Jakarta: The National Transportation Safety Committee (KNKT) released their final report on the accident of Lion Air PQ-LQP aircraft on Friday, October 25, 2019.
The agency found that nine factors contributed to the crash of the Boeing 737 Max plane.
On October 29, 2018, the aircraft was being operated as a scheduled passenger flight from Soekarno-Hatta International Airport, Jakarta with intended destination of Depati Amir Airport, Pangkal Pinang, when the aircraft disappeared from radar after informing Air Traffic Controller that they had flight control, altitude and airspeed issues.
The aircraft impacted the water in Tanjung Karawang, West Java, all person on board perished and the aircraft destroyed.
According to KNKT chairman Soerjanto Tjahjono, on October 26 2018, the SPD (speed) and ALT (altimeter) flags on the Captain’s primary flight display first occurred on the flight from Tianjin, China to Manado, Indonesia.
Following reoccurrence of these problems, on October 28, 2018, the left angle of attack (AOA) sensor was replaced in Denpasar.
The installed left AOA sensor had a 21° bias which was undetected during the installation test in Denpasar.
"The erroneous AOA resulted in different indications during the flight from Denpasar to Jakarta, including IAS (indicated airspeed) DISAGREE, ALT (altitude) DISAGREE, FEEL DIFF PRESS (feel differential pressure) light, activations of Maneuvering Characteristics Augmentation System (MCAS) and left control column stick shaker which were active throughout the flight. The flight crew was able to stop the repetitive MCAS activation by switched the stabilizer trim to cut out," Soerjanto said.
On October 29, 2019, the aircraft was operated from Jakarta with intended destination of Depati Amir Airport, Pangkal Pinang. According to the DFDR and the CVR, the flight had same problems as previous flight from Denpasar to Jakarta.
"The flight crew started the IAS DISAGREE Non-Normal Checklist (NNC), but did not identify the runaway stabilizer. The multiple alerts, repetitive MCAS activations, and distractions related to numerous ATC communications contributed to the flight crew difficulties to control the aircraft," Soerjanto said.
The MCAS was a new feature introduced on the Boeing 737-8 (MAX) to enhance pitch characteristics with flaps up during manual flight in elevated angles of attack. The investigation considered that the design and certification of this feature was inadequate. The aircraft flight manual and flight crew training did not include information about MCAS.
"On March 10, 2019, similar accident occurred in Ethiopia involved a Boeing 737-8 (MAX) experiencing erroneous of AOA," Soerjanto said.
Here are nine factors that contributed to the crash:
1. During the design and certification of the Boeing 737-8 (MAX), assumptions made about pilot response to malfunctions which, even though consistent with current industry guidelines, turned out to be incorrect.
2. Based on the incorrect assumptions about pilot response and an incomplete review of associated multiple flight deck effects, MCAS's reliance on a single sensor was deemed appropriate and met all certification requirements.
3. MCAS was designed to rely on a single AOA sensor, making it vulnerable to erroneous input from that sensor.
4. The absence of guidance on MCAS or more detailed use of trim in the flight manuals and in pilot training, made it more difficult for flight crews to properly respond to uncommanded MCAS.
5. The AOA DISAGREE alert was not correctly enabled during Boeing 737-8 (MAX) development. As a result, it did not appear during flight with the mis-calibrated AOA sensor, could not be documented by the flight crew and was therefore not available to help maintenance identify the mis-calibrated AOA sensor.
6. The replacement AOA sensor that was installed on the accident aircraft had been mis-calibrated during an earlier repair. The mis-calibration was not detected during the repair.
7. The investigation could not determine that the installation test of AOA sensor was perform(ed) properly; however the mis-calibration was not detected.
8. Lack of documentation in the aircraft flight and maintenance log about the continuous stick shaker and use of the Runaway Stabilizer NNC meant that information was not available to the maintenance crew in Jakarta nor was it available to the accident crew, making it more difficult for each to take the appropriate actions.
9. The multiple alerts, repetitive MCAS activations and distractions related to numerous ATC communications were not able to be effectively managed. This was caused by the difficulty of the situation and deficiencies in manual handling, NNC execution and flight crew communication, leading to ineffective CRM application and workload management. These deficiencies had previously been identified during training and reappeared during the accident flight.