WASHINGTON- A federal safety board blamed faulty repair of a wing crack and weak federal regulation for a seaplane crash that killed 20 people in Florida in 2005.

All five National Transportation Safety Board members were highly critical of the management of financially troubled Chalk's Ocean Airways, whose 58-year-old Grumman G-73T Turbine Mallard crashed Dec. 19, 2005.

"It glares at you that this was a poorly operated airline," board chairman Mark Rosenker said.

Spokesmen for Chalk's and for the Federal Aviation Administration said their workers complied with all safety requirements and inspections for the aged aircraft.

The twin-engine seaplane carrying 18 passengers and two crew members lost its fuel-laden right wing and then exploded shortly after takeoff from Miami en route to Bimini Island. The plane crashed into a ship channel just east of Miami Beach at 2:30 p.m.

The board found that pre-existing cracks caused the right wing to break off during normal flight conditions, which set off an explosion of the fuel tank inside the wing. It said there was nothing the crew could have done to save the plane.

The board said the company had placed thin, metal sheets over a 16-inch crack in the wing after it was troubled by regular fuel leaks, but did not fix a crack in a support strut. As a result, the remaining cracks were not visible to pilots in preflight inspection. And the board concluded the plane crashed because the repair was not sufficient to restore the wing's strength.

Although there are no records describing the repair, the board said metallurgical tests indicated Chalk's did the work. But Dennis M. O'Hara, lawyer for Chalk's, said, "Chalk's did not make that repair." He said Chalk's thinks the repair was made before it bought the aircraft in 1999 or 2000.

The board said another cause of the accident was the "failure of the Federal Aviation Administration to detect and correct deficiencies in the company's maintenance program."

FAA spokesman Les Dorr responded that his agency "did not have any indication that Chalk's maintenance program was inadequate. It served them well for many, many years."

Dorr said the FAA maintenance inspector completed all his assigned tasks at Chalk's "so it's difficult to see how the FAA is a cause."

The board's aviation safety director, Tom Haueter, said problems at Chalk's should have prompted the FAA to step up its surveillance and the company to do more than it did, including multiple fuel leaks from the wing that failed and similar cracking found and repaired months earlier on the plane's sister aircraft.

Under pressure from board member Debbie Hersman, the board agreed to have its staff add an additional finding that these and other factors, such as the money-losing company's financial troubles and practice of having pilots double as safety managers, should have alerted FAA to increase surveillance.

The board staff also said the company's March 2005 internal examination of the wing should have found the cracks, but Gregory Feith, a former board staff investigator, disputed that.

"You can't just stick a flashlight into the wing, because you don't know what you're looking for," Feith said.