It sounds like a hypothetical problem, like something you might find in one of those conversation-starting party games: If a baby is born on an airplane, where would that baby's citizenship be located? The country they're flying over? The country where the plane took off? Where it's going to land? Somewhere else entirely?
It turns out this is not at all a hypothetical situation. In September 2021, a passenger from Morocco gave birth in the middle of a Turkish Airlines flight between Istanbul, Turkey, and Chicago. In July 2019, a baby was born on a flight between Doha, Qatar, and Beirut, Lebanon, that was diverted to Kuwait so the mother and baby could get immediate care. And during the U.S. evacuation from Afghanistan in 2021, an Afghan evacuee gave birth on a C-17 troop transport plane.
The citizenship of babies born midair like these depends on several factors. Many countries, including the United States, grant citizenship to anyone born in their territorial airspace or waters. That's known in the legal world by its Latin name, "jus soli," or "right of the soil." Other countries rely on "jus sanguinis," or "right of the blood," in these cases. That means the baby's citizenship depends on its parents' citizenship.
Let's take our party conversation a step further: What if the baby is born over the ocean where territorial rights aren't in play and jus sanguinis isn't an option for some reason? In that case, it could fall to the nationality of the airplane itself. All aircraft have the nationality of the country in which they are registered, no matter where takeoff and landing happen. This rule only applies, though, if the child would otherwise be stateless.
Jus soli and jus sanguinis will almost always have a citizenship solution before anyone's nationality has to be determined by on the registration of the aircraft.