Understanding Air Safety in the Jet Age/Fire Down Below - ValuJet Flight 592
Fires can occur anywhere. The most common, perhaps unsurprisingly, are engine fires. But bad decisions and bad practice can put a plane at risk from fire in more unusual ways. ValuJet Flight 592 was a DC-9 on a domestic passenger flight between Miami International Airport, in Florida, and Hartsfield-Jackson Atlanta International Airport in Georgia. It disappeared over the Florida Everglades on 11 May 1996.
There were 105 passengers on board, as well as a crew of two pilots and three flight attendants, bringing the total number of people on board to 110. At 2:04 pm, 10 minutes before the disaster, the DC-9 took off from runway 9L and began a normal climb.
At 2:10 pm, Captain Candalyn Kubeck and First Officer Richard Hazen heard a loud bang in their headphones, and noticed the plane was losing electrical power. Seconds later, flight attendant Mandy Summers entered the cockpit and advised the flight crew of a fire in the passenger cabin. Passengers' shouts of "fire, fire, fire" were recorded on the plane's cockpit voice recorder when the cockpit door was opened. Though the ValuJet flight attendant manual stated that the cockpit door should not be opened when smoke or other harmful gases might be present in the cabin, the intercom was disabled and there was no other way to inform the pilots of what was happening.
Kubeck and Hazen immediately asked air traffic control for a return to Miami due to smoke in the cockpit and cabin, and were given instructions for a return to the airport. One minute later, Hazen requested the nearest available airport. Kubeck began to turn the plane left in preparation for the return to Miami.
Flight 592 disappeared from radar at 2:13:42 pm. It rolled onto its side and crashed to the ground nose-first in the Francis S. Taylor Wildlife Management Area in the Everglades, a few miles west of Miami, at a speed in excess of 500 mph. The crew continued to fly the plane until about seven seconds before impact, likely until the front left floor beams collapsed and caused failure of the flight controls. Everyone on board was killed. Recovery of the aircraft and victims was made extremely difficult by the location of the crash. The nearest road of any kind was more than a quarter of a mile away from the crash scene, and the location of the crash itself was a deep-water swamp. The DC-9 shattered on impact leaving very few large portions of the plane intact. Sawgrass, alligators, and risk of bacterial infection from cuts plagued searchers involved in the recovery effort. No intact bodies were ever recovered, only human remains.
The NTSB investigation eventually determined that the fire that downed Flight 592 began in a cargo compartment below the passenger cabin. The cargo compartment was of a Class D design, in which fire suppression is accomplished by sealing off the hold from outside air. Any fire in such an airtight compartment will in theory quickly exhaust all available oxygen and then burn itself out. As the fire suppression is accomplished without any intervention by the crew, such holds are not equipped with smoke detectors. However, the NTSB determined that just before takeoff, expired chemical oxygen generators were placed in the cargo compartment in five boxes marked COMAT (Company-Owned MATerial) by ValuJet's maintenance contractor, SabreTech, in contravention of FAA regulations forbidding the transport of hazardous materials in aircraft cargo holds. Failure to cover the firing pins for the generators with the prescribed plastic caps made an accidental activation much more likely. Rather than covering the firing pins, the SabreTech workers simply taped the cords around the cans, or cut them, and used tape to stick the ends down. It is also possible that the cylindrical, tennis ball can-sized generators were loaded on board in the mistaken belief that they were just empty canisters, thus being certified as safe to transport in an aircraft cargo compartment. SabreTech employees indicated on the cargo manifest that the "oxy canisters" were "empty" instead of being expired oxygen generators. ValuJet employees interpreted this to mean that they were empty oxygen canisters, when in fact they were neither simple oxygen canisters, nor empty.
Chemical oxygen generators, when activated, produce oxygen. As a byproduct of the exothermic chemical reaction, they also produce a great quantity of heat. These two together were sufficient not only to start an accidental fire, but also to produce enough oxygen to keep the fire burning. The fire risk was made much worse by the presence of combustible aircraft wheels in the hold. Two main tyres and wheels and a nose tyre and wheel were also included in the COMAT. NTSB investigators theorized that when the plane experienced a slight jolt while taxiing on the runway, an oxygen generator activated, producing oxygen and heat. Laboratory testing showed that canisters of the same type could heat nearby materials up to 250C, enough to ignite a smouldering fire. The oxygen from the generators fed the resulting fire in the cargo hold without any need for outside air, defeating the airtight fire suppression design. A pop and jolt heard on the cockpit voice recorder and correlated with a brief and dramatic spike in the altimeter reading in the flight data recorder were attributed to the sudden cabin pressure change caused by a semi-inflated aircraft wheel in the cargo hold exploding in the fire.
Smoke detectors in the cargo holds can alert the flight crew of a fire long before the problem becomes apparent in the cabin, and a fire suppression system buys valuable time to land the plane safely. In February 1998, the FAA issued revised standards requiring all Class D cargo holds to be converted by early 2001 to Class C or E; these types of holds have additional fire detection and suppression equipment. For the victims it was far too late.
The NTSB report placed responsibility for the accident on three parties:
- SabreTech, for improperly packaging and storing hazardous materials,
- ValuJet, for not supervising SabreTech, and
- the FAA, for not mandating smoke detection and fire suppression systems in cargo holds.
ValuJet was grounded by the FAA on June 16, 1996. It was allowed to resume flying again on September 30, but never recovered from the crash. In 1997, the company merged with AirTran Airways. Although ValuJet was the nominal survivor, the ValuJet name was so tarnished by this time that it was scrapped in favor of the AirTran name. In 2006, AirTran did not make any major announcements on the crash's 10th anniversary out of respect for the victims' families.
Many families of the Flight 592 victims were outraged that ValuJet was not prosecuted, given the airline's poor safety record. ValuJet's accident rate was not only one of the highest in the low-fare sector, but 14 times higher than those of the major airlines. In the aftermath of the accident, an internal FAA memo surfaced questioning whether ValuJet should have been allowed to stay in the air. The victims' families also point to statements made by ValuJet officials immediately after the crash that appeared to indicate the company knew the generators were on the plane, and in fact had ordered them returned to Atlanta rather than properly disposed of in Miami.