Data link messages indicating Air France Flight 447 encountered electrical and pressurization problems while operating in severe weather are among the scant clues available to investigators as they try to unravel what forces brought down the Airbus A330.

"This will not be an easy investigation," said Paul-Louis Arslanian, chief of the French accident investigation bureau (BEA), following the disappearance of the Airbus A330-200 off the northeast coast of Brazil during the night of May 31-June 1; 228 people were on board. The key to Flight 447's fate is in its flight data recorders - which lie in the 9,000-ft.-deep section of the Atlantic Ocean near the islands of St. Peter and St. Paul, about 205 mi. from the Fernando de Noronha archipelago (see map).

"Not only is the depth of the ocean an issue, but the rough terrain of the seabed in that region," notes Arslanian, who warns that the FDRs may not be recovered. Although both Honeywell-built devices have low-band beacons to attract attention, their range is limited, he notes. Still, he's optimistic that some probable-cause finding may be possible even without the recorders; the BEA plans to issue an initial report on the known facts by month's end.

Flight 447 departed Rio de Janeiro for Paris on the evening of May 31. About 4 hr. later, contact was lost: Its final messages indicate that the A330 had encountered turbulence and experienced both electrical and pressurization problems. It is highly unusual for accidents to occur during midcruise. The aircraft left radar coverage about 15 min. later, flying at 35,000 ft. and at 453 kt.

The BEA, assisted by Air France and Airbus representatives, is leading the probe. Last week, NTSB investigators, as well as representatives from engine manufacturer General Electric and Honeywell, maker of the A330's ADIRU (aircraft data inertial reference unit) joined their French counterparts to help determine the cause of the accident - the first fatal one involving an A330 in commercial service. (The only other fatal A330 crash occurred during flight trials in 1994 and was attributed to crew error.)

For now, there are no solid answers, just questions as to what caused the crash: Was there an inflight breakup, the result of the aircraft exceeding limit loads during severe turbulence? Did a lightning strike disable the highly redundant fly-by-wire flight control system? Was terrorism or sabotage involved?

The Brazilian military, which led the bulk of the wreckage search, discovered a fuel spill covering a 20-km. (12.4-mi.) area on the sea surface. Brazil's defense minister, Nelson Jobim, says that fuel indicates the aircraft exploded in flight, effectively ruling out terrorism. However, Arslanian says no conclusions can yet be drawn regarding whether the aircraft hit the ocean surface intact or broke up in flight.

The last communication from the aircraft consisted of a series of Acars (automated communications and reporting system) messages sent at 0214 Zulu (4:14 a.m. Paris time) and received by Air France. They came in over a 3-min. period but amount to only about 1 min. worth of data. The messages reported an electrical fault and pressurization problem. Arslanian says analysis of these transmissions has just begun.

The final data were sent just as the aircraft was exiting a cloud cluster but after it had already been subject to numerous updrafts over a 75-mi. stretch, says meteorologist Tim Vasquez of Garland, Tex.-based Weather Graphics.

Whatever factors are unearthed by investigators, weather - specifically turbulence - is likely to have been a causative or contributing factor in the crash.