An Indonesia AirAsia Airbus A320-200 at Singapore Changi International Airport. Source: Flickr
The Indonesia AirAsia crash off the Indonesian coast last year was a result of a technical fault and a failed attempt by the aircrew to address it, not bad weather, investigators said.
The Airbus A320-200 crashed into the Java Sea 42 minutes after taking off from Surabaya on Java on December 28 en route to Singapore. All 162 people on board died.
Investigators said Flight 8501’s problems began when an alarm sounded in the cockpit on four separate occasions, warning that an important computer system helping to control the rudder was malfunctioning.
Using a toy airplane to demonstrate the erratic flight path, investigators said the crew lost control of the plane.
It appears a member of staff tried to reset the system by replacing a circuit breaker.
The procedure is used on the ground, like resetting a jammed computer, but it is not seen as safe in the air. Soerjanto Tjahjono, the head of Indonesia’s National Transportation Safety Committee, announced in Jakarta that the reset disengaged the plane’s autopilot and auto-thrust systems, and the pilots failed to keep the plane under control after that.
“The circuit breaker was pulled out and then pushed in again,” he announced. “It caused some electrical distraction.”
Soerjanto said there was no indication who had reset the circuit breaker.
Investigators said the weather played no part in the crash despite the fact it was flying in heavy storm clouds when the pilots lost control.
The report was critical of the failure of the plane’s rudder travel limiter system, which restricts rudder movement to a safe range when the aircraft is flying at high speed and high altitude. The investigators blamed a cracked solder joint on a circuit board “which led to a loss of electrical continuity”.
Investigators said the maintenance records showed that the rudder limiter system on-board had problems on 23 occasions last year.
“At the time, it was considered minor damage,” said Nurcahyo Utomo, a retired Indonesian pilot and one of the investigators. “It was not a concern at the time.”
“[The pilot] said, ‘Pull down, pull down.’ But when you pull down [the gear controls] the plane goes up. To make the plane go down you need to push, so this order was confusing.”
The report said after the circuit breaker was reinserted, the aircraft rolled to the left before levelling out. It was flying at an altitude of 32,000 feet, then steeply ascended by 5,000 feet before stalling. It then rolled hard to the left again and fell out of control, nose first at 20,000 feet per minute.
The national safety committee has issued recommendations to AirAsia, Airbus and the aviation authorities in Indonesia, the United States and Europe regarding the crash, including that commercial pilots should undergo flight simulator training to handle a recreation of the situation.