Technically, the software for many airlines will allow you to complete a purchase for two different flights at the same time, but it is almost always a violation of the airline’s Contract of Carriage. Most major carriers use automated "revenue integrity" systems that scan for duplicate bookings—defined as the same passenger name on two flights that are physically impossible to fly (e.g., departing at the same time or overlapping). If the system flags you, the airline reserves the right to cancel one or both of the reservations without notice to free up the seats for other passengers. While you might occasionally "get away with it" on two separate airlines, doing so within the same alliance (like Star Alliance or Oneworld) often triggers the same automated sweep. If you genuinely need a second seat for extra space or a musical instrument, you must book it through a specific "Extra Seat" process rather than a second individual booking to avoid having your primary ticket voided by the system.