Tragic Crash of American Airlines Flight 587

During the flight, the airplane's engines were found detached and located several blocks north and east of the crash site. The impact and subsequent fire completely destroyed the aircraft, resulting in the loss of all 260 people on board as well as 5 individuals on the ground. Flight 587 followed regulations outlined in 14 Code of Federal Regulations (CFR) Part 121 and operated under an instrument flight rules flight plan. This tragic accident occurred under clear weather conditions. It is important to note that the involved airplane was a brand new delivery to American Airlines on July 12, 1988.

The Airbus A300 had accumulated 37,550 flight hours and 14,934 cycles at the time of the accident. The A300's history dates back to May 1969 when development began, and its first flight occurred in October 1972. The A300B2 and A300B4 models were introduced into service in May 1974 and June 1975 respectively. In December 1980, the development of the A300-600 series started as a derivative of the A300B2/B4, with its first flight happening in July 1983 and certification taking place in March 1984.

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Prior to the accident, there were a total of 242 A300-600 series airplanes being used globally.

The A300-605R is a variant of the A300-600 series aircraft. The engine type is indicated by the "5", and its fuel storage capacity in the horizontal stabilizer is denoted by the "R" (National Transportation Safety Board [NTSB], 2004, p. 14). Regarding First Officer Information, Stan Molin, aged 34, was employed by American Airlines in March 1991. He held an ATP certificate and an FAA first-class medical certificate dated October 18, 2001.

The certificate required him to wear corrective lenses when using its privileges.

The first officer received a type rating on the A300 in November 1998, having previously flown Shorts 360, Beechcraft 99, and DeHavilland DHC-6 airplanes in commuter and regional operations. Prior to his employment with American Airlines, he had accumulated 3,220 hours total flying time in commercial and general aviation. American Airlines records also showed that he had accumulated 4,403 hours total flying time, including 1,835 hours as an A300 second-in-command. The A300-600 vertical stabilizer and rudder were constructed using composite materials, which are mixtures of distinct materials unified into one combined material. In particular, carbon fiber is a type of graphite made up of long and thin sheets or ribbons that are used to reinforce materials like epoxy resins and other thermosetting materials.

We refer to these reinforced materials as composites because they consist of multiple components. Carbon fiber reinforced composites possess remarkable strength considering their lightweight nature. In fact, they often surpass the strength of steel while being significantly lighter. As a result, they can effectively replace metals in various applications such as airplane and space shuttle parts, tennis rackets, and golf clubs (Carbon Fiber, 2005, p. 1).

The fracture of the right rear main attachment lug was determined by NASA-Langley and Airbus analyses to be the most likely initial failure in the rudder's structural integrity.

The results show that the vertical stabilizer broke away from the fuselage due to excessive stress. This started with the fracture of the right rear lug while the vertical stabilizer was subjected to aerodynamic loads that were approximately double the approved limit load design envelope. Moreover, once the right rear main attachment lug broke, all the other attachment fittings would also break, even without any further increase in external loading (NTSB, 2004, p. 115). As for the Flight Control System, the A300B2/B4 model utilized a rudder control system that employed a Variable Lever Arm (VLA) to restrict rudder travel.

Most other transport category aircraft feature a similar design for the rudder-ratio changer. In the case of the VLA, the pilot's control over the rudder decreased as the aircraft's speed increased. The rudder pedals consistently moved the same distance, resulting in a proportionate change in the rudder's effectiveness based on speed. However, Airbus introduced a completely redesigned rudder system in 1988 for the new A300-600 model. This modification significantly altered both the function and handling characteristics of the aircraft. The new system incorporated a variable stop actuator (VSA), which is also present in the MD-80.

The VSA restricted the pilot's use of the rudder, reducing the distance the rudder pedals moved as the rudder movement decreased in relation to speed. However, this system had a flaw that did not provide the same level of protection as the design used in McDonnell aircraft. The MD-80, on the other hand, limits rudder travel and offers protection through a mechanism called rudder "blow down," which activates when the pilot demands more rudder travel than the structure can handle. Redundant system designs like this are commonly found in commercial aviation.

The Airbus Flight Crew Operations Manual (FCOM) does not change its language even after changing the A300 design. The rudder system is addressed similarly to other manufacturers. On aircraft equipped with a blow-down system, the force capability of the hydraulic actuators is limited to restrict the maximum rudder deflection output in response to changes in airspeed or aircraft configuration. Vortices form due to the pressure difference between the upper and lower surfaces of a lifting wing. The equalization of pressure at the wing tips causes air particles to move from the lower wing surface to the upper surface, balancing the pressure above and below the wing.

The wing experiences two movements of air: the downward flow caused by the wing's motion through the atmosphere, and the oncoming free-stream flow of air approaching the wing. These two movements combined result in an inclined inward flow of air on the upper wing surface and an inclined outward flow of air on the lower wing surface. This flow of air is strongest at the wing tips and decreases to zero at the mid-span point, where it becomes parallel to the free-stream direction. As the air leaves the trailing edge of the wing, there is a separation between the air from the upper surface and the lower surface. This separation creates helical paths, or vortices.

A continuous line of vortices forms behind the wing, with the strongest vortex at the tips gradually decreasing to zero at the middle. Shortly after, these vortices combine and form two cylindrical vortices known as "tip vortices." These tip vortices extend from the wing tips and have a tendency to sink and roll towards each other further downstream. Eventually, the tip vortices dissipate, but this transformation, affected by viscosity, can be a time-consuming process and pose a potential danger to other aircraft.

The tip vortices generate added downward flow (or downwash) behind the wing within its wingspan. From the perspective of an observer in the air, all the air within the vortex system moves downward (referred to as downwash), while the air outside the vortex system moves upward (known as upwash). An aircraft that flies perpendicular to the flight path of the airplane creating the vortex pattern will experience upwash, downwash, and then upwash again. The transition from downwash to upwash, known as the gradient, can be significant at the tip vortices and may result in drastic movements for the aircraft passing through them.

Flying into a tip vortex can cause an airplane to roll over. If the airplane's control surfaces are not strong enough to counteract this rolling tendency, the pilot may lose control or, in extreme cases, the plane could experience structural failure (Langley Research Center, 2005, Chapter 4). The takeoff and landing of newer jumbo jets worsen the issue of severe tip vortices. These maneuvers are performed at low speeds and require high lift coefficients to keep the plane in flight.

The atmospheric conditions were suitable for a slow vortex decay. The wake vortex from Japan Air Lines flight 47 would have been around 100 seconds old, and flight 587 would have encountered the wake vortex before it rapidly decayed. The predicted circulation of the wake vortex at the times of the encounters would have been between 63 and 80 percent of its initial strength. During the public hearing, the main author of the wake vortex investigation report testified that the wake encountered was not unusual. (NTSB, 2004, p. 57)

Aircraft pilot coupling, previously known as Pilot Involved Oscillation (PIO), occurs when the aircraft dynamics, including the flight control system (FCS), and the pilot dynamics combine to create an unstable pilot-vehicle system. APC events can occur if the pilot's behavioral mode is inappropriate for the task, and these events are typically attributed to pilot error.

According to the committee, the severe APC events that are blamed on pilot error are actually caused by adverse APC, which leads the pilot to take actions that make the event worse. These APC problems are often related to the introduction of new designs, technologies, functions, or complexities. Aircraft are continuously being equipped with new technologies like FBW and fly-by-light flight control systems.

Opportunities for APC are likely to persist or increase, according to the Aeronautics and Space Engineering Board Commission on Engineering and Technical Systems National Research Council (1997, p. 19). The pilots of Flight 587 were unaware that the rudder controls on the A300-600 become more sensitive as airspeed exceeds 165 knots, leading to adverse APC tendencies in the lateral axis. The APC event during Flight AA587 was triggered by an unexpectedly sensitive reaction of the rudder to a 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 found themselves caught in an adverse APC/pilot involved oscillation mode when trying to counter the effects of an input. Specifically, after making a control wheel input followed by a rudder input to achieve a desired aircraft response, the rudder control system's over-sensitivity caused the pilot to make additional corrective rudder inputs in a cyclic manner as they tried to stabilize the aircraft. The crash of Flight AA587 was caused by the rudder's unexpectedly sensitive response to the pilot's initial pedal input during a wake vortex encounter. The pilot became caught in an adverse APC/pilot involved oscillation mode as they tried to counter the effects of that input, due to the unique characteristics in the aircraft’s flight control system design.

The pilot experienced over-sensitivity in the rudder control system when attempting to achieve a desired aircraft response. This led to the pilot making additional corrective rudder inputs in a cyclic manner to stabilize the aircraft. However, due to the sensitivity of the rudder controls and the powerful nature of the hydraulically driven rudder actuators, these corrective inputs caused rupture loads to rapidly generate without the pilot's knowledge. The Advanced Airplane Maneuvering Program (AAMP) training introduced response time delays to roll inputs in the training simulator. During this training, flight crews encountered delayed responses and turned to using the rudder to provide the necessary roll response for recovery purposes.