The pilots of EgyptAir Flight 990 deliberately pushed their plane into a sharp dive, but investigators so far see no evidence of fire, loss of pressure in the cabin or any other obvious reason for them to descend at all, according to data released yesterday by the National Transportation Safety Board.
The dive was so violent that unbelted passengers would have floated about the cabin.
There also is some preliminary indication that late in the dive, the two pilots may have been pushing and pulling hard in opposite directions on the controls. That analysis of the data by outside experts is not conclusive. If the pilots were struggling with the controls, there is no way yet to determine whether they were fighting with each other or with other passengers, or had panicked.
The new raw information from the aircraft's flight data recorder adds to the growing pile of evidence but does little to help investigators understand why the plane crashed early Oct. 31, killing all 217 people on board.
Safety board officials say it is becoming even more vital that they locate the Boeing 767's cockpit voice recorder, buried in the silt about 250 feet deep in the Atlantic Ocean, about 60 miles off the Massachusetts coast. Two unmanned submersibles, operating from Navy and civilian ships, have been probing along the dark ocean floor whenever weather allows. Rear Adm. William Sutton said the sea promises to be calm this weekend.
Safety Board Chairman Jim Hall, at a briefing in Newport, R.I., was careful to release only raw data with little or no interpretation. But hints in his statement, along with interpretation from aviation professionals and technical information provided by the Boeing Co. and Boeing manuals, paint a picture of a deliberate pilot-induced dive for no apparent reason followed by a number of pilot actions that are not used in normal flight.
The pilots appeared to be manipulating the plane's controls until the end of the recorder tape that has been read so far.
Investigators caution that it is too early in the probe to rule out any cause including the possibility the pilots were distracted or confused by some mechanical defect that did not show up on the recorder.
Hall said work remains to be done with the data recorder, including restoration of data on the last five seconds of water-damaged tape. The safety board's policy is to release data as soon as it becomes available, day by day.
Hall said that about eight seconds before the plane began its descent, its autopilot disengaged.
Then, power to the engines was reduced. Throttle positions in the cockpit were "consistent with this power reduction," he said, apparently meaning the crew rather than some mechanical defect pulled power back. Elevators, flat panels that control up and down movements, then pushed the plane into a power dive.
"For the next 20 seconds," Hall said, the dive produced a zero-gravity situation in the plane. That means passengers, beverage carts and anything not tied down were weightless and would have floated about the cabin.
About halfway through this portion of the descent, the aircraft reached its maximum speed--86 percent of the speed of sound--and a "master warning" activated. Hall said a master warning would activate for one of five reasons: airplane overspeed, loss of cabin pressure, an autopilot disconnect not initiated by the pilots, fire, or improper takeoff and landing configurations.
It is significant that the master warning did not sound until that point, apparently from overspeed. This strongly indicates that a pilot turned off the autopilot, and that there was no loss of cabin pressure or fire that would lead the pilots to descend.
The plane reached a 40-degree nose-down pitch angle and a speed of mach .94 during this portion of the dive, Hall said. Engine oil pressure dropped, but Boeing said this would be normal in a zero-gravity situation.
Then the nose-down angle began to lessen, and the plane began to pull out of the dive, producing a downward force of 2.5 times the force of gravity. This is far more typical of the forces on fighter planes than on a commercial airliner, but is still within the capabilities of a Boeing 767.
At that point, Hall said, "the data show a split between the left and right elevator positions"--meaning that the devices that usually move in tandem moved in opposite directions.
A Boeing spokesman said that the aircraft's "design allows for split elevators," but would not comment further.
Boeing manuals detail a "column breakout" mechanism that gives way if pilots are pushing with at least 50 pounds of pressure in opposite directions on the control column, allowing the elevators to split a limited distance.
For some unexplained reason, the pilots then shut down both engines.
From radar data, investigators know that the plane then climbed from about 16,000 feet to about 24,000 feet and began a final plunge into the ocean. There is no flight data recorder data for this period because it and the plane's radar transponder stopped at 16,700 feet.
However, aviators say a plane moving that fast would climb naturally even if the pilots let go of the controls. Other sources familiar with radar data say it seems likely the plane stalled at 24,000 feet and fell out of control.
At any time that the safety board uncovered any criminal act in this crash, the FBI would automatically take over the investigation. However, there is no indication they are ready to do so.
While the FBI says it is continuing to mount an aggressive investigation into the cause of the crash, and following up on leads and tips, it has not uncovered information that crime was involved.
"Whether we are talking about the crew members or the passengers on any leg of the flight while in the United States, we have not so far developed any information that would lead us to believe that a criminal or terrorist act caused the plane to go down," said FBI spokesman Joseph A. Valiquette. "There are some anomalies and unanswered questions we are pursuing, but our position remains, as it has been, that we don't have any evidence of a crime."
Valiquette said one anomaly is that the passengers on the flight included dozens of Egyptian military officials, which he said "poses questions for investigators as to whether they could have been a special target of someone or transporting something they shouldn't have been transporting."
Sources said, however, that none of the military officers apparently carried any personal firearms aboard the plane.