The ship that struck the Francis Scott Key Bridge and caused its collapse suffered power outages before it left port because of human error, but federal safety officials are still trying to figure out why it lost power in the moments before it hit the bridge, according to a new report from the National Transportation Safety Board.

The 24-page preliminary report — the first dispatch from any of the ongoing investigations — provides some context to what happened in the run-up to the March 26 bridge collapse. Yet it leaves unanswered major questions about exactly why the Dali, a container ship the size of the Chrysler Building, lost power when and where it did. Six construction workers were killed in the collapse, and a seventh was rescued.

Safety officials determined that the Dali lost power twice in the hours before its departure from the Port of Baltimore, with the first instance the result of human error: A crew member mistakenly closed an exhaust damper while performing maintenance. That caused the ship’s engine to stall and one of its generators to cut out. A second blackout happened in port when another generator didn’t have enough fuel pressure, according to the report.

The ship would lose power for a third and fourth time in the moments right before it slammed into the Key Bridge.

“The NTSB is still investigating the electrical configuration following the first in-port blackout and potential impacts on the events during the accident voyage,” safety officials wrote.

The safety board will issue a more detailed, final report in a year’s time or longer.

Tuesday’s release of the preliminary report comes a day before NTSB Chairwoman Jennifer Homendy and other federal transportation officials are set to testify before a U.S. House committee about the various investigations into the Key Bridge collapse.

Some details from the report:

What happened in port?

The in-port blackouts occurred while the Dali was docked at Seagirt Marine Terminal, about 10 hours before it would depart. During the second power outage, the Dali’s workers reopened the exhaust damper they had accidentally closed and reconnected the generator that had cut out because of that mistake.

While recovering from the second blackout, according to the report, crew members switched the ship’s configuration to two different breakers that had not been in use for months. When the Dali left port, those newly engaged breakers were still in use, according to the report.

While not explicitly stated, the report suggests the ship’s crew believed they had resolved any issues with the Dali before leaving Baltimore. The ship’s captain reported the Dali was in “good working order” to the Maryland bay pilots who boarded at Seagirt to help steer the ship through the Patapsco River and out of the Chesapeake Bay.

Was the Key Bridge protected?

The Key Bridge had some protection, the NTSB report found, but not enough to withstand the Dali’s crushing blow. The bridge’s two main support piers were surrounded by hollow, thin-walled concrete box structures. The Dali crashed into one of the fenders, destroying it and the bridge. There also were concrete structures in the water about 500 feet from the bridge piers on either side meant to protect the span from an oncoming ship. The Dali missed those structures, known as “dolphins.”

Federal officials said the bridge’s design made it especially susceptible to collapse in the event of a ship strike. Still, the bridge’s major components were rated as being in “satisfactory condition” during its last two inspections.

The NTSB is working with Maryland authorities to determine if protections for the Chesapeake Bay Bridge, which is similar in design to the Key Bridge, need updating. The Banner previously reported that it is likely the federal government will issue new regulations concerning bridge support, safety and shipping protocols.

Did ship fuel or tugboat departures play any role?

The report ruled out contaminated or “dirty” fuel as a possible cause for the fatal blackout. Maritime engineers and investigators said contaminated fuel or another issue with the engine could have played a role in the shipwide blackouts as the Dali approached the Key Bridge. However, the NTSB tested two fuel samples from the Dali, and neither identified any quality issues.

As had been previously reported in The Banner and elsewhere, two tugboats escorted the Dali out of port. Those tugs peeled off from the ship at 1:07 a.m. on March 26, about 22 minutes before it hit the Key Bridge. The Maryland pilot gave the order for the tugs to head off, which is “normal practice” in and around the Patapsco River, according to the report.

What happened to the construction workers and Dali’s crew?

As the Dali’s crew scrambled to avoid hitting the Key Bridge, at least one crewman was sent forward to the ship’s bow with orders to drop the portside anchor, according to the report. The report says one crewman was injured by falling debris when the bridge truss landed on the front of the Dali. It’s unclear if that’s the same crew member who was working to drop the anchor.

The report also confirmed what officials had previously said: A seven-person construction crew fell into the murky waters below, and only one was able to escape. All seven were in their vehicles at the time of the bridge collapse. The worker who escaped remained in the water for 20 minutes until a Maryland Transportation Authority Police boat picked him up.

An eighth person, a maintenance inspector, was walking the length of the Key Bridge when the Dali struck. He told investigators that he ran north, toward the Dundalk side, and was able to make it to safety before the rest of the bridge collapsed.

Video of the incident shows it was only a few seconds from when the Dali hit the Key Bridge to when it collapsed.

What’s next in Key Bridge probes?

Federal safety investigators are still trying to piece together exactly why the Dali lost power after leaving port, with the NTSB planning to further examine propulsion and electrical systems aboard cargo ships, according to the report.

It’s possible the safety board or another federal agency issues regulations or recommendations to prevent the possibility of future catastrophes. The preliminary report specifically mentioned possible vessel-size restrictions, tugboat escort requirements, and increasing bridge pier protections as possibilities.

Beyond the NTSB, the Coast Guard is conducting its own safety investigation. The FBI opened a criminal probe into the bridge collapse last month and raided the ship. The status of that investigation is unclear.