The French civil aviation investigative authority, BEA, is asking EASA and Airbus to consider issuing an airworthiness directive that would force operators of hundreds of Airbus A320-family aircraft to replace legacy flight management guidance computer (FMGC) with an updated version.
For aircraft equipped with those systems, the auto throttle will incorrectly increase thrust when approach speeds are too high at 50-150 ft. above the ground, exacerbating the speed problem. Airbus learned of the problem in 1996 and introduced an improved FMGC in 2001, but airlines do not get the upgrade for free. To date, the change-out has been voluntary, and the BEA says the cost of the equipment, “borne partly by the operator”, may be an “obstacle” to its replacement.
The auto throttle issue gained renewed prominence in a July 2013 accident involving an Hermes Airlines A321 that overran the runway at Lyon Saint-Exupery in instrument weather conditions after a too-fast, unstable approach. The aircraft, operating as a charter for Air Mediterranee, touched down 5,300 ft. past the threshold and exited the runway 1,000 ft. past the opposite threshold, damaging the engines but injuring none of the 174 passengers or five crew members.
BEA, in a final report issued on the incident, named a number of causes for the accident, including the inexperience and training of the first officer (the pilot–flying), the failure of both crew members to abort the unstable approach while in the air or during the extended flare above the runway, the fatigue potential of a 15-hour workday and the pilots’ lack of understanding of the control sticks.
During the flare both pilots were attempting to control the aircraft, with the sum of the inputs sent to the elevator control, rather than the captain taking over.
An analysis of the autothrottle revealed that the improper increase in thrust just before landing could have added as much as 1,600 ft. to the distance the aircraft traveled before touching down. BEA says none of the previous operators of the aircraft—Swissair and Air Mediterranee—had opted for FMGC replacement, and Hermes has been unaware of the issues when it purchased the A321.
Following the Lyon overrun, Airbus issued a special bulletin to alert operators equipped with the legacy FMGC of the issue. In June 2014, Airbus told the BEA that “operators were studying the proposed replacement. This concerned about 250 aircraft, and 36 of the aircraft were modified.”
BEA is asking EASA and Airbus to “define a period following which it determines” the effectiveness of replacement actions taken by airlines. “Without feedback from operators on their decision to replace the FMGCs concerned, it could then consider issuing an airworthiness directive,” BEA said.