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result in aircraft following too closely behind larger aircraft.
2. Pilots do not have sufficient information to determine relative flight paths
and maintain adequate separation distances relative to wake vortices.
AA 587 took off from Runway 31L with the required two minutes of separation from
JAL 47. Upon departing, the Air Route Traffic Control Center (ARTCC) gave the
accident aircraft a turn to the WAVEY intersection. This vector placed the American
airplane inside the turn of the preceding 747, effectively creating a rendezvous turn. The
flight path of the two airplanes is depicted in Figure 3.1 (Official Docket Aircraft
Performance Report 47). The turn immediately reduced the separation between the two
aircraft, exposing AA 587 to a more powerful wake vortex than the departure separation
should have assured. Additionally, the prevailing winds blew the vortices from the 747
into the flight path of the A300. Both of these hazards occurred without the knowledge of
the 587 flight crew, inadvertently exposing them to dramatically- increased risk.
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Figure 3.1 Depicted Flight Path of AA 587 and JAL 47
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Safety Recommendation 3
Safety Recommendation 4
The NTSB should recommend that the FAA reexamine the validity of
current ATC wake turbulence separation standards. Focus of the
review should be on the standards for the wide range of “heavy”
airplanes currently in operation, and for larger aircraft, such as the
Airbus A380 coming in the near future. This examination should
include new technology and should study proposals for improving
controller training and understanding of wake vortices, including
variables such as relative wind, atmospheric stability, and ATC
vectoring.
The NTSB should recommend the FAA comply with open Safety
Recommendation A-94-056 which states, “Require manufacturers of
turbojet, transport category airplanes to determine, by flight test or
other suitable means, the characteristics of the airplanes’ wake
vortices during certification environment.”
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C. ADVERSE AIRCRAFT PILOT COUPLING
Aircraft Pilot Coupling (APC) is one of the most challenging flight characteristics known
to aerodynamicists and designers of Flight Control Systems (FCSs). It is an unwanted
design flaw affecting the aircraft attitude and motion(s) once disturbed from stable state
conditions. Beginning with an initiating event, these flight characteristics form a
continuous or “closed-loop” interaction between the aircraft and the pilot (National
Research Council 14). The phenomena of APC events have often been associated with
the introduction of new technologies, functionalities, or complexities such as the change
on the A300 rudder control system.
“APC events are collaborations between the pilot and the aircraft in that they occur only
when the pilot attempts to control what the aircraft does. For this reason, pilot error is
often listed as the cause of accidents and incidents that include an APC ev ent. However,
the [NRC] committee believes that the 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. In these situations, it is often possible, after the fact, to analyze
the event carefully and identify a sequence of actions the pilot could have taken to
overcome the aircraft design deficiencies and avoid the event. However, it is typically not
feasible for the pilot to identify and execute the required actions in real time” (161).
National Research Council
The National Research Council (NRC) describes an APC event as both oscillatory and
non-oscillatory divergences from the desired flight path. The pilot is involved (due to his
or her responsibility to respond to an uncommanded aircraft motion) by manipulation of
the flight controls to modify or negate input in a “closed- loop” fashion that determines
the flight path of the airplane. The NRC has previously established that the most severe
oscillatory APC events show flight control rate limiting. Rate limiting of the A300 flight
controls has been confirmed by the ground tests conducted by the NTSB Human
Performance and Systems Groups, and Dr. Hess. FAA AC 25-7A also addresses rate
limiting as a root cause for APC. The irony of an APC event is that releasing the controls,
a procedure taught to test pilots but contrary to line pilot training, is one of the most
effective means to counter this adverse condition. Releasing the flight controls is viewed
as so desperate by U.S. aircraft certification authorities that the need to “open the loop” in
this manner to maintain control of an aircraft is considered unsatisfactory. Simply stated,
　
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