A310 Tail With No Rudder
Many recent news reports about the crash of Air France 447 focus on air speed sensors; specifically, pitot tubes that were known to be troublesome. If the speed sensing system gave false readings, which seems likely, the plane’s computer might have set the engine throttles incorrectly, leading to either a stall or over-speed and subsequent loss of control. Considering that the fly-by-computer system also ‘knew’ the plane’s true groundspeed based on GPS data, iced-over pitot tubes by themselves would not explain the crash. Other factors such as turbulence, lightning, and hail have been mentioned as possible candidates.
One factor that contributed to the fatal Airbus crash in 2001 and a close call in 2005 was failure of the fiber reinforced plastic rudder. Glass or carbon reinforced plastic parts are referred to as composites. The reinforced plastic skins are laminated to honeycombed cores made of various types of materials, including metal, cardboard, and various synthetics. The key to achieving the high strength to weight ratios that make composites attractive to aircraft designers is solid and continuous bonding of the laminations in the skins and between the skins and the core.
It turns out that the current maintenance procedure, the tap test, used to verify the integrity of composite parts like stabilizers, flaps and rudders does not discover small gaps or defects in the bonding of laminations or skins to cores. A few small defects won’t necessarily cause the rudder to disintegrate as it did on the A310 in 2005 or to shear off as it did on the A300 crash in 2001. However, extreme stress can cause a small defect to grow instantly into a large one.
In the case of American Airlines’ A300 in 2001, the pilot’s over-controlling of the plane in a wake turbulence event caused the rudder to snap. On Air Transat’s A310 in 2005, a rapid change in altitude caused the air trapped inside a delaminated area of the rudder to expand, exploding the part. The A300 crashed, killing 265 people. The pilot of the A310 managed to fly the plane without a rudder and land without any fatalities.
As the pilot of a Katana DA20, if I make the mistake of taking off on a very hot day, knowing the plastic structure might be softened enough to fail, that’s my personal risk; one that could kill me and a single passenger. The airline industry is putting thousands of pilots and passengers lives at risk flying in planes with plastic parts. Both the upcoming Boeing 787 and the Airbus A350 will have plastic fuselages in addition to the various plastic components already in planes such as the A330 lost last week. Until the airline industry adopts maintenance inspection equipment and procedures that can detect small, concealed defects in composite assemblies, I’ll prefer to fly in planes made of metal.