---
title: "ETSO-C178a — CS-ETSO · Avioverse"
description: "Aircraft Circuit Breakers 1 Applicability This ETSO provides the requirements that aircraft circuit breakers that are designed and manufactured on or…"
url: "https://avioverse.aero/regulations/easa/cs-etso/subpart-b/etso-c178a"
---

# ETSO-C178a

European Technical Standard Orders (CS-ETSO) · CS-ETSO · EAR revision 1 Oct 2026

IR Implementing rule

## ETSO-C178a

Aircraft Circuit Breakers

1 Applicability

This ETSO provides the requirements that aircraft circuit breakers that are designed and manufactured on or after the date of this ETSO must meet in order to be identified with the applicable ETSO marking.

2 Procedures

2.1 General

The applicable procedures are detailed in CS-ETSO, Subpart A.

2.2 Specific

None.

3 Technical conditions

3.1 Basic

3.1.1 Minimum Performance Standard

The applicable standards are those provided in Table 1 for the intended equipment class:

Table 1 — Equipment class standards

| Equipment Class | Equipment Type                                      | Minimum Performance Standards                                                                                                                                                       |
| --------------- | --------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| 1               | Alternating Current (AC) Arc Fault Circuit Breakers | SAE Aerospace Standard (AS) AS5692A, ‘ARC Fault Circuit Breaker (AFCB), Aircraft, Trip-Free Single Phase and Three Phase 115 VAC, 400 Hz - Constant Frequency’, dated December 2009 |
| 2               | Direct Current (DC) Arc Fault Circuit Breakers      | SAE Aerospace Standard (AS) AS6019, ‘ARC Fault Circuit Breaker (AFCB), Aircraft, Trip-Free 28 VDC’, dated June 2012                                                                 |
| 3               | AC or DC Thermal Circuit Breakers                   | SAE Aerospace Standard (AS) AS58091A, ‘Circuit Breakers, Trip-Free, Aircraft General Specification For’, dated May 2012                                                             |

3.1.2 Environmental Standard

See CS-ETSO, Subpart A, paragraph 2.1.

3.1.3 Software

See CS-ETSO, Subpart A, paragraph 2.2.

3.1.4 Airborne Electronic Hardware

See CS-ETSO, Subpart A, paragraph 2.3.

3.2 Specific

3.2.1 Failure Condition Classification

See CS-ETSO, Subpart A, paragraph 2.4.

4 Marking

4.1 General

See CS-ETSO, Subpart A, paragraph 1.2.

4.2 Specific

The class of the equipment shall be legibly and permanently marked.

5 Availability of referenced documents

See CS-ETSO, Subpart A, paragraph 3.

\[Amdt ETSO/8]

\[Amdt ETSO/17]

IR · ETSO-C178a — CS-ETSO · ED Decision 2022/018/R · CS-ETSO Easy Access Rules · EAR revision 1 Oct 2026

[All rules in SUBPART B – LIST OF ETSOs](https://avioverse.aero/regulations/easa/cs-etso/subpart-b)

Consolidated from the EASA Easy Access Rules (revision 1 Oct 2026, extracted 13 Oct 2026) for convenience. Not the official publication — verify against the Official Journal of the European Union and the EASA publications before operational use.