European call signs

[aa73]

Noticed that anytime I am in European airspace, many flights use a different number than their actual flight number, followed by a letter or two. Example, Ryanair Six Echo Golf. Just curious as to why they don't just use the actual flight number. Here in the US they use the actual flight number no matter how many digits it has - American 2297 would be "American Twenty-Two Ninety Seven." The only time they would use a letter here would be for a "stub" flight, when two flights have the same number (such as when a continuing flight is delayed and they launch another aircraft with the same #.) That can't be the case in Europe with so many letters after numbers that I hear one just one day can it?

Thanks for any clarification.

[PENKO]

That's is done to lower the risk of callsign confusion. For example (numbers made up) EZY2202 and EZY2302 and FR2022 on one busy approach frequency, which happens more often than you think.

I've been told that the system looks at actual ATC data and eliminates potential confusing callsign combinations.

[aa73]

Thanks Penko, I wonder if this system will make it to the USA. Just the other day in MIA we were AA588 right behind Comair 588 and yes there was confusion on at least two radio calls.

[low n' slow]

Similar callsigns makes it especially annoying when fellow colleagues only speak in numbers and not full callsigns...

When I flew regional traffic in finland, our company had a system of appending the first letter of the destination behind the callsign. That made it fairly easy to identify the direction of the traffic. Anything with a Hotel after the callsign was headed for helsinki. Found it quite helpful to get a picture of the traffic situation. I guess the system only works in small regions though.

/LnS

[jonathon68]

The suffix "delta" is filed and used by my operator for significantly delayed flights.

This is obviously to try and mitigate against having two flights with the same call sign on frequency. Folk-law says it has happened.

[Denti]

Probably depends on company rules about callsigns. We do not use "D" in this way, however we do use the postfix "P" for positioning flights (aka ferry-flights). Guess each company has slightly different rules. And even with those alpha numeric callsigns there are very similar callsigns on the same frequency sometimes.

[Fesch]

Luxair started to use these callsigns recently. Although their fleet is rather small, they managed to allocate the callsigns LGL61K and LGL61Q at almost the same EOBT. Thankfully this one was mitigated, but we still have LGL91J and LGL91E which are +- 20 minutes apart.

[Nipper1011]

The other reason for using numeric/alpha callsigns is to avoid possible confusion between numeric callsigns and headings/flight levels.

[His dudeness]

AFAIK, Lufthansa started this. They had numerous (literally!) problems with similiar sounding callsigns going into EDDF at the same time.

[Mikehotel152]

At Ryanair, most of us are relieved when we get a normal 'number-only' callsign rather than some of the impossible tongue-twisters we are usually assigned! :{

[Dave Clarke Fife]

This is the AIC explaining all......................................

The Civil Aviation Authority, Nats Ltd and many Airline Operators are concerned about the problems that result from the similarity of
airline RTF callsigns, which often give rise to both potential and actual flight safety incidents. It is recognised that callsign confusion can effect
safe and expeditious operations in UK Airspace.
1.2 In the past it has been difficult to quantify the extent to which confusion caused by similar RTF callsigns has contributed to incidents
or, if left unchecked, may have caused an incident. The UK CAA Mandatory Occurrence Reporting Scheme (MORS) database contains
many reports from Controllers and Flight Crew highlighting the problems associated with callsign confusion. Whilst this had established that
there are definite safety implications resulting from callsign confusion, a dedicated study was conducted in 1997/8 called the Aircraft Callsign
Confusion Evaluation Safety Study (ACCESS). The ACCESS report was published in April 2000 as CAP 704 and the data from that report
endorsed the published guidance to airlines and air traffic service providers about problems associated with aircraft callsign confusion.
2 Numeric Verses Alphanumeric Callsigns
2.1 A numeric callsign is one where the suffix consists of numbers only. An alphanumeric callsign is one where the suffix consists of
number(s) followed by one or more letters. Of the callsign confusion occurrences:
84% involved numeric only callsigns.
10% involved alphanumeric only callsigns.
4% involved a combination of alphanumeric and numeric callsigns.
2.2 Of the occurrences which were allocated ACCESS severity grades of A or B, the distribution changed as follows:
92% involved numeric only callsigns.
8% involved alphanumeric only callsigns.
none involved a combination of alphanumeric and numeric callsigns.
2.3 The most common identical numeric callsign suffixes were all numerical as follows:
101, 202, 333, 37, 837, 762, 924
3 General Advice to Airline Operators about Numeric and Alphanumeric Callsigns
3.1 Many airline operators continue to utilise their IATA commercial flight numbers as a callsign suffix. However, because they tend to
be allocated in batches of sequential and very similar numbers, callsign confusion occurs. Several airlines have switched to alphanumeric
callsign systems reasonably successfully in recent years. However, if every operator adopts alphanumerical callsigns, the limited choices
available within the maximum of 4 elements allowed in the callsign suffix means that callsign confusion, similar to the existing numeric
system, is likely to result.
3.2 Before changing to an effective all alphanumeric callsign system, which involves a significant amount of work especially for a large
airline, it is recommended that operators review their existing numeric callsign system to deconflict any similar numeric callsigns. Where
there is no effective solution to those callsigns that have a potential for numeric confusion, alphanumeric callsigns can be adopted.
Cancels AIC 107/2000
(Pink 14)
2.
SPECIFIC GUIDE LINES TO HELP REDUCE CALLSIGN CONFUSION
4 Airline Operators
4.1 When allocating callsigns Airline Operators are requested (in accordance with ICAO Annex 10 and Doc 8585) to:
a. Avoid use of similar numerical callsigns within own company;
b. 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 callsigns;
c. after implementation, ensure there is a tactical response system to review and amend callsigns where necessary;
d. consider starting flight number element sequences with a higher number eg 6 and above;
e. try to minimise use of callsigns involving four digits and, wherever possible, use no more than three digits;
f. avoid multiple use of the same digit eg ABC555;
g. exhaust numerical possibilities first, before using alphanumeric callsign systems. If alphanumeric callsigns are inevitable, coordinate
letter combination with existing operators, taking into account all other airspace and airport users;
h. try to avoid using alphanumeric callsigns which correspond to the last two letters of the destination’s ICAO location indicator eg
ABC 96LL for flight inbound to London Heathrow where the ICAO indicator is EGLL;
i. consider a balance of alphanumeric and numeric callsigns;
j. consider a more random system of RTF callsign/flight number allocation different from the allocated aircraft commercial flight
schedule number eg Operator ticket/flight number AB 555 RTF Callsign ABC 5LF;
k. is similar numbered callsigns are inevitable, allow a significant time and /or geographical split between aircraft using similar
callsigns;
l. when useful capacity in the allocation of flight number and/or alphanumeric callsigns has been reached, consider applying for
and using a second company callsign designator eg ‘shuffle’;
m. ensure user airport information systems can cope with conversation of RTF callsigns (for ATC use) back to commercial flight
numbers for passenger and airport use.
n. avoid, whenever practicable, flight numbers ending in a zero or five eg 5 may be confused visually with s and zero when
combined with two digits, ie 150, may be confused with a heading/level;
o. avoid use of similar/reversed digits/letters in alphanumeric callsigns eg ABC 87MB and ABC 78BM;
p. in alphanumeric callsigns avoid phonetic letters that can be confused with another operator designator prefix eg D - Delta (the
airline).
5 Flight Crew
5.1 If in doubt about an ATC instruction, do not use readback for conformation.
5.2 Positively confirm instructions with ATC if any doubt exists between flight crew members.
5.3 Always use headsets especially during times of high RTF loading.
5.4 Do not clip transmissions.
5.5 Confirm unexpected instructions for any particular stage of flight.
5.6 Advise ATC if it is suspected that another aircraft has maintained an instruction. ATC may be unaware of this fact.
5.7 Exercise particular caution when members of the Flight Crew are involved in other tasks, and may be monitoring the RTF.
5.8 At critical stages of flight actively monitor ATC instructions and compliance with them.
5.9 Use full RTF callsign at all times.
5.10 Use correct RTF procedures and discipline at all times.
3.
6 Controllers
6.1 Exercise particular caution when language difficulties may exist.
6.2 Advise adjacent sector/airports if it is felt that potential confusion may exist between aircraft likely to enter their airspace.
6.3 The similarity of some aircraft callsigns on the same frequency can cause confusion which may lead to an incident. Controllers are
to warn pilots concerned and, if necessary, instruct one or both aircraft to use alternative callsigns while they are on the frequency. Manual
of Air Traffic Services - MATS Part 1 Appendix E Page E-6 refers.
6.4 Do not clip transmissions.
6.5 Do not use readback time to execute other tasks.
6.6 Ensure clearances are readback correctly.
6.7 Monitor flight crew compliance with RTF callsign use.
6.8 Use correct RTF discipline at all times.
7 Reporting Callsign Confusion
7.1 Airline Operators
7.1.1 Airline Operators should forward reports on callsign confusion incidents which meet MOR criteria to Safety Investigation Data
Department (SIDD).
7.2 Flight Crew
7.2.1 Flight Crew are requested to use company Air Safety or other designated report forms where application, or standard CA1673 MOR
forms submitted to their operations in accordance with standard company procedure.
7.3 Controllers
7.3.1 Controllers are requested to use the standard ‘SRG 1602’ report form submitted to the SIDD in accordance with standard procedure.
8 Information Required
8.1 Callsigns of aircraft concerned;
aircraft type;
date and time in UTC;
sector or geographical location;
RTF frequency;
phase of flight;
was there actual confusion and for whom?;
was there a high risk of potential confusion, and why?;
where actual callsign confusion occurred, what were the safety implications? eg Conflict Alert (TCAS/STCA);
loss of separation;
increased workload;
did any Airline Operator/ATC remedial action result?