The pilot of AirAsia Flight 8501 had left his seat in the plane’s cabin to disconnect the plane’s Flight Augmentation Computer (FAC) when the aircraft lost control, two people familiar with the investigation told the Reuters news service.
That computer limits the extent to which the aircraft can be pushed to its operating limits but the AirAsia Airbus 320 can be flown without it.
Information about the FAC comes to light a month after the Dec. 28 crash, after investigators with Indonesia’s National Transportation Safety Commission (NTSC) found wreckage on the sea bottom and recovered the plane’s two flight recorders.
Flight 8501 crashed in bad weather on a routine flight from Surabaya, Indonesia, to Singapore.
Dozens of bodies have been recovered but most are believed to still be inside the plane’s fuselage on the sea bottom.
Flight 8501 plane had requested an altitude change to avoid a thunderstorm shortly before it disappeared from radar and was lost.
“The co-pilot pulled the plane up, and by the time the captain regained the controls it was too late,” a person familiar with the investigation told Reuters.
But why the pilot, Vriyanto, decided to disconnect the FAC after taking control of the plane from co-pilot Remy Plesel, and why the more-experienced flier was unable to pull the plane out of a dive after it stalled still is unknown.
“You can reset the FAC, but to cut all power to it is very unusual,” an A320 pilot who declined to be identified told Reuters.
“You don’t pull the circuit breaker unless it was an absolute emergency — I don’t know if there was one in this case, but it is very unusual,” the pilot said.
Information that has emerged from the investigation so far has focused on airplane maintenance and training, but officials say it is too early to make any conclusions and have not ruled out any possible causes, Reuters said.
Investigators were said to be focusing on FAC maintenance records and the pilots’ reactions to the problems.
Reuters said the decision to disconnect the FAC at the circuit breaker was made after the plane’s pilots tried, apparently unsuccessfully, to reset the device.
There is a FAC reset button on the Airbus 320’s pilot panel but the circuit breaker is behind where the co-piklot sits, requiring the pilot to rise in order to engage it, Reuters said.
AirAsia declined to comment on the latest revelations while the accident is under investigation.
But the head of the NTSC investigation, Mardjono Siswosuwarno, told reporters this week that it was too early in the probe to determine whether the accident was due to pilot error or mechanical problems.
Indonesia has not released its preliminary accident report.
The NTSC said Thursday that the jet was in sound condition and all crew members were properly certified.
