Flight control sensors replaced by southwestern type involved in an air crash with Lion Air

A Southwest spokesperson said the sensors had not failed and had been removed as a precautionary part of a troubleshooting process. She said that at least one had been repaired.

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

Since the accident, which killed 189 people, Boeing has warned airlines of the possibility of erroneous data from so-called "angle-of-attack" sensors. "We have not encountered a sensor problem or sensor leak as described in Boeing's newsletter," said the Southwest spokeswoman.

The incidents in the southwest did not result in an emergency and no one was injured. They caused what appears to be routine reports from mechanics checking for sensor problems. The documents show that one was written October 9 in Baltimore and the other on October 21 in Houston. They indicate that both sensors have been repaired.

Turn the knob

Pulling on the caliper will not prevent an anti-stall system from Boeing's new 737 MAX aircraft from preventing the fall if the sensor data is wrong. But turning off the system will do it.

In older Boeing 737 models,

a common practice of pulling on the control column prevents the cockpit systems from automatically pushing down the nose of the aircraft.

In the new Boeing 737 Max models,

removing the yoke will not work if its anti-stall system receives erroneous data from the sensors.

But an existing procedure works both:

pilots operate switches to prevent the aircraft from pushing the nose down.

Just eight days later, shortly after takeoff of the Jakarta Air Lion aircraft on October 29, an angle attack sensor of this flight sent incorrect data to the computers of the flight control, according to Indonesian and American investigators. Boeing and the Federal Aviation Administration then sent high priority safety warnings indicating that the problem was occurring. The resulting sequence of events is at the heart of international accident research.

Boeing and the FAA did not comment immediately on Southwest's maintenance documents. The spokeswoman for the southwestern United States said the carrier had replaced the two sensors in October on the same plane, and determined that they were not at the origin of the self-accelerating problem. An angle attack sensor has been replaced as part of routine maintenance for two other Southwest 737 MAX 8s, due to external damage, such as a collision of birds in flight.

Security experts point out that it is too early to provide definitive answers to the LIon Air tragedy, as many other factors are at stake. But so far, investigators have suspected problems with the lon Air tragedy. angle of attack that could have triggered a series of interactions between various flight control computers and the actions of the pilot leading to the crash.

As part of the US-Indonesia cooperation effort to unravel this complex interaction between automated systems and the Lion Air flight deck crew, investigators are now analyzing lessons learned over the years. about the potentially dire consequences of defective or unreliable attack angle indicators, according to US government and industry security experts.

Aircraft manufacturers and aviation safety regulators have long understood and mastered the risks associated with flight controls arising from such malfunctions on a number of other models, including A330 long-haul aircraft and A340 of Airbus SE, as well as on the widely used A320 and A321 narrow-body aircraft of the European manufacturer.

An important aspect of the Lion Air spacecraft is whether Boeing engineers and technical managers, under FAA supervision, fully integrated the lessons learned from the cockpit automation design for the 737 fleets. MAX 8 and MAX 9. There are currently more than 200 Max variants delivered worldwide, out of the 737 total in the thousands.

Certification processes for new models "take into account lessons learned from incidents and in-service events," an FAA spokesperson said in a written statement Thursday, but "special attention needs to be paid to comparisons because the aircraft systems are not all identical and meet the needs "differently from the sensor inputs. "

The spokesman confirmed that a look back at previous security events, including those caused by angle-of-attack issues – and how the agency responded to them – was "part of ongoing investigation ".

Since the October crash, Boeing officials have refused to discuss the details of the investigation or flight control system currently under consideration, saying they were helping and cooperating with investigators and regulators.

Without saying more, the Chicago aircraft manufacturer said the last 737 models were safe and that the pilots had already received adequate checklists to counter the risks associated with repeated and automated dive orders. Boeing also said that he "was taking all steps to fully understand all aspects" of the accident.

But at this point, much of the investigative work – led by the Indonesian authorities but assisted by US investigators, FAA regulators and Boeing himself – seems focused on the potential dangers associated with angle values. problematic attack.

The Lion Air pilots indicated that prior to the crash they were not aware of the new flight control system being investigated by the investigators.

"Not only me, but also others," said Yusni Maryan, chief pilot of the Indonesian airline, which is piloting the MAX jet aircraft. "[Boeing] did not specifically mention it. "

Boeing did not comment on the communications with specific airlines or their pilots.

Ben Otto contributed to this article.

Write to Andy Pasztor at [email protected] and Andrew Tangel at [email protected]