Review Policy on ACAS Phraseology

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Review Policy on ACAS Phraseology

47TH ANNUAL CONFERENCE, Arusha, Tanzania, 10-14 March 2008

WP No. 95

Review Policy on ACAS Phraseology

Presented by TOC

Summary

On 22nd November 2007, Amendment 5 of ICAO Doc 4444 Air Traffic Management was included. One of the changes with this amendment had to do with the reporting of Traffic Collision Avoidance System (TCAS) Resolution Advisories (RAs), on which IFATCA accepted Policy at the 2006 Conference in Kaohsiung. After having reviewed the changes to Doc 4444 Air Traffic Management and comparing these to IFATCA Policy, TOC concluded that the changes have resulted in a great improvement of ICAO procedures. However, TOC also concluded that the controller can still be placed in a situation in which he/she cannot issue a safe alternative clearance. In such a situation, the controller has a responsibility to manage the emergency situation and will at all times has a duty of care, but cannot accept that he resumes responsibility until separation has been established. This working paper contains draft recommendations reflecting this position.

Introduction

1.1  In 2006, IFATCA Policy was accepted on the reporting of Traffic Collision Avoidance System (TCAS) Resolution Advisories (RAs). WP84 of the Kaohsiung conference made mention of a State Letter that was circulated in 2005, in which a intended change of the TCAS RA reporting was described. This change was later communicated as Amendment 5 to ICAO Doc 4444 Air Traffic Management, and this amendment has been included on 22nd November 2007.

1.2  This working paper will review IFATCA Policy on this matter, and compare it to Amendment 5 of ICAO Doc 4444 Air Traffic Management. The choice for using the Amendment is intentional, as it clearly shows the changes made to the original text.

Discussion

2.1  All parts of the IFATCA Policy on this matter are discussed separately and compared to the procedures as published in Amendment 5 of ICAO Doc 4444 Air Traffic Management. Following this comparison, the recommendation is made whether the policy should be deleted, retained or amended.

2.2  IFATCA Policy is:

“Pilots shall only report TCAS RAs on the frequency that require a departure or deviation from the current ATC clearance or instruction.”

 

2.2.1.  Amendment 5 to ICAO Doc 4444 Air Traffic Management states:

“Note.— Pilots are required to report RAs which require a deviation from the current ATC clearance or instruction (see PANS-OPS, Volume I, Part III, Section 3, Chapter 3, 3.2 c) 4)). This report informs the controller that a deviation from clearance or instruction is taking place in response to an ACAS RA.”

2.2.2.  The IFATCA Policy above is recommended for deletion.

2.3. IFATCA Policy is:

“Once an aircraft departs or deviates from the current ATC clearance or instruction in response to a resolution advisory or when a pilot reports a TCAS RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft under control until the pilot reports clear of conflict and separation has been established. This must be automatic and unambiguous, and must happen irrespective of whether the aircraft is manoeuvring or not and also whether or not the ATC clearance is left.”

 

2.3.1  Amendment 5 to ICAO Doc 4444 Air Traffic Management states:

“15.7.3.3 Once an aircraft departs from its ATC clearance or instruction in compliance with a resolution advisory an RA, or a pilot reports an RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft affected as a direct consequence of the manoeuvre induced by the resolution advisory RA. The controller shall resume responsibility for providing separation for all the affected aircraft when:

a)  the controller acknowledges a report from the flight crew that the aircraft has resumed the current clearance; or

b)  the controller acknowledges a report from the flight crew that the aircraft is resuming the current clearance and issues an alternative clearance which is acknowledged by the flight crew.”

2.3.2  There are subtle differences between IFATCA Policy and the text above. Easiest is to focus on the differences. The text is separated in two parts as only the first part of the text in the Amendment is easy to compare to the IFATCA Policy.

IFATCA Policy:

“Once an aircraft departs or deviates from the current ATC clearance or instruction in response to a resolution advisory or when a pilot reports a TCAS RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft under control …”

Amendment 5 of ICAO Doc 4444 Air Traffic Management: 

“Once an aircraft departs from its ATC clearance or instruction in compliance with an RA, or a pilot reports an RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft affected as a direct consequence of the manoeuvre induced by the RA.”

The differences shown above are only very minor and therefore require no additional discussion. Only exception is the last part. IFATCA Policy speaks of “any aircraft under control” while the ICAO Doc 4444 Air Traffic Management speaks of “any other aircraft affected as a direct consequence of the manoevre induced by the RA”. The difference is advantageous when looking at controller responsibilities, as also aircraft not under control of the controller involved are also included in the ICAO procedure. For these reasons the change is acceptable and the first part of IFATCA Policy is recommended for deletion.

2.3.3 The second part of the IFATCA Policy focuses on the moment that the controller resumes responsibility:

IFATCA Policy: 

“… until the pilot reports clear of conflict and separation has been established. This must be automatic and unambiguous, and must happen irrespective of whether the aircraft is manoeuvring or not and also whether or not the ATC clearance is left.”

Amendment 5 of ICAO Doc 4444 Air Traffic Management:

“The controller shall resume responsibility for providing separation for all the affected aircraft when:

a) the controller acknowledges a report from the flight crew that the aircraft has resumed the current clearance; or

b) the controller acknowledges a report from the flight crew that the aircraft is resuming the current clearance and issues an alternative clearance which is acknowledged by the flight crew.”

The main difference between the two is the fact that IFATCA Policy indicates that the controller resumes responsibility after the report from the pilot, and separation has been established. The last part was included in the text intentionally, this with the intention to cover situations when the pilot returns to the original clearance, which is no longer a safe clearance. Both options a) and b) above could still result in a situation in which an aircraft departs from its ATC clearance in compliance with an RA, subsequently return to or resume the current clearance, and still place the controller in a situation in which a controller cannot issue a safe alternative clearance. In this case the controller has a responsibility to manage the emergency situation and will at all times have a duty of care, but simply cannot accept that he/she resumes responsibility until separation has been established.

2.3.4 It is recommended that IFATCA Policy is amended to reflect the arguments above.

Conclusions

3.1.  TOC has reviewed IFATCA Policy on ACAS phraseology and has concluded that with the Amendment 5, ICAO Doc 4444 Air Traffic Management has been greatly improved.

3.2.  In a situation in which an aircraft departs from its ATC clearance in compliance with an RA, subsequently returns to or resumes the current clearance, the controller can still be placed in a situation in which he/she cannot issue a safe alternative clearance. In this case the controller has a responsibility to manage the emergency situation and will at all times have a duty of care, but simply cannot accept that he resumes responsibility until separation has been established.

3.3. While discussing this subject, TOC did not find the time to completely and satisfactorily address it. Further work is required to ensure that all possible viewpoints have been taken into consideration.

Recommendations

It is recommended that;

4.1.  IFATCA Policy on page 3212 of the IFATCA Manual:

“Pilots shall only report TCAS RAs on the frequency that require a departure or deviation from the current ATC clearance or instruction.

Once an aircraft departs or deviates from the current ATC clearance or instruction in response to a resolution advisory or when a pilot reports a TCAS RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft under control until the pilot reports clear of conflict and separation has been established. This must be automatic and unambiguous, and must happen irrespective of whether the aircraft is manoeuvring or not and also whether or not the ATC clearance is left.”

is amended to read:

“After an aircraft has departed from its ATC clearance or instruction in compliance with an RA, or a pilot has reported an RA, the controller shall not resume responsibility for providing separation, until separation has been established for all affected aircraft.”

and is listed as IFATCA Provisional Policy.

4.2.  This item is included in the 2008/09 Technical Work Programme for further study.

References

IFATCA Manual version 2007.

ICAO State Letter AN 13/2.1-07/36, subject: Approval of Amendment 5 to the PANS-ATM, date 22 June 2007.

ICAO Procedures for Air Navigation Services – Air Traffic Management Doc 4444, Fourteenth Edition 2001, Amendment 5.

Last Update: September 29, 2020  

April 11, 2020   466   Jean-Francois Lepage    2008    

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