NATIONAL BUREAU OF STANDARDS REPORT

4741

Development of Optimum Runway Lights for Jet Aircraft

Interim Report No. 1

By

C. A. Douglas

I. Nimeroff

A. N. Hill

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C., and its major field laboratories in Boulder, Colorado, is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section carries out specialized

research, development, and engineering in the field indicated by its title. A brief description of

the activities, and of the resultant reports and publications, appears on the inside back cover of

this report.

WASHINGTON, D. C.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instru- ments. Magnetic Measurements. Process Technology. Engineering Electronics. Electronic

Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenic Physics.

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Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid

State Physics. Electron Physics. Atomic Physics. Nuclear Physics. Radioactivity. X-rays.

Betatron. Nucleonic Instrumentation. Radiological Equipment. AEC Radiation Instruments.

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Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics.

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Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Mineral Products. Ceramic Engineering. Porcelain and Pottery. Glass. Refractories.

Enameled Metals. Concreting Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems.

Analogue Systems. Applications Engineering. • Office of Basic Instrumentation • Office of Weights and Measures

BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials.

Gas Liquefaction.

Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular

Propagation Services.

Radio Propagation Engineering. Frequency Utilization Research. Tropospheric Propagation

Research.

Radio Standards. High Frequency Standards Branch: High Frequency Electrical Standards.

Radio Broadcast Service. High Frequency Impedance Standards. Microwave Standards Branch:

Extreme High Frequency and Noise. Mieroyvave Frequency and Spectroscopy. Microwave

Circuit Standards.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0201-20-2331 June 1956 4741

Development of Optimum Runway Lights for Jet Aircraft

Interim Report No. 1

By

Co A 0 Douglas

I. Nimeroff

A. No Hill

Prepared for

Equipment Laboratory

Wright Air Development Center

Department of the Air Force

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprinting, or reproduction of this report in any form, either in whole or in part, is prohibited

unless permission Is obtained in wrltingfrom theOffice of theDirector, National Bureau of Standards, Washington

25, D. C. Such permission is not needed, however, by a Government agency for which a report has been specifically prepared if that agency wishes to reproduce additional copies of that particular report for its own use,
1<
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0201-20-2331 June 1956 4741

Development of Optimum Runway Lights for Jet Aircraft

Interim Report No. 1

By

C. A. Douglas

I. Nimeroff

A. N. Hill

Prepared for

Equipment Laboratory

Wright Air Development Center

Department of the Air Force

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprinting, or reproduction of this report in any form, either in whole or in part, is prohibited

unless permission Is obtained in writing from theOffice of the Director, National Bureau of Standards, Washington

25, D. C, Such permission is not needed, however, by a Government agency for which a report has been specifically prepared If that agency wishes to reproduce additional copies of that particular report for its own use,

TABLE OP CONTENTS

Page

Abstract 1

1. Objective of the Project 1

2. Scope of the Investigation 2

3. Visual Guidance Requirements of a Visual Landing- 2

Aids System

4. Results of Pilot Interviews 3

4*1 Sumnary of Pilot Interviews 4

5, Location and Identification of the Airport 6

60 Location and Identification of the Runway 9

7, Runway Identification Lights 10

7*1 Beam Spread 11

7*2 Intensity-Distribution Requirements 11

7*3 Flash Frequency 12

7*4 Specification Requirements for Runway 12

Identification Lights

8 0 Circling-Guidance Lights 13

8*1 Intensity-Distribution Requirements 13

8*2 Comparative Regions of Guidance 18

8.3 Intensity Control of Circling-Guidance 18

Lights

8*4 Procurement of Circling-Guidance Lights 20

8*5 Required Spacing of Circling-Guidance Lights 20

9. Threshold Lighting 20

9*1 Function 20

9*2 Placement 21

9.3 Required Beam Spread 21

9.4 Spacing of Lights in Threshold Bars 22

9.5 Length of Threshold Bars 22

9.6 Color of Threshold Lights 23

9.7 Unidirectional vs. Bidirectional Threshold 23

Lights

9*8 End-of-Runway Lights 23

9e 9 Recommended Threshold Lighting System 24
TABLE OF CONTENTS (coni.)

Page

10a Conclusions 24

11a Recommendations 25

Figures 1 - 8 26 - 33

Appendix Af Reports and Memoranda Forwarded to 34

Wright Air Development Center

Appendix B, Air Bases Visited During Survey of 35

Operational Requirements of Runway

Lights for Jet Aircraft

Appendix C„ Visibility and Visual Range 36

Explanation of Terms and Symbols

Allard's Law

36

37

Appendix Dt Threshold Lights 40

Explanation of Terms and Symbols 40

Derivation of Equations 40
LIST OF FIGURES

Figure Caption Page

1 Regions of Guidance,, Airfield Beacons 26

2 Circling Approach Patterns 27

3 Minimum Intensity Distribution of 28

Circling-Guidance Lights for Transmissivity of 0,3 per Mile

4 Recommended Intensity Distribution,, 29

Circling-Guidance Lights

5 Regions of Guidance of Runway Lights* 30

Transmissivity 0*9 per Mile

6 Regions of Guidance of Runway Lights 31

Transmissivity 0o l per Mile

7 Required Beam Spread of Threshold Lights 32

8 Proposed Threshold Lighting System 33

C-l Visibility Factor for Lights 39

D-l Mechanical Considerations in Determination 42

of Beam Spread of Threshold Lights

LIST OF TABLES

Page

Table 1 Recommended Minimum Effective Intensity 7

of Airfield Beacons

Table 2a Intensity Requirements of Fighter-Aircraft 14

Approach Pattern

Table 2b Intensity Requirements of Bomber-Aircraft 15

Approach Pattern

Table 3 Representative Intensities of Runway and 16

Overrun Lights

Table 4 Recommended Intensity Distribution of 17

Circling-Guidance Lights

Table C-l Reported Visibilities* D* Corresponding to 38

Transmissivities* T
. • > 4
Development of Optimum Runway Lights for Jet Aircraft

Interim Report No. 1

ABSTRACT

This report is the first of a series describing the development of runway lights for jet aircraft at the National Bureau

of Standards for the Equipment Laboratory, Wright Air Development

Center, under contract number 33 (616) -54-6.

1. OBJECTIVE OF THE PROJECT

The objective of the project as outlined in Exhibit

WCLEE5-42, dated 4 June 1953, "Study to Determine the Optimum

Runway Light Design for Jet Aircraft" was 1) the study of the

operational procedures of jet aircraft in landing and on the

ground and the effects of these procedures upon the optical and

mechanical design of the runway light; 2) the development of a suitable compromise between the conflicting optical and mechanical requirements and the recommendations of a design based upon

this analysis; 3) fabrication of sample lights conforming to

this design.

During the early phases of the project it became apparent

that the operational and intensity- distribution requirements

of runway lights could not be developed without considering

the functions and intensity distributions of the other components of the visual landing aids system. Therefore, the scope

of the project was expanded to include a study of the performance of these components with the development of the intensity

distribution requirements of all components of an integrated

system of landing aids other than approach lights. The intensity - distribution requirements of these components are based on the

following premises.

The runway lighting system and related lighting systems

should 1) furnish all the visual guidance required for circling

approaches performed under visual flight rules (VFR) with no

consideration given to the guidance supplied by the approach lights,

if any, or from extraneous lighting, from the time the airfield is

located until the aircraft has turned off the runway after completing the landing; 2) furnish the visual guidance required for

t
-2 -

straight-in approaches on runways where no approach lights are

installed; and 3) provide the visual guidance required for the

final stages of landings on runways with high-intensity approach lights.

2.

SCOPE OF THE INVESTIGATION

The development program is being conducted along the following courses %

1. Determination of the optical requirements of the

components of a runway lighting system by means of: a) pilot

interviews to determine the operational requirements of the

system,, the deficiencies of the present system,, and the acceptability of proposed modifications; b) photometric testing of

existing and prototype lights; and c) computation of the visual

range and glare zones of these lights.

2. Determination of the mechanical requirements of the

lights by interviewing maintenance personnel and inspecting

facilities to determine deficiencies in the present units,, by

computing loads imposed upon landing gear by obstructions on the

runway surface,, by testing the mechanical strength of present

and prototype lights,, and by tests of the electrical characteristics of the lights.

3. Procurement and laboratory testing of prototype lights.

4. Preparation of specifications for lights proposed for

service tests.

The four phases of the investigation are being conducted

concurrently. The results of the investigation to date have

been reported in 32 reports and memoranda (in addition to

monthly reports) which were prepared and forwarded to Wright Air

Development Center as individual tasks were completed. The

reports are listed in Appendix A s

3.

VISUAL“GUIDANCE REQUIREMENTS OF A VISUAL LANDING-AIDS SYSTEM

A satisfactory visual landing-aids system should supply the

following visual guidance during a visual approach to an airfield and during a landing*
-3~

1, During the initial penetrations

a, Location and identification of the airport,

bo Location and identification of the runway,

2, During a circling approach;

a. Distance from and direction of the runway* so that

the downwind leg Can be flown parallel to and at

the desired distance from the runway,

b. Location of and distance from the threshold and

direction of the runway during the turn from the

downwind leg to the base leg* on the base leg*

and during the turn from the base leg to the

final leg of the approach pattern,

3, On the final legs

a. Location of and distance from the threshold,

b. Location of the horizontal plane through the

threshold.

c. Location and direction of the runway axis,

d. Height above the runway or distance above or below

a preferred glide path.

4, During flareout and touchdowns

a. Height above the runway.

b. Direction of the runway.

c. “Horizon."

d. Lateral boundaries of a safe landing area,

5, During rollouts

a. Lateral boundaries of the runway surface,

b. Direction of the runway axis,

c. Location of turnoffs,

do Distance from and location of the upwind end of the

runway.

During takeoff the visual guidance required of the runway

light system is essentially the same as that required in the last

phase of the approach and in the rollout. A system meeting the

requirements for guidance during landing should also meet the requirements for guidance during takeoff.

4. RESULTS OF PILOT INTERVIEWS

In order to determine the effect of the performance character«= istics of and operating procedures with jet aircraft on the
~4~

operational requirements of runway light systems* eleven air bases

were visited where more than 80 pilots representing the organizations operating from these bases and 20 Air Installations personnel

were interviewed® The -air bases visited during the survey are

listed in Appendix B.

In general* pilots from each squadron operating jet aircraft assigned to the Air Base attended the pilot interview conference® During the conference all phases of the landing,, from

the time the airfield is sighted until the aircraft is turned off

the runway, were discussed with reference to the use of the

present visual landing aids and their deficiencies for jet aircraft operation, and to needed improvements or modifications®

The data obtained during these visits and their effect upon the

design of the components of the visuhl landing-aids system will be

discussed in detail in the sections of this report covering the

components® Detailed reports of the interviews were prepared

and sent to the sponsor immediately after each visit* I21-32T *

4.1 Summary of Pilot Interviews*

1. The pilots desire to locate and identify the airport and

the runway from as great a distance as possible. This is of

particular importance to the pilots of jet aircraft because of

the high fuel consumption at low altitudes and the lower fuel

reserve.

2* The present airport beacon is not visible at the altitudes

at which jet aircraft are operated. The pilots were unanimous in

their opinion and emphatic in their statement that the present

beacon is inadequate.

3. Bfcny pilots considered an approach light system which

provides adequate guidance during the approach more important

than an improved runway light system.

4. The type C»1 high- Intensity runway lights are considered

satisfactory for straight-in approaches, rollout and takeoff.

5. The present runway light systems, both mediumTM and highintensity, are not sufficiently visible from positions off the

runway axis when they are operated at the clear- weather brightness settings.

Figures in brackets indicate references to the detailed reports

listed in Appendix A.
6. The pilots desire a more positive means of identifying

the runway lights as a runway lighting system,,

7. Pilots sometimes lose the runway lights when turning on

to the downwind or base legs of the approach pattern,

8 0 The downwind corner of the runway should be well marked

and identified, as the start of the turn onto the base leg is

determined by the position of that corner,

9.

Many pilots consider the present system of threshold

lights inadequate,

10. At some bases the pilots were well satisfied with the

way the intensity of the lights was controlled. At others,, they

complained that the lights were always too bright. In particular,

pilots did not want to have the glare increased on the final leg

of the approach pattern in order to obtain better guidance on the

other legs.

11. Few pilots were concerned with loss of dark adaptation

on takeoff.

12. Gaps in the runway lighting system caused by intersections

are not considered serious except in the touchdown area. There

was definite opposition to having lights that project above the

runway surface in the intersections.

13. Turnoffs from the runway are inadequately marked, particularly where there are no taxiway lights.

14c The majority of the pilots either favor or have no objection to using red lights to mark the upwind end of the runway,

15. In very low visibility landings the pilots are more concerned with finding and seeing the runway (or approach) lights

than they are with the adverse effects of glare from the lights.

16. The only unusual type of damage to runway- light units

that could be attributed to the operation of jet aircraft was

that to the cone-mounted M~1 units.

17.

Some means of lighting the arresting barrier at the

upwind end of the runway is considered desirable.
I3o The pilots have very little depth perception at night

when flaring out over a black-top runway without runway markings*

The runway lights alone do not provide adequate depth perception*

19* Rain or snow on the center panel of the canopy of

fighters causes so much distortion that under these conditions

the pilot obtains guidance only from the lights he sees through

the sides of the canopy* Thus* lights located across the

threshold or the upwind end of the runway are of little value in

judging distance from these points* Distance marking is* therefore,, considered essential and some elevation guidance* preferably

in the approach-light system* is desirable* Threshold lights

should extend outboard of the runway lights*

20* Lack of uniformity in the lighting systems from airfield

to airfield results in unnecessary confusion*

5o LOCATION AND IDENTIFICATION OF THE AIRPORT

The location and identification of the airport is properly

the function of the airport beacon and not of the runway lighting

system* However* in the design of a runway lighting system* the

visual guidance supplied-by visual aids other then the runway

lights must be considered* The pilots interviewed were unanimous

in their statement that the vertical coverage of the present airport beacon (Specification MIL-L-5630) is inadequate for the

operation of jet aircraft* When the aircraft is above an altitude

of 200 000 feet during VFR conditions* the airport is located not

by means of the beacon* but by extraneous lighting on the field

or in surrounding areas when the pilot is familiar with the location of these lights* or by radio aids* To be useful* the beacon

should be visible and identifiable from a distance of 30 miles

at altitudes of 20,000 to 30*000 feet when the visibility is M un°

restricted**9 and from the range station from altitudes of 3000 to

5000 feet when the visibility is somewhat restricted*

When the beacon could be seen* the flash coding of the present

beacon was considered adequate*

Since it is impracticable to design runway lights having the

intensity distribution necessary to cover the region in which the

beacon should be visible, and since the design of an efficient

runway lighting system presupposes a knowledge of the location of

the airport, consideration wa&»given to the intensity distribution

requirements for the beacon*
-7-

In computing the required intensity distribution, an atmospheric transmissivity^ Tt of 0.9 per mile was taken as the minimum

transmissivity for "clear" weather* The visibility of a 25-

candle light is approximately 10 miles with this transmissivity.

Similarly, a transmissivity of 0,3 per mile was taken as the

minimum transmissivity for approaches under Visual Flight Rules*

The visibility of a 25-candle light corresponding to this transmissivity is 3 miles, (See Appendix C for definitions of

terms and a discussion of the laws pertaining to visibility.)

The proposed regions of guidance of the beacon for the two

visibility conditions are shown in figure 1« For clear weather

the region of guidance is defined by lines joining the points

sL, h, and Point & is 30 miles from the beacon at an altitude

of 30,000 feet; k is directly above the beacon at an altitude of

10.000 feet; and £. is 30 miles from the beacon at an altitude of

5.000 feet. For restricted visibility, a is 5 miles from the

beacon at an altitude of 5,000 feet; h is directly over the beacon

at an altitude of 3C 000 feet; and & is 5 miles from the beacon at

an altitude of 3,000 feet.

The effective intensities, Ie , required for a light at

point 0 to be seen from selected positions on the boundaries of

the regions of guidance were then computed using the selected

transmissivities. The angles of elevation, 0, of each of the

selected positions were also computed. From the results of these

computations recommended minimum effective intensities were developed and are listed in table I.

Table I. Recommended Minimum Effective Intensity

of Airfield Beacons

Minimum Effective Intensity

Elevation Angle White Green

(Degrees) (Candles) (Candles)

0 to 2 7, 500 1,100

2 to 12 50,000 7, 500

12 to 15 7,500 1,100

15 to 20 lp 000 150

20 to 30 500 75

30 to 60 200 30

60 to 90 100 15

As the exact location of the airport beacon is given by the

white flashes, the minimum effective intensity of the green
flashes can be as low as 15% of that of the white flashes.

The regions of guidance determined from these specified

intensities are shown in figure 1* In addition* the region of

guidance expected of the minimum beacon meeting the specification is shown. For comparison the regions of guidance of the

present beacon, computed from intensity- distribution measurements made at the Equipment Laboratory* are included.

Consideration was given to the flash cycle of the airport

beacon. The flash characteristics of the present beacon are

considered unsatisfactory since the flash characteristic varies

with the angle of elevation from which the beacon is observed

and the transmittance of the light path between the beacon and

the observer. When the angle of elevation fts 10 degrees or more,

the separation of the two white beams is so small that these

beams will appear as a single flash. At lower angles of view

when the threshold intensity is less than the intensity between

the two white beams, the white signal will appear to be a single

flash with two peaks® When the threshold intensity is greater

than the intensity between the two peaks, the signal will be

two separate flashes. In addition, because of the higher

speeds of modern aircraft, it is desirable to decrease the interval between the white and the green flashes. Therefore,

increasing the interval between the white flashes to at least

two-tenths, and preferably to one-third, of the flash cycle

appears desirable. Consideration should also be given to decreasing the period of the flash cycle from 10 seconds to 5

seconds. This change would, however, decrease the effective

intensity of the flashes*

Note that the intensity- distribution requirements of the

beacon are given in terms of effective intensity. When a light

signal consists of separate flashes, the instantaneous intensity

during the flashes must be greater than the intensity of a steady

light in order to obtain threshold visibility. The effective

intensity of a flashing light is defined as the intensity of a steady light which will produce the same visual effect as does

the flashing light. Effective intensity is computed from the

* Photometric Curves, Numbers 1198A to F, of Lighting Section,

Equipment Laboratory, Wright Air Development Center.
-9-

equation developed by Blondel and Rey, *

0,2 + t2 - tj

(1)

where Ie is the effective intensity, I is the instantaneous

intensity, and ti and are the times of the beginning and end

of the flash. Trie times, and ^ are chosen so that the

value obtained for Ie is a maximum* Methods of easily deter^

raining these limits were developed in NBS Report No, 4554. ^

The effective intensity of the white and green flashes of the

present beacon is about 25% of the peak intensity of these

flashes.

6. LOCATION Am IDENTIFICATION OF THE RUNWAY

One of the problems reported in the pilot interviews was

that of locating and identifying the runway at night. The

farther out the runway is located and identified, the more

easily the pilot can plan the approach. The pilots, naturally,

desire to see the runway lights from as far out as possible and

from all directions. The minimum acceptable visual range for

VFR approaches is five miles, and the maximum visual range

required was considered to be ten miles. The aircraft is generally less than 5000 feet above the ground during the period

when the runway lights are used for guidance.

The difficulties are twofold. The off-runway intensity of

the present high-intensity runway lights is sufficient (about

1500 candles) to provide the desired visual range in clear

weather when the light system is operated with an intensity step

5 corresponding to an intensity setting of 100%. The off-runway

intensity of the medium^! nfcensity runway lights under these

conditions is marginal, about 400 candles. The off-runway intensity of both types of lights is much too low to provide the

desired visual range when the lights are operated on intensity

steps 1 or 2. These steps give intensities of 0,2% or 1% when a type C-3 regulator is used and 1% or 3% when a type C-2 regulator

is used. Thus in clear weather, if the intensity setting of the

* A 0 Blondel and J, Rey, Journal de Physique 1* 530 and 643 (1911).
•“ 10*

light system is adjusted so that the runway lights will not be

glaring during the flareout and touchdown* the intensity in the

off-runway directions will be only a few candles,

A pilot familiar with a field is often able to obtain sufficient guidance from such extraneous lighting as ramp lights*

security lights*, etc. e which have a much higher intensity than

the off-runway intensity of runway lights operated on a lowintensity step, These lights furnish little guidance to a pilot approaching a strange field*

The second difficulty is that of identifying the runway lights

as runway lights once they are seen. When the lights are operated

on intensity steps 4 or 5 (25% or 100% relative intensity) the intensity of the main beams of the runway light is so much greater

than the intensity of the extraneous lights that the runway lights

are conspicuous to aircraft near the extended centerline of the

runway* When the system is operated on steps 1 or 2 this is not

the case f and runway lights are often confused with street lights

even when the aircraft is within the main beams of the lights®

These difficulties can be solved in a direct manner: a) install lights that will have sufficient intensity in the off-runway

directions when the runway light system is operated on intensity

steps 1 and 2 ; and b) install lights at the ends of the rows of

runway lights that by means of their coding will identify the

runway lights.

7, RUNWAY IDENTIFICATION LIGHTS

There are several possible methods of coding the runway

identification lights so that they can be distinguished from the

extraneous lights and will identify the runway lights: visibility

of the scattered light from a vertical beam, color, intensity*

and flash characteristics. The use of high-intensity vertical

beams was rejected because the visual range of such beams is not

sufficient under twilight conditions and under many nighttime

conditions. The visual range of the beam of the ceilometer projector is typical of projectors of this type. The ceilometer at

Washington National Airport is about 7 miles from the National

Bureau of Standards grounds. Its beam has never been seen during

night tests from the roof of the East Building of the Bureau although many of these tests required observation of lights of the

airport and surrounding area.
- 11 -

The use of color alone or intensity alone as a means of

identification would require more power than is considered desirable, Several lights with 180-degree horizontal coverage and

extended vertical coverage would be required, and the intensity

of these lights would have to be at least ten times the intensity

of the surrounding extraneous lights. The use of flashing lights

appears to be the most practical solution. It can be shown by

means of Blondel and Rey's law that, for a given power input and

lamp efficiency, the effective intensity of a rotating beacon

will be about a hundred times that of a fixed light having

360° horizontal coverage, Langmuir and Westendorp* found that

extraneous lights near a flashing light had a surprisingly little

effect on the time required to find the flashing light even

though the intensities of these lights were many times the effective intensities of the flashing light. Therefore, obtaining

suitable intensities in a rotating beacon-type identification

light is relatively easy.

7.1 Beam Spread,

The vertical beam spread of the runway identification lights

should be sufficiently great that an aircraft at an elevation of

2000 feet and 10 miles from the runway and an aircraft at an elevation of 5000 feet and 5 miles from the runway will be within

the beam of the light. Thus the beam should extend vertically

from 2° to 10°,

7.2 Intensity-Distribution Requirements.

The choice of effective intensity of this beam is somewhat

arbitrary. An effective intensity of 250 candles is sufficient

to produce an illuminance of 1 mile candle at a distance equal to

the reported visibility. This is, however, considered insufficient

since these lights should be conspicuous at this distance. Field

observations of steady lights indicate that an illuminance of

about 20 mile candles is the optimum illuminance,** To obtain this

illuminance an effective intensity of 5000 candles is required.

* Langmuir, and Westendorp, Physics JL, 273 (1931). ** F, C. Breckenridge and C„ A, Douglas, 111. Eng. 4Q, 785 (1945).
12

This intensity will also provide a visual range about 1*5 times

the visibility. The intensity toward the runway should be sufficiently low that these lights will not be glaring to pilots of

aircraft on the final leg of the approach pattern. A maximum

intensity of 100 candles toward the runway* that specified for

the type C-l runway lights, is considered suitable. Since the

sources in these units will not be point sources, even with

mechanical shielding an appreciable region is required for the

transition between an intensity of more than 5000 candles to one

of less than 100 candles. With PAR 56-type lamps this transition

will require about 20° of azimuths

Since the distance the runway identification lights should

be visible is not constant but is proportional to the visibility,

the lights should be operated at constant intensity and not adjusted for the visibility. No adverse effects of glare are

expected from this procedure* The National Bureau of Standards

Field Laboratory at Areata, California, has operated flashing

lights located 1000 feet from the threshold on the extended runway centerline with an effective intensity of about 15,000

candles with no complaints of glare*

7*3 Flash Frequency*

Tests of the flashing rates for aircraft position and anticollision lights indicate that the flash frequency of these

lights should be at least 40 flashes per minute* Flight observations of an experimental runway identification lighting system

made at the Technical Development and Evaluation Center, Indianapolis, indicate that 40 flashes per minute is the minimum flash

rate which should be used for runway identification lights*

7*4 Specification Requirements for Runway Identification Lights*

The use of flashing lights to identify the runway lights is

recommended. These lights should be installed at the four corners

of the runway, outboard of the threshold lights. Thus they will

not only identify the runway lights but will also mark the ends

of the runway, a feature pilot interviews showed desirable*

Synchronizing the lights so that they appear to flash simultaneously seems desirable* The runway identification lights should

meet the following general requirements*

a. The lights shall be designed so that they will operate

from a 6,6-ampere series runway-light circuit*

b* The change in intensity shall be as small as feasible as the intensity setting of the runway lights is changed from step 1

to step 5®
13-

c* The flash frequency shall be at least 40 flashes per minute and preferably higher*

d* The effective intensity of the light should be at least

5000 candles for all angles of elevation between 2° and 10° for all

azimuth angles greater than 10° outboard of the runway axis*

e* The effective intensity for all azimuth angles greater than

10° inboard of the runway axis shall not exceed 100 candles*

A specification based on these requirements has been developed

in cooperation with the Lighting Section, Equipment Laboratory,

Wright Air Development Center, and has been issued as Exhibit WCLEE5-

68A, dated 18 October 1955e In order to obtain runway identification

lights for service testing, bids have been requested twice for lights

conforming to this exhibit, but no satisfactory bid has been received*

Therefore the National Bureau of Standards Shops are now preparing

preliminary design drawings and an estimate of the cost of producing

lights for service test*

8* CIRCLING-GUIDANCE LIGHTS

In addition to the runway identification lights, lights are

required which outline the runway in sufficient detail so that the

pilot can plan and execute his approach pattern. The pilot interviews

indicated that the present runway lights are inadequate for this purpose*

8,1 Intensity-Distribution Requirements*

The intensity-distribution requirements for circling-guidanee

lights which will provide adequate guidance during circling approaches

of both bomber and fighter aircraft were determined as follows. The approach patterns used by various types of aircraft were determined from

data given in technical orders and from statements obtained during the

pilot interviews. Selected points in the approach paths were described

in terms of altitude, a, pitchout radius, r, and position, p. These

points, I to VIII, are shown schematically on figures 2a and 2b* Elevation angles, 8, azimuth angles, 0, and lin@=of=sight distances* d,

were then computed relative to the first runway light, A* on the left

side of the runway for each of the selected points in each approach

path* The results of these computations are shown in figures 2c and 2d.

For each position the elevation angle relative to the first light is

given*

The minimum intensity required to produce visual ranges equal to

the maximum distance between the light at A and the selected points in

the approach paths was computed for several transmissivities, assuming

a pilot threshold of 1 mile candle. These intensities are listed in

tables 2a and 2b*
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-16~

Intensity-distribution diagrams can be obtained from the intensities given in tables 2a and 2b« For example, figure 3 is a polar

plot of the intensities required for both the bomber and the fighter

approach patterns when the atmospheric transmissivity is 0*3 per

mile (visibility 3 miles)*

Note that, except for the initial approach, the intensities

required for the fighter-aircraft approach pattern are low and that

the angles of elevation at which the lights are viewed are generally

greater than 10°. Because of the short viewing distances, there is

little decrease in the intensity required on the downwind and base

legs as the visibility increases from 2 miles to 10 miles* The

present runway lights provide adequate guidance during the initial

approach when the aircraft is near the runway axis and within the

main beam of the lights* The intensity in the off-runway directions

is marginal at the required elevation angles during clear weather

when the lights are operated on the lowest intensity settings*

The intensities required for the bomber approach pattern are,

of course, greater and at lower angles of elevation on the downwind

and base legs. Over much of the pattern these intensities are of

the same order as the intensity of the main beam and much greater

than the off-axis intensity of present runway and overrun lights

operated at the settings recommended for the corresponding visibility

as indicated in table 3*

Table 3. Representative Intensities of Runway and Overrun Lights

Reported

Visibility

(miles)

Recommended

Intensity

Setting

(percent)

Representative

Main Beam

Intensity

(candles)

Representative

Off-Axis

Intensity

(candles)

C-l & C-2 M-l C-l C-2 M-l C-l €-2 M-l

Lights Light Light Light Light Light Light Light

>10 0*2 1 30 40 20 2 6 1

5-10 1 3 150 200 60 10 30 3

2-5 5 10 750 1000 200 50 150 10

1-2 25 30 3750 5000 600 250 750 30

<1 100 100 15000 20000 2000 1000 3000 100

Source of Data;

C^l Light, NBS Report 2 1 P-5/54

C-2 Light, Photometric Curves Numbers 1170A-J, 1169&-I,

Section, Equipment Laboratory, Wright Air Development

Center

M-l Light, NBS Report 21P-17/55
-17-

It is obvious that a simple redesign of the runway light to

provide the intensities required in the off-axis directions during

clear weather is not sufficient. Such a light would require about

a tenfold increase in lamp wattage. Most of this additional power

would be wasted during periods of low visibility when straight-in

approaches are used and intensity-setting steps 4 or 5 are used*

Separate lights operating at intensity settings different from

those used in the lights providing light down the runway are

necessary.

The intensity-distribution requirements for this light were

developed from the data of table 2 and figures 2 c and 2 d ff and through discussions with personnel of the Equipment Laboratory,

Wright Air Development Center, The recommended distribution is

plotted in figure 4 and tabulated in table 4,

Table 4. Recommended Intensity Distribution of

Circling-Guidance Lights

Elevation Angle

(degrees)

Azimuth Angle

(degrees)

Minimum Intensity

(candles)

2 to 8 95 - 100 1,000

260 - 265

100 - 120 5,000

240 - 260

120 - 130 1,000

230 - 240

130 - 150 800

210 - 230

150 - 210 600

0 to 2, and 8 to 12 95 - 100

260 - 265

800

100 - 120 1,000

240 - 260

120 - 150 600

210 - 240

150 - 210 400

12 to 20

20 to 60

95 - 265 200

95 - 265 100
-18

Tbp distribution was made symmetric about the 0° - 180®

line although figure 4 indicates that the intensities required in

the direction of the base leg are higher than those required i®

the upwind direction* (The differences for lights in the center

of the runway are greater than those shown in figure 4 for a light near the threshold of the runway,) This decision was based

upon the premises that circling -guidance lights of only one type

would be used on a runway and that both left-hand and right-hand

patterns would be flown. The intensities recommended are a compromise between the essentially uniform horizontal intensity distribution required to locate the runway, the high intensities

needed in the direction of the base leg during restricted visibility;, and power consumption,

B0 2 Comparative Regions of Guidance,

Comparative visual ranges of present runway and overrun

lights and of circling-guidance lights with the recommended intensity distribution when the atmospheric transmissivity is 0e 9

(10-mile visibility) and 0,1 (2-raile visibility) are shown in

figures 5 and 6, (The choice of the intensity settings for the

circling -guidance lights will be discussed below,) Note the difference in visual range in the direction of the base leg. When

considering the relatively small differences in visual range in

the direction of the downwind leg during poor visibility it should

be remembered that for the conditions shown the type C-l and M-l

lights provide no guidance whatever for an aircraft flying a pattern in which the downwind leg is 2 miles from the runway and

the only guidance obtained on the base leg is that obtained when

the aircraft comes within the main beam of the runway lights on

the far side of the runway,

8*3 Intensity Control of Circling-Guidance Lights,

If these circling-guidance lights are to be operated from

the series circuits supplying the runway lights* some method of

reducing the change in intensity and power consumption as the

current in the series circuit is varied is necessary. Otherwise,,

circling^guidance lights which provided adequate intensity when

the system was on step 1 would consume excessive power when the

system was on steps 4 and 5, (The power consumption would increase about 10 times between steps 1 and 5,)
-19-

In order to reduce the required regulator capacity* it is

highly desirable that the circling-guidance lights be turned off

when the system is on intensity setting 5 (100% intensity) . This is permissible since circling-guidance lights are of little*

if any, value in weather conditions which require this intensity

setting. If the circling-guidance lights are turned off when

the system is on step 5, then a regulator which is loaded to

capacity by the runway lights when on step 5 will not be overloaded on step 4 by these runway lights plus a group of circlingguidance lights which have a power consumption on step 4 equal

to 30% of the capacity of the regulator.

Use of saturable isolating transformers was first considered*

This method is unsatisfactory in several ways: a) It does not

provide the constancy of intensity desired; b) The power required

on step 5 is greater than on the lower steps; therefore, overcurrent relays would be required at each circling-guidance light

if the load is to be reduced when the system is on step 5; c)

Since these transformers operate at low power factor when the

system is on the higher intensities, the additional regulator

capacity which would be required is considerably greater than the

rated load of the lamps of the circling-guidance lights; d) The

distortions produced in the waveform of the system adversely

affect the regulation of some types of regulators.

Following a suggestion made by the Lighting Section,

Equipment Laboratory, Wright Air Development Center, that use

of a saturable reactor connected in parallel with the lamp be

considered as a means of controlling lamp current in place of a saturable isolating transformer, the principles of such a control

were developed in cooperation with the Lighting Section. This

control would utilize a direct- current winding to increase the

saturation. The direct current would be obtained by using a rectifier connected into the circuit so that its output current

is a function of the system current. With such a control it is

hoped that it will be possible to obtain a relative intensity of

at least 30% in the circling-guidance lights when the relative

intensity of the runway lights is 0o 2% (step 1) and to obtain a relative intensity in the circling-guidance lights of approximately 100% when the relative intensity of the runway lights

varies from 1% to 25% (steps 2, 3, and 4). It should also be

possible to decrease the reactance of this shunt control when the

relative intensity of the runway lights is 100%, so that the
^20-

relative intensity of the circling-guidanee lights is 5% or less,

thereby producing a significant unloading of the regulators.,

8*4 Procurement of Circling-Guidance Lights*

The intensity-distribution and control requirements have

been incorporated in Exhibit WCLEE5-69, dated 20 October 1955,

which was prepared in co-operation with the Lighting Section,

Equipment Laboratory* This exhibit was used by the National

Bureau of Standards in obtaining quotations for the design and

manufacture of circling-guidance lights* A contract for 22 lights

conforming to this exhibit has been awarded to the A'G’A Division

of Elastic Stop Nut Corporation.

8.5 Required Spacing of Circling “Guidance Lights.

The pilots indicated during the pilot interviews that they

desired, as would be expected, a circling-guidance light at each

runway light. This requires a spacing between lights of 200 feet.

Such an installation, although desirable, would require more

power than is available in most runway lighting systems* To determine the maximum useful spacing, simulated circling-guidance

lights were installed by the Civil Aeronautics Administration,

Technical Development Evaluation Center, at Indianapolis, under a Wright Air Development Center project. Test flights werejnade

using spacings between lights of 400, 800, and 1200 feet. xfce appearance of the pattern with these spacings indicates tnat a spacing of 1000 feet is optimum.

9. THRESHOLD LIGHTING

9.X -Function.

Threshold lights have two primary functions^ to indicate the

location of the ends of the runway, and to provide a ’’horizon* 99 Indication of the location of the ends of the runway implies that

a judgment of distance from the threshold lights can be made.

This requires that there be sufficient "texture" in the pattern

of threshold lights for adequate judgment of distance. This texture can be obtained by means of the spacing of the lights in the

threshold bars* Providing a horizon requires that the lenath of

the bars be such that the bars subtend an angle of about l® at

the pilot's eye.
-21-

9.2 Placement.

Because of the poor forward visibility of some types of

fighter aircraft when in the flareout attitude, and because

of the adverse effects of rain and snow on the center panels of

the canopies of fighter aircraft, the fighter pilots interviewed

preferred that the threshold bars be outboard of the runway

lights* This placement will also increase the "horizon” effect*

9.3 Required Beam Spread.

The minimum required horizontal beam spread of threshold

lights was computed on the premise that the aircraft should be

within the main beam of these lights as the turn is made from the

base leg to the final leg of the approach pattern. The relation

between minimum horizontal beam spread 0, aircraft speed v, angle

of bank p, and distance x, between the base leg of the approach

pattern and the threshold is

where g is the gravitational constant. (See Appendix D for

derivation of equation.) Figure 7 shows the relation between

x and P for representative values of 0 and for four approach

speeds.

In considering these figures the following should be noteds

1. These computations assume that the beams of the threshold

lights are horizontally aligned so that one edge of the main beam

is parallel to the runway axis.

2. The beam spread of 8° was selected as being representative of the present threshold lights, and 15° as being irepresentagive of PAR 56 approach lights. (Since the axis of these lights

is aligned with the runway, only half of the beam spread is

effective.)

3. If the intensity of the runway lighting system is

adjusted so that there is no glare along the runway, the runway

and threshold lights will be very difficult to see from base-leg

positions until the region of their main beams is entered.

x .I2 cot

g -an i

(2 )
=22=

The following conclusions may be drawn?

lo The horizontal beam spread of the present threshold

lights is not sufficient for the threshold lights to provide adequate guidance during the turn from the base leg to the final leg

of the approach unless the distance of the base leg is kept large

and/or the angle of bank is large®

2 0 If the maximum desirable angle of bank is limited to 15°

and the base leg is to be kept within 2 miles of the runway* a minimum beam spread of about 40® is required for approach speeds

of 150 knots or less®

3« If the maximum desirable angle of bank is 30®* and the

base leg is 2 miles from the runway* the minimum horizontal beam

spread is about 20® for approach speeds of 150 knots or less and

40° for approach speeds of 250 knots or less®

4® Therefore* to provide threshold lights to permit an aircraft to land from a base leg as near as 2 miles from the runway*

flying at speeds up to 250 knots* and turning with an angle of

bank of 30®* a 40® minimum horizontal beam spread for threshold

lights is recommended®

90 4 Spacing of lights in Threshold Bars®

Flight tests were made at the CAA Technical Development

Evaluation Center* IndianapoliSo using several spacings between

the lights in threshold bars® There was no noticeable difference

in the appearance of the bars when 2®5-£oot and 5=£oot spacings

were used® However* when the bars are viewed from distances of

one mile or more* the effective intensity of a bar with a 2®5=foot

spacing will be twice that of the bar with a 5-foot spacing®* A

10-foot spacing appeared slightly too great® From these observations it appears that a spacing of 5 to 8 feet will be satisfactory®

9® 5 Length of Threshold Bars®

The choice of length for the threshold bars* or wings* is

somewhat arbitrary since no data applicable to the problem were

available® When some fighter-type aircraft are within a half mile

of the threshold* only one bar or wing will be visible because of

the obscuration produced by the aircraft structure as the aircraft

* J® Bo DeBoer* Philips Research Reports* 224 (1951)
-23-

approaches the flare oat or nose-up attitude,, In addition,, during

rain and snow, vision through the center panels of some canopies

is poor 0 Therefore the threshold bars should be long enough so

that the desired horizon guidance will be obtained from one bar

when the aircraft is within a half mile of the threshold*,

If an angular length of 1° is taken as the minimum* then

the bars should be at least 45 feet long* Flight observations

at Indianapolis indicated that a length of 40 feet would be

satisfactory,, Current Air Force regulations require 40-foot

wings for new installations,,

9C 6 Color of Threshold Lights,,

Present standards specify the use of green lights to mark

both ends of the runway,, Under poor visibility conditions,, the

differentiation between green and white lights is less certain

than that between red and white lights,, This suggests the use

of red lights to mark the upwind end of the runway* The pilot

interviews indicated no serious objection to this use of red

lights and many of the pilots favored it«

9*7 Unidirectional vs„ Bidirectional Threshold Lights*

The use of bidirectional threshold lights with a beam spread

of 30° to 40° is considered unnecessary* On rollout or takeoff

the aircraft is sufficiently close to the centerline of the runway that the beam spread of the present threshold lights is adequate for marking the upwind end of the runway* In addition*

pilots report that on takeoff they make little use of the horizon

guidance of the threshold light* Thus* long bars are not required on the upwind end of the runway* Therefore* . a system

using a combination of some unidirectional and some bidirectional

lights appears desirable*

9*8 End-of-Runway Lights*

Some lights are needed between the threshold bars to mark

the end of the runway paving for aircraft taxying out for takeoff

or completing their rollout* These lights should be mounted at

the edge of the runway paving and should* therefore* be flushtype lights* The intensity required for this use is relatively

low* only a few candles* However* unless saturable transformers

are used* obtaining this intensity when the runway lighting system is operating on step 1 requires that the intensity be
-24~

above 1000 candles when the system is on step 5* Thus, consideration should be given either to the use of low-intensity lights connected to the taxiway lighting circuits or to the use of lights of

such intensity that they will be compatible with the other threshold

lights*

9.9 Recommended Threshold Lighting Systems.

A proposed threshold lighting system based upon the above considerations is shown in figure 8* It is recommended that tests be

made of this system^

10« CONCLUSIONS

I* The coverage of the present airfield beacon is inadequate

for jet aircraft operation*

2* For jet aircraft operation it is essential that the runway

be located and identified from as great a distance as practicable*

The off-axis guidance of the present runway lights is inadequate

when the lighting system is operated on the brightness settings used

for clear weather* The present runway lighting systems provide no

positive means of identification.

•3* It is not practicable to obtain sufficient off-axis guidance

from the lights of a high-intensity runway lighting system which

supply the axial guidance*

4, The downwind corner of the runway should be well marked and

visible from the downwind leg. None of the lights used in present

runway lighting systems has a satisfactory intensity distribution for

this function with the landing pattern used by the large jet bombers.

5* The beam spread of the present threshold lights is not sufficient to provide satisfactory guidance during the turn from the

base leg to the final leg of the approach with aircraft with high

approach speeds*

6, The intensity distribution of the present high-intensity

runway lights is satisfactory for straight-in approaches when the

distance between the rows of runway lights is 200 feet or less and is

marginal when the distance between rows is 300 feet. These lights

appear to be satisfactory mechanically.

7* Gaps in the runway lighting system are not considered serious except in the touchdown area and where the gaps are very long.

8. In low-visibility approaches the pilots are more concerned

with finding and seeing the runway lights than they are with the

adverse effects of glare*

9* The marking of the turnoffs from the runways is inadequate.

10. Information relative to the length of runway remaining is

considered essential on both landing and takeoff. Lights located

across the upwind end of the runway are of little value in indicating this distance, particularly when there is rain or snow on the

center panel (bullet-proof glass) of the canopy of fighters.
-25-

11. The use of red lights to mark the upwind end of the runway

appears desirable and is acceptable to the pilots*

12. Lack of uniformity in the lighting systems from airfield

to airfield results in undesirable confusion 0

11. RECOMMENDATIONS

It is recommended thats

1. Airfield beacons meeting the intensity distribution requirements of table I be obtained and tested for operational suitability.

2. Tests be made of a beacon in which the internal between the

Mwhite TO flashes is at least two-tenths of the flash cycle, to determine

pilot acceptance of this coding c 3. Runway identification lights conforming to the requirements

of Section 7 be procured and installed outboard of the threshold

lights on a runway with high-intensity lighting at two or more airfields for tests of operational suitability and pilot acceptance.

4. Cire ling-guidance lights conforming to the requirements of

Section 8 be procured and installed on runways with high-intensity

lighting at two or more airfields for tests of operational suitability

and pilot acceptance.

5. Service tests be made of threshold lighting systems modified

by the addition to the outboard ends of the threshold lighting system

of unidirectional lights having a horizontal beam spread of approximately 30°.

6. Development of a light suitable for installation across the

end of the runway between the wings of the threshold lighting system

be made a task of this project.

7. Development of an improved system of marking the principal

taxiway turn-offs be made a task of this project.

8. A system providing information as to the length of runway

remaining, suitable for use by day and by nighto be developed and

tested for operational suitability.

9* Flight and service tests be made to determine pilot acceptance of the use of red lights to mark the upwind end of the runway.

10. A study of the feasibility and design considerations of

lights suitable for use on the runway between heavy-duty pavement and

paved shoulders and in intersections be made a part of this project.
- 26- Regions of Guidance

Airfield Beacons

Regions of Guidance

Proposed V // / /&

Distance, d, (miles)

Figure I
- 27 - Circling Approach Patterns

Figure 2
Minimum

Intensity

Distribution

</> •$— x:

cp

a>0c o -g

'dO1 er* c

“ob

PO

Figure
Figure 4 »
-30-

Regions of Guidance of Runway Lights 1 Transmissivity 0.9 per mile

(10-miie visibility )

Figure 5
- 31 - Regions of Guidance of Runway Lights

Transmissivity O.J per mile

( 2-mi le vlsibilit y )
Distance

of

Base

Leg

from

Runway,

*

,

(miles)

-32 - Required Beam Spread of Threshold Lights

Angie of Bonk, /, (degrees)

Figure 7
Proposed

Threshold

Lighting

co

X

Flush-Type

Light

<nb|

+

Runway

Identification

Light,

White,

flashing

80

times

per

minute.
«34~

APPENDIX A

REPOTS AND MEMORANDA FORWARDED TO WRIGHT AIR DEVELOPMENT CENTER

1„ Memoranda® Report

2. Memorandum Report

3. Memorandum Report

4 0

5. Memorandum Report

6. Memorandum Report

7. Letter Report

8. Letter Report

9. MBS Report 4086

10« Memorandum Report

11. Memorandum Report

12 « Tentative Draft

13 e Tentative Draft

14. NBS Report 4358

15. NBS Report 4449

16* NBS Report 4554

17 * NBS Report 4565

18. NBS Report 4574

19. Travel Report

20. Travel Report

- 32*

Feasibility of Using Completely Flush Lights

Runway Locator Lights

Computation of the Loads Developed in the

Landing Gear When an Airplane Taxies Over

a Runway Light

Overlays of Runway Patterns of Selected

Airfields

Analysis of the Operational Requirements of

Threshold Lights

Recommendations for Intensity Distributions

of Airport Beacons

Effective Intensity of Flashing Lights

Intensity Requirements for Circling -Guidance

Lights of Runway Lighting Systems

Results of Static Loading Tests of Elfaca

Gratings by Aircraft Tires

Guidance for Circling Approaches

Required Length of Flush-Type Lights

Specification for a Fixed Cireling-Guidamee

Light

Specification for Flashing Runway Identification Light

Static Loading Tests of Flush-Type RunwayLight Heads

Analysis of Mercury Lamps and Filter Combinations for Use as Aviation-Green Lights

Computation of the Effective Intensity of

Flashing Lights

Static Loading Tests of Ae G.A0 ExpendableTop Runway-Light Head Assemblies with Glass

Covers

Landing Gear Loads Resulting from Taxying

Airplane Over a Projecting Runway light.

Progress Report 1

Memo of Visit to CAA Technical Development

and Evaluation Center* Indianapolis*

Indiana? February 16 - 18* 1955

Summary of Flight Tests of Downwind and

Threshold Lights at Indianapolis* Indiana*

April 13 & 14* 1955

Reports of Interviews at Air Force Bases
-35-

APPENDIX B

AIR BASES VISITED DURING SURVEY OF

OPERATIONAL REQUIREMENTS OF RUNWAY LIGHTS FOR JET AIRCRAFT

Wright-Patterson Air Force Base, Ohio

Andrews Air Force Base, Maryland

Shaw Air Force Base, South Carolina

Hunter Air Force Base, Georgia

Presque Isle Air Force Base, Maine

Dow Air Force Base, Maine

Westover Air Force Base, Massachusetts

Barnes Field, Westfield, Massachusetts

Lockbourne Air Force Base, Ohio

James Connally Air Force Base, Texas

Headquarters, Flight Training Comnand, Waco, Texas

McChord Air Force Base, Washington

I
-36-

APPENDIX C

VISIBILITY AND VISUAL RANGE

Explanation of Terms and Symbols*

V

0 Visibility;

(Day) The maximum distance at which large black

objects can be seen and identified when seen

against a sky or fog background*

(Night) The maximum distance at which a light with

'• an intensity of 25 candles can be seen*

These definitions are analagons to the information

to the information reported by the leather Bureau*

V Visual Range; -the maximum distance at which a particular

light (or object) can be seen*

K Visibility Factor; The ratio of the visual range of the

object or light of interest to the visibility*

K - ¥/V0

* (!)

I Candle power or Luminous Intensity; The luminous intensity

or eandlepower* in a particular direction,, of a light

source*

E Illumination; The density of luminous flux incident upon

a surface* In this report the unit of illumination

used is the mile candle* A mile candle is the illumination produced on a surface by a source with an intensity

of one candle one mile distant when the air is perfectly

clear*

E^ Illumination-Threshold; The minimum illumination of the

eye at which a light of small angular extent can be

found and seen steadily* In this report a value ©f 1

mile candle at the outside of the canopy is used for the

pilot 9 s threshold at night* This is twice the classic

value of 0*5 mile candle* The use of the higher value

is considered desirable because of the increased absorption in the center panel of the canopy* th® increased number of lighted instruments* and the greater

complexity of the cockpit of modern aircraft* which

reduces the time and effort the pilot can use in visual

search*,
-37-

APPENDIX C (cont.)

E "Standard” Illumination-Thresholds The illumination0 threshold applicable to a weather or ground observer.

A value of 0.1 mile candle is used for E0 in this

report. This value is approximately equal to that

obtained in field tests during periods of low visibility.* These studies indicate that the threshold

decreases with increasing visibility. However, in

view of the uncertainties in the other parameters of

interest, a constant value of illumination-threshold

is used in this report.

T Transmissivity; The ratio of the light which remains in

a collimated beam after passing through a unit distance of the atmosphere to the incident light,

Allard's Law.

The illumination produced by a source of intensity I at a distance x when the atmospheric transmissivity is T is found by

means of the familiar relation

E = ITVx2

. (2)

This relation, generally known as Allard's Law, follows from the

inverse-square law and the definition of transmissivity. When E

becomes equal to E*, the illumination-threshold, x is equal to V,

the visual range oi the light-, so that

E

t = IT

V/V^ (3)

If a standard value, E 0, is assigned to E

t

, the illuminationthreshold, and a standard intensity, I 0, to the lights being used

as visibility marks, the visual range of the light is equal to

V0, the visibility, so that

E

0 = I 0T

V7v0

2

. .(4)

* Douglas and Young, CAA Technical Development Report *47 (1945).

D. S„ Weather Bureau, Final Approach Visibility Studies Fiscal

Year 1952, Progress Report Part II, March 1953; and Fiscal

Year 1953 Progress Report, November 1953.
APPENDIX C (conto)

An intensity of 25 candles for X 0 is assumed for the reference lights used in visibility observations* This intensity was

selected as being representative of the lights used as visibility

marks* and has been generally accepted in the United States,**

If E

0

is 0*1 mile candle and I 0

is 23 candles, then

T

V

° = 0.004Vo2

(5)

The transmissivities, T, selected for use in the computations of visual range in this report and the corresponding visibilities^ rounded to the nearest ' value used in meteorological

reports, computed from equation (5) are given in table C-I*

Table C-I, Reported Visibilities, D, Corresponding

to Transmissivities, T

Transmissitivies (T) Reported Visibility (D)

per mile miles

0*005

,05

*1

0 3

0 6

o9

The effect of source intensity upon the visual range of

lights at night as a function of visibility is illustrated in

figureC-1* In preparing this figure, visibilities, V0, were

computed by means of equation (5) and the visual ranges corresponding to the selected intensities by means of equation (3)

using a value of 1 mile candle for E^, Note that when the

visibility is low, large changes in intensity have comparatively

little effect on the visibility factor, or the visual range*

lo

1*5

2 * 3*

5*

10*

* Douglas and Young, CAA Technical Development Report *47 (1945), ** U* S, Weather Bureau, Final Approach Visibility Studies, Fiscal

Year 1952, Progress Report Part II, March 1953; and Fiscal

Year 1953, Progress Report, November 1953*
Visibility

Factor

For

Lights

co in ro oj ” o

(°A/A JO) m 'JOtooj ^ 4 ! I ! q S s

j

a

«/> 0> E

o

>*.

Io

>

Figure

CH
-40

APPENDIX D

THRESHOLD LIGHTS

Explanation of Terms and Symbols,

0 Beam spread: The angle in degrees between the extended

centerline of the runway and the line of sight to the

threshold lights when the lights are first detected

from the base leg,

x Distance from the base leg to the runway,

r

ft Radius of the quarter-circular path of an aircraft during

its turn onto the final leg# starting at the time the

light is detected,

m Mass of the aircraft,

g Gravitational acceleration# equal to 32,2 feet per second,

Fw

Dropping forces The force that acts downward on the aircraft because of the mass of the aircraft and gravitational

acceleration,. This force acts perpendicular to the earth # s surface,

F^ Lifting forces The force that acts upward, essentially perpendicular to the plane of the wings# to maintain the

aircraft aloft,

F

c Centrifugal forces Equal to# but acting in a direction

opposite to# the resultant of the lifting force and the

dropping force,

P Banking angles The angle in degrees between the plane of the

wings and the horizontal plane,

rp The radius of the turn resulting from the banking angle,

v Speed of the aircraft.

Derivation of Equations,

From figure D-l it can be seen that

r^ = x tan 0 ( 1 )
APPEM)IX D (cont.)

The point where the aircraft path coincides with the extended

centerline of the runway is x (1-tan 0)* For beam spreads

greater than 45°, tan 9 is greater than 1, that is, the coincidence point is over the runway. The beam spread of the threshold lights, therefore, need not exceed 45° under any approach

condition, distance of base leg from the runway, and aircraft

speed.

From figure D-l can be seen, assuming a perfectly coordinated turn, that = Fc cot 0 (2)

Applying elementary equations from mechanics,

F

c = H?. and F

w

= mg,

P

to equation (2) gives

v

2

r Q = — cot 0 e (3)

p g

But as the radius of the turn resulting from 0 is the same as

that of the quarter-circle turn onto the final leg,

r 0 = re

• (4)

This implies that the right-hand side of equation (3) equals

that of equation (1), Solving for x gives,
- 42- Mechanical Considerations

in Determination of Beam Spread

of 1 Threshold Lights
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