The Dali, which sails under the flag of Singapore, lost power twice on March 26 before hitting the bridge and causing it to collapse, killing six construction workers who were on the structure at the time. The first blackout was caused when electrical breakers powering most of the vessel’s equipment and lighting unexpectedly tripped, the National Transportation Safety Board said in a report Tuesday.

The crew eventually was able to restore electrical power, but then a second blackout occurred only 0.2 miles from the bridge. They regained power, but the ship lacked the propulsion needed to avoid striking the bridge, safety inspectors found. 

It wasn’t the first time the ship experienced blackouts. Two also occurred while the vessel was in the Port of Baltimore. The first, occurring about 10 hours before the vessel left port, was caused when a member of the ship’s crew mistakenly closed an inline engine exhaust damper, causing the engine to stall, the NTSB said. A second blackout occurred shortly afterwards due to insufficient fuel pressure for an online generator. 

The Baltimore bridge collapse shut a major shipping and transportation artery and caused billions of dollars worth of damage. President Joe Biden has pressed Congress to quickly approve funds to rebuild the structure.