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.
“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.
The FAA grounded all 737 MAX jets on March 13, three days after the Ethiopian Air accident. Boeing recently said it would book $1 billion in expenses tied to the groundings and related business disruptions. Boeing hasn't addressed why it turned off the feature, called “AOA disagree alerts,” without informing customers. After the Lion Air crash, Southwest asked Boeing to activate the alerts on its MAX planes.
This move, along with questions about why the alert system had been turned off, prompted FAA inspectors overseeing Southwest to consider in December recommending that the airline's MAX fleet be grounded while they assessed whether pilots needed additional training about the alerts. But those internal FAA discussions didn't go up the agency's chain of command, according to documents reviewed by The Wall Street Journal.
A Southwest spokeswoman said that before the Lion Air crash, the carrier had assumed the alerts were “operable on all MAX aircraft.” Boeing “did not indicate an intentional deactivation,” she said.
In previous 737 models, the alerts appear as colored lights in the cockpit when a plane's twin angle-of-attack sensors provide significantly different data from each other. In the MAX, they serve the same purpose but additionally are intended to warn pilots that MCAS, the new automated system implicated in both accidents, could misfire because of faulty sensor data.
MCAS commands that automatically push down the nose of a plane when it appears to be in danger of stalling can overpower a pilot's efforts to get out of a dive by pulling the nose up. In the Ethiopian jet, which lacked the disagree alerts, it took more than four minutes for the pilots to realize that incorrect data from one of the sensors were prompting MCAS to push the jet's nose down, according to investigators' preliminary report.
A Boeing spokesman said last week that from now on, “customers will have the AOA disagree alerts as standard” on all MAX aircraft, including those already delivered to airlines. Boeing is devising a new software package that aims to fix MCAS by making it less powerful, while also restoring the alerts.
The moves are among the safeguards the plane maker and FAA have embraced to get the MAX fleet back in the air.
Boeing hasn't said why it turned off the feature without informing customers.
Although the alerts were reactivated, some midlevel FAA officials who oversaw Southwest briefly considered the possibility of grounding its roughly 30 MAX aircraft until the agency established whether pilots needed new training, according to documents reviewed by the Journal.
Less than a month after the Lion Air jet went down, one FAA official wrote that AOA related issues on MAX jetliners “may be masking a larger systems problem that could recreate a Lion Air-type scenario.”
About two weeks later, other internal emails referred to a “hypothetical question” of restricting MAX operations, with one message explicitly stating: “It would be irresponsible to have MAX aircraft operating with the AOA Disagree Warning system inoperative.”
The same message alluded to the FAA's power: “We need to discuss grounding [Southwest's] MAX fleet until the AOA Warning System is fixed and pilots have been trained” on it and related displays. Within days, the concerns were dismissed by some involved in the discussions.
These people concluded that the alerts provided supplemental pilot aids rather than primary safety information, and therefore no additional training was necessary. Boeing and the FAA continued to publicly vouch for the aircraft's safety.
However, these concerns are being pursued by congressional, criminal and Transportation Department investigators, people with knowledge of inquiries said.
On Wednesday, a Boeing spokesman said that while the internal FAA discussions were under way last year, “there was no data that indicated the fleet should be grounded.”
American Airlines Group Inc. was one of the few U.S. carriers that paid for the package of MAX safety features that included the sensor warning lights. The airline has said it did so in part to obtain the warning system.
—Andrew Tangel, Robert Wall and Alison Sider contributed to this article.
BY ANDY PASZTOR