JAKARTA – A malfunctioning automatic throttle may have caused the pilots of a Sriwijaya Air jet to lose control, resulting in the Boeing 737-500's crash into the Java Sea last month, Indonesian investigators said Wednesday.
National Transportation Safety Committee investigators said they are still struggling to understand why the jet nosedived into the water minutes after taking off from Jakarta on Jan. 9, killing all 62 people on board.
The investigators issued a preliminary report that provided new details of the pilots’ struggle to fly the plane from almost as soon as it became airborne.
The lead investigator, Nurcahyo Utomo, said the left engine's throttle lever moved backward on its own while autopilot was engaged, reducing the power output of that engine before the jet plunged into the sea.
He said pilots of previous flights had reported problems with the automatic throttle system on the 26-year-old jet.
The pilots' last conversation with air traffic control was about 4 minutes after takeoff, when the crew responded an instruction to go up to 13,000 feet. The plane's flight data recorder showed the plane reached an altitude of 10,900 feet and then began declining, Utomo said.
While on autopilot, power to the left engine was reduced while the right engine's power remained steady. The pilot fought to bring the plane up, but it rolled onto its left side, Utomo said. A minute later the data recorder showed that the automatic throttle had been disengaged as the plane pitched down. The flight data recorder stopped recording a few seconds later.
“So far, we don’t know if the engine’s throttle was broken or not, but it’s an anomaly since the left throttle moved far back and the right did not,” Utomo said, adding that movements of an auto throttle are linked to 13 other components of the plane.