Composite Structures For Aircraft Not All They Are "Cracked Up" To Be
Recent NTSB safety recommendation concerning
A recent NTSB Safety Recommendation should be of great concern to aircraft manufacturers, airlines and their passengers. It concerns the “disbonding” of the composite rudders on some A300 Airbus airliners. It seems hydraulic fluid delaminates the bonding agent and allows the plies of composite material to separate. The danger is that strength of the composite structure is compromised, such that it is no longer useful as an aircraft structure and can result in a catastrophic separation in flight.
Everyone loves composites these days. Why? Because they are light, rigid, strong and increasingly easy to build. They are stronger than their steel and aluminum counterparts and are infinitely lighter. Aircraft manufacturers, ever mindful of the needs of their airline customers, especially fuel costs, are trying to make structures lighter so less power and less fuel will carry the same number of passengers less expensively. Also, since large composite panels can now be made efficiently, small aluminum panels can be substituted with huge sheets of composite structure, cutting manufacturing costs and the price of the finished aircraft.
The rush to larger and more complex structures, however, must be tempered with the very high risk of in flight break-up and a deadly crash caused by unforeseen structural failure or disbonding from the ever present leakage of hydraulic fluid from the myriad of hydraulically operated systems in aircraft, like landing gear, flaps and flight controls. These systems, operating at thousands of pounds per square inch pressure, leak frequently, and a leak where fluid accumulates and remains for long periods can be deadly.
What’s needed is a substitute for the highly toxic, corrosive and composite destroying hydraulic fluid now in use, one that will not disbond composite structures. If this step is not taken at once, we are asking for trouble — and it will be big trouble. New aircraft are increasingly large, carrying more and more people. An Airbus 380 carrying 800 people cannot shed a major structure with impunity. Already the wing failed a critical ultimate load test, and the less than optimal results were double talked away by engineers. No amount of double talk will adequately explain to hundreds of families the industry’s failure in the face of this knowledge to make absolutely certain that hydraulic fluid doesn’t cause an airplane to crash.
Hopefully, and I am not optimistic, the pressures of competition will cause aircraft manufacturers in both hemispheres to address this deadly problem. They have been forewarned!
- Arthur Alan Wolk