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Mode Aviation
Reference No. AR201500050
Date reported 24 June 2015
Concern title Confusion resulting from similar call signs in the Queensland area
Concern summary

The concern related to a number of flight which are operating in the airspace north of Brisbane with similar call signs.

Industry / Operation affected Aviation: Air transport
Concern subject type Aviation: Airspace

Reporter's concern

The reporter expressed a safety concern related to the confusions arising from the similarity of flight numbers being used by flights in the Queensland area.

‘[Airline 1] 1666’ (1666) flying from [location 1] to Brisbane, and ‘[airline 1] 1556’ (1556) flying from [location 2] to Sydney were on the same frequency north of Brisbane. 1666 was descending through 1556’s level on a near parallel track.

An instruction to turn on to an easterly heading intended for 1556 was acknowledged by 1666. The controller acted immediately to abort this and used single numerals very clearly in the call signs.

The phraseology using group flight number call signs, for example ‘Fifteen fifty six’ and ‘Sixteen Sixty six’ is easily misheard - and in some cases - 15 and 16 included- uses as many  syllables as simply using the individual numbers.

These flights operate in the peak tourist time bracket and two are commonly on same frequency, at times in close proximity.

On some days, [airline 2] 1558 and 1559 from Sydney to [location] and return to Sydney can also be in the system. When that flight is operated by a different aircraft type it uses a different flight number which alleviates the problem.

Overall, the specific call signs used and the system of how numbers are enunciated should be reconsidered. It is very important that it is clear to both the flight crew and the controllers which aircraft is being communicated with to ensure that aircraft remain separated.

Operator's response (Operator 1)

Airservices Australia appreciates the opportunity to respond to the reported concern regarding call sign confusion.

Airservices notes that while the International Civil Aviation Organization (ICAO) guidance exists, the designation and use of call signs is influenced by the requirements of aircraft operators.

Currently Airservices relies on reporting of call sign confusion issues by air traffic controllers via our safety occurrence reporting system to engage with the relevant operator on an opportunity basis. In response to the reported concern, Airservices has identified an opportunity to review this process to ensure the robustness of operator follow up, noting that Airservices does not have any authority to resolve the identified issues.

In addition, Airservices will engage with the Civil Aviation Safety Authority (CASA) to identify any opportunity for safety educational activity to increase industry awareness of existing guidance, reporting mechanisms and safety lessons in relation to the allocation and use of call signs.

Airservices notes that AIP GEN 3.4 provides mitigation measures for pilots and ATC to avoid call sign confusion occurrences.

You may wish to also refer this REPCON to CASA for input from a regulatory perspective.

Attachment 1 - AIP GEN 3.4

4.15.2 Pilots must be certain that aircraft identification is complete and clearly identified before taking action on an ATC clearance. ATS will use full or abbreviated call signs in accordance with section 4.21

4.21 The pilot may only use an abbreviated call-sign when initiated by ATS. When aware of similar/identical call-signs, ATS will take action to minimise errors by:

a) emphasising certain numbers/letters

b) repeating the entire call-sign, egQANTAS451QANTAS451, or

c) repeating the prefix, eg QANTAS451 QANTAS, or

d) asking pilots to use a different call-sign, either temporarily or for the duration of the flight.

Pilots should use the phrase "VERIFY CLEARANCE FOR (complete call-sign)" if doubt exists concerning proper identity.

Operator's response (Operator 2)

As part of our [Airline 1] safety management system, flight crew are encouraged to report all occurrences of this nature. These reports are entered into our database, reviewed by our investigation team and risk rated. Where required, incidents are investigated and on a number of occasions, corrective action has been implemented to prevent recurrence.

Where the source of the confusion has been with ATC, our investigation department has liaised with Airservices for resolution.

We currently have procedures to minimise call sign confusion but in response to this REPCON and in consultation with Airservices Australia we will review our procedures.

Operator's response (Operator 3)

We [Airline 2] respond favourably to call sign amendment when it is raised by credible sources such as Airservices or crews directly and it is proven that genuine conflict/confusion exists. As the veracity of this report has not been confirmed through either source, we will not take immediate action but will continue to monitor the situation and will act on any information received through that process.

Regulator's response (Regulator 1)

CASA has reviewed the REPCON and notes that the selection of call signs is influenced by the requirements of operators which is relevant to both domestic and foreign certificate holders.

It appears the airlines have implemented their respective safety management systems appropriately and reviewed their procedures. The information published in the Aeronautical Information Publication (AIP) also provides appropriate guidance.

Airservices is required to comply with Doc 4444 under CASR Part 172. There is a relevant section in Doc 4444 on call sign similarity resulting in confusion:

  • 15.7.5 Change of radiotelephony (RTF) call sign for aircraft
  • 15. 7.5.1 An ATC unit may instruct an aircraft to change its type of RTF call sign, in the interests of safety, when similarity between two or more aircraft RTF call signs are such that confusion is likely to occur.
  • 15. Any such change to the type of call sign shall be temporary and shall be applicable only within the airspace(s) where the confusion is likely to occur.
  • To avoid confusion, the ATC unit should, if appropriate, identify the aircraft which will be instructed to change its call sign by referring to its position and/or level.
  • When an ATC unit changes the type of call sign of an aircraft, that unit shall ensure that the aircraft reverts to the call sign indicated by the flight plan when the aircraft is transferred to another ATC unit, except when the call sign change has been coordinated between the two ATC units concerned.
  • The appropriate ATC unit shall advise the aircraft concerned when it is to revert to the call sign indicated by the flight plan.

While the suggestion to add a more unique digit or letter to a call sign is worthy of consideration, the course of action may in itself give rise to potential for error. In concert with the AIP procedures referred in the Airservices response, these call sign confusion incidents can be mitigated by pilots adhering to the published phonetic pronunciations of numbers and letters as well as being prepared to challenge any radio communication that is not clearly understood.


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Last update 19 November 2015