(Reuters) -United Airlines' venture capital arm said on Wednesday it has invested in aerospace startup Astro Mechanica, which develops airframe designs and propulsion systems for supersonic aircraft, signaling renewed industry interest in ultra-fast jets.

The Trump administration has been pushing to lift a ban on supersonic air transport over land imposed in 1973, directing the FAA to repeal the supersonic speed limit as long as aircraft do not produce an audible sonic boom on the ground.

The era of regular commercial supersonic flights ended in 2003 when Concorde, flown by Air France and British Airways, was retired after 27 years of service.

Supersonic aircraft have been criticized by environmentalists for burning more fuel per passenger than comparable subsonic planes.

United Airlines had previously backed the prospect of supersonic flights, with an order for 15 of Boom Supersonic's "Overture" aircraft it placed in 2021.

United Airlines Ventures did not disclose the size of its investment in Astro Mechanica.