Callsign Letters added to Flight Numbers

[Golf-Mike-Mike]

This may well have been posted before so please re-direct me if so. I've recently become engrossed in Watch Air Traffic - LIVE! (http://www.flightradar24.com) which allows me to identify anything over-flying where I live. I've noticed that it is common practice for airline callsigns to have additional letters added to the flight number (eg VIR6N for Virgin 6, RYR4CB for Ryanair 4, EZY617D for EasyJet 617). Do these letters have a pattern and why are they added if the flight number is already unique ?

[HEATHROW DIRECTOR]

They are unique to particular flights and are supposed to assist in preventing callsign confusion on R/T. It is not unusual for two aircraft in the same are to have very similar callsigns, perhaps with the same number suffix e.g. Speedbird 123 and Delta 123. By adding a one or two letter suffix confusion may be prevented.

[Golf-Mike-Mike]

thanks for that. Do you know if there is any logic to the letters they choose, looks random to me but can't be. Perhaps honed over time to avoid similar flights known to be scheduled at similar times ?

[HEATHROW DIRECTOR]

No, I don't know how they are allocated but I'm sure that someone more knowledgeable will appear soon.... The same letters are used for a particualr flight every day... e.g Virgin 123XX will always be used for that particular service, irrespective of the aircraft used.

[flyinthesky]

At the company I work for (TCX) we have just implemented a huge change to our callsign allocation. Previously, the callsign was the flight no with a letter suffix (K=outbound, L=inbound etc), however the programme is now too large for this and there were too many similarities leading to possible confusion.

All short haul flights have a callsign which now consists of 2 numbers and 2 letters e.g Kestrel 23LB. However even that is not simple. Each callsign has to be checked against departure and arrival airports to ensure that the number and letter sequence cannot correlate to any of the taxiway routings/ holds etc. This is again to try and ensure that there is no mistaking instructions or adding ambiguity.

It took one individual 4 months to work out all of this as you can imagine it to be very complex.

Not all companies are the same, but that is how we have decided to do it. Hope that helps.

[HEATHROW DIRECTOR]

flyinthesky.. Thanks very much for that.. I had no idea it was that complex. (Perky-cirrus.. told you someone knowledgeable would be along).

[Defruiter]

Judging by some of the awful ones that have been appearing lately from one airline in particular, I assumed they just put lots of numbers and letters in a hat and picked them out! :-P

[goldox]

This reminded me that many years ago, some flights did not seem to use flight numbers, but the reg instead as the call sign (does this still happen, maybe for charters etc?)

I well remember listening to "London Director" from the comfort of my bedroom in South London, with my brand new "skyways" radio and trying to understand the transmissions. I was totally puzzled by the callsign "Zero Zero Golf" in a rather heavy accent.

I only cottoned on when he changed to next frequency and gave full reg:

It was Sierra (not Zero), good old SP-LSG a LOT AN-24.

[G SXTY]

How long have you got? The short answer to your question is that the callsigns are (in theory) random.

The slightly longer answer is that this is being driven by callsign confusion; confusion between individual aircraft and ATC, between aircraft within the same company, and between aircraft belonging to different companies. The traditional method - using an aircraft's flight number as its callsign - is struggling to keep up with the growth of air traffic, and is arguably no longer fit for purpose. Take out everything that could be confused with a heading, flight level or pressure setting, and the pot of available numbers is already reduced. Then consider that many flight numbers on high frequency city pairs start off with xxx1 on the day's first flight and continue sequentially through to xxx9 or xx10, and that more than one airline employs this method, and you will appreciate the potential for similar numbers to keep cropping up at similar times.

And be in no doubt it is a flight safety hazard. Callsign confusion results in runway incursions, alt busts, aircraft turning the wrong way, you name it. So what to do? Adding letters to the callsign based on route is a good start, but there is still confusion for opposite direction traffic with similar callsigns, e.g. Low Cost 952J inbound on the same frequency as the 953J on the way out (been there, heard it). And, unless it is done in co-operation between airlines, there is still the risk of different airlines with very similar callsigns in the same piece of airspace at the same time. Unbelievably, Lufthansa had a flight with an identical alpha-numeric callsign to my airline, and both were scheduled to arrive at the same airport within minutes of each other. What are the chances?

I'm glad to say that my lot take the issue extremely seriously, and are exceptionally quick to respond and change callsigns as soon as they're advised of any possible confusion, but a permanent solution requires a Europe-wide effort with all parties co-operating. Eurocontrol are working on this, but given the complexity of the task and the number of airlines involved, I wouldn't hold your breath.

As a start, NATS in the UK have rolled out a computer system for use by UK carriers, which is capable of 'deconflicting' callsigns so that no two aircraft should be in the same piece of airspace at the same time with similar callsigns. Several airlines are now using the system, hence some of the tongue twisters (and I bet some of our friends at Swanick just love us at the moment) but, touch wood, I have yet to encounter any callsign confusion since we started using it.

[Coffin Corner]

GSXTY

You work for the same airline as me, there have been a few instances of callsigns that are only 1 digit out. The system isn't perfect.
What gets me is why they feel the need to change every single one. If you think about it, it has to be alot less than ½ the callsigns that conflict. With this in mind there should only be a need to change ½ of a 3rd of all callsigns (1/6th) at worst. All I hear now is the said airline's pilots (myself included) getting even more confused with the new system.

Complete and utter overkill if you ask me.

[Golf-Mike-Mike]

Many thanks all for your replies. I wonder if a simpler system (mind you it might confuse the hell out of the pilots) would be to go back to flight numbers, with the possible addition of a letter to help them stand out over the RT, then leave it to ATCs in each section of airpace to either leave things as they are for all a/c under their control, or "allocate" a new suffix for the period under their control to help distinguish two similar names.
This would be similar to low level traffic outside the airways being told to use full callsign to distinguish from another similar one, eg G-WACD and G-SACD would both be told to use full callsign until one moves on to another controller. So if two airliners Speedbird 25H and Speeedbird 35H were on frequency one might be told to use c/s Speedbird 25MM instead (to keep the syllables down). The same would be true of ground traffic from the tower. I had no idea that airlines were even trying to avoid confusion with taxiway and hold identities as well. Anyway if NATS and Co. are on to it obviously it's a sufficient concernt to find a solution - one day.
:)

[Golf-Mike-Mike]

Hi, I have heard registrations being used instead of an airline flight-number-based callsign for aircraft on delivery or going to maintenance.
And general aviation aircraft flying in the airways will often use their registration if their operator doesn't have a callsign prefix, eg like Cabair.

[Neptunus Rex]

Perky
I don't know about EZY or the others, but in the company I used to work for, it was all very simple. All callsigns had the company prefix followed by three numbers that related to the flight number for that route, and was the same as on the passenger tickets. Outbound were even numbers, inbound odds. So, a flight from A to B could be Chipper 230, The return flight, Chipper 231. A second schedule on the same route, same day would be Chipper 1230 and so on.
The suffix 'D' was used for delayed flights, so that other company aircraft (and perhaps our mates in Air Traffic) would give them priority.

[Mr_Grubby]

Perky.

I can't answer your question about callsigns but I see you live in Berks and are watching the Watch Air Traffic site.

If you are near Heathrow, you might find this site interesting.

AirNav RadarBox - Screen Shot refreshed Every minute (http://www.heathrowcam.net/liveradar.php)

Clint.

[Golf-Mike-Mike]

Hi Mr Grubby, very interesting site, thanks
:)

[Golf-Mike-Mike]

Hi FlyintheSky,
Just a selection of TCX callsigns over Berks in the last few days:
479K
89GE
69YD
18WD
26L
32ND
91C
Surprised that Golf and Mike don't figure more as they're only one syllable.

[wiccan]

Eons ago, [when BA flew from airfields other than London] BA123 was the (say) Milan-Manch flight D for Domestic

[HEATHROW DIRECTOR]

<<the c/s changed to BA123D for Domestic>>

Reminds me... some Heathrow international stands could be allocated for domestic flights and when the stand number was passed it had an X suffix, e.g Bravo 19X.

One day the R/t on London Ground went something like this:

A/C: "Bealine xxx leaving 28L"
GMC: "Bealine XXX, inner taxiway, stand B19X"
A/c: "Inner taxiway B19"
GMC: "Don't forget the kiss on the bottom - B19X"
2nd A/C: "Hey what's going on?
A/C: "I don't know but I think old Honky Tonk on ground has been out with the boys".

They don't make 'em like that nowadays.....

[Golf-Mike-Mike]

@ Heathrow Director

priceless! :):)

[CaptainBloggs]

We used to use the 3 digit flight number as a callsign, which fitted marvelessly with the 3 digit rotary dial on the control column. But then as the company expanded we started using 4 digit flight numbers. This was a huge problem for lazy pilots like me who could no longer read their callsign from the dial on the control column. But just when we thought we'd mastered this additional letter, the company decided to go 'alpha-numeric'.

It's a long story, and the reasons given are controversial, but nevertheless, the bright spark who promoted the idea moved on 'to pursue other career opportunities outside the company'.

That said, after a brief return to normality, we were once again faced with alpha-numeric callsigns. As stated by others, it helps gaurd against callsign confusion, but it doesn't always appear logical how they derive the mix. It was fully explained in a brief prior to implementation, but it was far beyond me, I'm afraid - something to do with the French, apparently.

[Peter47]

I'm not an expert in this area, but various prefixes may be added:

'P' A positioning flight
'Y' Flight operating a day late
'F' A flight without passengers*
'C' A charter flight (used by an airline like BA out of LHR)

*a useful way of identifying positioning flights during the BA cabin crew dispute. A number of flights were shown as cancelled on the BA website but operated without passengers and could be picked up on the lhr-lgw.co.uk website.

Proper experts may be able to add to the list.