Air France has just admitted that it cannot hold out hope any longer of re-establishing contact with flight AF447. By now, the company says, this Airbus A330-200 from Rio de Janeiro to Paris would have run out of fuel if it were still airborne.
At present, information is very sparse. According to the airline, the last report from the aircraft provided evidence of an electrical short circuit that occurred shortly after encountering turbulence, and possibly a lightning strike. Aircraft are designed to be able to survive lightning strikes. They have to be, because they occur often, usually causing minor damage but, very rarely, serious damage to electrical or control systems.
Modern aircraft are so reliable and have so many backups for every system that a single electrical fault, or even the loss of an entire circuit, would be easily dealt with if that were all that had occurred. If the fault has been correctly interpreted as a short-circuit, that raises the spectre of an electrically-caused fire, and fire is always serious in an aircraft. But at this point there is no access to evidence of that type.
An event like this is the kind the aviation world hoped it would not see again, because it involves a world class carrier flying the latest generation of airliner, and it occurred en route, not during take-off or landing in difficult weather. It's a chilling reminder that nothing is impossible, however unthinkable.
For anyone who doubts that a certain type of electrical fault could start a fire that could bring an aeroplane down, whether the fault was initiated by a lightning strike or something else (this example was something else), look at the Canadian Transportation Safety Board's report on the Swissair 111 Boeing MD-11 accident at Peggy's Cove, Halifax on 2 September 1998.