What Brought AirAsia Flight 8501 Down?

Indonesian investigators have determined what brought down the AirAsia passenger plane that crashed into the Java Sea nearly nearly a year ago, killing all 162 people on board.

Indonesia AirAsia Flight 8501 crashed as a result of technical failures and the crew’s response to them, according to a report published Tuesday by Indonesia’s National Transportation Safety Committee. Australia, France, Singapore, and Malaysia joined Indonesia in the months-long investigation.

Flight 8501 took off from Surabaya, Indonesia, on December 28, 2014, bound for Singapore. Just 42 minutes into the two-hour fight, the Airbus dropped off radar screens in Jakarta. Search crews located the wreckage in January, and recovered the plane’s black boxes, which contain flight data and audio from inside the cockpit.

According to the report, a system that controlled the movement of the aircraft’s rudder failed four times, sounding alarms that could be heard on the cockpit audio recording. Each time, the pilots reset the computer system that controls a range of airplane functions, including rudder movement, by turning it off and then on again. Operations resumed normally. The trouble began seconds later, when someone inside the cockpit attempted to reset the computer system again, this time by pulling out and then reinserting circuit breakers.

This reset led to an electrical interruption to the computer system, causing autopilot to disengage, according to the report. The aircraft ascended sharply by several thousand feet, and then stalled.

The lead pilot can be heard on the cockpit audio saying “level,” “pull down,” and “slowly” several times. The second pilot, a native of France, can be heard saying in French, “What is going wrong?”

The Airbus rolled to the left, and then began plummeting down at 20,000 feet per minute. No emergency message was transmitted by the crew before air-traffic controllers lost contact with the aircraft.

Investigators traced the failure of both the rudder and computer systems to a cracked solder joint inside circuit boards. The rudder system had experienced problems 23 times since January 2014, according to the airline’s maintenance records cited in the report.

Investigators did not cite human error as a contributing factor to the crash, but said “subsequent flight crew action leading to inability to control the aircraft … resulted in the aircraft departing from the normal flight envelope and entering prolonged stall condition that was beyond the capability of the flight crew to recover.”

The report said “the consequences of resetting [circuit breakers] in flight are not described in Airbus documents. It requires good understanding of the aircraft system to be aware of the consequences.”

Indonesia AirAsia Flight 8501 was flying through storm clouds at the time of the crash, but the report found that weather conditions did not affect the aircraft.

The plane was carrying 155 passengers and seven crew. All but seven of the victims were from Indonesia.

Indonesia AirAsia is a low-cost airline based in Tangerang. Between 2007 and 2010, the airline was banned from flying to the European Union due to safety reasons.