Federal officials recovered data from the cargo ship Dali’s black box Tuesday night and sent it to their lab for review, according to an official with the National Transportation Safety Board.

The data came from a device, known as a voyage data recorder, which logs key information about a ship, like audio from the bridge, radio transmissions and engine or rudder performance. Investigators can review that information in the wake of an accident, helping to determine what may have went wrong.

Early Tuesday the Dali, a 984-foot-long cargo ship, crashed into the Francis Scott Key Bridge on its way out of the Chesapeake Bay. The bridge collapsed seconds after the ship struck it, and a crew of construction workers filling potholes on the bridge deck plunged into the waters below.

The Dali suffered an apparent propulsion issue in the minutes before it hit a support pylon for the bridge. Video of the incident shows the ship appear to lose power twice in the moments before it hit the bridge. Ship tracking data also shows the Dali began to veer off course in the minutes before. Black smoke could be seen spewing from the vessel, although it’s unclear if that was due to a mechanical issue or the crew attempting to brake by throwing the engine in reverse.

Federal authorities have shared little information about what may have caused malfunctions aboard the ship.

“The NTSB doesn’t speculate,” Board Chair Jennifer Homendy said about the status of her agency’s inquiry. “We provide facts.”

News of NTSB investigators boarding the Dali in the overnight hours comes as officials begin to outline the scope of the investigation into the fatal accident. Six construction workers are presumed dead.

Federal authorities went back aboard the boat Wednesday afternoon.

Homendy said investigators are expected to remain in Baltimore for five to 10 days, but the investigation could take up to two years to complete. She said a preliminary report could be released in two to four weeks.

“We will not hesitate to issue an urgent safety recommendation at any time,” Homendy said.

The ship, a Singapore-flagged vessel, is likely to remain in the Chesapeake Bay for some time as investigators document the scene.

The U.S. Coast Guard is helping with efforts to recover the construction crew’s bodies. The Maryland Transportation Authority Police was able to stop traffic from coming across the bridge after the ship issued a mayday call, and two construction workers survived.

The NTSB maintains a go team of investigators who are on call 24/7 to respond to accidents, said Thomas Roth-Roffy, a retired marine engineer who spent nearly two decades with the agency. That’s along with specialists who are on standby.

Board officials designate an investigator-in-charge who coordinates efforts, including managing specialists who’ll examine specific aspects of the accident, Roth-Roffy said.

“The investigation by the NTSB is very, very wide,” Roth-Roffy said. “They collect everything they can.”

Roth-Roffy completed about 35 investigations during his tenure with the NTSB, and he led the inquiry into how the Cosco Busan, a 901-foot container ship, struck a tower of the San Francisco-Oakland Bay Bridge in 2007.

When the NTSB arrives on scene, Roth-Roffy said, it will hold an organizational meeting. That’s where chairs of different groups — nautical factors, human factors, engineering — will introduce themselves and ask people in the room if they want to invite individuals to join their team. Those could include the owner and operator of the vessel. Lawyers are excluded from that process.

Roth-Roffy said interviewing witnesses as quickly as possible is critical for the investigation. He said in his experience those often take place off the ship at places such as a hotel conference room. And they could last several hours.

That’s because memories fade or can become contaminated with speaking to colleagues or consuming news coverage. Investigators will request a 72-hour history for people on the vessel that documents their work and sleep hours, he said.

His practice was to ask each group chair to provide a list of documents to request. Those could include maintenance reports, inspection reports and classification documents, Roth-Roffy said.

Investigators, he said, could collect physical evidence for analysis if there appeared to have been a mechanical failure.

These inquiries are dynamic.

Following the initial period on scene, Roth-Roffy said, the team could identify a new area of investigation and pull on that thread.

Sometimes, Roth-Roffy said, there are legal roadblocks including if witnesses refuse to be interviewed. The NTSB also might have to subpoena information such as medical records.

Roth-Roffy said ships have a document called a safety management system that outlines requirements for maintenance and repairs and procedures for special emergency situations. He said investigators will examine that document and how it’s been implemented.

Maryland Gov. Wes Moore said he’s overwhelmed with the amount of support that the state has received, and promised transparency into the investigation around the bridge collapse.

“Now that now that we’ve transitioned to the recovery phase, my promise to them is this: I will devote every single resource to making sure that you receive closure,” Moore said. “The thing that we know is wherever the investigation leads that we will follow and we will make sure there’s true accountability.”