How Airline Ticket Numbers Work
5 min read
Every electronic airline ticket issued today carries a 13-digit ticket number. It looks like a random string — 176-2342567890 or 057 2401234567 — but each part is structured and carries specific information about the issuing airline, the document form, the serial number, and a validation digit. Understanding this structure helps agents quickly identify which airline issued a ticket, detect transcription errors, and work with conjunction tickets on long itineraries.
The structure of a 13-digit ticket number
The standard IATA format breaks the 13 digits into segments. A shorthand notation for the pattern is AAA-FCSSSSSSSC, where AAA is the three-digit airline accounting code, F is the form code, C is a check sequence, S characters are the serial number, and the final C is the check digit. In practice you will most often see the number written as a three-digit group, a hyphen or space, and then ten more digits.
Pattern: AAA-FCSSSSSSSC
176-2342567890
057 2401234567| Part | Example value | Meaning |
|---|---|---|
| Airline accounting code | 176 | Three-digit IATA numeric prefix identifying the issuing airline. 176 = Emirates. |
| Form code | 2 | Identifies the form type (typically 2 for automated e-ticket documents) |
| Serial number | 34256789 | Unique document serial number assigned sequentially by the airline or GDS |
| Check digit | 0 | Final digit computed using modulus-7; validates the number has not been miscopied |
Breaking down the first example ticket 176-2342567890: the airline accounting code is 176, which is the IATA numeric code for Emirates. The next digit, 2, is the form code. The digits 34256789 form the serial number unique to this document. The final digit, 0, is the check digit. Together these ten digits after the prefix uniquely identify this single ticket document worldwide.
The airline prefix is not the same as the two-letter IATA code
Airlines are identified in two different IATA systems that serve different purposes. The two-letter alphabetic code — EK for Emirates, BA for British Airways, QR for Qatar Airways — is the one you see on flight segments in a PNR and on departure boards. The three-digit numeric code — 176 for Emirates, 125 for British Airways, 157 for Qatar Airways — is the accounting and document code. This numeric prefix is embedded in every ticket issued by or on behalf of that airline, whether the ticket is sold direct, through a travel agent, or through an online booking tool.
The distinction matters because a ticket does not have to be issued by the operating carrier. When a travel agent tickets an itinerary on a neutral airline document, the ticket may carry the issuing carrier's numeric prefix even if the flights are operated by another airline. Interline agreements determine whose stock is used. When you need to identify the responsible airline for a fare dispute or a refund, read the three-digit prefix on the ticket number — not just the flight number in the itinerary. For a full lookup of airlines and their IATA codes, see the airlines reference.
The modulus-7 check digit
The last digit of every airline ticket number is a check digit computed using a modulus-7 algorithm. To verify it, take the first twelve digits of the ticket number (the three-digit prefix followed by the nine document digits), divide that twelve-digit number by 7, and compute the remainder. The remainder should equal the final check digit. This mechanism catches transcription errors — a single transposed digit will almost always produce a different remainder and immediately reveal itself as invalid. GDS systems and airline check-in systems run this validation automatically when a ticket number is entered, so an agent mistyping a digit will receive an error rather than silently applying the wrong ticket.
Conjunction tickets for long itineraries
A single electronic ticket document holds a maximum of four flight coupons. Most round-trip or simple connecting itineraries fit comfortably within that limit. However, complex multi-leg journeys — a round-the-world routing or an itinerary with more than four separate flight segments — require more coupons than a single ticket can carry. In that case the airline or agent issues two or more ticket documents that are linked together as a conjunction ticket set.
Conjunction ticket numbers are sequential. If the first ticket in a set is 176-2342567890, the second is typically 176-2342567891, the third 176-2342567892, and so on. The GDS stores the conjunction relationship so that all documents in the set are treated as one logical ticket for purposes of pricing, endorsement, and reissue. When you look up a conjunction ticket in a GDS, the system will display all documents in the set together and require you to handle them as a unit — you cannot reissue one document without addressing the others.
Conjunction tickets require extra care when processing changes, refunds, or reissues. Partial refunds on one coupon must be balanced against the others in the set to ensure the fare construction and taxes remain correct across all documents. Many automated reissue tools handle this automatically, but it is important to recognise a conjunction set from the sequential ticket numbers before beginning any ticket change process.
The last digit of a ticket number is a modulus-7 check digit. If a ticket number you have been given does not pass this check, it has likely been miscopied — verify it with the issuing airline or agent before processing.