The announcement comes after investigators reported that cracks were found in the main support beam of a wing from the plane that crashed. The wing separated from the rest of the aircraft before the plane plunged into the water.
Chalk's Ocean Airways operates four other seaplanes.
Mark Rosenker, acting chairman of the National Transportation Safety Board, stopped short of saying the cracking was the sole reason the right wing fell off the 58-year-old plane Monday shortly after it took for the Bahamas.
"We've seen fatigue. We don't know why that fatigue appeared. That is what we're trying to determine," Mark Rosenker, acting chairman of the National Transportation Safety Board, said Wednesday morning. "This crack appears to extend through a majority of the spar at the location of the separation."
But Rosenker told a news conference that the cracking should have been found and repaired, although it would have taken "a very serious" inspection to find it.
"This is very significant because it suggests the wing was badly compromised before it took off," Orr says. "While investigators still want to review all of the wreckage and the cockpit voice recorder, this discovery of metal fatigue is very close to a 'smoking gun.'"
The Chalk's Ocean Airways plane plummeted into the Government Cut channel off the southern tip of Miami Beach in front of horrified beachgoers.
The cracks were in the main support beam that connected the wing to the fuselage. Rosenker said that if Chalk's officials had known about the cracking "they would have repaired it and we wouldn't be here today. I don't think they knew it."
The propeller and engine were still attached when salvage crews raised the right wing from the channel Tuesday. Crews began raising the rest of the plane from 35 feet of water Wednesday and Rosenker said inspectors will closely examine the remaining part of the support beam.
The salvagers will use balloons to float the plane's fuselage to the surface slowly to avoid damaging it any further, Coast Guard spokesman Dana Warr said.
Amateur video of the crash is giving the NTSB a huge lead, reports CBS News correspondent Mark Strassmann.
"It's rare you get to see an accident while it's going on. So we believe there's a great deal of information to be gleaned from it," said Rosenker.
Investigators also planned to scour maintenance and flight records for evidence of work done on the plane.
Rosenker said the plane's age could have been a factor in the cracking. The plane was retrofitted in the 1980s with more powerful engines, but it wasn't clear what role if any that played in the cracking, Rosenker said.
Chalk's officials had no immediate comment Wednesday.