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.

--- D'Bridge 3.99 SR41