UPDATE / The pilots requested to return to base shortly before losing contact, said Yohanes Sirait, a spokesman for the country's air navigation authorities. "The (traffic) control allowed that, but then it lost contact," Sirait added.
UPDATE 2 / Crashed Lion Air flight JT610 had technical problem in previous flight, but had been resolved according to procedure - Indonesia Lion Air CEO
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Unconfirmed source - There’s an screenshot from the electronic tech log doing the rounds on the inter web. The crew operating the previous sector inbound to Jakarta made an entry that they experienced unreliable airspeed on Takeoff. They ran the NNC, deemed the CAPT instruments to be unreliable and handed over PF duties to the FO and continued for safe landing. The same aircraft was snagged for unreliable airspeed a day prior.
According to the official familiar with the bulletin, Boeing warns operators that the angle of attack issue can occur during only manual flight. The erroneous AOA input can pitch the aircraft’s stabilizer trim down for up to 10 seconds as a time. The plane maker is expected to caution pilots to use the electric stabilizer trim to reverse the downward stabilizer trim, but the nose-over can begin again five seconds after those switches are released.
The repeated uncommanded nose down action can be stopped by deactivating the stabilizer trim system, according to the official. Boeing warns that the stabilizer system can reach its full downward position if not counteracted by pilot trimming the aircraft and disconnecting the stabilizer trim system. The service bulletin is likely to be the prelude to a formal airworthiness directive from the Federal Aviation Administration. The bulletin is expected to be issued as early as Wednesday morning, according to Bloomberg News, which first reported the impending operator notification
According to factual information during the investigation, the KNKT identified findings as follows:
- On 28 October 2018, a Boeing 737-8 (MAX) aircraft registered PK-LQP was operated as a scheduled passenger flight from Denpasar to Jakarta. Prior to the flight, the Angle of Attack (AoA) sensor had been replaced and tested.
- The DFDR showed the stick shaker activated during the rotation and remained active throughout the flight. About 400 feet, the PIC noticed on the Primary Flight Display (PFD) that the IAS DISAGREE warning appeared.
- The PIC cross checked both PFDs with the standby instrument and determined that the left PFD had the problem. The flight was handled by the SIC.
- The PIC noticed that as soon the SIC stopped trim input, the aircraft was automatically trimming aircraft nose down (AND). After three automatic AND trim occurrences, the SIC commented that the control column was too heavy to hold back. The PIC moved the STAB TRIM switches to CUT OUT.
- The pilot performed three Non-Normal Checklists (NNCs) consisting of Airspeed Unreliable, ALT DISAGREE, and Runaway Stabilizer. None of the NNCs performed contained the instruction “Plan to land at the nearest suitable airport”.
- After parking in Jakarta, the PIC informed the engineer about the aircraft problem and entered IAS (Indicated Air Speed) and ALT (altitude) Disagree and FEEL DIFF PRESS (Feel Differential Pressure) light problem on the Aircraft Flight Maintenance Log (AFML).
- The PIC also reported the flight condition through the electronic reporting system of the company A-SHOR.
- The engineer performed flushing the left Pitot Air Data Module (ADM) and static ADM to rectify the IAS and ALT disagree followed by operation test on ground and found satisfied. The Feel Differential Pressure was rectified by performed cleaned electrical connector plug of elevator feel computer. The test on ground found the problem had been solved.
- At 2320 UTC, (29 October 2018, 0620 LT) the aircraft departed from Jakarta using runway 25L and intended destination Pangkal Pinang. The DFDR recorded a difference between left and right Angle of Attack (AoA) of about 20° and continued until the end of recording. During rotation the left control column stick shaker activated and continued for most of the flight.
- According to the weight and balance sheet, on board the aircraft were two pilots, five flight attendants and 181 passengers consisted of 178 adult, one child and two infants. The voyage report showed that the number of flight attendant on board was six flight attendants.
- During the flight the LNI610 SIC asked the TE controller to confirm the altitude of the aircraft and later also asked the speed as shown on the TE controller radar display. The LNI610 SIC reported experienced „flight control problem‟.
- After the flaps retracted, the FDR recorded automatic aircraft nose down (AND) trim active for 10 seconds followed by flight crew commanded aircraft nose up (ANU) trim. The flaps extended to 5 and the automatic AND trim stopped.
- At 23:25:18 UTC, the flaps retracted to 0 and several seconds later, the automatic AND trim and flight crew commanded ANU trim recorded began again and continued for the remainder of the flight.
- The LNI610 PIC advised the controller that the altitude of the aircraft could not be determined due to all aircraft instruments indicating different altitudes and requested to the controller to block altitude 3,000 feet above and below for traffic avoidance.
- The flight crew and the flight attendants held valid licenses and medical certificates and certified to operate B737.
- The Aircraft Flight Maintenance Log (AFML) recorded that since 26 October 2018 until the occurrence date, several problems occurred related to airspeed and altitude flag appeared on Captain (left) Primary Flight Display (PFD) three times, SPEED TRIM FAIL light illumination and MACH TRIM FAIL light illumination two times and IAS (Indicated Airspeed) and ALT (Altitude) Disagree shown on the flight Denpasar to Jakarta the day before the accident flight.