The Preliminary report (available here) shows the following timeline. I have put some extracts here:
- At 05:38:00 Take off roll commenced
- At 05:38:44, shortly after liftoff, the left and right recorded AOA values deviated. Left AOA decreased to 11.1° then increased to 35.7° while value of right AOA indicated 14.94°. Then after, the left AOA value reached 74.5° in ¾ seconds while the right AOA reached a maximum value of 15.3°. At this time, the left stick shaker activated and remained active until near the end of the recording. Also, the airspeed, altitude and flight director pitch bar values from the left side noted deviating from the corresponding right side values. The left side values were lower than the right side values until near the end of the recording.
- At 05:38:46 and about 200 ft radio altitude, the Master Caution parameter changed state. The First Officer called out Master Caution Anti-Ice on CVR. Four seconds later, the recorded Left AOA Heat parameter changed state.
- At 05:39:22 and about 1,000 feet the left autopilot (AP) was engaged (it disengaged about 33 seconds later), the flaps were retracted and the pitch trim position decreased to 4.6 units.
- At 05:39:45, Captain requested flaps up and First-Officer acknowledged. One second later, flap handle moved from 5 to 0 degrees and flaps retraction began.
- At 05:39:55, Autopilot disengaged,
- At 05:39:57, the Captain advised again the First-Officer to request to maintain runway heading and that they are having flight control problems.
- At 05:40:00 shortly after the autopilot disengaged, the FDR recorded an automatic aircraft nose down (AND) activated for 9.0 seconds and pitch trim moved from 4.60 to 2.1 units. The climb was arrested and the aircraft descended slightly.
- At 05:40:03 Ground Proximity Warning System (GPWS) “DON’T SINK” alerts occurred.
- At 05:40:12, approximately three seconds after AND stabilizer motion ends, electric trim (from pilot activated switches on the yoke) in the Aircraft nose up (ANU) direction is recorded on the DFDR and the stabilizer moved in the ANU direction to 2.4 units. The Aircraft pitch attitude remained about the same as the back pressure on the column increased.
- At 05:40:20, approximately five seconds after the end of the ANU stabilizer motion, a second instance of automatic AND stabilizer trim occurred and the stabilizer moved down and reached 0.4 units.
- At 05:40:27, the Captain advised the First-Officer to trim up with him.
- At 05:40:28 Manual electric trim in the ANU direction was recorded and the stabilizer reversed moving in the ANU direction and then the trim reached 2.3 units.
- At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and FirstOfficer confirmed stab trim cut-out.
- At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance of AND automatic trim command occurred without any corresponding motion of the stabilizer, which is consistent with the stabilizer trim cutout switches were in the ‘’cutout’’ position
- At 05:40:44, the Captain called out three times “Pull-up” and the First-Officer acknowledged.
- At 05:40:50, the Captain instructed the First Officer to advise ATC that they would like to maintain 14,000 ft and they have flight control problem.
- From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units. During this time, aft force was applied to the control columns which remained aft of neutral position. The left indicated airspeed increased from approximately 305 kt to approximately 340 kt (VMO). The right indicated airspeed was approximately 20-25 kt higher than the left. The data indicates that aft force was applied to both columns simultaneously several times throughout the remainder of the recording.
- At 05:41:20, the right overspeed clacker was recorded on CVR. It remained active until the end of the recording.
- At 05:41:30, the Captain requested the First-Officer to pitch up with him and the First-Officer acknowledged.
- At 05:41:32, the left overspeed warning activated and was active intermittently until the end of the recording.
- At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try.
- At 05:41:54, the First-Officer replied that it is not working.
- At 05:42:54, both pilots called out “left alpha vane”.
- At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough.
- At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002 ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units.
- At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording.
- The left Indicated Airspeed increased, eventually reaching approximately 458 kts and the right Indicated Airspeed reached 500 kts at the end of the recording. The last recorded pressure altitude was 5,419 ft on the left and 8,399 ft on the right
Flight profile from runway to last captured ADS-B point (Dave Reid)
The Ethiopian Airlines CEO at the crash site (Photo: Ethiopian Airlines)
The Interim Report
- 1. The aircraft has a valid certificate of airworthiness and maintained in accordance with applicable regulations and procedures;
- 2. There were no known technical problems before departure.
- 3. The aircraft weight and balance was within the operating limits.
- 4. The takeoff roll and lift-off was normal, including normal values of left and right angle-of-attack (AOA). During takeoff roll, the engines stabilized at about 94% N1. From this point for most of the flight, the N1 Reference remained about 94%.
- 5. Shortly after lift-off, the left and right recorded AOA values deviated. 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.
- 6. Right after the deviation of the AOA the left stick shaker activated and remained active until the near end of the recording. The pitch Flight Director (F/D) bars disappeared on both left hand and right hand Primary Flight Displays (PFD). As the aircraft crossed 400 ft Radio Altitude the right and left pitch F/D bars appeared again.
- 7. Immediately after the LH AOA sensor failure, the left AOA erroneous values affected the LH FD pitch command, and the RH and LH Flight Director (FD) pitch bars started to display different guidance.
- 8. The Stall Management Yaw Damper Computer -1 (SMYDC 1) computed LH minimum operational speed and LH stick shaker speed greater than VMO (340 kt) without any alert or invalidity detection.Thus; the indicated LH airspeed was inside the minimum speed (red and black) band.
- 9. Approximately five seconds after the end of the crew manual electrical trim up inputs, a third automatic nose-down trim(MCAS) triggered. There was no corresponding motion of the stabilizer, which is consistent with the stabilizer trim cutout switches being in the ‘’cutout’’ position
- 10. The right hand over speed clacker sounded and it remained active until the end of the recording. The RH speed values varied between 360 kt and 375 kt (RH values). On the LH PFD, the LH computed airspeed oscillated between 335 kt and 350 kt.
- 11. Approximately five seconds after the last manual electric trim up input, a fourth automatic trim nose-down (MCAS) triggered. The stabilizer moved from 2.3 to 1 unit. The vertical speed decreased and became negative 3 s after the MCAS activation.
- 12. The difference training from B737NG to B737 MAX provided by the manufacturer was found to be inadequate.
- 13. The AOA Disagree message did not appear on the accident aircraft as per the design described on the flight crew operation manual.
- 14. AOA failure detection feature of the ADIRU 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 and ALT flag never appeared on the PFD.
- 15. MCAS design on single AOA inputs made it vulnerable to undesired activation.
- 16. The specific failure modes that could lead to uncommanded MCAS activation, such as an erroneous high AOA input to the MCAS, were not simulated as part of the functional hazard assessment validation tests. 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.
- 1. The design of MCAS should consider the use of data from both AOA and/or other independent systems for redundancy.
- 2. The regulator shall confirm all probable causes of failure have been considered during functional hazard assessment.
- 3. The manufacturer shall insure the minimum operational speedcomputed by the SMYD to be within logical value. There should also be logic to validate the computation.
- 4. 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.
- 5. The manufacture should confirm the AOA DISAGREE alert is functional whether the optional angle of attack indicator is installed or not.
- 6. The EAIB endorses the NTSB safety recommendation A-19-10 found in appendix 1