AIC 12 2020 CALL SIGN SIMILARITY

1 DESCRIPTION

1.1 The presence of similar call signs by aircraft operating in the same area, at the same time, and on the same frequency may at times give rise to potential and actual confusion and misunderstanding between pilots and ATCOs, resulting in errors that may lead to safety related incidents. This hazard is usually referred to as “Call Sign Similarity”.

1.2 Call sign similarity is one of the major causes for aircraft taking a clearance not issued for them or ATC issuing a clearance to an aircraft it was not intended to.

1.3 Airlines mainly use their IATA commercial flight numbers as call sign. However, because they tend to be allocated in batches of sequential and very similar numbers, Call Sign Similarity can occur.

1.4 As a result of the global focus raised on the Call Sign Similarity hazard, many airlines are now using alphanumeric call signs. This action is significantly reducing the number of call sign similarity encounters. However, continued vigilance is necessary to address this safety issue.

2 PURPOSE

The purpose of this AIC is to recommend the best courses of action in order to minimize the risk of Call sign confusion, and to mandate procedures for reporting and managing occurrences when call sign similarity leads to actual call sign confusion.

3 GUIDELINES ‐ Airline Operators (AO)

3.1 Call signs shall be allocated in accordance with ICAO Annex 10 and Doc 8585. Additional measures include:

3.1.1 Avoid use of phonetically similar call signs on the same RTF frequency at the same time, within own company;

3.1.2 Avoid certain formats that are especially likely to lead to confusion: number sequences beginning with a low number; long number sequences (Maximum four); repeated digits; and letter sequences which correspond with the last two letters of the destination ICAO location indicator.

3.1.3 Co‐ordinate advance planning, whenever possible, with other Operators (ideally prior to commencement of summer and winter season) to reduce to a minimum any similar numeric and alphanumeric elements of call signs;

3.1.4 After implementation ensure there is a tactical response system to review and amend call signs where necessary;

3.1.5 Consider starting flight number element sequences with a higher number e.g. 6 and above;

3.1.6 Avoid multiple use of the same digit e.g. ABC555;

3.1.7 Consider a more random system of call sign/flight number allocation different from the allocated aircraft commercial flight schedule number e.g. Operator ticket/flight number AB 555 Call sign ABC 5LF;

3.1.8 If similar numbered call signs are inevitable, allow a significant time and/or geographical split between aircraft using similar call signs;

3.1.9 Avoid use of similar/reversed digits/letters in alphanumeric call signs e.g. ABC 87MB and ABC 78BM;

3.1.10 In alphanumeric call signs avoid phonetic letters that can be confused with another operator designator prefix e.g. D ‐ Delta (The Airline).

3.2 Implement a call sign de‐confliction program within your airline, to review and if necessary amend call signs.

3.3 When call sign similarity between two or more aircraft leads to actual call sign confusion, which have or potentially could have compromised the safety of the aircraft, the occurrence shall be reported through the GCAA online (www.gcaa.gov.ae) incident reporting system (Reporting of Safety Incidents – ROSI) or through the operator’s ASR (the operator will subsequently file the report in the ROSI system).

4 GUIDELINES ‐ Flight Crew

4.1 Use correct RTF procedures and discipline at all times.

4.2 Do not use read back for confirmation if in doubt about an ATC instruction,

4.3 Positively confirm instructions with ATC if any doubt exists between flight crew members.

4.4 Always use headsets during times of high RTF loading. Always wear a headset when members of the flight crew are involved in other tasks and may not be monitoring the RTF.

4.5 Do not clip transmissions.

4.6 Always question unexpected instructions for any particular stage of flight.

4.7 Advise ATC if any of the following situations is observed:

4.7.1 Two or more aircraft with similar call signs are on the RTF frequency;

4.7.2 It is suspected that an aircraft has taken a clearance not intended for it;

4.7.3 It is suspected that another aircraft has misinterpreted an instruction;

4.7.4 A blocked transmission is observed.

4.8 At critical stages of flight actively monitor ATC instructions and compliance with them.

4.9 Use full RTF call signs at all times, unless call sign abbreviation has been introduced by ATC.

4.10 When call sign similarity between two or more aircraft leads to actual call sign confusion, which have or potentially could have compromised the safety of the aircraft, the occurrence shall be reported through the GCAA online (www.gcaa.gov.ae) incident reporting system (Reporting of Safety Incidents – ROSI) or through the operator’s ASR (the operator will subsequently file the report in the ROSI system).

5 GUIDELINES – Air Traffic Service Provider

5.1 Exercise particular caution when language difficulties may exist.

5.2 Advise adjacent FIR/sectors/ATS units whenever call sign similarity may potentially lead to call sign confusion between aircraft planned to enter their areas of responsibility.

5.3 The similarity of some aircraft call signs on the same frequency can cause confusion which may lead to an incident. Controllers shall warn pilots concerned and, if necessary, instruct one or both aircraft to use alternative call signs while they are on the frequency. (ICAO PANS‐ATM Doc 4444 –, Chapter 12.3.1.5 and 15.7.5 refers – see NOTE 1 and 2 below).

5.4 Do not Clip transmissions.

5.5 Do not use read back time to execute other tasks.

5.6 Ensure clearances are read back correctly.

5.7 Monitor flight crew compliance with RTF call sign use.

5.8 Use correct RTF phraseology, procedures and discipline at all times.

5.9 A transmission could be blocked when two or more aircraft are responding to the same clearance. Typically the controller would hear a partial or garbled read back. If a blocked transmission is suspected, ensure that both aircraft retransmit their messages and confirm carefully that a clearance has not been taken by an aircraft for which it was not intended.

5.10 Ensure that aircraft operators are made aware of any actual or potential Call Sign Similarity reported by air traffic controllers.

5.11 When call sign similarity between two or more aircraft, or vehicles and ground personnel, leads to actual call sign confusion, which have or potentially could have compromised the safety of the aircraft, the occurrence shall be reported through the GCAA online (www.gcaa.gov.ae) incident reporting system (Reporting of Safety Incidents – ROSI).

NOTE 1: Change of radiotelephony call sign for aircraft

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.
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.

NOTE 2: Phraseology

CHANGE OF CALL SIGN
... to instruct an aircraft to change its type of call sign	a) CHANGE YOUR CALL SIGN TO (new call sign) [UNTIL FURTHER ADVISED];
... to advise an aircraft to revert to the call sign indicated in the flight plan	b) REVERT TO FLIGHT PLAN CALL SIGN (call sign) [AT (significant point)].

6 Guidelines for Airport Operators

Ensure user airport information systems can cope with conversion of call signs (for ATC use) back to commercial flight numbers for passenger and airport use.

7 CONCLUSION

7.1 UAE Air Traffic Services Providers shall:

7.1.1 Establish procedures for the management and reporting of occurrences when call sign similarity leads to actual call sign confusion, and reference the procedure in the ATS Operations Manual, e.g. LATSI;

7.1.2 Reinforce the management of Call Sign Similarity with ATCO’s: implementing related available resources.

7.1.3 Establish the management of Call Sign Similarity as part of the syllabus for the ATCO Annual ECT.

7.1.4 Distribute this AIC to the ATCOs workforce.

7.2 UAE Operators shall:

7.2.1 Establish procedures for the management and reporting of Call Sign Similarity;

7.2.2 Reinforce the management of Call Sign Similarity with aircrew: implementing related available resources.

7.2.3 Distribute this AIC to the Flight Crew workforce.

7.2.4 Implement a call sign de‐confliction program within your airline, to review and if necessary amend call signs.

7.2.5 Use the Call Sign Similarity Tool (CSST) to de‐conflict similar call signs embedded in their schedules and so reduces the incidence of Call Sign Similarity events.

Contact

Aeronautical Information Circular - United Arab Emirates

General Civil Aviation Authority

CALL SIGN SIMILARITY

INTRODUCTION