The Flight Augmentation Computers (FAC) on the A320 jet is made of two computers, a primary and a back-up. Their functions include controlling the rudder to help keep the aeroplane steady and detecting sudden changes in wind speed and direction. While an outage in the FAC could not have caused the crash, if they fail, the pilots would have been forced to rely on their manual flying skills under intense pressure.
Indonesian investigators today said that black box recordings show that the co-pilot of the plane, Frenchman Remi Plesel, was at the controls when it went down.
According to unnamed Reuters sources, the investigators of the crash, which occurred on 28 December 2014, are looking at the maintenance records of a "key part" of the FAC and are assessing how the pilots may have handled the plane if it had failed.
"There appears to be some issue with the FAC," a source told Reuters.
The investigators are also reportedly hoping to get more information from manufacturer Airbus and the Malaysian airline AirAsia.
Indonesian authorities have said that the jet, Flight QZ 8501 from Surabaya to Singapore, suddenly climbed from its cruising height and then stalled, before falling into the Java Sea in Indonesia. All 162 people on board perished.
In the months leading up to the crash, Indonesian magazine Tempo reported a series of maintenance problems with the computerised rudder system of the QZ 8501 aircraft.
Although rudder problems have not been identified as a cause of the crash in pictures of the wreckage, Reuters' sources claim that the investigation has extended to include the FAC computers after analysing some of the data from the black box voice and flight data recorders.
Furthermore, a glitch in the rudder system could be an explanation for why the jet did not automatically correct itself when it stalled.
However, the sources reiterated that a failure in the FAC computers cannot alone cause an aircraft to crash. If they fail, control of the aircraft is automatically handed back to the pilots to fly manually, albeit under highly stressful conditions.
In a statement to Reuters, Airbus said that the A320 aircraft "remains fully controllable if you lose the two FACs.
"The consequence of losing the two FACs is that the pilot has to fly manually like a conventional aircraft."
Following a design review, in October, airlines were given four years to upgrade the FACs on A320 aircraft at the next repair opportunity.
The Indonesian National Transport Safety Committee (NTSC) has submitted its preliminary report into the crash to the International Civil Aviation Organisation, but it will not be made public for another seven months.
Image credit: Airbus - AirAsia A320 aircraft