Airlines unprepared for plastic planes

Tag : Fuse Carriers

AIRLINES are desperate. With jet fuel over $4 per gallon and stillclimbing, American, United and other major carriers are raisingfares, cutting flights, trimming fleets and laying off pilots.They're also ordering fuel-efficient Boeing 787s and AirbusA350XWBs — the new generation of plastic planes.
These new aircraft promise 20-percent-lower fuel consumption.Replacing heavier traditional aluminum alloys, 50 percent of theirskins, panels and load-bearing structures are comprised of lighter,stiffer carbon-fiber-reinforced-plastic (CFRP) composites. Then addthe latest, most fuel-efficient engine technology. Sounds good.
But beneath these advantages danger lurks — novel maintenancechallenges for which neither airlines nor the Federal AviationAdministration (FAA) are prepared. Overall, today's jetliners havereached a plateau of such aerodynamic and propulsive efficiencythat individual Boeing 737s or Airbus A300 aircraft often spend twoor three decades in service, as will new 787s and A350s.
Regarding fleet recapitalization, that was good news for theairlines' bottom line — and for their stockholders —until fuse pin metal fatigue allowed engines to fall off the wingsof 747s and corrosion caused the 1988 explosive decompression of anAloha 737 at 24,000 feet, as the top of the fuselage peeled backand sucked out a flight attendant.
Now, composite aircraft components have also begun to rain from thesky.
Shortly after takeoff in November 2001, the entire compositevertical fin of American Airlines' Flight 587 was ripped from theA300's fuselage; 265 people died. On March 6, 2005, an AirTransatAirbus A310 barely made it back to Cuba after its all-compositerudder disintegrated at 35,000 feet, possibly triggered by anuncommanded rudder pulse similar to one that may have doomed Flight587. This spring, a composite panel detached and tumbled to Earthfrom the trailing edge of the left wing of an older US Airways 757.
The list goes on. Stiff, rustproof composite components may belighter than metal alloy parts they replace, but they can then failcatastrophically. We have begun to learn, too, that they have aunique "fatigue plateau." After tens of thousands of flight andpressurization cycles, they can undergo hidden disbonding,delamination and ply separation from impacts or stresses fromin-flight upsets.
Moisture (humidity, hydraulic leaks) can intrude between plylayers, followed by expansion-contraction, freeze-thaw cyclesacross the 150-degree temperature range often encountered duringjetliners' multiple daily flights at altitudes up to 37,000 feet.
Following the American's 587 disaster (and as late as 2005), Airbusrecommended only external visual inspection or an inadequatesurface tap test for composite structures suspected of internalflaws. Trying other methods, American Airlines found additionalA300s with damaged fins. Yet only now, according to a leadingindustry publication, is the FAA-sponsored National Institute forAviation Research beginning to look "into fluid ingression damagemechanisms in composite sandwich structures."
It may have results by 2010 — when such research should havebegun 30 years ago. With the flying public facing increased dangeras composite structures age, questions need answering: Do airlinesstock the range of new nondestructive testing technologies neededto test panels and struts of differing thicknesses and compositecomposition? Are airline and outside technicians fully trained onthese machines?
When will the FAA and its European counterpart, EASA, mandatespecific inspection intervals for differing composite parts?Honeycomb sandwich panels and load-bearing CFRP attachment lugsrequire different time intervals. Flight 587 crashed, but in 1991and 1997, an Airbus A310 and an A300 had suffered upsets in whichtheir vertical stabilizers endured stresses higher than evenultimate load projections — and survived.
When will EASA and the FAA mandate that Airbus relabel its ultimateload projection as its in-service limit load — consequentlyrequiring that it strengthen by 50 percent all A300 fins in airlinefleets? What about upgraded testing standards for new Airbus A380and A350XWB designs?
Earlier Boeing 777s and Airbus A320s have many composite componentsbeginning to reach the fatigue plateau cited above. Moreover, withthe superjumbo A380 now in service and the largely composite 787and A350XWB both soon to fly, airlines and the FAA must quicklyaddress new and complex challenges of composite structure testingand maintenance — before disaster strikes again. Lee Gaillard's articles on aviation issues have appeared in Airwaysmagazine, as well as numerous newspapers and magazines. In 2005, heserved on a panel of consultants for "Airline Cracks," an ITV-West(Bristol, United Kingdom) telecast examining the safety ofcomposite structures in commercial jetliners.