WASHINGTON - Though it's far too early to know why a 58-year-old seaplane broke apart in flight near Miami Beach, investigators will look at the aircraft's structure for problems associated with its age.

Older airplanes have been a concern for federal safety officials since 1988, when fatigue cracking caused the roof of an Aloha Airlines Boeing 737 to peel off over Maui. A flight attendant was sucked out of the airplane and lost at sea.

That accident focused attention on the problem of metal fatigue.

Another accident — the fuel tank explosion that brought down TWA Flight 800 off the coast of Long Island in 1996 — brought attention to the problem of aging systems. Safety investigators believe a chafed wire may have caused a spark that ignited fumes in the Boeing 747's fuel tank.

"Aloha obviously started the whole issue of aging structures," said former

National Transportation Safety Board chairman Jim Hall. "With TWA 800 we looked at the whole question of aging systems." 

The TWA 747 was 25 years old and had logged 90,000 hours of flight in 18,000 cycles of takeoffs and landings.

The Aloha 737 was 19 years old at the time of the accident, but had taken off and landed more than 80,000 times.

The Aloha accident, and a subsequent law passed by Congress in 1991, prompted the

Federal Aviation Administration to step up its requirements for inspections and maintenance of aging aircraft. 

The agency routinely issues directives to airlines to inspect for tiny cracks that can lead to bigger fractures and for old wiring that can spark and cause an explosion.

The FAA ordered all aircraft that were at least 24 years old as of Dec. 8, 2003, to be inspected by the FAA by Dec. 5, 2007,

 according to agency spokeswoman Laura Brown.

Hall said the age of aircraft is a serious issue that will grow in importance as struggling airlines rely on older fleets.

Though he was unwilling to speculate about the cause of the Chalk Ocean Airways crash on Monday, he said, several possibilities come to mind: engine corrosion could create an out-of-balance situation or saltwater corrosion might have weakened the structure and caused the wing to detach.

Bernard Loeb, former director of aviation safety for the NTSB, acknowledged that the public wonders whether a 50- or 60-year-old airplane should be allowed to fly or to carry paying passengers.

He says that older airplanes aren't necessarily less safe.

"There's something in it," Loeb said. "But if the maintenance and inspections programs are carried out appropriately, airplanes can fly safely at that age."

Loeb said a number of things could have caused the Grumman Mallard seaplane to plunge into the ocean shortly after takeoff.

"I think it's absolutely too early to speculate ( from this link)