Communiqués

TSB # A16/2005

(Gatineau, Quebec, August 11, 2005) - The Transportation Safety Board of Canada (TSB) today released its final report (A02O0406) into two similar incidents that occurred at Toronto/Lester B. Pearson International Airport on December 7, 2002. The investigation revealed that, in both occurrences, the aerodynamic shape of the aircraft's wing flaps was modified by ice, and that, in such icing conditions, the Airbus A321 normal, lateral flight control laws programmed into the elevator aileron computer provided higher roll efficiency, which resulted in a reduced stability, causing the aircraft to roll slightly from side to side.

In both occurrences, the pilots applied right and left control inputs to try to stop the rolling movement, but the magnitude of the oscillations increased. The combination of the weather conditions, modified aircraft aerodynamics, and pilot input resulted in airplane-pilot coupling (commonly referred to as pilot-induced oscillations).

The flight crews of both aircraft had been informed that moderate-to-severe icing conditions would be in effect at the time of landing. Both crews followed the appropriate instructions for flight in these icy conditions. However, the crews were not trained in recovering from airplane-pilot coupling oscillations; such training was not required by regulation.

Airbus responded to these incidents by providing operational recommendations for moderate-to-severe icing conditions. These recommendations include the use of a specific flap selection, minimizing the time flaps are extended during icing conditions, establishing minimum approach speeds when ice is suspected on aircraft parts not equipped with de-icing equipment, and increasing the landing distance.

Air Canada also issued an Aircraft Technical Bulletin stating that, as a precautionary measure, aircraft are not to be landed with full flaps extended and that prolonged flight in icing conditions with slats extended should be avoided.

The Airbus A321-211 was the aircraft used in both instances. The first incident occurred at approximately 4:00 p.m. when Air Canada Flight 457, with 123 passengers and 6 crew members on board, experienced roll oscillations as it was on final approach for landing. The second incident, which occurred approximately three hours later on the same day, involved Air Canada Flight 1130, carrying 165 passengers and 7 crew members. The pilots used different landing configurations and both succeeded in landing the aircraft safely without further incidents. There was no damage to either aircraft or injury to the crew or passengers.

The TSB is an independent agency that investigates marine, pipeline, railway and aviation transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.

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