Aug 20 (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.