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Definition
aircraft system based on secondary surveillance radar (SSR) (3.1.121) 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
NOTE 1 The terms “ACAS” and “TCAS” (traffic alert and collision avoidance system) are often used interchangeably however there is a difference between the two terms: ACAS is typically used when referring to the technical standard, concept or implementation; TCAS is typically used when referring to implementation of the technical standards and concept.
NOTE 2 ACAS sXu is a derivative of ACAS and provides a capability for smaller “uncrewed aircraft system (UAS)” (3.1.137) (which are defined in the relevant MOPS (minimum operational performance standard[s]) as UAS with a wingspan, or equivalent, of 25 feet or less). ACAS sXu is intended for vehicles that are not secondary “surveillance radar (SSR) transponder” (3.1.121) transponder- or “automatic dependent surveillance broadcast (ADS-B)” (3.1.19)- equipped.
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BSI Flex 1903 v2:2024-06 community preview
This is an interactive version 2 of BSI Flex 1903. The aim of the standard is to create a lexicon of standard terms and acronyms used in this sector. Please note, content is still undergoing internal review and there may be minor changes at full publication.
We welcome your engagement and comments on this version to help inform the development of the standard. We would also welcome general feedback including what terms could be considered for future versions and these can be made through our dedicated feedback page .
airborne collision avoidance system (ACAS)
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