WASHINGTON — A nine-month federal investigation into the fatal crash last year of a Virgin Galactic spaceship found that the company hired to build and test the vehicle failed to properly train its pilots and did not implement basic safeguards to prevent the human error that caused the accident.

The National Transportation Safety Board on Tuesday announced that the probable cause of the October crash of a test flight was a mix of human error and systematic failures by Scaled Composites, the company that designed and was operating Virgin Galactic’s SpaceShipTwo.

The spacecraft, designed to take paying passengers to the edge of Earth’s atmosphere, crashed in the Mojave Desert, killing co-pilot Michael Alsbury, 39, and injuring pilot Peter Siebold, 43, who ejected from the vehicle at an altitude of more than 40,000 feet.

The NTSB had earlier concluded that Alsbury mistakenly unlocked a “feather” system on the spaceship that allows two wings to stand upright and create drag on the vehicle. With the wings unlocked prematurely, the spaceship broke apart in midair.

But at Tuesday’s hearing, board members focused on the safety culture at Scaled Composites, particularly how it trained its pilots and the systems that could have prevented a premature unlocking of the system.

It determined that the company “failed to consider and protect against the possibility that a single human error could result in a catastrophic hazard.”

Scaled Composites also did not ensure that “pilots adequately understood the risks of unlocking the feather early,” the investigation found.

NTSB member Robert Sumwalt said that Scaled “put all their eggs in the basket of the pilot doing it correctly.” But, he said, humans will inevitably make mistakes.

Kevin Mickey, a spokesman for Scaled Composites, which is owned by Northrop Grumman, said that “safety has always been a critical component of Scaled’s culture and, as the NTSB noted today, our pilots were experienced and well-trained.”

He said the company has “already made changes in the wake of the accident to further enhance safety. We will continue to look for additional ways to do so.”

Virgin Galactic said it has “already implemented changes as a result of the accident,” including putting in place an “inhibitor” that would prevent the feather from being prematurely unlocked.

NTSB officials also questioned whether the Federal Aviation Administration, under pressure to issue or deny flight permits within a 120-day period, rushed Scaled Composites’ test-flight application without fully vetting it.

The NTSB recommended that the FAA more thoroughly examine permit applications to make sure they ensure safety.

An FAA spokesman said the agency takes “all NTSB recommendations very seriously” and that the agency has 90 days to review them and respond.