The aircraft, a DC-9-32, registered N904VJ, was the 496th DC-9 assembled at the Long Beach plant, was 27 years old at the time and had been previously flown by Delta Air Lines. Its first flight was April 18, 1969. Delivered to Delta on May 27, 1969, as N1281L, the airframe flew for Delta until the end of 1992, when it was retired and sold back to McDonnell Douglas. McDonnell Douglas then sold the plane to ValuJet in 1993. The aircraft was powered by two Pratt & Whitney JT8D-9A turbofan engines.
The aircraft had suffered a series of incidents in the two years before the crash, including two aborted takeoffs and eight emergency landings. Engine and pressurization errors were the primary issues in several of the incidents. In May 1995, the FAA issued a re-wiring directive for all DC-9 cockpits because the wire bundles in the switch panel could cause "fire and uncontrolled smoke throughout the cockpit as a result of chafing and shorting."
In the flight deck were two experienced pilots: Captain Candi Kubeck (35) and First Officer Richard Hazen (52). Captain Kubeck had accumulated 8,928 total flight hours throughout her career (including 2,116 hours on the DC-9) and First Officer Hazen had more than 11,800 total flight hours throughout his career, with 2,148 of them on the DC-9.
On the afternoon of May 11, 1996, Flight 592 pushed back from gate G2 in Miami after a delay of 1 hour and 4 minutes due to mechanical problems. There were 105 passengers, mainly from Florida and Georgia, 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 EDT, 10 minutes before the disaster, the DC-9 took off from runway 9L (now runway 8R) and began a normal climb.
The NTSB quickly determined that just before takeoff, 144 expired chemical oxygen generators, each slightly larger than the size of a tennis ball can, had been placed in the cargo compartment in five boxes marked COMAT (company material) by ValuJet's maintenance contractor, SabreTech, in violation of Federal Aviation Administration (FAA) regulations forbidding the transport of hazardous materials in passenger aircraft cargo holds. Failure to cover the generators' firing pins with the prescribed plastic caps made an accidental activation much more likely. The investigation revealed that rather than covering them, the cords attached to the firing pins were simply cut or duct-taped around the cans, and Scotch tape was also used to stick the ends down. SabreTech employees indicated on the cargo manifest that the "oxy canisters", which were loosely packed in the boxes that were each sealed with tape and bubble wrap, were "empty". ValuJet workers then loaded the boxes in the cargo hold in the mistaken belief that the devices that they contained were just empty canisters, thus being certified as supposedly "safe" to transport on a passenger aircraft, when in fact they were neither simple oxygen canisters, nor empty.
Chemical oxygen generators, when activated, produce oxygen for passengers if the plane suffers a decompression. However, they also produce a great quantity of heat due to the exothermic nature of the chemical reaction involved. Therefore, not only could the heat and generated oxygen start a fire, but the oxygen could also keep the fire burning. The fire was worsened by the presence of two main aircraft tires (one of them mounted on a main wheel) and a nose tire and wheel that were also included in the list of materials shipped as COMAT. Investigators determined that one of the oxygen generators was likely triggered when the plane experienced a slight jolt while taxiing. As the aircraft taxied and took off, the activated generator got hotter and hotter. Soon, the boxes and surrounding packaging ignited, starting a fire.
At 2:10 PM, the passengers started to smell smoke. At the same time, the pilots heard a loud bang in their headphones and noticed the plane was losing electrical power. The sag in electrical power and the bang were eventually determined to be the result of a tire in the cargo hold exploding. Seconds later, a flight attendant entered the cockpit and informed the flight crew of a fire in the passenger cabin. Passengers' shouts of "fire, fire, fire" were recorded on the cockpit voice recorder (CVR) when the cockpit door was opened. Though ValuJet's flight attendant training 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 not functional and informing the pilots of what was happening was difficult. The flight data recorder (FDR) indicated a progressive failure of the DC-9's electrical and flight control systems due to the spreading fire.
Kubeck and Hazen immediately asked air traffic control for a return to Miami due to the increasing 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, the exact time that it crashed. Eyewitnesses nearby watched as the plane banked sharply, rolled onto its side and nosedived into the Francis S. Taylor Wildlife Management Area in the Everglades, a few miles west of Miami, at a speed in excess of 507 miles per hour (816 km/h). Kubeck lost control of the plane less than 10 seconds before impact. Examination of debris suggested that the fire had burned through the floorboards in the cabin, resulting in structural failure and damage to cables underneath the instrument panels. The NTSB report on the accident stated, "the Safety Board cannot rule out the possibility that the flightcrew was incapacitated by smoke or heat in the cockpit during the last 7 seconds of the flight." Interruptions in the cockpit voice recorder occurred on two occasions, one as long as 1 minute 12 seconds. The aircraft hit the water at 2:13:42 PM EDT, about 10 minutes after takeoff. The impact site was on the western edge of Florida Water Conservation Area 3B, between two levees, in an area known as the L-67 Pocket.
None of the 110 passengers or crew on board survived the accident. Additionally, 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 mile (400 m) away from the crash scene, and the location of the crash itself was a deep-water swamp with a floor of solid limestone. The aircraft was destroyed on impact, with no large pieces of the fuselage remaining. Sawgrass, alligators, and risk of bacterial infection from cuts plagued searchers involved in the recovery effort.
According to the NTSB's report, two witnesses fishing nearby testified that "they saw a low-flying airplane in a steep right bank. According to these witnesses, as the right bank angle increased, the nose of the airplane dropped and continued downward. The airplane struck the ground in a nearly vertical attitude."
They reported seeing no external damage or any sign of fire or smoke other than the engine exhaust. A group of sightseers in a small private plane also witnessed the crash and provided a nearly identical account, stating that Flight 592 seemed to "disappear" after hitting the swamp and they could see nothing but scattered small debris, part of an engine, and a large pool of jet fuel near the crash site.