An investigation into the deadly crash of a Virgin Galactic spaceship has found that a function to help the craft descend into the atmosphere was deployed early, a federal safety official said on Sunday, adding pilot error could not be ruled out.

The National Transportation Safety Board (NTSB) is leading the investigation into what caused the spacecraft to crash in California’s Mojave Desert during a test flight on Friday, killing one pilot and badly injuring the other.

SpaceShipTwo’s rotating tail boom, a key safety feature for re-entering the atmosphere, rotated early, Christopher Hart, acting chairman of the NTSB, said late on Sunday, though he said it was too early to say whether this had caused the crash.