Why Lightning Didn't Destroy Air France Jet

A NASA researcher who did groundbreaking work in lightning protections for aircraft says that he'd be "astounded" if lightning caused the Air France crash over the Atlantic Ocean, because of the extensive shielding and other protections built into modern aircraft, including the A-330 that disappeared between Rio de Janeiro and Paris on Monday.

"They might have taken a hit, but it would have been part of a larger and more traumatic thing that must have happened to them," says Bruce Fisher, now chief engineer for NASA's Langley research services directorate.

Today, the Wall Street Journal reported that investigators were pursuing a different theory: that an air-speed sensor may have iced over and malfunctioned, causing the pilots to think that they were flying slower than they really were. If this caused them to increase speed excessively--and they then encountered very severe turbulence--it could have caused structural failure.

In the 1980s, in the wake of aircraft disasters caused by lightning, NASA's Langley Research Center assessed threats that lightning can pose to advanced fly-by-wire systems (in which wires convey pilot instructions to motors on control surfaces, replacing pneumatic and hydraulic systems) and electronic displays, as well as to composite structures. Fisher flew a research aircraft through severe storms and lightning-prone atmospheric conditions, deliberately drawing lightning strikes and gathering data that then went into modifications for aircraft design standards.

Today, among other changes that resulted from this work, electronics are shielded and grounded, and composite skins, where used, are layered with wires on their outside surfaces so that lightning will be conveyed from one end of the plane to another rather than punching a hole through the fuselage. Fisher says that based on what he has read, "the electrical faults were over 7 or 8 minutes, and it occurred 10 minutes after it had gone through the area of weather. It suggests it didn't look like a massive electrical failure; it would have been something that was a slow propagation of a problem. But we don't know."

The Journal reported that an air-speed sensor failure would be consistent with this chain of faults. The paper wrote, "The sequence of messages automatically sent by the plane to Air France's maintenance in the flight's last minutes--from autopilot disconnect through flight monitoring system failures, then flight-control failures and depressurization--has helped fuel the investigators' theory."