Federal investigators revealed that the cargo ship Dali experienced power blackouts hours before it left the Port of Baltimore and again just before it collided with the Francis Key Bridge, resulting in the deaths of six construction workers. The National Transportation Safety Board (NTSB) detailed these findings in a preliminary report on Tuesday, marking the most comprehensive account of the incident to date.

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The first power outage occurred roughly 10 hours before departure, triggered by a crew member mistakenly closing an exhaust damper during maintenance, which caused one of the ship’s diesel engines to stall. A backup generator kicked in but soon failed due to insufficient fuel pressure, leading to a second blackout. The crew then reconfigured the ship’s electrical system in preparation for departure.

Shortly after setting sail on March 26, the Dali lost steering and propulsion near the bridge due to another power outage caused by tripped breakers. This failure occurred as the ship approached the bridge, rendering it unable to avoid crashing into one of the bridge’s support columns.

The NTSB report describes how crew members scrambled to address these electrical issues, manually resetting breakers and attempting to restore power. Despite their efforts, the ship experienced another blackout just before the crash. Pilots on board called for tugboats, attempted to drop anchor, and issued a mayday call, but it was too late to prevent the disaster.

The collision caused the 1.6-mile steel span to collapse into the Patapsco River, killing six workers who were on a break in their vehicles. One worker survived by escaping his truck, and a road maintenance inspector narrowly avoided the collapse by running to safety.

The Dali, en route to Sri Lanka with shipping containers and supplies, was grounded amid the wreckage of the bridge. On Monday, a controlled demolition was conducted to remove the remaining span of the bridge from the ship’s bow. The Dali is expected to be refloated and returned to the Port of Baltimore soon.

The NTSB continues to investigate the power failures and is working with Hyundai, the manufacturer of the ship’s electrical system, to determine the cause of the breaker issues. The final report, which will include more detailed findings, is expected to take over a year to complete. Meanwhile, the FBI has launched a criminal investigation into the circumstances leading up to the collapse.

The Dali had arrived in the U.S. from Singapore on March 19, making stops in Newark, New Jersey, and Norfolk, Virginia, before docking in Baltimore. Investigators noted that there were no reported power outages at these other ports.

The NTSB’s mission, as stated by board chair Jennifer Homendy, is to understand why and how the incident occurred to prevent future tragedies.