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Many airlines have their own callsigns for use over the radio. A British Airways plane is called "Speedbird", US Airways was "Cactus", etc. So why doesn't Delta Air Lines do the same? It would seem to need one a lot more than others, since "Delta" is the NATO Phonetic Alphabet name for "D", so it would seem to present a huge potential for confusion.

Atlanta airport, Delta's headquarters, uses "Dixie" for the letter, specifically to avoid confusion with the airline. It just seems easier and safer to me for the airline to adopt a callsign rather than deviating from the phonetic alphabet.

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    $\begingroup$ Same reason they allow Clarence Over and his co-pilot Roger to fly. $\endgroup$ – Brian Drummond Dec 1 at 11:56
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    $\begingroup$ @BrianDrummond - but will they give Clarence clearance for Victor's vector? $\endgroup$ – Bob Jarvis - Reinstate Monica Dec 1 at 16:24
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    $\begingroup$ @BobJarvis-ReinstateMonica Roger, Roger. $\endgroup$ – HiddenWindshield Dec 1 at 18:47
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    $\begingroup$ @HiddenWindshield: I been listenin' to that crap since I was at UCLA! You tell your old man to try dragging Walton or Lambier up and down the court all night! $\endgroup$ – Bob Jarvis - Reinstate Monica Dec 1 at 19:03
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    $\begingroup$ @HiddenWindshield I had to revert your edit. There are already answers to your original questions, and we cannot tolerate edits that make answers obsolete. If you have a follow up question, ask it separately. $\endgroup$ – Federico Dec 2 at 11:10
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Delta Air Lines uses the ICAO three-letter designator DAL and the ICAO telephony designator (also known as callsign) DELTA.

In general, callsigns should be similar or equal to the name of the airline according to the following ICAO rules:

3.2 In the registration of telephony designators the following rules will apply:

a) the chosen telephony designator should attempt to resemble the name of the aircraft operating agency or its function and be distinct and dissimilar from any other telephony designators in Doc 8585. Ideally it should reflect correlation between the three-letter designator, the telephony designator and the name of the aircraft operating agency or its function (examples: ARO – ARROW – Arrow Aviation; RAJ – RAJI – Raji Airlines);

b) in order to reduce the length of transmission the telephony designator should be brief, comprising if possible one word of two or three syllables. It should not exceed two words;

c) three-letter designators may not be used in phonetic form as telephony designators. However, telephony designators of long standing (such as KLM or TWA) may be retained, provided that an acceptable alphabetic representation is used (example: KAY-ELL-EMM); and

d) the telephony designator should be easily and phonetically pronounceable in at least one of the following languages: English, French, Russian, Spanish.

(ICAO Doc 8585 3. Telephony designators, emphasis mine)

Different callsigns can exist for two reasons:

  • Old callsigns: Several old airlines use callsigns that existed before these rules were made, like e.g. KLM as mentioned in c). British Airways inherited the callsign SPEEDBIRD from BOAC in 1974, which in turn inherited it from Imperial Airways in 1939. It is named after the design of the Speedbird logo.

  • Conflicting callsigns: When the airline name is too similar (or equal) to an existing callsign, a different one must be chosen, like e.g. Norwegian mentioned in J. Hougaard's answer. US Airways inherited CACTUS from America West in 2008:

    Early in its history, the airline used the call sign “America West” but it often caused confusion with other airlines ending in “west” (Southwest, Northwest, Skywest). The FAA suggested that America West come up with a new call sign. The company held an employee contest to come up with the new name. Cactus was chosen.

    (aerosavvy.com)

While Delta Air Lines is quite old ("Passenger operations began on June 17, 1929", Wikipedia), it did not chose a different callsign. I can only speculate on why, but note that the ICAO phonetic alphabet is only officially used for civilian aviation since 1 April 1952. Before than, other alphabets were common, including the Allied military phonetic spelling alphabets, which used DOG instead of DELTA, so there was no conflict at the time.

Using a different word when confusion is likely (like DIXIE in Atlanta), is explicitly allowed in the US:

ATC facilities may also request pilots to use phonetic letter equivalents when aircraft with similar sounding identifications are receiving communications on the same frequency.

(AIM 4−2−7. Phonetic Alphabet)

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    $\begingroup$ "The company held an employee contest to come up with the new name." ... the winner should have been Hairy McAirface. $\endgroup$ – Cœur Dec 1 at 11:34
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    $\begingroup$ +1 for the "Speedbird" history lesson alone! $\endgroup$ – FreeMan Dec 2 at 14:27
  • $\begingroup$ @Cœur Thankfully, it wasn't an online competition. ;) $\endgroup$ – reirab Dec 2 at 19:20
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    $\begingroup$ +1 for pointing out that the 'DELTA' callsign predates the ICAO phonetic alphabet. This is almost certainly why Delta was allowed to use that callsign. If someone tried to register, say, "JULIET" as a callsign today, it would most likely be rejected. Also, if the ICAO phonetic alphabet were being created today, they probably would've picked something other than 'Delta' for 'D.' $\endgroup$ – reirab Dec 2 at 19:51
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Delta DOES have its own callsign. It's "DELTA".

There are literally thousands of airlines in the world, many of which have designated radio telephony callsigns. Some of them are very close or even identical to the airline name, others are more diverse.

Bianfable gives a good explanation regarding the origin of the Speedbird callsign. While not the case with Speedbird, there are examples of airlines who needed to choose callsigns very different from their name simply because the other callsign was already in use by someone else. One example is Norwegian. They use the callsign "Nor Shuttle" (and a few others), probably because the callsign "Norwegian" was already in use - by the Norwegian Air Force. But, generally speaking, a callsign will be close or identical to the airline name.

A full list of airline callsigns is available in ICAO DOC 8585.

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    $\begingroup$ The downvoter is very welcome to leave constructive criticism so that I can improve my answer $\endgroup$ – J. Hougaard Nov 30 at 18:15
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    $\begingroup$ Your speculation about "Speedbird" is wrong. The Speedbird logo and callsign pre-date BIH by about 70 years. $\endgroup$ – Mark Nov 30 at 19:16
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    $\begingroup$ @Mark Thanks for the tip. For another times sake, feel free to edit an answer if it contains information that is obviously wrong. $\endgroup$ – J. Hougaard Nov 30 at 19:45
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    $\begingroup$ Ok, perhaps I should have worded my question differently. Why doesn't Delta Airlines have a callsign that's different from a NATO alphabet word? $\endgroup$ – HiddenWindshield Nov 30 at 21:58
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    $\begingroup$ @StephenS At the time this answer was posted, it did address my question as I had worded it. $\endgroup$ – HiddenWindshield Dec 1 at 18:50
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If we look away from airlines for a minute, almost all callsigns are simply letters (and numbers) from the phonetic alphabet.

Because Radio Telephony uses fairly specific formats, the likelihood of confusion is pretty low. " Delta 1234, after the landing traffic, line up and wait" simply can't mean anything other than what it's supposed to. It's got no other interpretation that makes sense, and isn't really any different to "November 123 Foxtrot, after the landing....."

Remember, the phonetic alphabet is there to make letters easier to understand - it's not there to denote that you are speaking in letters. There are lots of words in the alphabet that are just normal words (and deliberately so).

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    $\begingroup$ That is true. However, you can a Delta flight number 8074 and you can have a aircraft registered as D-8074 on the frequency. It is always a callsign, but delta can be just a letter in the callsign, not the airline callsign. $\endgroup$ – Vladimir F Dec 2 at 13:04
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    $\begingroup$ @VladimirF: Registration call signs are prefixed with the make/model (◄ important step), and also shortened. For example: "Schneider Delta 7-4" in Germany, and "Schneider 0-74" in USA (different shortening rules). $\endgroup$ – ymb1 Dec 2 at 13:27
  • $\begingroup$ @ymb1 I have only the Czech phraseology L-document and such a prefix is only possible, not necessary. Also, I don't recall hearing it in my listenings but I don't do it too often. "Type a)–the characters corresponding to the registration marking of the aircraft, or Type b)–... aircraft operating agency followed ...the registration marking...; Type c)... operating agency, followed by the flight identification. Note 1:The name of the aircraft manufacturer or of the aircraft model may be used as radiotelephony prefix to the Type a) callsign." $\endgroup$ – Vladimir F Dec 2 at 13:47
  • $\begingroup$ So the "important step" is actually only a possibility in a note. I am pretty sure the document cited follows the ICAO and EUROCONTROL rules. $\endgroup$ – Vladimir F Dec 2 at 13:49
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    $\begingroup$ @VladimirF At least there will still be one difference between German-registered callsigns and Delta ones in Europe: The Delta callsigns will almost certainly end in "Heavy." $\endgroup$ – reirab Dec 2 at 20:03
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In addition to the other answers I found a paragraph on HistoricWings.com which mentions this "problem".

Local Variations Based on Need

The international standard remains not quite completely standard, however, even to this day. You might notice, for instance, that when flying from Hartsfield-Jackson Atlanta International Airport, where Delta Airlines is based, the air traffic controllers and ground controllers might use “Dixie” or “David” instead of “Delta” so as to avoid confusion in routine communications with the name of the main airline that is hubbed there. An example might be help to demonstrate why this important:

Delta 551, Atlanta Ground, confirm Delta; taxi via Lima, Delta, Mike to runway 27 right.

Clearly, this is a lot more understandable if the phonetic “Delta” is swapped out for “David”, as follows:

Delta 551, Atlanta Ground, confirm David; taxi via Lima, David, Mike to runway 27 right.

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