NTSB Suspects Problems in Airbus 300 Series Airplanes

The controversy continues over the airworthiness of the Airbus 300 series airplane's vertical stabilizer and rudder design. With this concern specifically noted, the NTSB has issued Safety Recommendation A-10-119 and -120 and Reiteration of NTSB Safety Recommendation A-04-63.

While the NTSB brought up their findings in the November 12, 2001 crash of an Airbus A300-605R,1 N14053, operated as American Airlines flight 587, they also specified concerns over another incident... albeit one far less tragic. The NTSB specified that on January 10, 2008, about 0848 central standard time, an Airbus Industrie A319, Canadian registration C-GBHZ, operated as Air Canada flight 190, experienced an in-flight upset after encountering wake turbulence from a 747 while climbing from flight level (FL) 360 to FL370.5 The flight crew declared an emergency and diverted the flight to Calgary, where it landed uneventfully. Of the 5 crewmembers and 83 passengers on board, 2 crewmembers and 8 passengers sustained minor injuries, and 3 passengers sustained serious injuries. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the scheduled domestic passenger flight from Victoria International Airport, British Columbia, Canada, to Toronto Pearson International Airport, Ontario, Canada. The Transportation Safety Board of Canada investigated this accident; the NTSB and Bureau d’Enquêtes et d’Analyses provided accredited representatives and technical advisors to the investigation.

Data from the flight data recorder (FDR) indicate that, during the upset, the airplane experienced several roll and vertical load factor oscillations and lost about 1,000 feet of altitude. Although the autopilot was engaged during the start of the wake vortex encounter, after about 3 seconds, the autopilot was disengaged, and there was a series of large oscillatory inputs on the left side-stick controller.7 In addition, the FDR recorded a series of three to four alternating rudder pedal inputs (right pedal, then left pedal) over the next 15 seconds. During these inputs, the airplane continued to oscillate in roll, reaching a maximum roll of 55º. At the same time, the recorded acceleration was also oscillating, with peaks of -0.46 G to +0.49 G of lateral load factor and peaks of -0.76 G to +1.57 G of vertical load factor.

Because of the severity of the upset, following the emergency landing at Calgary, the airplane was grounded pending an inspection by Airbus engineers. During an extensive inspection, the vertical stabilizer was removed from the airplane and scanned ultrasonically to inspect for damage to the stabilizer’s composite components. No damage was found, and the stabilizer was reattached and the airplane returned to service.

Although no damage to the stabilizer was found, an analysis of the accident performed by Airbus indicated that the rear vertical stabilizer attachment fitting sustained loads 29 percent above its design limit load. Simulation work performed by Airbus revealed that these high loads were primarily the result of the flight crew’s series of alternating rudder pedal inputs and were not the result of the wake turbulence. Information and animations provided by Airbus showed that if the pilots had not made any control inputs after the wake encounter, the airplane would have righted itself with minimum altitude loss and g-loading.

Vertical Stab of AA587

Via these new documents, the National Transportation Safety Board recommends that the European Aviation Safety Agency:

Modify European Aviation Safety Agency Certification Specifications for Large Aeroplanes CS-25 to ensure safe handling qualities in the yaw axis throughout the flight envelope, including limits for rudder pedal sensitivity. (A-10-119)

After the yaw axis certification standard recommended in Safety Recommendation A-10-119 has been established, review the designs of existing airplanes to determine if they meet the standard. For existing airplane designs that do not meet the standard, the European Aviation Safety Agency (EASA) should determine if the airplanes would be adequately protected from the adverse effects of a potential aircraft-pilot coupling (APC) after rudder inputs at all airspeeds. If adequate protection does not exist, EASA should require modifications, as necessary, to provide the airplanes with increased protection from the adverse effects of a potential APC after rudder inputs at high airspeeds. (A-10-120)

Vertical Stab of AA587

In addition, the National Transportation Safety Board reiterates the following recommendation to the European Aviation Safety Agency:

Review the options for modifying the Airbus A300-600 and the Airbus A310 to provide increased protection from potentially hazardous rudder pedal inputs at high airspeeds and, on the basis of this review, require modifications to the A300-600 and A310 to provide increased protection from potentially hazardous rudder pedal inputs at high airspeeds. (A-04-63)

FMI: www.ntsb.gov/recs/letters/2010/A-10-119-120.pdf