When Air France flight 447 plunged into the Atlantic more than a month ago, I began to wonder again about the safety of these new airliners that have composite materials replacing metal for many key structural elements and are heavily reliant on computer-controlled flight and navigation systems. My mind went back to November 2001 and the Airbus that lost its tail on departure from JFK and crashed in Queens, so close to 9/11 that many initially thought it was a terrorist act. Turns out the pilots overcontrolled the aircraft in wake turbulence causing the rudder to snap off. Frankly, that was a first for me, and I am fairly sure for American who trained the pilots to react as they did.
The Airbus rudder is attached to the empennage by composite material. The more composite the manufacturer can use, the more weight that is saved. This is good because you can replace that weight with passengers and fuel. More efficient engines add to the plane’s capability to carry farther, faster, and more effectively; however, the issue is, at what cost to safety. Please, I am not saying nor implying that aircraft manufacturers deliberately step outside the safety envelop for the sake of greater rpms. I am wondering, however, if all that can be done to ensure maximum safety on these new aircraft is being recognized.
Each growth of a commercial airline type will have a higher proportion of composite material and an extensive array of electronic and computer schemes. The new Airbus 350 and the Boeing Dreamliner are nearly all-composite aircraft, the latter 80 percent by volume, by weight 50 percent. The problem facing us with Flight 447 is the absolute need to answer why and how it went down.
At this point anything suggested is speculative until the black boxes are recovered. This will probably not happen. So it becomes necessary to hypothesize. From what I have read, theories include: pilot error in flying into a severe thunderstorm (this is already being mentioned by Air France management indicating that other flights managed to change radar settings and were able to fly around the storm); the pitot tubes iced up depriving the crew of vital airspeed information; in reaction to the turbulence and unreliable airspeed information the crew over sped the aircraft causing it to break up; does lightning have a harmful effect on composite materials; and finally do composite materials degrade more easily and faster than aluminum.
The answers that I have researched seem viable. To pilot error, the crew was highly experienced and had flown this route many times prior. Re the pitot tubes, the Airbus uses three and the air data computer selects the reading from any two that agree. As none agreed on 447, it shifted control from fully automatic mode to alternate mode. The latter is about the same as the amount of computer control on the 777. The pilots then have a well-learned backup procedure to maintain airspeed and attitude control. Finally, as there were other flights that traversed this weather system at the same time, it is difficult to accept the aircraft had so many systems failures and suffered break-up in the air due to weather. As to lightning penetrating and damaging the composite materials, all aircraft composites are required to contain layers of metal foil connected to grounding points so as to short circuit and seep away episodic electric currents.
Finally we come to composite materials. Do composite materials degrade more quickly and simply than metal? The use of composite material is relatively new, within the last 20 to 25 years. Shock and stress can lead to failure by delamination of the bonded material. There have been instances where composite material was found to be delaminated by hydraulic fluid. Because of this a certified technician using visual techniques or acoustics must check the integrity of composite panels regularly. It requires uninterrupted application, excellent ambient light, and proper training.
How long does it take for composite material to break down? What is the normal service life? This can be better determined by breaking down the sources of intermittent and cyclic stress, such as aerodynamics, mechanics, thermal, electrical, etc. Here is the crux, it may be that for an equal amount of safety for composite structures they may need to be replaced more often than metal.
Aircraft technicians on the front line of the aircraft airworthiness will be the best verifiers of the integrity of these new composites. So it is essential that those charged with maintaining these aircraft receive the proper training and conditions in which to do this job.
Interestingly, as I write this, I see my esteemed friend John Goglia on television commenting on the Southwest 737 hole. As he states, incredulous as it may be, here is another example of the right preventive maintenance not getting done in sufficient time, thus exposing the flying public to unnecessary danger. John has always told it like it is. Good for him.
