Last week, Virgin Galactic announced it has successfully conducted the fourth gliding flight test of its SpaceShipTwo, the VSS Unity – an all-carbon fiber composite, suborbital rocket-powered spaceplane.

The SpaceShipTwo is based on the award-winning SpaceShipOne designed by Scaled Composites founder and ACMA Hall of Fame member Burt Rutan. The rocket plane can take a crew of two pilots and up to six passengers to space. It starts its flight attached to a mothership, the WhiteKnightTwo. The space plane then gets carried to an altitude of about 50,000 feet (15,000 meters) by WhiteKnightTwo, and then dropped.

The VSS Unity debuted and had its first official flight last year. Last week’s marked another key milestone: the first test of the spaceplane’s feather re-entry system. The “feather” refers to the space between the plane’s twin tail booms.

According to Popular Mechanics, during the unpowered flight, the feather was reconfigured in flight the same way they will be on reentry during an actual flight to suborbital space. The twin tails of the craft essentially fold up to provide aerodynamic braking on reentry. This is unique from traditional feathering in aviation, which involves rotating the propellers of a turboprop engine to reduce drag in the event that the engine fails.

Virgin Galactic says data analysis from the flight will take some time, but that initial reports from the pilots were “extremely encouraging.”

“Once data reviews are complete, we will move forward with our testing program—pressing onward with additional glide flights designed to expand our envelope of flight weights and centers of gravity,” Virgin Galactic wrote in a blog post.

To check out the feather flight in action, watch the video below: