Not including losses attributable to terrorism, rebellion or military action, Airbuses have been involved in 23 fatal crashes causing the deaths of 2,584 passengers, crew members and people on the ground. In addition, there have been five nonfatal accidents causing 21 serious injuries.
While the overall number of accidents and fatalities are not disproportionate to the crash experience of Boeing aircraft, three of the Airbus crashes involved a separation of the composite vertical stabilizer (tail fin) from the fuselage. Five hundred, or one in five of the Airbus deaths, including 228 from Air France Flight 447, resulted from these three crashes.
In addition, Airbus composite stabilizers, rudders and couplers have also been involved in a number of other emergency in-flight incidents that did not lead to crashes, injuries or deaths.
There is now a question whether all Airbus aircraft equipped with composite stabilizers and rudders should be grounded until the cause of the crash of Flight 447 can be identified and it can be determined if the aircraft can be inspected, safely repaired, and returned to service.
Used in law, science and philosophy, a rule known as Occam’s Razor requires that the simplest of competing theories be preferred to the more complex, and/or that explanations of unknown phenomena be sought first in terms of known quantities.
We do not know if Air France Flight 447 was brought down by a lightning storm, a failure of speed sensors, rudder problems or pilot error. What we do know is that its plastic tail fin fell off and the plane fell almost seven miles into the ocean killing everyone aboard.
What are Composites?
The essential definition of a plastic is the capability of being molded or modeled. Thus, the word can be accurately used to describe the various processes by which "composite" materials are coated, laminated and shaped into the various structures used in the construction of an aircraft.
Basically, a composite "indicates the use of different materials that provide strengths, light weight, or other functional benefits when used in combination that they cannot provide when used separately. They usually consist of a fibre-reinforced resin matrix. The resin can be a vinyl ester, epoxy, or polyester, while the reinforcement might be any of a variety of fibres, ranging from glass through carbon, boron, and a number of proprietary types." [1]
There are both advantages and disadvantages to using plastic composites instead of metal. They "have lower density and greater strength and stiffness than aluminum, therefore a smaller lighter structure can carry the same load." [2]
Composite materials can be shaped and molded far easier than aluminum into compound curves for maximum drag reduction and it is easier to get smooth surfaces for laminar flow designs which allows for increased speeds. [3]
Among the risks of using plastic composites are: (a.) Strengths varies from batch to batch and it’s difficult to detect voids; (b.) lightning protection is very poor since the material does not conduct electricity; c.) materials degrade in the sun due to ultraviolet rays; (d.) delamination problems are caused by moisture; and (e.) composites tend to break without warning at failure loads, unlike aluminum which can bend and still survive and usually provide some warning prior to failure. [4]
If plastic composites "are bumped, beaten or excessively shaken, they can develop microscopic cracks that, if allowed to fester, can widen and critically weaken" the material. Delamination is another concern "in which heat, cold, humidity or manufacturing errors cause layers of the composite to separate." [5]
Use of Composites by Airbus
The first "composite" materials used in aircraft construction consisted of plastic-impregnated wood, such as that used by Howard Hughes in his famous "flying boat" in World War II. [6]
As experience was gained through the use of fiberglass, the aircraft industry began to occasionally use composites for nonstructural applications, such as baggage doors. By the Sixties, at about the time Airbus was being created, the aircraft industry was prepared to consider using plastic materials in more critical structures.
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