Published: Thu, November 08, 2018
Worldwide | By Isabel Fisher

Mystery deepens on Lion Air crash after Boeing bulletin

Mystery deepens on Lion Air crash after Boeing bulletin

Investigators probing the Lion Air crash off the coast of Indonesia, in which all 189 on board were killed, found that one of the "angle of attack" sensors on the Boeing 737 Max jet provided erroneous data.

The US aerospace giant has issued an "operations manual bulletin" to airlines using the aircraft, telling them how to deal with "erroneous input" from sensors.

Global plane manufacturer Boeing has issued airlines new guidelines warning of a potentially faulty sensor that may have caused the Lion Air Flight 601 crash tragedy.

Indonesian investigators said Wednesday that an AOA sensor on the jet was replaced the day before the doomed flight, on October 28, when a pilot flying the same aircraft on a different route, from Bali to Jakarta, reported problems with it.

The angle-of-attack sensor is meant to measure the angle between air flow and a reference line on the frame or wings so that they maintain lift.

Boeing is reportedly preparing a bulletin to all operators of the new 737 model warning that erroneous readings from a flight-monitoring system can cause the planes to aggressively dive, Bloomberg quoted a person familiar with the matter.

This affects almost 250 aircraft flown by U.S. airlines like Southwest, American and United, the FAA said.

The Boeing 737 Max has three such blade-shaped sensors.


Soerjanto Tjahjono, chairman of the National Transport Safety Committee, told media that that airspeed indicator malfunctions on the jet's last four flights, and that this issue was intertwined with the AOA sensor issue.

KNKT is planning to simulate a flight to assess the impact of sensor damage at Boeing's engineering simulator facility in Seattle. The Boeing bulletin only reminds operators of the plane to follow the procedure and doesn't require any physical fixes that could take the aircraft out of service.

And in this case the procedure for dealing with the problem it is what is called a "memory item" - pilot's commit them to memory. "We think this is an issue that is important because there are more than 200 Max planes around the world", Capt. Nurcahyo Utomo, the transportation safety committee's lead accident investigator, told the Times.

On the fatal flight, the plane hit the water at very high speed after it had been cleared to return to the airport minutes after becoming airborne.

Pilots are trained to disengage the angle-of-attack sensors from the plane's computers when they get false readings.

Lion Air JT610 plunged into the Java Sea less than half an hour after taking off from Jakarta on a flight to Pangkal Pinang city.

Search and rescue agency head Muhammad Syaugi tearfully apologised Monday as relatives' clamour for answers grew louder, with accusations that the pace of recovery is lagging.

Body parts are still being recovered and divers continue to hunt for the cockpit voice recorder.

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