results: 

From (AI : y~2 = [ z~ 2 + (x~ - xB)’] tan 2 eBAZ 

From (A2): yA2 = R2 DME - ‘m l2 - (XD - x;)2 

Hence 

l2 - ( XD - x$)Z - 2 p&~+ - R~~~ - ‘m (xh - xB)2]tan 2 eBAZ 

Expansion of (A5) will yield a quadratic in XA. 

trigonometric identity will simplify the result: 

Use of the following 

Equation (A51 reduces to the form 

xi2 + bx; + c = 0 

where b & c are defined by: 

48 
The above equations may be rewritten in terms of only one trig function: 

The solution to (A61 is 

x' - m 

and the expression for YA is obtained from (A3): 

Yrn ' = + (.e - xB)2y tan %AZ 

The value for zi must be supplied from a source external to the MLS back 

azimuth equipment. 

In implementing (A91 for $, , one must determine the proper sign on the 

radical. 

aircraft on approach (in front azimuth coverage). 

quantity under the radical in (A9) passes through zero. Logic in the computer 

automatically selects the correct sign. 

study only contended with one switch of sign. However, in general, additional 

sign changes can occur depending on the aircraft position relative to the back 

azimuth and DME transmitters. 

account for the most general case. 

For the geometry assumed here, the sign will be negative for an 

The sign switches when the 

It should be noted that the present 

More sophisticated logic would be required to 

49 
APPENDIX B - WIND AND TURBULENCE MODELS 

0 

Included in the simulation are options for winds, whose magnitudes are a 

function of altitude, and for turbulence as additive terms to the winds. 

factor that is a function of altitude is denoted W and is defined by 

The 

- 

1 + ss 

W = 0.43 log h + 0.35 

where h is the altitude in feet. 

wind magnitudes in knots) when the airplane is on the ground are used to 

compute the three wind components at altitude: 

Input values for S,, Sy, and S, (the 

w, = w s, 

wy = w sy 

iJ, = w s, 

The tail wind component S, was simulated as 10 knots, and the cross wind 

S Value for S, was assumed Y 

zero. 

was +15 or -15 knots depending on the case. 

Turbulence is a random variable that may be added to the above winds. 

noise is passed through first order filters whose parameters are functions of 

the wind components as shown in the following figure: 

White 

OWN = 1.0 

FILTER PARAMETERS 

LONG ITU DI N AL LATER A L V ERTl CA L 

dSEC) 6O0/VTAs 600/V,,, 

30/vTAS 

o(KT) 0.15Wx 0.1 5 wy 1.5 

50 
Outputs of the filters are denoted U 

total simulated winds : 

V , W and are used to form the 9’ 9 9 

9 WTX = w, + u 

WTY = w + vg 

WTZ = w, + wg 

Y 

51 
APPENDIX C - MLS ANGLE AND RANGE NOISE 

Angle and range signals as output from the MLS receiver will contain noise. 

For simulation purposes, additive noise has been included in the azimuth, 

elevation, and DME range variables eAZ, BEL, 81 RDbiE respectively. 

variables were modified to include this additive noise: 

The 

- 

'EL - 'EL(TRUE) + ~EL(NOISE) 

For purposes of simulation, white noise was shaped by filters to obtain the 

angle and range noise components. The figure below shows how these noise 

components were calculated (All cases in this study used these components) : 

I I 

GAIN SHAPING FILTER RECEIVER 

FILTER 

DME 

wp = 0.001 RADISEC wQ = 0.001 RADISEC 

w,, = 0.16RADlSEC wh = 0.34RADlSEC wh = 0.245 RADISEC 

AZIMUTH ELEVATION - 

wQ = 0,001 RADISEC 

a = 154.7 WN 

u = 53.4 FT REC 

aWN = 0.064 aWN = 0.024 

aREC = 0.02DEG aREC = 0.0097 DEG 

52 
Standard Bibliographic Page 

. Report No. 

NASA CR-178312 

2. Government Accession No. 3. Recipient's Catalog No. 

I. Title and Subtitle 5. Report Date 

SIMULATION OF AUTOMATIC PRECISION DEPARTURES AND 

MISSED APPROACHES USING THE MICROWAVE LANDING SYSTEM 

13. Type of Report and Period Covered 

2. Sponsoring Agency Name and Address 

CON TRACTOR REPORT 

14. Sponsoring Agency Code 

NATIONAL AERONAUTICS AND SPACE ADMINSTRATION 

WASHINGTON, D.C. 20546 

LANGLEY TECHNICAL MONITOR: C. R. SPITZER 

FAA TECHNICAL MONITOR: W. F. WHITE 

5. Supplementary Notes 

JULY, 1987 

'6. Performing Organization Code 

6. Abstract 

This report presents results of simulated precision departures and missed 

approaches using MLS guidance concepts. The study was conducted under the 

Terminal Configured Vehicle (TCV) Program, and is an extension of previous 

work by DAC in 1986 under the Advanced Transport Operating System (ATOPS) 

Technology Studies Program, contract NAS1-18028. 

'. Author(s) 

J. B. FEATHER 

DOUGLAS AIRCRAFT COMPANY 

1. Performing Organization Name and Address 

3855 LAKEWOOD BLVD. 

The study model included simulation of an MD-80 aircraft, an autopilot, and a 

MLS guidance computer that provided lateral and vertical steering commands. 

Precision departures were evaluated for San Francisco runway 28R using a noise 

abatement procedure. 

noise and under various environmental conditions , Missed approaches were 

considered for the same runway, where lateral MLS guidance maintained the 

aircraft along the extended runway centerline. 

missed approach cases, pitch autopilot take off and go around modes of 

operation were used in conjunction with MLS lateral guidance. 

Several curved path departures were simulated with MLS 

In both the departures and the 

8. Performing Organization Report No. 

10. Work Unit No. 

11. Contract or Grant No. 

LONG BEACH, CA. 90846 NAS1- 167n7 

For sale by the National Technical Information Service, Springfield, Virginia 22161 

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

MICROWAVE LANDING SYSTEM (MLS) 

MISSED APPROACH GUIDANCE 

PRECISION DEPARTURE GUIDANCE 

NASA Langley Form 63 (June 1985) 

18. Distribution Statement 

UNCLASSIFIED - UNLIMITED 

.9. Security Classif.(of this report) 20. Security Classif.(of this page) 

UNCLASSIFIED UNCLASSI F I ED 

21. No. of Pages 22. Price 

66