The crew of EgyptAir Flight 990 appears to have taken the plane into a controlled but unusually steep descent that eventually led to its deadly crash into the Atlantic, according to information released yesterday by the National Transportation Safety Board.
Information culled from the flight data recorder paints a picture of a plane without problems that would directly affect its control, such as a major explosion, an engine shutdown, uncommanded movement of a control surface such as a rudder, or the movement of a control surface on one wing but not the other. The plane also made no abrupt movements that might indicate a struggle for cockpit controls.
What investigators have found so far heightens the need for recovering the plane's cockpit voice recorder because the flight data recorder doesn't provide information on what the crew was seeing or saying, or whether someone other than the pilots was in the cockpit and contributing to the plane's descent.
The data recorder--often called a "black box" even though it is orange--indicates that, at 33,000 feet, the crew for some reason felt a need to get the Boeing 767 down as rapidly as possible, effectively diving at a rate that few commercial pilots or passengers ever experience.
Despite its steep descent, the jet remained stable on the same compass heading, apparently under human control because the autopilot disconnected about eight seconds before the descent began.
What remains a mystery is what prompted the dive. Nothing in the recorder rules out some form of criminal act or some serious mechanical problem, such as depressurization of the cabin that would lead the crew to make the plane descend rapidly. Unfortunately for investigators, the recorder does not measure cabin pressure.
NTSB Chairman Jim Hall emphasized that all the data are preliminary and subject to revision. However, the information so far tends to confirm radar analysis that the plane went into a steep descent while making no significant turns either to the left or right until late in the crash sequence.
Hall said the flight data recorder ceased operating at the same time that the plane's transponder stopped delivering altitude data to air traffic controllers--at about 16,700 feet. That means that the recorder does not contain any information about the plane's sudden climb from about 16,000 feet to 24,000 feet before it made a final plunge into the Atlantic about 60 miles off the coast of Massachusetts early on Oct. 31. That information was gleaned from radar data supplied by a special Air Force group. All 217 people on board were killed.
Hall also specifically said that there is no evidence of deployment of the plane's thrust reversers, which provide supplemental braking on landing by reversing the airflow from the jet engines. There had been speculation about thrust reverser deployment because that was the cause of the first crash of a Boeing 767, in 1991.
Hall said the aircraft does not appear to have reached supersonic speed during its descent, even though the radar analysis had said that it was possible.
According to a preliminary time line released by Hall:
* The plane's autopilot disconnected about eight seconds before the initial descent. Sources close to the investigation said that, so far, they do not know whether it was turned off manually or automatically.
* Investigators have recovered data from the time the plane was as far down as 19,000 feet, but they are still trying to recover information from five to 10 additional seconds. Investigators said privately that water contaminated the last part of the tape, meaning that it must be read slowly through various recovery techniques rather than by computer.
Experts from the NTSB, the Federal Aviation Administration, the Egyptian government, the Boeing Co. and Pratt & Whitney have been organized to further analyze the recorder data. So far, only a small portion, covering the end of the flight, has been read.
Meanwhile, bad weather predicted for the search area may force the suspension of recovery efforts for a day or two. The focus of the efforts is on finding the cockpit voice recorder.