If the expectation is that the composite tail fin may be torn off when that happens, then perhaps composites should not be used in that structure. Although aluminum vertical stabilizers may be heavier and accordingly provide less fuel economy, the fact is that there is no history of metal tail fins being torn from fuselages in commercial passenger aircraft in the past half century. This is true even though there has been a history of rudder problems, which necessarily caused the same stress on metal stabilizers as was caused to the composite tail of AA587.
While the crash of Air France Flight 447 is still under investigation, a variety of likely suspects, including lightning, severe thunderstorm, and clogged speed sensors are being advanced as possible causes. However, passenger airplanes have been flying through storms for the past 50 years and there is no history of metal vertical stabilizers being torn off.
In fact, the National Oceanic and Atmospheric Administration makes a practice of flying through the most severe hurricanes to collect forecast data using ordinary Gulfsteam and Orion turboprop aircraft. There is no history of any of them being blown apart.
Critical structures on aircraft, particularly those intended to carry passengers, cannot be constructed of materials that fail to anticipate that they will be exposed to extreme stress at some point during their lifetime. It is true that, ultimately, all materials can be made to fail, why should passenger’s lives be included in the equation or the experiment to determine the breaking point?
Should the Use of Composite Materials Be Prohibited in Critical Structures in Commercial Passenger Aircraft? The use of composite materials in commercial aircraft is for one reason only – to save operating costs. The bottom line in this discussion is not how much money can be saved by composites. The true bottom line is the physical fact that composites fracture when they reach their limit, while metal usually bends before breaking.
Boeing and Airbus are the only two viable commercial manufacturing companies designing and delivering passenger aircraft, and they are competing in every market and with every product line. They are in a race to develop the least heavy aircraft to carry the greatest weight the greatest distance for the least amount of fuel possible.
If the Federal Aviation Administration and the National Transportation Safety Board should decide that, until such time as the composite structural design and manufacturing technology becomes sufficiently mature for all applications, composite materials could be prohibited for a common set of structures, including those most critical to flight operations.
That way, the playing field will be equal, and competition will still favor innovation in all other areas.
Should Commercial Passenger Aircraft Using Composite Materials in Critical Structures Be Regularly Inspected by Technology That Reaches Below the Surface to Identify Hidden Defects? The experience of the Federal Express rudder (see above) illustrates completely why ultrasound and other technologically advanced devices that can look below the surface are essential to the prevention of catastrophic crashes.
The rudder was taken out of service because of visible damage, and upon ultrasound inspection was found to have internal disbonding damage that could spread further during flight. Fortunately, we will never know if or when the rudder would have failed, or if its failure would have brought down the aircraft.
The current European Aviation Safety Agency ordered testing on Airbus composite rudders only applies to the A300/310 series, with only about 20 wide-body A330 and A340 planes included in the order.
The order does not include any of the almost 4,000 A320 series aircraft or the remaining A330, A340 or the new A380 aircraft. Nor does it include the composite vertical stabilizers, or any composite couplers used to connect these structures.
Consideration should also be given to including Boeing aircraft, such as the 777 that operates with a composite tail fin, in the inspection order.
Other than for the time and expense of conducting the test, it is far more likely that opposition from manufacturers and operators will be based on the fear that internal defects will be found and that replacement could cost up to a million dollars per plane. What value can be placed upon a baby’s life, or the life of any passenger?
Should All Aircraft Manufactured with Composite Materials in Critical Structures Be Grounded Until They Can Be Inspected For Hidden Defects? The most deadly crash in U.S. aviation history occurred on May 25, 1979 when an American Airlines DC10 crashed on takeoff from Chicago’s O’Hare Airport, as a wing pylon failed and an engine fell off. All 273 people aboard were killed.
The entire DC10 fleet was immediately grounded until it could be determined that the pylon bolts were at fault.