What happened
On the morning of the accident, a Boeing 737 MAX operated by Lion Air departed from runway 25L at Jakarta-Soekarno-Hatta Airport, destined for Pangkal Pinang. The flight was carrying 181 passengers and 8 crew members. Shortly after takeoff at 06:21 local time, the aircraft encountered significant technical difficulties. While the crew had received clearance to climb, the plane was unable to exceed an altitude of 5,375 feet, exhibiting unstable speed and altitude readings.
Following the onset of these issues, the pilot declared an emergency and attempted to return to the departure airport. During this return maneuver, while flying at 3,650 feet and a speed of 345 knots, the aircraft experienced a loss of control. The plane entered a steep dive and crashed into the Kerawang Sea approximately 12 minutes after its initial departure, roughly 63 km northeast of Jakarta. The impact caused the aircraft to disintegrate. There were 189 fatalities and no survivors were found.
Findings
Initial investigations into the wreckage and flight data suggested that the aircraft may have been subject to repeated automatic nose-down trim commands from the horizontal stabilizer. This behavior was linked to the flight control system receiving incorrect, high-value inputs from a single Angle of Attack (AOA) sensor. Such erroneous data can trigger the stick shaker and various cockpit alerts, including IAS, ALT, and AOA DISAGREE warnings.
These automated trim adjustments are part of the Maneuvering Characteristics Augmentation System (MCAS), a feature designed by Boeing to prevent stalls in the MAX series. Although Boeing had previously issued an Operations Manual Bulletin in November 2018 regarding erroneous AOA sensor inputs, and the FAA had issued an emergency Airworthiness Directive to revise procedures for runaway stabilizer trim, the system's logic contributed to the fatal descent.