American Airlines is looking to more than double its cargo-only flights in September, putting more of its underutilized planes to use as passenger demand continues to be weak.

The Fort Worth-based airline said it will increase its cargo-only routes to 32 next month after re-launching cargo-only flights in March, with 20 strategic flights to two key destinations. The airline’s last freighter flight took place in 1984.

This means more than 1,000 scheduled cargo-only flights for September. 

Since March, American has been steadily increasing its cargo-only service and has so far moved about 45 million tons of goods, mostly to overseas destinations such as Frankfurt and Shanghai.

All of the cargo-only flights will be on American Airline’s widebody Boeing 777 and 787 jets.

“A plan that began as an experiment has now grown exponentially over the last six months,” American Airline said. “Since being reintroduced, American’s cargo-only flights — which hadn’t been operated in more than 35 years — have moved more than 45m pounds of cargo around the world.”

Combined with passenger flights on widebody airplanes that carry cargo, American will fly about 2,200 cargo flights next month.

“We didn’t have a playbook. We’d never done this before,” said Maulin Vakil, American’s director of cargo customer care, in a statement. “We began to explore how much cargo we could take if we couldn’t transport passengers.”

The cargo-only flights include daily trips from Dallas-Fort Worth (DFW) to foreign destinations such as Beijing, Tokyo, Amsterdam, Frankfurt, Paris and Madrid. There are also cargo-only flights from DFW to Rome and Dublin, Ireland, that operate twice a week.

“While figuring out the safety, logistics and economics of the flight was a challenge, team members were prepared for the test,” American Airlines said. “Crews were briefed, safety procedures were established, and international rules were carefully followed. Four days after the team set their plan into motion, American operated a Boeing 777-300 from DFW to FRA as its first cargo-only flight of the 21st century,” it added.

American Airlines also expanded its cargo-only flights to Asian destinations such as Hong Kong, Shanghai, Beijing and Seoul.

American Airlines is also running 14 cargo-only domestic flights, including several from DFW to Miami, Chicago, Los Angeles, Honolulu and Kahului in Hawaii.