AGING OF CIRCUIT BREAKERS

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航空

CUSTOMER SERVICES DIRECTORATE AIRBUS
1 ROND POINT MAURICE BELLONTE
31707 BLAGNAC CEDEX FRANCE
TELEPHONE + 33 (5) 61 93 33 33
TELEX AIRBU 530526F SERVICE INFORMATION LETTER
SIL NUMBER: 20-017
PAGE: 1 of 3
DATE: June 28/2004
REVISION:
SUBJECT:
ATA CHAPTER:
AIRCRAFT TYPE:
APPLICABILITY:
1. PURPOSE:
A300, A300-600, A310, A318, A319, A320, A321, A330, A340, A340-500/600
20-00
ALL
REFERENCES: - OIT AI/SE-E 999.0071/02 dated 24 July 2002
- FAA Report DOT/FAA/AR-01/118 dated November 2002
- SIL 20-013
- Electrical Standard Practices Manual (ESPM) – Chapter 20
AGING OF CIRCUIT BREAKERS
The above referenced OIT provided a description of the background of Aging Transport
Systems Rulemaking Advisory Committee (ATSRAC) and FAA Enhanced Airworthiness
Program for Airplane Systems (EAPAS).
As a complement to the referenced OIT concerning the results of the ATSRAC Tasks, this
SIL is intended to provide additional information on the FAA Aging Electrical Systems
Research Program and particularly on the Aging Circuit Breaker study.
AIRBUS
SERVICE INFORMATION LETTER
SIL NUMBER: 20-017
PAGE: 2 of 3
DATE: June 28/2004
REVISION:
2. BACKGROUND
The EAPAS is an overall program that outlines the recommendations of the ATSRAC but
is also intended to focus on all aircraft systems, including mechanical systems. The
current focus of this program revolves around aging wiring systems and provides
strategies for how the FAA and industry will work to improve the airworthiness of wire
systems through near-term and long-term actions, with the intent to disseminate the
outcomes throughout the industry.
The EAPAS also includes an extensive Aging Electrical System Research Program. This
program is intended to conduct research into aging wiring systems to determine
mechanisms that drive the aging process, develop tools to better inspect and maintain
wiring, and develop technologies that mitigate the hazards associated with wiring failure.
3. DESCRIPTION
As part of the Aging Electrical System Research Program, the FAA sponsored a test
program to evaluate the performance of circuit breakers removed from some retired
large transport aircraft (B727 and DC-10 aircraft) and issued in November 2002 a report
ref. DOT/FAA/AR-01/118 to disseminate the results of this study.
The purpose of this test was to provide data needed to determine to what extent circuit
breakers removed from retired aircraft have degraded from their original performance
specification parameters. The test program encompassed visual and X-Ray
examination, voltage drop test, current overload test, insulation resistance test and
failure analysis.
Results indicated that circuit breakers installed on aircraft with extended service life would
continue to protect the electrical wire provided that adequate attention is placed on the
need to control circuit breaker aging characteristics throughout their life. The report makes
several recommendations aiming at improving the reliability of circuit breakers, and
reducing maintenance related problems, including:
- Cycle circuit breakers periodically with no power,
- Need for instructions to protect the back of circuit breaker panels during routine
maintenance,
- Need for instructions on cleaning the back of circuit breaker panels,
- Need to inspect circuit breaker panels for loose, broken or misapplied wire termination
hardware,
- Need to inspect circuit breakers for overheating and arcing,
- Need for instructions to use the correct wire termination hardware,
The FAA is now considering the results of this test program and more particularly the
benefits of thermal circuit breaker cycling.
AIRBUS
SERVICE INFORMATION LETTER
SIL NUMBER: 20-017
PAGE: 3 of 3
DATE: June 28/2004
REVISION:
4. AIRBUS ACTION
Even if the circuit breakers used during the test program were not removed from Airbus
aircraft, Airbus have reviewed the results and recommendations for potential application on
their aircraft.
As far as circuit breaker inspections are concerned (for loose, broken, incorrect or
misapplied termination hardware, overheating and electrical arcing), Airbus has already
initiated the process of developing an Enhanced Zonal Analysis Procedure (EZAP) for all
their aircraft types (ref. SIL 20-013). EZAP is a logic process to be applied to all zones
containing wiring that allows determination of a need for tasks to minimize the presence of
combustible material (cleaning tasks); and the need for either standalone General Visual
Inspections or dedicated Detailed Inspections of specific wiring installations.
The new tasks generated by application of the procedure will be added in the Maintenance
Review Board (MRB) report and the Maintenance Planning Document (MPD) will be
updated to reflect MRB Report revision.
Airbus will ensure that application of EZAP will consider circuit breaker panels to permit
visual inspection of circuit breakers.
As far as cycling of circuit breakers is concerned, and based on the lower and higher current
overload results, it can be concluded that cycling the breaker on and off will improve the
voltage drop rated current and circuit breaker’s current overload characteristics.
Airbus is therefore in agreement with this recommendation and then recommends that
operators perform an initial manual cycling of all thermal circuit breakers on and off at least
one time under no power within an initial 24-month period and thereafter at intervals not to
exceed 36 months.
This repetitive task will be included in the next MPD revision (not later than end of 2005),
with the SIL referenced as the source document. Pending the issue of that revision,
operators may use the following allocated MPD task numbers in their approved
maintenance programmes:
- A300: 240000-0503-2
- A300-600: 240000-03-1
- A310: 240000-04-1
- A318/A319/A320/A321: 240000-17-1
- A330/A340: 240000-01-1