Long Before First 737 MAX Crash, Boeing Knew A Key Sensor Warning Light Wasn’t Working, But Told No One (excerpt)
(Source: Seattle Times; published May 5, 2019)
By Dominic Gates
SEATTLE --- Boeing admitted Sunday that it knew well over a year before the first crash of a 737 MAX in Indonesia last October that a warning light linked to a key sensor on the 737 MAX wasn’t working on most of the airplanes, but it informed neither the Federal Aviation Administration (FAA) nor the airlines operating the jet about the problem until after that crash.

The warning light is significant because it warned of a malfunction in one of the jet’s Angle of Attack (AOA) sensors, a fault that began the sequence of events that led to both the Lion Air crash in October and the Ethiopian Airlines crash in March.

The alert worked only on planes flown by airlines that had bought a separate and optional AOA indicator added to the main flight display panel. Boeing disclosed the existence of the problem publicly only last week after a story in the Wall Street Journal. It disclosed its prior knowledge on Sunday only after a follow-up story.

Furthermore, even MAX operators like American Airlines that had bought the optional indicator were misinformed by Boeing last year after the Lion Air crash about how the warning light operates.

As Boeing deals with the crisis following the loss of 346 lives in two crashes and works to convince the FAA, the airlines and the public that the MAX should be allowed to fly again as early as next month, the lack of transparency and confusion is challenging Boeing’s credibility.

“The more and more we learn with each day, the more challenging it is to rebuild the trust,” said American Airlines Captain Dennis Tajer, spokesman for the Allied Pilots Association (APA). “This slow toxic drip of full disclosure only after full discovery … (has) got to stop if we are going to rebuild the trust that has been so deeply violated.” (end of excerpt)

Click here for the full story, on the Seattle Times website.


Boeing Statement on AOA Disagree Alert
(Source: Boeing; issued May 05, 2019)
On every airplane delivered to our customers, including the MAX, all flight data and information needed to safely operate the aircraft is provided in the flight deck on the primary flight deck displays. This information is provided full-time in the pilots’ primary field of view, and it always has been.

Air speed, attitude, altitude, vertical speed, heading and engine power settings are the primary parameters the flight crews use to safely operate the airplane in normal flight. Stick shaker and the pitch limit indicator are the primary features used for the operation of the airplane at elevated angles of attack. All recommended pilot actions, checklists, and training are based upon these primary indicators. Neither the angle of attack indicator nor the AOA Disagree alert are necessary for the safe operation of the airplane. They provide supplemental information only, and have never been considered safety features on commercial jet transport airplanes.

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

Approximately a week after the Lion Air accident, on November 6, 2018, Boeing issued an Operations Manual Bulletin (OMB), which was followed a day later by the FAA’s issuance of an Airworthiness Directive (AD). In identifying the AOA Disagree alert as one among a number of indications that could result from erroneous AOA, both the OMB and the AD described the AOA Disagree alert feature as available only if the AOA indicator option is installed.

Boeing discussed the status of the AOA Disagree alert with the FAA 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. 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 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.


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