Tests designed to reveal potentially catastrophic damage to aircraft can be dangerously ineffective.
In March 2005, passengers on board an Air Transat Airbus A310 flying from Varadero, Cuba, to Quebec City in Canada, had a nasty scare when a loud bang was followed by the plane rolling violently from side to side. It landed safely, but its 8.2-metre carbon-composite rudder had sheared off.
Last week, a by Canada鈥檚 Transportation Safety Board (TSB) concluded that a flaw in the rudder鈥檚 composite material was to blame. The composite is made of polymer resin strengthened by embedded carbon fibres. Under stress, the fibres can separate from the surrounding resin, creating a gap that weakens the material.
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Engineers test for gaps by tapping the surface and listening for a change of pitch, but the TSB says that pre-flight tests appeared to show nothing amiss with the A310鈥檚 rudder. When TSB investigators exposed damaged composites to air pressure changes similar to those caused by changing altitude during flights, they found that 鈥渢he areas of the damage almost doubled instantly鈥�. They conclude that the gap in the A310鈥檚 rudder was small enough to pass unnoticed in the tests but expanded in flight, causing the rudder to break up.
Boeing and Airbus, among others, use the tap test. The TSB hopes to inspire the use of more reliable tests.Boeing鈥檚 , scheduled for launch next year and , due in 2012, will both have fuselages made with composite material.
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