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Swissair Plane's Flight Recorder Contained Incorrect Information

By Al Baker and Sylvia Adcock
HALIFAX, Nova Scotia

The sophisticated avionics computers on Swissair Flight 111 apparently began generating faulty information to the plane's flight data recorder about five minutes before the recorder cut off and radar contact with the jumbo jet was lost.

Investigators declined to say how much of the data was faulty as they continued analyzing the reams of data from the black box aboard the MD-11 that crashed off Nova Scotia Sept. 2, killing all 229 aboard. But it has become apparent that during the last five minutes of the recording, the plane's computers were going haywire, possibly the result of an electrical problem or a fire.

"A progressive number of parameters exhibit anomolies in the final minutes of the flight recording," said Vic Gerden, chief investigator for the Transportation Safety Board of Canada. "These anomolies were determined to be fault codes generated by avionics systems on the aircraft." Investigators are looking into whether electrical sources to the plane's circuitry were burning and causing the computers to behave erratically, sources said. The plane has three electrical power sources, one from each engine.

The digital flight data recorder is one of the newer models and records 100 kinds of data, called parameters, on the plane's flight, including the position of various wing flaps, altitude and speed, and the function of flight control systems. The flight data recorder gets its information through a device in the electronics bay beneath the cockpit, which receives information from various parts of the plane.

The recorder's data are still being analyzed. Investigators are working backwards through 25 hours of data, also looking for problems on previous flights of the 7-year-old MD-11. Investigators in Switzerland are also poring over Swissair maintenance records.

Investigators haven't determined if the data will reveal what was going on with systems on the plane, but they express optimism that further analysis will yield clues.

Gerden said the faulty codes recorded are "a result of not having the normal signal, the normal parameter." A digital device, the recorder spews out information in sequences of 1s and 0s, but in many cases "that parameter is not getting the 1s and 0s the way it normally would," Gerden said.

The recorder compares the digital information it is receiving against a standard and if it doesn't match the standard, there is a discrepancy, Gerden said.

Investigative sources said investigators are interested in how the plane's computerized systems might fail, and the effect of a fire in the electronics bay. They also plan to look into whether the pilots had enough valid information from the computers.

John Thom, a spokesman for Boeing's former McDonnell Douglas division that built the plane, said the computer systems on the plane have backups. And even if the plane lost all its electronic functions, he said, the plane could still fly with hydraulics that don't depend on electrical power, and a battery back-up provides selected flight information to pilots.

Investigators believe the plane hit the water at 22 seconds past 9:31 p.m., based on seismographic information from the Geological Survey of Canada in Nova Scotia. Investigators also said the transponder, which emits a radar signal to air traffic controllers, failed about five minutes earlier, at four seconds past 9:26 p.m.