Two major pieces of cargo ship El Faro are missing from the wreckage that's been found on the bottom of the Atlantic Ocean.

The National Transportation Safety Board issued an update on the sunken ship Tuesday.

The NTSB said a remote operated vehicle located the port and starboard sides of the vessel and found it to be in an upright position.

However, the navigation bridge and the deck below are missing from the vessel and have not been found in the nearby debris field.

Also missing is the voyage data recorder.

The NTSB said the U.S. Navy will use sonar to generate a map of the debris field in an effort to locate the bridge structure.

El Faro went missing on Oct. 1 during Hurricane Joaquin. El Faro had 28 crew members from the United States and five from Poland. The ship was heading to Puerto Rico on Sept. 29 from Jacksonville on a regular cargo supply run.

What's next to recover El Faro?

El Faro is 15,000 feet beneath the waves. That's deeper than the final resting place of the Titanic.

What's involved in efforts to recover the data recorder of the cargo ship El Faro? What about the bodies of the 33 crew who were aboard when the ship sank off the Bahamas a month ago during Hurricane Joaquin?

David Gallo of the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts, who helped locate the wreckage of an Air France jetliner off Brazil in 2011 and joined one of the final expeditions to the Titanic's ocean grave, spoke to The Associated Press on Monday about the challenges and decisions facing recovery workers.

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AP: What's the next step for recovery crews?

Gallo: They are going to use a robot called CURV (the U.S. Navy's Cable-controlled Underwater Recovery Vehicle). They will start ... looking and documenting the damage of the ship and trying to describe it. They are starting in a way to collect forensic information. The goals are they want to recover the voyage data recorder, which is like the black boxes on a plane. And secondly and most importantly, for the sake of the families and loved ones, to recover any human remains that might be there.

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AP: What kind of ocean conditions are they dealing with?

Gallo: This is in about 3 miles of water. That's even deeper than the Titanic. There may be some ups and downs, some bumps, but I think the sea floor should be fairly easy to work with in that area. They won't have to worry about running into the side of a cliff or something like that.

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AP: What kind of condition is the ship likely to be in?

Gallo: They know its sitting upright, which is odd. It's in one piece. That part surprised me, because typically when it sinks like that it will be crushed by the pressure. So any air pockets inside the ship would be crushed, unless the ship is thoroughly filled with water so there is nothing for the ocean to crush. This would suggest to me that the hull filled fairly quickly with water and the ship sank fairly quickly. It didn't go down slowly with air pockets.

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AP: How difficult is it to physically recover the data recorder and any human remains?

Gallo: It's going to be difficult to get into that ship. They are going to have to find a way in, and if they can't find a way in they have the ability to cut their way in.

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AP: Is there any possibility that humans could get involved at that depth?

Gallo: A submarine could get to that depth, and I think this is one of those cases where a submarine is pretty well suited to do that kind of work.

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AP: How has technology shaped ocean-based search and recovery?

Gallo: Every single year, about 10 ships of this size sink somewhere out in the ocean. In the past, we would commit the ships and the souls aboard to the deep for eternity. But now here we are with this technology. We go fairly routinely into this thing we once called eternity.