15 Years since ValuJet Flight 592
It’s been 15 years since the famous ValuJet crashed into the Everglades, a tragic accident that did much to focus our views on cost-savings and in-flight safety. There’s been a lot of discussion of the flight, including a National Geographic Seconds From Disaster episode.
On the 11th of May in 1996, ValuJet Flight 592 disappeared. The domestic passenger flight had taken off from Miami International Airport, en route to Atlanta, with 110 people on board. The departure at 14:04:09 seemed normal but a few minutes later, there was an unexpected sound.
14:10:02 (Sound of click.)
14:10:03 (Sound of chirp heard on cockpit area microphone channel with simultaneous beep on public address channel.)
14:10:07 Pilot: What was that?
14:10:08 Co-pilot: I don’t know.
14:10:15 Pilot: We got some electrical problems.
14:10:17 Co-pilot: Yeah. That battery charger’s kickin’ in. Ooh, we gotta — .
14:10:20 Pilot: We’re losing everything.
14:10:21 Tower: Critter five-nine-two, contact Miami center on one-thirty-two-forty-five, so long.
14:10:22 Pilot: We need, we need to go back to Miami.
14:10:23 (Sounds of shouting from passenger cabin.)
14:10:25 Female voices in cabin: Fire, fire, fire, fire.
The pilots contacted Miami Departure and declared that they needed to return to Miami immediately. Miami Departure gave vectors but within a minute, the pilots realised they were not going to make it. At 14:11 the first officer asked for the closest airport available but the radio was breaking up and Miami Departure did not understand the request. It was too late. By 14:12, there was no response from the flight crew and the intra-cockpit recording consists of the sounds of rushing air. The controller continued to try to guide the plane, based on the descent path he could see on the radar.
Flight 592: One-four-zero. (That was the last transmission from ValuJet Flight 592).
Miami Departure: Critter 592, keep the turn around heading one-two-zero.
Miami Departure: Critter 592, contact Miami approach on corrections. No, you just keep my frequency.
Miami Departure: Critter 592, you can turn left heading one-zero-zero and join runway one-two localizer at Miami.
Miami Departure: Critter 592 descend and maintain 3,000.
Miami Departure: Critter 592, Opa Locka Airport’s about 12 o’clock at 15 miles.
American Eagle Flight 809: OK, 35-17. How did critter make out?
American Eagle Flight 809 never received a response.
Flight 592 disappeared from radar at 14:13:42, less than four minutes after the unexpected soft click that alerted the pilots.
A fisherman saw the plane come down.
On a muggy May afternoon in 1996 an emergency dispatcher in southern Florida got a call from a man on a cellular phone. The caller said, “Yes. I am fishing at Everglades Holiday Park, and a large jet aircraft has just crashed out here. Large. Like airliner-size.”
The dispatcher said, “Wait a minute. Everglades Park?”
“Everglades Holiday Park, along canal L-sixty-seven. You need to get your choppers in the air. I’m a pilot. I have a GPS. I’ll give you coordinates.”
“Okay, sir. What kind of plane did you say? Is it a large plane?”
“A large aircraft similar to a seven-twenty-seven or a umm … I can’t think of it.”
“Yes, sir. Okay. You said it looked like a seven-twenty-seven that went down?”
“Uh, it’s that type aircraft. It has twin engines in the rear. It is larger than an executive jet, like a Learjet.”
“It’s much bigger than that. I won’t tell you it’s a seven-twenty-seven, but it’s that type aircraft. No engines on the wing, two engines in the rear. I do not see any smoke, but I saw a tremendous cloud of mud and dirt go into the sky when it hit.”
“It was white with blue trim.”
“White with blue trim, sir?”
“It will not be in one piece.”
At the time of the accident, it was clear that the aircraft had suffered an in-flight fire of unexpected ferocity and very little warning. How could this happen? The fire started in the cargo hold classified as D, which means it was not required to include fire suppression units nor smoke detectors. This didn’t seem much of a risk: these cargo holds are not created for the transportation of hazardous materials. Besides, the hold was airtight. Fire would have a limited amount of oxygen and as result it would cease to burn very quickly, without needing crew intervention. Effectively, the built-in fire suppression is oxygen starvation.
Except that in this case, the hold was full of oxygen.
The class D cargo hold had been loaded with five boxes of unexpended oxygen generators which were improperly packed and which the airline was not authorised to transport.
ValuJet had purchased three MD-80 jets a few months earlier and the maintenance contact was given to SabreTech Corporation. The maintenance included the inspection of the oxygen generators on the planes, of which many were past their expiration date. ValuJet agreed that all the oxygen generators should be replaced and directed SabreTech to do so.
There were some 144 oxygen generators removed from the jets. Of these, six were reported as expended. The rest held oxygen and should have had their pin disabled with legally required safety caps.
These generators worked using a chemical reaction which had a side-effect of getting hot. Very hot.
When heated to its decomposition temperature by the action of the percussion cap, a chemical reaction begins in the core whereby the NaClO3 is reduced to sodium chloride (NaCl) and the oxygen is liberated as a gas. The oxygen flows through the granular insulation between the chemical core and the outlet shell of the generator toward the outlet end of the generator. At the outlet end, the oxygen flows through a series of filters, through the outlet manifold, and into the plastic tubes connected to the reservoir bags on the mask assembly.
The chemical reaction is exothermic, which means that it liberates heat as a by-product of the reaction. This causes the exterior surface of the oxygen generator to become very hot; the maximum temperature of the exterior surface of the oxygen generator during operation is limited by McDonnell Douglas specification to 547 °F when the generator is operated at an ambient temperature of 70 to 80 °F. Manufacturing test data indicate that when operated during tests, maximum shell temperatures typically reach 450 to 500 °F.
However, the safety caps required were not available and the generators were stored without them. The boxes were not clearly labelled. The generators themselves were tagged with green “repairable” labels which had the reason for removal written near the bottom: “out of date” or “expired”. One mechanic stated that they were under pressure to complete the work and had been working 12-hour shifts and 7-day weeks. The mechanics were aware that the canisters still required safety caps. The oxygen generators were temporarily collected into five cardboard boxes without packaging material.
On the 4th of May, the work cards associated with the MD-80s were signed off. The focus was on the MD-80s and the new generators, rather than the transport of the old generators for repair. The mechanics who signed work cards did not look in the boxes and did not check the canisters for safety caps. One stated that he was reassured that the problem would be taken care of “in stores”.
The boxes were left at the hold in the ValuJet section of SabreTech’s shipping and receiving area. No one at the hold was informed that the boxes contained hazardous materials.
The boxes were in the way. On the 8th of May, a stock clerk quickly re-packed the oxygen generators with bubble pack and labelled the boxes as containing “aircraft parts”. He noted the green labels: as far as he knew, oxygen canisters which were marked with a green label were empty and in need of refilling.
He spoke to a receiving clerk to have the five boxes and 9 tires shipped to ValuJet in Atlanta. He stated that the contents of the boxes were “Oxygen Canisters – Empty.”
According to the stock clerk, he identified the generators as “empty canisters” because none of the mechanics had talked with him about what they were or what state they were in, and that he had just found the boxes sitting on the floor of the hold area one morning. He said he did not know what the items were, and when he saw that they had green tags on them, he assumed that meant they were empty. The stock clerk stated in postaccident interviews that he believed green tags indicated that an item was “unserviceable,” and that red tags indicated an item was “beyond economical repair” or “scrap.” When asked if he had read the entries in the “Reason for Removal” block on these tags, he said that he had not.
The stock clerk asked a SabreTech driver to take the boxes to the ValuJet ramp area. The boxes were unloaded onto a baggage cart and signed off by a ValuJet employee.
On the 11th of May, the oxygen generators – five boxes of hazardous material without safety caps – were loaded on top of the rubber tires in the class D cargo hold of Flight 592. ValuJet’s policy was not to transport hazardous materials such as the chemical oxygen generators under any circumstances. Even if the generators had been properly packaged with safety caps, they should not have been transported by Flight 592. But the crew believed that the cargo consisted of a few old tires and boxes of empty canisters.
According to the ramp agent inside the cargo compartment when the boxes were being loaded, “I was stacking—stacking the boxes on the top of the tires.” The ramp agent testified at the Safety Board’s public hearing that he remembered hearing a “clink” sound when he loaded one of the boxes and that he could feel objects moving inside the box. He told Safety Board investigators that when the loading was completed, one of the large tires was lying flat on the compartment floor, with the small tire laying on its side, centered on top of the large tire. He further indicated that the COMAT boxes were also loaded atop the large tire, positioned around the small tire, and that the boxes were not wedged tightly.
When the NTSB recreated the hold scenario in a test, they reached temperatures of about 2,000°F (1,100°C) at 10 minutes after ignition. The fourth test peaked at 3,000°F (1,650°C). A main gear tire, inflated to 50psi, ruptured 16 minutes after the first oxygen generator was activated.
Based on this timing, the NTSB report believes that one of the oxygen generators was actuated during the loading of the plane or possibly as late as the take-off roll. The abundance of oxygen and the liner of the cargo hold meant there was no early indication of smoke or fire. The unexpected sound in the cockpit was a result of the rupturing of the main gear tire in the hold, long after the temperatures in the hold had reached 2,000°F (1,100°C). The crew still did not know the extent of the problem until the fire breached the cargo compartment ceiling and the smoke reached the passenger cabin.
Because of the lack of evidence from the CVR, FDR, and the wreckage, the Safety Board was unable to determine with certainty the reason for the loss of control that occurred at that time. However, examination of the wreckage showed that before the impact the left side floor beams melted and collapsed, which would likely have affected the control cables on the captain’s side. It is possible that the first officer might have taken over flying from the captain, but the remaining control cables also were possibly affected by distorting floor beams. Based on the continuing degradation of flight controls and the damage to cabin floorboards in the area of the flight controls, the Safety Board concludes that the loss of control was most likely the result of flight control failure from the extreme heat and structural collapse; however, the Safety Board cannot rule out the possibility that the flight crew was incapacitated by smoke or heat in the cockpit during the last 7 seconds of the flight.
The accident report, 142 pages not including the appendixes, concluded that probably causes were:
- the failure of SabreTech to properly prepare, package, and identify unexpended chemical oxygen generators before presenting them to ValuJet for carriage
- the failure of ValuJet to properly oversee its contract maintenance program to ensure compliance with maintenance, maintenance training, and hazardous materials requirements and practices
- the failure of the Federal Aviation Administration to require smoke detection and fire suppression systems in class D cargo compartments.
The ValuJet story played out for months. A heartbreaking story of family losses juxtaposed with a web of a lack of oversight, error compounding error. A story of tumbling dominoes led to the crash.
Fifteen years later the stark memorial stands on the side of the Tamiami Trail, a series of descending columns that, in the shape of an arrow, point northeasterly towards the crash site 8 miles away.
The legacy of the ValuJet crash is indeed vast. Lawyer Mike Eidson, who represented two families that lost loved ones is quick to note, “ We have not had an accident like this fire in cargo holds since this happened.”
That’s because in the wake of the crash, the FAA has tightened oversight of maintenance companies and slapped strict regulations on what could be shipped in airline cargo holds. In addition the FAA quadrupled the inspectors who check out cargo shipments on passenger jets.
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