(AP Photo/Edouard H. R. Gluck)
Police divers were using sonar to find the engine, which was believed to be in the water.
"Once we get the flight data recorder it will give us the radar so we can figure out where the engine separated from the plane," said NTSB spokesman Peter Knudson.
As investigators scoured the wreckage of the Airbus A320, many of the 155 people aboard recounted survivor stories and hailed the pilot as a hero who delivered them from certain death.
The pilot, Chesley B. "Sully" Sullenberger III, was in good spirits and showing no outward signs of stress from the ordeal, a pilots union official said.
His wife, in an interview outside their California home, called him "a pilot's pilot" and said talk of him being a national hero was "a little weird."
A person briefed on Sullenberger's radio communications said the pilot considered emergency landings at two airports after his plane suffered a double bird strike, but twice told air controllers he was unable to make them. He told controllers he planned to go into the river, instead. The person spoke on condition of anonymity because of the ongoing investigation.
Air traffic controllers first gave Sullenberger directions to return to New York City's LaGuardia Airport, but he replied, "unable." Then he saw the Teterboro airstrip in the northern New Jersey suburbs, got clearance to go there, but then again responded, "unable." He then said he was going into the river.
It was not immediately clear when the engine broke off, but such scenarios can happen in bird strikes.
If the engine takes in a very large bird — or several birds at once — they could break several fan blades, causing an imbalance in the engine's rotation and severe vibrations, said Kevin Poormon, who tests the ability of aircraft engines to withstand bird strikes.
If the engine doesn't shut down right away, those vibrations conceivably could be strong to cause the engine to come loose from its mounting, Poormon said.
In a photograph of the plane as it approached the river, it appeared to have both engines.
Passengers were effusive in their praise for how Sullenberger, co-pilot Jeff Skiles and crew handled the landing and evacuation.
Mark P. Hood, of Charlotte, N.C., said he felt a jolt ripple through the jet as though a baseball bat hit the engine close to the George Washington Bridge.
"I think everyone was holding their breath, making their peace, saying their prayers," Hood said Friday.
Passenger Billy Campbell said he approached Sullenberger while they were standing on a rescue raft in the frigid cold.
"I leaned over and grabbed his arm, and I said I just want to thank you on behalf of all of us," Campbell told NBC's "Today" show. "He just said, 'You're welcome.'"'
National Transportation Safety Board investigators were focussed on recovering the plane's black box and interviewing the crew about the accident.
The aircraft, built in 1999, was tethered to a pier on the tip of lower Manhattan on Friday — about four miles from where it touched down. Only a gray wing tip could be seen jutting out of the water.
Crews of NYPD divers went underwater Friday to inspect the belly of the plane to make sure it was stable enough to lift and secure a bed of ropes underneath it.
Police and emergency crews also pulled about 15 pieces of carry-on luggage, the door of the plane, sheared pieces of metal and flotation devices from the water.
Arnold Witte, president of the Donjon Marine salvage company, said it was unclear whether the plane would be pulled out in one or several segments, or whether it could be raised on Friday.
"We want to get the plane recovered as soon as possible but we want to do it a safe way," NTSB spokeswoman Kitty Higgins said.
Federal Aviation Administration spokeswoman Laura Brown said there was no immediate indication the incident was "anything other than an accident."
The plane, bound for Charlotte, N.C., took off from LaGuardia Airport at 3:26 p.m. Less than a minute later, the pilot reported a "double bird strike" and said he needed to return to LaGuardia, said Doug Church, a spokesman for the National Air Traffic Controllers Association.
If the accident was hard to imagine, so was the result: Besides one victim with two broken legs, there were no other reports of serious injuries to the 155 people aboard.
Passengers quickly realized something was terrifyingly wrong.
"I heard an explosion, and I saw flames coming from the left wing, and I thought, `This isn't good,"' said Dave Sanderson, 47, who was heading home to Charlotte from a business trip.
Then came an ominous warning from the captain: "Brace for impact because we're going down," said passenger Jeff Kolodjay, 31.
The 150 passengers and five crew members were forced to escape as the plane quickly became submerged up to its windows in 36-degree water. Dozens stood on the aircraft's wings on a 20-degree day, one of the coldest of the winter, as commuter ferries and Coast Guard vessels converged to rescue them.
At a City Hall ceremony Friday to honor those who came to the aid of the stranded passengers, Mayor Michael Bloomberg said Sullenberger's actions "inspired people around the city, and millions more around the world."
Bloomberg planned to present the pilot with the key to the city.
Lorrie Sullenberger and her two daughters emerged from her Danville, Calif., home Friday and called her husband "a pilot's pilot who "loves the art of the airplane."
Sullenberger, 57, of Danville, Calif., is a former Air Force fighter pilot who has flown for US Airways for 29 years. He also runs a safety consulting firm.
Lorrie Sullenberger said hearing her husband's story "was really a shock. ... My husband said over the years that it's highly unlikely for any pilot to ever have any incident in his career, let alone something like this."
She called talk of her husband being a national hero "a little weird."
The pilot's sister, Mary Margaret Wilson, said she had a gut feeling her brother was at the controls when she heard a passenger plane safely landed in the Hudson River.
"When I first saw it on TV, they were saying it was an amazing landing, like one in a million. And I thought to myself, 'That's something my brother could do,"' said Wilson, a Dallas resident.
James Ray, a spokesman for the U.S. Airline Pilots Association, said he spoke with Sullenberger on Friday and described him as being "in good shape physically, mentally and in good spirits."
Ray said the flight crew was resting and likely would meet with investigators later Friday or Saturday. He said the crew has been asked not talk to the press about the accident until after the NTSB investigation is complete.
From 1990 to 2007, there were nearly 80,000 reported incidents of birds striking nonmilitary aircraft, about one strike for every 10,000 flights, according to the Federal Aviation Administration and the Department of Agriculture.
Thursday's river landing took place almost exactly 27 years after an Air Florida plane bound for Tampa crashed into the Potomac River just after takeoff from Washington National Airport, killing 78 people. Five people on that flight survived.
Associated Press writers Joan Lowy, Michael J. Sniffen and Eileen Sullivan in Washington; David B. Caruso, Verena Dobnik, Sara Kugler, Marcus Franklin, Samantha Gross, Deborah Hastings, Colleen Long and Richard Pyle in New York; Emery P. Dalesio in Raleigh; Victor Epstein in Weehawken, N.J.; Sam Hananel in Washington; Jeff Carlton in Dallas; and Harry R. Weber in Atlanta contributed to this report.