Mystery deepens on Lion Air crash after Boeing bulletin

Mystery deepens on Lion Air crash after Boeing bulletin

Mystery deepens on Lion Air crash after Boeing bulletin

The doomed Lion Air flight that crashed into the sea, killing 189 passengers last month, was found to have a malfunctioning air speed indicator for its last four flights - and, crucially, at the time of the crash, according to the head of Indonesia's National Transportation Safety Committee.

Experts say the angle of attack is a crucial parameter that helps the aircraft's systems understand whether its nose is too high relative to the current of air - a phenomenon that can throw the plane into an aerodynamic stall and make it fall.

Transport safety committee chairman Soerjanto Tjahjono said airspeed indicator malfunctions on the jet's last four flights, which were revealed by an analysis of the flight data recorder, were intertwined with the sensor issue.

The pilots union at Southwest Airlines Co., the biggest customer of the 737 Max, hasn't received any reports from its members of problems with faulty sensor readings, said Jon Weaks, president of the Southwest Airlines Pilots Association.

Pilots had reported a problem with one of the plane's instruments on a flight the day before the crash. In 2015, a wasp nest plugged the sensors on an Allegiant Air jet leaving St. Petersburg, Florida, forcing pilots to cut the flight short and land in Orlando.

Flight crews should follow a separate protocol to halt the plane's potentially risky action, according to the bulletin.

If this happens (un-commanded nose-down stabilizer trim) pilots can respond by pushing a switch on their control column (yoke), however, 737's computers will resume trying to dive as soon as the switch is released the new Boeing bulletin said. Of course, this is something they already overwhelmingly do, as we can see from the generally incredible recent safety record in global aviation, but clearly something went very wrong here that shouldn't have.

The airworthiness directive covers all 737-8 and 737-9 aircraft and is similar to a service bulletin issued by Boeing, after the manufacturer conducted an analysis in the wake of the fatal Lion Air crash on October 29.

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A winglet on the first Boeing 737 MAX airliner is pictured at the company's manufacturing plant in Renton, Washington, on December 8, 2015.

Over 200 737 Max jets are already in use in commercial aviation, Bloomberg added, though Boeing has orders for 4,500 more.

"Lion Air said the problem was fixed, is it true the problem was cleared?" asked Bambang Sukandar, whose son was on the flight.

The JT610 flight sped up as it suddenly lost altitude and then vanished from radar just minutes after take-off.

Body parts are still being recovered and searchers continue to hunt for the cockpit voice recorder. That last step appears to be what the Lion Air pilots didn't do, perhaps because they couldn't recall the procedure or they weren't fully aware of what precisely was happening.

Pilots should follow a separate procedure to halt the potentially risky action by the plane, the bulletin said.

Indonesia's National Search and Rescue Agency (Basarnas) chief Muhammad Syaugi told reporters yesterday morning: "We made a decision to extend our evacuation operation by another three days, specifically for Basarnas".

The Lion Air crash was the first involving the type of plane, which airlines introduced into service previous year.

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