A day after Ethiopian Airlines released its preliminary report, Boeing has confirmed that the 737 Max 8 has an additional problem in its flight control software that will require more time to fix. These issues are reportedly separate from the anti-stall system failures believed to have caused the loss of Flight 302. The additional issues affect software controlling flaps and other flight-control surfaces. It is not clear if these additional flaws contributed to the loss of Lion Air 610 or Flight 302.
These additional errors are responsible for Boeing’s slipped timeline in delivering the 737 Max 8’s software updates to the FAA. Boeing has declared that the problem is “relatively minor” but did not offer details of how the flaws would have impacted flight, when they would have been encountered, or whether they’ve previously been responsible for any known issues. “We are taking steps to thoroughly address this relatively minor issue and already have the solution in work to do that,” Boeing told the Washington Post.
Meanwhile, the Ethiopian Airlines data released to date shows clear evidence that the MCAS system was involved in the aircraft’s loss, even if the system isn’t mentioned by name.
Note: There is a discrepancy in the Ethiopian report between the text and graphics regarding which AOA sensor was misreporting data. The text implies that the left sensor is the sensor that failed, but a graph in the Ethiopian report may have been mislabeled to indicate that the right sensor failed. Here’s text from the actual report:
At 05:38:44, shortly after liftoff, the left and right recorded AOA values deviated. Left AOA decreased to 11.1° then increased to 35.7° while value of right AOA indicated 14.94°. Then after, the left AOA value reached 74.5° in ¾ seconds while the right AOA reached a maximum value of 15.3°. At this time, the left stick shaker activated and remained active until near the end of the recording. Also, the airspeed, altitude and flight director pitch bar values from the left side noted deviating from the corresponding right side values. The left side values were lower than the right side values until near the end of the recording. (All emphasis added).
The graphic below from the Washington Post shows the right sensor as being the failure point, but this corresponds to the labeling in a different section of the Ethiopian Airlines report. We’ve communicated with WaPo, who is checking back with their own contacts. We will update this report to confirm whether it was the right or left sensor that failed as soon as we know more.
The last sentence of the paragraph could be read as a statement summarizing the entire data set. Our supposition is that it’s only meant to apply to the airspeed, altitude, and flight director pitch bar values, meaning that it was these values that were lower than the reported values on the right side and not the AOA values. On page 25/33, Ethiopian Airlines again reiterates that the failure was on the left side of the aircraft rather than the right.
Boeing has acknowledged that the MCAS system was involved in the loss of the aircraft, stating:
The full details of what happened in the two accidents will be issued by the government authorities in the final reports, but, with the release of the preliminary report of the Ethiopian Airlines Flight 302 accident investigation, it’s apparent that in both flights the Maneuvering Characteristics Augmentation System, known as MCAS, activated in response to erroneous angle of attack information.