American Airlines Tries to Pin Blame on Design Defect

Air Safety Week, Oct 25, 2004

Airbus disagrees sharply over causeof Flight 587 crash

The outcome of a bitterly contested investigation into a crash that occurred 10 years ago should guide the probable cause of an investigation that is being resolved this week, according to American Airlines [AMR] officials.

The current case involves the Nov. 12, 2001, crash of American Flight 587, involving the tailfin separation on an Airbus A300-600, which led to the deaths of all 260 persons aboard and five persons on the ground (see ASW, Nov. 25, 2002). The National Transportation Safety Board (NTSB) completes its investigation with an Oct. 26 public hearing.

On the eve of that hearing, American officials point to the NTSB's findings in the Oct. 31, 1994, fatal crash at Roselawn, Ill., of an American Eagle ATR 72 twin-turboprop, which at the time was flying in icing conditions. In its investigation, the safety board concluded that a lack of information sharing about previous ATR 72 incidents in icing conditions led to "inadequate oversight" of the airplane's vulnerability to flight in icing conditions. The pilot's actions, or lack thereof, and continued flight on autopilot while a ridge of ice accreted on the wings, were not mentioned in the NTSB's probable cause, which instead lambasted French manufacturer Avions de Transport Regional (ATR) and French and U.S. regulatory authorities. Ultimately, the de-icing boots on the ATR 72 were modified to cover a substantially greater portion of the wing chord.

Similarly, American officials maintain that the A300-600 rudder system is unusually prone to back-and-forth rudder movements (known as "reversals") that can place excessively high loads on the tailfin because of the sensitivity of the rudder pedals and the susceptibility of the rudder controls to aircraft pilot coupling (APC). In APC, the flying pilot's rudder pedal inputs can become out-of-phase with the movement of the rudder, causing a rapid buildup of aerodynamic forces on the fin. In the Flight 587 case, a series of such rudder reversals led to nearly twice the force (about 1.93 of limit load) than the fin was designed to withstand. American officials see a similar outcome to the Roselawn crash a decade ago - a mandate for the manufacturer to modify the rudder control system to reduce its sensitivity and to increase its ability to prevent excessive loads on the fin.

Airbus officials flatly disagree. "An improperly trained pilot can break any airplane," said John Lauber, vice president of safety and technical affairs for Airbus North America. Lauber, like his counterparts at American Airlines, has been steeped in the details of the investigation from day one. He sees no need to modify the rudder control system on the A300-600. "We have 17 million hours of experience on that airplane [model], without one comment on the rudder pedal sensitivity," he said. To add to his point, Lauber said no comments concerning sensitivity were ever received from American, either, following a 1997 upset involving another one of its A300-600 aircraft (Flight 903).

Airbus officials maintain that the Flight 587 copilot, First Officer Sten Molin, applied a rapid series of full rudder pedal movements that precipitated loss of the tailfin. Had Molin ceased such actions, or had the airplane been flying on autopilot, the rudder reversals would not have occurred and the airplane would have safely flown through the wake vortex it was encountering from a preceding Japan Air Lines B747 as the two airplanes climbed on slightly different paths out of New York's John F. Kennedy International Airport.

The opposing views can be boiled down to American Airlines blaming inadequacies in the rudder control system, and Airbus pointing to training that predisposed American's pilots to make excessive and inappropriate use of an inherently safe rudder system. The present controversy recalls an earlier dispute over the safety of the B737 rudder control system, which came to the fore following the fatal 1994 crash of USAir Flight 427 from an uncommanded rudder reversal. Boeing alleged the pilots caused the crash; the pilots union retorted the system was at fault. Following the USAir accident, the B737 rudder power control system design was modified substantially, and many pilots feel the redesign vindicated their concerns about the safety of the rudder system (see ASW, Oct. 14, 2002).

With the ATR 72 and the B737 design changes as precedent, more particularly the latter since it involves a rudder control system, American officials envision - or hope for - a similar outcome regarding the A300-600 in the Flight 587 case. Airbus officials stoutly disagree. The stage is set for controversy, with the NTSB as arbiter in a high visibility case involving a foreign manufacturer of growing dominance with the full force of the European Union in the background, and the largest airline in the United States. In the Roselawn crash case, manufacturer ATR went so far as to directly challenge the NTSB's probable cause and, by implication, impugn the board's competence (see ASW, Oct., 25, 1999). A repeat of the charged controversy surrounding the ATR 72 could be in the offing. That saga remains a case study in the opposite of the vaunted term "harmonization," but rather a sharp disharmony of views, dragging on for years, with the NTSB eventually modifying its findings, albeit only slightly and more symbolically than substantively (see ASW, Sept. 30, 2002).