Dive teams are ceasing operations on the Potomac River because they have recovered all of the bodies they’re able to without moving the fuselage, two sources familiar with the operation told ABC News.

About 40 bodies have been recovered so far, including at least one of the soldiers from the Army helicopter, the sources said.

Additional bodies and human remains will need to be extracted from the wreckage once it is lifted to the surface of the river.

Crews are bracing for the possibility that some of the victims will not be recovered because of the fireball that resulted from the collision, the sources said.

-ABC News’ Katherine Faulders and Aaron Katersky

Samuel Lilley, the first officer on board American Airlines Flight 5342, recently got engaged, his sister, Tiffany Gibson, told ABC News.

"He was an amazing person. He loved people. He loved adventure. He loved traveling. He was excited. He was young. He was so young, and he was excited about life and his future and getting a dog and a house and kids. And it's just, this is just tragic," she said.

Samuel Lilley’s former brother-in-law, Greg Gibson, remembered him for his passion for flying and willingness to help others.

Samuel Lilley died on the same flight path his father, Timothy Lilley, flew for years. Timothy Lilley flew Black Hawk helicopters for the Army, transporting passengers over the Potomac River from his base in Virginia.

“We were stationed in Virginia, and [Timothy Lilley] flew that same route back and forth to the Pentagon, over and over and over again until he retired,” Tiffany Gibson said.

-ABC News’ Peter Charalambous

National Transportation Safety Board investigators are on the scene of the crash and plan to have a preliminary report within 30 days, NTSB Board Member Todd Inman said.

Flight recorders have not yet been recovered but the NTSB is "comfortable and confident" that the recorders will be recovered, Inman said.

The NTSB does not know enough facts to rule in or out human or mechanical factors at this time, Inman said.

"Our investigative team will be on scene as long as it takes in order to obtain all of the perishable evidence and all the fact finding that is needed to bring us to a conclusion of probable cause," Inman said. "Our mission is to understand not just what happened, but why it happened, and to recommend changes to prevent it from happening again."

NTSB Chairwoman Jennifer Homendy added that they do have "substantial" information but do not want to share anything before it’s verified.

The three Army Soldiers aboard the Black Hawk were very experienced, according to an Army official who briefed reporters in a phone briefing.

Jonathan Koziol, a retired Army chief warrant officer with more than 30 years of flight experience, told reporters that the flight was a nighttime qualification flight with an instructor pilot evaluating an experienced pilot on the flight routes that their unit routinely flies day and night around the Potomac River.

Jimmie Cummings, a spokesman for the Army’s Combat Readiness Center at Fort Novosel, Alabama, said that just like all soldiers who must meet regular qualifications for their weapons, Army aviators have to meet annual qualifications, regardless of their flight experience. For aviators, that means flying under different conditions, which could mean flying in daytime or nighttime.

Koziol confirmed that the instructor pilot had more than 1,000 flight hours and that the pilot being evaluated had more than 500 hours. The evaluated pilot was in command of the flight, but if an emergency was to occur the instructor would have taken control of the helicopter.

Koziol said the maximum altitude for this route is 200 feet; the helicopter appeared to be flying at about 350 feet, according to sources.

Part of the unit’s responsibility is to fly VIPs around the D.C. area, and that includes getting them out of the area if "something really bad happens," he said, "so they do need to be able to understand the environment, the air traffic, the routes, to ensure the safe travel of our senior leaders throughout our government."

Koziol described the helicopter flight corridor above the Potomac as "a relatively easy corridor to fly, because you're flying down the center of the river, and it's very easily identifiable, especially at night" because there aren’t a lot of lights.

The helicopter had a black box with a voice and flight data recorder.

-ABC News’ Luis Martinez