---
title: "ETSO-2C521 A1 — CS-ETSO · Avioverse"
description: "Electronic Flight Bag (EFB) Software Applications 1 Applicability This ETSO provides the requirements that electronic flight bag software applications…"
url: "https://avioverse.aero/regulations/easa/cs-etso/subpart-b/etso-2c521"
---

# ETSO-2C521 A1

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

IR Implementing rule

## ETSO-2C521 A1

Electronic Flight Bag (EFB) Software Applications

1 Applicability

This ETSO provides the requirements that electronic flight bag software applications that are designed 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 standard is that provided in EUROCAE ED-273, ‘Minimum Operational Performance Standard for Electronic Flight Bag (EFB) Software Applications’, dated August 2021.

3.1.2 Environmental Standard

Not applicable.

3.1.3 Software

See the software development assurance method described in EUROCAE ED-273, ‘Minimum Operational Performance Standard for Electronic Flight Bag (EFB) Software Applications’, Section 2.4.

Alternatively, see CS-ETSO, Subpart A, paragraph 2.2.

3.1.4 Airborne Electronic Hardware

Not applicable.

3.2 Specific

3.2.1 Failure Condition Classification

A safety risk assessment must be performed per EUROCAE ED-273, ‘Minimum Operational Performance Standard for Electronic Flight Bag (EFB) Software Applications’, Section 2.2. The assumptions, mitigation and prevention means identified in this risk assessment must be made available to the aircraft operator as required by the standard.

Alternatively, see CS-ETSO, Subpart A, paragraph 2.4.

3.2.2 Documentation

The applicant shall develop and make available to the aircraft operator the operational, loading and configuration instructions as defined in EUROCAE ED-273, Chapter 4, including the following data.

— The minimum performance specifications for the EFB Host Platform (Hardware + Operating system). These should be consistent with the environment that has been used to demonstrate the functionalities of the EFB application.

— The test procedures to be performed by the installer once the EFB application is loaded and configured into the final host platform. Please refer to EUROCAE ED-273, Section 4.2, for additional guidance.

4 Marking

4.1 General

The application shall include a function permitting the user to retrieve the markings required by CS-ETSO, Subpart A, paragraph 1.2.

Note: The date of the official release of the EFB software application is a means to comply with point 21.A.807(a)(3).

4.2 Specific

None.

5 Availability of Referenced Documents

See CS-ETSO, Subpart A, paragraph 3.

\[Amdt ETSO/17]

\[Amdt ETSO/18]

IR · ETSO-2C521 — CS-ETSO · 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.