The pilots of AirAsia Flight QZ8501 cut power to a critical computer system that normally prevents planes from going out of control shortly before it plunged into the Java Sea, two people with knowledge of the investigation said.

The action appears to have helped trigger the events of Dec. 28 last year, when the Airbus Group A320 climbed so abruptly that it lost lift and it began falling with warnings blaring in the cockpit, the people said. All 162 on board were killed.

The pilots had been attempting to deal with alerts about the flight augmentation computers, which control the A320’s rudder and also automatically prevent it from going too slowly. After initial attempts to address the alerts, the flight crew cut power to the entire system, which is comprised of two separate computers that back each other up, the people said.

While the information helps show how an A320’s flight-protection system could have been bypassed, it does not explain why the pilots pulled the plane into a steep climb, the people said. Even with the computers shut off, the pilots should have been able to fly the plane manually, they said.

Airbus discourages pilots from cutting power to systems because electronics in the highly computerized aircraft are interconnected and turning off one component can affect others, Safety Operating Systems chief executive officer John Cox said in an interview.

“Particularly with an Airbus you don’t do that,” said Cox, a former A320 pilot.

what -AirAsia Flight QZ8501 cut power to a critical computer system that normally prevents planes from going out of control shortly before it plunged into the Java Sea

when-Dec. 28 last year

why-out power to a critical computer system that normally prevents planes 

who-AirAsia Flight QZ850

how-not given