The airplane’s engines also separated in flight and were found several blocks north and east of the main wreckage site. All 260 people aboard the airplane and 5 people on the ground were killed, and the airplane was destroyed by impact forces and a post-crash fire. Flight 587 was operating under the provisions of 14 Code of Federal Regulations (CFR) Part 121 on an instrument flight rules flight plan. Visual meteorological conditions prevailed at the time of the accident. The accident airplane was delivered new to American Airlines on July 12, 1988.
At the time of the accident, the airplane had accumulated 37,550 flight hours and 14,934 cycles. History of Airbus A300 The development of the A300 airplane began in May 1969, and the first flight of an A300 occurred in October 1972. The A300B2 and A300B4 models entered service in May 1974 and June 1975, respectively. The development of the A300-600 series airplane (a derivative of the A300B2/B4) began in December 1980, the first flight of an A300-600 occurred in July 1983, and the airplane was certificated in March 1984.
Before the accident, 242 A300-600 series airplanes were in service worldwide.
The A300-605R is one of several variants of the A300-600 series airplane. The “5” refers to the type of engine installed on the airplane and the “R” refers to the airplane’s ability to carry fuel in the horizontal stabilizer. (National Transportation Safety Board [NTSB], 2004, p. 14) First Officer Information The first officer, Stan Molin age 34, was hired by American Airlines in March 1991. He held an ATP certificate and an FAA first-class medical certificate dated October 18, 2001, with a limitation that required him to wear correcting lenses while exercising the privileges of the certificate.
The first officer received a type rating on the A300 in November 1998. According to American Airlines records, the first officer had flown Shorts 360, Beechcraft 99, and DeHavilland DHC-6 airplanes in commuter and regional operations under 14 CFR Parts 121 and 135. He had accumulated 3,220 hours total flying time in commercial and general aviation before his employment with American Airlines. American Airlines records also indicated that the first officer had accumulated 4,403 hours total flying time, 26 including 1,835 hours as an A300 second-in-command. (National Transportation Safety Board [NTSB], 2004, p. 1) Rudder Structure The A300-600 vertical stabilizer and rudder were constructed with composite materials, that is, mixtures that contain two or more distinct materials that are unified into one combined material. (NTSB, 2004, p. 15) Composite materials Carbon fiber is a form of graphite in which these sheets are long and thin. You might think of them as ribbons of graphite. Bunches of these ribbons like to pack together to form fibers, hence the name carbon fiber. These fibers aren’t used by themselves. Instead, they’re used to reinforce materials like epoxy resins and other thermosetting materials.
We call these reinforced materials composites because they have more than one component. Carbon fiber reinforced composites are very strong for their weight. They’re often stronger than steel, but a whole lot lighter. Because of this, they can be used to replace metals in many uses, from parts for airplanes and the space shuttle to tennis rackets and golf clubs. (“Carbon Fiber,” 2005, p. 1) Rudder Structural Analyses NASA-Langley’s and Airbus’ analyses determined that the fracture of the right rear main attachment lug was the most probable initial failure.
The analyses indicated that, The vertical stabilizer fractured from the fuselage in overstress, starting with the right rear lug while the vertical stabilizer was exposed to aerodynamic loads that were about twice the certified limit load design envelope and after the right rear main attachment lug fractured, all of the remaining attachment fittings would fracture with no increase in external loading. (NTSB, 2004, p. 115) Flight Control System The A300B2/B4 model used a rudder control system employing a Variable Lever Arm (VLA) to limit rudder travel.
A similar rudder-ratio changer design is also found in most other transport category aircraft. The VLA limited the amount of rudder available to the pilot as the airplane’s speed increased. The rudder pedals consistently moved the same physical distance, yielding a proportion of rudder relative to speed. In 1988, Airbus implemented a completely new rudder design, which significantly modified the function of the previous model and hence, the handling qualities of the new A300-600 airplane design. This new system used a variable stop actuator (VSA) which is also found in the MD-80.
The VSA also limited the amount of rudder available to the pilot. The difference in this system is that the distance which the rudder pedals moved also decreased as the rudder movement decreased in proportion to speed. A significant flaw in the design failed to offer the same kind of protection as in the McDonnell design. The MD-80 limits rudder travel and affords protection in the form of rudder “blow down” should an operator demand more rudder travel (with resultant excessive load) than the structure can withstand. These kinds of redundant system designs are common in commercial aviation.
The Airbus Flight Crew Operations Manual (FCOM) addresses the rudder system much like any other manufacturer and, in fact, did not change the language of the FCOM even after changing the A300 design from the VLA to the VSA system. (Allied Pilots Association, 2002, p. 9) Blow-Down System On an aircraft equipped with a hinge moment limiting (or “blow-down”) system, a device is employed to limit the force capability of the hydraulic actuators, and thereby aerodynamic forces limit the maximum rudder deflection output as airspeed or aircraft configuration changes. American Airlines, 2004, p. 11) Vortices and Wake Turbulence Vortices form because of the difference in pressure between the upper and lower surfaces of a wing that is operating at a positive lift. Since pressure is a continuous function, the pressures must become equal at the wing tips. The tendency is for particles of air to move from the lower wing surface around the wing tip to the upper surface (from the region of high pressure to the region of low pressure) so that the pressure becomes equal above and below the wing.
In addition, there exists the oncoming free-stream flow of air approaching the wing. If these two movements of air are combined, there is an inclined inward flow of air on the upper wing surface and an inclined outward flow of air on the lower wing surface. The flow is strongest at the wing tips and decreases to zero at the mid-span point as evidenced by the flow direction there being parallel to the free-stream direction. When the air leaves the trailing edge of the wing, the air from the upper surface is inclined to that from the lower surface, and helical paths, or vortices, result.
A whole line of vortices trails back from the wing, the vortex being strongest at the tips and decreasing rapidly to zero at mid-span. A short distance downstream, the vortices roll up and combine into two distinct cylindrical vortices that constitute the “tip vortices. ” The tip vortices trail back from the wing tips and they have a tendency to sink and roll toward each other downstream of the wing. Again, eventually the tip vortices dissipate, their energy being transformed by viscosity this change may take some time and may prove to be dangerous to other aircraft.
The tip vortices cause additional down flow (or downwash) behind the wing within the wingspan. For an observer fixed in the air, all the air within the vortex system is moving downward (called down wash) whereas all the air outside the vortex system is moving upward (called up wash). An aircraft flying perpendicular to the flight path of the airplane creating the vortex pattern will encounter up wash, downwash, and up wash in that order. The gradient, or change of downwash to up wash, can become very large at the tip vortices and cause extreme motions in the airplane flying through it.
An airplane flying into a tip vortex also has a large tendency to roll over. If the control surfaces of the airplane are not effective enough to counteract the airplane roll tendency, the pilot may lose control or, in a violent case, experience structural failure. (Langley Research Center, 2005, Chapter 4) The takeoff and landings of the new generation of jumbo jets compound the problems of severe tip vortices. During takeoff and landing, the speed of the airplane is low and the airplane is operating at high lift coefficients to maintain flight.
The atmospheric conditions aloft were favorable for a slow rate of vortex decay. The wake vortex from Japan Air Lines flight 47 would have had an age of about 100 seconds, and flight 587 would have encountered the wake vortex at a time before vortex linking and rapid vortex decay. The predicted circulation of the wake vortex at the times of the apparent encounters would have been between 63 and 80 percent of the vortex’s initial strength. In testimony at the public hearing, the main author of the wake vortex investigation report stated that, even though his ork supported a wake encounter, the wake was “nothing extraordinary. ”(NTSB, 2004, p. 57) Aircraft Pilot Coupling Aircraft pilot coupling (APC) was previously known as Pilot Involved Oscillation (PIO). An APC event is when the dynamics of the aircraft (including the flight control system [FCS]) and the dynamics of the pilot combine to produce an unstable pilot vehicle system. APC events can result if the pilot is operating with a behavioral mode that is inappropriate for the task at hand, and such events are properly ascribed to pilot error.
However, the committee believes that most severe APC events attributed to pilot error are the result of adverse APC that misleads the pilot into taking actions that contribute to the severity of the event. (Aeronautics and Space Engineering Board Commission on Engineering and Technical Systems National Research Council, 1997, p. 14) APC problems are often associated with the introduction of new designs, technologies, functions, or complexities. New technologies, such as FBW and fly-by-light flight control systems, are constantly being incorporated into aircraft.
As a result, opportunities for APC are likely to persist or even increase. (Aeronautics and Space Engineering Board Commission on Engineering and Technical Systems National Research Council, 1997, p. 19) Flight 587 APC Event What the pilots of Flight 587 did not know was that the rudder controls on the A300-600 become increasingly sensitive as airspeed increases above 165 knots; this unique sensitivity creates adverse APC propensities primarily in the lateral axis. Flight AA587’s APC event was triggered by an unexpectedly sensitive response of the rudder to an initial, single pedal input by the pilot during a wake vortex encounter.
Due to the unique characteristics in the aircraft’s flight control system design, the pilot became caught in an adverse APC/pilot involved oscillation mode as he attempted to counter the effects of that input. Specifically, after making a control wheel input followed by a rudder input intended to achieve a desired aircraft response, the over-sensitivity of the rudder control system induced the pilot to make additional, essentially cyclic, corrective rudder inputs as he attempted to stabilize the aircraft. American Airlines, 2004, p. 60) Probable Cause of Flight AA587 Crash Flight AA587 crash was triggered by an unexpectedly sensitive response of the rudder to an initial, single pedal input by the pilot during a wake vortex encounter. Due to the unique characteristics in the aircraft’s flight control system design, the pilot became caught in an adverse APC/pilot involved oscillation mode as he attempted to counter the effects of that input.
Specifically, after making a control wheel input followed by a rudder input intended to achieve a desired aircraft response, the over-sensitivity of the rudder control system induced the pilot to make additional, essentially cyclic, corrective rudder inputs as he attempted to stabilize the aircraft. Unknown to the pilot, because of the sensitivity of the rudder controls and the powerful nature of the hydraulically driven rudder actuators, these corrective inputs rapidly generated rupture loads. (American Airlines, 2004, p. 0) An aspect of Advanced Airplane Maneuvering Program (AAMP) training relative to upset recovery techniques introduced response time delays to roll inputs in the training simulator. Flight crews in training, when encountering the delayed responses during roll upsets, reverted to use of the rudder in order to provide the necessary roll response to initiate recovery.
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