Performance Assessment of the Terma 

Obstruction Light Control System as an 

Aircraft Detection Lighting System

June 2016

DOT/FAA/TC-TN16/41

This document is available to the U.S. public through the National 

Technical Information Services (NTIS), Springfield, Virginia 22161.

This document is also available from the Federal Aviation Administration 

William J. Hughes Technical Center at actlibrary.tc.faa.gov.

U.S. Department of Transportation

Federal Aviation Administration

ote technical note tech
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1. Report No.

DOT/FAA/TC-TN16/41

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

 4. Title and Subtitle 

PERFORMANCE ASSESSMENT OF THE TERMA OBSTRUCTION 

LIGHT CONTROL SYSTEM AS AN AIRCRAFT DETECTION 

LIGHTING SYSTEM

5. Report Date

June 2016 

6. Performing Organization Code

ANG-E26

7. Author(s)

James Patterson, Jr.* and Garrison Canter** 

8. Performing Organization Report No.

 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

*Federal Aviation Administration **SRA International, Inc.

William J. Hughes Technical Center A CSRA Company 

Aviation Research Division 1201 New Road 

Airport Technology R&D Branch Suite 242 

Atlantic City International Airport, NJ 08405 Linwood, NJ 08221 

11. Contract or Grant No. 

12. Sponsoring Agency Name and Address

U.S. Department of Transportation 

Federal Aviation Administration

Airport Engineering Division 

800 Independence Ave. SW 

Washington, DC 20591

13. Type of Report and Period Covered

Technical Note

14. Sponsoring Agency Code

AAS-100

15. Supplementary Notes

Mike DiPilato, of CSRA International Inc., provided technical support during this performance assessment.

16. Abstract

Federal Aviation Administration (FAA) Airport Technology Research and Development Branch (ATR) personnel conducted a 

performance assessment of the Terma Obstruction Light Control (OLC) System. The purpose of this assessment was to determine 

if the Terma OLC system meets the aircraft detection lighting system requirements specified in FAA Advisory Circular (AC) 

70/7460-1L, “Obstruction Marking and Lighting,” Chapter 14 Aircraft Detection Lighting Systems. 

FAA ATR personnel assessed the Terma OLC at the Tehachapi Wind Resource Area, located near Mojave, California. This

performance assessment, consisting of demonstrations, flight testing, and data analysis was conducted on April 15, 2015. In the 

performance assessment, a series of flight patterns were flown against the Terma OLC system to demonstrate whether it could meet 

the FAA performance requirements specified in AC 70/7460-1L. The Terma OLC system performed according to the 

manufacturer’s specifications and met the performance requirements identified in AC 70/7460-1L. 

17. Key Words

Aircraft Detection Lighting System, Obstruction light control, 

Obstruction lighting, Terma, ADLS

18. Distribution Statement 

This document is available to the U.S. public through the 

National Technical Information Service (NTIS), Springfield, 

Virginia 22161. This document is also available from the Federal 

Aviation Administration William J. Hughes Technical Center at 

actlibrary.tc.faa.gov.

19. Security Classif. (of this report)

 Unclassified

20. Security Classif. (of this page)

 Unclassified

21. No. of Pages

 44

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.
iii

TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY vii

INTRODUCTION 1

Purpose 1

Background 1

Objectives 2

Related Documentation 2

AIRCRAFT DETECTION LIGHTING SYSTEM STANDARDS 3

TERMA OLC SYSTEM CHARACTERISTICS AND SPECIFICATIONS 5

Terma OLC System Operational Description 6

Terma OLC System Radar Description 6

Terma OLC System Perimeters 7

Terma OLC System Fail-Safe Design 7

TERMA OLC SYSTEM INSTALLATION DESCRIPTION AT THE TWRA 8

THE FAA ASSESSMENTS OF THE TERMA OLC SYSTEM AT THE TWRA 12

The FAA Flight Assessment 12

The FAA Component Failure Assessment 14

RESULTS 14

Basic Function Assessment 14

Detection Performance Assessment 16

Component Failure Assessment 28

CONCLUSIONS 28

REFERENCES 29

APPENDICES 

A—Advisory Circular 70/7460-1L, Obstruction Lighting and Marking, Chapter 14 - 

Aircraft Detection Lighting Systems

B—Terma Obstruction Light Control System Information
iv

LIST OF FIGURES

Figure Page

1 Required ADLS Detection Coverage 4

2 Terma OLC System Concept 5

3 Terma OLC System Radar Configuration 7

4 Wind Turbines at the TWRA 9

5 Google Earth Map Showing Ground Clutter Around TWRA Assessment Site 9

6 Terma SCANTER 5202 PSR Installed at TWRA 10

7 The OLC System Indicator Lamp Used in Assessment 10

8 Relative Position of Warning Zone to Terma OLC System Radar 11

9 Piper Tri-Pacer Used for Assessment 13

10 The GPS Flight Track Data From the Aircraft 13

11 Flight Assessment as Observed on Terma OLC System Monitor 15

12 Terma OLC System Cumulative Radar Tracks Overlaid on the FAA Aircraft’s 

GPS Track 16

13 Flight Adjacent to North Edge of Warning Zone 18

14 Flight Directly Through the Warning Zone to the Northeast 19

15 Circling Flight Over the Warning Zone 20

16 Continuation of Circling Flight Over the Warning Zone, Then Exit to the East 21

17 Flight Over Radar Site, Then Directly to the Warning Zone 22

18 Flight to the Warning Zone With Aircraft Initially Hidden Behind a Mountain 23

19 Second Flight to Warning Zone With Aircraft Initially Hidden Behind a Mountain 24

20 Second Circling Flight Over the Warning Zone 25

21 Continuation of Second Circling Flight Over the Warning Zone 26

22 Descending Flight Into the Warning Zone 27
v 

LIST OF TABLES

Table Page

1 The GPS Coordinates of Terma OLC PSR and Warning Zone at TWRA 11
vi

LIST OF ACRONYMS

AC Advisory Circular

ADLS Aircraft detection lighting system

AGL Above ground level

ATR Airport Technology Research and Development Branch 

BITE Built-in test equipment

CFR Code of Federal Regulations

FAA Federal Aviation Administration

FCC Federal Communications Commission

GPS Global positioning system

IP Internet protocol

NM Nautical mile 

OLC Obstruction light control

PSR Primary surveillance radar

SCADA Supervisory control and data acquisition

SM Statute mile

TWRA Tehachapi Wind Resource Area
vii/viii

EXECUTIVE SUMMARY

Federal Aviation Administration (FAA) Airport Technology Research and Development Branch 

(ATR) personnel conducted a performance assessment of the Terma Obstruction Light Control 

(OLC) system. The purpose of this assessment was to determine if the Terma OLC system 

meets the aircraft detection lighting system (ADLS) requirements specified in FAA Advisory 

Circular (AC) 70/7460-1L, “Obstruction Marking and Lighting,” Chapter 14 – Aircraft Lighting 

Detection Systems. 

Aircraft detection lighting systems continuously monitor the airspace around an obstruction or 

group of obstructions for aircraft; and when the detection system detects an aircraft in its 

airspace, the system sends an electronic signal to the lighting control unit, which turns on the 

lights. Once the aircraft clears the obstruction area and there is no longer a risk of collision, the 

detection system turns off the lights and the system returns to standby mode. 

The United States has experienced a steady increase in the number of applications for 

construction of telecommunication towers and wind turbines. Any temporary or permanent 

structure, including telecommunication towers and wind turbines, that exceeds an overall height 

of 200 feet (61 meters) above ground level or exceeds any obstruction standard contained in Title 

14 Code of Federal Regulations Part 77, “Safe, Efficient Use, and Preservation of the Navigable 

Airspace,” should be marked and/or lighted with FAA-approved paint markings or lighting 

fixtures to ensure that they are visible to pilots at night. Due to the number of existing 

telecommunication towers and wind turbines, combined with expected future construction, the 

number of obstructions that have these required lighting fixtures has greatly increased. As a 

result, it has created a light pollution nuisance to residents living near these obstructions. Using 

an ADLS could have a positive impact on this problem, while still providing a sufficient level of 

safety for pilots operating at night in the vicinity of these obstructions. 

FAA ATR personnel assessed the Terma OLC system at the Tehachapi Wind Resource Area, 

located near Mojave, California. This performance assessment, consisting of demonstrations, 

flight testing, and data analysis was conducted on April 15, 2015. In the performance 

assessment, a series of flight patterns were flown against the Terma OLC system to demonstrate 

whether it could meet the FAA performance requirements specified in AC 70/7460-1L. The 

Terma OLC system performed according to the manufacturer’s specifications and met the 

performance requirements identified in AC 70/7460-1L.
1 

INTRODUCTION 

PURPOSE. 

Federal Aviation Administration (FAA) Airport Technology Research and Development Branch 

(ATR) personnel conducted a performance assessment of an aircraft detection lighting system 

(ADLS) developed by Terma, referred to herein as Terma obstruction light control (OLC) 

system. The purpose of this assessment was to determine if the Terma OLC system meets the 

ADLS requirements specified in Chapter 14 of FAA Advisory Circular (AC) 70/7460-1L, 

“Obstruction Marking and Lighting.” [1] 

BACKGROUND. 

In recent years, several companies have developed detection systems that monitor the airspace 

around an obstruction or group of obstructions to automatically turn the obstruction lighting on 

or off as needed. Such systems continuously monitor the airspace around their location; and 

when the detection system detects an aircraft in its airspace, the system sends an electronic signal 

to the lighting control unit, which turns on the lights. Once the aircraft clears the obstruction

area and there is no longer a risk of collision, the ADLS turns the lights off and the system 

returns to standby mode. These detection systems are typically (1) mounted directly on the 

obstruction, (2) positioned on a dedicated tower close to the obstruction, or (3) mounted on a 

stand-alone structure located in the vicinity of the obstruction at an optimized vantage point to 

ensure that the sensor can cover the entire volume of airspace around the obstruction. In addition

to controlling the obstruction lighting, some vendors have suggested using supplemental warning 

tools, such as an audible warning message or supplemental lighting that catches the pilot’s

attention, thereby providing an additional warning to the pilot that they are operating in close 

proximity to an obstruction.

The United States has experienced a steady increase in the number of applications for

construction of telecommunication towers and wind turbines, partially because of government 

mandates to improve the nation’s emergency communication network and to increase the amount 

of renewable energy generation. These telecommunication towers and wind turbines have begun 

to heavily occupy almost every corner of the country. Projections show that the accelerated rate 

of construction will continue well into the next decade. Any temporary or permanent structure, 

including these telecommunication towers and wind turbines, that exceeds an overall height of 

200 ft (61 m) above ground level (AGL) or exceeds any obstruction standard contained in Title 

14 Code of Federal Regulations (CFR) Part 77, “Safe, Efficient Use, and Preservation of the 

Navigable Airspace,” [2] should be marked and/or lighted with FAA-approved paint markings or 

lighting fixtures to ensure that they are visible to pilots. Due to the number of existing 

telecommunication towers and wind turbines, combined with the expected construction of new 

structures, the number of obstructions that have FAA-required light fixtures has greatly 

increased. As a result, it has created a light pollution nuisance to residents living near these 

obstructions. Using an ADLS could have a positive impact on this problem, while still providing 

a sufficient level of safety for pilots operating at night in the vicinity of these obstructions.

From 2011 to 2015, ATR personnel have worked closely with several ADLS vendors to better

understand the technologies, their capabilities, and the level of performance that would be
2 

necessary to safely integrate this concept into the National Airspace System. One major 

milestone achieved during the ADLS standards development was to enable the sensors to detect 

aircraft beyond the required 3 nautical miles (NM) from the obstruction, which would ensure that 

the lighting was on and the pilot was able to visually acquire the lights 3 NM away from the

obstruction. The 3-NM visibility requirement is important because it ties directly to the inflight

visibility requirements for a flight conducted under Visual Flight Rules. In 2013, ATR personnel

first developed standards for ADLS that were based on technical reviews, discussions, and flight

tests of ADLS in the United States and Canada. These ATR-developed standards have since

been used by the FAA as the baseline to which new ADLSs, like the Terma OLC system, were

tested against. The ATR-developed standards have since been integrated into AC 70/7460-1L as

Chapter 14, titled “Aircraft Detection Lighting Systems,” which was published in December 

2015 [1]. 

OBJECTIVES. 

The overall objective of this assessment was to conduct a performance assessment of the Terma

OLC system according to the requirements and standards for ADLSs in Chapter 14 of 

AC 70/7460-1L. This technical note describes the performance assessment of the Terma OLC 

system conducted at the Tehachapi Wind Resource Area (TWRA), located near Mojave,

California. 

RELATED DOCUMENTATION. 

The guidelines that have been in place for obstruction marking and lighting have remained 

mostly unchanged for the last 10 to 20 years and have proved to be sufficient for warning pilots 

of the presence of an obstruction. The recent update of AC 70/7460-1L does, however, include 

new material that is designed to improve safety, and at the same time, attempts to reduce the 

impact of obstruction lighting on nearby communities and wildlife. The introduction of ADLS 

suggests that the traditional obstruction lights remain the same in intensity, flash rate, and 

performance, but that the lights can be controlled by an automatic radar-activated monitoring 

system. 

The following FAA documents provide a significant amount of information and guidance 

pertaining to the lighting of obstructions:

• AC 150/5345-43, “Specification for Obstruction Lighting Equipment.” 

This document specifies the lighting equipment and fixtures that should be used for

lighting obstructions. The color of the light, flash rate, intensity, and various electrical 

and performance requirements are all addressed in this document.

Obstruction lights are given “L” type designations, which are described in this AC. The 

performance characteristics for the particular lights mentioned in this assessment are as 

follows:
3 

- L-864—Red flashing obstruction light, 2000 peak Candela, a minimum 750 

Candela, with a 3-degree vertical beam spread, flashing at a rate between 20 and 

40 flashes per minute. This light is required on wind turbines.

• FAA Technical Note DOT/FAA/TC-TN12/9, “Evaluation of New Obstruction Lighting 

Techniques to Reduce Avian Fatalities,” James W. Patterson, Jr., May 2012.

This document describes research conducted by FAA ATR personnel in which 

researchers evaluated a proposal to omit or flash the normally steady-burning red 

obstruction lights as a way to mitigate their impact on birds, due to their unique color and 

flash pattern. 

AIRCRAFT DETECTION LIGHTING SYSTEM STANDARDS

Based on the result of research efforts conducted by FAA ATR personnel, Chapter 14 of AC

70/7460-1L is the first fully comprehensive set of standards for ADLSs that has been published 

worldwide. Earlier research efforts in Canada and the United States led to the development of a 

few sets of very ambiguous descriptions of the technology, but it did not provide any specific 

guidance on the required range, coverage area, detection target size, or operational requirements 

for the technology. The following are the key ADLS operational requirements introduced in 

Chapter 14 of AC 70/7460-1L [1], which is included in its entirety in appendix A.

1. The system should be designed with sufficient sensors to provide complete detection 

coverage for aircraft that enter a three-dimensional volume of airspace, or coverage area, 

around the obstruction(s) (see figure 1), as follows:

a. Horizontal detection coverage should provide for obstruction lighting to be 

activated and illuminated prior to aircraft penetrating the perimeter of the volume, 

which is a minimum of 3 NM (5.5 km) away from the obstruction or the perimeter 

of a group of obstructions.

b. Vertical detection coverage should provide for obstruction lighting to be activated 

and illuminated prior to aircraft penetrating the volume, which extends from the 

ground up to 1000 ft (304 m) above the highest part of the obstruction or group of 

obstructions, for all areas within the 3-NM (5.5-km) perimeter defined above.

2. The ADLS should activate the obstruction lighting system in sufficient time to allow the 

lights to illuminate and synchronize to flash simultaneously prior to an aircraft 

penetrating the volume defined above. The lights should remain on for a specific time 

period, as follows:

a. For ADLSs capable of continuously monitoring aircraft while they are within the 

3-NM/1000-ft (5.5-km/304-m) volume, the obstruction lights should stay on until 

the aircraft exits the volume. In the event detection of the aircraft is lost while 

being continuously monitored within the 3-NM/1000-ft (5.5-km/304-m) volume, 

the ADLS should initiate a 30-minute timer and keep the obstruction lights on 
4 

until the timer expires. This should provide the untracked aircraft sufficient time 

to exit the area and give the ADLS time to reset.

b. For ADLSs without the capability of monitoring aircraft targets in the 

3-nm/1000 ft (5.5-km/304-m) volume, the obstruction lights should stay on for a 

preset amount of time, calculated as follows:

i. For single obstructions: 7 minutes.

ii. For groups of obstructions: (the widest dimension in nautical miles + 6) x 

90 seconds equals the number of seconds the light(s) should remain on.

3. In the event of an ADLS component or system failure, the ADLS should automatically 

turn on all the obstruction lighting and operate in accordance with AC 70/7460-1L as if it 

was not controlled by an ADLS. The obstruction lighting must remain in this state until 

the ADLS and its components are restored.

4. In the event that an ADLS component failure occurs and an individual obstruction light

cannot be controlled by the ADLS, but the rest of the ADLS is functional, that particular 

obstruction light should automatically turn on and operate in accordance with AC 

70/7460-1L as if it was not controlled by an ADLS, and the remaining obstruction lights 

can continue to be controlled by the ADLS. The obstruction lighting will remain in this 

state until the ADLS and its components are restored.

5. The ADLS’s communication and operational statuses shall be checked at least once every 

24 hours to ensure both are operational.

6. Each ADLS installation should maintain a log of activity data for a period of no less than 

the previous 15 days. This data should include, but not be limited to, the date, time, 

duration of all system activations/deactivations, track of aircraft activity, maintenance 

issues, system errors, communication and operational issues, lighting outages/issues, etc.

Figure 1. Required ADLS Detection Coverage [1] 
5 

In 2014, FAA ATR personnel completed an ADLS assessment, with the objective of validating 

the ADLS standards in AC 70/7460-1L. This assessment is described in FAA Technical Note 

DOT/FAA/TC-TN15/54, “Performance Assessment of the Laufer Wind Aircraft Detection

System as an Aircraft Detection Lighting System.” This technical note concluded the following: 

...the performance requirements provided in AC 70/7460-1L for ADLSs remain 

valid and provide for a technology that offers a satisfactory level of safety for the 

flying public, while at the same time, reduces the impact of obstruction lights on 

nearby communities and migratory bird populations. [3] 

Chapter 14 of AC 70/7460-1L also contains language that allows for ADLSs to have an optional

voice/audio feature that transmits a low-power, audible warning message over an aviation 

frequency licensed by the Federal Communications Commission (FCC) in the 

MULTICOM/UNICOM frequency band to provide pilots additional information on the 

obstruction they are approaching. The Terma OLC system does not offer this option, so these 

requirements do not apply to this assessment.

TERMA OLC SYSTEM CHARACTERISTICS AND SPECIFICATIONS 

The Terma OLC system uses a SCANTER 5202 primary surveillance radar (PSR) to detect 

aircraft within range of a wind farm or obstruction area and follows the general description 

provided in AC 70/7460-1L. For instance, when there are no aircraft in the vicinity of the wind 

turbine farm or obstruction, the warning lights remain off. When aircraft are detected in the 

vicinity, the lights are activated (turned on). When all aircraft have safely left the vicinity, the 

lights are deactivated (turned off). The Terma OLC system allows wind turbine farm warning 

lights to remain safely off at night when aircraft are not in the area.

As shown in figure 2, Terma’s OLC system concept consists of one or more SCANTER 5202 

PSR system, including an antenna and a global positioning system (GPS) synchronized light 

control connected via a supervisory control and data acquisition (SCADA) internet protocol (IP) 

network [4]. 

Figure 2. Terma OLC System Concept [4] 
6 

TERMA OLC SYSTEM OPERATIONAL DESCRIPTION. 

The Terma OLC system operates as follows:

1. Prior to reaching the light activation perimeter of the warning zone 

(3-NM/1000-ft (5.5-km/304-m) volume), aircraft are detected and tracked by the

SCANTER 5202 PSR(s). 

2. The PSR sends a signal through the SCADA IP network to the GPS Synchronized OLC

system when the aircraft reaches the light activation perimeter of the warning zone. 

3. The OLC system turns on the obstruction light(s). 

4. The PSR tracks the aircraft until it exits the warning zone light activation perimeter 

(3-NM/1000-ft (5.5-km/304-m) volume). 

5. The OLC system determines when to turn the lights off after verifying that no aircraft are 

within the warning zone. 

TERMA OLC SYSTEM RADAR DESCRIPTION. 

Terma’s SCANTER 5202 PSR, illustrated in figure 3, is a solid-state X-band radar. SCANTER 

5000 series PSRs are in use throughout the world in a variety of applications, including airport 

surface movement surveillance [4]. These PSRs utilize a combination of technologies, such as 

solid-state power amplifiers; multiple transmission frequencies (i.e., frequency diversity); pulsecompression; coherent integration; and signal processing, designed to detect and track very small 

cooperative and noncooperative targets in high-clutter environments, under a variety of weather

conditions (e.g., heavy rain and fog), and within and around a wind farm despite the turbulence 

and clutter created by the wind turbines themselves. Using high spatial resolution, high dynamic 

range, and side lob suppression the system can filter out noise caused by the spinning turbine 

blades. Airborne targets are primarily tracked using Doppler-processed signals [4]. These are 

supplemented by normal radar signals to follow targets with minimal radial velocities, such as 

helicopters. Terma states that the system has a range of 18 km (approximately 11.18 statute 

miles (SM)), with a total coverage of up to 1000 km2

 [5]. Therefore, Terma has proposed their 

OLC system for use at larger wind farms and wind farms with varied layouts. Appendix B 

contains additional information provided by Terma regarding this system.
7 

Figure 3. Terma OLC System Radar Configuration [4] 

TERMA OLC SYSTEM PERIMETERS. 

Terma’s OLC system includes three zones to ensure adequate identification of obstructions and 

compliance with AC 70/7460-1L: 

• Outer Detection Zone: Aircraft are detected and tracked by radar in this area, but the 

obstruction lights are not turned on until one of the aircraft enters the warning zone.

• Inner Warning Zone: Lights in the Obstruction Area are activated when aircraft enter this 

zone, and the lights remain lit while any aircraft is within this area. This zone will be 

located a minimum of 3 NM (5.5 km) away from the obstruction or the perimeter of a 

group of obstructions. 

• Obstruction Area: This is a broadly defined area that includes lighted obstruction(s), 

such as a wind farm. 

TERMA OLC SYSTEM FAIL-SAFE DESIGN. 

The Terma OLC system includes multiple self-testing functions to provide fail-safe protection. 

When a failure occurs, the obstruction lights are turned on until the Terma OLC system and its 

components functions are restored [6]. Built-in test equipment (BITE) in the Terma OLC system 

provides continuous system status monitoring. The BITE monitors mains-on time, solid-state 
8 

power amplifier status, forward power, noise figure, internal voltages and temperatures, turning 

unit status, and other parameters. Diagnostic tests are performed when the system starts up, 

including the following [6]: 

• Module presence test 

• Data link test 

• Memory test of all circuits 

The BITE also reports the following when monitoring the system during operation [6]: 

• BITE errors/warnings 

• Signal activity and processes

• Connectivity to OLC system

• Internal supply voltages 

• Noise figure, internal voltages, and temperatures 

• Forward power 

• Reverse power 

• Status from motor, gear, and optional inputs providing antenna status 

• Temperatures 

• Internal power supplies

The status of each BITE parameter is assessed automatically to ensure consistent operation. If 

any parameter is detected outside of normal operating specifications, error messages are 

automatically sent through the IP network interface and all obstruction lights are activated. Error 

records are stored automatically by the system in a log for future inspection [6]. 

TERMA OLC SYSTEM INSTALLATION DESCRIPTION AT THE TWRA

Terma installed its OLC system at the TWRA, located near Mojave, California. The TWRA is a

large wind turbine farm on and around the Tehachapi Mountains containing a mix of turbines 

manufactured by different vendors. Examples of the wind turbines installed in the TWRA are 

shown in figure 4. This is a challenging radar coverage environment due to the mountainous 

terrain and ground clutter caused by the quantity of wind turbines. For example, figure 5 shows

the locations of individual wind turbines in the vicinity of the assessment site, which are 

represented by colored points. The position of the radar is indicated by a red rectangle. It should 

be noted that for this assessment, the dimensions of the warning zone did not meet the 

requirement of extending at least 3 NM from the obstruction area as called for in 

AC 70/7460-1L. This was due to the assessment focusing on the system’s ability to activate an

indicator lamp when an aircraft was detected in a given area, rather than monitoring the 

activation of lighting on a specific obstruction or group of obstructions.
9 

Figure 4. Wind Turbines at the TWRA

Figure 5. Google Earth Map Showing Ground Clutter Around TWRA Assessment Site 

(The colored points indicate wind turbine locations.) 
10

The Terma OLC system installation at TWRA utilized one SCANTER 5202 PSR. This radar 

was mounted on the top of a specially designed shipping container. The radar mounting 

configuration is shown in figure 6. 

Figure 6. Terma SCANTER 5202 PSR Installed at TWRA

Because the Terma OLC system had not yet been connected to obstruction lighting in the wind 

farm, the OLC system was instead connected to the indicator lamp shown in figure 7. This 

indicator lamp provided a visual indication to ATR personnel observing the system that the OLC 

system could activate the light at the appropriate times when the aircraft entered and exited the 

warning zone airspace.

Figure 7. The OLC System Indicator Lamp Used in Assessment
11

The yellow polygon shown in figure 8 depicts the perimeter of the warning zone used for the 

assessment. This warning zone was 2 SM long and 1 SM wide, and the center of the zone was 

located approximately 4.5 NM southeast of the radar position. Although the size of this warning 

zone did not meet the 3-NM (5.5-km) perimeter requirement of AC 70/7460-1L, Terma’s 

engineers indicated that the perimeter could be expanded as needed to fully encompass the 

required airspace volume. The reduced size of the warning zone allowed ATR personnel to 

conduct performance assessments with greater efficiency due to there being less distance to 

cover when flying through the zone. Table 1 provides the coordinates of Terma OLC system 

radar position and four corners of the warning zone used for the assessment. 

Figure 8. Relative Position of Warning Zone to Terma OLC System Radar

Table 1. The GPS Coordinates of Terma OLC PSR and Warning Zone at TWRA

Location Latitude Longitude

Terma OLC PSR SCANTER Radar 35°03'56.03"N 118° 23'02.96"W

Warning Zone – North Corner 35°02'05.39"N 118° 18'25.55"W

Warning Zone – East Corner 35°01'45.22"N 118° 17'23.33"W

Warning Zone – South Corner 35°00'21.07"N 118° 18'53.02"W

Warning Zone – West Corner 35°00'45.85"N 118° 19'53.01"W
12

THE FAA ASSESSMENTS OF THE TERMA OLC SYSTEM AT THE TWRA

THE FAA FLIGHT ASSESSMENT. 

To properly assess the performance of the Terma OLC system, ATR personnel developed a 

series of flight patterns to assess the system’s response to aircraft operating around the warning 

zone at various altitudes, flight paths, speed, etc. These flight patterns were based on similar 

ones conducted during a previous FAA ADLS assessment [3]. Each pattern was designed to 

assess a specific parameter of the ADLS to determine if the system meets the requirements in 

AC 70/7460-1L. Two flights were conducted, during which these six specific flight patterns 

were flown, in some cases multiple times. The six flight patterns are described below: 

1. The aircraft flew through the center of the warning zone and exited the other side.

2. The aircraft flew inside the warning zone adjacent to its outer edge.

3. The aircraft flew over the radar site, and then flew directly to the warning zone after radar 

contact was lost.

4. The aircraft completed several tight circles inside the warning zone, and then exited the 

zone at a different heading from the entry heading. 

5. The aircraft flew toward and over the warning zone at least 1500 ft AGL, and then 

steeply descended into the warning zone. 

6. The aircraft flew toward the warning zone from a location where terrain masked the 

aircraft from initially being detected by the ADLS. The intent of this pattern was to 

identify how quickly the Terma ADLS could detect the aircraft without the benefit of 

early detection.

ATR personnel used the Piper PA-22 Tri-Pacer, shown in figure 9, to conduct the flight patterns. 

A notable characteristic of this aircraft is the outer skin of its wings and sections of fuselage is

made of fabric rather than metal. The aircraft was owned and flown by a pilot with a 

commercial pilot certificate. All flights were operated out of the Mojave Air and Space Port, 

which was located approximately 20 SM southeast of the Terma OLC system installation. 

Figure 10 shows a Google Earth map image overlaid with the flight tracks (shown in blue) 

recorded by a GPS unit on board the aircraft.
13

Figure 9. Piper Tri-Pacer Used for Assessment

Figure 10. The GPS Flight Track Data From the Aircraft
14

THE FAA COMPONENT FAILURE ASSESSMENT. 

ATR personnel were unable to directly assess the Terma OLC system’s fail-safe mechanisms, 

which activate the obstruction lighting in the event of a component failure. However, Terma 

engineers did provide documentation of the fail-safe capabilities of the OLC system to ATR 

personnel. A comprehensive assessment of these features is planned to be conducted at a later 

date by ATR personnel once Terma’s OLC system is connected to an obstruction lighting system 

and becomes fully operational. 

RESULTS

The performance assessment of the Terma OLC system was based on the specifications and 

criteria provided in AC 70/7460-1L. AC 70/7460-1L lists specifications for basic functions, 

detection performance, and system output. The following sections document the performance of 

the Terma OLC system along with the data collected during the performance assessment and 

discuss how it relates to the AC 70/7460-1L performance specifications.

BASIC FUNCTION ASSESSMENT. 

Prior to the assessment flight, the Terma OLC system was turned on, and ATR personnel 

verified that the system was up and running. ATR personnel verified that, without any aircraft 

present in the area, the system continuously scanned the area and kept the indicator lamp off. 

Before beginning the scheduled flight patterns, ATR personnel confirmed that the system was 

standing by and was not tracking any other aircraft in the area. With the system ready and the

indicator lamp off, ATR personnel proceeded to evaluate the Terma OLC system’s detection 

performance.

ATR personnel at the radar site monitored the Terma OLC system monitor and communicated 

with the ATR personnel on board the aircraft via a two-way radio. Figure 11 shows a screenshot 

of the flight track as it appeared on this monitor during the assessment. When the aircraft 

entered the warning zone, ATR personnel confirmed the indicator lamp connected to the OLC

system was activated and stayed lit while the aircraft was in the zone. Conversely, when the 

aircraft exited the warning zone, ATR personnel confirmed the indicator lamp had deactivated. 
15

Figure 11. Flight Assessment as Observed on Terma OLC System Monitor

During the assessment flights, the Terma OLC system recorded radar tracks for all airborne 

targets operating within the vicinity of the system while the performance assessment was being 

conducted. These radar tracks were exported as Keyhole Markup Language files viewable in 

Google Earth. Figure 12 shows a record of the entire FAA assessment flight pattern. The dotted 

magenta lines represent the real-time tracks produced from the Terma SCANTER OLC PSR, and 

the solid blue lines represent the tracks recorded by the GPS on board the aircraft. 
16

Figure 12. Terma OLC System Cumulative Radar Tracks Overlaid on the FAA Aircraft’s 

GPS Track

DETECTION PERFORMANCE ASSESSMENT. 

To demonstrate that the Terma OLC system was able to meet the detection performance 

requirements for an ADLS, ATR personnel developed and conducted a series of flight 

maneuvers designed to assess the system’s detection capabilities. Descriptions of the maneuvers 

and the results of the Terma OLC system’s detection capability are as follows:

• Flight Inside the Warning Zone Adjacent to its Outer Edge

The Terma OLC system detected the aircraft 4.3 NM from the warning zone perimeter 

and activated the indicator lamp when the aircraft entered the warning zone. The 

indicator lamp deactivated as the aircraft exited the warning zone heading southwest. 

Figure 13 shows events 1-4 for this flight pattern. 

• Flight Directly Through the Center of the Warning Zone and Exiting the Other Side

The Terma OLC system detected the aircraft 1.2 NM outside the warning zone perimeter 

and activated the indicator lamp when the aircraft entered the zone, flying toward the 

northeast. Figure 14 shows events 5-8 for this flight pattern. 

• Completion of Several Tight Circles Inside the Warning Zone, Then Exiting the Zone at a 

Different Heading From the Entry Heading 

The Terma OLC system maintained radar contact with the aircraft at a range of 2.75 NM

from the warning zone and activated the indicator lamp as the aircraft entered the 
17

warning zone. The system tracked the aircraft even as it conducted a series of steep 

circling maneuvers within the warning zone. As the aircraft exited and re-entered the 

zone at random headings during these turns, the Terma OLC system recognized it as the 

same aircraft that had entered the perimeter and activated the indicator lamp as required. 

Figures 15 and 16 show events 9-15 for this flight pattern. 

• Flight Over the Radar Site, Then Flying Directly Through the Warning Zone After Radar 

Contact is Lost

The Terma OLC system lost contact with the aircraft as it flew directly over the radar 

site; however, this is typical of all radar systems, which are not designed to detect aircraft 

above the radar antenna. This gap is known as the cone of silence. Terma’s OLC system 

was able to re-acquire the aircraft within 1.1 NM as it flew toward the warning zone

perimeter, activating the indicator lamp when the aircraft entered the perimeter. The 

Terma OLC system then deactivated the indicator lamp as the aircraft left the zone 

heading southeast. Figure 17 shows events 16-19 for this flight pattern. 

• Flights to the Warning Zone From a Location Where Terrain Masked the Aircraft From 

Initially Being Detected by the ADLS

On two separate flights manuevers, the Terma OLC system successfully detected the 

aircraft as soon as it appeared from behind a mountain on the west of the warning zone. 

As soon as the Terma OLC system detected the aircraft (still outside the warning zone

perimeter), the system continued to monitor the aircraft’s track and activated the indicator 

lamp when the aircraft entered the warning zone perimeter. After the aircraft flew 

through the warning zone and exited the area, the Terma OLC system deactivated the 

indicator lamp, as required. Figures 18 and 19 show events 20-26 for these flight 

patterns. 

• Circling Flight Over the Warning Zone (second flight)

During a second flight, the Terma OLC system again detected and maintained contact 

with the aircraft as it circled inside the warning zone, activating and deactivating the 

indicator lamp as required when the aircraft exited and re-entered the zone. Figures 20 

and 21 show events 27-32 for this flight pattern.

• Flight to and Over the Radar Site, Then Steeply Descending Into the Warning Zone

Although contact with the aircraft was lost as it flew directly over the radar site and 

steeply descended behind mountains as it approached the warning zone, the Terma OLC 

system detected the aircraft with enough time to activate the indicator lamp as it entered 

the warning zone perimeter. After the aircraft completed the descent and exited the area, 

the Terma OLC system deactivated the indicator lamp as required. Figure 22 shows 

events 33-36 for this flight pattern. 
18

Event 1:

• Aircraft 

approaches the 

warning zone 

from the 

northeast.

• Indicator lamp

is off.

Event 2:

• Aircraft is 

detected and 

tracked by 

radar prior to 

reaching the 

warning zone. 

• Indicator lamp

is off. 

Event 3:

• Aircraft 

penetrates the 

warning zone

perimeter 

heading west. 

• Indicator lamp

is on. 

• Aircraft is 

continuously 

monitored

within the 

warning zone. 

Event 4:

• Aircraft exits 

the warning 

zone to the 

west. 

• Indicator lamp

is off. 

Figure 13. Flight Adjacent to North Edge of Warning Zone (events 1-4) 
19

Event 5:

• Aircraft 

approaches the 

warning zone 

from the 

southwest. 

• Indicator lamp

is off.

Event 6:

• Aircraft is 

detected and 

tracked by 

radar prior to 

reaching the 

warning zone. 

• Indicator lamp

is off. 

Event 7:

• Aircraft 

penetrates the 

warning zone 

perimeter

heading 

northeast. 

• Indicator lamp

is on.

• Aircraft is 

continuously 

monitored 

within the 

warning zone.

Event 8:

• Aircraft exits 

the warning 

zone to the 

northeast. 

• Indicator lamp

is off.

Figure 14. Flight Directly Through the Warning Zone to the Northeast (events 5-8) 
20

Event 9:

• Aircraft 

approaches the 

warning zone 

from the northeast. 

• Indicator lamp

is off.

Event 10:

• Aircraft is 

detected and is 

tracked by 

radar prior to 

reaching the 

warning zone. 

• Indicator lamp

is off.

Event 11:

• Aircraft 

penetrates the 

warning zone 

perimeter

heading to the 

southwest. 

• Indicator lamp

is on.

• Aircraft is 

continuously 

monitored 

within the 

warning zone.

Event 12:

• Aircraft 

initiates a 540° 

left turn, 

exiting the 

warning zone to 

the southeast. 

• Indicator lamp

is off.

Figure 15. Circling Flight Over the Warning Zone (events 9-12) 
21

Event 13:

• Aircraft 

continues its

left turn 

outside the 

warning zone.

• Indicator lamp

is off.

Event 14:

• Aircraft 

penetrates the 

warning zone 

perimeter and 

continues its 

540° left turn 

inside the 

warning zone.

• Indicator lamp

is on.

• Aircraft is 

continuously 

monitored 

within the 

warning zone.

Event 15: 

• Aircraft begins 

a right turn, 

exiting the 

warning zone

to the east. 

• Indicator lamp

is off.

Figure 16. Continuation of Circling Flight Over the Warning Zone, Then Exit to the East (events 13-15) 
22

Event 16: • Aircraft flies 

directly over 

the radar site, 

makes a 180° 

turn and 

begins to 

approach the 

warning zone 

from the northwest. 

• Indicator lamp

is off.

Event 17:

• Aircraft is 

reacquired and 

tracked by 

radar prior to 

reaching the 

warning zone. 

• Indicator lamp

is off.

Event 18:

• Aircraft 

penetrates the 

warning zone 

perimeter

heading 

southeast. 

• Indicator lamp

is on.

• Aircraft is 

continuously 

monitored 

within the 

warning zone.

Event 19:

• Aircraft and 

exits the 

warning zone to 

the southeast. 

• Indicator lamp

is off.

Figure 17. Flight Over Radar Site, Then Directly to the Warning Zone (events 16-19) 
23

Event 20:

• Aircraft 

approaches the 

warning zone 

from the 

southwest then 

suddenly 

appears from 

behind the 

mountain.

• Indicator lamp

is off.

Event 21:

• Aircraft is 

detected and is 

tracked by 

radar shortly 

before entering 

the warning 

zone. 

• Aircraft 

penetrates the 

warning zone 

perimeter

heading 

northeast. 

• Indicator lamp

is on.

Event 22:

• Aircraft is 

continuously 

monitored 

within the

warning zone.

• Aircraft exits 

the warning 

zone to the 

northeast.

• Indicator lamp

is off.

Figure 18. Flight to the Warning Zone With Aircraft Initially Hidden Behind a Mountain (events 20-22) 
24

Event 23:

• Aircraft 

approaches the 

warning zone 

from the 

southwest then 

suddenly 

appears from 

behind the 

mountain.

• Indicator lamp

is off.

Event 24:

• Aircraft is 

detected and is 

tracked by 

radar.

• Indicator lamp

is off.

Event 25:

• Aircraft 

penetrates the 

warning zone 

perimeter.

• Indicator lamp

is on.

• Aircraft is 

continuously 

monitored 

within the 

warning zone.

Event 26:

• Aircraft exits 

the warning 

zone to the 

southeast. 

• Indicator lamp

is off.

Figure 19. Second Flight to Warning Zone With Aircraft Initially Hidden Behind a Mountain (events 23-26) 
25

Event 27:

• Aircraft 

approaches the 

warning zone 

from the south. 

• Aircraft is 

detected and is 

tracked by 

radar.

• Indicator lamp

is off.

Event 28:

• Aircraft 

penetrates the 

warning zone 

perimeter

heading north. 

• Indicator lamp

is on.

• Aircraft is 

continuously 

monitored 

within the 

warning zone.

Event 29:

• Aircraft exits 

the warning 

zone heading 

northwest.

• Aircraft begins

a 270° left turn 

towards the 

warning zone, 

approaching 

from the 

northwest. 

• Indicator lamp

is off.

Event 30:

• Aircraft 

continues its 

turn and 

penetrates the 

warning zone 

perimeter

heading 

southeast. 

• Indicator lamp

is on.

Figure 20. Second Circling Flight Over the Warning Zone (events 27-30) 
26

Event 31:

• Aircraft 

continues the 

270° left turn 

inside the 

warning zone.

• Aircraft is 

continuously 

monitored 

within the 

warning zone.

• Indicator lamp

is on. 

Event 32:

• Aircraft exits 

the warning 

zone to the 

north. 

• Indicator lamp

is off.

Figure 21. Continuation of Second Circling Flight Over the Warning Zone (events 31-32) 
27

Event 33:

• Aircraft flies 

over the radar 

site. 

• Radar contact 

is lost.

• Indicator lamp

is off. 

Event 34:

• Aircraft 

approaches 

warning zone 

from the 

northwest.

• Aircraft is not

yet detected by 

radar.

• Indicator lamp

is off.

Event 35:

• Aircraft is 

detected by 

radar prior to 

reaching 

warning zone.

• Aircraft 

descends into

the zone from 

1500 ft AGL 

heading 

southeast.

• Indicator lamp

is on. 

Event 36:

• Aircraft exits

the warning 

zone to the 

southeast

• Indicator lamp

is off. 

Figure 22. Descending Flight Into the Warning Zone (events 33-36) 
28

COMPONENT FAILURE ASSESSMENT. 

To demonstrate that the Terma OLC system was able to meet the component failure 

requirements for an ADLS, ATR personnel conducted a series of activities designed to test the 

system’s component failure responses. Descriptions of the activities and the results of the Terma 

OLC system’s failure response are as follows:

• Individual Component and Obstruction Light Control Failure

These functions were unable to be assessed due to the limited installation at the site. 

However, Terma engineers did provide the documentation of the fail-safe capabilities of 

the OLC system to ATR personnel.

• Communication and Status Monitoring

ATR personnel verified that the Terma OLC system communication and operational 

status were checked at least once every 24 hours to ensure both are operational. 

• Target Size

ATR personnel confirmed that the Terma OLC system could detect an object with a 

cross-sectional area of 1 square meter or more within the detection area. This was 

accomplished by flying an aircraft straight toward the Terma OLC system radar unit, 

which resulted in the system detecting the narrow profile of the aircraft. 

• Activity Log

The Terma indicated that the data could be stored for an indefinite amount of time, 

depending on the user’s requirement, which satisfies the 15-day requirement of AC 

70/7460-1L. 

• FCC Part 15 Compliance

Based on the documentation provided to the ATR personnel by the Terma engineers, it 

was verified that the Terma OLC system components do not use FCC Part 15 devices [7]. 

• Audio/Voice Option

The Terma OLC system does not currently offer a voice/audio option; therefore, this was 

not evaluated. As stated in AC 70/7460-1L, this is not a required ADLS component.

CONCLUSIONS

The Federal Aviation Administration (FAA) Airport Technology Research and Development 

Branch evaluated the Terma Obstruction Light Control (OLC) system at the Tehachapi Wind 

Resource Area, located near Mojave, California. A performance assessment, consisting of 

demonstrations, flight testing, and data analysis was conducted on April 15, 2015. In this

performance assessment, a series of flight patterns were flown against the Terma OLC system to 
29/30

demonstrate that it could meet the FAA’s performance requirements for aircraft detection 

lighting systems. The Terma OLC system performed according to the manufacturer’s 

specifications and met the performance requirements identified specified in FAA Advisory 

Circular (AC) 70/7460-1L, “Obstruction Marking and Lighting.” 

REFERENCES

1. Federal Aviation Administration, “Obstruction Marking and Lighting,” Advisory Circular 

(AC) 70/7460-1L, December 4, 2015.

2. U.S. Federal Register, Title 14 Code of Federal Regulations, Part 77, “Safe, Efficient 

Use, and Preservation of the Navigable Airspace,” Government Printing Office, 

Washington DC.

3. Patterson, James, Jr., “Performance Assessment of the Laufer Wind Aircraft Detection 

System as an Aircraft Detection Lighting System,” FAA technical note DOT/FAA/TCTN15/54, September 2015.

4. Terma, “Coverage Report for OLC Demo, California,” March 2015.

5. Terma, “SCANTER 5000 Radar Series Radar-Based Obstruction Light Control,” 2015. 

6. Terma, “SCANTER 5202 System Features: Built-in Test Equipment,” 2015. 

7. U.S. Federal Register, Title 47 Code of Federal Regulations, Part 15, “Radio Frequency 

Devices,” Government Printing Office, Washington, DC.
A-1 

APPENDIX A—ADVISORY CIRCULAR 70/7460-1L, CHAPTER 14, AIRCRAFT 

DETECTION LIGHTING SYSTEMS 1

CHAPTER 14. AIRCRAFT DETECTION LIGHTING SYSTEMS

14.1 Purpose.

Aircraft Detection Lighting Systems (ADLS) are sensor-based systems designed to detect 

aircraft as they approach an obstruction or group of obstructions; these systems automatically 

activate the appropriate obstruction lights until they are no longer needed by the aircraft. This 

technology reduces the impact of nighttime lighting on nearby communities and migratory birds 

and extends the life expectancy of obstruction lights.

14.2 General Standards.

14.2.1 The system should be designed with sufficient sensors to provide complete detection 

coverage for aircraft that enter a three-dimensional volume of airspace, or coverage area, around 

the obstruction(s) (see Figure A-27 in Appendix A), as follows:

1. Horizontal detection coverage should provide for obstruction lighting to be activated and 

illuminated prior to aircraft penetrating the perimeter of the volume, which is a minimum of 3 

NM (5.5 km) away from the obstruction or the perimeter of a group of obstructions.

2. Vertical detection coverage should provide for obstruction lighting to be activated and 

illuminated prior to aircraft penetrating the volume, which extends from the ground up to 1,000 

feet (304 m) above the highest part of the obstruction or group of obstructions, for all areas 

within the 3 NM (5.5 km) perimeter defined in subparagraph 14.2.1 1 above.

3. In some circumstances, it may not be possible to meet the volume area defined above 

because the terrain may mask the detection signal from acquiring an aircraft target within the 3 

NM (5.5 km) perimeter. In these cases, the sponsor should identify these areas in their 

application to the FAA for further evaluation.

4. In some situations, lighting not controlled by the ADLS may be required when the 3 NM 

(5.5 km) perimeter is not achievable to ensure pilots have sufficient warning before approaching 

the obstructions.

14.2.2 The ADLS should activate the obstruction lighting system in sufficient time to allow the 

lights to illuminate and synchronize to flash simultaneously prior to an aircraft penetrating the 

volume defined above. The lights should remain on for a specific time period, as follows:

 

1 Federal Aviation Administration, “Obstruction Marking and Lighting,” Advisory Circular (AC) 70/7460-1L, 

December 4, 2015.
A-2 

1. For ADLSs capable of continuously monitoring aircraft while they are within the 3 

NM/1,000 foot (5.5 km/304 m) volume, the obstruction lights should stay on until the aircraft 

exits the volume. In the event detection of the aircraft is lost while being continuously monitored 

within the 3 NM/1,000 foot (5.5 km/304 m) volume, the ADLS should initiate a 30-minute timer 

and keep the obstruction lights on until the timer expires. This should provide the untracked 

aircraft sufficient time to exit the area and give the ADLS time to reset.

2. For ADLSs without the capability of monitoring aircraft targets in the 3 nm/1,000 foot 

(5.5 km/304 m) volume, the obstruction lights should stay on for a preset amount of time, 

calculated as follows:

a. For single obstructions: 7 minutes.

b. For groups of obstructions: (the widest dimension in nautical miles + 6) x 90 seconds 

equals the number of seconds the light(s) should remain on.

14.2.3 Acceptance of ADLS applications will be on a case-by-case basis and may be modified, 

adjusted, or denied based on proximity of the obstruction or group of obstructions to airports, 

low-altitude flight routes, military training areas, or other areas of frequent flight activity. It may 

be appropriate to keep certain obstructions closest to these known activity areas illuminated 

during the nighttime hours, while the remainder of the group’s obstruction lighting is controlled 

by the ADLS.

14.2.4 Project sponsors requesting ADLS use should include in their application maps or 

diagrams indicating the location of the proposed sensors, the range of each sensor, and a visual 

indication showing how each sensor’s detection arc provides the full horizontal and vertical 

coverage, as required under paragraph 14.2.1. In the event that detection coverage is not 100 

percent due to terrain masking, project sponsors should provide multiple maps or diagrams that 

indicate coverage at the affected altitudes. A sample diagram is shown in Figure A-27 in 

Appendix A.

14.2.5 Types of ADLS Component or System Failure Events.

1. In the event of an ADLS component or system failure, the ADLS should automatically 

turn on all the obstruction lighting and operate in accordance with this AC as if it was not 

controlled by an ADLS. The obstruction lighting must remain in this state until the ADLS and its 

components are restored.

 

2. In the event that an ADLS component failure occurs and an individual obstruction light 

cannot be controlled by the ADLS, but the rest of the ADLS is functional, that particular 

obstruction light should automatically turn on and operate in accordance with this AC as if it was 

not controlled by an ADLS, and the remaining obstruction lights can continue to be controlled by 

the ADLS. The obstruction lighting will remain in this state until the ADLS and its components 

are restored.

3. Complete light failure should be addressed in accordance with Chapter 2 paragraph 2.4.
A-3/A-4 

14.2.6 The ADLS’s communication and operational status shall be checked at least once every 

24 hours to ensure both are operational.

14.2.7 The ADLS should be able to detect an aircraft with a cross-sectional area of 1 square 

meter or more within the volume, as required in subparagraphs 14.2.1 1 and 14.2.1 2.

14.2.8 Each ADLS installation should maintain a log of activity data for a period of no less than 

the previous 15 days. This data should include, but not be limited to, the date, time, duration of 

all system activations/deactivations, track of aircraft activity, maintenance issues, system errors, 

communication and operational issues, lighting outages/issues, etc.

14.2.9 Operational Frequencies.

1. Unlicensed devices (including FCC Part 15) devices cannot be used for this type of 

system.

2. Any frequency used for the operation of ADLS must be individually licensed through the 

FCC. 

14.3 Voice/Audio Option.

14.3.1 ADLS may include an optional voice/audio feature that transmits a low-power, audible 

warning message to provide pilots additional information on the obstruction they are 

approaching.

14.3.2 The audible transmission should be in accordance with appropriate FAA and FCC 

regulations.

14.3.3 The audible transmission should be over an aviation frequency licensed by the FCC and 

authorized under the Code of Federal Regulations Title 47- Part 87.483 (excluding 121.5 MHz).

Note: Using air traffic control frequencies in the 117.975-MHz to 137-MHz frequency band is 

prohibited for this operation.

14.3.4 The audible message should consist of three quick tones, followed by a verbal message 

that describes the type of obstruction the system is protecting. Appropriate terms to be used 

include tower(s), wind turbine(s), or power line(s).

14.3.5 The audible message should be repeated three times or until the system determines the 

aircraft is no longer within the audible warning area defined in the following paragraph.

14.3.6 The audible message should be considered as a secondary, final warning and should be 

activated when an aircraft is within 1/2 NM (926 m) horizontally and 500 feet (152 m) vertically 

of the obstruction. The use of, or variation to, the audible warning zone may occur, depending on 

site-specific conditions or obstruction types.
B-1 

APPENDIX B—TERMA OBSTRUCTION LIGHT CONTROL SYSTEM INFORMATION
B-2 
B-3 
B-4