What happened
On 29 October 2018, a Boeing 737-8 (MAX), registered as PK-LQP, operated by PT. Lion Mentari Airlines, was involved in a fatal accident near Tanjung Karawang, West Java. During the flight, the aircraft experienced significant flight control issues that led to a loss of control. The accident resulted in fatalities and extensive damage to the aircraft.
The investigation
The KNKT examined the aircraft's flight recorders, including the Digital Flight Data Recorder (DFDR) and Cockpit Voice Recorder (CVR), alongside maintenance records and system analyses. The investigation focused on the functionality of the Air Data Inertly Reference System (ADIRS) and the Angle of Attack (AOA) sensors. Investigators scrutinized the maintenance history of the AOA sensors and the certification process of the Maneuvering Characteristics Augmentation System (MCAS). The inquiry also reviewed the training records of the flight crew and the organizational safety management systems of the operator and maintenance providers.
Findings
- The investigation established that a faulty Angle of Attack (AOA) sensor provided erroneous data to the aircraft's flight systems.
- The MCAS activated repeatedly due to the incorrect sensor input, causing the horizontal stabilizer to trim the aircraft nose-down.
- Maintenance records indicated that a previously removed AOA sensor had been replaced with a unit that possessed a known bias.
- There were significant issues regarding the adequacy of the certification process for the MCAS, specifically concerning the assumptions made about pilot reaction times and workload during a failure.
- The crew faced extreme workload and difficulty managing the automated system's uncommanded inputs during the critical phases of flight.