The first manned flight of Boeing's Starliner space capsule has been postponed again, and is now scheduled for April, NASA announced Thursday.

The US space agency wants to establish a second means of transport to the International Space Station (ISS) for its astronauts, with the SpaceX capsule already in service.

But Boeing has suffered a series of setbacks that significantly delayed its program, including a failed test flight in 2019. The finally succeeded in May 2022 in reaching the ISS for the first time—without a crew on board.

Boeing had then hoped to make its first manned flight in 2022, before it was first pushed back to February 2023.

The new delay announced Thursday allows to regulate the traffic to the Space Station, NASA said in a statement, without giving more details.

This test flight, called CFT (for "Crew flight test"), will carry two NASA astronauts, Barry Wilmore and Sunita Williams. They should stay about two weeks in the ISS, NASA said Thursday.

If the mission is successful, the Boeing capsule will finally be certified and begin its operational flights, at a date yet to be determined.