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ATSAW applications refer to the operational use of the ATSAW function in a given context.
3.6. DESCRIPTION OF ATSAW
The Airborne Traffic Situational Awareness (ATSAW5) function displays traffic information to the flight crew like a TCAS. However, the main differences are:
- The ATSAW function listens to ADS-B messages broadcast by surrounding aircraft. The ATSAW function is also called ADS-B IN function
(refer to Figure 3-11 and 2.1.3.7 – Automatic Dependent Surveillance – Broadcast (ADS-B)). The ATSAW function displays only surrounding aircraft equipped with an ADS-B OUT emitter that operates on 1090 MHz (e.g. Mode S EHS transponder capable of ADS-B OUT).
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The ATSAW traffic information is enriched. Compared to TCAS traffic information, the ATSAW function provides in addition, but not limited to, the flight identification, the orientation, the speed and the wake vortex category of surrounding aircraft (refer to 3.6.1 – Enriched Traffic Information).
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The ATSAW function do not provide any alerts. For collision avoidance purposes, the flight crew must refer to TCAS indications.
5 ATSAW is the AIRBUS designation. ATSA is the ICAO standard designation.
A new TCAS computer supports the ATSAW function. Therefore, TCAS and ATSAW information are seamlessly integrated (refer to 3.6.4.2.4 – Combination of TCAS and
The new TCAS computer still provides TA and RA when aircraft separations are not sufficient. In addition, it provides enriched information to the flight crew thanks to the ATSAW function.
Own aircraft
XPDR ADS-B Out
ADS-B In TCAS
TCAS ADS-B In
ADS-B ground
ADS-B Out XPDR
receiver
ADS-B data flow
Figure 3-11: ADS-B data broadcast and collection
3.6.1. ENRICHED TRAFFIC INFORMATION
As a reminder, a conventional TCAS is able to determine the range, the bearing and the relative altitude of intruders within 30 NM (refer to 3.1 – Description of ACAS – TCAS). The TCAS computer capable of ATSAW is able to listen to ADS-B messages up to 100 NM behind and ahead of the aircraft, and up to 30 NM on either side of the aircraft.
Thanks to the information available in the Extended Squitter (refer to 2.1.3.8 – Extended Squitter), the ATSAW function provides for any surrounding aircraft capable of ADS-B OUT:
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The flight number6 -The heading
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The position -The ground speed
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The relative altitude -The indicated air speed
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The vertical tendency -The wake vortex category.
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