Generally, most airline computer systems will flag and eventually cancel "duplicate" bookings for the same passenger on the same flight, as their algorithms assume it is an error or an attempt to "hold" seats. However, if you need extra space for physical comfort or to transport a musical instrument, many airlines in 2026 offer an "Extra Seat" or "Double Seat" service (like IndiGo's 6E Double Seat). This allows you to purchase a second seat under a single PNR (Passenger Name Record), which often comes with a small additional baggage allowance. Crucially, you must use the specific "Extra Seat" booking process rather than just buying two separate tickets in your name; the latter will likely lead to the "duplicate" system deleting one of the reservations, potentially leaving you with only one seat at the airport.