OXYGEN generators are safety devices. They are small steel canisters mounted in airplane ceilings and seatbacks and linked to the flimsy oxygen masks that dangle in front of passengers when a cabin loses pressurization. To activate oxygen flow the passenger pulls a lanyard, which slides a retaining pin from a spring-loaded hammer, which falls on a minute explosive charge, which sparks a chemical reaction that liberates the oxygen within the sodium-chlorate core. This reaction produces heat, which may cause the surface temperature of the canister to rise to 500° Fahrenheit if the canister is mounted correctly in a ventilated bracket, and much higher if it is sealed in a box with other canisters, which may themselves be heating up. If there is a good source of fuel nearby, such as tires and cardboard boxes, the presence of pure oxygen will cause the canisters to burn ferociously. Was there an explosion on Flight 592? Perhaps. But in any event the airplane was blowtorched into the ground.
It is ironic that the airplane's own emergency-oxygen system was different—a set of simple oxygen tanks, similar to those used in hospitals, that do not emit heat during use. The oxygen generators in Flight 592's forward cargo hold came from three MD-80s, a more modern kind of twin jet, which ValuJet had recently bought and was having refurbished at a hangar across the airport in Miami. As was its practice for most maintenance, ValuJet had hired an outside company to do the job—in this case a large firm called SabreTech, owned by Sabreliner, of St. Louis, and licensed by the FAA to perform the often critical work. SabreTech, in turn, hired contract mechanics from other companies on an as-needed basis. It later turned out that three fourths of the people on the project were just such temporary outsiders. The vulnerability of American wageworkers could be sensed in their testimony after the accident. They inhabited a world of boss men and sudden firings, with few protections or guarantees for the future. As the ValuJet deadline approached, they worked in shifts, day and night, and sometimes through the weekend as well. It was their contribution to our cheap flying.
We will never know everyone at fault in this story. ValuJet gave the order to replace oxygen generators on the MD-80s, most of which had come to the end of their licensed lifetimes. It provided SabreTech with explicit removal procedures and general warnings about the dangers of fire. Over several weeks SabreTech workers extracted the generators and taped or cut off their lanyards before stacking most of them in five cardboard boxes that happened to be lying around the hangar. Apparently they believed that securing the lanyards would keep the generators from being fired inadvertently. What they did not do was place the required plastic safety caps over the firing pins—a precaution spelled out on the second line of ValuJet's written work order. The problem for SabreTech was that no one had such caps, or cared much about finding them. Ultimately the caps were forgotten or ignored. At the end of the job, in the rush to complete batches of paperwork on all three MD-80s, two mechanics routinely "pencil-whipped" the problem by signing off on the safety-cap line as well as on the others, certifying that the work had been done. SabreTech inspectors and supervisors signed off on the work too, apparently without giving the caps much thought.
The timing is not clear. For weeks the five boxes stood on a parts rack beside the airplanes. Eventually mechanics lugged them over to SabreTech's shipping-and-receiving department, where they sat on the floor in the area designated for ValuJet property. A few days before the accident a SabreTech manager told the shipping clerk to clean up the area and get all the boxes off the floor in preparation for an upcoming inspection by Continental Airlines, a potential customer. The boxes were unmarked, and the manager did not care what was in them.
The shipping clerk then did what shipping clerks do, and prepared to send the oxygen generators home to ValuJet headquarters, in Atlanta. He redistributed them equally among the five boxes, laying the canisters horizontally end to end, and packing bubble wrap on top. After sealing the boxes he applied address labels and ValuJet company-material stickers, and wrote "aircraft parts." As part of the load he included two large main tires and a smaller nose tire—at least two of which were mounted on wheels. The next day he asked a co-worker, the receiving clerk, to make out a shipping ticket, and to write "oxygen canisters—empty" on it. The receiving clerk wrote "Oxy Canisters" and then put "Empty" between quotation marks, as if he did not believe it. He also listed the tires.
The cargo stood for another day or two, until May 11, when the SabreTech driver had time to deliver the boxes across the airport to Flight 592. There the ValuJet ramp agent accepted the material, though federal regulations forbade him to, even if the generators were empty, since canisters that have been discharged contain a toxic residue, and ValuJet was not licensed to carry any such officially designated hazardous materials. He discussed the cargo's weight with the copilot, Richard Hazen, who also should have known better. Together they decided to place the load in the forward hold, where ValuJet workers laid one of the big main tires flat, placed the nose tire at the center of it, and stacked the five boxes on top of it around the outer edge, in a loose ring. They leaned the other main tire against a bulkhead. It was an unstable arrangement. No one knows exactly what happened then, but it seems likely that the first oxygen generator ignited during the loading or during taxiing or on takeoff, as the airplane climbed skyward.
Two weeks later and halfway through the recovery of the scorched and shattered parts a worker finally found the airplane's cockpit voice recorder, the second black box sought by the investigators. It had recorded normal sounds and conversation up to the moment—six minutes after takeoff—when the flight-data recorder indicated a pulse of high pressure. The pulse may have been one of the tires exploding. In the cockpit it sounded like a chirp and a simultaneous beep on the public-address system. The captain, Candalyn Kubeck, asked, "What was that?"
Hazen said, "I don't know."
They scanned the airplane's instruments and found sudden indications of electrical failure. It was not the cause but a symptom of the inferno in the hold—the wires and electrical panels were probably melting and burning along with other, more crucial parts of the airplane—but the pilots' first thought was that the airplane was merely up to its circuit-breaking tricks again. The recording here is garbled. Kubeck seems to have asked, "About to lose a bus?" Then, more clearly, she said, "We've got some electrical problem."
Hazen said, "Yeah. That battery charger's kickin' in. Oooh, we gotta ..."
"We're losing everything," Kubeck said. "We need, we need to go back to Miami."
Twenty seconds had passed since the strange chirp in the cockpit. A total electrical failure, though serious, was not in those sunny conditions a life-threatening emergency. But suddenly there was incoherent shouting from the passenger cabin, and women and men screaming, "Fire!" The shouting continued for thirteen seconds and then subsided.
Kubeck said, "To Miami," and Hazen put in the call to Jesse Fisher, the air-traffic controller. When Fisher asked, "What kind of problem are you having?" Kubeck answered, off-radio, "Fire," and Hazen transmitted his urgent "Smoke in the cockpit. Smoke in the cabin."
Investigators now presume that the smoke was black and thick, and perhaps poisonous. The recorder picked up the sound of the cockpit door opening, and the voice of the chief flight attendant, who said, "Okay, we need oxygen. We can't get oxygen back there." Did she mean that the airplane's cabin masks had not dropped, or that they had dropped but were not working? If the smoke was poisonous, the masks might not have helped much, since by design they mix cabin air into the oxygen flow. The pilots were equipped with better, isolating-type masks and with goggles, but may not have had time to put them on. Only a minute had passed since the first strange chirp. Now the voice recorder captured the sound of renewed shouting from the cabin. In the cockpit the flight attendant said, "Completely on fire."
The recording was of little use to the NTSB's technical investigation, but because it showed that the passengers had died in agony, it added emotional weight to a political reaction that was already spreading beyond the details of the accident and that had begun to call the entire airline industry into question. The public, it seemed, would not be placated this time by standard reassurances and the discovery of a culprit or two. The press and the NTSB had put aside their on-site antagonism and had joined forces in a natural coalition with Congress. The questioning was motivated not by an immediate fear of unsafe skies (despite the warnings of Mary Schiavo, a federal whistle-blower who claimed special insight) but rather by a more nuanced suspicion that competition in the open sky had gone too far, and that the FAA, the agency charged with protecting the flying public, had fallen into the hands of industry insiders.