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- Contributing factors [are] define[d] as actions, omissions, events, conditions, or a combination thereof, which, if eliminated, avoided or absent, would have reduced the probability of the accident or incident occurring, or mitigated the severity of the consequences of the accident or incident. The presentation is based on chronological order and not to show the degree of contribution.
1. During the design and certification of the Boeing 737-8 , assumptions were made about flight-crew response to malfunctions that, even though consistent with current industry guidelines, turned out to be incorrect.
2. Based on the incorrect assumptions about flight-crew 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-flight crew 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 development. As a result, it did not appear during flight with the miscalibrated AoA sensor, could not be documented by the flight crew, and was therefore not available to help maintenance identify the miscalibrated AoA sensor.
6. The replacement AoA sensor that was installed on the accident aircraft had been miscalibrated during an earlier repair. This miscalibration was not detected during the repair.
7. The investigation could not determine that the installation test of the AoA sensor was performed properly. The miscalibration 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 performance in manual handling, NNC execution, and flight-crew communication, leading to ineffective CRM application and workload management. These performances had previously been identified during training and reappeared during the accident flight. (en)
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