NTSB report on AA 587 spreads blame
While the NTSB determined that “unnecessary and too aggressive” rudder inputs by the first officer broke the vertical stabilizer off American Airlines Flight 587, there was plenty of blame to spread among the airline, U.S. and French aviation regulators and Airbus Industrie, builder of the A300-605R that crashed into the community of Belle Harbor, N.Y., on Nov. 12, 2001.
AA 587 had just taken off from John F. Kennedy International Airport bound for the Dominican Republic when it crashed in a residential area near the Rockaway Beach area of Queens, killing all 260 people on board and five people on the ground.
The A300’s vertical stabilizer and rudder separated in flight and were found in Jamaica Bay, about one mile north of the main wreckage site. The two engines, which also separated from the aircraft seconds before it hit the ground, were found several blocks north and east of the main wreckage.
The NTSB said the vertical stabilizer was torn off in flight as a result of aerodynamic loads that were created by the first officer’s unnecessary and excessive rudder pedal inputs after the aircraft encountered wake turbulence from a Japan Air Lines Boeing 747-400 that had taken off minutes before it. Investigators said the A300 would have passed through the wake turbulence successfully if the pilots had done nothing with the rudder.
But the Safety Board found that the first officer, who was the pilot flying, inappropriately manipulated the rudder back and forth several times after the A300 encountered the wake vortex of the JAL 747 for the second time. The aerodynamic loads placed on the vertical stabilizer due to the sideslip that resulted from the rudder movements were beyond the ultimate design strength of the vertical stabilizer.
Because the crash came just two months after 9/11, there were fears initially that AA 587 had fallen victim to another terrorist attack. But the NTSB found no such evidence, nor did any law enforcement agencies provide evidence that the accident might have stemmed from criminal conduct. The Board said that witnesses who reported seeing the airplane on fire were most likely seeing misting fuel released from broken fuel lines, a fire from the initial release of fuel or the effects of engine compressor surges.
And the Board found that the composite material used in constructing the vertical stabilizer was not a factor in the accident because the tail failed well beyond its certified design limits.
The NTSB said that, although other pilots provided generally positive comments about the first officer’s abilities, two pilots noted incidents that indicated he had a tendency to overreact to wake-turbulence encounters. His use of the rudder was not an appropriate response to the turbulence, which in itself provided no danger to the stability of the aircraft, the Board found.
The NTSB said that American Airlines’ Advanced Aircraft Maneuvering Program (AAMP) contributed to the accident by providing an unrealistic and exaggerated view of the effects of wake turbulence on heavy transport-category aircraft. In addition, the Board found that because of its high sensitivity, the A300-600 rudder control system is susceptible to potentially hazardous rudder pedal inputs at higher speeds.
The Board emphasized that before the crash of Flight 587, American Airlines was not providing adequate training for pilots on what effect rudder pedal inputs have on the A300-600 at high airspeeds, and how the airplane’s rudder travel limiter system works.
The Safety Board’s airplane performance study showed that the high loads that eventually overstressed the vertical stabilizer were the result solely of the pilot’s rudder pedal inputs and were not associated with wake turbulence.
John O’Callaghan, head of the Board’s aircraft performance group, said the first officer’s four full alternating rudder inputs were “inappropriate” and put the A300 outside the normal flight regime when the vertical tail broke off.
In fact, had the first officer stopped making inputs at any time before the vertical stabilizer failed, according to the Board, the natural stability of the aircraft would have returned the sideslip angle to near zero degrees, and the accident would not have happened.
Robert Benzon, NTSB investigator-in-charge, said that American’s AAMP ground school encouraged pilots to use rudder during recovery from upsets and the airline’s simulator exercise re-creating excessive bank angle “could have provided negative training” to the first officer. He added that the A300-600 rudder control system is susceptible to “potentially hazardous” rudder pedal inputs at higher airspeeds.
The A300-600 rudder control system couples a rudder travel limiter system that increases in sensitivity with airspeed–which is characteristic of variable-stop designs–with the lightest pedal forces of all the transport-category aircraft the NTSB evaluated during the investigation of Flight 587.
The Safety Board said that new certification standards are needed to ensure that future airplane designs minimize the potential for aircraft-pilot coupling (APC) susceptibility and to better protect against high loads in the event of large rudder
inputs. APC, also known as pilot-induced oscillation, represents a disparity between the pilot’s intention and the airplane’s response.
To minimize the potential for APC events, the NTSB concluded, transport-category pilots would benefit from training about the role that alternating full control inputs can play in such events and training that emphasizes that alternating full rudder inputs are not necessary to control a transport-category airplane. Investigators said the rudder usage should be limited to crosswind landings and engine failures.
Although the NTSB determined that the probable cause of the crash “was the in-flight separation of the vertical stabilizer as a result of the loads beyond the ultimate design [load] that were created by the first officer’s unnecessary and excessive rudder pedal input,” the Board said that the A300-600 rudder system design and elements of American’s training were contributing factors.
Airbus and American Airlines have been at odds for some time, with the airline blaming the Airbus rudder design and the manufacturer pointing to American’s training syllabus. Some of the acrimony stems from a 1997 incident in which an American A300-605R stalled during a leveloff at 16,000 feet. After the airplane landed, damage was found to the rudder on that aircraft–Flight 903–and American accused Airbus of withholding information about its rudder system.
But the Board said there was no connection between Flight 903 and the rudder-design issues involved in Flight 587.
The NTSB determined that the probable cause of the Flight 903 upset was the flight crew’s failure to maintain adequate airspeed–which led to the inadvertent stall–and their subsequent failure to use proper stall recovery techniques.
The NTSB recommended that the FAA:
- Modify FAR Part 25 standards to include a certification standard that will ensure safe handling qualities in the yaw axis throughout the flight envelope, including limits for rudder pedal sensitivity. In addition, the agency should determine whether existing aircraft are protected from the adverse effects of a potential aircraft-pilot coupling after rudder inputs at all airspeeds, and require modification if necessary.
- Review options for modifying the A300-600 and the A310 to provide increased protection from potentially hazardous rudder pedal inputs at high airspeeds and, on the basis of this review, require modifications to provide increased protection.
- Develop guidance for transport-category pilots that stresses that multiple full-deflection, alternating flight control inputs should not be necessary to control a transport airplane and that such inputs might be indicative of an adverse APC event.