Parse a 13-digit IATA electronic ticket number into its component parts and validate its check digit.

Steps

1. Split the ticket number into a 3-digit airline numeric (accounting) code, a 4-digit form code, and a 6-digit serial number (3+4+6 = 13 digits), per the structure documented in IATA e-ticketing references and reflected in GDS ticketing docs.
2. Look up the airline separately from its 3-digit accounting code (e.g., 001 = American Airlines, 006 = Delta) — don't infer the airline from the ticket number without a lookup table.
3. Take the 10-digit document number (form code + serial number) and compute its remainder modulo 7.
4. Compare that remainder to the ticket's check digit — GDS platforms such as Amadeus display it appended to the ticket number (e.g., after a slash) in ticketing entries, computed the same way, so a valid check digit equals document-number mod 7 (a value 0-6).
5. Flag any ticket number whose trailing check digit is 7, 8, or 9, or that fails the mod-7 comparison, as malformed or mistyped before using it in downstream lookups.
6. Treat the ticket number as distinct from the PNR/booking reference (a separate 6-character alphanumeric code) — don't conflate the two when validating user-entered references.