---
title: "Airborne collision avoidance system (ACAS) — EASA Definition · Avioverse"
description: "Article 2, Regulation (EU) No 923/2012: ‘airborne collision avoidance system (ACAS)’ means an aircraft system based on secondary surveillance radar (SSR)…"
url: "https://avioverse.aero/glossary/easa/airborne-collision-avoidance-system"
---

# airborne collision avoidance system (ACAS)

EASA defines “airborne collision avoidance system (ACAS)” in 2 regulations, worded for each regulation's scope. The wording below is reproduced verbatim from the EASA Easy Access Rules, with a link to the paragraph it comes from.

> ‘airborne collision avoidance system (ACAS)’ means an aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft that are equipped with SSR transponders;

Article 2 · Standardised European Rules of the Air (SERA) · Regulation (EU) No 923/2012 · Easy Access Rules, 26 Aug 2025 revision · [Read Article 2](https://avioverse.aero/regulations/easa/sera/cover-regulation/powers-and-recital#article-2)

> ‘airborne collision avoidance system (ACAS)’ means an aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft that are equipped with SSR transponders;
>
> (8) ‘entity originating aeronautical data and aeronautical information’ – means any public or private entity responsible for origination of aeronautical data and aeronautical information used as a source for aeronautical information products and services. These entities do not include ATM/ANS providers referred to in point (2) of Article 2 of this Regulation and aerodromes defined in point (1)(e) of Article 2 of Regulation(EU) 2018/1139.’

Article 2 · Air Traffic Management / Air Navigation Services · Regulation (EU) 2017/373 · Easy Access Rules, 12 Mar 2025 revision · [Read Article 2](https://avioverse.aero/regulations/easa/atm-ans/cover-regulation/powers-and-recitals#article-2)

## Defined in the same article

- [accuracy](https://avioverse.aero/glossary/easa/accuracy)
- [advisory airspace](https://avioverse.aero/glossary/easa/advisory-airspace)
- [advisory route](https://avioverse.aero/glossary/easa/advisory-route)
- [aerial work](https://avioverse.aero/glossary/easa/aerial-work)
- [aerobatic flight](https://avioverse.aero/glossary/easa/aerobatic-flight)
- [aerodrome](https://avioverse.aero/glossary/easa/aerodrome)
- [aerodrome control service](https://avioverse.aero/glossary/easa/aerodrome-control-service)
- [aerodrome control tower](https://avioverse.aero/glossary/easa/aerodrome-control-tower)