On July 5 the French BEA (Bureau d’Enquetes et d’Analyses) released its much anticipated final report on Air France 447, the Airbus A330-200 that crashed in the South Atlantic on June 1, 2009. The nighttime accident, the result of a chain of events brought on by a lack of valid airspeed data after all three of the aircraft’s pitot tubes froze, killed all 228 people aboard when the aircraft plummeted from FL380 to the surface of the Atlantic, essentially out of control.
The BEA cited a number of concerns that could affect future aircraft designs. The A330’s angle-of-attack information, a crucial piece of data that might have allowed the pilots to understand more quickly the relationship of the aircraft’s wing to the air passing around it, was not available to the crew.
According to the BEA, 7.5 to 8.0 seconds elapsed between the sound of the first autopilot disconnect warning and the sound of the first stall warning in the A330. While the autopilot and autothrottle system disconnected, the flight director remained active and alternately displayed conflicting information to the pilots, most likely adding to a host of confusing messages.
The report also speaks to how that lack of angle-of-attack information, in conjunction with an Airbus design trait that silenced aural stall warnings when the speed decayed below 60 knots, might have confused the crew into believing the aircraft was still flying when in fact it was not. At one point in the final four minutes of the flight, the stall warning sounded continuously for 54 seconds.
The BEA also said that the pitot tubes installed aboard the accident aircraft “met requirements that were stricter than certification standards. The EASA had analyzed [before the accident] pitot-probe icing events; it had confirmed the severity of the [pitot] failure and decided not to make the probe change mandatory.”
The report calls into question some actions of the three pilots during the final four minutes of flight. In one section, the report says, “Although having identified and called out the loss of the airspeed indications, neither of the two copilots called [for] the ‘unreliable IAS [indicated airspeed] procedure.’” The captain was not on the flight deck at the onset of this event.
During the period when the stall warning did sound for 54 continuous seconds, neither of the pilots seemed to react verbally to the warnings. Because the captain had left the cockpit for a planned rest break, the BEA also noted that there was no formal CRM training at Air France for how two first officers should interact during an emergency. AIN Safety will report more about the BEA’s findings in future editions.