The Airborne Collision Avoidance System II (ACAS II) was introduced in order to reduce the risk of mid-air collisions or near mid-air collisions between aircraft. It serves as a last-resort safety net irrespective of any separation standards.
Flight crews and controllers must have a clear understanding of ACAS II requirements and operating procedures, so ACAS II safety benefits can be realised. That understanding is achieved through initial and recurrent training.
Training Guidance for Pilots
ICAO guidelines stipulate both practical manoeuvre training, using aircraft simulators (or suitable CBT), and theory training for pilots. ACAS should be included in recurrent training sessions and flight crews must be tested to ensure they are fully conversant with ACAS procedures, capabilities and limitations, and are able to respond correctly.
The ICAO guidelines list 22 learning points relating to operational use and four items of best practice. Training objectives cover theory of operations, pre-flight operations, general in-flight operations, response to TAs, and response to RAs.
Essential academic training includes:
- System operation: advisory thresholds; ACAS limitations; ACAS inhibits;
- Operating procedures: use of controls; display interpretation; use of the TA-only mode; crew coordination; reporting requirements.
Manoeuvre training should include scenarios which verify pilot interpretation and responses to both TAs and RAs. The scenarios should include:
- Initial RAs that do and don’t require a change in vertical speed;
- Maintain rate RAs;
- Altitude crossing RAs;
- Increase rate RAs;
- RA reversals;
- Weakening RAs;
- RAs issued while the aircraft is at a maximum altitude; and
- Multi-aircraft encounters.
The scenarios should also include demonstrations of the consequences of not responding to RAs, slow or late responses, and manoeuvring opposite to the direction called for by the displayed RA.
The ICAO guidelines for pilot training on ACAS / TCAS are contained in Chapter 5 of Doc. 9863 (ACAS Manual) and in the attachments to Doc. 8168 (PANS-OPS). Additional training guidance is included in JAA’s. The guidance material is accessible via 'Further Reading' below.
Note that while the principal and essential technical and operational features of ACAS are introduced in the following, it is not, on its own, considered complete training:
- EUROCONTROL: TCAS version 7.1 for pilots
ACAS Procedures Concerning Controllers
Although ACAS is an avionics system, it can have significant impact on ATM operations. Therefore, air traffic controllers should have a good understanding of ACAS operations and procedures. ACAS events are relatively rare, hence the controller exposure to this events is low, which reinforces the need for recurrent training.
The ICAO guidelines for controller training on ACAS / TCAS are contained in Chapter 6 of Doc. 9863 (ACAS Manual). ACAS procedures to be followed by ATC are provided in Doc 4444 (PANS ATM). The relevant sections of these documents can be acceesed via 'Further Reading' below.
Additionally, the EUROCONTROL Specification for the ATCO Common Core Content Initial Training details the minimum training requirement in the basic syllabus as well as for each rating.
For additional information consult the EUROCONTROL presentation (link provided below) that has been designed to support the training of controllers. Note that it is not designed or intended to meet the complete training requirements, but it does introduces the principal and essential technical and operational features of ACAS.
- EUROCONTROL:TCAS version 7.1 for controllers
- Airborne Collision Avoidance System (ACAS)
- ACAS Regulation and Procedures
- Incorrect use of TCAS Traffic Display
- ACAS: Guidance for Controllers
- Regulation 1332/2011 for laying down common airspace usage requirements and operating procedures for airborne collision avoidance subsequently amended by Regulation 2016/583
- EUROCONTROL ACAS bulletins, especially No 12 which deals specifically with Training
- EUROCONTROL: ACAS Guide - Airborne Collision Avoidance Systems, Edition 4.1, March 2022
- EUROCONTROL: Overview of ACAS II - (incorporating version 7.1), Version 3.0 – 12 January 2012
- EUROCONTROL: TCAS version 7.1 for pilots
- EUROCONTROL: TCAS version 7.1 for controllers
- EUROCONTROL: Safety Nets Guide, 21 May 2011
- EASA Safety Information Bulletin SIB No.: 2013-11, ACAS II – Manoeuvres based on Visual Acquisition of Traffic, 19 July 2013