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Experts wonder if cargo blew up // CRASH THEORY

Investigators of the crash of ValuJet Flight 592 are exploring whether explosion or fire in the plane's cargo hold crippled the DC-9 airplane over the Florida Everglades.

On Tuesday, they found evidence suggesting the possibility of a fire beneath the floor. Pieces from the plane's interior and a floor beam appeared to have soot on them.

They also discovered that the plane's cargo included 50 to 60 oxygen generators and three aircraft tires that ValuJet was shipping to Atlanta.

Investigators will be searching for them in the swamp to see if they exploded or caught on fire.

Oxygen generators are soda can-sized devices installed above passenger seats on some airplanes.

Pulling on the overhead mask removes a pin, causing a chemical reaction that produces oxygen for the passenger.

That reaction also makes the tiny devices very hot.

Investigators will be exploring whether any of the generators in the front cargo area suddenly activated.

A fire in that area could quickly spread to the plane's electrical system because it is close to the electronics bay, where navigational equipment is housed.

"It is a fact there was smoke," said Greg Feith, the lead investigator for the National Transportation Safety Board. "Now it's our job to find out what caused it."

In another important development Tuesday, the first reports from the flight data recorder suggested the pilots encountered electrical problems and a reduction in power in the right engine.

The first indication of trouble was a sudden drop in the indicated airspeed and altitude about 3{ minutes before the crash. The airspeed fell by 34 knots and the altitude dropped by 815 feet.

The device stopped recording while the plane was level at 7,207 feet. There were no data for the last 50 seconds of the flight.

Many important pieces are still buried in the Everglades. Investigators have not located the cockpit voice recorder. Sophisticated equipment that listens for the recorder's "ping" has been unsuccessful at locating the box in the muck.

"If it's buried in the mud," said Robert Francis, the NTSB's vice chairman, "the sonar will not pick up the pinger."

The investigation has also been focusing on the plane's electrical and air conditioning systems. Investigators want to know if a short circuit or malfunction in the air system sent smoke into the cabin and cockpit.

They are looking for some wire bundles that may have a tendency to chafe, short-circuit and cause smoke to come from an overhead panel.

Those wires are the subject of a new federal rule that requires airlines with DC-9s to inspect wires and, if necessary, apply "protective wrapping" to keep them from causing a short-circuit. Within six months, the wires must be rerouted.

The Federal Aviation Administration said Tuesday that the rule was issued last year for a different model of DC-9 but was expanded in April to cover all DC-9s. The rule is "intended the prevent the potential for fire and uncontrolled smoke throughout the cockpit," the agency said.

To remove wreckage from the Everglades muck, investigators have decided to go one layer at a time.

They will start by surveying the site from the air.

"Every time the water moves and the wind blows, something is uncovered," Feith said.

They will then remove the debris on the surface and steadily go deeper, trying not to damage any evidence as they go.

Francis said the plane was badly fragmented by the impact into the Everglades.

"We would be surprised if there was anything big," he said.

Despite the slow progress Tuesday, Francis was optimistic.

"I think we'll get what we need," he said. "The important thing for people realize is that this is going to take some time."

Finding the "other" black box

Seach teams on Monday got a lucky break when a diver stepped on the flight data recorder of ValuJet 592. But the cockpit voice recorder is still missing an important part of the crash investigation. The Navy plans on finding it with a smaller version of the equipment they use to find the black boxes of aircraft that crash in the ocean. The hand-held Pinger Locater System will be operated from the deck of an airboat, the only way in or out of the crash area. Search conditions

Water: From less than a foot to as much as five feet. Sawgrass peat: Relatively thick and fibrous, averaging about six feet deep, with occasional deeper pockets. Limestone: Extremely soft, porous limestone layer about 10 feet thick.

Pinger locater system: Placed just beneath the surface of water, the small (coffee-can sized) battery-operated pinger locater contains equipment that listens for the "pinging" sound made by the jetliner's black box. Any signal is fed into the operator's headphones.

Why the black boxes are important: Located in the rear of the jet, the digital flight recorder and cockpit voice recorder help investigators reconstruct a crash. The digital flight data recorder records speed, altitude, pitch and roll, flap and slat positions. The cockpit voice recorder automatically records noises, alarms and conversations in the cockpit, over the intercom and with the control tower.

Sources: Oceaneering Technologies, news reports.

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