Boeing Describes Why Max Did Not Carry Disagree Alert

 - May 6, 2019, 10:17 AM

Six days after AIN reported that early in the development of the 737 Max Boeing failed to recognize that a planned angle-of-attack indication disagree alert would not work on airplanes not equipped with an AOA indicator, the company issued a statement on Sunday attempting to explain why it did not tell airlines or the U.S. Federal Aviation Administration that feature did not come as standard equipment on the new model until the October 29, 2018 crash of Lion Air Flight 610.

“When the discrepancy between the requirements and the software was identified, Boeing followed its standard process for determining the appropriate resolution of such issues,” the company said. “That review, which involved multiple company subject matter experts, determined that the absence of the AOA disagree alert did not adversely impact airplane safety or operation. Accordingly, the review concluded, the existing functionality was acceptable until the alert and the indicator could be delinked in the next planned display system software update.”

Boeing added that senior company leadership did not know about the review and first became aware of the issue in the aftermath of the Lion Air crash.

Boeing issued an Operations Manual Bulletin (OMB) on November 6, and a day later the FAA issued an airworthiness directive. Both documents identified the AOA disagree alert as one among a number of indications that could result from an erroneous angle of attack and both described the alert feature as operable only in Max jets equipped with an AOA indicator. Only then did Boeing inform the FAA that its engineers found in 2017 that the display system software did not correctly meet the AOA disagree alert requirements and that the company took no further action because the issue did not adversely affect airplane safety or operation.

“In December 2018, Boeing convened a safety review board (SRB) to consider again whether the absence of the AOA disagree alert from certain 737 Max flight displays presented a safety issue,” said Boeing in Sunday’s statement. “That SRB confirmed Boeing’s prior conclusion that it did not. Boeing shared this conclusion and the supporting SRB analysis with the FAA.”