Federal investigators suffered a setback when no audible sound was found on the cockpit voice recorder recovered from a seaplane that crashed off Miami Beach.

But recovery of both parts of the plane's cracked wing where it separated from the fuselage, and video from the crash will help investigators, Mark Rosenker, the acting chairman of the National Transportation Safety Board, said at a briefing late Wednesday.

The Chalk's Ocean Airways plane, bound for the Bahamas, crashed off Miami Beach on Monday, killing all 20 people aboard.

Cracks were found in the support beam of the wing that fell off the 58-year-old seaplane, the NTSB said. Material has been sent for inspection to labs in Washington, where a microscope will be used to examine metal parts and cracks, Rosenker said.

"We're particularly interested in deep cracks and any potential corrosion," he told The Associated Press. "The maintenance records should give us a better picture," as the complex investigation continues.

Investigators had hoped to learn more from the cockpit voice recorder, which was found intact in the tail of the aircraft and flown to an NTSB lab in Washington for examination. But Rosenker said there was nothing readable on it.

"It is clearly disappointing," Rosenker said. "It is an element that is very helpful in aviation accidents."

The plane was not required to carry a second device, the flight data recorder, that might have shed additional light on the crash's cause.

The right wing was pulled from the water Tuesday. On Wednesday, crews used a crane to lift out the left wing, an engine, a propeller, part of the underbelly of the fuselage and parts of two landing gears. They also raised baskets of debris, including other parts of the fuselage.

Specialists planned to lay the wreckage, which amounts to 95 percent of the plane, on a floor Thursday to study it further.

Inspectors will try to determine whether fatigue cracks on the right wing support could have been found and repaired, and whether stress was a factor in the cracking that occurred. Rosenker said that detecting such cracks would have required sophisticated testing and would not have been readily apparent.

"This is not a walk-around type of inspection," he said.

Chalk's, which flies between Florida and the Bahamas, voluntarily grounded its remaining fleet Wednesday for inspection. Chalk's operates four other seaplanes, all the same model as the one that crashed.

Eighteen passengers and two crew members were killed in Monday's crash. Only 19 bodies have been recovered. At least 11 victims were returning home to the Bahamian island of Bimini, many of them after Christmas shopping jaunts.

The plane was retrofitted in the 1980s with more powerful engines, but it wasn't clear if that played any role in the cracking, Rosenker said. The engines' installer said it should not have played any role.

Current owner Jim Confalone bought Chalk's after it was forced into involuntary bankruptcy in 1999 under previous management when creditors sued the airline.