Addis Ababa, March 10, 2020 (FBC) –Ethiopia yesterday released an interim report on Ethiopian Airlines 737Max crash that killed 157 people a year ago.
The 136-page report issued by the Ministry of Transport, suggests that pilots faced challenge controlling the Boeing 737 MAX.
The report supports the initial findings by Ethiopian officials last April that Boeing’s Manoeuvring Characteristics Augmentation System (MCAS) made it impossible for crew to regain control of the aircraft.
Erroneous readings from an Angle of Attack (AOA) sensor led to four separate nose-down trim activations by the MCAS system, each requiring increasing strength by the pilots to regain control.
According to the report, the left and right recorded AOA values deviated shortly after take-off. The pilots notified air traffic control that they were encountering a “flight control problem.”
Investigators note, “The left AOA values were erroneous and reached 74.5° while the right AOA reached a maximum value of 15.3°. The difference between the left and the right AOA values was 59° and remained as such until near the end of the recording.”
Investigators found that, “the AOA Disagree message did not appear on the accident aircraft as per the design described on the flight crew operation manual.”
Also, the “AOA failure detection feature of the ADIRU (air data inertial reference unit) did not detect the erroneous AOA from the left AOA sensor because it only considers the value to be erroneous when the AOA value is outside the physical range. Thus; SPD (speed) and ALT flag never appeared on the PFD (primary flight display).”
Investigators also found fault with Boeing’s testing of the MCAS system. Specifically, that the manufacturer failed to test for failure modes “that could lead to uncommanded MCAS activation” including an erroneous high AOA input.
“As a result, additional flight deck effects (such as IAS DISAGREE and ALT DISAGREE alerts and stick shaker activation) resulting from the same underlying failure (for example, erroneous AOA) were not simulated and were not documented in the stabilizer trim and auto flight safety assessment,” they write.
Ethiopian investigators suggested the design of MCAS should include redundancies in the use of data “from both AOA and/or other independent systems.”
They also recommended that regulators certifying the aircraft should “confirm all probable causes of failure have been considered during functional hazard assessment.”
Additionally, Ethiopian investigators found that the difference training from B737NG to B737 MAX provided by Boeing to the airline’s pilots was “inadequate.”
They recommended, “The difference training should also include simulator sessions to familiarize with normal and non-normal MCAS operation. The training simulators need to be capable of simulating AOA failure scenarios.”