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One year has passed since the flight accident Ethiopian 302 operated on a Boeing 737 MAX, a new preliminary report was released.
After the fatal crash of the Ethiopian flight 302 everything changed in the industry, especially for Boeing. Hours after this event and due to the notorious similarities with the accident of the flight of Lion Air also operated on a 737 MAX, this model plane was left on the ground.
It is already a year since this accident and the Ethiopian civil aviation authority revealed the interim or preliminary report of what are the advances of the investigation that has been carried out together with regulatory entities of the world, seeking to reveal the chain of events that led to this situation.
Ethiopian preliminary report 302 Boeing 737 MAX
In the lengthy document 136 pages detail the first findings of the investigation and since it is not yet a final report, no industry recommendations detailed, manufacturer, airline or regulatory bodies.
Findings
The report highlights the following points:
- The aircraft had a valid certificate of airworthiness and in accordance with applicable regulations and procedures;
- There were no known technical issues prior to departure.
- Aircraft weight and balance were within operational limits.
- Takeoff and takeoff run were normal, including left and right normal values
angle of attack (AOA). During the takeoff roll, the engines stabilized in about 94% of N1. From this point for most of the flight, the reference N1 remained around the 94%. - Shortly after takeoff, AOA values recorded on the left and right deviated. In the left AOA the values were erroneous and reached 74.5° while in the right AOA it reached a maximum value of 15.3°. The difference between the left and right AOA values was 59° and remained so until near the end of the recording..
- Just after the deviation of the AOA, the left stick shaker was activated and remained active until the end of the recording. The flying pitch bars (F/D) disappeared on both primary flight screens (PFD).
- Approximately five seconds after the end of the crew manual electrical trim inputs, a third automatic nose-down adjustment (MCAS) it was activated. There was no corresponding
stabilizer movement, which is consistent with the stabilizer cutoff switches being in the "off" position. - The speed clacker sounded and remained active until the end of the recording. The speed values varied between 360 kt and 375 kt.
- Approximately five seconds after the last manual electrical adjustment input, quarter
automatic nose down adjustment (MCAS) it was activated. The stabilizer moved from 2.3 a 1 degrees. Vertical velocity decreased and became negative 3 seconds after MCAS activation. - The difference in training from B737NG to B737 MAX provided by the manufacturer was inadequate.
- The AOA disagreement message did not appear on the accident aircraft as designed in the flight crew operating manual.
- The ADIRU AOA failure detection function did not detect the wrong AOA in the Left AOA Sensor because it only considers the value wrong when the AOA value is out of range.
- The design of MCAS on individual AOA inputs made it vulnerable to unwanted activation.
- The specific failure modes that could lead to an unwanted MCAS activation, as an AOA erroneous entry were not simulated as part of functional risk assessment testing. As a result, various effects occur in flight (such as IAS DISAGREE and ALT DISAGREE alerts and stick shaker activation) resulting from the same underlying fault (for instance, Wrong AOA) were not simulated or documented in the aircraft manual.
security recommendations
Finally, the document recommends that the system MCAS must obtain information from both AOAs, so that you get redundant information.
It also mentions that it is necessary to carry out simulator sessions so that the crews that go from NG to MAX become familiar with the normal and abnormal procedure of the MCAS system., for which the training system must be able to simulate AOA failures.
To close, the board of inquiry recommends that the manufacturer should confirm that the AOA DISAGREE alert works regardless of whether or not the angle of attack indicator is installed on aircraft of this type.
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