Flight 592 departed Miami International Airport (MIA) on May 11, 1996 bound for Hartsfield Atlanta International Airport on its routine flight. It was a Sunday afternoon. The airplane was a 27-year-old McDonnell Douglas DC-9 aircraft operated by a discount carrier known at the time as Valujet. Flight 592 pushed back from gate G2 in Miami after a delay of 1 hour and 4 minutes due to mechanical problems. At 2:04 pm, the DC-9 took off from runway 9L and began a normal climb. At 2:10 p.m. the flight crew noted an electrical problem.

Seconds later, a flight attendant entered the cockpit and advised the flight crew of the fire. 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 may be present in the cabin, the intercom was disabled, and there was no other way to inform the pilots of what was happening. By this time, the plane’s interior was completely on fire.Flight 592 disappeared from radar at 2:14 p.m. and crashed in the Everglades, a few miles west of Miami.

What went wrong on Flight 592?The NTSB determined that the fire that downed Flight 592 began in a cargo compartment below the passenger cabin. The cargo compartment’s fire suppression created a no-air recycling environment, so a standard fire would have simply run out of air and burned itself out. 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 just duct 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 onboard in the mistaken belief that they were just canisters, and that they were empty, thus being certified as safe to transport in an aircraft cargo compartment. SabreTech employees indicated on the cargo manifest that the “canisters” were empty, when in fact they were not.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 produce the extra oxygen needed to keep the fire burning, made much worse by the presence of combustible aircraft wheels in the hold. NTSB investigators theorized that when the plane experienced a slight jolt while taxiing on the runway, an oxygen generator unintentionally activated, producing oxygen and heat.

Laboratory testing showed that canisters of the same type could heat nearby materials up to 500 °F (260 °C), enough to ignite a smoldering fire. The oxygen from the generators fed the resulting fire in the cargo hold. A pop and jolt heard on the cockpit voice recording and correlated with a brief and dramatic spike in the altimeter reading in the flight data recording were attributed to the sudden cabin pressure change caused by a semi-inflated aircraft wheel in the cargo hold exploding in the fire. (Two main tires and wheels and a nose tire and wheel were also included in the COMAT)

Fault

The NTSB report split blame for the crash among three parties:

•on SabreTech, for improperly preparing, packaging, indentifying and storing hazardous materials,

•on ValuJet, for not supervising SabreTech, and

•on the FAA, for not mandating smoke detection and fire suppression systems in cargo holds. (Case summary reprinted from NTSB Probable Cause Report)