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A year before the first crash of a 737 MAX, Boeing was aware of software
problems with the plane. Boeing admitted on Sunday that a few months after the
delivery of the 737 MAX in May 2017, it was discovered that a warning system
in the cockpits was not working properly.
 
The AOA Disagree Alert only appeared to work in combination with another
optional function, the AOA indicator. From its own research, Boeing concluded
that the non-working safety option did not mean a deterioration of flight
safety.
 
The American aviation authority FAA was not informed until a week after the
first accident. The FAA subsequently issued an Airworthiness Directive (AD).
 
The 737 MAX airplanes have been on the ground worldwide since mid-March. This
is because of two fatal aircraft accidents in a short time, in Indonesia with
a Lion Air aircraft and in Ethiopia with an aircraft from Ethiopian Airlines.
They were found to be caused by the MCAS safety system that repeatedly pressed
down the nose due to a malfunctioning Angle of Attack (AOA) sensor.
 
It is not clear whether specifically the non-functioning AOA Disagree Alert
also played a role in the crashes. The software update that Boeing is
currently working on does ensure that the AOA Disagree Alert becomes a
standard option on the 737 MAX. The Angle of Attack indicator remains optional.
 
Read the full Boeing statement below:
 
Boeing Statement on AOA Disagree Alert 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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