Investigators combing through the wreckage of ValuJet Flight 592 said Sunday they have found pieces of hazardous oxygen-producing canisters imbedded in a fire-damaged tire that had been in the cargo hold of the DC-9 that crashed May 11 with 110 people aboard.
They also indicated that as many as 119 fully charged canisters could have been loaded on the plane in a haphazard manner - without the safety caps that are supposed to be on the firing mechanisms of the canisters.
The canisters contain a chemical that generates oxygen under high heat. If accidentally discharged, each canister is capable of producing sustained external heat of up to 500 degrees Fahrenheit.
Greg Feith, investigator in charge for the National Transportation Safety Board, refused to speculate on a cause of the DC-9’s crash into Florida’s Everglades, saying his investigators are “not going to stop and shift their entire effort to the cargo hold and these oxygen canisters.”
However, facts laid out by Feith at a news conference near the scene of the crash northwest of Miami raise the possibility that the poorly packed and poorly loaded canisters somehow fell in the cargo hold, ignited and started a smoky fire among the tires that were in the same hold. The smoke - and possibly the fire - eventually worked its way into the cockpit and the passenger cabin.
The canisters not only had no firing-pin protection but also were mislabeled “empty” rather than “hazardous material.”
Several of the boxes were placed loose in the cargo hold on top of the tires, possibly in a position where they could have turned over during takeoff or in turbulence.
Two aviation sources said the canisters have hair triggers when the safety caps are off, requiring only a pound of force to detonate. “It doesn’t take much to fire them off,” said one source.
The oxygen canisters aboard Flight 592 are used on some aircraft - not the DC-9 - to feed oxygen to passenger masks in an emergency. When passengers pull the masks down, firing pins ignite sodium chlorate inside the canisters, producing oxygen as the chemical burns. Above passenger seats, the canisters are well-insulated.
At least three times before when they had been loaded as cargo, the canisters have caused aircraft fires, including one in 1986 in Chicago that destroyed a DC-10. Aviation sources also said there have been less serious incidents - in Oakland, Calif., in 1992 and San Francisco in 1993 - in which damage was confined to single cargo containers of Qantas Airlines and Federal Express.
Feith said a Miami aircraft repair facility, Sabre Tech, removed the expired canisters from three ValuJet MD-80 aircraft two to three months ago and stored them in cardboard boxes. At some point, a Sabre Tech official discovered the boxes and ordered them returned to ValuJet.
“It is our understanding that in the process of trying to account for inventory and that kind of thing in a storage room, these passenger service units … and some tires … were being sent back to ValuJet since they were ValuJet’s property,” Feith said.
Sabre Tech delivered the boxes to the ValuJet ramp at the Miami airport, where an airline employee told the Sabre Tech employee to leave them on a baggage cart.
Shortly afterward, the baggage crew loaded the boxes aboard the plane. They were marked as company material - not hazardous material - and the shipping manifest said they were “empty.”
A Sabre Tech shipping clerk, according to Sabre Tech spokesman Kenneth P. Quinn, noted green tags on the canisters, which designates them as unserviceable. “In his mind, he believed they may have been empty,” Quinn said, and ordered another employee to list them that way on the shipping manifest.
If a hot oxygen-fed fire in the cargo hold caused the crash, that is certain to resurrect recommendations to the Federal Aviation Administration for fire-detection systems and automatic fire extinguishers in aircraft cargo holds.
The FAA has resisted such systems in favor of fire-retardant liners. However, the requirements for the liners do not take into account the effect that hazardous materials could have in feeding the severity of a fire.
The National Transportation Safety Board has recommended several times that cargo holds be fitted with better fire safety apparatus, the last such recommendation coming in 1993 after the probe of a 1988 in-flight fire.
American Airlines Flight 132 landed at Nashville, Tenn., with smoke in the cabin and a hot floor which required passengers to move away from the affected area. The fire was extinguished on landing. Investigators found illegally shipped textile-treatment chemicals in the hold.
The FAA, responding to that recommendation, said new fire extinguisher systems would be too costly and would not protect against a super-hot fire from “the illegal shipment of powerful oxidizers.”