Part 3
It must be noted that, after the crash of AA 587 on Nov. 12, 2001, the NTSB focused immediately on pilot actions onboard the aircraft. Despite the fact that no pilot had ever been implicated in causing a crash by over-controlling the flight controls to the point of causing the flight controls—let alone the massive vertical fin-- to be damaged, in Safety Recommendation A-02-01 and -02 the NTSB issued a dire warning on pilot use of the rudder. Essentially re-defining foundational definitions of basic aviation, including the concept of Maneuvering Speed (the speed under which a pilot may exercise full control of any flight control surface without exceeding the structural integrity of the aircraft)—a foundation of pilot knowledge on aircraft limitations since the dawn of commercial aviation, the NTSB declared that successive rudder swings could cause loads on the aircraft that could indeed rip the entire tail off of the airframe. To remedy this problem, the NTSB dictated that pilots be given special “rudder training” on how to fly.
Specific areas of concern included composite inspection, uncommanded rudder and rudder design
The pilot letter went on to say:
Every pilot, regardless of what airplane they are flying now, or will be flying in the future, needs to be aware of these issues and how they affect continued safe operations. At the end of the day, we are the ones who must ensure that we are operating in the safest environment possible and are not taking unacceptable risks.
…and raised eight specific areas of concern:
We believe that the information developed in this presentation will lead to the following conclusions:
(1) That visual inspection techniques presently used to verify the integrity of composite materials are inadequate. That NDI (nondestructive inspection) technology must be developed and applied to all aircraft that utilize composite parts, both diagnostically and in preventive maintenance procedures. That all A300-600 aircraft be immediately subjected to a baseline NDI in order to ensure the structural integrity of composite materials.
(2) That the structural certification requirement for the rudder and vertical stabilizer for ALL commercial aircraft should be re-evaluated, especially when considering the properties of structures made of composites versus metal.
(3) That A300 flight control systems have had a disproportionate number of serious malfunctions/failures, resulting in uncommanded rudder movements. As a result, there are serious concerns about reliability of operation and the affect on safe operations.
(4) That the inherent qualities of composite materials and our present understanding of their properties may make them unsuitable for major load-bearing structures.
(5) That the A300 design philosophy in certain areas (e.g. -- rudder limiter and vertical stabilizer attachment) may need to be reviewed for appropriateness, when juxtaposed with certification requirements of the vertical stabilizer and rudder plus the properties and characteristics of composite materials.
(6) That pilot training has been seriously deficient in regards to what constitutes safe versus unsafe application of flight controls.
(7) That the inaccurate definition of maneuvering speed should be corrected in light of the current certification standards, and that the flying community should be made aware of the dangers of rudder reversals through detailed and specific training.
(8) That when considering the cumulative deficiencies of composite technology, certification standards, rudder design and flight control malfunctions; serious consideration should be given to grounding the A300-600 fleet until such time as the safety of the flying public can be assured.
Our letter went on to discuss each area of concern in detail. One portion, concerning the length of time that composites are used in commercial aviation, was discussed by industry experts:
Most experts agree that composites are stiff (non-ductile) when compared to metals and have differing thermal coefficients than metals at attachment points. Also, air and water are invariably entrained during the manufacturing process. As the aircraft operates over a wide range of external temperatures and pressure altitudes, these water and air deposits expand and contract, eventually causing delamination (fatigue) within the composite. These, plus other known and unknown factors affect composite material to one extent or another, ultimately reducing its utility. According to Dr. Debra Chung, Director of the Composites Research Lab at the University of New York at Buffalo, composites thought to have a useful life of 30 years may, in fact, only last 1/3 of that original estimate because they become brittle and lose elasticity. So an aircraft which is expected to operate for 30,000 cycles, may only last 10,000. Charles F. Marschner [1], a pioneer in the use of plastics in aircraft structures, reminds us that “the laws of physics and mechanics are immutable – today’s composites still have no ductility as do wrought metals.”