The first warning of trouble aboard ValuJet Flight 592 came six minutes after takeoff, when the pilots learned of a fire in the passenger cabin, investigators said Monday after listening to the cockpit voice recorder for the first time.
Minutes later, the plane crashed into the Florida Everglades, killing all 110 passengers aboard. Investigators are still trying to determine what happened in the plane’s final moments on May 11.
“It appears that the cockpit door opened,” National Transportation Safety Board Vice Chairman Robert Francis said at a news conference. “There were verbal indications from the cockpit that there was fire in the passenger cabin.”
The tape indicates the pilots were told that passengers were having difficulty getting oxygen although Francis said “it remains to be determined” whether that was caused by problems with emergency oxygen masks or from smoke filling the cabin.
The voice recorder, recovered Sunday after two weeks of underwater searching, was in good condition although investigators said the tape was difficult to decipher because of background noise.
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The tape runs for 30 minutes, but Francis said it was possible there were gaps, just as there were in the plane’s data recorder, recovered earlier, which stopped 50 seconds before the flight ended.
The voice recording is being reviewed by a group that includes NTSB investigators and outside experts, including representatives from ValuJet and the aircraft’s maker, McDonnell Douglas. It could be days before investigators know if the information is helpful, Francis said.
“At this stage, we have not had the opportunity to do enough work on the tape to say how much help it’s going to be,” he said. “The tape itself is in good condition. The information on the tape is very, very difficult to decipher right now.”
One problem in understanding the tape is background noise in the cockpit, Francis said. Another problem could be damage done to the tape during the 15 days it was submerged in the Everglades.
“We were extremely fortunate that we came out with an intact piece of tape,” said Francis, who displayed the mangled metal case that held the recorder.
In the center of the case was a deep puncture, evidence of an immense collision between the recorder and something else as the plane hit the ground and disintegrated.
The penetration of the recorder case, which is meant to withstand the worst of crashes, underscored the speed at which the jet plummeted when it fell 7,500 feet.
Investigators still do not know the cause of the crash, but they are focusing on two areas: volatile oxygen generators, more than 100 of which were being carried in the cargo hold, and the plane’s electrical system.
NTSB officials hope to find electrical cables or circuit breakers, which would give them a better idea whether the source of the fire was the electrical system. Several pieces from oxygen generators have been found in one of several tires that were also being carried in the plane’s hold. Searchers have recovered pieces around the hold which show smoke or soot damage.
Oxygen generators are regular equipment aboard passenger aircraft and are used to provide backup oxygen when the plane decompresses. Investigators are trying to determine whether the generators carried in the plane’s hold were full.
If accidentally activated, the canisters can generate intense heat and possibly cause a fire. Wherever the fire started and whatever the cause, it quickly engulfed the passenger cabin.
On Sunday, investigators said that fire damage had been found on an aluminum frame of a passenger seat. It takes at least 500 degrees to melt the frame, raising the possibility of intense heat in the cabin prior to impact. Taped conversations from the airport control towers indicated there was smoke in the cockpit.
But Francis said that nothing had been recovered yet that suggested fire in the cockpit. A police diver found the elusive voice recorder Sunday just before the searching was to be suspended because of an approaching thunderstorm. The outer case of the recorder was damaged by the impact, but the tape was intact.
On Memorial Day, with the voice recorder found, there were fewer searchers at the crash scene. Investigators, though, are not finished scouring the site. Nearly 40 percent of the plane’s wreckage has been recovered.
A chicken-wire mockup of the front cargo area at a nearby airport continues to be reconstructed as parts are recovered.
Investigators plan to ignite oxygen generators inside the model to see how they affect the rest of the cargo hold and airplane, said Greg Feith, lead investigator for the safety board.
A 49-foot backhoe was supposed to begin dredging the impact crater over the weekend, but that has been delayed to at least Wednesday because of problems getting it in place.