Swissair Computers Gave Out Faulty Data, Probers Say -- Investigation Of Fatal Crash Is Continuing
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 was faulty as they continued analyzing the data from the black box aboard the MD-11 that crashed off Nova Scotia Sept. 2, killing all 229 aboard.
The MD-11, like other late-model jet aircraft, has what aviators call a "glass cockpit" because the pilots' main focus is not gauges and dials but six computer screens on which information about the flight is displayed.
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.
Investigators are working backwards through 25 hours of data, also looking for problems on previous flights of the 7-year-old MD-11.
Vic Gerden, chief investigator for the Transportation Safety Board of Canada, said the faulty codes recorded are "a result of not having the normal signal, the normal parameter."
The recorder compares the digital information it is receiving against a standard and if it doesn't match the standard, there is a discrepancy, or fault code, Gerden said.
Sources said investigators are interested in how the plane's computerized systems might fail, and the effect of a fire in the electronics bay. John Thom, a spokesman for McDonnell Douglas, said the computer systems on the plane have backups. And even if the plane lost all of its electronic functions, he said, the plane could still fly with hydraulics that don't depend on electrical power, and a battery backup 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, which recorded a "peak event" at that time from the direction of Peggy's Cove. 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.
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