Boeing Co. didn’t tell Southwest Airlines Co. and other carriers when they began flying its 737 MAX jets that a safety feature found on earlier models that warns pilots about malfunctioning sensors had been deactivated, according to government and industry officials.

Federal Aviation Administration safety inspectors and supervisors responsible for monitoring Southwest, the largest 737 MAX customer, also were unaware of the change, the officials said.

The alerts inform pilots whether a sensor known as an “angle-of-attack vane” is transmitting errant data about the pitch of a plane’s nose. Accident investigators have linked such bad data to the deadly Ethiopian Airlines crash in March and the Lion Air crash last year; both planes lacked the alert system.

In the 737 MAX, which features a new automated stall-prevention system called MCAS, Boeing made those alerts optional; they would be operative only if a carrier bought a package of additional safety features.

Southwest’s management and cockpit crews didn’t know about the lack of the warning system for more than a year after the planes went into service in 2017, industry and government officials said. They and most other airlines operating the MAX learned about it only after the Lion Air crash in October led to scrutiny of the plane’s revised design.

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“Southwest’s own manuals were wrong” about the availability of the alerts, said the Southwest pilots union president, Jon Weaks. Since Boeing hadn’t communicated the modification to the carrier, the manuals reflected incorrect information, he said.

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