NTSB Says Ship That Hit Baltimore Bridge Lost Power Twice Before Departure

In the hours before a wayward cargo ship lost electrical power and knocked down Baltimore’s Francis Scott Key Bridge, killing six people, the vessel suffered two blackouts while still in port, according to a preliminary report released on Tuesday.

In a 24-page summary of findings so far, investigators with the National Transportation Safety Board said the Dali cargo vessel had experienced at least two electrical failures on the day before the accident, causing the crew to adjust the configuration of the electrical system about 10 hours before setting out.

The investigators said they were still examining what effect the earlier repairs may have had. But they said it was apparent that the trouble that led to the accident began when the vessel’s electrical circuit breakers tripped, leading to a loss of propulsion and steering capacity.

Investigators recounted the crew’s desperate efforts to restore electrical power and halt the ship’s drift toward the bridge. They described how one of eight maintenance workers still on the bridge that night managed to sprint to safety moments before the bridge collapsed.

To power the electrical supply, the 947-foot-long vessel had four generators driven by diesel engines. N.T.S.B. investigators tested the fuel being burned at the time of the failure and found no concerns about the quality.

Investigators said the electrical problems in port began when crews were working on an exhaust scrubber system on one of the diesel engines. A worker mistakenly closed an exhaust damper, stalling the engine and shutting off the generator. Workers restored power for a short period using another generator, but insufficient fuel pressure caused an electrical breaker on that generator to trip.

In the process of recovering from the blackouts, the crew switched from using their normal electrical circuit breakers to an alternative set of breakers, which were in use when the ship departed, the N.T.S.B. report found.

The vessel departed the Port of Baltimore around 1 a.m. on March 26 and traveled along a heavily used shipping channel that would take it under the Francis Scott Key Bridge. With all systems appearing to work properly, the senior harbor pilot in charge of the ship handed over control to an apprentice and stood by.

But as the ship approached the bridge, about six-tenths of a mile away, the alternative breakers suddenly tripped at around 1:25 a.m., according to the report, triggering a blackout that knocked out both the propulsion and steering. Crew members reported that the ship’s emergency generator started and that the crew was able to briefly restore electrical power. The senior pilot took control of the ship.

At around 1:27 a.m., after ordering the rudder to turn hard to the port side, the pilot ordered an anchor to be dropped. Around the same time, the ship suffered a second blackout after two more breakers tripped.

The crew was able to restore electrical power but was not able to restore the ship’s propulsion. As the authorities on the bridge rushed to close the bridge to traffic, the vessel drifted and ultimately crashed into one of the bridge’s supports at a little after 1:29 a.m. A crew member said he was releasing the brake on the port anchor as the bridge was already beginning to fall, and had to run to escape it.

Six of the eight construction workers on the bridge were killed. One was able to run to safety. Another plunged into the water in his truck but was able to escape and was rescued by a police boat about 15 minutes later.

Investigators were able to collect the ship’s data and speak with crew members, who all tested negative for alcohol. The F.B.I. has also launched a criminal investigation into the crash.

The accident has spawned questions in the shipping industry about how to better protect against such a disaster at a time when cargo vessels have grown much larger. Transportation officials have been re-examining structural protection systems on bridges, which in some cases are missing or flawed, that are supposed to deflect wayward ships away from bridge piers.

The N.T.S.B. said that along with continuing to investigate the design and operation of the Dali’s power system, it was also looking at whether there were adequate systems in place to protect the piers on the bridge from wayward ships. Its ultimate findings could include recommendations for possible mitigation measures, such as limits on vessel sizes or more extensive use of tugboats.

The cargo ship’s wreckage remains in the water. On Monday evening, crews working to dislodge the Dali set off dozens of small explosives placed around a huge section of bridge that had been blanketing the bow of the ship since the night of the collapse. The operation appeared to send the section of bridge into the water in a giant plume of black smoke. When the wreckage on top of the Dali is cleared, the ship will be refloated and brought back to the port.

Campbell Robertson contributed reporting.