Boeing knew of 737 Max technical issue a year before fatal crashes

Boeing was aware of a technical issue with the 737 Max a year before the aircraft was involved in two fatal accidents.

The US manufacturer said it had inadvertently made an alarm feature optional instead of standard, but stressed that this did not jeopardise flight safety.

All 737 Maxs were grounded in March after an Ethiopian Airlines flight crashed, killing 157 people.

Five months earlier, 189 people were killed in a Lion Air crash in Indonesia.

The worldwide fleet of 737 Max aircraft totalled 387 aircraft at the time of the grounding.

The feature involved is known as the Angle of Attack (AOA) Disagree alert, designed to let pilots know when two different sensors were reporting conflicting data.

Boeing said it had intended to provide the feature as standard, but did not realise until deliveries had begun that it was only available if airlines purchased an optional indicator.

It said it had intended to deal with the problem in a later software update, the BBC reported.

Boeing maintained that the software problem “did not adversely impact airplane safety or operation”.

The company said in statement: “The Boeing design requirements for the 737 Max included the AOA Disagree alert as a standard, standalone feature, in keeping with Boeing’s fundamental design philosophy of retaining commonality with the 737NG.

“In 2017, within several months after beginning 737 Max deliveries, engineers at Boeing identified that the 737 Max display system software did not correctly meet the AOA Disagree alert requirements.

“The software delivered to Boeing linked the AOA Disagree alert to the AOA indicator, which is an optional feature on the Max and the NG. Accordingly, the software activated the AOA Disagree alert only if an airline opted for the AOA indicator.

“When the discrepancy between the requirements and the software was identified, Boeing followed its standard process for determining the appropriate resolution of such issues.

“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.”

The review concluded that the existing functionality “was acceptable until the alert and the indicator could be delinked in the next planned display system software update”.

Boeing added: “Senior company leadership was not involved in the review and first became aware of this issue in the aftermath of the Lion Air accident.”

The firm said: “Boeing is issuing a display system software update, to implement the AOA Disagree alert as a standard, standalone feature before the Max returns to service.

“When the Max returns to service, all Max production aircraft will have an activated and operable AOA Disagree alert and an optional angle of attack indicator.

“All customers with previously delivered Max airplanes will have the ability to activate the AOA Disagree alert.’

It remains unclear when the 737 Max will be allowed to return to service.


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