DOT/FAA/AR-05/28 

Office of Aviation Research 

Washington, D.C. 20591

115 Vac Single-Phase Arc-Fault 

Circuit Breaker Flight Test 

Robert Pappas 

July 2005 

Final Report 

This document is available to the U.S. public 

through the National Technical Information 

Service (NTIS), Springfield, Virginia 22161. 

U.S. Department of Transportation 

Federal Aviation Administration
NOTICE 

This document is disseminated under the sponsorship of the U.S. 

Department of Transportation in the interest of information exchange. The 

United States Government assumes no liability for the contents or use 

thereof. The United States Government does not endorse products or 

manufacturers. Trade or manufacturer's names appear herein solely 

because they are considered essential to the objective of this report. This 

document does not constitute FAA certification policy. Consult your local 

FAA aircraft certification office as to its use. 

This report is available at the Federal Aviation Administration William J. 

Hughes Technical Center's Full-Text Technical Reports page: 

actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF). 
 Technical Report Documentation Page

1. Report No.

DOT/FAA/AR-05/28

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

5. Report Date 

July 2005

 4. Title and Subtitle 

115 Vac SINGLE-PHASE ARC-FAULT CIRCUIT BREAKER FLIGHT TEST 6. Performing Organization Code

7. Author(s)

Robert Pappas 

8. Performing Organization Report No. 

10. Work Unit No. (TRAIS) 

 

9. Performing Organization Name and Address

Federal Aviation Administration 

William J. Hughes Technical Center 

Airport and Aircraft Safety 

Research and Development Division 

Airworthiness Assurance Branch 

Atlantic City International Airport, NJ 08405

11. Contract or Grant No.

 

13. Type of Report and Period Covered

 Final Report

12. Sponsoring Agency Name and Address

U.S. Department of Transportation 

Federal Aviation Administration

Office of Aviation Research 

Washington, DC 20591

14. Sponsoring Agency Code

 ANM-10

15. Supplementary Notes 

16. Abstract 

In December 1999, the Federal Aviation Administration (FAA), the Naval Air Systems Command, and the Office of Naval 

Research initiated a joint research and development program aimed at the development of arc-fault circuit breakers (AFCB) 

suitable for the protection of aircraft electrical wiring. Two independent contracts for the development of 115 Vac single-phase 

AFCBs were awarded; one to the Eaton Aerospace Company and one to the Hendry Telephone Company. Each contractor was to 

develop arc-fault algorithms and deliver developmental circuit breakers to the FAA and the U.S. Navy for flight test. AFCB 

detection algorithms were required to be sensitive enough to rapidly identify an arc condition and, conversely, not so sensitive 

that the device trips on normal electrical transients associated with various load equipment current signatures and electrical power 

systems operations such as bus transfers. The deliverable circuit breakers were also to be a form-fit replacement for existing

thermal magnetic breakers’ easy retrofit into aging aircraft. The FAA conducted subsequent flight-testing in an FAA-owned 

Boeing 727-25C aircraft. Eight aircraft circuits were selected for fitting with AFCBs. The circuits provided a cross section of 

load types powered from various aircraft power busses. An instrumentation system was installed to record the voltage and current 

waveforms associated with each circuit to assist in the analysis of any AFCB failure and nuisance-tripping events. This report 

describes the flight test effort for evaluating the performance of the developmental AFCBs. In total, the flight test effort was 

comprised of 118.9 hours flight time during which 929.7 operational hours of AFCB data were collected. All flight hours were 

accumulated using normal aircraft operational profiles. 

17. Key Words 

Arc-fault circuit breaker, Flight test, Eaton, Hendry 

18. Distribution Statement 

This document is available to the public through the National 

Technical Information Service (NTIS) Springfield, Virginia 

22161.

19. Security Classif. (of this report) 

 Unclassified

20. Security Classif. (of this page) 

 Unclassified

21. No. of Pages 

 186 

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized
TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY ix 

1. INTRODUCTION 1 

1.1 Purpose 1 

1.2 Background 1 

1.3 Test Objective 2 

2. EQUIPMENT INSTALLATION 3 

2.1 Aircraft Description 3 

2.2 Arc-Fault Circuit Breaker Flight Test Installation Description 3 

2.2.1 Circuit Breaker Installation and Connection 3 

2.2.2 Instrumentation Equipment and Interfaces 4 

2.3 Electrical Connections 5 

2.4 Aircraft Test Circuits 6 

2.5 Nicolet Odyssey Data Recorder 7 

2.6 N40 Wiring Baseline 7 

3. FLIGHT TEST STATISTICS 8 

3.1 Eaton Flight Test Statistics 8 

3.2 Hendry Flight Test Statistics 9 

4. SAMPLE DATA RECORDINGS 11 

5. FLIGHT TEST 13 

5.1 Eaton Flight Test Plan 13 

5.1.1 Introduction 13 

5.1.2 Flight Test Goals 14 

5.1.3 System Description 14 

5.1.4 Certification Requirements 15 

5.1.5 Flight Test Profile Requirements 15 

5.1.6 Limitations 15 

5.1.7 Emergency Procedures 16 

5.1.8 Normal Procedures 16 

iii
5.2 Eaton Discrepancies 18 

5.2.1 Discrepancy 1 18 

5.2.2 Discrepancy 2 19 

5.3 Eaton Troubleshooting Procedures 19 

5.3.1 Arc-Fault Troubleshooting Background 19 

5.3.2 Detailed Troubleshooting Procedures 20 

5.3.3 Detailed Process Flow Chart 21 

5.4 Hendry Test Plan 23 

5.4.1 Introduction 23 

5.4.2 Objective 23 

5.4.3 Scope 24 

5.4.4 Flight Test Goals 24 

5.4.5 System Description 24 

5.4.6 Aircraft Installation 25 

5.4.7 Certification Requirements 25 

5.4.8 Flight Test Profile Requirements 25 

5.4.9 Limitations 26 

5.4.10 Emergency Procedures 26 

5.4.11 Normal Procedures 27 

5.5 Hendry Discrepancies 28 

5.5.1 Discrepancy 1 29 

5.5.2 Discrepancy 2 29 

5.5.3 Discrepancy 3 29 

5.5.4 Discrepancy 4 29 

5.5.5 Discrepancy 5 30 

5.6 Hendry Troubleshooting Procedures 30 

5.6.1 Arc-Fault Troubleshooting Background 30 

5.6.2 Detailed Troubleshooting Procedures 31 

5.6.3 Detailed Process Flow Chart 31 

5.7 Summary of Test Results 34 

5.7.1 Eaton Summary 34 

5.7.2 Hendry Summary 35 

iv
APPENDICES 

Appendix A—Flight Test Certification Plan 

Appendix B—Eaton Flight Test Plan 

Appendix C—Eaton Ground Checkout Procedures 

Appendix D—Eaton Flight Test Records 

Appendix E—Eaton Troubleshooting Procedures 

Appendix F—Hendry Flight Test Plan 

Appendix G—Hendry Ground Checkout Procedures 

Appendix H—Hendry Flight Test Records 

Appendix I—Hendry Troubleshooting Procedures 

Appendix J—Time Domain Reflectometer Test Results 

Appendix K—Arc-Fault Circuit Breaker Wiring 

v
LIST OF FIGURES 

Figure Page 

1 Eaton Aerospace Corporation Prototype AFCBs 2 

2 Hendry Telephone Products AFCB 2 

3 Arc-Fault Circuit Interrupter-Junction Box 4 

4 Nicolet Data Recorder and Junction Box 5 

5 BNC Breakout Box to Nicolet Data Recorder 6 

6 Nicolet Odyssey Data Recorder 7 

7 Eaton Flight Test Hours 9 

8 Eaton AFCB Operating Hours 9 

9 Hendry Flight Test Hours 10 

10 Hendry AFCB Operating Hours 10 

11 Auxilary Power Unit-to-Engine Power Transfer Transient Waveform 11 

12 Cabin Ceiling Light Turn-On Transient Waveform 12 

13 Landing Light In-Rush Current Waveform 12 

14 Guillotine (Dry-Arc) Arc-Fault Test Waveform 13 

15 Eaton Detailed Process Flow Chart 21 

16 Hendry Detailed Process Flow Chart 32 

LIST OF TABLES 

Table Page 

1 Eaton AFCB Test Circuit Breaker Locations 16 

2 Hendry AFCB Test Circuit Breaker Locations 27 

vi
LIST OF ACRONYMS 

AFCB Arc-fault circuit breaker 

AFCI-JB Arc-fault interrupter-junction box 

APU Auxiliary power unit 

FAA Federal Aviation Administration 

MIDO Manufacturing Inspection District Office 

NAVAIR Naval Air Systems Command 

SCR Silicone control rectifier 

STC Supplemental type certificate 

TDR Time domain reflectometer 

vii/viii 
EXECUTIVE SUMMARY

In December 1999, the Federal Aviation Administration (FAA), the Naval Air Systems 

Command, and the Office of Naval Research initiated a joint research and development program 

aimed at the development of arc-fault circuit breakers (AFCB) suitable for the protection of 

aircraft electrical wiring. 

Two independent contracts for the development of 115 Vac single-phase AFCBs were awarded; 

one to the Eaton Aerospace Company and one to the Hendry Telephone Company. Each 

contractor was to develop arc-fault algorithms and deliver developmental circuit breakers to the 

FAA and the U.S. Navy for flight test. AFCB detection algorithms were required to be sensitive 

enough to rapidly identify an arc condition and, conversely, not so sensitive that the device trips 

on normal electrical transients associated with various load equipment current signatures and 

electrical power systems operations such as bus transfers. The deliverable circuit breakers were 

also to be a form-fit replacement for existing thermal magnetic breakers’ easy retrofit into aging 

aircraft. 

Eaton delivered the developmental circuit breakers to the FAA and U.S. Navy in August 2001 

and Hendry delivered in June 2002. The FAA William J. Hughes Technical Center, Atlantic 

City International Airport, New Jersey, conducted subsequent flight-testing. For the flight test 

effort, the circuit breakers were installed in an FAA-owned Boeing 727-25C aircraft. Eight 

aircraft circuits were selected for fitting with AFCBs. The circuits provided a cross section of 

load types powered from various aircraft power busses. An instrumentation system was installed 

to record the voltage and current waveforms associated with each circuit to assist in the analysis 

of any AFCB failure and nuisance-tripping events. 

This report describes the flight test effort for evaluating the performance of the developmental 

AFCBs. In total, the flight test effort was comprised of 118.9 hours flight time during which 

929.7 operational hours of AFCB data were collected. All flight hours were accumulated using 

normal aircraft operational profiles. 

ix/x
1. INTRODUCTION. 

1.1 PURPOSE. 

This report describes the flight test effort conducted to evaluate the performance of arc-fault 

circuit breakers (AFCB) in a Federal Aviation Administration (FAA)-owned Boeing 727-25C 

aircraft. This report provides a factual summary of the Eaton and Hendry flight test results. 

Flight-testing of the Eaton breakers was completed in September 2001 and flight-testing of the 

Hendry breakers was completed in October 2002. The effort was performed by the FAA 

William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. 

1.2 BACKGROUND. 

In December 1999, the FAA, the Naval Air Systems Command (NAVAIR), and the Office of 

Naval Research initiated a joint research and development program aimed at the development of 

AFCBs suitable for the protection of aircraft electrical wiring. The Eaton Aerospace Corporation 

and the Hendry Telephone Company were awarded the contract to independently develop 115 

Vac, 400-Hz AFCBs. The goal was to add arc-fault protection to existing thermal protection in a 

package not to exceed an MS24571 size circuit breaker. 

Each AFCB contract was tailored around the vendor’s proposals. The Eaton contract duration 

was 24 months and was completed in December 2001. Hendry, who teamed with Texas 

Instruments, performed under a 33-month contract completed in October 2002. Each vendor 

proposed various designs for detecting an arcing fault. Existing detection methods developed for 

60-Hz residential applications and 48 Vdc telephone systems had to be modified to work on 

aircraft 115 Vac, 400-Hz electrical systems. Program completion was predicated upon delivery 

of 20 prototype AFCBs for flight-testing aboard FAA and NAVAIR aircraft. 

AFCB detection algorithms must be sensitive enough to rapidly identify an arc condition and, 

conversely, not so sensitive that the device trips on normal electrical transients associated with 

various load equipment current signatures and electrical power systems operations such as bus 

transfers. Unintended trips are referred to as nuisance trips. 

Development of effective arc-fault detection algorithms is only one of two major developmental 

challenges. The other challenge is packaging the arc-fault components along with the 

components for thermal overcurrent protection into a standard aircraft circuit breaker package. 

The difficulty posed by this requirement is best illustrated by example. Repackaging an average 

residential AFCB into an MS24571 package or smaller requires at least a 50% reduction in 

packaging volume. Exacerbating this challenge is the requirement to operate in an aircraft 

environment at temperature ranges between -20o

 and +71oC, altitudes of 0-45,000 feet, with 

vibration, electromagnetic interference, and operating on electrical systems with many unusual 

electrical transients. Both companies exceeded the program goal and developed AFCBs in 

packages substantially smaller than the MS24571 goal. Figures 1 and 2 show the Eaton and 

Hendry prototype AFCBs, respectively. 

1
FIGURE 1. EATON AEROSPACE CORPORATION PROTOTYPE AFCBs 

(Two left breakers are 400-Hz prototypes. Right breaker is a 60-Hz residential breaker.) 

FIGURE 2. HENDRY TELEPHONE PRODUCTS AFCB 

1.3 TEST OBJECTIVE. 

The objective of the AFCB flight test program was to evaluate the nuisance trip characteristics of 

each vendor’s AFCB prototypes. A nuisance trip is a nonthermal opening of the AFCB when an 

arc-fault condition is not present. Nuisance trips are most likely when loads are initially turned 

2
on, or during bus transfers and other transient conditions. However, nuisance trips can occur at 

any time, due to a random transient or other electrical system upset. 

To achieve the flight test objective, the goal for the flight test program was simple. Operate the 

breakers on the aircraft, following standard aircraft operating procedures, for at least 25 hours 

and up to 50 hours if possible. Additional flight hours increase the likelihood that the AFCB 

prototypes are exposed to as many potential nuisance trip conditions as possible. 

It is important to stress that evaluation of the arc-fault detection implementation methods and trip 

time performance was not a flight test program objective. The vendors conducted hundreds of 

dry- and wet-arc tests during the development process to evaluate the arc-fault detection 

performance of their product. More importantly, conducting arc-fault tests in flight is a hazard to 

the aircraft and crew. All breakers were subjected to manufacturer conformance testing and 

were subjected to FAA dry-arc (guillotine) tests prior to installation on the aircraft. 

It must also be noted that the flight tests were not part of a product qualification program. The 

AFCBs tested in this program were engineering prototypes, not production representative units. 

In addition, there is no standard performance specification for AFCBs currently published. 

However, development of an AFCB performance specification continues in the SAE AE-8B1 

Protective Devices Subcommittee and is expected to be completed in the near future. 

2. EQUIPMENT INSTALLATION. 

2.1 AIRCRAFT DESCRIPTION. 

Testing was performed at the William J. Hughes Technical Center aboard the FAA’s only large 

transport category aircraft. The aircraft is a B-727-25C (tail number N40) aircraft manufactured 

in 1967. Three main engine generators, an auxiliary power unit (APU), and an emergency 

battery bus electrically power the aircraft. On the ground, the aircraft is powered by the APU or 

from a ground power unit. The AFCBs were tested using all sources of power except for the 

emergency battery. The aircraft is equipped with a 400- to 60-Hz converter that supplies 

115 V/60 Hz power to the project instrumentation and data recorder. 

The aircraft was flown under an experimental certificate issued by the local FAA Field Service 

District Office. 

2.2 ARC-FAULT CIRCUIT BREAKER FLIGHT TEST INSTALLATION DESCRIPTION. 

2.2.1 Circuit Breaker Installation and Connection. 

The AFCBs were not installed in the aircraft circuit breaker panel because they were 

nonqualified prototypes. Therefore, the breakers were installed in a separate arc-fault circuit 

interrupter-junction box (AFCI-JB) that contained all the AFCBs and instrumentation interfaces. 

It is important to note that the AFCBs were connected in series with the load side of the existing 

aircraft thermal circuit breakers. Existing circuit protection aboard the aircraft was not 

compromised in any way by this installation. Additionally, a trigger test point was brought out 

from each breaker and used to activate an audible alarm and put the instrumentation recorder in a 

high sampling rate mode. 

3
The AFCB installation consisted of the following components: 

a. Eight Eaton or Hendry prototype AFCBs of the following ratings: one 2.5 amps (A), 

three 5 A, two 7.5 A, one 10 A, and one 15 A. The AFCBs were mounted inside the 

AFCI-JB. 

b. One AFCI-JB. The AFCI-JB (figure 3) housed the eight AFCB units. It also contained 

eight current transformers for monitoring the current flowing through each of the eight 

AFCBs and a voltage divider network for monitoring the voltages on the line and load 

side of each breaker. The AFCI-JB is mounted in the rear, left side of the cockpit behind 

the observer jump seat. The AFCI-JB has bypass switches that disable the AFCBs, if 

desired, by the pilot in command. The banana plug jacks along the bottom of the front 

side provide convenient electrical access to the line and load side of each AFCB to assist 

in testing and troubleshooting activities. The AFCI-JB was fabricated using standard best 

practices and in accordance with Advisory Circular 43.13-1B and was designed to 

contain any possible AFCB failures. 

c. Two AFCI-JB test unit wire harnesses, P18 and P6 (for connection to the P18 and P6 

circuit breaker panels, respectively). 

FIGURE 3. ARC-FAULT CIRCUIT INTERRUPTER-JUNCTION BOX 

2.2.2 Instrumentation Equipment and Interfaces. 

The flight test instrumentation was mounted in the cabin of the aircraft. The following 

equipment was installed to support the data collection effort. 

a. One 24-channel Nicolet Odyssey data recorder. (The data recorder was upgraded to 32 

channels for the Hendry AFCB flight tests.) 

b. One BNC breakout box. The breakout box routed the signals from the shielded, twisted 

pair wires in the interface harness (see paragraph c) to a standard BNC connector, one for 

4
each input channel on the data recorder. The BNC breakout box and the Odyssey data 

recorder were mounted in the cabin of the aircraft, as shown in figure 4. 

c. One AFCI-JB, BNC breakout box interface harness. This harness contained shielded, 

twisted pair wires for carrying the signals obtained in the AFCI-JB to the BNC breakout 

box. 

d. Twenty-four 36-inch BNC connector cables. These cables connected the outputs on the 

BNC breakout box to each input channel on the data recorder. 

e. One Trigger Alarm. The trigger alarm was an audio/visual alarm that illuminated a 

warning light and sounded a siren in the event the data recorder experienced a trigger 

signal, indicating a potential AFCB trip or other anomaly. Pressing a pushbutton 

mounted on the alarm resets the alarm. 

FIGURE 4. NICOLET DATA RECORDER AND JUNCTION BOX 

2.3 ELECTRICAL CONNECTIONS. 

The electrical connections for the system are shown schematically in FAA drawing 9854415, as 

shown in appendix K. The AFCBs mounted within the AFCI-JB will be electrically in series 

with the load side of the existing circuit breakers. The AFCI-JB wire harnesses, P-18 and P-6, 

connect the load side of the each aircraft circuit breaker to the line side of the respective AFCB 

and the load side of the each AFCB to the feed wire for the respective load. The AFCI-JB-BNC 

breakout box interface harness connected the AFCI-JB to the BNC breakout box. 

Connections between the BNC breakout box and the Odyssey data recorder are shown in 

figure 5. 

5
FIGURE 5. BNC BREAKOUT BOX TO NICOLET DATA RECORDER 

2.4 AIRCRAFT TEST CIRCUITS. 

The prototype AFCBs were tested on the aircraft circuits indicated below. The circuits were 

selected through an iterative process. First, all ac loads on the aircraft were identified. All flight 

critical and essential loads were eliminated. Three-phase motor loads were also eliminated. 

From the remaining circuits, a cross section of loads was selected to optimize the mix of load 

types (resistive, inductive, electronic, etc.) These loads are specified below. 

• Left inboard landing lights, 7.5 A, 115 Vac, ac bus number 1, circuit breaker panel P18-4. 

• Left outboard navigation light, 5 A, 115 Vac, ac bus number 2, circuit breaker panel 

P18-4. 

• Left window lights, 10 A, 115 Vac, transfer bus, circuit breaker panel P18-3. 

• Left ceiling lights, 15 A, 115 Vac, transfer bus, circuit breaker panel P18-4. 

• DME-2, 2.5 A, 115 Vac, ac radio bus number 2, circuit breaker panel P18-2. 

• Auxiliary pitot heat, 5 A, 115 Vac, ac bus number 2, circuit breaker panel P6-1. 

• Window heat, first officers window 4 and 5, 5 A, 115 Vac, ac bus number 3, circuit 

breaker panel P6-1. 

6
• 400- 60-Hz inverter (phase A only), 15 A, 115 Vac, ac bus number 2, project power 

junction box (located in E&E bay). 

2.5 NICOLET ODYSSEY DATA RECORDER. 

A Nicolet Odyssey data recorder (figure 6) was used to record all data from the AFCB-JB. The 

Nicolet is a sophisticated data recorder that samples at a rate of 100 kHz per channel. Data 

recording rates are programmable for speeds between 1 and 100 kHz. To conserve hard disk 

space, data was normally recorded at the 1 kHz rate. When the data recorder detected a trigger, 

indicating that an AFCB was tripping, the recording rate would immediately change to the 100 

kHz rate, capturing a high-resolution recording of the voltage and current on each AFCB for 100 

ms before and after the trigger condition. 

The capture of this data was important for several reasons. First, the current waveform data is 

crucial in determining if the fault condition was a real arc fault or a nuisance trip condition. If a 

real arc was suspected, a rigorous troubleshooting effort is required to find the location of the 

fault on the aircraft prior to release for flight, as spelled out in the Eaton Troubleshooting 

Procedures in appendix E. If the condition is determined to be a nuisance trip, the data is sent to 

the AFCB developer for analysis, and possible modification of the arc-fault detection algorithms 

in the AFCB. 

FIGURE 6. NICOLET ODYSSEY DATA RECORDER 

2.6 N40 WIRING BASELINE. 

As required in the Eaton Ground Test Checkout Procedures shown in appendix C, the eight 

circuits involved in the AFCB testing were required to have an electrical characteristic baseline 

7
established prior to commencing the flight test. CM Technologies was brought in to use its 

electrical characterization and diagnostics time domain reflectometer (TDR) to measure and 

record the baseline. 

Baselines were established to assist the troubleshooting process in the event that an AFCB trip 

occurred. If the recorded data clearly indicated that the event was nuisance related, then 

troubleshooting of the aircraft circuits would not be necessary. However, if the data recorded 

was inconclusive, then it might be necessary to troubleshoot the aircraft circuit. Because an arc 

fault can alter the impedance characteristics of a wire, it was determined that the TDR may help 

locate the approximate location of the arc. 

During a TDR test, an electric pulse is transmitted down the wire under test. Wherever an 

impedance change is encountered, part of the energy of the pulse is reflected back to the source. 

The reflections are captured as a trace. The initial trace is stored as a characteristic baseline 

against which future traces are compared. In the event of a suspected arc fault, the wire would 

be recharacterized and the new trace compared to the original baseline. When the traces are 

overlaid, separations indicate potential areas where the wire has been damaged. Appendix J 

contains the baseline characterization data from the N40 tests. 

During both the Eaton and Hendry flight test programs, no arc faults were encountered, and it 

was not necessary to recharacterize any circuits with the TDR measurement equipment. 

3. FLIGHT TEST STATISTICS. 

The combined flight evaluation included 118.9 hours of testing. During this time, a total of 

929.7 AFCB operational hours and data were accumulated. The Flight Test Certification Plan is 

shown in appendix A. 

3.1 EATON FLIGHT TEST STATISTICS. 

Figures 7 and 8 contain the summarized Eaton flight test data. Figure 7 shows the flight hour 

data, and figure 8 shows the cumulative AFCB operational hours. The Eaton AFCBs 

accumulated 30.9 flight hours and 228.2 operational hours. Appendix D contains the detailed 

data on the flights. 

The Eaton flight test program commenced on 10 September 2001. On the morning of 11 

September, the aircraft was powered-up and ready for taxi and takeoff when the World Trade 

Center and Pentagon attacks began to unfold. This flight and all other flights for the week were 

cancelled. The program was able to resume testing on 17 September. During the period of 20-

25 September, a number of instrumentation and crew availability problems were experienced 

that further impacted accumulation of flight time. Flying resumed on 26 September and 

continued through 03 October. At this point, the aircraft was removed from experimental status 

to support other scheduled FAA research and development (R&D) flight test programs and the 

Eaton flight test program was completed. 

8
0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

Flight Hour

s

Daily Flight Hours Cumulative Flight Hours

FIGURE 7. EATON FLIGHT TEST HOURS 

0.0

50.0

100.0

150.0

200.0

250.0

AFCB Operational Hour

s

Daily AFCB Operating Hours Cumulative AFCB Operating Hours

FIGURE 8. EATON AFCB OPERATING HOURS 

3.2 HENDRY FLIGHT TEST STATISTICS. 

Figures 9 and 10 contain the summarized Hendry flight test data. Figure 9 shows the flight hour 

data, and figure 10 shows the cumulative AFCB operational hours. The Hendry AFCBs 

9
accumulated 88.0 flight hours and 701.5 operational hours. Appendix D contains the detailed 

data on the flights. 

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

8/5/2002

8/6/2002

8/6/2002

8/15/2002

8/15/2002

8/16/2002

8/19/2002

8/19/2002

8/20/2002

8/23/2002

9/23/2002

9/24/2002

9/24/2002

9/25/2002

9/26/2002

9/26/2002

9/30/2002

9/30/2002

9/30/2002

10/1/200210/1/2002

10/2/2002

10/3/2002

10/3/2002

10/4/2002

10/6/2002

10/6/2002

10/7/2002

10/8/2002

10/8/2002

10/9/2002

10/9/2002

10/10/2002

10/11/2002

Flight Hours

Daily Flight Hours Cumulative Flight Hours

FIGURE 9. HENDRY FLIGHT TEST HOURS 

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

8/5/20028/6/20028/6/2002

8/15/2002

8/15/2002

8/16/2002

8/19/2002

8/19/2002

8/20/2002

8/23/2002

9/23/2002

9/24/2002

9/24/2002

9/25/2002

9/26/2002

9/26/2002

9/30/2002

9/30/2002

9/30/2002

10/1/2002

10/1/2002

10/2/2002

10/3/2002

10/3/2002

10/4/2002

10/6/2002

10/6/2002

10/7/2002

10/8/2002

10/8/2002

10/9/2002

10/9/2002

10/10/2002

10/11/2002

AFCB Operation Hours

Daily AFCB Operating Hours Cumulative AFCB Operating Hours

FIGURE 10. HENDRY AFCB OPERATING HOURS 

Initial bench testing (guillotine tests), aircraft installation, and debug flight-testing were 

conducted between 19 June 2002 and 2 July 2002 with test AFCBs not in a common algorithm 

configuration. At the conclusion of these tests, it was decided that flight-testing would not be 

10
started until all eight installed AFCBs were of the same configuration (amp rating excepted). 

The circuit breakers were sent to Hendry for rework and returned to the FAA on 31 July 2002 for 

reinstallation and flight-testing. During this time frame, the Odyssey recorder was returned to 

the manufacturer for an 8-channel upgrade (to 32 channels total) and warranty replacement (a 

digital signal processor chip on the other signal processing boards). The flight test commenced 

on 5 August 2002. A second gap in consecutive flight test time occurred between 24 August and 

22 September 2002 when the aircraft experienced a fuel tank leak. Flying resumed on 23 

September and continued until 11 October 2002. During this period, the flight profile included 

approximately 120 approaches. At this point, the aircraft was removed from experimental status 

to support other scheduled FAA R&D flight test programs, and the Hendry flight test program 

was completed. 

4. SAMPLE DATA RECORDINGS. 

Figures 11 through 14 are waveform examples that can be expected during normal operation of 

aircraft equipment and must be accounted for in the algorithms incorporated in an AFCB. The 

waveforms were obtained during the course of this flight test program and were recorded with 

the Nicolet data recorder. 

Figure 11 shows an example of the voltage waveforms encountered during a power transfer from 

APU to engine. 

FIGURE 11. AUXILARY POWER UNIT-TO-ENGINE POWER TRANSFER 

TRANSIENT WAVEFORM 

Start-up current transients can often be many times the rated current of the circuit breaker. The 

transient current is one factor that most arc-fault detection algorithms monitor. Examples of 

typical cabin ceiling light transient current are shown in figure 12. Peak current on the cabin 

ceiling lights was 42 A, nearly three times the rated current of the circuit. 

11
FIGURE 12. CABIN CEILING LIGHT TURN-ON TRANSIENT WAVEFORM 

Inboard landing light start-up transients are shown in figure 13. The peak in-rush current on the 

inboard landing light was 46 A, more than six times the rated current of the AFCB. 

FIGURE 13. LANDING LIGHT IN-RUSH CURRENT WAVEFORM 

Figure 14 shows an example of a guillotine (dry-arc) arc-fault test. Note again, the high-current 

transients over 100 A. This test was conducted on each AFCB prior to installation to verify the 

functionality of the arc detection and trip circuitry. In this particular test, the first trigger 

occurred within two cycles of the guillotine. Current shutdown occurred within one-half cycle of 

the trigger. Current is only limited by the source impedance and the wire characteristics between 

the source and the fault. 

12
FIGURE 14. GUILLOTINE (DRY-ARC) ARC-FAULT TEST WAVEFORM 

5. FLIGHT TEST. 

5.1 EATON FLIGHT TEST PLAN. 

5.1.1 Introduction. 

The FAA William J. Hughes Technical Center R&D flight test program performed a minor 

modification to their B-727-25C aircraft. This temporary modification involved the installation 

of eight AFCB prototypes manufactured by Eaton Aerospace Controls. The AFCBs were 

installed for a 2-week experimental flight test period in support of AFCB R&D. 

The AFCBs were installed in an AFCI-JB that enclosed all the AFCBs and required 

instrumentation. The AFCBs were not mounted in the aircraft circuit breaker panels. It is 

important to note that the AFCBs were connected in series with the load side of the existing 

thermal circuit breakers. In other words, current circuit protection aboard the aircraft was not 

compromised in any way by this installation. 

The electrical, system, and mechanical integration of this installation was accomplished at 

Atlantic City International Airport using FAA technical and engineering personnel. The New 

York Aircraft Certification Office granted the engineering personnel authority to approve 

electrical systems and structures data via FAA Form 8110-3. 

It is important to note that no arc faults will be created in the aircraft. The purpose of the flighttesting is to evaluate nuisance tripping only. Arcing will not intentionally be created aboard the 

aircraft in flight or on the ground. The Eaton Flight Test Plan is shown in appendix B. 

13
5.1.2 Flight Test Goals. 

The following list describes the goals of the experimental flight test program, listed in order of 

importance. 

• Complete at least 50 (or more) flight hours but not less than 25 hours. Data generated 

during these flights is critical to the AFCB R&D program and for obtaining approval of 

the N40 one-only supplemental type certificate (STC). 

• Evaluate the operation of the AFCBs under standard B-727 operational procedures. 

• Evaluate the operation of the AFCB instrumentation and Odyssey data recording system 

for future unmanned data collection. 

5.1.3 System Description. 

The AFCB installation consists of the following: 

• Eight Eaton prototype AFCBs of the following ratings: two 5 A, three 7.5 A, one 10 A, 

and two 15 A (mounted in the AFCI-JB). 

• One AFCI-JB 

• Two AFCI-JB test unit wire harnesses, P18 and P6 

• One 24-channel Nicolet odyssey data recorder 

• One BNC breakout box 

• One AFCI-JB—BNC breakout box interface harness 

• Twenty-four 36-inch BNC connector cables 

• One trigger alarm 

The AFCI-JB contained the eight AFCB units. The test unit was mounted in the rear, left side of 

the cockpit. The test unit has bypass switches that disable the AFCBs if desired. The test unit 

was fabricated using standard best practices and in accordance with AC 43.13-1B and contain 

any possible AFCB failure. 

The electrical connections for the system are shown schematically in appendix K. The AFCBs 

mounted within the AFCI-JB were electrically in series with the load side of the existing circuit 

breakers. The AFCI-JB wire harnesses, P-18 and P-6, connect the load side of the each aircraft 

circuit breaker to the line side of the respective AFCB and from the load side of the each AFCB 

to the feed wire for the respective load. 

14
The BNC breakout box and the Odyssey data recorder were mounted in the cabin of the aircraft. 

The AFCI-JB/BNC breakout box interface harness connects the AFCI-JB to the BNC breakout 

box. 

The 24 BNC connectors on the BNC breakout box are connected to the Odyssey data recorder 

with 36-inch BNC coaxial cables. 

Detailed installation instructions are provided in the AFCB Ground Test Checkout Procedures in 

appendix C. 

5.1.4 Certification Requirements. 

There are no FAA technical standard orders for the equipment installed during this modification. 

Experimental flight test was performed to collect data necessary to obtain a one-only STC to 

install the AFCBs aboard N40 for an extended evaluation period. 

5.1.5 Flight Test Profile Requirements. 

N40 was operated in conformance with standard B-727 operations. The purpose of the flight test 

is to maximize the number of flight hours. Duration and distance of flights was at the discretion 

of the pilot in command and within the operating restrictions established by the Manufacturing 

Inspection District Office (MIDO). 

No excessive cycling of the aircraft is necessary. 

As established by the MIDO, flight restrictions were removed to the maximum extent possible 

upon completion of flight hour thresholds established by the MIDO. 

5.1.6 Limitations. 

It was proposed that the first 10 flight hours (phase 1) be conducted within a 50-mile radius from 

Atlantic City International Airport. Upon satisfactory completion of this 10-hour period, it was 

requested that the remainder of the flights be conducted without restrictions (phase 2). 

An ACT-370 Safety Officer was on all phase 1 flights. 

An FAA engineer (or designee) had to be aboard the aircraft during all AFCB flight tests to 

operate the Odyssey data recorder. 

No AFCB-equipped circuit was to be operated in flight after an AFCB trip on the circuit, unless 

the pilot in command orders the operation of the circuit during an emergency. In this case, the 

flight engineer has to switch the associated bypass switch on the AFCI-JB to the bypass position. 

In addition, after an AFCB trip, the flight engineer shall pull the associated circuit breaker on the 

aircraft circuit breaker panel. Troubleshooting shall be performed in accordance with the AFCB 

Troubleshooting Procedures in appendix E. 

15
If there are two or more AFCB trips on a single electrical bus, the flight test shall be terminated 

and the aircraft will return to the base immediately. 

5.1.7 Emergency Procedures. 

In the event of an emergency (related or unrelated to the AFCB testing), the following 

procedures had to be followed if ordered by the pilot in command. 

The flight engineer shall bypass all the AFCBs by closing the AFCB bypass switches on the 

AFCB-JB located behind the captain’s chair. 

• The flight engineer will set each AFCB to the open position. 

• The engineer operating the system will power off the Odyssey data recorder. 

If power must be removed from the AFCB-JB, the following steps will be completed: 

• The flight engineer will open the eight circuit breakers on the aircraft circuit breaker 

panels. A colored button or other tag will uniquely identify these breakers. The eight 

circuit breakers and their respective locations are summarized in table 1. 

TABLE 1. EATON AFCB TEST CIRCUIT BREAKER LOCATIONS

AFCB 

No. Circuit Breaker Identity Panel/Location 

Rating 

(A) Bus 

1 Left Inboard Landing Lights P18-4 Lighting 7 115 Vac Bus No. 1 

2 Navigation Lights P18-4 Lighting 5 115 Vac Bus No. 2 

3 Window Lights P18-3 Lighting and 

Passenger 

Accommodations 

10 115 Vac Transfer Bus 

4 Left Ceiling Lights P18-3 Lighting and 

Passenger 

Accommodations 

15 115 Vac Transfer Bus 

5 DME-2 P18-3 Electronic Load 

Circuit Breaker 

3 115 Vac Radio Bus No. 2 

6 Heater-Pitot-Aux P6-1 Miscellaneous ac, 

Anti-Ice and Rain 

5 115 Vac Bus No. 2 

7 First Officers Window 4 & 5 P6-1 Miscellaneous ac, 

Anti-Ice and Rain 

5 115 Vac Bus No. 3 

8 Project Power Project Power Junction 

Box 

10 115 Vac Bus No. 2 

5.1.8 Normal Procedures. 

5.1.8.1 Preflight. 

• Review flight plan with flight crew and all passengers. 

• Review emergency procedures with flight crew and all passengers. 

16
• Review all normal procedures with flight crew and all passengers. 

• Flight engineer set all bypass switches on the AFCI-JB to normal. 

• Apply power to the aircraft (ground power or APU). 

• Flight engineer open AFCB-1, AFCB-2, AFCB-3, AFCB-4, AFCB-6, and AFCB-7. 

Close AFCB-5 and AFCB-8. 

• Turn Odyssey data recorder to ON and wait for system to boot up and initialize. Start 

recording. Note the date, time, and recording number. 

• Flight engineer close AFCB-1, AFCB-2, AFCB-3, AFCB-4, AFCB-6, and AFCB-7 on 

the AFCI-JB. 

• If on ground power, start APU. Start Odyssey data recording and instruct flight engineer 

to transfer power from ground power to APU power. Stop data recording as soon as 

power transfer is complete. Record the date, time, and file name of the recording in the 

test logbook. Note that the recording was a ground power to APU transfer. 

• If on APU power, start aircraft engines. Start Odyssey data recording and instruct flight 

engineer to transfer power from APU to engine generators. Stop data recording as soon 

as power transfer is complete. Record the date, time, and file name of the recording in 

the test logbook. Note that the recording was an APU to engine generator power transfer. 

• Start the Odyssey data recording. Data will be recorded at the slow rate, 1 kHz. Note the 

date, time, and file name in the test logbook. Also note the general conditions (weather, 

etc.) at this time. 

• Proceed to flight phase in accordance with standard B-727 start-up procedures. 

5.1.8.2 Flight. 

• Monitor Odyssey data recording system. The visual and aural trigger alarm mounted 

adjacent to the Odyssey data recorder will initiate when an AFCB has tripped and the 

Odyssey data recorder will automatically begin recording at the high sampling rate 

(100 kHz). 

• If the trigger alarm sounds, depress the red reset button mounted on the trigger alarm 

enclosure to silence the trigger and extinguish the trigger alarm lights. 

• Stop the data recording and start a new data recording file. 

• Note the date, time, and the number of the AFCB(s) that caused the trigger. Also note the 

flight conditions and other information pertinent to the trigger event in the test logbook. 

Also note the new file name in the logbook with the start time of the recording. 

17
5.1.8.3 Postflight. 

• Continue to follow the flight procedures. 

• Prior to engine shutdown, start APU or apply ground power. Switch aircraft power to 

APU or ground power. Shut engines in accordance with standard B-727 operational 

procedures. 

• Shutdown the Odyssey data recorder. 

• Shutdown aircraft in accordance with standard B-727 operational procedures. 

5.2 EATON DISCREPANCIES.

The Eaton circuit breakers did not experience any nuisance trips during the flight test program. 

There were two AFCB discrepancies. In both cases, the units failed to latch in the closed 

position. These units were sent to Eaton for evaluation. 

5.2.1 Discrepancy 1. 

• Problem Reported: The 10-A AFCB will not latch when the button is in the set position 

and no power is applied to the breaker. 

• Initial Investigation: Discrepancy confirmed. 

• Actions Taken for Investigation: The potting was removed from the calibration screw. 

After backing off the calibration screw, the problem continued. Next, the unit’s potting 

was removed, and the unit was opened, but the problem continued. The electronics were 

then removed from the device. During the inspection of the mechanical side of the 

breaker, a problem was noted. The brazed area that attaches the bimetal to the terminal 

had broken. This caused the bimetal to pull away from its calibrated position preventing 

the unit from latching. 

• Corrective Action: In the brazing process, the bimetal was established by a bend in the 

bimetal foot prior to brazing to the buss bar or the terminal. It was discovered that the 

angle of the bimetal foot to the terminal made it difficult to transfer the heat properly and 

form a complete braze joint. The bimetal angle was modified, allowing the brazing 

fixture to make full contact across the bimetal foot for better heat transfer. The prototype 

flight test units delivered to the FAA were all constructed using the old brazing process. 

All flight test units delivered to the U.S. Navy were constructed using the new brazing 

process. The U.S. Navy units did not experience this problem, indicating a successful 

resolution of the problem. It is also important to note that all the units were prototypes, 

built substantially by hand and not representative of the manufacturing processes that will 

ultimately be used when the units are in full production. 

18
5.2.2 Discrepancy 2. 

• Problem Reported: 7.5-A AFCB failed to latch after an initial trip during the power-up. 

The flight crew removed the trigger wire from its connector to investigate why the unit 

would not stay closed. During their investigation, the flight crew noticed a spark when 

the trigger signal wire touched the grounded portion of the AFCI-JB. After the spark, the 

flight crew measured 115 VRMS on the signal wire and disabled the circuit breaker. 

• Initial Investigation: Discrepancy confirmed. 

• Actions Taken for Investigation: The potting was removed from the calibration screw. 

After backing off the calibration screw, the problem continued. Next, the unit’s potting 

was removed, and the unit was opened, but the problem continued. The electronics were 

then removed from the device. In the inspection of the electronics power board, the 

silicone control rectifier (SCR) had been destroyed, indicating a high in rush of current. 

The coil of the device was still intact, indicating an alternative current path. During the 

inspection of the mechanical side of the breaker, a problem was noted. The brazed area 

that attaches the bimetal to the terminal had broken. This caused the bimetal to pull away 

from its calibrated position, preventing the unit from latching. 

• Corrective Action: The initial cause of the problem was the same as the 10-A AFCB (a 

broken braze on the bimetal). This condition caused the breaker to receive a trip signal 

from the electronics. The trip signal wire touching the airframe provided an unrestricted 

source of current, which damaged the SCR. In production of AFCBs, the trigger signal 

wire will not be present. The FAA AFCI-JB will be redesigned to monitor trip current 

without requiring a trigger signal wire for the AFCB. The proposed method will be to 

monitor current on the ground connection for a large current spike, which would indicate 

the trip coil had been fired. 

The Eaton testing was completed prior to the instrumentation modifications. However, the 

instrumentation changes were completed prior to the Hendry testing. 

5.3 EATON TROUBLESHOOTING PROCEDURES. 

5.3.1 Arc-Fault Troubleshooting Background. 

Although AFCBs can detect arcing on the circuit in which it is installed, it cannot determine the 

location of the arc along the circuit. Furthermore, means for easily troubleshooting an arc fault 

after an AFCB trip are under development but not currently available. This plan has been 

developed to establish a procedure for troubleshooting AFCB trips, should they occur. 

An understanding of current methods of troubleshooting thermal trips will clarify the additional 

measures needed to troubleshoot an AFCB trip and specifically the procedures that will be 

followed during the FAA AFCB flight test program. 

Troubleshooting circuit breakers is an iterative process. Generally, after a thermal circuit 

breaker trip, troubleshooting begins by evaluating the load(s) powered by the circuit. The load is 

19
either tested for correct operation or is removed and replaced if its correct operation cannot be 

directly determined. The circuit is powered, and if no additional trips are noted, the corrective 

action is considered complete. If additional trips of the same circuit occur, there are several 

options for corrective action. The load may still be suspected, and the problem may not be 

reproducible on the ground. The circuit breaker itself may be suspect and replaced (tripping of 

thermal circuit breakers under normal conditions or failure of a circuit breaker to stay closed 

when depressed, are two common circuit breaker failure modes). Usually, the last item to be 

checked is the circuit wiring, mainly because of the inherent difficulties in testing and inspecting 

the wiring. 

AFCBs add another dimension of complexity to the troubleshooting problem. AFCBs have two 

trip modes, thermal (current overload) and arc fault. There are unique procedures for 

troubleshooting each mode, and unfortunately, if one procedure fails to identify the problem, it 

may be necessary to complete the other procedure to be certain that the problem has been 

resolved. Future AFCBs will have the ability to indicate if the trip mode was thermal- or arc 

fault-related. The prototypes flown in this test program will not have this feature. However, the 

data recording instrumentation will be triggered by the AFCBs arc-fault detection circuit and, 

therefore, it will be known with certainty if the trip mode was thermal versus arc fault. 

If the trip mode was arc-fault related, the question remains, Was the arc trip a real arc or was it a 

nuisance trip? The instrumentation being used in these flights will record the current waveforms 

immediately before and after the AFCB indicates that an arc is present and a trip is initiated. 

This data will be analyzed by Eaton to determine if it appears to be a real arc or a nuisance trip. 

If it is certain that the trip was nuisance-related, then the breaker will be reset and flight-testing 

may resume. If a nuisance trip is not certain, then further diagnostics will be required. 

Provisions have been made to baseline the condition of the wiring on the eight circuits that will 

be used in the tests with TDR. During ground testing of the AFCB test system, each AFCBequipped circuit will be characterized with TDR. This data will form a baseline measurement 

against which future measurements will be compared. Changes in the measurement indicate 

possible locations at which the arcing may have occurred. 

At this point, it is unclear if TDR is sensitive enough to detect the damage incurred by a wire 

during an arcing condition. If the TDR fails to identify the location of the fault, visual inspection 

of the circuit must be performed to determine the source of the fault. 

5.3.2 Detailed Troubleshooting Procedures. 

Qualified FAA personnel under the direction of the Electrical Systems Designated Engineering 

Representative, ACT-370, performed all troubleshooting. Upon an AFCB arc-fault trip, the 

Odyssey data recording system will record the current and voltage waveforms from the eight 

circuits equipped with AFCBs. A thermal trip of the AFCB or the aircraft circuit breaker will 

not cause the Odyssey to trigger on and record this data. Therefore, it will be known 

immediately if the trip was caused by an arc fault. 

20
5.3.3 Detailed Process Flow Chart. 

Figure 15 shows a detailed process flow chart for the Eaton AFCB. 

Odyssey Trigger?

(Y/N)

Download 

Odyssey 

Waveform Data

Email Odyssey 

Waveform Data 

to Eaton

Obtain TDR 

Data From 

Tripped Circuit

Email TDR Data 

to CM Tech. For 

Analysis

TDR 

Changed 

from 

baseline?

Nuisance 

Confirmed 

Conduct ground 

tests on circuit 

N

Email TDR Data 

to CM Tech. For 

Analysis

Damage 

location 

discernable?

Locate fault and 

repair 

Conduct ground 

tests on circuit 

Y

Y

Nuisance

Arc Fault

Probable 

arc fault 

or 

nuisance 

trip?

Obtain TDR 

Data From 

Tripped Circuit

Conduct ground 

tests on circuit 

Conduct visual 

inspection of 

circuit wiring

Damage 

location 

discernable?

Locate fault and 

repair

2

N

N Y

Y N

1

Start:Circuit 

Breaker Trip

AFCB 

Trip or 

Aircraft 

CB Trip?

AFCB

1

Aircraft CB

FIGURE 15. EATON DETAILED PROCESS FLOW CHART 

21
1

Troubleshoot and repair IAW 

Standard Operating Procedures for 

thermal circuit breaker trips 

Conduct ground tests on circuit 

Ground 

tests 

check 

ok?

Obtain TDR 

Data From 

Tripped Circuit

Email TDR Data 

to CM Tech. For 

Analysis

TDR 

Changed 

from 

baseline?

Aircraft and 

circuit returned 

to service 

Re-baseline 

circuit TDR 

characterization 

End

N

Damage 

location 

discernable?

Locate fault and 

repair 

Conduct ground 

tests on circuit 

Conduct visual 

inspection of 

circuit wiring

Damage 

location 

discernable?

Locate fault and 

repair

2

N

Conduct ground 

tests on circuit 

Y

Y

FIGURE 15. EATON DETAILED PROCESS FLOW CHART (Continued) 

22
2

Aircraft and 

circuit returned 

to service 

Re-baseline 

circuit TDR 

characterization 

Ground 

tests 

check 

ok?

Y

Replace AFCB 

N

Ground 

tests 

check 

ok?

Repeat 

troubleshooting 

procedure

End

End

Y

N

FIGURE 15. EATON DETAILED PROCESS FLOW CHART (Continued) 

5.4 HENDRY TEST PLAN. 

5.4.1 Introduction. 

This test plan defines the flight test procedures for evaluating the performance of AFCBs in an 

FAA-owned B-727-25C aircraft. The effort was conducted at the FAA William J. Hughes 

Technical Center. 

5.4.2 Objective. 

The objective of this task was to conduct an in-flight evaluation of AFCB performance. 

The FAA William J. Hughes Technical Center R&D Flight Program performed a minor 

modification to their B-727-25C aircraft. This temporary modification involved the installation 

of eight AFCB prototypes manufactured by the Hendry Corporation. The AFCBs were installed 

for a 6-month evaluation period in support of AFCB R&D. 

23
5.4.3 Scope. 

The scope of this effort was to install AFCBs manufactured by the Hendry Corporation in an 

FAA-owned B-727-25C aircraft and conduct a flight evaluation of the developmental AFCBs. 

Data recorded included line voltage, load voltage, and current for each of the installed breakers. 

Data reduction efforts of any occurring arc faults will include identification of relationships 

between the trip conditions. 

5.4.4 Flight Test Goals. 

The following list describes the goals of the experimental flight test program, listed in order of 

importance. 

• Complete 50 or more hours of developmental flight test evaluation but not less than 25 

hours. Data generated during these flights is critical to the AFCB R&D program and for 

obtaining approval of the N40 one-only STC. 

• Evaluate the operation of the AFCBs under standard B-727 operational procedures. 

• Evaluate the operation of the AFCB instrumentation and Odyssey data recording system 

for future unmanned data collection. 

The complete flight records for Hendry flight test are shown in appendix H. 

5.4.5 System Description. 

The equipment installed for the arc-fault flight evaluation included developmental prototype 

AFCBs installed in a junction box, an instrumentation recorder and interconnecting cables, and 

wire harnesses. These items are described in the following sections. 

5.4.5.1 Arc-Fault Circuit Breakers. 

Eight Hendry prototype AFCBs of the following ratings: one 2.5 A, three 5 A, one 7.5 A, one 10 

A, and two 15 A (mounted in the AFCI-JB). 

5.4.5.2 Arc-Fault Circuit Interrupter-Junction Box and Aircraft Harnesses. 

• One AFCI-JB 

• Two AFCI-JB Test Unit wire harnesses, P18 and P6 

5.4.5.3 Instrumentation Equipment. 

• One 24-channel Nicolet Odyssey data recorder 

• One BNC Breakout Box 

• One AFCI-JB BNC breakout box interface harness 

• Twenty-four 24-inch BNC connector cables 

• One Trigger Alarm 

24
5.4.5.4 Aircraft Interfaces. 

The electrical connections for the system are shown schematically in appendix K. The AFCBs 

mounted within the AFCI-JB were electrically in series with the load side of the existing circuit 

breakers. The AFCI-JB wire harnesses, P-18 and P-6, connected the load side of the each 

aircraft circuit breaker to the line side of the respective AFCB and from the load side of the each 

AFCB to the feed wire for the respective load. 

It is important to note that the AFCBs were connected in series with the load side of the existing 

thermal circuit breakers. In other words, current circuit protection aboard the aircraft was not 

compromised in any way by this installation. 

The onboard Project Power Inverter provided 120-Vac, 60-Hz power for the data acquisition 

system. 

5.4.6 Aircraft Installation. 

The AFCBs were installed in an AFCI-JB that enclosed all the AFCBs and required 

instrumentation interfaces. The AFCI-JB was mounted in the rear, left side of the cockpit. The 

test unit had bypass switches that would disable the AFCBs if desired. 

The BNC breakout box and the Odyssey data recorder were mounted in the cabin of the aircraft. 

The electrical installation was completed in accordance with drawing number 9854415 under the 

guidance of the William J. Hughes Technical Center Electrical Systems Designated Engineering 

Representative. 

Detailed instructions for completing the installation can be found in the AFCB Hendry Ground 

Checkout Procedures Report in appendix G. 

5.4.7 Certification Requirements. 

There were no FAA Technical Standard Orders for the equipment being installed during this 

modification. Experimental flight tests were performed to collect data necessary to obtain a oneonly STC to install the AFCBs aboard N40 for an extended evaluation period. 

5.4.8 Flight Test Profile Requirements. 

N40 was operated in conformance with standard B-727 operations. The purpose of the flight test 

was to maximize the number of flight hours. The duration and distance of the flights were at the 

discretion of the pilot in command and within the operating restrictions established by the 

MIDO. The Hendry Flight Test Plan is shown in appendix F. 

No excessive cycling of the aircraft was necessary. 

As established by the MIDO, flight restrictions shall be removed to the maximum extent possible 

upon completion of flight hour thresholds established by the MIDO. 

25
5.4.9 Limitations. 

It was proposed that the first five flight hours (phase 1) be conducted within a 100-mile radius 

from Atlantic City International Airport. Upon satisfactory completion of this 5-hour period, it 

was requested that the remainder of the flights be conducted without restrictions (phase 2). 

An ACT-370 safety officer was on all phase 1 flights. 

An FAA engineer (or designee) had to be aboard the aircraft during all AFCB flight tests to 

operate the Odyssey data recorder. 

No AFCB-equipped circuit was operated in flight after an AFCB trip on the circuit, unless the 

pilot in command ordered the operation of the circuit during an emergency. In this case, the 

flight engineer had to switch the associated bypass switch on the AFCI-JB to the bypass position. 

In addition, after an AFCB trip, the flight engineer had to pull the associated circuit breaker on 

the aircraft circuit breaker panel. Troubleshooting had to be performed in accordance with the 

AFCB Troubleshooting Procedures. 

If there are two or more AFCB trips on a single electrical bus, the flight test was terminated, and 

the aircraft returned to the base immediately. 

5.4.10 Emergency Procedures. 

In the event of an emergency (related or unrelated to the AFCB testing), the following 

procedures had to be followed if ordered by the pilot in command. 

• The flight engineer shall bypass all AFCBs by closing the AFCB bypass switches on the 

AFCI-JB located behind the captain’s chair. 

• The flight engineer will set each AFCB to the open position. 

• The engineer operating the system will power off the Odyssey data recorder. 

If power must be removed from the AFCI-JB, the following steps will be completed: 

• The flight engineer will open the eight circuit breakers on the aircraft circuit breaker 

panels. A colored button or other tag will uniquely identify these breakers. The eight 

circuit breakers and their respective locations are summarized in table 2. 

26
TABLE 2. HENDRY AFCB TEST CIRCUIT BREAKER LOCATIONS 

AFCB 

Circuit 

No. Circuit Breaker Identity Panel/Location 

Rating 

(A) Bus 

1 Left Inboard Landing Lights P18-4 Lighting 7 115 Vac Bus No. 1 

2 Navigation Lights P18-4 Lighting 5 115 Vac Bus No. 2 

3 Window Lights P18-3 Lighting and 

Passenger Accommodations 10 115 Vac Transfer Bus 

4 Left Ceiling Lights P18-3 Lighting and 

Passenger Accommodations 15 115 Vac Transfer Bus 

5 DME-2 P18-3 Electronic Load 

Circuit Breaker 3 115 Vac Radio Bus No. 2 

6 Heater-Pitot-Aux P6-1 Miscellaneous ac, AntiIce and Rain 5 115 Vac Bus No. 2 

7 First Officers Window 4 & 5 P6-1 Miscellaneous ac, AntiIce and Rain 5 115 Vac Bus No. 3 

8 Project Power Project Power Junction Box 10 115 Vac Bus No. 2 

5.4.11 Normal Procedures. 

5.4.11.1 Preflight. 

• Review flight plan with flight crew and all passengers. 

• Review emergency procedures with flight crew and all passengers. 

• Review all normal procedures with flight crew and all passengers. 

• Flight engineer will set all bypass switches on the AFCI-JB to normal except S8 (leave in 

BYPASS) and S1. Leave S1 in BYPASS until landing light is on, and then switch S1 to 

NORMAL. 

• Apply power to the aircraft (ground power or APU). 

• Flight engineer closes all AFCBs. 

• Turn Odyssey data recorder to ON and wait for system to boot up and initialize. Start 

recording. Note the date, time, and recording number. 

• If on ground power, start APU. Start Odyssey data recording and instruct flight engineer 

to transfer power from ground power to APU power. Record the date, time, and file 

name of the recording in the test logbook. Note that the recording was a ground power to 

APU transfer. 

• If on APU power, start aircraft engines. Continue Odyssey data recording and instruct 

flight engineer to transfer power from APU to engine generators. Record the date, time, 

27
and file name of the recording in the test logbook. Note that the recording was an APU 

to engine generator power transfer. 

• Continue the Odyssey data recording. Data will be recorded at the slow rate, 1 kHz. 

Note the date, time, and file name in the test logbook. Also, note the general conditions 

(weather, etc.) at this time. 

• Proceed to flight phase in accordance with standard B-727 start-up procedures. 

5.4.11.2 Flight. 

• Monitor Odyssey data recording system. The visual and aural trigger alarm mounted 

adjacent to the Odyssey data recorder will initiate when an AFCB has tripped and the 

Odyssey data recorder will automatically begin recording at the high sampling rate, 

100 kHz. 

• If the trigger alarm sounds, press the red reset button mounted on the trigger alarm 

enclosure to silence the trigger and extinguish the trigger alarm lights. 

• Note the date, time, and the number of the AFCB(s) that caused the trigger. Also note the 

flight conditions and other information pertinent to the trigger event in the test logbook, 

as well as the new file name with the start time of the recording. 

5.4.11.3 Postflight. 

• Continue to follow the flight procedures. 

• Prior to engine shutdown, start APU or apply ground power. Switch aircraft power to 

APU or ground power. Shut engines in accordance with standard B-727 operational 

procedures. 

• Download data files from the Odyssey data recorder. 

• Shutdown the Odyssey data recorder. 

• Shutdown aircraft in accordance with standard B-727 operational procedures. 

5.5 HENDRY DISCREPANCIES. 

After correction of discrepancies discovered during initial ground integration and debug flight 

test and establishment of a common baseline configuration (amp rating excepted) for all test 

breakers, the Hendry circuit breakers still experienced multiple instrumentation trigger and 

circuit breaker trip occurrences during the flight test program. There were two distinct 

categories of recurring AFCB discrepancies. In both cases, a work around was developed to 

allow the flight test program to continue. Additionally, there were three other trip occurrences 

during the flight test program that could be considered nuisance trips. The corrective actions, 

though labeled undetermined, will be addressed on the follow-on phase of this research project. 

28
5.5.1 Discrepancy 1. 

• Problem Reported: The circuit breakers would provide a false instrumentation trigger 

output during power transfers, indicating a circuit breaker trip when the breaker did not 

trip. 

• Initial Investigation: Confirmed this occurred in the absence of an unusual current 

waveform. Consultation with factory confirmed that the signal was indeed a false 

instrumentation trigger signal and not a missed trip. 

• Corrective Action: Undetermined. Hendry will investigate this at a later date. 

• Work Around Effected: Instrumentation operator would actively monitor the alarm 

during power transfer, reset if activated, confirm that no circuit breaker had tripped, and 

note conditions at time of trigger signal. Continue flight test. 

5.5.2 Discrepancy 2. 

• Problem Reported: Ceiling light 10-A AFCB would occasionally trip during light turn on 

and rapid switch cycling. 

• Action Taken: Discrepancy confirmed. Nonuniform, nonrepetitive high-current 

waveform observed. Note that rapid switch cycling is not a standard procedure. 

• Corrective Action: Undetermined. Hendry to analyze waveforms and determine 

corrective algorithm changes at a later date. 

• Work Around Effected: Continue with flight test noting conditions when trip occurs. 

5.5.3 Discrepancy 3. 

• Problem Reported: Pitot heat 5-A AFCB tripped approximately 30 minutes into flight. 

• Action Taken: In accordance with the test plan, the circuit was put into BYPASS for the 

remainder of the current flight. After the flight, the AFCB trip event was discussed with 

the flight engineer. It was agreed that the trip was an anomaly and that the flight test 

could safely be continued with the AFCB in the circuit. No further trips of this circuit 

breaker occurred. 

• Corrective Action: Undetermined. 

5.5.4 Discrepancy 4. 

• Problem Reported: Window heat 5-A circuit breaker tripped when the mechanic was 

conducting aircraft preflight and bringing the APU on-line. The mechanic was unable to 

reset the breaker until power was removed from the breaker by placing the S1 switch in 

STANDBY. No instrumentation recording was available because of being in the initial 

stages of preflight. 

29
• Action Taken: In accordance with the test plan, the AFCB trip event was discussed with 

the flight engineer. It was agreed that the trip was an anomaly and that the flight test 

could safely be continued with the AFCB in the circuit. No further trips of this circuit 

breaker occurred. 

• Corrective Action: Undetermined. 

5.5.5 Discrepancy 5. 

• Problem Reported: Landing light 7.5-A AFCB tripped during landing light turn-on. The 

problem occurred as the throttles were being advanced at the start of taxi onto runway. 

• Action Taken: After the aircraft was safely in flight, the trip was discussed with the 

flight engineer. There was agreement that this trip occurred under conditions similar to 

those experienced during debug flights at the beginning of the program, and the AFCB 

could be reset without impacting flight safety. 

• Corrective Action: Undetermined. 

5.6 HENDRY TROUBLESHOOTING PROCEDURES. 

5.6.1 Arc-Fault Troubleshooting Background. 

Although AFCBs can detect arcing on the circuit in which it is installed, it cannot determine the 

location of the arc along the circuit. Furthermore, means for easily troubleshooting an arc fault 

after an AFCB trip are under development but not currently available. This plan was developed 

to establish a procedure for troubleshooting AFCB trips, should they occur. 

An understanding of current methods of troubleshooting thermal trips will clarify the additional 

measures needed to troubleshoot an AFCB trip, and specifically, the procedures that will be 

followed during the FAA AFCB flight test program. 

Troubleshooting circuit breakers is an iterative process. Generally, after a thermal circuit 

breaker trip, troubleshooting begins by evaluating the load(s) powered by the circuit. The load is 

either tested for correct operation or is removed and replaced if its correct operation cannot be 

directly determined. The circuit is powered, and if no additional trips are noted, the corrective 

action is considered complete. 

If additional trips of the same circuit occur, there are several options for corrective action. The 

load may still be suspected, but the problem may not be reproducible on the ground. The circuit 

breaker itself may be suspect and replaced (tripping of thermal circuit breakers under normal 

conditions or failure of a circuit breaker to stay closed when depressed, are two common circuit 

breaker failure modes). Usually, the last item to be checked is the circuit wiring, mainly because 

of the inherent difficulties in testing and inspecting the wiring. 

AFCBs add another dimension of complexity to the troubleshooting problem. AFCBs have two 

trip modes, thermal (current overload) and arc fault. There are unique procedures for 

troubleshooting each mode, and unfortunately, if one procedure fails to identify the problem, it 

30
may be necessary to complete the other procedure to be certain that the problem has been 

resolved. Future AFCBs will have the ability to indicate if the trip mode was thermal- or arc 

fault-related. The prototypes flown in this test program will not have this feature. However, the 

data recording instrumentation will be triggered by the AFCBs’ arc-fault detection circuit, and 

therefore, it will be known with certainty if the trip mode was thermal versus arc fault. 

If the trip mode was arc fault-related, the question remains was the arc trip a real arc or was it a 

nuisance trip? The instrumentation being used in these flights will record the current waveforms 

immediately before and after the AFCB indicates that an arc is present and a trip is initiated. 

This data will be analyzed by Hendry Aerospace to determine if it appears to be a real arc or a 

nuisance trip. If it is certain that the trip was nuisance related, then the breaker will be reset and 

flights testing may resume. If a nuisance trip is not certain, then further diagnostics will be 

required. 

Provisions have been made to baseline the condition of the wiring on the eight circuits that will 

be used in the tests with TDR. During ground testing of the AFCB test system, each AFCB 

equipped circuit will be characterized with TDR. This data will form a baseline measurement 

against which future measurements will be compared. Changes in the measurement indicate 

possible locations at which the arcing may have occurred. 

At this point, it is unclear if TDR is sensitive enough to detect the damage incurred by a wire 

during an arcing condition. If the TDR fails to identify the location of the fault, visual inspection 

of the circuit must be performed to determine the source of the fault. 

5.6.2 Detailed Troubleshooting Procedures. 

All troubleshooting shall be performed by qualified FAA personnel under the direction of the 

Electrical Systems Designated Engineering Representative, ACT-370. 

Upon an AFCB arc-fault trip, the Odyssey data recording system will record the current and 

voltage waveforms from the eight circuits equipped with AFCBs. A thermal trip of the AFCB or 

the aircraft circuit breaker will not cause the Odyssey to trigger on and record this data. 

Therefore, it will be known immediately if the trip was caused by an arc fault. The Hendry 

Trouble Shooting Procedures are in appendix I. 

5.6.3 Detailed Process Flow Chart. 

Figure 16 shows the detailed process flow chart of the Hendry AFCB. 

31
Odyssey Trigger?

(Y/N)

Download 

Odyssey 

Waveform Data

Email Odyssey 

Waveform Data 

to Hendry

Obtain TDR 

Data From 

Tripped Circuit

Email TDR Data 

to CM Tech. For 

Analysis

TDR 

Changed 

from 

baseline?

Nuisance 

Confirmed 

Conduct ground 

tests on circuit 

N

Email TDR Data 

to CM Tech. For 

Analysis

Damage 

location 

discernable?

Locate fault and 

repair 

Conduct ground 

tests on circuit 

Y

Y

Nuisance

Arc Fault

Probable 

arc fault 

or 

nuisance 

trip?

Obtain TDR 

Data From 

Tripped Circuit

Conduct ground 

tests on circuit 

Conduct visual 

inspection of 

circuit wiring

Damage 

location 

discernable?

Locate fault and 

repair

2

N

N Y

Y N

1

Start:Circuit 

Breaker Trip

AFCB 

Trip or 

Aircraft 

CB Trip?

AFCB

1

Aircraft CB

FIGURE 16. HENDRY DETAILED PROCESS FLOW CHART 

32
1

Troubleshoot and repair IAW 

Standard Operating Procedures for 

thermal circuit breaker trips 

Conduct ground tests on circuit 

Ground 

tests 

check 

ok?

Obtain TDR 

Data From 

Tripped Circuit

Email TDR Data 

to CM Tech. For 

Analysis

TDR 

Changed 

from 

baseline?

Aircraft and 

circuit returned 

to service 

Re-baseline 

circuit TDR 

characterization 

End

N

Damage 

location 

discernable?

Locate fault and 

repair 

Conduct ground 

tests on circuit 

Conduct visual 

inspection of 

circuit wiring

Damage 

location 

discernable?

Locate fault and 

repair

2

N

Conduct ground 

tests on circuit 

Y

Y

FIGURE 16. HENDRY DETAILED PROCESS FLOW CHART (Continued) 

33
2

Aircraft and 

circuit returned 

to service 

Re-baseline 

circuit TDR 

characterization 

Ground 

tests 

check 

ok?

Y

Replace AFCB 

N

Ground 

tests 

check 

ok?

Repeat 

troubleshooting 

procedure

End

End

Y

N

FIGURE 16. HENDRY DETAILED PROCESS FLOW CHART (Continued) 

5.7 SUMMARY OF TEST RESULTS. 

5.7.1 Eaton Summary. 

Although the desired target of 50 flight test hours was not reached, the goal of at least 25 hours 

was exceeded. The Eaton arc-fault circuit breaker (AFCB) performance was excellent. No 

nuisance trips were encountered. The anomalies encountered were related to one of the 

prototype assembly processes. The process associated with brazing the bimetallic element to the 

AFCB terminal was modified, eliminating the problem. U.S. Navy flight-testing, which lagged 

the Federal Aviation Administration (FAA) testing by several weeks, provided verification that 

corrective action was successful. 

The tests provided convincing evidence that the Eaton AFCBs were highly resistant to nuisance 

tripping when exposed to a diverse set of load conditions and electrical transients. The large 

number and variety of arc-fault tests conducted by Eaton, the U.S. Navy, and the FAA 

previously validated the sensitivity of the Eaton AFCBs to arc detection. The Eaton design 

appears to have successfully balanced arc-fault sensitivity and resistance to nuisance trips. This 

balance is essential for the successful implementation of arc-fault technology into aircraft 

electrical 

34
distribution systems. In addition, the breakers tested were built to an MS14105 package size that 

was much smaller than the MS24571 size specified in the contract. This ensures that the breaker 

will be widely compatible for simple retrofit into the majority of transport aircraft circuit breaker 

installations. 

5.7.2 Hendry Summary. 

There were 88 hours of flight-testing, well in excess of the desired 50-hour target. The Hendry 

AFCB performance was acceptable. Nuisance trips were encountered only during repeatable 

power transfer and equipment turn-on transient conditions. These anomalies could easily be 

worked around during the flight test program. Because of the pace of the program and limited 

aircraft availability, it was not possible to retest with AFCBs containing revised algorithm 

implementation. 

The tests showed that the Hendry AFCBs were highly resistant to nuisance tripping when 

exposed to a diverse set of load conditions and electrical transients. However, the fact that 

tripping did occur during normal operational transients indicated that the algorithms used to 

effect an arc-fault trip and their implementation are not yet mature. The breakers tested were 

built to a package size that was smaller than the MS24571 size specified in the contract. From 

this perspective, the breakers will be compatible for simple retrofit into the majority of transport 

aircraft circuit breaker installations. 

35/36
APPENDIX A—FLIGHT TEST CERTIFICATION PLAN

A-1/A-2
Certification Plan 

For 

Eaton Aerospace Controls 

400Hz/120V Arc Fault Circuit Breakers (AFCB) 

On 

FAA Technical Center 

Boeing 727-25C Aircraft 

N40 

June 2001 

FAA William J. Hughes Technical Center 

Engineering and Modification Section, ACT-370 

Maintenance, Inspection, and Repair Section, AAR-433 

Prepared by: R.A. Pappas 

 J. Beres 

Approved by: Armando Gaetano 

 Manager, Engineering & Modifications Section 

A-3/A-4
1. Introduction 

The Federal Aviation Administration (FAA), William J. Hughes Technical Center R&D 

Flight Program is performing a modification to their Boeing 727-25C aircraft. This 

temporary modification involves the installation of eight arc fault circuit breaker (AFCB) 

prototypes manufactured by Eaton Aerospace Controls. The AFCB’s are to be installed for a 

six-month evaluation period in support of AFCB research and development. 

The AFCB’s will be installed in a pre-furnished Arc Fault Test Unit that will enclose all the 

AFCB’s and required instrumentation. The AFCB’s will not be mounted in the aircraft 

circuit breaker panels. It is important to note that the AFCB’s will be connected in series 

with the load side of the existing thermal circuit breakers. In other words, current circuit 

protection aboard the aircraft will not be compromised in any way by this installation. 

The electrical, system, and mechanical integration of this installation will be accomplished at 

Atlantic City International Airport (ACIAP) using FAA technical and engineering personnel. 

The engineering personnel have been granted authority to approve “electrical systems” and 

“structures” data via FAA Form 8110-3, by the New York Aircraft Certification Office 

(NYACO). The engineering of this installation has been completed and the engineers are 

currently compiling reports to show compliance with applicable Federal Aviation 

Regulations (FAR). All data will be submitted to the NYACO with sufficient time for 

review, prior to flight-testing. 

When the installation of the system is completed, avionics inspectors from the FAA 

Technical Center Repair Station (#MK1R336K) will perform a “conformity inspection” to 

determine that the aircraft complies with the approved electrical drawings. Concurrently, 

ground testing will be completed in accordance with the procedures specified in the Ground 

Checkout Procedures report. 

All data for this installation will be approved via FAA Form 8110-3. Upon completion of 

this modification and appropriate ground checkout procedures, the FAA Technical Center’s 

Certified Repair Station will return the aircraft to service via FAA Form 337. After being 

returned to service, the aircraft must undergo a Flight Check of the system. The Flight Check 

shall be performed in accordance with Flight Checkout Procedures report. This evaluation 

should result in approval of the Airplane Flight Manual Supplement by the New York 

Aircraft Certification Office (NYACO). 

2. Background 

The integration of arc fault detection into circuit breakers represents a revolutionary change 

in circuit protection; which has changed little in the last thirty to forty years. There is 

abundant evidence of arc faults in all types of aircraft. Laboratory data clearly demonstrates 

that the current generated during an arcing fault can be very high, yet quite intermittent. The 

bimetallic elements in thermal breakers do not react quickly enough, if at all, to this ticking 

arc fault condition. If left unchecked, the arcing condition can develop into an arc tracking 

condition, potentially destroying a major portion of, or an entire wire bundle. Arcing can 

also result in many other serious safety hazards. 

A-5
In 1999, the FAA and the Navy established a joint R&D project to develop aircraft AFCB’s. 

The goal of this effort is to develop a circuit breaker that integrates arc fault protection 

together with existing thermal protection into a form, fit, and functional replacement of 

existing thermal circuit breakers. In laboratory testing, the AFCB prototypes have been very 

effective in the detection of arcing faults. 

In contrast to thermal breakers, which are passive in nature, AFCB’s actively monitor the 

circuits on which they are installed. Due to the nature of electrical systems, there are times 

when a normal condition may ‘look’ similar to an arc fault. When such a condition trips an 

arc fault circuit breaker, it is defined as a nuisance trip. AFCB designs minimize the 

occurrence of nuisance tripping and maximize sensitivity to arc fault detection. 

To address nuisance tripping, the FAA, Navy, and the AFCB developers, have conducted 

extensive tests to characterize the normal operation of electrical loads, and perturbations to 

electrical systems during normal events such as bus transfers, power on/off, transfer of power 

sources, etc. Laboratory tests today have provided a high level of confidence that nuisance 

tripping is being successfully controlled. 

The certification request will permit the FAA to temporarily install AFCB’s aboard the 

B727-25C (N40) with the purpose of evaluating the circuit breakers, in-flight, over a sixmonth period. This will assure that the AFCB’s are evaluated against a wide range of actual 

electrical conditions. 

3. System Description 

The AFCB installation will consist of the following: 

a. Eight (8) - Eaton Aerospace Corporation prototype arc fault circuit breakers of the 

following ratings: two 5A, three 7.5A, one 10A, and two 15A. 

b. One (1) - Arc Fault Test Unit enclosure. 

c. Two (2) – Arc Fault Test Unit Interface wire harnesses. 

d. One (1) - 16 channel Nicolet Odyssey data recorder (or similar) 

e. Eight (8) - AC Voltage probes (100X), Line-to-ground, 115 volt, 1 MHz. 

f. Eight (8) - AC Current Transformers (CT), either 100:5 amps or 50:5 amps. 

The Arc Fault Test Unit will contain the eight AFCB units, the voltage probes, and the 

current transformers. The test unit will be mounted in the rear, left side of the flight deck. 

The test unit will have by-pass switches that will disable the AFCB’s if desired. The test unit 

will be fabricated using standard best practices and in accordance with AC 43.13-1B and 

contain any possible AFCB failure. Attachment (1) contains a general description of the Arc 

Fault Test Unit developed by Boeing for AFCB flight-testing. The FAA AFTU will be 

equivalent to this unit except that it will contain eight AFCB’s rather than six. 

The AFCB’s will be located inside the Arc Fault Test Unit and will be connected in series 

with the load side of the existing circuit breakers. A wire harness will be provided to connect 

the instrumentation to the project rack mounted data recorder located in the cabin. Current 

levels of safety provided by the existing circuit breakers will not be diminished in any way. 

A-6
4. Certification Requirements 

All aspects of this modification will be in accordance with FAR Part 25, Airworthiness 

Standards: Transport Category Airplanes. The Issue Paper dated 4/6/01, for AFCB 

Installation provides alternative means of compliance where this equipment installation 

cannot meet the regulations. 

There are no FAA Technical Standard Orders for the equipment being installed during this 

modification. This modification is being performed to support AFCB research and 

development, and will be temporary, not to exceed six months. 

5. Method of Compliance 

Several methods will be used to determine compliance with FAR Part 25 during this 

modification. While each item in the Preliminary Compliance Checklist, Table 1, will be 

discussed at length in the appropriate report, the following paragraphs provide samples of the 

methods that will be used. 

a. Analyses 

 Items such as a determination of the electrical load and factor of safety for equipment 

mounting trays will be proven by analysis. (Refer to Electrical System Substantiation and 

Mechanical Structures Substantiation reports.) 

b. Test 

 Equipment checkout procedures will be available to conduct these tests. (Refer to 

proposed Ground and Flight Evaluation Procedures.) 

c. Software Compliance 

Not applicable. 

d. Design 

The installation was designed so the position of each piece of equipment is located in a 

suitable location. Electrical equipment is installed in compliance with conventional B727 

electrical distribution and load shedding practices. (Refer to Electrical System Substantiation 

and Mechanical Structures Substantiation reports.) 

6. Functional Hazard Assessment Summary 

The AFCB is designed to the highest levels of safety and is not a risk to the aircraft. A 

Systems Safety Analysis will be produced in accordance with AC 25.1309-1A. 

7. Operational Considerations 

The AFCB provides a greater level of electrical circuit protection than the thermal breakers 

currently installed. However, AFCBs may occasionally be unnecessarily tripped by a normal 

load start-up or electrical transient. If such a nuisance trip occurs, the circuit will not be 

reset, and appropriate troubleshooting will take place when the aircraft returns to the FAA 

Technical Center. At anytime during a flight, each AFCB can be removed from the circuit 

by simply throwing a toggle switch mounted on the Arc Fault Test Unit. 

A-7
During this period of installation, the AFCB’s will only be installed on non-critical circuits. 

No arc testing will be performed on the aircraft. This testing is to evaluate nuisance tripping 

only. 

The airplane flight manual and operating procedures shall be appropriately supplemented. 

8. Certification Documentation 

Compliance with applicable regulations will be documented on FAA Form 8110-3. The 

aircraft will be returned to service via Form 337. The Flight Manual Supplement will be 

approved by the NYACO upon successful completion of flight-testing. 

9. Schedule 

The B727 will be modified in accordance with the following schedule. 

 

13 July 2001 Modification Complete 

16 July 2001 Begin ground checkout (Conformity inspection) 

20 July 2001 All reports to NYACO 

09 July 2001 Begin experimental flight test program 

27 July 2001 Complete experimental flight test program 

25 July 2001 NYACO Safety Review Board 

27 July 2001 Flight test with NYACO 

01 August 2001 Ground checks and inspections complete. Aircraft returned to 

service. 

Changes to the schedule will be promptly reported to the NYACO. 

10. Use of Designees 

The following FAA Technical Center Employees have authorization to approve data via 

FAA Form 8110-3. This authorization has been granted by the NYACO. 

Armando Gaetano Structures 

Tim Hogan Structures 

John Beres Electrical Systems 

A-8
Table 1 - Preliminary

FAR Part 25 Compliance Checklist 

FAA Technical Center B-727 (N40) 

Arc Fault Circuit Breaker Installation 

Title Method Documentation Reference FAR 

Part 25 Subpart C - Structure 25.301 Loads Limit and ultimate loads Mechanical Substantiation 

Report 

25.303 Factor of Safety FOS applied to limit loads. " 25.305 Strength and Deformation Components have adequate strength " 25.307 Proof of Structure Strength and deformation required by 25.305 met " 25.561 Emergency Landing Conditions Applied to equipment on the flight deck " Part 25 Subpart D – Design and Construction 25.601 Design and Construction/General Installation IAW manufacturer and AC 43.13-1B Mechanical Substantiation 

Report 

25.603 Materials 2024-T3 Aluminum/MIL-HDBK-5F chart " 25.605 Fabrication Methods Installation IAW manufacturer and AC 43.13-1B " 25.607 Fasteners None subject to rotation " 25.609 Protection of Structure Protected from deterioration, corrosion, etc. " A-925.611 Accessibility Provisions Means provided to allow inspections " 25.613 Material Strength Properties and Design 

Values 

IAW MIL-HDBK-5F " 

Part 25 Subpart F - Equipment 25.1301 Function and Installation MIL-C-5809-Circuit Breakers, Trip Free, Aircraft; MIL-PRF83383-CIRCUIT BREAKERS, REMOTE CONTROL, 

THERMAL, TRIP FREE GENERAL SPECIFICATION FOR; SAE Draft Spec-Arc Fault Circuit Breakers, Trip Free, Aircraft; 

Signal Compatibility and Electrical Substantiation Report 

Manufacturers Environmental Test Data; AFCB Installation Issue Paper. 

25.1307 Miscellaneous Equipment Circuit breakers are installed in series with the load side of 

existing aircraft breakers. 

" 

25.1309 Equipment Systems and Installation Built to environmental specifications for standard (thermal) 

circuit breakers, MIL-C-5809, and Remote Control Circuit Breakers (RCCB), MIL-PRF-83383 and AFCB Installation Issue Paper. 

" 

25.1316 System Lighting Protection Meet lightning testing per DO-160C, Section 22.0 " 25.1351 Electrical Systems and Equipment/General Accessible means to disconnect electrical power by crew " 
Title Method Documentation Reference FAR 

members 

25.1353 Electrical Equipment and Installations Using best practices for electrical equipment and installations. " 25.1357 Circuit Protective Devices Existing thermal type, re-settable, trip-free circuit breakers in 

series with AFCB breakers under test. AFCB Installation Issue Paper. 

" 

25.1363 Electrical System Tests Components built and tested to meet applicable aircraft 

environmental conditions. 

" 

25.1431 Electronic Equipment Electronic equipment operation is not affected by this 

installation. 

" 

Part 25 Subpart G – Operating Limitations and Information 25.1541 Markings and Placards/General New equipment/breakers identifiable in manner visible to 

crew. 

Draft Flight Manual Supplement 

25.1581 Airplane Flight Manual/General Draft flight manual supplement. " 25.1585 Operating Procedures Draft flight manual supplement. " 

A-10
N-40 Arc Fault Circuit Breaker Installation 

Report Listing 

Report 

Document Number Contents Status 

Certification Plan E01-02 Reference: AC 21-40, § 2-2.b 

System Description E01-03 Basic description of AFCB 

system as installed in N-40. 

Mechanical Substantiation Report E01-04 Structural load analysis of 

installed AFCB components, 

applicable drawings, and FAR 

compliance discussion. 

Signal Compatibility and 

Electrical Substantiation 

E01-05 Signal compatibility, wiring 

diagrams, and FAR 

compliance discussion 

System Safety Assessment E01-06 System Safety Analysis as per 

AC 25.1309-1A 

Environmental Test Plan E01-07 Testing IAW DO-160 or 

equivalent 

Updated Compliance Checklist E01-08 Applicable FAR's and Method 

of Compliance 

Ground Checkout Procedures E01-09 

Flight Checkout Procedures E01-10 

Flight Test Procedures E01-11 

AFCB Troubleshooting 

Procedures 

E01-12 Provides instructions for 

investigating the source of any 

AFCB trip prior to 

reenergizing the circuit. 

Flight Manual Supplement E01-13 Provides relevant information 

to flight crew on AFCB 

operation. 

A-11/A-12
APPENDIX B—EATON FLIGHT TEST PLAN

B-1/B-2
Flight Test Plan 

For 

Eaton Aerospace Controls 

400Hz/120V Arc Fault Circuit Breakers (AFCB) 

On 

FAA Technical Center 

Boeing 727-25C Aircraft N40 

July 2001 

FAA William J. Hughes Technical Center 

Engineering and Modification Section, ACT-370 

Maintenance, Inspection, and Repair Section, AAR-433 

Prepared by: R.A. Pappas 

Reviewed by: J. Beres 

Approved by: Armando Gaetano 

 Manager, Engineering & Modifications Section 

B-3/B-4
1. Introduction 

The Federal Aviation Administration (FAA), William J. Hughes Technical Center R&D 

Flight Program is performing a minormodification to their Boeing 727-25C aircraft. This 

temporary modification involves the installation of eight arc fault circuit breaker (AFCB) 

prototypes manufactured by Eaton Aerospace Controls. The AFCB’s are to be installed for a 

two-week experimental flight test period in support of AFCB research and development. 

The AFCB’s will be installed in an Arc Fault Circuit Interrupter-Junction Box (AFCI-JB) 

that will enclose all the AFCB’s and required instrumentation. The AFCB’s will not be 

mounted in the aircraft circuit breaker panels. It is important to note that the AFCB’s will be 

connected in series with the load side of the existing thermal circuit breakers. In other words, 

current circuit protection aboard the aircraft will not be compromised in any way by this 

installation. 

The electrical, system, and mechanical integration of this installation will be accomplished at 

Atlantic City International Airport (ACIAP) using FAA technical and engineering personnel. 

The engineering personnel have been granted authority to approve “electrical systems” and 

“structures” data via FAA Form 8110-3, by the New York Aircraft Certification Office 

(NYACO). The engineering of this installation has been completed and the engineers are 

currently compiling reports to show compliance with applicable Federal Aviation 

Regulations (FAR). 

This flight test plan describes the purpose of the test, the objectives of the flight tests, and the 

flight test profiles to be flown during the test period. 

2. Background 

The integration of arc fault detection into circuit breakers represents a revolutionary change 

in circuit protection; which has changed little in the last thirty to forty years. There is 

abundant evidence of arc faults in all types of aircraft. Laboratory data clearly demonstrates 

that the current generated during an arcing fault can be very high, yet quite intermittent. The 

bimetallic elements in thermal breakers do not react quickly enough, if at all, to this ticking 

arc fault condition. If left unchecked, the arcing condition can develop into an arc tracking 

condition, potentially destroying a major portion of, or an entire wire bundle. Arcing can 

also result in many other serious safety hazards. 

In 1999, the FAA and the Navy established a joint R&D project to develop aircraft AFCB’s. 

The goal of this effort is to develop a circuit breaker that integrates arc fault protection 

together with existing thermal protection into a form, fit, and functional replacement of 

existing thermal circuit breakers. In laboratory testing, the AFCB prototypes have been very 

effective in the detection of arcing faults. 

In contrast to thermal breakers, which are passive in nature, AFCB’s actively monitor the 

circuits on which they are installed. Due to the nature of electrical systems, there are times 

when a normal condition may ‘look’ similar to an arc fault. When such a condition trips an 

arc fault circuit breaker, it is defined as a nuisance trip. AFCB designs minimize the 

occurrence of nuisance tripping and maximize sensitivity to arc fault detection. 

B-5
To address nuisance tripping, the FAA, Navy, and the AFCB developers, have conducted 

extensive tests to characterize the normal operation of electrical loads, and perturbations to 

electrical systems during normal events such as bus transfers, power on/off, transfer of power 

sources, etc. Laboratory tests today have provided a high level of confidence that nuisance 

tripping is being successfully controlled. 

AFCB flight-testing is necessary to be certain that nuisance tripping has been controlled in 

the AFCB design. The purpose of the experimental flight test period is to monitor the 

performance of the AFCBs and provide this data to the NYACO in support of a one only 

STC. The STC will permit the FAA to install AFCB’s aboard the B727-25C (N40) for the 

purpose of evaluating the circuit breakers, in-flight, over a six-month period. This will 

assure that the AFCB’s are evaluated against a wide range of actual electrical conditions. 

It is important to note that no arc faults will be created in the aircraft. The purpose of the 

flight testing is to evaluate nuisance tripping only. Arcing will not intentionally be created 

aboard the aircraft in flight or on the ground. 

3. Flight Test Goals 

The following list describes the goals of the experimental flight test program, listed in order 

of importance. 

 Complete at least 50 (or more) flight hours but not less than 25 hours. Data generated 

during these flights is critical to the AFCB research and development program and for 

obtaining approval of the N-40 one-only STC. 

 Evaluate the operation of the arc fault circuit breakers under standard B727 

operational procedures. 

 Evaluate the operation of the AFCB instrumentation and Odyssey data recording 

system for future unmanned data collection. 

4. System Description 

The AFCB installation will consist of the following: 

a. Eight (8) - Eaton Aerospace Corporation prototype arc fault circuit breakers of the 

following ratings: two 5A, three 7.5A, one 10A, and two 15A (Mounted in AFCI 

Junction Box). 

b. One (1) – AFCI-JB. 

c. Two (2) – AFCI-JB Test Unit wire harnesses, P18 and P6. 

d. One (1) - 24 channel Nicolet Odyssey data recorder. 

e. One (1) – BNC Breakout Box. 

f. One (1) – AFCI Junction Box – BNC Breakout Box Interface Harness. 

g. Twenty-four (24) – 36-inch BNC connector cables. 

h. One (1) – Trigger Alarm 

B-6
The AFCI-JB will contain the eight AFCB units. The test unit will be mounted in the rear, 

left side of the cockpit. The test unit will have by-pass switches that will disable the AFCB’s 

if desired. The test unit will be fabricated using standard best practices and in accordance 

with AC 43.13-1B and contain any possible AFCB failure. 

The electrical connections for the system are shown schematically in FAA Drawing Number 

9854415, Arc Fault Circuit Breaker Wiring. The AFCB’s mounted within the AFCI-JB will 

be electrically in series with the load side of the existing circuit breakers. The AFCI-JB wire 

harnesses, P-18 and P-6, connect the load side of the each aircraft circuit breaker to the line 

side of the respective AFCB and from the load side of the each AFCB to the feed wire for the 

respective load. 

The BNC Breakout Box and the Odyssey data recorder will be mounted in the cabin of the 

aircraft. The AFCI-JB/BNC Breakout Box Interface Harness connects the AFCI-JB to the 

BNC Breakout Box. 

The 24 BNC connectors on the BNC Breakout Box are connected to the Odyssey data 

recorder with 36” BNC coaxial cables. 

Detailed installation instructions are provided the AFCB Ground Test Checkout report. 

4. Certification Requirements 

There are no FAA Technical Standard Orders for the equipment being installed during this 

modification. Experimental flight test is being performed to collect data necessary to obtain 

a one only STC to install the AFCB’s aboard N40 for an extended evaluation period. 

5. Flight Test Profile Requirements 

N40 will be operated in conformance with Standard B727 Operations. The purpose of the 

flight test is to maximize the number of flight hours. Duration and distance of flights will be 

at the discretion of the pilot in command and within the operating restrictions established by 

the MIDO. 

No excessive cycling of the aircraft is necessary. 

As established by the MIDO, flight restrictions shall be removed to the maximum extent 

possible upon completion of flight hour thresholds established by the MIDO. 

If possible, the aircraft will fly to Sarasota, Florida to permit Eaton Aerospace Corporation 

engineers an opportunity to assess the AFCB installation aboard the aircraft. A flight to 

Atlanta, Georgia will also be conducted, if possible, to permit Atlanta ACO engineers to 

observe the installation. 

6. Limitations 

It is proposed that the first 10 flight hours (Phase 1) be conducted within a 50-mile radius 

from Atlantic City International Airport. Upon satisfactory completion of this 10-hour 

period, it is requested that the remainder of the flights be conducted without restrictions 

(Phase 2). 

An ACT-370 Safety Officer will be on all Phase 1 flights. 

An AAR-430 engineer (or designee) must be aboard the aircraft during all AFCB flight tests 

to operate the Odyssey data recorder. 

B-7
No AFCB equipped circuit shall be operated in-flight after an AFCB trip on the circuit, 

unless the pilot in command orders the operation of the circuit during an emergency. In this 

case, the flight engineer shall switch the associated by-pass switch on the AFCI-JB to the 

bypass position. In addition, after an AFCB trip, the Flight Engineer shall pull the associated 

circuit breaker on the aircraft circuit breaker panel. Troubleshooting shall be performed in 

accordance with the AFCB Troubleshooting Procedures. 

If there are two or more AFCB trips on a single electrical bus, the flight test shall be 

terminated and the aircraft will return to base immediately. 

Limitations established by the MIDO shall be adhered to. 

7. Emergency Procedures 

In the event of an emergency (related or unrelated to the AFCB testing), the following 

procedures will be followed if order by the pilot in command. 

The flight engineer shall by-pass all the AFCB’s by closing the AFCB by-pass switches on 

the AFCB-JB located behind the Captains chair. 

 The flight engineer will set each AFCB to the open position. 

 The Odyssey data recorder will be powered off by the engineer operating the system. 

If power must be removed from the AFCB-JB the following steps will be completed: 

 The flight engineer will open the eight circuit breakers on the aircraft circuit breaker 

panels. These breakers will be uniquely identified by a colored button or other tag. 

The eight circuit breakers and their respective locations are summarized in Table 1 

below. 

B-8
AFCB 

# CB Identity Panel/Location Rating (Amps) Bus 

1 Left Inboard Landing Lights P18-4 Lighting 7 115VAC Bus No. 1 

2 Navigation Lights P18-4 Lighting 5 115VAC Bus No. 2 

3 Window Lights 

P18-3 Lighting and 

Passenger 

Accommodations 

10 115VAC Transfer 

Bus 

4 Left Ceiling Lights 

P18-3 Lighting and 

Passenger 

Accommodations 

15 115VAC Transfer 

Bus 

5 DME-2 P18-3 Electronic Load 

Circuit Breaker 3 115VAC Radio Bus No. 2 

6 Heater-Pitot-Aux P6-1 Miscellaneous AC, 

Anti-Ice & Rain 5 115VAC Bus No. 2 

7 First Officers Window 4 & 5 P6-1 Miscellaneous AC, 

Anti-Ice & Rain 5 115 VAC Bus No. 3 

8 Project Power Project Power Junction 

Box 10 115VAC Bus No. 2 

Table 1 

8. Normal Procedures 

a. Preflight 

 Review flight plan with flight crew and all passengers. 

 Review emergency procedures with flight crew and all passengers. 

 Review all normal procedures with flight crew and all passengers. 

 Flight engineer set all bypass switches on the AFCI-JB to normal. 

 Apply power to the aircraft (Ground power or APU). 

 Flight engineer open AFCB-1, AFCB-2, AFCB-3, AFCB-4, AFCB-6, and AFCB-7. 

Close AFCB-5 and AFCB-8. 

 Turn Odyssey data recorder to ON and wait for system to boot up and initialize. 

Start recording. Note the date, time, and recording number. 

 Flight engineer close AFCB-1, AFCB-2, AFCB-3, AFCB-4, AFCB-6, and AFCB7, on the AFCI-JB. 

 If on ground power, start APU. Start Odyssey data recording and instruct flight 

engineer to transfer power from ground power to APU power. Stop data recording 

as soon as power transfer is complete. Record the date, time, and filename of the 

recording in the test logbook. Note that the recording was a ground power to APU 

transfer. 

 If on APU power, start aircraft engines. Start Odyssey data recording and instruct 

flight engineer to transfer power from APU to engine generators. Stop data 

recording as soon as power transfer is complete. Record the date, time, and 

B-9
filename of the recording in the test logbook. Note that the recording was an APU 

to engine generator power transfer. 

 Start the Odyssey data recording. Data will be recorded at the slow rate, 1kHz. 

Note the date, time, and filename in the test logbook. Also note the general 

conditions (weather, etc.) at this time. 

 Proceed to flight phase in accordance with standard B727 start-up procedures. 

b. Flight 

 Monitor Odyssey data recording system. The visual and aural trigger alarm 

mounted adjacent to the Odyssey data recorder will initiate when an AFCB has 

tripped and the Odyssey data recorder will automatically begin recording at the high 

sampling rate, 100kHz. 

 If the trigger-alarm sounds, depress the red reset button mounted on the trigger 

alarm enclosure to silence the trigger and extinguish the trigger alarm lights. 

 Stop the data recording and start a new data recording file. 

 Note the date, time, and the number of the AFCB(s) that caused the trigger. Also 

note the flight conditions and other information pertinent to the trigger event in the 

test logbook. Also note the new file name in the logbook with the start time of the 

recording. 

c. Postflight 

 Continue to follow the flight procedures. 

 Prior to engine shutdown, start APU or apply ground power. Switch aircraft 

power to APU or ground power. Shut engines in accordance with standard B727 

operational procedures. 

 Shutdown the Odyssey data recorder. 

 Shutdown aircraft in accordance with standard B727 operational procedures. 

End of flight test procedures.

B-10
APPENDIX C—EATON GROUND CHECKOUT PROCEDURES

C-1/C-2
Ground Test Checkout 

For 

Eaton Aerospace Controls 

400Hz/120V Arc Fault Circuit Breakers (AFCB) 

On 

FAA Technical Center 

Boeing 727-25C Aircraft N40 

July 2001 

FAA William J. Hughes Technical Center 

Engineering and Modification Section, ACT-370 

Maintenance, Inspection, and Repair Section, AAR-433 

Prepared by: R.A. Pappas, AAR-433 

Reviewed by: J. Beres, ACT-370 

Approved by: Armando Gaetano 

Manager, Engineering & Modifications Section, ACT-370 

C-3/C-4
1. Introduction 

The Federal Aviation Administration (FAA), William J. Hughes Technical Center (WJHTC) 

R&D Flight Program is performing a minor modification to their Boeing 727-25C aircraft. 

This temporary modification involves the installation of eight arc fault circuit breaker 

(AFCB) prototypes manufactured by Eaton Aerospace Controls. The AFCB’s are to be 

installed for a six-month evaluation period in support of AFCB research and development. 

The AFCB’s will be installed in a pre-furnished Arc Fault Circuit Interrupter-Junction Box 

(AFCI-JB) that will enclose all the AFCB’s and required instrumentation. The AFCB’s will 

not be mounted in the aircraft circuit breaker panels. It is important to note that the AFCB’s 

will be connected in series with the load side of the existing thermal circuit breakers. In 

other words, current circuit protection aboard the aircraft will not be compromised in any 

way by this installation. 

The electrical, system, and mechanical integration of this installation will be accomplished at 

Atlantic City International Airport (ACIAP) using FAA technical and engineering personnel. 

The engineering personnel have been granted authority to approve “electrical systems” and 

“structures” data via FAA Form 8110-3, by the New York Aircraft Certification Office 

(NYACO). The engineering of this installation has been completed and the engineers are 

currently compiling reports to show compliance with applicable Federal Aviation 

Regulations (FAR). 

This report describes the ground checkout procedures to be conducted prior to commencing 

flight test. All steps in this procedure shall be successfully completed. 

2. Background 

The integration of arc fault detection into circuit breakers represents a revolutionary change 

in circuit protection; which has changed little in the last thirty to forty years. There is 

abundant evidence of arc faults in all types of aircraft. Laboratory data clearly demonstrates 

that the current generated during an arcing fault can be very high, yet quite intermittent. The 

bimetallic elements in thermal breakers do not react quickly enough, if at all, to this ticking 

arc fault condition. If left unchecked, the arcing condition can develop into an arc tracking 

condition, potentially destroying a major portion of, or an entire wire bundle. Arcing can 

also result in many other serious safety hazards. 

In 1999, the FAA and the Navy established a joint R&D project to develop aircraft AFCB’s. 

The goal of this effort is to develop a circuit breaker that integrates arc fault protection 

together with existing thermal protection into a form, fit, and functional replacement of 

existing thermal circuit breakers. In laboratory testing, the AFCB prototypes have been very 

effective in the detection of arcing faults. 

In contrast to thermal breakers, which are passive in nature, AFCB’s actively monitor the 

circuits on which they are installed. Due to the nature of electrical systems, there are times 

when a normal condition may ‘look’ similar to an arc fault. When such a condition trips an 

arc fault circuit breaker, it is defined as a nuisance trip. AFCB designs minimize the 

occurrence of nuisance tripping and maximize sensitivity to arc fault detection. 

C-5
To address nuisance tripping, the FAA, Navy, and the AFCB developers, have conducted 

extensive tests to characterize the normal operation of electrical loads, and perturbations to 

electrical systems during normal events such as bus transfers, power on/off, transfer of power 

sources, etc. Laboratory tests today have provided a high level of confidence that nuisance 

tripping is being successfully controlled. 

The certification request will permit the FAA to temporarily install AFCB’s aboard the 

B727-25C (N40) with the purpose of evaluating the circuit breakers, in-flight, over a sixmonth period. This will assure that the AFCB’s are evaluated against a wide range of actual 

electrical conditions. 

3. System Description 

The AFCB installation will consist of the following: 

a. Eight (8) - Eaton Aerospace Corporation prototype arc fault circuit breakers of the 

following ratings: one 2.5 A, three 5A, one 7.5A, one 10A, and two 15A (Mounted in 

AFCI Junction Box). 

b. One (1) – AFCI-JB. 

c. Two (2) – AFCI-JB Test Unit wire harnesses, P18 and P6. 

d. One (1) - 24 channel, Nicolet Odyssey data recorder. 

e. One (1) – BNC Breakout Box. 

f. One (1) – AFCI Junction Box – BNC Breakout Box Interface Harness. 

 Twenty-four (24) – 36-inch BNC connector cables. 

g. One (1) – Trigger Alarm 

The AFCI Junction Box (AFCI-JB) will contain the eight AFCB units. The test unit will 

be mounted in the rear, left side of the cockpit. The test unit will have by-pass switches 

that will disable the AFCB’s if desired. The test unit will be fabricated using standard 

best practices and in accordance with AC 43.13-1B and contain any possible AFCB 

failure. 

The electrical connections for the system are shown schematically in FAA Drawing Number 

9854415, Arc Fault Circuit Breaker Wiring. The AFCB’s mounted within the AFCI-JB will 

be electrically in series with the load side of the existing circuit breakers. The AFCI-JB wire 

harnesses, P-18 and P-6, connect the load side of the each aircraft circuit breaker to the line 

side of the respective AFCB and from the load side of the each AFCB to the feed wire for the 

respective load. 

The BNC Breakout Box and the Odyssey data recorder will be mounted in the cabin of the 

aircraft. The AFCI-JB/BNC Breakout Box Interface Harness connects the AFCI-JB to the 

BNC Breakout Box. 

The 24 BNC connectors on the BNC Breakout Box are connected to the Odyssey data 

recorder with 36” BNC coaxial cables. 

Detailed installation instructions are provided in Section 4. 

C-6
4. Certification Requirements 

There are no FAA Technical Standard Orders for the equipment being installed during 

this modification. Experimental flight test is being performed to collect data necessary to 

obtain a one only STC to install the AFCB’s aboard N40 for an extended evaluation 

period. 

5. Installation of AFCB Test System On N40 

The electrical installation shall be completed in accordance with drawing number 

9854415 under the guidance of the WJHTC Electrical Systems Designated Engineering 

Representative (DER), Code ACT-370. The mechanical installation shall be completed 

under the guidance of the WJHTC Mechanical Systems DER, Code ACT-370. 

The following list contains general instructions for completing the installation. The 

installation shall be completed in accordance with all existing safety requirements and the 

necessary approvals shall be obtained in advance of starting the installation. 

 The two AFCI-JB Interface wire harnesses, P-18 and P-6, shall be connected to 

the thermal circuit breakers in accordance with FAA Drawing number 9854415. 

Harness P-18 shall be connected to the: 

 Left Inboard Landing Lights (7.5A) 

 Navigation Lights (5A) 

 Window Lights (10A) 

 Left Ceiling Lights (15A) 

Harness P-6 shall be connected to the: 

 DME-2 (3A) 

 Auxiliary Pitot Heat (5A) 

 First Officers Window (5A) 

 AC Project Power (15A) 

 Mount the AFCI-JB in the flight deck as per the Mechanical Systems DER 

instructions. 

 Mount the Odyssey and the BNC Breakout Box in the cabin rack per the 

Mechanical Systems DER instructions. 

 Insure that all mounting is secure. 

 Route the AFCI-JB harnesses and the AFCI-JB/Breakout Box harness. Do not 

mate the harnesses to the AFCI-JB or the breakout box until electrical tests have 

been completed. Do not secure the harness until electrical tests have been 

completed. 

C-7
6. Ground Checkout Procedures 

Part A: Conduct AFCB Electrical Tests

 Confirm that the P-18 and P-6 harnesses from the aircraft circuit breaker panels to 

P1 and P2 on the AFCI-JB are disconnected from the AFCI-JB. 

 Prior to connecting the harnesses to the AFCI-JB, perform the following 

continuity and isolation checks performed in accordance with Table 1. 

AFCI-JB 

Connector 

Test Points 

AFCB-x Position 

(Open/Closed) 

(x =1,2,3,4,5,6,7,8)

AFCB By-Pass Switch 

S-x (Open/Closed) 

(x = 1,2,3,4,5,6,7,8) 

Observed 

Condition 

P1, 1 and 2 AFCB-1, Closed S-1, Open Short 

P1, 4 and 5 AFCB-2, Closed S-2, Open Short 

P1, 7 and 8 AFCB-3, Closed S-3, Open Short 

P1, 10 and 11 AFCB-4, Closed S-4, Open Short 

P2, 1 and 2 AFCB-5, Closed S-5, Open Short 

P2, 4 and 5 AFCB-6, Closed S-6, Open Short 

P2, 7 and 8 AFCB-7, Closed S-7, Open Short 

P2, 10 and 11 AFCB-8, Closed S-8, Open Short 

P1, 1 and 2 AFCB-1, Open S-1, Open Open 

P1, 4 and 5 AFCB-2, Open S-2, Open Open 

P1, 7 and 8 AFCB-3, Open S-3, Open Open 

P1, 10 and 11 AFCB-4, Open S-4, Open Open 

P2, 1 and 2 AFCB-5, Open S-5, Open Open 

P2, 4 and 5 AFCB-6, Open S-6, Open Open 

P2, 7 and 8 AFCB-7, Open S-7, Open Open 

P2, 10 and 11 AFCB-8, Open S-8, Open Open 

P1, 1 and 2 AFCB-1, Open S-1, Closed Short 

P1, 4 and 5 AFCB-2, Open S-2, Closed Short 

P1, 7 and 8 AFCB-3, Open S-3, Closed Short 

P1, 10 and 11 AFCB-4, Open S-4, Closed Short 

P2, 1 and 2 AFCB-5, Open S-5, Closed Short 

P2, 4 and 5 AFCB-6, Open S-6, Closed Short 

P2, 7 and 8 AFCB-7, Open S-7, Closed Short 

P2, 10 and 11 AFCB-8, Open S-8, Closed Short 

AFCB-1, Red & Black Banana Plug Sockets AFCB-1, Closed S-1, Open Short 

AFCB-2, Red & Black Banana Plug Sockets AFCB-2, Closed S-2, Open Short 

AFCB-3, Red & Black Banana Plug Sockets AFCB-3, Closed S-3, Open Short 

AFCB-4, Red & Black Banana Plug Sockets AFCB-4, Closed S-4, Open Short 

C-8
AFCB-5, Red & Black Banana Plug Sockets AFCB-5, Closed S-5, Open Short 

AFCB-6, Red & Black Banana Plug Sockets AFCB-6, Closed S-6, Open Short 

AFCB-7, Red & Black Banana Plug Sockets AFCB-7, Closed S-7, Open Short 

AFCB-8, Red & Black Banana Plug Sockets AFCB-8, Closed S-8, Open Short 

AFCB-1, Red & Black Banana Plug Sockets AFCB-1, Open S-1, Open Open 

AFCB-2, Red & Black Banana Plug Sockets AFCB-2, Open S-2, Open Open 

AFCB-3, Red & Black Banana Plug Sockets AFCB-3, Open S-3, Open Open 

AFCB-4, Red & Black Banana Plug Sockets AFCB-4, Open S-4, Open Open 

AFCB-5, Red & Black Banana Plug Sockets AFCB-5, Open S-5, Open Open 

AFCB-6, Red & Black Banana Plug Sockets AFCB-6, Open S-6, Open Open 

AFCB-7, Red & Black Banana Plug Sockets AFCB-7, Open S-7, Open Open 

AFCB-8, Red & Black Banana Plug Sockets AFCB-8, Open S-8, Open Open 

AFCB-1, Red & Black Banana Plug Sockets AFCB-1, Open S-1, Closed Short 

AFCB-2, Red & Black Banana Plug Sockets AFCB-2, Open S-2, Closed Short 

AFCB-3, Red & Black Banana Plug Sockets AFCB-3, Open S-3, Closed Short 

AFCB-4, Red & Black Banana Plug Sockets AFCB-4, Open S-4, Closed Short 

AFCB-5, Red & Black Banana Plug Sockets AFCB-5, Open S-5, Closed Short 

AFCB-6, Red & Black Banana Plug Sockets AFCB-6, Open S-6, Closed Short 

AFCB-7, Red & Black Banana Plug Sockets AFCB-7, Open S-7, Closed Short 

AFCB-8, Red & Black Banana Plug Sockets AFCB-8, Open S-8, Closed Short 

TABLE 1 – AFCI-JB CHECKOUT 

 Open the eight AFCB’s in the AFCI-JB. 

 Open S-1 through S-8 on the AFCI-JB. 

 Open the eight aircraft circuit breakers. 

 With aircraft power off, connect harness P-18 to AFCI-JB connector P-1 and harness 

P-6 to AFCI-JB connector P2. 

 Apply power (ground power or APU) to the aircraft. Close the eight aircraft circuit 

breakers and verify that the associated load is not energized. 

 Close AFCI-JB S-1 and verify via visual means that the LEFT INBOARD 

LANDING LIGHTS are operating. Open S-1. 

 Close AFCI-JB S-2 and verify via visual means that the OSCILLATING 

NAVIGATION LIGHTS are operating. Open S-2. 

 Close AFCI-JB S-3 and verify via visual means that the WINDOW LIGHTS – LEFT 

SIDE are operating. Open S-3. 

C-9
 Close AFCI-JB S-4 and verify via visual means that the PASSENGER CEILING 

LIGHTS – LEFT SIDE are operating. Open S-4. 

 Close AFCI-JB S-5 and verify via visual means that the DME is operating. Open S5. 

 Close AFCI-JB S-6 and verify via the Pitot Ammeter that the HEATER-PITOT-AUX 

is operating. Open S-6. 

 Close AFCI-JB S-8 and verify that the PROJECT POWER is operating. Open S-8. 

 Close AFCB-1 and verify via visual means that the LEFT INBOARD LANDING 

LIGHTS are operating. Open AFCB-1. 

 Close AFCB-2 and verify via visual means that the OSCILLATING NAVIGATION 

LIGHTS are operating. Open AFCB-2. 

 Close AFCB-3 and verify via visual means that the WINDOW LIGHTS – LEFT 

SIDE are operating. Open AFCB-3. 

 Close AFCB-4 and verify via visual means that the PASSENGER CEILING LIGHTS 

– LEFT SIDE are operating. Open AFCB-4. 

 Close AFCB-5 and verify via visual means that the DME is operating. Open AFCB5. 

 Close AFCB-6 and verify via the Pitot Ammeter that the HEATER-PITOT-AUX is 

operating. Open AFCB-6. 

 Close AFCB-8 and verify that PROJECT POWER is operating. Open AFCB-8. 

 Open the eight aircraft circuit breakers. 

 Connect the P-3 connector on the AFCI-JB to P-4 on the BNC Breakout Box with the 

AFCI-JB/BNC Breakout Box Interface Harness. 

 Using the 36” BNC connector cables, connect the BNC Breakout Box to the Odyssey 

data recorder in accordance with Table 2. For the eight channels noted in Table 2, 

install a 50 Ohm in-line terminator between the BNC cable and the Odyssey data 

recorder. 

From BNC Breakout Box 

Connector BNC-x 

(x = 1,2,3.....22,23,24) 

To Odyssey Data Recorder 

Channel Number x 

(x = 1,2,3.....22,23,24) 

50-Ohm In-line 

Terminator Required? 

 (Y/N) Description 

BNC-1 1 N AFCB–1 Line Volts 

BNC-2 2 N AFCB-1 Load Volts 

BNC-3 3 Y AFCB-1 Current 

BNC-4 4 N AFCB–2 Line Volts 

BNC-5 5 N AFCB-2 Load Volts 

BNC-6 6 Y AFCB-2 Current 

BNC-7 7 N AFCB–3 Line Volts 

BNC-8 8 N AFCB-3 Load Volts 

BNC-9 9 Y AFCB-3 Current 

C-10
BNC-10 10 N AFCB–4 Line Volts 

BNC-11 11 N AFCB-4 Load Volts 

BNC-12 12 Y AFCB-4 Current 

BNC-13 13 N AFCB–5 Line Volts 

BNC-14 14 N AFCB-5 Load Volts 

BNC-15 15 Y AFCB-5 Current 

BNC-16 16 N AFCB–6 Line Volts 

BNC-17 17 N AFCB-6 Load Volts 

BNC-18 18 Y AFCB-6 Current 

BNC-19 19 N AFCB–7 Line Volts 

BNC-20 20 N AFCB-7 Load Volts 

BNC-21 21 Y AFCB-7 Current 

BNC-22 22 N AFCB–8 Line Volts 

BNC-23 23 N AFCB-8 Load Volts 

BNC-24 24 Y AFCB-8 Current 

Table 2 

 Turn on the Odyssey data recorder. Odyssey data recorder takes several minutes to 

complete the boot process. 

 Close the eight aircraft circuit breakers. Verify that the voltage and current inputs to 

the data recorder are reading zero. 

 Close AFCB-1 and verify via visual means that the LEFT INBOARD LANDING 

LIGHTS are operating. Verify that the voltage and current waveforms are being 

properly measured on the Odyssey data recorder channels 1, 2, and 3. 

 Close AFCB-2 and verify via visual means that the OSCILLATING NAVIGATION 

LIGHTS are operating. Verify that the voltage and current waveforms are being 

properly measured on the Odyssey data recorder channels 4, 5, and 6. 

 Close AFCB-3 and verify via visual means that the WINDOW LIGHTS – LEFT 

SIDE are operating. Verify that the voltage and current waveforms are being 

properly measured on the Odyssey data recorder channels 7, 8, and 9. 

 Close AFCB-4 and verify via visual means that the PASSENGER CEILING LIGHTS 

– LEFT SIDE are operating. Verify that the voltage and current waveforms are being 

properly measured on the Odyssey data recorder channels 10, 11, and 12. 

 Close AFCB-5 and verify via visual means that the DME is operating. Verify that the 

voltage and current waveforms are being properly measured on the Odyssey data 

recorder channels 13, 14, and 15. 

 Close AFCB-6 and verify via the Pitot Ammeter that the HEATER-PITOT-AUX is 

operating. Verify that the voltage and current waveforms are being properly 

measured on the Odyssey data recorder channels 16, 17, and 18. 

 Close AFCB-7. Verify that the voltage and current waveforms are being properly 

measured on the Odyssey data recorder channels 19, 20, and 21. 

 Close AFCB-8 and verify that PROJECT POWER is operating. Verify that the 

voltage and current waveforms are being properly measured on the Odyssey data 

recorder channels 22, 23 and 24. 

C-11
 Open and close the Left Inboard Landing Lights aircraft circuit breaker five times. 

Verify that AFCB-1 did not nuisance trip during the five open-close cycles. 

 Open and close the Navigation Lights aircraft circuit breaker five times. Verify that 

AFCB-2 did not nuisance trip during the five open-close cycles. 

 Open and close the Window Lights aircraft circuit breaker five times. Verify that 

AFCB-3 did not nuisance trip during the five open-close cycles. 

 Open and close the Left Ceiling Lights aircraft circuit breaker five times. Verify that 

AFCB-4 did not nuisance trip during the five open-close cycles. 

 Open and close the DME-2 aircraft circuit breaker five times. Verify that AFCB-5 

did not nuisance trip during the five open-close cycles. 

 Open and close the Auxiliary Pitot Heat aircraft circuit breaker five times. Verify 

that AFCB-6 did not nuisance trip during the five open-close cycles. 

 Open and close the First Officers Window aircraft circuit breaker five times. Verify 

that AFCB-7 did not nuisance trip during the five open-close cycles. 

 Open and close the AC Project Power aircraft circuit breaker five times. Verify that 

AFCB-8 did not nuisance trip during the five open-close cycles. 

 With the eight aircraft circuit breakers and the eight AFCB’s closed switch from 

ground power to APU power. Verify that no nuisance trips occurred. Switch from 

APU power to engine power. Verify that no nuisance trips occurred. Reverse this 

process and verify that no nuisance trips occurred after each step. Repeat this cycle 

four additional times. 

 With aircraft electrical power on (ground, APU, or engine) and the aircraft circuit 

breakers closed, begin recording on the Odyssey by pressing the record button. Open 

AFCB-1. The trigger alarm shall activate. Close AFCB-1 and reset the trigger alarm. 

Repeat this process for AFCB-2 through AFCB-8. 

 With aircraft electrical power on (ground, APU, or engine) and the aircraft circuit 

breakers and AFCB’s closed, test aircraft systems in accordance with the B727 

Standard Start-up checklist. An Odyssey data recording shall be made as each load is 

tested. For voice communication, conduct transmission checks on each radio. No 

AFCB’s shall nuisance trip during these tests. Confirm that the AFCB’s and 

instrumentation do not interfere with the operation of system. 

C-12
Part B: Conduct Time Domain Reflectometry Baseline Tests

The eight AFCB test circuits will be characterized using a Time Domain Reflectometry 

(TDR) technique. The purpose of this test is to baseline the existing condition of each circuit 

to be used as a reference benchmark. If an AFCB should trip during flight test, a new TDR 

measurement of the effected circuit will be conducted and compared to the original 

benchmark. This will assist in determining the presence and location of the fault. 

The TDR testing will be conducted by CM Technologies under the supervision of John 

Beres. 

TDR Tools and Equipment: 

The tools and equipment listed below shall be supplied by CM Technologies. 

• Electrical Characterization and Diagnostics (ECADTM) System 1100. The 

ECADTM system injects a pulse of 1V amplitude, and 400μsec pulse width. In the 

worst case, the maximum energy of the pulse is 8μJ. The pulse applied in the 

Excited Dielectric Test (EDT), described below, is even lower. The pulse 

amplitude is only 200 mV and the pulse width is narrower than the 400μsec pulse 

used in the standard TDR test. 

• Agilent 86100A Oscilloscope Mainframe with 54754A Time Domain 

Reflectometer Plug-in Module. 

• Tabor 8020 Function Generator. 

• Coupling network, test lead cables, and clips.

TDR PRECAUTIONS 

The ECADTM System 1100 is designed to test de-energized wires. Computer logic first 

checks the circuit for AC and DC voltage and will not permit an automatic test if a 

significant voltage level is found (greater than 5 VDC or VAC). Attempting to test 

energized wiring may damage the ECAD instrumentation and/or represent a safety 

hazard to test personnel. 

TDR TEST SUPERVISION 

 The WJHTC Electrical Systems DER, Code ACT-370 is responsible for 

managing the arc fault circuit breaker installation and testing aboard N40. The 

CM Technologies field engineer shall discuss the test plan with the Electrical 

Systems DER to ensure compliance with all applicable FAA quality and/or testing 

procedures. 

 The WJHTC Electrical Systems DER, Code ACT-370 (or designee) shall be 

responsible for opening any panels to gain access to breakers, opening breakers to 

de-energize circuits, and restoring the circuits to an operational (pre-test) 

condition. 

C-13
TDR PROCEDURE 

ECADTM System 1100 Equipment Setup: 

 Locate the ECADTM System 1100 near the circuits to be tested. Ideally, the 

equipment will be located within 10 to 25 feet from the test location. 

 Provide the equipment with a source of 120 VAC, 60 Hz power. 

 Connect power, signal, and test leads to the equipment as required. 

 Turn on the ECADTM System 1100 and start the data acquisition software. 

 Load the AFCB database files. 

 Execute the system self-test. The self-test checks the proper operation of each 

instrument card and measures the electrical properties associated with the test 

lead. 

ECADTM Testing: 

 Select the device/circuit to be tested from the ECAD AFCB database. 

 Verify the circuit to be tested matches the circuit descriptive data (CDD) 

displayed in the ECADTM software. Also, verify the circuit to be tested is deenergized. 

 Connect the ECADTM test clips to the circuit as indicated in the HIGH TEST PT 

and LOW TEST PT fields of the CDD screen. 

 Using a digital multi-meter, measure resistance from the conductor to aircraft 

ground. If resistance is less than 500kΩ stop the test and find troubleshoot the 

circuit wiring. If greater than 500kΩ, proceed to next step. 

 The Insulation Resistance (IR) TEST VOLTS field of the CDD screen indicates 

the MAXIMUM IR test voltage that is allowed. The maximum applied voltage 

will be 50VDC. Testing at voltages greater than this value could damage circuit 

components. A value of zero (0) volts in this field indicates that an IR test is not 

to be performed for this configuration. 

 Initiate a TEST of the selected configuration. 

 Review the measurement data as required. 

 Repeat ECAD Testing steps until all of the eight circuits have been characterized. 

Excited Dielectric Test (EDT) Equipment Setup: 

 Locate the EDT test equipment near the circuits to be tested. Ideally, the 

equipment will be located within 10 to 25 feet from the test location. 

 Provide the equipment with a source of 120 VAC, 60 Hz power. 

 Connect power, signal, and test leads to the equipment as required. 

 Turn on the Agilent 86100A. 

C-14
EDT Testing: 

 Connect the alligator test clips to the same test locations that were used during the 

ECAD testing. 

 Acquire three (3) TDR signatures using three (3) forcing function frequencies. 

The three frequencies will be determined from the insulation materials used in the 

circuit under test. 

 Waveforms will be named and saved for storage in the Agilent 86100A. 

 Review the TDR waveform as required. 

 Repeat EDT Testing steps until all of the test configurations have been completed. 

Circuit Restoration: 

 Disconnect all test clips. 

 Restore the circuit to normal as directed by the Electrical Systems DER. 

 Perform functional test on the restored circuit, if needed. 

Successful completion of these steps will confirm that the installation is functioning 

properly. 

End of Ground Checkout Procedure. 

C-15/C-16
APPENDIX D—EATON FLIGHT TEST RECORDS

D-1/D-2
Eaton Flight Test Records 

EATON FLIGHT TEST HOURS 

 Circuit Breaker Hours

Flight Date From To 

In Service 

Time 

Block 

Time 

Cumulative In 

Service 

Cumulative 

Block 

Block 

Time 

Cumulative 

Block 

 

1 9/10/01 KACY KACY 0.8 1.2 0.8 1.2 9.6 9.6 

2 9/17/01 KACY KACY 1.9 2.2 2.7 3.4 17.6 27.2 

3 9/17/01 KACY KACY 1.6 1.8 4.3 5.2 14.4 41.6 

4 9/18/01 KACY KACY 1.7 2.0 6.0 7.2 16.0 57.6 

5 9/18/01 KACY KACY 1.7 2.0 7.7 9.2 16.0 73.6 

6 9/19/01 KACY KACY 2.4 2.7 10.1 11.9 21.6 95.2 

7 9/26/01 KACY KACY 1.7 1.9 11.8 13.8 13.3 108.5 

8 9/27/01 KACY KACY 1.7 2.0 13.5 15.8 14.0 122.5 

9 9/27/01 KACY KACY 1.2 1.5 14.7 17.3 10.5 133.0 

10 10/1/01 KACY KPBI 2.3 2.6 17.0 19.9 18.2 151.2 

11 10/1/01 KPBI KACY 2.4 2.4 19.4 22.3 16.8 168.0 

12 10/2/01 KACY KATL 1.3 1.9 20.7 24.2 13.3 181.3 

13 10/2/01 KATL KACY 1.6 2.0 22.3 26.2 14.0 195.3 

14 10/3/01 KACY KSRQ 2.1 2.3 24.4 28.5 16.1 211.4 

15 10/3/01 KSRQ KACY 2.0 2.4 26.4 30.9 16.8 228.2 

D-3
D-4
D-5
D-6
D-7
D-8
D-9
D-10
D-11
D-12
APPENDIX E—EATON TROUBLESHOOTING PROCEDURES

E-1/E-2
Troubleshooting Procedures 

For 

Eaton Aerospace Controls 

400Hz/120V Arc Fault Circuit Breakers (AFCB) 

On 

FAA Technical Center 

Boeing 727-25C Aircraft N40 

July 2001 

FAA William J. Hughes Technical Center 

Engineering and Modification Section, ACT-370 

Maintenance, Inspection, and Repair Section, AAR-433 

Prepared by: R.A. Pappas, AAR-433 

Reviewed by: J. Beres, ACT-370 

Approved by: Armando Gaetano 

Manager, Engineering & Modifications Section, ACT-370 

E-3/E-4
1. Introduction 

The Federal Aviation Administration (FAA), William J. Hughes Technical Center (WJHTC) 

R&D Flight Program is performing a minormodification to their Boeing 727-25C aircraft. 

This temporary modification involves the installation of eight arc fault circuit breaker 

(AFCB) prototypes manufactured by Eaton Aerospace Controls. The AFCB’s are to be 

installed for a six-month evaluation period in support of AFCB research and development. 

The AFCB’s will be installed in a prefurnished Arc Fault Circuit Interrupter-Junction Box 

(AFCI-JB) that will enclose all the AFCB’s and required instrumentation. The AFCB’s will 

not be mounted in the aircraft circuit breaker panels. It is important to note that the AFCB’s 

will be connected in series with the load side of the existing thermal circuit breakers. In 

other words, current circuit protection aboard the aircraft will not be compromised in any 

way by this installation. 

The electrical, system, and mechanical integration of this installation will be accomplished at 

Atlantic City International Airport (ACIAP) using FAA technical and engineering personnel. 

The engineering personnel have been granted authority to approve “electrical systems” and 

“structures” data via FAA Form 8110-3, by the New York Aircraft Certification Office 

(NYACO). The engineering of this installation has been completed and the engineers are 

currently compiling reports to show compliance with applicable Federal Aviation 

Regulations (FAR). 

This report describes the troubleshooting procedures to be conducted in the event there is an 

AFCB trip during ground testing or flight testing. All steps in this procedure shall be 

successfully followed until the source of the AFCB trip has been identified and corrected in 

accordance with this procedure and to the satisfaction of the WJHTC Electrical Systems 

DER, Code ACT-370. 

2. Background 

The integration of arc fault detection into circuit breakers represents a revolutionary change 

in circuit protection; which has changed little in the last thirty to forty years. There is 

abundant evidence of arc faults in all types of aircraft. Laboratory data clearly demonstrates 

that the current generated during an arcing fault can be very high, yet quite intermittent. The 

bimetallic elements in thermal breakers do not react quickly enough, if at all, to this ticking 

arc fault condition. If left unchecked, the arcing condition can develop into an arc tracking 

condition, potentially destroying a major portion of, or an entire wire bundle. Arcing can 

also result in many other serious safety hazards. 

In 1999, the FAA and the Navy established a joint R&D project to develop aircraft AFCB’s. 

The goal of this effort is to develop a circuit breaker that integrates arc fault protection 

together with existing thermal protection into a form, fit, and functional replacement of 

existing thermal circuit breakers. In laboratory testing, the AFCB prototypes have been very 

effective in the detection of arcing faults. 

In contrast to thermal breakers, which are passive in nature, AFCB’s actively monitor the 

circuits on which they are installed. Due to the nature of electrical systems, there are times 

when a normal condition may ‘look’ similar to an arc fault. When such a condition trips an 

E-5
arc fault circuit breaker, it is defined as a nuisance trip. AFCB designs minimize the 

occurrence of nuisance tripping and maximize sensitivity to arc fault detection. 

To address nuisance tripping, the FAA, Navy, and the AFCB developers, have conducted 

extensive tests to characterize the normal operation of electrical loads, and perturbations to 

electrical systems during normal events such as bus transfers, power on/off, transfer of power 

sources, etc. Laboratory tests today have provided a high level of confidence that nuisance 

tripping is being successfully controlled. 

The certification request will permit the FAA to temporarily install AFCB’s aboard the 

B727-25C (N40) with the purpose of evaluating the circuit breakers, in-flight, over a sixmonth period. This will assure that the AFCB’s are evaluated against a wide range of actual 

electrical conditions. 

3. System Description 

The AFCB installation will consist of the following: 

a. Eight (8) - Eaton Aerospace Corporation prototype arc fault circuit breakers of the 

following ratings: one 2.5 A, three 5A, one 7.5A, one 10A, and two 15A (Mounted in 

AFCI Junction Box). 

b. One (1) – AFCI-JB. 

c. Two (2) – AFCI-JB Test Unit wire harnesses, P18 and P6. 

d. One (1) - 24 channel, Nicolet Odyssey data recorder. 

e. One (1) – BNC Breakout Box. 

f. One (1) – AFCI Junction Box – BNC Breakout Box Interface Harness. 

g. Twenty-four (24) – 36-inch BNC connector cables. 

h. One (1) – Trigger Alarm 

The AFCI Junction Box (AFCI-JB) will contain the eight AFCB units. The test unit will be 

mounted in the rear, left side of the cockpit. The test unit will have by-pass switches that will 

disable the AFCB’s if desired. The test unit will be fabricated using standard best practices 

and in accordance with AC 43.13-1B and contain any possible AFCB failure. 

The electrical connections for the system are shown schematically in FAA Drawing Number 

9854415, Arc Fault Circuit Breaker Wiring. The AFCB’s mounted within the AFCI-JB will 

be electrically in series with the load side of the existing circuit breakers. The AFCI-JB wire 

harnesses, P-18 and P-6, connect the load side of the each aircraft circuit breaker to the line 

side of the respective AFCB and from the load side of the each AFCB to the feed wire for the 

respective load. 

The BNC Breakout Box and the Odyssey data recorder will be mounted in the cabin of the 

aircraft. The AFCI-JB/BNC Breakout Box Interface Harness connects the AFCI-JB to the 

BNC Breakout Box. 

The 24 BNC connectors on the BNC Breakout Box are connected to the Odyssey data 

recorder with 36” BNC coaxial cables. 

E-6
Detailed installation instructions are provided in Section 4. 

4. Certification Requirements 

There are no FAA Technical Standard Orders for the equipment being installed during this 

modification. Experimental flight test is being performed to collect data necessary to obtain 

a one only STC to install the AFCB’s aboard N40 for an extended evaluation period. 

E-7
5. Installation of AFCB Test System On N40 

The electrical installation shall be completed in accordance with drawing number 9854415 

under the guidance of the WJHTC Electrical Systems Designated Engineering Representative 

(DER), Code ACT-370. The mechanical installation shall be completed under the guidance 

of the WJHTC Mechanical Systems DER, Code ACT-370. 

The following list contains general instructions for completing the installation (Full 

installation instructions are contained in the AFCB Ground Test Checkout Report). The 

installation shall be completed in accordance with all existing safety requirements and the 

necessary approvals shall be obtained in advance of starting the installation. 

 The two AFCI-JB Interface wire harnesses, P-18 and P-6, shall be connected to 

the thermal circuit breakers in accordance with FAA Drawing number 9854415. 

Harness P-18 shall be connected to the: 

 Left Inboard Landing Lights (7.5A) 

 Navigation Lights (5A) 

 Window Lights (10A) 

 Left Ceiling Lights (15A) 

Harness P-6 shall be connected to the: 

 DME-2 (3A) 

 Auxiliary Pitot Heat (5A) 

 First Officers Window (5A) 

 AC Project Power (15A) 

 Mount the AFCI-JB in the flight deck as per the Mechanical Systems DER 

instructions. 

 Mount the Odyssey and the BNC Breakout Box in the cabin rack per the 

Mechanical Systems DER instructions. 

 Insure that all mounting is secure. 

 Route the AFCI-JB harnesses and the AFCI-JB/Breakout Box harness. Do not 

mate the harnesses to the AFCI-JB or the breakout box until electrical tests have 

been completed. Do not secure the harness until electrical tests have been 

completed. 

E-8
6. Arc Fault Troubleshooting – General Background 

Although AFCB’s can detect arcing on the circuit in which it is installed, it cannot determine 

the location of the arc along the circuit. Furthermore, means for easily troubleshooting an arc 

fault after and AFCB trip are under development but not currently available. This plan has 

been developed to establish a procedure for troubleshooting AFCB trips, should they occur. 

An understanding of current methods of troubleshooting thermal trips will clarify the 

additional measures needed to troubleshoot an AFCB trip and specifically the procedures that 

will be followed during the FAA AFCB flight test program. 

Troubleshooting circuit breakers is an iterative process. Generally, after a thermal circuit 

breaker trip, troubleshooting begins by evaluating the load(s) powered by the circuit. The 

load is either tested for correct operation, or is removed and replaced if its correct operation 

cannot be directly determined. The circuit is powered and if no additional trips are noted the 

corrective action is considered complete. 

If additional trips of the same circuit occur, there are several options for corrective action. 

The load may still be suspected, and the problem may not be reproducible on the ground. 

The circuit breaker itself may be suspect and replaced (tripping of thermal circuit breakers 

under normal conditions, or failure of a circuit breaker to stay closed when depressed, are 

two common circuit breaker failure modes). Usually, the last item to be checked is the 

circuit wiring, mainly because of the inherent difficulties in testing and inspecting the wiring. 

AFCB’s add another dimension of complexity to the troubleshooting problem. AFCB’s have 

two trip modes, thermal (current overload) and arc fault. There are unique procedures for 

troubleshooting each mode, and unfortunately, if one procedure fails to identify the problem 

it may be necessary to complete the other procedure to be certain that the problem has been 

resolved. Future AFCB’s will have the ability to indicate if the trip mode was thermal or arc 

fault related. The prototypes flown in this test program will not have this feature. However, 

the data recording instrumentation will be triggered by the AFCB’s arc fault detection circuit 

and therefore it will be known with certainty if the trip mode was thermal versus arc fault. 

If the trip mode was arc fault related, the question remains was the arc trip a real arc or was it 

a nuisance trip? The instrumentation being used in these flights will record the current 

waveforms immediately before and after the AFCB indicates that an arc is present and a trip 

is initiated. This data will be analyzed by Eaton Aerospace to determine if it appears to be a 

real arc or a nuisance trip. If it is certain that the trip was nuisance related, then the breaker 

will be reset and flights testing may resume. If a nuisance trip is not certain, then further 

diagnostics will be required. 

Provisions have been made to baseline the condition of the wiring on the eight circuits that 

will be used in the tests with Time Domain Reflectometry (TDR). During ground testing of 

the AFCB test system, each AFCB equipped circuit will be characterized with TDR. This 

data will form a baseline measurement against which future measurements will be compared. 

Changes in the measurement indicate possible locations at which the arcing may have 

occurred. 

E-9
At this point, it is unclear if TDR is sensitive enough to detect the damage incurred by a wire 

during an arcing condition. If the TDR fails to identify the location of the fault, visual 

inspection of the circuit must be performed to determine the source of the fault. 

7. Detailed Troubleshooting Procedures 

All troubleshooting shall be performed by qualified FAA personnel under the direction of the 

Electrical Systems DER, Code ACT-370. 

Upon an AFCB arc fault trip, the Odyssey data recording system will record the current and 

voltage waveforms from the eight circuits equipped with AFCB’s. A thermal trip of the 

AFCB or the aircraft circuit breaker will not cause the Odyssey to trigger on and record this 

data. Therefore, it will be known immediately if the trip was caused by an arc fault. 

Appendix A contains the detailed process flow charts. 

E-10
Appendix A 

Troubleshooting Process Flowcharts 

E-11
E-12

Odyssey Trigger?

(Y/N)

Download 

Odyssey 

Waveform Data

Email Odyssey 

Waveform Data 

to Eaton

Obtain TDR 

Data From 

Tripped Circuit

Email TDR Data 

to CM Tech. For 

Analysis

TDR 

Changed 

from 

baseline?

Nuisance 

Confirmed 

Conduct ground 

tests on circuit 

N

Email TDR Data 

to CM Tech. For 

Analysis

Damage 

location 

discernable?

Locate fault and 

repair 

Conduct ground 

tests on circuit 

Y

Y

Nuisance

Arc Fault

Probable 

arc fault 

or 

nuisance 

trip?

Obtain TDR 

Data From 

Tripped Circuit

Conduct ground 

tests on circuit 

Conduct visual 

inspection of 

circuit wiring

Damage 

location 

discernable?

Locate fault and 

repair

2

N

N Y

Y N

1

Start:Circuit 

Breaker Trip

AFCB 

Trip or 

Aircraft 

CB Trip?

AFCB

1

Aircraft CB
E-13

1

Troubleshoot and repair IAW 

Standard Operating Procedures for 

thermal circuit breaker trips 

Conduct ground tests on circuit 

Ground 

tests 

check 

ok?

Obtain TDR 

Data From 

Tripped Circuit

Email TDR Data 

to CM Tech. For 

Analysis

TDR 

Changed 

from 

baseline?

Aircraft and 

circuit returned 

to service 

Re-baseline 

circuit TDR 

characterization 

End

N

Damage 

location 

discernable?

Locate fault and 

repair 

Conduct ground 

tests on circuit 

Conduct visual 

inspection of 

circuit wiring

Damage 

location 

discernable?

Locate fault and 

repair

2

N

Conduct ground 

tests on circuit 

Y

Y
E-14

2

Aircraft and 

circuit returned 

to service 

Re-baseline 

circuit TDR 

characterization 

Ground 

tests 

check 

ok?

Y

Replace AFCB 

N

Ground 

tests 

check 

ok?

Repeat 

troubleshooting 

procedure

End

End

Y

N
APPENDIX F—HENDRY FLIGHT TEST PLAN

F-1/F-2
Arc Fault Circuit Breaker 

Flight Test Program 

Flight Test Plan 

for 

Hendry Arc Fault Circuit Breaker (AFCB) Installation 

on 

FAA Technical Center 

Boeing 727-25C Aircraft N40 

27 June 2002 

FAA William J. Hughes Technical Center 

Engineering and Modification Section, ACT-370 

Maintenance, Inspection, and Repair Section, AAR-480 

Prepared by: R.A. Pappas, AAR-480 

Reviewed by: J. Beres, ACT-370 

Approved by: Armando Gaetano 

 Manager, Engineering & Modifications Section, ACT-370 

F-3/F-4
Table of Contents 

1.0 INTRODUCTION..................................................................................................................... 7

1.1 Background .................................................................................................................. 7

1.2 Objective ...................................................................................................................... 7

1.3 Scope ............................................................................................................................ 8

2.0 FLIGHT TEST GOALS ........................................................................................................... 8

3.0 SYSTEM DESCRIPTION........................................................................................................ 8

3.1 Arc Fault Circuit Breakers ........................................................................................... 8

3.2 Arc Fault Circuit Interupter - Junction Box and Aircraft Harnesses............................ 8

3.3 Instrumentation Equipment .......................................................................................... 8

3.4 Aircraft Interfaces......................................................................................................... 8

4.0 AIRCRAFT INSTALLATION .................................................................................................. 9

5.0 CERTIFICATION REQUIREMENTS ...................................................................................... 9

6.0 FLIGHT TEST PROFILE REQUIREMENTS .......................................................................... 9

7.0 LIMITATIONS ....................................................................................................................... 10

8.0 EMERGENCY PROCEDURES ............................................................................................ 11

9.0 NORMAL PROCEDURES.................................................................................................... 12

9.1 Preflight...................................................................................................................... 12

9.2 Flight .......................................................................................................................... 12

9.3 Postflight .................................................................................................................... 13

F-5/F-6
1.0 INTRODUCTION 

This document defines the flight test procedures for evaluating the performance of Arc Fault 

Circuit Breakers (AFCBs) in an FAA owned Boeing 727-25C aircraft. The effort will be 

conducted by the United States (U.S.) Federal Aviation Administration (FAA) at the William J. 

Hughes Technical Center (WJHTC), Atlantic City, New Jersey. 

1.1 BACKGROUND

The integration of arc fault detection into circuit breakers represents a revolutionary change in 

circuit protection; which has changed little in the last thirty to forty years. There is abundant 

evidence of arc faults in all types of aircraft. Laboratory data clearly demonstrates that the 

current generated during an arcing fault can be very high, yet quite intermittent. The bimetallic 

elements in thermal breakers do not react quickly enough, if at all, to this ticking arc fault 

condition. If left unchecked, the arcing condition can develop into an arc tracking condition, 

potentially destroying a major portion of, or an entire wire bundle. Arcing can also result in 

many other serious safety hazards. 

In 1999, the FAA and the Navy established a joint R&D project to develop aircraft AFCBs. The 

goal of this effort is to develop a circuit breaker that integrates arc fault protection together with 

existing thermal protection into a form, fit, and functional replacement of existing thermal circuit 

breakers. In laboratory testing, the AFCB prototypes have been very effective in the detection of 

arcing faults. 

In contrast to thermal breakers, which are passive in nature, AFCBs actively monitor the circuits 

on which they are installed. Due to the nature of electrical systems, there are times when a 

normal condition may ‘look’ similar to an arc fault. When such a condition trips an arc fault 

circuit breaker, it is defined as a nuisance trip. AFCB designs minimize the occurrence of 

nuisance tripping and maximize sensitivity to arc fault detection. 

To address nuisance tripping, the FAA, Navy, and the AFCB developers, have conducted 

extensive tests to characterize the normal operation of electrical loads, and perturbations to 

electrical systems during normal events such as bus transfers, power on/off, transfer of power 

sources, etc. Laboratory tests today have provided a high level of confidence that nuisance 

tripping of AFCBs is being successfully controlled. 

AFCB development has progressed to the point where flight tests are appropriate to demonstrate 

compliance with applicable Federal Aviation Regulations (FARs). 

1.2 OBJECTIVE

The objective of this task is to conduct an in-flight evaluation of AFCB performance. 

The Federal Aviation Administration (FAA), William J. Hughes Technical Center (WJHTC) 

R&D Flight Program is performing a minor modification to their Boeing 727-25C aircraft. This 

temporary modification involves the installation of eight AFCB prototypes manufactured by the 

Hendry corporation. The AFCBs are to be installed for a six-month evaluation period in support 

of AFCB research and development. 

F-7
1.3 SCOPE

The scope of this effort is to install AFCBs manufactured by the Hendry corporation in an FAA 

owned Boeing 727-25C aircraft and conduct a flight evaluation of the developmental AFCBs. 

Data recorded includes line voltage, load voltage, and current for each of the installed breakers. 

Data reduction efforts of any occurring arc faults will include identification of relationships 

between the trip conditions. 

2.0 FLIGHT TEST GOALS 

The following list describes the goals of the experimental flight test program, listed in order of 

importance. 

 Complete fifty (50) or more hours of developmental flight test evaluation but not less 

than twenty-five (25) hours. Data generated during these flights is critical to the 

AFCB research and development program and for obtaining approval of the N-40 

one-only STC. 

 Evaluate the operation of the arc fault circuit breakers under standard B727 

operational procedures. 

 Evaluate the operation of the AFCB instrumentation and Odyssey data recording 

system for future unmanned data collection. 

3.0 SYSTEM DESCRIPTION 

The equipment being installed for the Arc Fault flight evaluation includes developmental 

prototype AFCBs installed in a junction box, an instrumentation recorder and interconnecting 

cables and wire harnesses. These items are described in the following paragraphs. 

3.1 ARC FAULT CIRcUIT BREAKERS

Eight (8) - Hendry prototype arc fault circuit breakers of the following ratings: one 2.5 A, 

three 5A, one 7.5A, one 10A, and two 15A (mounted in AFCI Junction Box). 

3.2 ARC FAULT CIRCUIT INTERUPTER - JUNCTION BOX AND AIRCRAFT HARNESSES

One (1) – AFCI-JB. 

Two (2) – AFCI-JB Test Unit wire harnesses, P18 and P6 

3.3 INSTRUMENTATION EQUIPMENT

One (1) - 24 channel, Nicolet Odyssey data recorder. 

One (1) – BNC Breakout Box. 

One (1) – AFCI JB – BNC Breakout Box Interface Harness. 

Twenty-four (24) – 24-inch BNC connector cables. 

One (1) – Trigger Alarm 

3.4 AIRCRAFT INTERFACES

The electrical connections for the system are shown schematically in FAA Drawing Number 

9854415, Arc Fault Circuit Breaker Wiring. The AFCBs mounted within the AFCI-JB will be 

electrically in series with the load side of the existing circuit breakers. The AFCI-JB wire 

harnesses, P-18 and P-6, connect the load side of the each aircraft circuit breaker to the line side 

F-8
of the respective AFCB and from the load side of the each AFCB to the feed wire for the 

respective load. 

It is important to note that the AFCBs will be connected in series with the load side of the 

existing thermal circuit breakers. In other words, current circuit protection aboard the aircraft 

will not be compromised in any way by this installation. 

The on-board Project Power Inverter provides 120VAC 60Hz power for the Data Acquisition 

System. 

4.0 AIRCRAFT INSTALLATION 

The AFCBs will be installed in an Arc Fault Circuit Interrupter-Junction Box (AFCI-JB) that 

will enclose all the AFCBs and required instrumentation interfaces. The AFCI-JB will be 

mounted in the rear, left side of the cockpit. The test unit will have bypass switches that will 

disable the AFCBs if desired. 

The BNC Breakout Box and the Odyssey data recorder will be mounted in the cabin of the 

aircraft. 

The electrical installation shall be completed in accordance with drawing number 9854415 under 

the guidance of the WJHTC Electrical Systems Designated Engineering Representative (DER. 

The mechanical installation shall be completed under the guidance of the WJHTC Mechanical 

Systems DER. 

Detailed instructions for completing the installation can be found in the AFCB Ground Checkout 

Procedures Report. 

5.0 CERTIFICATION REQUIREMENTS 

There are no FAA Technical Standard Orders for the equipment being installed during this 

modification. Experimental flight test is being performed to collect data necessary to obtain a 

one only STC to install the AFCBs aboard N40 for an extended evaluation period. 

6.0 FLIGHT TEST PROFILE REQUIREMENTS 

N40 will be operated in conformance with Standard B727 Operations. The purpose of the flight 

test is to maximize the number of flight hours. Duration and distance of flights will be at the 

discretion of the pilot in command and within the operating restrictions established by the 

MIDO. 

No excessive cycling of the aircraft is necessary. 

As established by the MIDO, flight restrictions shall be removed to the maximum extent possible 

upon completion of flight hour thresholds established by the MIDO. 

If possible, the aircraft will fly to Santa Barbara, California to permit Hendry engineers an 

opportunity to assess the AFCB installation aboard the aircraft. A flight to Seattle, Washington 

will also be conducted, if possible, to permit FAA Transport Directorate, ANM-100 engineers to 

observe the installation. 

F-9
7.0 LIMITATIONS 

It is proposed that the first 5 flight hours (Phase 1) be conducted within a 100-mile radius from 

Atlantic City International Airport. Upon satisfactory completion of this 5-hour period, it is 

requested that the remainder of the flights be conducted without restrictions (Phase 2). 

An ACT-370 Safety Officer will be on all Phase 1 flights. 

An AAR-480 engineer (or designee) must be aboard the aircraft during all AFCB flight tests to 

operate the Odyssey data recorder. 

No AFCB equipped circuit shall be operated in-flight after an AFCB trip on the circuit, unless 

the pilot in command orders the operation of the circuit during an emergency. In this case, the 

flight engineer shall switch the associated bypass switch on the AFCI-JB to the bypass position. 

In addition, after an AFCB trip, the Flight Engineer shall pull the associated circuit breaker on 

the aircraft circuit breaker panel. Troubleshooting shall be performed in accordance with the 

AFCB Troubleshooting Procedures. 

If there are two or more AFCB trips on a single electrical bus, the flight test shall be terminated 

and the aircraft will return to base immediately. 

Limitations established by the MIDO shall be adhered to. 

F-10
8.0 EMERGENCY PROCEDURES 

In the event of an emergency (related or unrelated to the AFCB testing), the following 

procedures will be followed if ordered by the pilot in command. 

The flight engineer shall bypass all AFCBs by closing the AFCB bypass switches on the 

AFCI-JB located behind the Captains chair. 

 The flight engineer will set each AFCB to the open position. 

 The Odyssey data recorder will be powered off by the engineer operating the system. 

If power must be removed from the AFCI-JB the following steps will be completed: 

 The flight engineer will open the eight circuit breakers on the aircraft circuit breaker 

panels. A colored button or other tag will uniquely identify these breakers. The eight 

circuit breakers and their respective locations are summarized in Table 1 below. 

Table 1 – AFCB Test Circuit Breaker Locations 

AF

CB 

Circ

uit# 

CB Identity Panel/Location Rating 

(Amps) Bus 

1 Left Inboard Landing Lights P18-4 Lighting 7 115VAC Bus No. 1 

2 Navigation Lights P18-4 Lighting 5 115VAC Bus No. 2 

3 Window Lights P18-3 Lighting and 

Passenger Accommodations 10 115VAC Transfer Bus 

4 Left Ceiling Lights P18-3 Lighting and 

Passenger Accommodations 15 115VAC Transfer 

Bus 

5 DME-2 P18-3 Electronic Load 

Circuit Breaker 3 115VAC Radio Bus 

No. 2 

6 Heater-Pitot-Aux P6-1 Miscellaneous AC, 

Anti-Ice & Rain 5 115VAC Bus No. 2 

7 First Officers Window 4 & 5 P6-1 Miscellaneous AC, 

Anti-Ice & Rain 5 115 VAC Bus No. 3 

8 Project Power Project Power Junction Box 10 115VAC Bus No. 2 

F-11
9.0 NORMAL PROCEDURES 

9.1 PREFLIGHT

 Review flight plan with flight crew and all passengers. 

 Review emergency procedures with flight crew and all passengers. 

 Review all normal procedures with flight crew and all passengers. 

 Flight engineer set all bypass switches on the AFCI-JB to normal except S8 (leave 

in BYPASS) and S1. Leave S1 in BYPASS until Landing light is on, then switch 

S1 to NORMAL. 

 Apply power to the aircraft (Ground power or APU). 

 Flight engineer close all AFCBs. 

 Turn Odyssey data recorder to ON and wait for system to boot up and initialize. 

Start recording. Note the date, time, and recording number. 

 If on ground power, start APU. Start Odyssey data recording and instruct flight 

engineer to transfer power from ground power to APU power. Record the date, 

time, and filename of the recording in the test logbook. Note that the recording was 

a ground power to APU transfer. 

 If on APU power, start aircraft engines. Continue Odyssey data recording and 

instruct flight engineer to transfer power from APU to engine generators. Record 

the date, time, and filename of the recording in the test logbook. Note that the 

recording was an APU to engine generator power transfer. 

 Continue the Odyssey data recording. Data will be recorded at the slow rate, 1kHz. 

Note the date, time, and filename in the test logbook. Also note the general 

conditions (weather, etc.) at this time. 

 Proceed to flight phase in accordance with standard B727 start-up procedures. 

9.2 FLIGHT

 Monitor Odyssey data recording system. The visual and aural trigger alarm 

mounted adjacent to the Odyssey data recorder will initiate when an AFCB has 

tripped and the Odyssey data recorder will automatically begin recording at the high 

sampling rate, 100kHz. 

 If the trigger-alarm sounds, press the red reset button mounted on the trigger alarm 

enclosure to silence the trigger and extinguish the trigger alarm lights. 

 Note the date, time, and the number of the AFCB(s) that caused the trigger. Also 

note the flight conditions and other information pertinent to the trigger event in the 

test logbook. Also note the new file name in the logbook with the start time of the 

recording. 

F-12
9.3 POSTFLIGHT

 Continue to follow the flight procedures. 

 Prior to engine shutdown, start APU or apply ground power. Switch aircraft 

power to APU or ground power. Shut engines in accordance with standard B727 

operational procedures. 

 Download data files from the Odyssey data recorder 

 Shutdown the Odyssey data recorder. 

 Shutdown aircraft in accordance with standard B727 operational procedures. 

- - End of flight test procedures. - - 

F-13/F-14
APPENDIX G—HENDRY GROUND CHECKOUT PROCEDURES 

G-1/G-2
Arc Fault Circuit Breaker 

Flight Test Program 

Ground Checkout Procedures 

for 

Hendry 

115 VAC Single Phase 

Arc Fault Circuit Breaker (AFCB) Installation 

on 

FAA Technical Center 

Boeing 727-25C Aircraft N40 

18 June 2002 

FAA William J. Hughes Technical Center 

Engineering and Modification Section, ACT-370 

Maintenance, Inspection, and Repair Section, AAR-480 

Prepared by: R.A. Pappas, AAR-480 

Reviewed by: J. Beres, ACT-370 

Approved by: Armando Gaetano 

 Manager, Engineering & Modifications Section, ACT-370 

G-3/G-4
Table of Contents 

1.0 INTRODUCTION 7

1.1 Background 7 

1.2 Objective 7 

1.3 Scope 8 

2.0 CERTIFICATION REQUIREMENTS 8

3.0 SYSTEM DESCRIPTION 8

3.1 Arc Fault Circuit Breakers 8 

3.2 Arc Fault Circuit Interupter - Junction Box and Aircraft Harnesses 8 

3.3 Instrumentation Equipment 8 

3.4 Aircraft Interfaces 9 

3.5 Power Requirements 9 

4.0 AIRCRAFT INSTALLATION 9

4.1 AFCB Installation Instructions 9 

4.2 Instrumentation Equipment Installation Instructions 9 

5.0 GROUND CHECKOUT PROCEDURES 10

5.1 AFCB Electrical Tests 10 

5.2 AFCB Test Circuit Time Domain Reflectometry Baseline Tests 10 

APPENDIX A – AFCB INSTALLATION INSTRUCTIONS / VERIFICATION SHEET 11

APPENDIX B - AFCB ELECTRICAL TEST PROCEDURES / VERIFICATION 

SHEET 12

APPENDIX C – TIME DOMAIN REFLECTOMETRY BASELINE TEST 

PROCEDURES / VERIFICATION SHEET 21

G-5/G-6
1. INTRODUCTION

This document defines the procedures for installing Arc Fault Circuit Breakers (AFCBs) in an 

FAA owned Boeing 727-25C aircraft and performing a ground test prior to a flight evaluation of 

the AFCBs. The effort will be conducted by the United States (U.S.) Federal Aviation 

Administration (FAA) at the William J. Hughes Technical Center (WJHTC), Atlantic City, New 

Jersey. 

1.1 BACKGROUND

The integration of arc fault detection into circuit breakers represents a revolutionary change in 

circuit protection; which has changed little in the last thirty to forty years. There is abundant 

evidence of arc faults in all types of aircraft. Laboratory data clearly demonstrates that the 

current generated during an arcing fault can be very high, yet quite intermittent. The bimetallic 

elements in thermal breakers do not react quickly enough, if at all, to this ticking arc fault 

condition. If left unchecked, the arcing condition can develop into an arc tracking condition, 

potentially destroying a major portion of, or an entire wire bundle. Arcing can also result in 

many other serious safety hazards. 

In 1999, the FAA and the Navy established a joint R&D project to develop aircraft AFCBs. The 

goal of this effort is to develop a circuit breaker that integrates arc fault protection together with 

existing thermal protection into a form, fit, and functional replacement of existing thermal circuit 

breakers. In laboratory testing, the AFCB prototypes have been very effective in the detection of 

arcing faults. 

In contrast to thermal breakers, which are passive in nature, AFCBs actively monitor the circuits 

on which they are installed. Due to the nature of electrical systems, there are times when a 

normal condition may ‘look’ similar to an arc fault. When such a condition trips an arc fault 

circuit breaker, it is defined as a nuisance trip. AFCB designs minimize the occurrence of 

nuisance tripping and maximize sensitivity to arc fault detection. 

To address nuisance tripping, the FAA, Navy, and the AFCB developers, have conducted 

extensive tests to characterize the normal operation of electrical loads, and perturbations to 

electrical systems during normal events such as bus transfers, power on/off, transfer of power 

sources, etc. Laboratory tests today have provided a high level of confidence that nuisance 

tripping of AFCBs is being successfully controlled. 

AFCB development has progressed to the point where flight tests are appropriate to demonstrate 

compliance with applicable Federal Aviation Regulations (FARs). 

1.2 OBJECTIVE

The objective of this task is to conduct an in-flight evaluation of AFCB performance. 

The Federal Aviation Administration (FAA), William J. Hughes Technical Center (WJHTC) 

R&D Flight Program is performing a minor modification to their Boeing 727-25C aircraft. This 

temporary modification involves the installation of eight AFCB prototypes manufactured by the 

G-7
Hendry Corporation. The AFCBs are to be installed for a six-month evaluation period in support 

of AFCB research and development. 

1.3 SCOPE

The scope of this effort is to install AFCBs manufactured by Hendry in an FAA owned Boeing 

727-25C aircraft and conduct a flight evaluation of the developmental AFCBs. Data recorded 

includes line voltage, load voltage, and current for each of the installed breakers. Data reduction 

efforts of any occurring arc faults will include identification of relationships between the trip 

conditions. 

2. CERTIFICATION REQUIREMENTS

The certification request will permit the FAA to temporarily install AFCBs aboard the B727-25C 

(N40) with the purpose of evaluating the circuit breakers, in-flight, over a six-month period. 

This will assure that the AFCBs are evaluated against a wide range of actual electrical 

conditions. 

There are no FAA Technical Standard Orders for the equipment being installed during this 

modification. Experimental flight test is being performed to collect data necessary to obtain a 

one only STC to install the AFCBs aboard N40 for an extended evaluation period. 

3. SYSTEM DESCRIPTION

The equipment being installed for the Arc Fault flight evaluation includes developmental 

prototype AFCBs installed in a junction box, an instrumentation recorder and interconnecting 

cables and wire harnesses. These items are described in the following paragraphs. 

3.1 ARC FAULT CIRCUIT BREAKERS

Eight (8) - Hendry prototype arc fault circuit breakers of the following ratings: one 2.5 A, 

three 5A, one 7.5A, one 10A, and two 15A (mounted in AFCI Junction Box). 

3.2 ARC FAULT CIRCUIT INTERRUPTER - JUNCTION BOX AND AIRCRAFT 

HARNESSES

One (1) – AFCI-JB. 

Two (2) – AFCI-JB Test Unit wire harnesses, P18 and P6 

3.3 INSTRUMENTATION EQUIPMENT

One (1) - 24 channel, Nicolet Odyssey data recorder. 

One (1) – BNC Breakout Box. 

One (1) – AFCI JB – BNC Breakout Box Interface Harness. 

Twenty-four (24) – 24-inch BNC connector cables. 

One (1) – Trigger Alarm 

G-8
3.4 AIRCRAFT INTERFACES

The electrical connections for the system are shown schematically in FAA Drawing Number 

9854415, Arc Fault Circuit Breaker Wiring. The AFCBs mounted within the AFCI-JB will be 

electrically in series with the load side of the existing circuit breakers. The AFCI-JB wire 

harnesses, P-18 and P-6, connect the load side of the each aircraft circuit breaker to the line side 

of the respective AFCB and from the load side of the each AFCB to the feed wire for the 

respective load. 

3.5 POWER REQUIREMENTS

120VAC 60Hz power is required for power to the Data Acquisition System. The on board 

Project Power Inverter provides this power. 

4. AIRCRAFT INSTALLATION

The electrical, system, and mechanical integration of this installation will be accomplished at 

Atlantic City International Airport (ACIAP) using FAA technical and engineering personnel. 

The engineering personnel have been granted authority to approve “electrical systems” and 

“structures” data via FAA Form 8110-3, by the New York Aircraft Certification Office 

(NYACO). 

The AFCBs will be installed in an Arc Fault Circuit Interrupter-Junction Box (AFCI-JB) that 

will enclose all the AFCBs and required instrumentation. The AFCBs will not be mounted in the 

aircraft circuit breaker panels. It is important to note that the AFCBs will be connected in series 

with the load side of the existing thermal circuit breakers. In other words, current circuit 

protection aboard the aircraft will not be compromised in any way by this installation. 

The AFCI-JB will contain the eight AFCB units. The AFCI-JB will be mounted on the floor in 

the rear, left side of the flight deck. The test unit will have by-pass switches that will disable the 

AFCBs if desired. The test unit will be fabricated using standard best practices and in 

accordance with AC 43.13-1B and contain any possible AFCB failure. 

The electrical installation shall be completed in accordance with drawing number 9854415 under 

the guidance of the WJHTC Electrical Systems Designated Engineering Representative (DER). 

The mechanical installation shall be completed under the guidance of the WJHTC Mechanical 

Systems DER. 

4.1 AFCB INSTALLATION INSTRUCTIONS

The installation shall be completed in accordance with all existing safety requirements and the 

necessary approvals shall be obtained in advance of starting the installation. 

General instructions for completing the installation can be found at Appendix A. 

4.2 INSTRUMENTATION EQUIPMENT INSTALLATION INSTRUCTIONS

The BNC Breakout Box and the Odyssey data recorder will be mounted in the cabin of the 

aircraft. The AFCI-JB/BNC Breakout Box Interface Harness connects the AFCI-JB to the BNC 

G-9
Breakout Box. The 24 BNC connectors on the BNC Breakout Box are connected to the Odyssey 

data recorder with 24” BNC coaxial cables. 

General instructions for completing the installation can be found at Appendix A. 

5. GROUND CHECKOUT PROCEDURES

After completion of the installation the following tests shall be conducted to demonstrate that the 

AFCB equipment was successfully integrated and operates properly. 

5.1 AFCB ELECTRICAL TESTS

After the mechanical and electrical installation of the AFCB equipment has been accomplished 

the electrical tests presented at Appendix B shall be successfully completed and the results 

documented to support certification. 

5.2 AFCB TEST CIRCUIT TIME DOMAIN REFLECTOMETRY BASELINE TESTS

Time Domain Reflectometry Baseline Tests to characterize the test circuits were performed 

during the previous series of flight tests using AFCBs from another manufacturer. Since the 

same test circuits are being used for this test the TDR Baseline Tests will not be performed. The 

procedures for these tests are shown at Appendix C. If, during integration and other testing, it is 

determined that a repeat of the TDR testing is required the equipment and contractor are 

available to support this series of tests. 

- - End of Ground Checkout Procedure - - 

G-10
APPENDIX A – AFCB INSTALLATION INSTRUCTIONS / VERIFICATION SHEET 

The installation shall be completed in accordance with all existing safety requirements and the 

necessary approvals shall be obtained in advance of starting the installation. The following are 

general instructions for completing the installation. Record completion and any observations in 

the Completed/Comments column. 

Step Procedure Completed/Comments 

1 The two AFCI-JB Interface wire harnesses, P-18 and 

P-6, shall be connected to the thermal circuit breakers 

in accordance with FAA Drawing number 9854415. 

Harness P-18 shall be connected to the following four 

aircraft circuits: 

1. Left Inboard Landing Lights (7.5A) 

2. Navigation Lights (5A) 

3. Window Lights (10A) 

4. Left Ceiling Lights (15A) 

Harness P-6 shall be connected to the following four 

aircraft circuits: 

1. DME-2 (3A) 

2. Auxiliary Pitot Heat (5A) 

3. First Officers Window (5A) 

4. AC Project Power (15A) 

2 Mount the AFCI-JB in the flight deck as per the 

Mechanical Systems DER instructions. 

3 Mount the Odyssey and the BNC Breakout Box in the 

cabin rack per the Mechanical Systems DER 

instructions. 

4 Insure that all mounting is secure. 

5 Route the AFCI-JB harnesses and the AFCIJB/Breakout Box harness. Do not mate the harnesses 

to the AFCI-JB or the breakout box until electrical 

tests have been completed. Do not secure the harness 

until electrical tests have been completed. 

- - End of Detailed Installation Instructions - - 

Installation completed by _____________________ Verified by ________________________ 

 Name and Date Name and Date

G-11
APPENDIX B - AFCB ELECTRICAL TEST PROCEDURES / VERIFICATION SHEET 

The following Electrical Test Procedures shall be conducted to verify that there is continuity and 

no shorts in the AFCB project equipment and aircraft wiring. Record completion and any 

observations in the Completed/Comments column. 

Step Procedure Completed/Comments 

1 Open the eight (8) aircraft circuit breakers for the 

circuits being monitored during the AFCB Flight 

Test Program 

2 Confirm that the P-18 and P-6 harnesses from the 

aircraft circuit breaker panels to P1 and P2 on the 

AFCI-JB are disconnected from the AFCI-JB. 

3 Prior to connecting the harnesses to the AFCI-JB, 

perform the following continuity and isolation 

checks performed in accordance with Table 1. 

Table 1 – AFCI-JB Checkout 

AFCI-JB 

Connector 

Test Points 

AFCB-x Position 

(Open/Closed) 

(x =1,2,3,4,5,6,7,8) 

AFCB By-Pass Switch

S-x (Normal/Bypass) 

(x = 1,2,3,4,5,6,7,8) 

Expected 

Test Point 

Condition 

Observed 

Condition 

(see Note) 

P1, 1 and 2 AFCB-1, Closed S-1, Normal Short 

P1, 4 and 5 AFCB-2, Closed S-2, Normal Short 

P1, 7 and 8 AFCB-3, Closed S-3, Normal Short 

P1, 10 and 11 AFCB-4, Closed S-4, Normal Short 

P2, 1 and 2 AFCB-5, Closed S-5, Normal Short 

P2, 4 and 5 AFCB-6, Closed S-6, Normal Short 

P2, 7 and 8 AFCB-7, Closed S-7, Normal Short 

P2, 10 and 11 AFCB-8, Closed S-8, Normal Short 

P1, 1 and 2 AFCB-1, Open S-1, Normal Open 

P1, 4 and 5 AFCB-2, Open S-2, Normal Open 

P1, 7 and 8 AFCB-3, Open S-3, Normal Open 

P1, 10 and 11 AFCB-4, Open S-4, Normal Open 

P2, 1 and 2 AFCB-5, Open S-5, Normal Open 

P2, 4 and 5 AFCB-6, Open S-6, Normal Open 

P2, 7 and 8 AFCB-7, Open S-7, Normal Open 

P2, 10 and 11 AFCB-8, Open S-8, Normal Open 

P1, 1 and 2 AFCB-1, Open S-1, Bypass Short 

P1, 4 and 5 AFCB-2, Open S-2, Bypass Short 

G-12
P1, 7 and 8 AFCB-3, Open S-3, Bypass Short 

P1, 10 and 11 AFCB-4, Open S-4, Bypass Short 

P2, 1 and 2 AFCB-5, Open S-5, Bypass Short 

P2, 4 and 5 AFCB-6, Open S-6, Bypass Short 

P2, 7 and 8 AFCB-7, Open S-7, Bypass Short 

P2, 10 and 11 AFCB-8, Open S-8, Bypass Short 

AFCB-1, Red & 

Black Banana 

Plug Sockets 

AFCB-1, Closed S-1, Normal Short 

AFCB-2, Red & 

Black Banana 

Plug Sockets 

AFCB-2, Closed S-2, Normal Short 

AFCB-3, Red & 

Black Banana 

Plug Sockets 

AFCB-3, Closed S-3, Normal Short 

AFCB-4, Red & 

Black Banana 

Plug Sockets 

AFCB-4, Closed S-4, Normal Short 

AFCB-5, Red & 

Black Banana 

Plug Sockets 

AFCB-5, Closed S-5, Normal Short 

AFCB-6, Red & 

Black Banana 

Plug Sockets 

AFCB-6, Closed S-6, Normal Short 

AFCB-7, Red & 

Black Banana 

Plug Sockets 

AFCB-7, Closed S-7, Normal Short 

AFCB-8, Red & 

Black Banana 

Plug Sockets 

AFCB-8, Closed S-8, Normal Short 

AFCB-1, Red & 

Black Banana 

Plug Sockets 

AFCB-1, Open S-1, Normal Open 

AFCB-2, Red & 

Black Banana 

Plug Sockets 

AFCB-2, Open S-2, Normal Open 

AFCB-3, Red & 

Black Banana 

Plug Sockets 

AFCB-3, Open S-3, Normal Open 

AFCB-4, Red & 

Black Banana 

Plug Sockets 

AFCB-4, Open S-4, Normal Open 

AFCB-5, Red & 

Black Banana 

Plug Sockets 

AFCB-5, Open S-5, Normal Open 

G-13
AFCB-6, Red & 

Black Banana 

Plug Sockets 

AFCB-6, Open S-6, Normal Open 

AFCB-7, Red & 

Black Banana 

Plug Sockets 

AFCB-7, Open S-7, Normal Open 

AFCB-8, Red & 

Black Banana 

Plug Sockets 

AFCB-8, Open S-8, Normal Open 

AFCB-1, Red & 

Black Banana 

Plug Sockets 

AFCB-1, Open S-1, Bypass Short 

AFCB-2, Red & 

Black Banana 

Plug Sockets 

AFCB-2, Open S-2, Bypass Short 

AFCB-3, Red & 

Black Banana 

Plug Sockets 

AFCB-3, Open S-3, Bypass Short 

AFCB-4, Red & 

Black Banana 

Plug Sockets 

AFCB-4, Open S-4, Bypass Short 

AFCB-5, Red & 

Black Banana 

Plug Sockets 

AFCB-5, Open S-5, Bypass Short 

AFCB-6, Red & 

Black Banana 

Plug Sockets 

AFCB-6, Open S-6, Bypass Short 

AFCB-7, Red & 

Black Banana 

Plug Sockets 

AFCB-7, Open S-7, Bypass Short 

AFCB-8, Red & 

Black Banana 

Plug Sockets 

AFCB-8, Open S-8, Bypass Short 

* Note - A measurement of 2.1 Megohms between test points will be seen when an open condition is expected. This 

is due to the voltage divider circuit added for instrumentation purposes. 

Step Procedure Completed/Comments 

4 Open the eight AFCBs in the AFCI-JB. 

5 On the AFCI-JB set S-1 through S-8 to Normal. 

6 Open the eight aircraft circuit breakers. 

7 With aircraft power off, connect harness P-18 to 

AFCI-JB connector P-1 and harness P-6 to AFCIJB connector P2. 

8 Apply power (ground power or APU) to the 

aircraft. 

9 Close the eight aircraft circuit breakers and verify

G-14
that the associated loads are not energized. 

10 Set AFCI-JB S-1 to Bypass, turn on using the 

cockpit switch and verify via visual means that 

the LEFT INBOARD LANDING LIGHTS are 

operating. Set S-1 to Normal. 

11 Set AFCI-JB S-2 to Bypass, turn on using the 

cockpit switch and verify via visual means that 

the OSCILLATING NAVIGATION LIGHTS are 

operating. Set S-2 to Normal. 

12 Set AFCI-JB S-3 to Bypass, turn on using the 

cockpit switch and verify via visual means that 

the WINDOW LIGHTS – LEFT SIDE are 

operating. Set S-3 to Normal. 

13 Set AFCI-JB S-4 to Bypass, turn on using the 

cockpit switch and verify via visual means that 

the PASSENGER CEILING LIGHTS – LEFT 

SIDE are operating. Set S-4 to Normal. 

14 Set AFCI-JB S-5 to Bypass, turn on using the 

cockpit switch and verify via visual means that 

the DME-2 is operating. Set S-5 to Normal. 

15 Set AFCI-JB S-6 to Bypass, turn on using the 

cockpit switch and verify via the Pitot Ammeter 

that the HEATER-PITOT-AUX is operating. Set 

S-6 to Normal. 

16 Set AFCI-JB S-7 to Bypass, turn on using the 

cockpit switch and verify via visual means that 

the FIRST OFFICER’S WINDOW HEATER is 

operating. Set S-7 to Normal. 

17 Set AFCI-JB S-8 to Bypass, turn on using the 

cockpit switch and verify that the PROJECT 

POWER is operating. Set S-8 to Normal. 

18 Close AFCB-1, turn on using the cockpit switch 

and verify via visual means that the LEFT 

INBOARD LANDING LIGHTS are operating. 

Open AFCB-1. 

19 Close AFCB-2, turn on using the cockpit switch 

and verify via visual means that the 

OSCILLATING NAVIGATION LIGHTS are 

operating. Open AFCB-2. 

20 Close AFCB-3, turn on using the cockpit switch 

and verify via visual means that the WINDOW 

LIGHTS – LEFT SIDE are operating. Open 

AFCB-3. 

21 Close AFCB-4, turn on using the cockpit switch 

and verify via visual means that the 

PASSENGER CEILING LIGHTS – LEFT SIDE

G-15
are operating. Open AFCB-4. 

22 Close AFCB-5, turn on using the cockpit switch 

and verify via visual means that the DME-2 is 

operating. Open AFCB-5. 

23 Close AFCB-6, turn on using the cockpit switch 

and verify via the Pitot Ammeter that the 

HEATER-PITOT-AUX is operating. Open 

AFCB-6. 

24 Close AFCB-7, turn on using the cockpit switch 

and verify by via visual means that the FIRST 

OFFICER’S WINDOW HEATER is operating. 

Open AFCB-7. 

25 Close AFCB-8, turn on using the cockpit switch 

and verify that PROJECT POWER is operating. 

Open AFCB-8. 

26 Open the eight aircraft circuit breakers. 

27 Connect the P-3 connector on the AFCI-JB to P-4 

on the BNC Breakout Box with the AFCIJB/BNC Breakout Box Interface Harness. 

28 Using the 24” BNC connector cables, connect the 

BNC Breakout Box to the Odyssey data recorder 

in accordance with Table 2. For the eight 

channels noted in Table 2, install a 50-Ohm inline terminator between the BNC cable and the 

Odyssey data recorder. 

G-16
Table 2 – Odyssey Channel Assignments 

From BNC Breakout Box 

Connector BNC-x 

(x = 1,2,3.....22,23,24) 

To Odyssey Data Recorder 

Channel Number x 

(x = 1,2,3.....22,23,24) 

50-Ohm In-line 

Terminator Required? 

 (Y/N) 

Measurement 

Parameter 

Description 

BNC-1 1 N AFCB–1 Line Volts 

BNC-9 9 N AFCB-1 Load Volts 

BNC-17 17 Y AFCB-1 Current 

BNC-2 2 N AFCB–2 Line Volts 

BNC-10 10 N AFCB-2 Load Volts 

BNC-18 18 Y AFCB-2 Current 

BNC-3 3 N AFCB–3 Line Volts 

BNC-11 11 N AFCB-3 Load Volts 

BNC-19 19 Y AFCB-3 Current 

BNC-4 4 N AFCB–4 Line Volts 

BNC-12 12 N AFCB-4 Load Volts 

BNC-20 20 Y AFCB-4 Current 

BNC-5 5 N AFCB–5 Line Volts 

BNC-13 13 N AFCB-5 Load Volts 

BNC-21 21 Y AFCB-5 Current 

BNC-6 6 N AFCB–6 Line Volts 

BNC-13 13 N AFCB-6 Load Volts 

BNC-22 22 Y AFCB-6 Current 

BNC-7 7 N AFCB–7 Line Volts 

BNC-14 14 N AFCB-7 Load Volts 

BNC-23 23 Y AFCB-7 Current 

BNC-8 Open N AFCB–8 Line Volts 

BNC-15 15 N AFCB-8 Load Volts 

BNC-24 24 Y AFCB-8 Current 

Coax from AFCI-JB 

BNC-Trigger 

8 N Odyssey Trigger Input

Step Procedure Completed/Comments 

28 Turn on the Odyssey data recorder. The Odyssey 

data recorder takes several minutes to complete 

the boot process. 

29 Close the eight aircraft circuit breakers. Verify 

that the voltage and current inputs to the data 

recorder are reading zero. 

30 Close AFCB-1, turn on using the cockpit switch 

and verify via visual means that the LEFT 

INBOARD LANDING LIGHTS are operating. 

Verify that the voltage and current waveforms are 

being properly measured on the Odyssey data 

recorder channels 1, 9, and 17. 

31 Close AFCB-2, turn on using the cockpit switch 

G-17
and verify via visual means that the 

OSCILLATING NAVIGATION LIGHTS are 

operating. Verify that the voltage and current 

waveforms are being properly measured on the 

Odyssey data recorder channels 2, 10, and 18. 

32 Close AFCB-3, turn on using the cockpit switch 

and verify via visual means that the WINDOW 

LIGHTS – LEFT SIDE are operating. Verify that 

the voltage and current waveforms are being 

properly measured on the Odyssey data recorder 

channels 3,11, and 19. 

33 Close AFCB-4, turn on using the cockpit switch 

and verify via visual means that the 

PASSENGER CEILING LIGHTS – LEFT SIDE 

are operating. Verify that the voltage and current 

waveforms are being properly measured on the 

Odyssey data recorder channels 4, 12, and 20. 

34 Close AFCB-5, turn on using the cockpit switch 

and verify via visual means that the DME is 

operating. Verify that the voltage and current 

waveforms are being properly measured on the 

Odyssey data recorder channels 5, 13, and 21. 

35 Close AFCB-6, turn on using the cockpit switch 

and verify via the Pitot Ammeter that the 

HEATER-PITOT-AUX is operating. Verify that 

the voltage and current waveforms are being 

properly measured on the Odyssey data recorder 

channels 6, 14, and 22. 

36 Close AFCB-7, turn on using the cockpit switch 

and verify by via visual means that the FIRST 

OFFICER’S WINDOW HEATER is operating. 

Verify that the voltage and current waveforms are 

being properly measured on the Odyssey data 

recorder channels 7, 15, and 23. 

37 Close AFCB-8, turn on using the cockpit switch 

and verify that PROJECT POWER is operating. 

Verify that the voltage and current waveforms are 

being properly measured on the Odyssey data 

recorder channels 8, 16 and 24. 

38 Open and close the Left Inboard Landing Lights 

aircraft circuit breaker five times. Verify that 

AFCB-1 did not nuisance trip during the five 

open-close cycles. 

39 Open and close the Navigation Lights aircraft 

circuit breaker five times. Verify that AFCB-2 

did not nuisance trip during the five open-close 

G-18
cycles. 

40 Open and close the Window Lights aircraft circuit 

breaker five times. Verify that AFCB-3 did not 

nuisance trip during the five open-close cycles. 

41 Open and close the Left Ceiling Lights aircraft 

circuit breaker five times. Verify that AFCB-4 

did not nuisance trip during the five open-close 

cycles. 

42 Open and close the DME-2 aircraft circuit 

breaker five times. Verify that AFCB-5 did not 

nuisance trip during the five open-close cycles. 

43 Open and close the Auxiliary Pitot Heat aircraft 

circuit breaker five times. Verify that AFCB-6 

did not nuisance trip during the five open-close 

cycles. 

44 Open and close the First Officers Window aircraft 

circuit breaker five times. Verify that AFCB-7 

did not nuisance trip during the five open-close 

cycles. 

45 Open and close the AC Project Power aircraft 

circuit breaker five times. Verify that AFCB-8 

did not nuisance trip during the five open-close 

cycles. 

46 With the eight aircraft circuit breakers and the 

eight AFCBs closed switch from ground power to 

APU power. Verify that no nuisance trips 

occurred. Switch from APU power to engine 

power. Verify that no nuisance trips occurred. 

Reverse this process and verify that no nuisance 

trips occurred after each step. Repeat this cycle 

four additional times. 

47 With aircraft electrical power on (ground, APU, 

or engine) and the aircraft circuit breakers closed, 

begin recording on the Odyssey by pressing the 

record button. Open AFCB-1. The trigger alarm 

shall activate. Close AFCB-1 and reset the 

trigger alarm. Repeat this process for AFCB-2 

through AFCB-8. 

48 Turn on RADAR, IFF, RADAR Altimeter, and 

all Radios 

49 With aircraft electrical power on (ground, APU, 

or engine) and the aircraft circuit breakers and 

AFCBs closed, test aircraft systems in accordance 

with the B727 Standard Start-up checklist. An 

Odyssey data recording shall be made as each 

load is tested. For voice communication, conduct 

G-19
transmission checks on each radio. No AFCBs 

shall nuisance trip during these tests. Confirm 

that the AFCBs and instrumentation do not 

interfere with the operation of the aircraft system. 

50 Save all instrumentation recordings and download 

to removable disc. 

51 Turn off instrumentation equipment 

52 Set AFCI-JB S1 thru AFCI-JB S8 to BYPASS 

53 Open AFCB-1 through AFCB-8 

54 Shut down Aircraft Power IAW standard 

operating procedures 

- - End of AFCB Electrical Tests - - 

Electrical Tests completed by _________________ Verified by ________________________ 

 Name and Date Name and Date 

G-20
APPENDIX C – TIME DOMAIN REFLECTOMETRY BASELINE TEST 

PROCEDURES / VERIFICATION SHEET

Conduct Time Domain Reflectometry Baseline Tests

The eight AFCB test circuits will be characterized using a Time Domain Reflectometry 

(TDR) technique. The purpose of this test is to baseline the existing condition of each 

circuit to be used as a reference benchmark. If an AFCB should trip during flight test, a 

new TDR measurement of the effected circuit will be conducted and compared to the 

original benchmark. This will assist in determining the presence and location of the fault. 

The TDR testing will be conducted by CM Technologies under the supervision of John 

Beres. 

TDR Tools and Equipment: 

The tools and equipment listed below shall be supplied by CM Technologies. 

• Electrical Characterization and Diagnostics (ECADTM) System 1100. The ECADTM

system injects a pulse of 1V amplitude, and 400μsec pulse width. In the worst case, the 

maximum energy of the pulse is 8μJ. The pulse applied in the Excited Dielectric Test 

(EDT), described below, is even lower. The pulse amplitude is only 200 mV and the 

pulse width is narrower than the 400μsec pulse used in the standard TDR test. 

• Agilent 86100A Oscilloscope Mainframe with 54754A Time Domain Reflectometer 

Plug-in Module. 

• Tabor 8020 Function Generator. 

• Coupling network, test lead cables, and clips.

TDR Precautions 

The ECADTM System 1100 is designed to test de-energized wires. Computer logic first 

checks the circuit for AC and DC voltage and will not permit an automatic test if a 

significant voltage level is found (greater than 5 VDC or VAC). Attempting to test 

energized wiring may damage the ECAD instrumentation and/or represent a safety 

hazard to test personnel. 

TDR Test Supervision 

The WJHTC Electrical Systems DER is responsible for managing the arc fault circuit 

breaker installation and testing aboard N40. The CM Technologies field engineer shall 

discuss the test plan with the Electrical Systems DER to ensure compliance with all 

applicable FAA quality and/or testing procedures. 

G-21 
 The WJHTC Electrical Systems DER (or designee) shall be responsible for opening 

any panels to gain access to breakers, opening breakers to de-energize circuits, and 

restoring the circuits to an operational (pre-test) condition. 

TDR Procedure 

ECADTM System 1100 Equipment Setup: 

 Locate the ECADTM System 1100 near the circuits to be tested. Ideally, the 

equipment will be located within 10 to 25 feet from the test location. 

 Provide the equipment with a source of 120 VAC, 60 Hz power. 

 Connect power, signal, and test leads to the equipment as required. 

 Turn on the ECADTM System 1100 and start the data acquisition software. 

 Load the AFCB database files. 

 Execute the system self-test. The self-test checks the proper operation of each 

instrument card and measures the electrical properties associated with the test lead. 

ECADTM Testing: 

 Select the device/circuit to be tested from the ECAD AFCB database. 

 Verify the circuit to be tested matches the circuit descriptive data (CDD) displayed in 

the ECADTM software. Also, verify the circuit to be tested is de-energized. 

 Connect the ECADTM test clips to the circuit as indicated in the HIGH TEST PT and 

LOW TEST PT fields of the CDD screen. 

 Using a digital multi-meter, measure resistance from the conductor to aircraft ground. 

If resistance is less than 500kΩ stop the test and troubleshoot the circuit wiring. If 

greater than 500kΩ, proceed to next step. 

 The Insulation Resistance (IR) TEST VOLTS field of the CDD screen indicates the 

MAXIMUM IR test voltage that is allowed. The maximum applied voltage will be 

50VDC. Testing at voltages greater than this value could damage circuit components. 

A value of zero (0) volts in this field indicates that an IR test is not to be performed 

for this configuration. 

 Initiate a TEST of the selected configuration. 

 Review the measurement data as required. 

 Repeat ECAD Testing steps until all of the eight circuits have been characterized. 

Excited Dielectric Test (EDT) Equipment Setup: 

 Locate the EDT test equipment near the circuits to be tested. Ideally, the equipment 

will be located within 10 to 25 feet from the test location. 

 Provide the equipment with a source of 120 VAC, 60 Hz power. 

G-22 
 Connect power, signal, and test leads to the equipment as required. 

 Turn on the Agilent 86100A. 

EDT Testing: 

 Connect the alligator test clips to the same test locations that were used during the 

ECAD testing. 

 Acquire three (3) TDR signatures using three (3) forcing function frequencies. The 

three frequencies will be determined from the insulation materials used in the circuit 

under test. 

 Waveforms will be named and saved for storage in the Agilent 86100A. 

 Review the TDR waveform as required. 

 Repeat EDT Testing steps until all of the test configurations have been completed. 

Circuit Restoration: 

 Disconnect all test clips. 

 Restore the circuit to normal as directed by the Electrical Systems DER. 

 Perform functional test on the restored circuit, if needed. 

- - End of Time Domain Reflectometry Baseline Tests - - 

Attach test results to this verification sheet. 

TDR Tests completed by _____________________ Verified by ________________________ 

 Name and Date Name and Date 

G-23/G-24 
APPENDIX H—HENDRY FLIGHT TEST RECORDS 

H-1/H-2
Hendry Flight Test Records 

HENDRY FLIGHT TEST HOURS 

 Circuit Breaker Hours

Flight Date From To 

In Service 

Time 

Block 

Time 

Cumulative In 

Service 

Cumulative 

Block 

Block 

Time 

Cumulative 

Block 

 

1 8/5/02 KACY local 1.2 1.6 1.2 1.6 12.8 12.8 

2 8/6/02 KACY KSYR 2.2 2.3 3.4 3.9 18.4 31.2 

3 8/6/02 KSYR KACY 0.9 1.3 4.3 5.2 10.4 41.6 

4 8/15/02 KACY KGTF 4.3 4.5 8.6 9.7 36.0 77.6 

5 8/15/02 KGTF KBFI 1.4 1.7 10.0 11.4 13.6 91.2 

6 8/16/02 KBFI KACY 4.2 4.5 14.2 15.9 36.0 127.2 

7 8/19/02 KACY KGTF 4.4 4.5 18.6 20.4 36.0 163.2 

8 8/19/02 KGTF KANC 3.8 4.2 22.4 24.6 33.6 196.8 

9 8/20/02 KANC local 0.1 0.4 22.5 25.0 3.2 200.0 

10 8/23/02 KACY local 1.9 2.1 24.4 27.1 16.8 216.8 

11 9/23/02 KACY KMIA 2.3 2.5 26.7 29.6 20.0 236.8 

12 9/24/02 KMIA TSJ 2.3 2.5 29.0 32.1 20.0 256.8 

13 9/24/02 TSJ KMIA 2.4 2.6 31.4 34.7 20.8 277.6 

14 9/25/02 KMIA KMIA 3.1 3.5 34.5 38.2 25.5 303.1 

15 9/26/02 KMIA KMIA 2.4 2.6 36.9 40.8 20.8 323.9 

16 9/26/02 KMIA KACY 2.1 2.5 39.0 43.3 20.0 343.9 

17 9/30/02 KACY KGTF 4.1 4.3 43.1 47.6 34.4 378.3 

19 9/30/02 KGTF KBFI 1.3 1.5 44.4 49.1 12.0 390.3 

20 9/30/02 KBFI KBFI 2.3 2.6 46.7 51.7 20.8 411.1 

21 10/1/02 KBFI KBFI 2.4 2.8 49.1 54.5 22.4 433.5 

22 10/1/02 KBFI KBFI 2.3 2.5 51.4 57.0 20.0 453.5 

23 10/2/02 KBFI KBFI 2.3 2.6 53.7 59.6 20.8 474.3 

24 10/3/02 KBFI KGRB 3.1 3.3 56.8 62.9 26.4 500.7 

25 10/3/02 KGRB KGRB 2.6 3.1 59.4 66.0 24.8 525.5 

26 10/4/02 KGRB KACY 1.7 2.2 61.1 68.2 17.6 543.1 

27 10/6/02 KACY KGRB 1.8 2.0 62.9 70.2 16.0 559.1 

29 10/6/02 KGRB KGRB 2.1 2.3 65.0 72.5 18.4 577.5 

30 10/7/02 KGRB KGRB 1.6 1.8 66.6 74.3 14.4 591.9 

31 10/8/02 KGRB KGTF 2.5 2.7 69.1 77.0 21.6 613.5 

32 10/8/02 KGTF KGTF 1.6 1.8 70.7 78.8 14.4 627.9 

33 10/9/02 KGTF KGTF 1.6 1.9 72.3 80.7 15.2 643.1 

34 10/9/02 KGTF KGTF 1.6 1.7 73.9 82.4 13.6 656.7 

35 10/10/02 KGTF KGTF 1.5 1.8 75.4 84.2 14.4 671.1 

36 10/11/02 KGTF KACY 3.6 3.8 79.0 88.0 30.4 701.5 

H-3
H-4
H-5
H-6
H-7
H-8
H-9
H-10
H-11
H-12
H-13
H-14
H-15
H-16
H-17
H-18
H-19
H-20
H-21
H-22
H-23
H-24
H-25/H-26
APPENDIX I—HENDRY TROUBLESHOOTING PROCEDURES

I-1/I-2
Arc Fault Circuit Breaker 

Flight Test Program 

Troubleshooting Procedures 

for 

Hendry Arc Fault Circuit Breaker (AFCB) Installation 

on 

FAA Technical Center 

Boeing 727-25C Aircraft N40 

15 June 2002 

FAA William J. Hughes Technical Center 

Engineering and Modification Section, ACT-370 

Maintenance, Inspection, and Repair Section, AAR-433 

Prepared by: R.A. Pappas, AAR-433 

Reviewed by: J. Beres, ACT-370 

Approved by: Armando Gaetano 

 Manager, Engineering & Modifications Section, ACT-370 

I-3/I-4
Table of Contents 

1.0 INTRODUCTION..................................................................................................................... 7

1.1 Background .................................................................................................................. 7

1.2 Objective ...................................................................................................................... 7

1.3 Scope ............................................................................................................................ 8

2.0 FLIGHT TEST GOALS ........................................................................................................... 8

3.0 SYSTEM DESCRIPTION........................................................................................................ 8

3.1 Arc Fault Circuit Breakers ........................................................................................... 8

3.2 Arc Fault Circuit Interupter - Junction Box and Aircraft Harnesses............................ 8

3.3 Instrumentation Equipment .......................................................................................... 8

3.4 Aircraft Interfaces......................................................................................................... 8

4.0 AIRCRAFT INSTALLATION .................................................................................................. 9

5.0 CERTIFICATION REQUIREMENTS ...................................................................................... 9

6.0 ARC FAULT TROUBLESHOOTING...................................................................................... 9

6.1 Arc Fault Troubleshooting Background....................................................................... 9

6.2 Detailed Troubleshooting Procedures ........................................................................ 10

APPENDIX A – TROUBLESHOOTING PROCESS FLOWCHARTS........................................... 11

I-5/I-6
1.0 INTRODUCTION 

This document defines the troubleshooting procedures to be used during the Arc Fault Circuit 

Breakers (AFCBs) performance evaluation on in an FAA owned Boeing 727-25C aircraft. The 

effort will be conducted by the United States (U.S.) Federal Aviation Administration (FAA) at 

the William J. Hughes Technical Center (WJHTC), Atlantic City, New Jersey. 

1.1 BACKGROUND

The integration of arc fault detection into circuit breakers represents a revolutionary change in 

circuit protection; which has changed little in the last thirty to forty years. There is abundant 

evidence of arc faults in all types of aircraft. Laboratory data clearly demonstrates that the 

current generated during an arcing fault can be very high, yet quite intermittent. The bimetallic 

elements in thermal breakers do not react quickly enough, if at all, to this ticking arc fault 

condition. If left unchecked, the arcing condition can develop into an arc tracking condition, 

potentially destroying a major portion of, or an entire wire bundle. Arcing can also result in 

many other serious safety hazards. 

In 1999, the FAA and the Navy established a joint R&D project to develop aircraft AFCBs. The 

goal of this effort is to develop a circuit breaker that integrates arc fault protection together with 

existing thermal protection into a form, fit, and functional replacement of existing thermal circuit 

breakers. In laboratory testing, the AFCB prototypes have been very effective in the detection of 

arcing faults. 

In contrast to thermal breakers, which are passive in nature, AFCBs actively monitor the circuits 

on which they are installed. Due to the nature of electrical systems, there are times when a 

normal condition may ‘look’ similar to an arc fault. When such a condition trips an arc fault 

circuit breaker, it is defined as a nuisance trip. AFCB designs minimize the occurrence of 

nuisance tripping and maximize sensitivity to arc fault detection. 

To address nuisance tripping, the FAA, Navy, and the AFCB developers, have conducted 

extensive tests to characterize the normal operation of electrical loads, and perturbations to 

electrical systems during normal events such as bus transfers, power on/off, transfer of power 

sources, etc. Laboratory tests today have provided a high level of confidence that nuisance 

tripping of AFCBs is being successfully controlled. 

AFCB development has progressed to the point where flight tests are appropriate to demonstrate 

compliance with applicable Federal Aviation Regulations (FARs). 

1.2 OBJECTIVE

The objective of this task is to conduct an in-flight evaluation of AFCB performance. 

The Federal Aviation Administration (FAA), William J. Hughes Technical Center (WJHTC) 

R&D Flight Program is performing a minor modification to their Boeing 727-25C aircraft. This 

temporary modification involves the installation of eight AFCB prototypes manufactured by the 

Hendry corporation. The AFCBs are to be installed for a six-month evaluation period in support 

of AFCB research and development. 

I-7
1.3 SCOPE

The scope of this effort is to install AFCBs manufactured by the Hendry corporation in an FAA 

owned Boeing 727-25C aircraft and conduct a flight evaluation of the developmental AFCBs. 

Data recorded includes line voltage, load voltage, and current for each of the installed breakers. 

Data reduction efforts of any occurring arc faults will include identification of relationships 

between the trip conditions. 

2.0 FLIGHT TEST GOALS 

The following list describes the goals of the experimental flight test program, listed in order of 

importance. 

 Complete fifty (50) or more hours of developmental flight test evaluation but not less 

than twenty-five (25) hours. Data generated during these flights is critical to the 

AFCB research and development program and for obtaining approval of the N-40 

one-only STC. 

 Evaluate the operation of the arc fault circuit breakers under standard B727 

operational procedures. 

 Evaluate the operation of the AFCB instrumentation and Odyssey data recording 

system for future unmanned data collection. 

3.0 SYSTEM DESCRIPTION 

The equipment being installed for the Arc Fault flight evaluation includes developmental 

prototype AFCBs installed in a junction box, an instrumentation recorder and interconnecting 

cables and wire harnesses. These items are described in the following paragraphs. 

3.1 ARC FAULT CIRcUIT BREAKERS

Eight (8) - Hendry prototype arc fault circuit breakers of the following ratings: one 2.5 A, 

three 5A, one 7.5A, one 10A, and two 15A (mounted in AFCI Junction Box). 

3.2 ARC FAULT CIRCUIT INTERUPTER - JUNCTION BOX AND AIRCRAFT HARNESSES

One (1) – AFCI-JB. 

Two (2) – AFCI-JB Test Unit wire harnesses, P18 and P6 

3.3 INSTRUMENTATION EQUIPMENT

One (1) - 24 channel, Nicolet Odyssey data recorder. 

One (1) – BNC Breakout Box. 

One (1) – AFCI JB – BNC Breakout Box Interface Harness. 

Twenty-four (24) – 24-inch BNC connector cables. 

One (1) – Trigger Alarm 

3.4 AIRCRAFT INTERFACES

The electrical connections for the system are shown schematically in FAA Drawing Number 

9854415, Arc Fault Circuit Breaker Wiring. The AFCBs mounted within the AFCI-JB will be 

electrically in series with the load side of the existing circuit breakers. The AFCI-JB wire 

harnesses, P-18 and P-6, connect the load side of the each aircraft circuit breaker to the line side 

I-8
of the respective AFCB and from the load side of the each AFCB to the feed wire for the 

respective load. 

It is important to note that the AFCBs will be connected in series with the load side of the 

existing thermal circuit breakers. In other words, current circuit protection aboard the aircraft 

will not be compromised in any way by this installation. 

The on-board Project Power Inverter provides 120VAC 60Hz power for the Data Acquisition 

System. 

4.0 AIRCRAFT INSTALLATION 

The AFCBs will be installed in an Arc Fault Circuit Interrupter-Junction Box (AFCI-JB) that 

will enclose all the AFCBs and required instrumentation interfaces. The AFCI-JB will be 

mounted in the rear, left side of the cockpit. The test unit will have bypass switches that will 

disable the AFCBs if desired. 

The BNC Breakout Box and the Odyssey data recorder will be mounted in the cabin of the 

aircraft. 

The electrical installation shall be completed in accordance with drawing number 9854415 under 

the guidance of the WJHTC Electrical Systems Designated Engineering Representative (DER), 

Code ACT-370. The mechanical installation shall be completed under the guidance of the 

WJHTC Mechanical Systems DER, Code ACT-370. 

Detailed instructions for completing the installation can be found in the AFCB Ground Checkout 

Procedures Report. 

5.0 CERTIFICATION REQUIREMENTS 

There are no FAA Technical Standard Orders for the equipment being installed during this 

modification. Experimental flight test is being performed to collect data necessary to obtain a 

one only STC to install the AFCBs aboard N40 for an extended evaluation period. 

6.0 ARC FAULT TROUBLESHOOTING 

6.1 ARC FAULT TROUBLESHOOTING BACKGROUND

Although AFCBs can detect arcing on the circuit in which it is installed, it cannot determine the 

location of the arc along the circuit. Furthermore, means for easily troubleshooting an arc fault 

after and AFCB trip are under development but not currently available. This plan has been 

developed to establish a procedure for troubleshooting AFCB trips, should they occur. 

An understanding of current methods of troubleshooting thermal trips will clarify the additional 

measures needed to troubleshoot an AFCB trip and specifically the procedures that will be 

followed during the FAA AFCB flight test program. 

Troubleshooting circuit breakers is an iterative process. Generally, after a thermal circuit 

breaker trip, troubleshooting begins by evaluating the load(s) powered by the circuit. The load is 

either tested for correct operation, or is removed and replaced if its correct operation cannot be 

I-9
directly determined. The circuit is powered and if no additional trips are noted the corrective 

action is considered complete. 

If additional trips of the same circuit occur, there are several options for corrective action. The 

load may still be suspected, and the problem may not be reproducible on the ground. The circuit 

breaker itself may be suspect and replaced (tripping of thermal circuit breakers under normal 

conditions, or failure of a circuit breaker to stay closed when depressed, are two common circuit 

breaker failure modes). Usually, the last item to be checked is the circuit wiring, mainly because 

of the inherent difficulties in testing and inspecting the wiring. 

AFCB’s add another dimension of complexity to the troubleshooting problem. AFCB’s have 

two trip modes, thermal (current overload) and arc fault. There are unique procedures for 

troubleshooting each mode, and unfortunately, if one procedure fails to identify the problem it 

may be necessary to complete the other procedure to be certain that the problem has been 

resolved. Future AFCB’s will have the ability to indicate if the trip mode was thermal or arc 

fault related. The prototypes flown in this test program will not have this feature. However, the 

data recording instrumentation will be triggered by the AFCB’s arc fault detection circuit and 

therefore it will be known with certainty if the trip mode was thermal versus arc fault. 

If the trip mode was arc fault related, the question remains was the arc trip a real arc or was it a 

nuisance trip? The instrumentation being used in these flights will record the current waveforms 

immediately before and after the AFCB indicates that an arc is present and a trip is initiated. 

This data will be analyzed by Hendry Aerospace to determine if it appears to be a real arc or a 

nuisance trip. If it is certain that the trip was nuisance related, then the breaker will be reset and 

flights testing may resume. If a nuisance trip is not certain, then further diagnostics will be 

required. 

Provisions have been made to baseline the condition of the wiring on the eight circuits that will 

be used in the tests with Time Domain Reflectometry (TDR). During ground testing of the 

AFCB test system, each AFCB equipped circuit will be characterized with TDR. This data will 

form a baseline measurement against which future measurements will be compared. Changes in 

the measurement indicate possible locations at which the arcing may have occurred. 

At this point, it is unclear if TDR is sensitive enough to detect the damage incurred by a wire 

during an arcing condition. If the TDR fails to identify the location of the fault, visual inspection 

of the circuit must be performed to determine the source of the fault. 

6.2 DETAILED TROUBLESHOOTING PROCEDURES

All troubleshooting shall be performed by qualified FAA personnel under the direction of the 

Electrical Systems DER, Code ACT-370. 

Upon an AFCB arc fault trip, the Odyssey data recording system will record the current and 

voltage waveforms from the eight circuits equipped with AFCB’s. A thermal trip of the AFCB 

or the aircraft circuit breaker will not cause the Odyssey to trigger on and record this data. 

Therefore, it will be known immediately if the trip was caused by an arc fault. 

Appendix A contains the detailed process flow charts. 

I-10
APPENDIX A – TROUBLESHOOTING PROCESS FLOWCHARTS 

I-11
Odyssey Trigger?

(Y/N)

Download 

Odyssey 

Waveform Data

Email Odyssey 

Waveform Data 

to Hendry

Obtain TDR 

Data From 

Tripped Circuit

Email TDR Data 

to CM Tech. For 

Analysis

TDR 

Changed 

from 

baseline?

Nuisance 

Confirmed 

Conduct ground 

tests on circuit 

N

Email TDR Data 

to CM Tech. For 

Analysis

Damage 

location 

discernable?

Locate fault and 

repair 

Conduct ground 

tests on circuit 

Y

Y

Nuisance

Arc Fault

Probable 

arc fault 

or 

nuisance 

trip?

Obtain TDR 

Data From 

Tripped Circuit

Conduct ground 

tests on circuit 

Conduct visual 

inspection of 

circuit wiring

Damage 

location 

discernable?

Locate fault and 

repair

2

N

N Y

Y N

1

Start:Circuit 

Breaker Trip

AFCB 

Trip or 

Aircraft 

CB Trip?

AFCB

1

Aircraft CB

I-12
1

Troubleshoot and repair IAW 

Standard Operating Procedures for 

thermal circuit breaker trips 

Conduct ground tests on circuit 

Ground 

tests 

check 

ok?

Obtain TDR 

Data From 

Tripped Circuit

Email TDR Data 

to CM Tech. For 

Analysis

TDR 

Changed 

from 

baseline?

Aircraft and 

circuit returned 

to service 

Re-baseline 

circuit TDR 

characterization 

End

N

Damage 

location 

discernable?

Locate fault and 

repair 

Conduct ground 

tests on circuit 

Conduct visual 

inspection of 

circuit wiring

Damage 

location 

discernable?

Locate fault and 

repair

2

N

Conduct ground 

tests on circuit 

Y

Y

I-13
2

Aircraft and 

circuit returned 

to service 

Re-baseline 

circuit TDR 

characterization 

Ground 

tests 

check 

ok?

Y

Replace AFCB 

N

Ground 

tests 

check 

ok?

Repeat 

troubleshooting 

procedure

End

End

Y

N

I-14
APPENDIX J—TIME DOMAIN REFLECTOMETER 

TEST RESULTS 

J-1/J-2
Time Domain Reflectometer (TDR) 

Test Results 

for 

Arc-Fault Circuit Breaker Flight Test Installation 

On 

FAA Technical Center 

Boeing 727-25C Aircraft N40 

Conducted by: 

CM Technologies 

27-28 August 2001 

J-3/J-4
J-5
J-6
J-7
J-8
J-9
J-10
J-11
J-12
J-13
J-14
J-15
J-16
J-17
J-18
J-19
J-20
J-21
J-22
J-23
J-24
J-25/J-26
APPENDIX K—ARC-FAULT CIRCUIT BREAKER WIRING

K-1/K-2
K-3/K-4