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Indonesia NTSC issues preliminary report into Lion Air Flight 610 crash
Published on the 28th November 2018

Indonesia’s National Transportation Safety Committee has issued a preliminary report into the fatal crash of Lion Air flight 610, the 737 Max 8 aircraft, off the coast of Jakarta that killed all of the 189 people on board.

The report outlines the major factor that contributed to the accident, these centre on the new stall-prevention feature on the aircraft, the MCAS, that had activated shortly after take-off pushing down the aircraft’s nose to protect it against a perceived stall. The MCAS was found to have receive incorrect information from the angle-of-attack sensor. The report also finds issues with altitude and airspeed data during the flight even after the angle of attack (AOA) sensor was replaced and tested on the plane ahead of the preceding flight from Denpasar to Jakarta. 
 
A statement from Boeing highlights the section of the report that details the issues with the aircraft on its prior flight before Flight 610 following the replacement of the AOA sensor. “The engineer informed the pilot that the AOA sensor had been replaced and tested. The report does not include records as to the installation or calibration of the new sensor, nor does the report indicate whether the sensor was new or refurbished.  Although the report states that the pilot was satisfied by the information relayed by the engineer that the AOA sensor had been replaced and tested, on the subsequent flight the pilots again experienced problems with erroneous airspeed data, and also experienced automatic nose down trim.”
 
The pilots also reported a “flight control problem” with “all aircraft instruments indicating different altitudes” that forced them to ask flight control to confirm basic information including speed and altitude. Similar problems were reported the previous day on the same aircraft, but those pilots pulled up the nose and were able to switch off the automatic system. It is not known why this procedure wasn’t followed by the pilots on flight 610 since the cockpit recorder has not been found. 

The previous flight from Denpasar to Jakarta also experienced a “stick shaker activation” warning during the take-off rotation that remained active throughout the flight, which the report says rendered the aircraft un-airworthy condition with instructions to discontinue the flight and land immediately.  This procedure was not followed, however.
 
Boeing notes that the flight crew of the Oct. 28 flight turned off the stabilizer trim switches within minutes of experiencing the automatic nose down trim, and continued with manual trim through the end of the flight. The report further notes that the pilot performed three non-normal checklist procedures, including the runaway stabilizer non-normal checklist, which is a memory item prescribed by the 737 MAX Flight Crew Operations Manual, and reaffirmed in Boeing Flight Crew Operations Manual Bulletin TBC-19 and FAA Emergency Airworthiness Directive (AD) Number 2018-23-51, as the appropriate procedure to address unintended horizontal stabilizer movement, regardless of source. 
 
The report indicates that the remainder of the Oct. 28 flight was uneventful and that the flight continued to its destination. The report also states that, after landing, the pilot reported some of the experienced issues both on the aircraft maintenance log and to engineering. The report states that the pilot ran the runaway stabilizer non-normal check list, but it does not state that he communicated that fact in the maintenance documentation following that flight.
 
The following day, Oct. 29, shortly after taking off, the pilots experienced issues with altitude and airspeed data that the pilots had previously experienced on the earlier flights, due to erroneous AOA data. Data from the flight data recorder summarized in the report also makes clear that, as on the previous flight, the airplane experienced automatic nose down trim. In response, the flight crew repeatedly commanded nose up trim. This sequence repeated for the remainder of the flight, during which the flight crew was able to maintain control of the airplane for approximately ten minutes. Unlike as is stated with respect to the prior flight, the report does not state whether the pilots performed the runaway stabilizer procedure or cut out the stabilizer trim switches.
 
Boeing adds that it appreciates the NTSC for its “ongoing efforts to investigate the causes of the accident”, stressing that it is “taking every measure to fully understand all aspects of this accident, working closely with the US National Transportation Safety Board as technical advisors to support the NTSC as the investigation continues”.




 
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