Boeing knew of 737 MAX indicator problem in 2017

May 06, 2019
737 MAX
The 737 MAX on one of its test flights. Photo: Boeing.

Boeing has confirmed that it knew as far back as 2017 that an angle-of-attack warning light supposed to come as standard on the 737 MAX was not working as intended.

But the aerospace giant argues the angle-of-attack (AOA) disagree alert was not necessary for the safe operation of the aircraft.

Faulty AOA sensors were part of a chain of events that led to the crash of two 737 MAX aircraft within five months and it is not clear that having the alerts would have changed the outcome.

The Lion Air crash in October 2018, and another involving Ethiopian Airlines in March together resulted in 346 deaths.

The Wall Street Journal reported that Boeing did not share information about the problem with the AOA alert for about a year and then gave some airlines and pilots partial and inconsistent explanations.

It claimed senior FAA and airline officials were increasingly raising questions about Boeing’s transparency over the cockpit warnings.

Southwest said recently that Boeing documentation indicated the AOA disagree alert was functional in its MAX planes and it did not learn this was not the case until after the Lion Air crash.

READ: Boeing didn’t tell Southwest about disabled indicator.


The issue has arisen as a number of investigations are underway into the certification of the MAX aircraft and the company’s relationship with the FAA.

Boeing confirmed at that time that it intended for the AOA disagree alert to be a standard, standalone feature on the MAX but that this had not happened because of software issues.

In a further statement issued in the US on Sunday, the manufacturer said its engineers first identified the problem several months after deliveries started in 2017.

It said software delivered to Boeing linked the AOA Disagree alert to the AOA indicator, an optional feature on the MAX and the earlier 737 NG.

This meant the alert activated 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,’’ Boeing 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 said senior company leadership was not involved in the review and first became aware of the issue in the aftermath of the Lion Air accident.

It pointed to an operations manual bulletin issued on November 6, 2018 — a week after the Lion Air crash — that described the AOA disagree alert as only available if the AOA indicator option was installed.

The company also discussed the status of the AOA disagree alert with the US Federal Aviation Administration in the wake of the Lion Air accident.

“At that time, Boeing informed the FAA that Boeing engineers had identified the software issue in 2017 and had determined per Boeing’s standard process that the issue did not adversely impact airplane safety or operation,’’ it said.

“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.

“That SRB confirmed Boeing’s prior conclusion that it did not. Boeing shared this conclusion and the supporting SRB analysis with the FAA.”

Boeing has consistently maintained that all the data to safely operate the aircraft is on the primary flight displays and says this is the information used by pilots to fly a plane as well as in training and checklists.

This includes parameters such as airspeed, attitude, altitude, vertical speed, heading and engine power settings in normal flight or, in the case elevated angle of attack, the pitch limit indicator and stick shaker.

It reiterated in its latest statement that neither the angle of attack indicator nor the AOA disagree alert was necessary for the safe operation of the aircraft.

“They provide supplemental information only and have never been considered safety features on commercial jet transport airplanes,’’ it said.

Nonetheless, Boeing is issuing a display system software update that corrects the AOA indicator light problem and makes the function standard in all MAX aircraft.


  1. An internally convened Safety Review Board which supports the findings of a previous internal Safety Review Board and re confirms the Company's decision not to fit as standard an indicator which shows AOA position or include a warning to show when the 2 AOA sensors disagree.In the Ethiopian accident, the MCAS operation was based on erroneous 75 degree nose up input from the P1 AOA sensor. But the P2 AOA sensor was reading 15 degrees nose up, correct for the take off and climb configuration. A disagree light or an indicator showing the issue would have been very useful information for the crew to know during troubleshooting.