DHL cargo flights operated by Atlas Air are now departing Miami to Seoul on a regular basis, according to the flight tracking website Flightradar24.
The flights are in the air for around 17 hours at a time, which puts them among the longest in the world by operating time. They have been operating every day in recent days.
There does not appear to be a direct return flight to Miami. Instead, planes continue on to either Hong Kong or mainland China, and then return to Miami via Anchorage.
A nonstop flight returning from Seoul to Miami would likely go faster, based on a few recent flights run by Korean Air.
Flights from Seoul to Miami have been operated at least a few times by Korean over the past year, with a flying time of nearly 15 hours.
The longest passenger flight in the world by flying time is New York to Singapore. Flights that depart from New York to Singapore are in the air for over 18 hours, with flight departing from Singapore to New York lasting over 17 hours.
Planes flying from Miami to Seoul have both the Southern Air and DHL logos: