The pilots of AirAsia Bhd. Flight 8501 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, when the Airbus Group NV A320 plane climbed so abruptly that it lost lift and it began falling with warnings blaring in the cockpit, the people said. All 162 aboard 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 slow. After the initial attempts to address the alerts, the flight crew cut power to the entire system, which is comprised of two separate computers that serve as backups to each other, the people said.
While the information helps show how a normally functioning A320’s flight-protection system could have been bypassed, it doesn’t 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.
Flight 8501 climbed more than 5,000 feet (1,524 meters) in less than 30 seconds, rising above the altitude where it was authorized to fly, Ertata Lananggalih, an investigator with Indonesia’s National Transportation Safety Committee, said in Jakarta on Thursday.
The co-pilot, with 2,247 hours of flying experience, was at the controls and communicating with the ground while the captain, who had 20,537 hours, was monitoring, said Mardjono Siswosuwarno, the lead investigator of the crash. The account was the first description of the last moments of the plane.
