DIAGNOSTIC TOOLS of nondestructive evaluation are important in aircraft maintenance. Here an electromagnetic probe is used to look for flaws in metal parts; composites would require nonmagnetic probes. Image: JEFF CAPLAN NASA Langley Research Center
The November 12 crash of Flight 587 in New York City, in which the tail fin, or vertical stabilizer, of an Airbus A300 fell off, raised concerns about the increasing use of composites over metal. Composites consist of layers of carbon-fiber sheets impregnated with resin, making them lighter and stronger than the traditional aluminum. Preliminary crash reports from the National Transportation Safety Board indicate that composite layers on the Airbus had come apart, or delaminated, near the point where the stabilizer attaches to the aircraft body. When pilots attempted to maneuver with the tail's rudder in the wake turbulence from a preceding aircraft, the entire vertical stabilizer separated from the airplane, sending the A300 into a death spiral.
Aviation experts found the falling tail fin extremely strange. Unlike metal, composites don't "fatigue" with use--assuming no construction flaws, they remain as good as new over the years as long as the structure doesn't encounter forces greater than its design limit. The Airbus tail was made to withstand 50 percent more force than is typically encountered, although in February NTSB officials concluded that sudden back-and-forth movements of the rudder could damage the tail. Crash investigators now plan to use technologies for "nondestructive evaluation" to conduct a postmortem on the tail, in the hopes of determining whether the breakage stemmed from undetected, preexisting damage or whether composites contain some inherent flaw.
This article was originally published with the title Heads on Tails.