INTENSITY CONTROL OF FLASHERS - DTIC · 2018-11-08 · As a •esult of tie tube life tests and the...

Report HN. FAA-RD-i2-54

INTENSITY CONTROL OF FLASHERS

Bernard WeinsteinNational Aviation Facilities Experimental Center

Atlantic City, New Jersey 08405

(i TR4p,$

JUNE 1972

FINAL REPORT

Availability is unlimited. Document may be released to tweNational Technical Information Service, Springfield, Virginia22151, for sale to the public.

Prepared for

DEPARTMENT OF 4RANSPORTATIDNFEDERAL AVIATION ADMINISTRATION

National Airspace System Program OfficeWashington 0. C., 2 0 5 9 1

Rep,,od',d bv

NATIONAL TECHNICALINFORMATION SERVICE

U $ L"0o'-"' • C-

- /

.......................

The contents of -this report reflc;t the views of, the NationalAviation Facilities fixperimental Center, Atlantic City, NewJersey, W'hich is responsible for the facts and the accuracy of thedata presented hetein. The contents do not necessarily reflect theofficial views or policy of the Department of Transpqrtation. Thisýreport does not constitute a standard, specification or regulation.

The Federal Aviation Administration is respponsible for the promotion, regulationand s'jfety of civil a' i ation and for, the' developmetn and operation of a commonsystem Qf air navigation and air traffic control facilities which provides for thesafe and efficient u e of airspacc by1 hdc civil and military aircraft.

"The ýNational Aviation Facilities Ekperimental Center maintains laboratories,facilities, skills and services to support FAA research, development and ihiple-mentation programs through analysis, experimentation and evaluaition of aviationconcepts, procedures, systems and (.quipment.

TECHNICAL REPORT STANDARD TITLE PAGE

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

FAA-RD- 72- 54

4. Title and Subtitle 5. Report Date

INTENSITY CONTROL OF FLASHERS June 19726. Performing Organization Code

7. Author(s) 8. Pvrforming Organization Report No.

Bernard Weinstein- FAA-NA-72- 369. Performing Organization Name and Address 10. Work Unit No.National Aviation FacilitiesExperimental Center 11. Contract or Grant No.

Atlantic City, New Jersey 08405 Project No. 071-312-01X13. Type of Report oahd Period Covered

12. Sponsoring Agency Name and AddressFEDERAL AVIATION ADMINISTRATION Final ReportSystems Research and Development Service April 1970 - March 1972Washington, D. C. 20591 14. Sponsoring Agency Code

15. Supplementary Notes

16. AbstractThis report describes tests and experimentation wi~h intensity controlof condenser dischargE lights (flashers) with a three-step intensitycontrol, and used in a Runway Alignment indicator 4 ight (RAIL) Systemas part of a Medium Intensity Approach Light System with sequencedflashers (MALSR) during both day and night and over a wide rangeof visibility conditions. Also, test and experimentation were con-ducted with a voltage sensing circuit intended to operate the inten-sity controlled MALSR from the Control Tower using current changesin the runway lighting circuit. Two intensity controlled MALSR systems;one, 2,400 feet long on Runway 4, and another, 3,000 feet long onRunway 13 were flight tested during the evaluation. The resultsof the evaluation tests indicated the following: (1) the voltagesensing circuit using current changes in the runway lighting circuitprovided satisfactory operation of the MALSR from the Control Tower,(2) the intensity controlled MALSR operated satisfactorily andadequately supported flight operations during both day and night andover a wide range of visibility conditions, (3) compatible intensitylevels between the MALSR and the runway lights were obtained to providEa satisfactory intensity balance for flight operations during theweather conditions flown, and (4) the operation of condenser dischargelights during night VFR and IFR conditions were not distracting anddid not subject pilots to annoying glare.17. Key Words 18. Distribution Statement

Availability is unlimited. DocumentImay be released to the NationalTechnical Information Service,Springfield, Virginia 22151, forsale to the public.

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 58 $3.00 PC.9 5 KF

Form DOT F 1700.7 (8-69)

PREFACE

The author acknowledges the contributions made to theproject by NAFEC personnel in the Flight Operations Branch,the Photographic St ,.-ion, the Engineering Support Section,the Meterology La•b•,atorys the Electric Shop, the LandingSection, the Humar "`ngineering Branch and his associatesin the Airport Se':. .on. To project pilot, Irving Budoff,appreciation is pL .•ticularly expressed for his assistancein the flight tesi program.

Preceding page blankiii

TABLE OF CONTENTS

PageINTRODUCTION 1

Purpose 1Background 1

DISCUSSION 2Equipment Description 2Intensity Control Modification 2Voltage Sensing Circuit 4Flight Tests 4Test Results 4

CONCLUSIONS 6

APPENDIX A Photometric Tests and DrawingModification (22 pages) 1-1

APPENDIX B Summary of Pilot QuestionnaireData (13 pages) 2-1

Preceding page blank

v

LIST OF ILLUSTRATIONS

Figure Page

1 MALSR Configurations Tested 7

2 Simplified Diagram, Unmodified Flasher Circuit 8

3 Flasher Circuit Modified for Intensity Contzrol 9

4 Flasher Unit Top View (Unmodified) 10

5 Top View of Modified Flasher Unit 11

6 Block Diagram, Logic Circuit 12

7 Circuit Diagram, Logic Circuit 13

8 Pilot Questionnaire 14

1-1 Flash Tube Life Test (Zero Hours) 1-3

1-2 Flash Tube Life Test (95 hours) 1-.3

1-3 Flash Tube Life Test (200 Hours) 1-4




1-7 Vertical Traverse of 0.5 uF Capacitorat Zero Degrees Azimuth 1-6

1-b Vertical Traverse of 1.0 uF Capacitorat Zero Degrees Azimuth 1-7

1-9 Vertical Traverse of 2 uF Capacitorat Zero Degrees Azimuth 1-8



Preceding page blankvii

LIST OF ILLUSTRATIONS (continued)

Figure. Page


1-13 Horizontal Traverses of 0.5 uF Capacitor 1-12

1-14 Horizontal Traverses of 1 uF Capacitor 1-13


1-16 Horizontal Traverses of 4 uF'Capacitor 1-15


1-18 Flasher Photometer Output Pulses of 4 uF,30 uF Capacitors 1-17

1-19 Flasher Photometer Outpuy Pulses of 2 uF,1 uF Capacitors 1-18

1-20 Flasher Photometer Output Pulses of 0.5 uFCapacitors 1-19

1-21 FAA-1106 Modified for Intensity Control 1-20

1-22 MALSR Power and Control Wiring Diagram 1-21

viii

LIST OF TABLES

Table aige

1 MALSR and Runway Edge Light IntensitySettings 15

2-1 Number of Questionnaires Received UnderEach Condition 2-4

2-2 Number of Questionnaires by Length of System 2-4

ix

INTRODUCTION

Purpose

The purpose of this evaluation was to devise a suitablemethod of varying the intensity output of condenser dischargestrobe lights.(flashers) to eliminate distracting flasherglare during the hours of darkness; to design intensity levelsof sequenced flashers used with Medium Intensity ApproachLighting System with Runway Alignment Indicator Lights (MALSR),to provide a satisfactory intensity balance with the runwaylights for operations during day and night visual flight rules(VFR) and instrument flight rules (IFR); and to design and testa satisfactory method of operating the MALSR from theControl.Tower using changes in current in the runway lighting circuit,.

Background

In early 1970, the Federal Aviation Administration's (FAA),Systems Research and Development Service (SRDS) requested theNational Aviation Facilities Experimental Center 'NAFEC,)to develop a feasible method for controlling f] isher intensityof condenser discharge lights in order to eliminate distract-ing glare during the hours of darkness. This was in responseto several complaints concerning flasher glare from the RunwayAlignment Indicator Lights (RAIL) portion of the MALSR thatresulted in delays in commissioning several new MALSRinstallations.

The MALSR system (Figure 1) design limited tne MediumIntensity Approach Light (MALS) to two intenstcies, 100percent and 10 percent,and the RAIL to one intensity, 100 per-cent at all times. This combination of intensities made theflashers overly bright dnd unsuitable for night VFR operationsand the system was not compatible with the brightness stepsof the runway lights. NAFEC was requested to design and modifythe flashers with three-step intensity control in order thatthe MALSR with three-step brightness control could operatewith intensity levels comparable with those of the runway lights.In addition, NAFFC was requested to design and test a circuitfor achieving manual and automatic control of the three-stepintensity controlled MALSR from the runway edge light circuit.

Previous project work in Fina. Report NA-69-7 (RD-69-8),"Test and Evaluate RAIL for Approach Guidance," Project Nc.430-209-03X, investigated flasher glare reduction using glareshields and voltage control. Those methods were unsatisfactoryand in this effort intensity control was accomplished by varyingthe value of the flash discharge capacitor.

1

DISCUSSION

Equipment Description'

Intensity Control Modification: Experiments with inten-sity control were made inhouse with condenser dischargelight (flasher) units using the relationship between flashtubeenergy (power), capacitance, and voltage in the equation

w -c2W =CV

where W = Watt/seconds W/sC = capacitance in Microfarads (uF)V = Voltage in Kilo Volts (kV)

Intensity control was obtained by changing the values of C inthe equation which corresponds to Cl, the flashtube capacitor,shown in Figure 2 6f the simplified flasher circuit. Previoustests with intensity control conducted under Project 430-209-03Xattempted to change flasher intensity by varying the supplyvoltage across the flashtube., This method was unsatisfactoryas the limited range of intensity changes which resultedbefore flasher un~tability occurred could not be detected bythe eye. In the simplified circuit shown in i'igure 3, severalvalues of capacitors were substituted for Cl which resulted inintensity changes of 99 percent. The values of capacitorstested, their intensity distribution, and other photometricdata are shown in Appendix A Figures 1-1 through 1-20. Lifetests of the flashei. unit were conducted using a 2 uF, 2,500VDC condenser in place of the 30 uF, 2,500 VDC condensernor nally used in the circuit, to determine the effects ofcapacitor changes on tube life and flasher output. The resultsof the tests after 500 hours of operation indicated that -(1) Tube life was extended past the nominal specified valueof 500 hours, (2) Flasher operation was normal and remainrdstable for the average life of the tube specified for 500 roursor 3.5 million flashes, and, (3) Flasher output remainedessentially the same during the test.

As a •esult of tie tube life tests and the breadboardintensity control tests, it was decided to modify one flasherunit for,3-st°ep brightness control. If operation proved feasi-ble, flasher units type FAA-1106 would be modified to operatein a "RAIL" as part of a MALSR system. The modification shownin Appendix A, Figure 1-21, and photographs (Figures 4 and 5)required the addition of two capacitors and three relays tothe existing circuit, the relocation of several componentsand the removel of discharge relay K103. The two capacitorsand the switching relays provided the flasher unit with intensit"outputs of i perctLat (IS' ed) and 9 percent (1,300 cd) of -theoriginal intensity, or u- iurin?, right VFR and night IFR

2

weather operations. The original effective intensity output of15,000 cd would remain unchanged and would be used for day IFRoperations. MALS intensities of 4 percent (260 cd), (step #3),20 percent (1,300 cd), (step #4), and 100 percent (65500 cd)(step #5), would be paired with intensities of 1 percent,9 percent, and 100 percent on the MALSR system.

Preliminary intensity control tests conducted withone flasher unit indicated the necessity of a switching unitto operate the flasher circuitry in proper switching sequenceto eliminate~ arcing and burning of relay contacts due to excesshigh voltage.

A control unit consisting of switch S2 and relays K4,KS, K6. and K7 snown in Appendix A, Figure 1-22, was designed tooperate the MALSR on three-step brightness control. The unitused variable time delay relays to apply pc~wer and switchintensities to the flashers in the prcper seqjuence. In theflasher circuit, before intensities can be changed, power mustbe removed from the unit and the flash-tube capacitor allowedto discharge to a safe level. Likewise, intensity selectionmust be made first before power is applied to the flasherfrom the "off" position.

'V '~Eight condenser discharge lights were modified forthree-srep brightness control for use as a "RAIL" in a 3,000foot MALSR system installed on Runway 4 for flight tests toone-half mile visibility conditions. A waiver could not beobtained on Runway 4 to conduct flight testing below 1 mile.Subsequently, after sufficient 1-mile flight test data werecollected on Runway 4, the RAIL system was relocated to Run-way 13, combined with and reconfigured with an existingapproach light system (ALS) into a 3,000 foot MALSR forflight operations to one-half mile visibility. Split inten-sity operation was used on the flashers in the 3,000 footsystem for the medium intensity setting used for night IFRoperations. Flashers at stations 16, 18, 20, and 22 hadeffective intensity outputs of 1,200 candelas (ind flashersat stations 24, 26, 28, and 30 had an effective intensityý,ttput of 4,000 candelas. A 2,400 foot MALSR for use atglide slope angles greater than 2.750, (Handbook 6850.2) wasinstalled on Runway 4 for flight operations to 1-milevisibility conditions. The RAIL system was 600 feet shorterthan the 3,000 foot system and split intensities were notused for the flashers in the medium intensity setting. Out-side of that, the 2,400 foot intensity controlled system wasidentical to the 3,000 foot intensity controlled systcda.

3

Voitage Sensing Circuit: A voltage sensing circuitconsisting of a 6.6/6.6 ampere, 100-watt current isolatingtransformer, a variac, a stepdown transformer and a three-channel solid state logic circuit (Figures 6 and 7) wasdesigned to operate the three-step intensity controlled MALSRusing current changes in the runway lighting circuit.

Control of the MALSR was exercised from the controltower in the "automatic" mode of operation by changing theintensity setting of the Runway 4 detented brightness poten-tiometer from step 1 through step 5. In the "manual" mode,MALSR operation was controlled from the remote station,Building T-4 (Appendix A, Figure 1-22).

The logic circuit consisted of three solid stateswItching channels, whose function was to select and controlMALSR intensity levels from changing voltage levels fed in•f.om the series runway lighting circuit. Logic channel A,the low intensity channel, controlled relay X from a nominalcurrent reading of 3.4 amperes corresponding to a 4V to 7Vsignal input. Logic channel B and relay Y, the medium inten-sity channel, controlled MALSR operation front a nominalcurrent reading of 4.1 amperes corresponding to a 7V to 10Vinput signal. Logic channel C and relay Z, the high inten-sity channel, controlled MAMSR operation from currentreadings of 5.2 amperes or a 10V to 13V input signal.Protective circuitry was included to insure operation on onlyone MALSR intensity channel at d time. After the sensing cir-cuit was installed, erratic operation of the MALSR was experi-enced, due to misadjustment of the runway current regulatorand excessive "play" in the brightness detented potentiometercaused by worn detents in the switch section. This conditionwas remedied by replacing the detented brightness potentiometerand by adjusting the current regulator for normal operation,according to the specifications listed in Advisory CircularAC 150/5345-lOB, April 8, 1968.

The operation of the MIALSR from the control tower,using the voltage sensing circuit, was successfully demonstratedto SRDS and NAFEC personnel during night VFR operation.

Flight Tests: Flight evaluation tests consisting of66 approaches by 18 pilot subjects, using a wide variety ofaircraft from Aerocommander to Convair 880, were conductedduring day/night VIR/IFR visibility conditions. The purposeof the flight tests was to determine whether adequate guid-ance and identification was provided by the MALSR when it wasoperated at intensity levels preselected for compatibility withintensity levels of the runway lights for existing visibilityconditions.

4

Two intensity controlled MALSR systems were flighttested. A 3,000 foot system on Runway 13 (located initiallyon Runway 4) and a 2,400 foot system on Runway 4. Approachesto Runway 13 used ILS for operations down to 1/2 mile visibil-ities: to Runway 4, VOR/DME was used for flight operations to1 mile visibility conlitions. MALSR and runway light inten-sities were operated in accordance with preselected valueslisted in Table 1. The high intensity settings were used forday IFR operations, the medium intensity settings were usej fornight IFR, and the lcw intensity settings for night VFR opera-tions. Flight test data were provided from pilot questionnaires,(Figure 8) completed after each flight test. An analysis of.he' flight test data is located in Appendix B.

Test Results: For both day and night IFR operations, the3,000 foot and 400 foot MALSR systems provided a satisfactoryintensity balance with the runway edge lights and the intensi-ties were considered adequate for the operations conducted.With the exception of height guidance (which is generally con-sidered poor for any approach light system) the systemsadequately identified the approach zone and enabled the pilotsto maneuver as required to accomplish a successful instrument-to-visual transition and landing. The condenser discharge andsteady burning lighting were considered to be very importantand useful in the operations conducted.

For night VFR operations, the intensity levels ofboth systems were adequate and a satisfactory intensity bal-ance was obtained with the runway edge lights. Whereas, thesystems were considered very important to IFR operations,pilots rated the systems ds 'nice to have" in VFR conditions.

Whcn operating in visibility conditions below 1/2 mile(1/4 mile) the condenser discharge lights were visible for severalseconds ahead of the steady burning lights. During one approach,this resulted in a pilot un~atentionally banking the aircraftaway from the approach light 3ystem: indicating a lack of rollguidance for sustained flight with the condenser discharge lightsonly.

5.

CONCLUSIONS

Based on the results of the flight test evaluations andoperational tests, it is concluded that:

1. Both the long (3,000 foot) and short (2,400 foot) MALSRsystems will serve adequately in VFR weather conditions andin IFR weather conditions down to 1/2 mile visibility.

2. The long system will support operations on the lowerILS angles and the short system will support operations onthe higher ILS angles.

3. The "flashers" as developed with three intensity con-trols can be configured, if required by unusually bright ordark environments, to prevent glare at night, or increaseeffectiveness at night, by making adjustments in either orboth VFR or IFR settings used in the trIals at NAFEC.

4. A voltage sensing circuit in the runway edge lightsystem will provide satisfactory operations of the approachlight system.

6

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SOLID STATESWITCHES

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FIGURE 6 BLOCK DIAGRAM, LOGIC CIRCUIT

12

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13

QUESTIONNARIE

PROJECT NO. 071-312-01X

Rny. 4 or Rny. 13

PILOT AIRCRAFT DATE

WEATHER TIME

1. Did you request an intensity different than that programmedin the test plan for the-

Yes No

Runway edge lights.,Approach (steadyburning) lights?Strobe (flasher) lights?

2. If intensity changes were requested as indicated inquestion 1, did the change result in an improvement?Yes , no . If the answer is yes, please explainwhat was chang-e- and what improvement was obtained.

3. Was the guidance given by the combined system adequate for:

Yes No

a. Approach zone identification?b. Directional information?c. Roll Guidance?d. Height Guidance?

4. How would you rate the usefulness of the strobe (flasher)lights.

a. Nice to have.b. Unnecessaryc. Very important.

5. How would you rate the usefulness of the steady-burninglights?

a. Nice to have.b. Unnecessary.c. Very important

6. Did the system adequately support your operation in theweather conditions experienced? Yes _ No

7. Please provide additional comments on reverse side.

FIGURE 8. - PILOT QUESTIONNAIRE

14

IVI TABLE 1 MALSR AND RUNWAY EDGE LIGHT INTENSITTTES

RUNWAY EDGE LIGHTS 3000 ft MALSR 2400 ft MALSR

MALS RAILS MALS' RAILS'

STEP 5 STEP 5 (HIGH) HIGH STEP 5 HIGH HIGH

19000 CANDLES (cd) 6500 cd 15000 cd 6500 cd 15000 cd

MEDIUMSTEP 3 STEP 4 STEP 4 MEDIUM4000 cd &760 cd 1300 cd 1300 cd 4000 cd1200 cd

STEP 2 STEP 3 LOW STEP 3 LOW152 cd 260 cd 130 cd 260 cd 130 cd

15

APPENDIX A-

PHOTOMETRIC TESTS AND' DR.AWING MODIFICATION

p I

1-1

FIGURE 1-1 FLASH TUBE LIFE TEST (ZERO HOURS) %0o.

TIME

FIGURE 1-2 FLASH TUBE I IF T[ ST (95 HflKi j-

1-3

FIGURE 1-3 FLASH TUBE LIFE TEST (200 HOURS)

1-4

-II

FIGURE 1-5 FLASH TUBE LIFE TEST (425 HOURS)

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NOTES:

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-I

APPENDIX B

SUMMARY OF PILOT QUESTIONNAIRE DATA

2-1

SUMMARY OF PILOT QUESTIONNAIRE DATA, PROJECT 071-312-0IX,"Flight Test of MALS/RAILS With Intensity Control"

BACKGROUND

The Medium Intensity Approach Lightii.g System (MALS) and theRunway Alignment Indicator Lights (RAILS) were developed as potentialvisual guidance systems for runways lacking a full approach lightsystem (ALS). MALS is 1, 400 feet long and contains steady burninglights patterned after those of the full ALS. The RAIL system consistsof sequence flashing lights (strobes) beginning at the end of MALS andextending out an additional 1, 000 feet or an additional 1, 600 feet, toconstitute either a 2, 400-foot or a 3, 000-foot total system. RAILSused with MALS in this configuration is labeled MALS/RAILS or simplyMALSR.

Condenser discharge elements in earlier ALS's have generallyhad only a maximum setting. If found to be too bright, they could beturned off, but not turned down to a lower intensity, as could the varioussteady burning elements. A principal feature of this test was provisionof intensity steps on the strobes as well as on the steady burning elementsof ALS and runway lights. Further, an attempt was made to establishintensity steps for each lighting element that would be compatible withthe general illumination conditions of day versus night and VFR minimumsversus IFR conditions.

After the tests had been completed in part, and considerable evidencehad been accumulated at a 3, 000-foot-long MALSR, it wasdecided to test a 2, 400-foot-long system. Due to failure to obtain awaiver of landing minimums on runway 4, where it was desired but not

allowed to conduct VOR approaches down to 1/2-mile visibility, a portionof the flights was switched to runway 13 where ILS approaches could bemade. The result of these arrangements was tnat flights were conductedon two lengths of system, one length being duplicated by VOR approachesto one runway and ILS approaches to another, by day and night, and atnight under low visibility conditions (IFR) and longer visibilities. Table 2-1summarizes the experimental conditions.

There are two principal questions for analysis. First, did the pilotsfind the 3, 000-foot and the 2, 400-foot-long systems to provide adequateguidance under the various conditions of visibility? Second, were thepreselected intensity steps on lighting elements satisfactory? Since it is

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considered that the differences between the two 3, 000-foot-longsystems were not great enough from the pilot's eye position to mattex,and that the differences in instrument procedures should not detractmaterially from the meaningfulness of the questionnaire data, it wasdecided to pool the results on the two longer systems. This producedthe d'stribution of questionnaires shown in Table 2-2.

TABLE 2-1. - NUMBER OF QUESTIONNAIRES RECEIVEDUNDER EACH CONDITION

Length of System2,400 Feet 3,000 Feet

RW 4 RW 4 RW 13

Day IFR 11 7 7

IFR 9 0 9Night

VFR 16 15 2

TABLE 2.2. - NUMBER OF QUESTIONNAIRES BYLENGTH OF SYSTEM

Length of System2,400 Feet 3,000 Feet

Day IFR 11 14

IFR 9 9Night

VFR 16 17

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RESULTS

Day IFR

3, 000-Foot-Long System: In day IFR conditions, 14 series of

approaches were conducted by 12 different pilots in the Aero Commander,Gulfstream, and Convair 580 aircraft. On the four different days areasonably wide variety of daytime reduced visibility conditions wasexperienced, ceiling varying from 200 feet, with 1/2-mile visibility,to 700 feet and I miles. This insured that the preselected intensitysettings, which were step 5 for the MALS, step 5 for the runway edgelights, and step 3 for the RAILS, would be tested against a variety ofday IFR ambient brightnesses.

Since a primary focus of the test was the suitability of the pre-selected intensity steps, the first question asked "Did you request anintensity different than that programmed... for the runway edge lights ?Approach (steady burning) lights? Strobe lights?" In all 14 responsesfrom the 12 pilots the answers were no. Hence, the actual behavior ofthe pilots gave no grounds to believe that the intensity steps were foundto be grossly out of line. The second question was a follow-up to thefirst, asking whether intensity changes requested resulted in improvement.Since none of the runs had produced requests for changes, this query wasvoid.

The third item asked "Was the guidance given by the combinedsystem adequate for: a. Approach zone identification? b. Directionalinformation? c. Poll guidance? d. Height guidance?" If an approachlight system does anything at all, it must identify the approach zone andgive directional information. The 3, 000-foot-long systems under testreceived a near unanimous vote on these counts (14-0 sayi -,,g guidancewas adequate for approach zone identification and 13-1 approving theguidance for directional information). Roll guidance was conditionallyapproved, by a 10 yes, 2 no, 2 unsure division. Ten out of 12 answeringbarely meets the . 05 critierion in the binomial probability table. On thefinal item there was an even division, 6 approving height guidance, 6saying no, and 2 saying there was some limited height guidance present.Height guidance from visual signals other than a VASI or other specialapproach slope device is known to be a major problem in low visibility.Hence, it is not surprising that the pilots did not give a positive approvalto the 3, 000-loot economy system :v•r this feature which is not generallyapproved in other tests conducted without a VASI.

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Question 4 asked "How would you rate the usefulness of thestrobe lights?" After 12 series of runs, the pilot replied that thestrobe lights were "very important. " After the remaining two series,the p.;lots stated that the strobes were "nice to have. " In no case didthe -pilot select the alternative, "unnecessaly." Thus, the pilots gavea high rating to tile value of strobe lights in the abbreviated system.

The last of the multichoice questions repeated the same threealternatives (nice to have, unnecessary, very important) in asking"How would you rate the usefulness of the steady burning lights?" Asmight be expected, the results were similar to the previous questionon strobes, with 11 runs resulting in a rating of "very important" andthe balance going into the "nice to have" category. An approach lightor runway alignment light system would oe nothing at all without eithersteady burning or strobe lights. Both have been found to contribute inpast tests, and this result is not changed when using an economysystem.

The sixth question asked the overall evaluation, "Did the systemadequately support your operation in the weather conditions experienced.There were 12 affirmative responses, 1 negative, and a single equivo-cation in which the pilot marked yes and no. This last answer, whichcame from a series of runs with 200-300 feet ceiling and visibilityof 1-4 miles, was amplified by the comment that "clouds were below theminimum altitude, obscuring the lights from view. However, on the lastapproach, ceiling raised to a point where the approach light system wasvery helpful.... " With this comment we may take the answer to mean

that the system was approved when there was sufficient ceiling. Obviously,lights must be seen to be used, and the clouds may be so low that thepilot cannot get visual guidance information as soon as he wants it andneeds it.

Other comments made on the day IFR runs were, by the pilotsflying under best visibility conditions, "would like to see with (more)weather," and by those experiencing the lowest cloud deck, "due to lowceiling and good visibility, not a real good evaluation. " A pilot who flewunder minimum conditions commented, "(with) ceiling 200 feet... withfog, this shortened system appeared too skimpy for a safe operation.All runs were on the centerline and glideslope; had both been significantlydisplaced a missed approach could have resulted. " This contributionreminds us that the worst conditions benefit from a full guidance systeni.

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Not that it is needed to complete a landing when the aircraft is in thegroove all the way, but that flying raw information, or with a less thanCategory II ILS, wind displacements, or other conditions that forcethe pilot to hunt foi his approach path, even a full length, full strengthvisual system is not too much.

Results using the 3, 000-foot-long reduced element systemfor day IFR, then, were that the pilots stayed with the preset intensitysteps, found guidance adequate except for height guidance, a known

deficiency of approach and runway light systems, and, overall, foundthe test system to support approaches.

2, 400-Foot-Long System: In day IFR conditions II questionnaireswere produced. As with the longer system, no intensity changes wererequested by the pilots, and again that result made the second questicnnot applicable. The third question produced data similar to that obtainedwith the longer system. Votes were 11 to 0 saying that approach zoneidentification and directional information were given adequately by thecombined system. Roll guidance was approved 10 to 1 with one voting"fair" and, again, height guidance received the poorer endorsement,8 yeses, 2 nos, and 1 fair.

Ratings of the usefulness of the strobe lights came out 10 "veryimportant" and 1 "nice to have. " One pilot specified very important"applicable to precision minima, " and nice to have " applicable to non-precision minima." This would seem to imply that the strobes are veryimportant for IFR when that broad label is extended to its fulldimensions. Steady burning lights were rated "very important" by the

same 10 votes versus 1 "nice to have."

The key sixth question, "Did the system adequately supportyour operation... ?" received a 10 yes and 1 no vote. The negative camewith a 200-foot overcast and fog condition. The pilot commented "weatherwas little too low to evaluate runway 4," which is interpreted to mean

that the VOR approach procedure and shortened, economy, visual-guidancesystem left him with marginal guidance overall.

Added comments were mostly complimentary to the sys tem.One pilot said "under the weather conditions.. .I coubt that a safe operationcould have becn performed without the experimental lighting system. Thestrobes were the first positively identified lights on all runs ... .

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Another pilot stated '"Although the ceiling .vas soriewhat below (minimums),landings were made possible by use of the lighting system. " Summarizingthe results of his experience, another pilot said '"Light system wasadequate... for VOR minimums.., for runway 4, but is not adequate forlower minimums. System is too short for less than I mile (visibility),unless ILS type approach accomplished.... " Both of the additionalcomments were simply favorable. One pilot said ". .. the lights wereadequate." Another wrote "Aircraft broke out at 300 feet and strobesprovided good guidance and identification. For marginal weather conditionsthis system would make a great difference in safety. "

The results for the 2, 400-foot system in day IFR are virtuallyindistinguishable from the parallel conditions with the 3, 000-footsystem. Both were accepted with the preset intensity steps. Principalelements of the MALSR were rated very important, and the system wasvoted adequate to support the operation.

Night IFR

3, 000-Foot-Long System: In night IFR conditions, 9 series ofapproaches by seven pilots were made in the Gulfstream, Convair 580,and Convair 880 aircraft. Weather was poor in all cases with ceilingreported from 100 to 300 feet and visibility from 1/2 to I mile with rainand fog.

As with day IFR flights, the pilots did not request any changesin intensity steps for the runway edge lights or the strobe lights. Unlikethe day condition, one-third of all the night IFR runs did result in arequest for a change in the steady burning light stations in the ALS.The requested changt. was from step 3, the preselected standard, tostep 2, the next dimmer ,tep. One of the three pilots who requested thechange said it was no improvement, i.e. , "Lights were adequate but(were) more effective on step 3 for this visibility." Hence, only twopilots requested a reduction in steady burning light intensity and thenjudged the reduction beneficial. One of the two commented that, "Appro•.,lights at step 2 seemed to be about the same intentsity as runway lights.

Ratings of the guidance given by the combined sys:.em werepositive in all cases with the single exception of adequacy of heightguidance, where a single pilot rated guidance not adequate.

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Night IFR produced nearly duplicate results, compared to dayIFR, with respect to tht. rating of usefulness of strobe lights and steadyburning lights. The combined questions produced 16 ratings of "veryimportant" vers'us only 2 of "nice to have. No pilot rated either

central element "unnecessary."

The general question produced a positive vote, 9 to 0, that thesystem adequately supported the operation.

Appended comments were strongly favorable to the system,with one exception, that still is not really unfavorable. That comment,

stated that the pilot had to stay on instruments because of the low ceiling(200 feet), but went on to say 11... the copilot observing out the frontfound the entire system adequate." The other comments were: "Almostas effective under 300 feet/i /2-mile conditions as the full system, "1

"very favorably impressed with system under these conditions, "1 andfinally, "most acceptable."

Night IFR weather, then, confirmed the adequacy of the 3, 000-foot-long economy system. All lights were turned down from the daysteps, of course, edge lights going from step 5 to step 3, MALS fromstep 5 to step 4, and RAILS from step 3 to step 2. These settingsappeared adequate.

2, 400-Foot-Long System: Additional night IFR flights on theshorter system resulted in nine more questionnaires. Generally, theweather was improved by comparison to the night IFR approaches torunway 13, the ceiling being as low as 300 feet, but visibility rangingupward from 1 1/2 mile in rain.

A number of changes in intensity were requested. One groupof pilots began their approaches under what appeared to be VFR conditions,with the systems set at night VFR settings. Weather conditions deteriorated,and subsequently the flight was reclassified as IFR. The first of thesepilots asked that all three elements, runway edge lights, steady burninglights, and strobes be reset to the night IFR settings and found the changesresulted in improvement. Particularly it was mentioned that a highersetting made the strobes more prominent and more effective. Threeother pilots who flew that evening requested a total of four changes amongthem, and in each case they reported improved guidance with the greaterintensities. Comments included the point that, initially, at night VFR

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settings, the steady burning lights could be seen long before the strobeswere picked up. At the next higher setting, which was the regular IFRsetting, the str6bes were seen at the same range as the MALS.

This set of nine questionnaires generally went along with theformer set in rating the guidance of the combined system adequate.The divisions were 9-0 on approach zone identification, and 8-1 on thenext two aspects, directional information and roll guidance. Heightguidance, as before, got a lower approval, 7-2.

The consensus of the pilot ratings on usefulness on the strobelights and steady burning lights was favorable. Six said strobes were"very important, "1 one said "nice to have, " and the remaining two pilots

marked "nice to have" with the added comment of "at the higher setting."The only, "unnecessary" ratings were by these same two pilots with theadded comment "at the lower setting. " This means that the highersetting was needed to give sufficient range, a point already made incomments on the first two questions. Steady burning lights were ratedvery important by seven pilots and nice to have by two.

On the general question, did the system adequately support youroperation, eight said yes and one said no. This individual commentedthat he could not see because rain on the windshield was not properlycleared., Obviously, no visual guidance system will support operationswithout reasonable visibility through the windshield. Hence, we mayconclude that night: IFR with the 2, 400-foot system was generallysatisfactory, as it had been with the 3, 000-foot system.

Night VFR

3, 000-Foot-Long System: Night VFR conditions prevailed for thecompletion of 17 questionnaires with the full length MALSR. Reportedconditions ranged from 600-foot ceiling, 2 1/2 miles visibility, rapidlyimproving, to CAVU. Only one pilot requested a change in runway edgelight intensity setting, ;and this was a special case. On the night inquestion, flights began wi'1i IFR settings, but rapidly improving weathermade the IFR settings too bright. All three systems were switched toVFR settings which "... provided an adequate and comfortable operation."Hence, this pilot actually endorsed the settings which were appropriateto the class of flight, that having Laanged after the start.

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In contrast, nine pilots requested changes in the ,teady burningsettings, and seven requested changes for the strobe lights. There issome uncertainty in one case, but all requests for changes in steady

burning elements appear to have been requests for a lower setting. Thestrobes, on the other hand, were always changed to a higher setting.The goals of the pilots were long range identification of the approachzone from the stronger strobes and compatibility of elements. Pilotslooking at lowered steady burning settings reported an improvement incompatioility, but most of those looking at increased settings on thestrobes reported that the change did not actually help.

Guidance given by the combined system was rated adequate forapproach zone identification (16-0), directional information (17-0),

roll guidance (17-0), and height guidance (13-4). Usefulness of thestrobes was rated "nice to have" on 12 questionnaires, "unnecessary"on 1, and "very imrportant" on 4. Comments included "nice to have inclear visibility (but) very important for reduced visibility, " "veryimportant... where mort surface lights are in or near the approachzone, " "(would be very important at) strange airport, " and "nice to havefor straight-in approach, very important for circling approach." Use-fulness of the stcady burning lights was rated "nice to have" by 15 and"very important" by only 2. This outcome is different from that obtainedafter IFR flights and stems, no doubt, from the facL that in VFR conditionsthe runway is in sight during the approach. This makes a steady burningapproach light system more a help than a necessity.

The comprehensive question, "did the system adequatelysupport your operation... ?" was answered yes 17 times. MALSR wasconsidered clearly adequate for VFR. Added comments were fewer inthis better weather series. A representative item was "Not reallyrequired for this perfect weather condition." Another pilot summed upby writing, "System looks good for VFR. "

2,400-Foot-Long System: Night VFR prevailed for 16 series ofapproaches to the shortened system. None of the 16 requested a changein runway edge light intensity setting, confirming the finding on thelonger system that the predetermined setting is satisfactory in nightVFR. There were three requests for a lower intensity on the steadyburning lights, but ,uch a reduction could not be made and was notevaluated on the next item. The sti'obe light intensity was, like (,lerunway edge setting, accepted by all pilots,

All 16 questionnaires showed "yes" for all four parts of thethird question, guidance being rated adequate on all counts.

Usefulness of the strobe lights was rated "nice to have" bynine; "unnecessary" by four and "very important" by only three. Use-fulness of the steady burning lights produced an even division, eightrated "nice to have" and eight rated "very important. " Alongside thenice to have marks, several pilots added "for VFR." Another twomarked nice to have but unnecessary. Our interpretation of thesewidely divided rankings is that most pilots desire strobe lights forapproach zone identification and directional information but find theseguidance factors not absolutely essential in clear weather, particularlyat a familiar airport. Similarly, steady burning lights are a plus, butnot an essential, under these favorakle conditions.

The question asking "did the system adequately support youroperation... ?" received 16 "yes" marks "i',th one pilot adding notes onthree deficiencies. He found some edge lights weak, as if dirty, somesteady burning lights poorly aimed, and strobe lights too short to bereally useful. He found that the M..LS alone gave sufficient alignmentinformation. Overall, though, this pilot said "...the system is morethaxi adequate."

Added comments in this good weather series were few. Onepilot wrote "The overall system was extremely useful for this VFRoperation. " Another suggested cutting some trees that blocked someviews. Another finished by writing "Overall the system is excellent.Two pilots reported that the overall system was somewhat brigh* inclear night conditions. A further test at a secondary airport withapproach from 10 miles at 2, 500 feet was recommended by another.His idea was that the importance of strobes would be evident whererunway identification was more difficult.

These questionnaire answers and comments indicate that the2, 400-foot-long system attained, under night VFR conditions, a degreeof pilot acceptance roughly equivalent to that of the full length MALSR.

INTERPRETATION

Pilot responses indicate that ne MALS/RAILSq combined systemwith preset intensity steps is fully adequate and provides satisfactory

? -i.I

guidance. The only weakness noted with frequency is in provision ofheight guidance, where a substantial minority of the pilots failed thesystem.

Shortening the length of the system from 3, 000 feet to 2, 400 feetdid not detract materially from its usefulness. Intensity steps forsequence flashers proved a useful feature, and the preselected intensitysteps on the various subsystems proved adequate.

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