The Coast Guard report said an unconfirmed number of people were still missing, while those onboard the vessel were safe and none had been injured.

The report said the pilot will undergo “post-accident drug and alcohol testing.”

Homendy said at Tuesday afternoon’s news conference that the vessel data recorder will be “critical” to the investigation. She said agency investigators had chosen not to immediately board the vessel to secure the recorder, to “allow some time for the search and recovery,” but added that she expected to have more information Wednesday.

Similar to the “black boxes” found on airplanes, voyage data recorders can help investigators to identify the cause of an accident.

Homendy largely declined to answer specific questions about potential causes or contributing factors, including whether the vessel dropped anchor and whether there should have been additional protective structures around the bridge piers. She also declined to say whether the bridge had been flagged for safety deficiencies in the past, saying that it would “take time to dig through.”

In the January 2022 Fern Hollow Bridge collapse in Pittsburgh, she said, it took almost two years for NTSB investigators to get information on inspections, any actions taken in response to those inspections and whether records were maintained.

In that incident, the NTSB determined in a report released last month the city failed to act on maintenance and repair recommendations made in bridge inspection reports, which resulted in “progressive deterioration” and, ultimately, the bridge’s collapse. The report also said the Pennsylvania’s Department of Transportation had exercised insufficient oversight of the city’s bridge inspection program and that the bridge inspections did not properly evaluate the bridge.

“It’s a very meticulous process, where they have to dig through a lot of information,” Homendy said of potential past safety deficiencies. “It will not be something that we will be able to verify while on scene.”

Under federal regulations, major marine casualties are incidents that lead to the loss of six or more lives, the loss of a vessel weighing 100 tons or more, property damage above $500,000 or a “serious threat” to life, property or the environment.

The NTSB’s Office of Marine Safety is charged with determining the likely cause of each major casualty event and identifying safety recommendations, according to its website. Investigation reports prepared by the agency can include suggestions for state or federal agencies, vessel owners and industry groups, among others.

A 2022 NTSB report on its marine investigations describes a towing vessel’s 2021 contact with a lock gate in Louisiana. It was completed roughly a year after the incident.

In it, investigators evaluated the possibility that the tow captain experienced “sleep inertia,” the influence of a tidal current, and the effect of the loss of both the lock’s GPS feed and radio communications as the tow approached, which would limit the captain’s speed indication capabilities. Sleep inertia is defined as the temporary grogginess felt upon waking up.

In that case, the probable cause of the contact was the towing vessel captain’s “decision to assume the helm watch and attempt a predawn transit into the lock immediately after awakening.” The “lesson learned,” the agency report said, was that mariners should fully recover from sleep “before taking a watch and performing critical duties.”

More recent reports examine onboard fires, a fishing vessel’s capsizing and sinking, and a collision between a tugboat and tanker.

Since the Dali was Singapore flagged, Homendy said she was in contact with her counterpart from that Southeast Asian city-state, who planned to send personnel to Baltimore on Wednesday. The country also would be sending maritime and port regulators, she said.

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