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Angle-of-attack sensor replaced before 737 Max crash

Indonesia's National Transportation Safety Committee says an angle-of-attack sensor on the ill-fated Lion Air Boeing 737 Max 8 had been replaced a day before it crashed.

The committee says the sensor was replaced in Denpasar on 28 October, after pilots reported issues with the airspeed indicator.

Downloaded information from the recovered flight data recorder found that there was a "different [reading] on the angle-of-attack indicator" during a Denpasar-Jakarta flight on 28 October.

It adds that this was related to the faulty airspeed indication, which was first raised at a 5 November press conference by NTSC chief Soerjanto Tjahjono.

After the replacement, however, pilots that flew a Denpasar-Jakarta flight still found a 20° difference on the left-hand angle-of-attack sensor. During this flight, the pilots implemented "a number of procedures" to rectify the issues, and the jet subsequently landed in Jakarta safely.

The sensor that was removed in Denpasar has since been sent to NTSC offices in Jakarta, before being transferred to Boeing's headquarters in Chicago for further investigation. Investigators plan to reconstruct the flight and study the faults related to the sensor using Boeing's engineering simulator in Seattle.

Interviews have also been conducted with the pilots and cabin crews that operated PK-LQP prior to the crash, as well as technicians that maintained the jet in Denpasar, Jakarta, and Manado.

The NTSC adds that, based on issues faced by pilots on the Denpasar-Jakarta flight, it has recommended that Boeing notify 737 Max operators of the potential issues they could face with the sensors.

NTSC investigators and officials from Boeing and General Electric have identified some of the wreckage recovered from the seabed. These include the left CFM International Leap-1B engine, the right-hand main landing-gear, a tail section, aircraft sections 43, 44, 46 and 48, a cockpit oxygen bottle, a left-hand passenger door, and a wing-tip.

Boeing issued a operations manual bulletin on 6 November, directing operators to “existing flight crew procedures" to address circumstances involving erroneous angle-of-attack sensor information.

Indonesia's national search and rescue agency Basarnas has extended its mission to 10 November.

The Lion Air Max 8 was operating as flight JT610 from Jakarta's Soekarno-Hatta International airport to Pangkal Pinang when it crashed into the sea near the town of Karawang, claiming the lives of all 189 passengers and crew on board.

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