NASA and Boeing announced Wednesday that the first crewed flight of the Starliner spacecraft will now take place no earlier than July 21. This moves the vehicle’s flight, carrying NASA astronauts Suni Williams and Butch Wilmore, from the previously announced timeframe of April.

The manager of NASA’s Commercial Crew program, Steve Stich, said the delay was attributable to the extra time needed to close out the pre-flight review process of Starliner and also due to traffic from other vehicles visiting the space station in June and the first half of July.

“When we look at all the different pieces, most of the work will be complete in April for the flight,” Stich said during a teleconference with reporters. “But there’s one area that’s extending out into the May time frame, and this really has to do with the certification products for the parachute system.”