Southwest Replaced Flight-Control Sensors of the Kind Implications in Lion Air Crash

A Southwest spokeswoman said the sensors did not fail and were removed as a precautionary measure as part of a troubleshooting process. She said that at least one was repaired.

Investigators have confirmed that the same type of sensor failed on the Lion Air plane, but they have not determined exactly what happened between the failure and the accident.

Since the accident, which killed 1[ads1]89 people, Boeing has warned airlines about the potential for incorrect data from what are called angle-of-attack sensors. "We have not experienced a sensor error or flight problem as described in Boeing's bulletin," said Southwest spokeswoman.

The southwest events did not result in emergencies, and no one was injured. They asked what seems to be routine reports by mechanics to check out the problems with the sensors. One was written October 9 in Baltimore and the other October 21 in Houston, the documents show and they indicate that both sensors were repaired.

Flip the Switch

Returning to the yard will not stop a stall prevention system in Boeing's new 737 MAX plans, pushing down your nose if it gets poor sensor data. But turning off the system will.

In Boeing's older 737 models,

a common practice to pull back on the control column (ok) will stop cockpit systems from pushing down the planet's nose.

In Boeing's new 737 Max models,

that retract the yard, it will not work if the stall prevention system receives incorrect data from sensors.

But an existing procedure works for both:

Pilots flip switches to keep the plane from pushing the nose down.

Just eight days later, shortly after the Lion Air jets set off from Jakarta on 29 October, an angular frequency sensor on that plane sent incorrect data to flight control computers, according to Indonesian and American investigators. Boeing and the Federal Aviation Administration later sent out high priority security warnings highlighting the problem. The resulting sequence of events is the core of the International Crash Probe.

Boeing and FAA did not immediately comment on the Southwest Maintenance Document. The Southwest spokesman said that the carrier replaced the two sensors in October on the same aircraft, and found that they were not the source of the automotive gas problem. Two other Southwest 737 MAX 8s had an angle-of-attack sensor replaced as part of routine maintenance due to external damage, such as a bird attack during flight.

Security experts stress that it's too early for definitive answers about LIon Air tragedy because a host of other factors were at stake. But so far, investigators who suspect attacking difficulties may have touched a change of interaction between different flight control computers and pilots that lead to the accident.

As part of the collaborative US-Indonesian effort to solve the complex interaction between automated systems and Lion Air cockpit crews, investigators now investigate over the years of potentially serious consequences of defective or unreliable attack indication indicators, according to US security experts from the United States .

Planners and aviation security regulators have long realized and handled flight control hazards due to such malfunctions on a variety of other models, including long range Airbus SE A330 and A340 aircraft, as well as standard A320 and A321 narrow beam from the A320 European manufacturer.

An important aspect of the Lion Air probe is to investigate whether Boeing engineers and technical managers are monitored by FAA full Y incorporating the previous lessons in the design of cockpit automation for the 737 MAX 8 and MAX 9 fleet. There are currently over 200 Max variants that have been delivered worldwide, of thousands of a total of 737.

New Model Certification Processes "include assessment of current experiences from events and events in operation," said a FAA spokesman in a written statement on Thursday but "it must be taken into account when comparisons are made as flight systems are not all the same and respond differently to sensor inputs."

The spokesman confirmed that a look back at previous security events, including those caused by attacking difficulties and how The agency reacted to them – is "part of the ongoing investigation."

Since October crash, Boeing officials have refused to discuss specifications of the probe or flight control system being under control saying that they help and cooperate with investigators and regulators .

Without preparation, the Chicago plane maker has said the latest 737 models are safe, and pilots have previously provided adequate checklists to counteract hazards in repeated and automated nes commands. Boeing has also said that it is "taking every effort to understand all aspects" of the crash.

However, at this point, many of the investigative work has been led by Indonesian authorities, but assisted by American crash researchers, FAA and Boeing regulators themselves – appearing focused on potential hazards caused by problematic attack angles.

Lion Air pilots have suggested that they were not informed of the new flight control system performed by investigators before the crash.

"Not only me but also others," said Yusni Maryan, senior director of the Indonesia airline flying the MAX jets.

Boeing has not commented on specific airlines or their pilots.

-Ben Otto contributed to this article.

Write to Andy Pasztor at andy.pasztor@wsj.com and Andrew Tangel at Andrew.Tangel@wsj.com