Ethiopian airliner down in Africa
However, you might add, at no point was thrust reduced from 94% N1, which allowed the airspeed to reach around 375kts.... which at the final ND trim was unrecoverable.
None of the crew trim inputs at any point were sufficient to counter the MCAS ND trim events, which is really where things went wrong. Had they trimmed sufficiently and hit the cutouts, we'd not be have this exact discussion.
Also, the AOA was not offset for the entire flight, it appears to an event that occured some8 seconds after takeoff. Bird strike maybe?
- GY
None of the crew trim inputs at any point were sufficient to counter the MCAS ND trim events, which is really where things went wrong. Had they trimmed sufficiently and hit the cutouts, we'd not be have this exact discussion.
Also, the AOA was not offset for the entire flight, it appears to an event that occured some8 seconds after takeoff. Bird strike maybe?
- GY
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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.
First Officer called out Master Caution Anti-Ice on CVR. Four seconds later, the recorded
Left AOA Heat parameter changed state.
Edit: The sequence in this crash was slightly different, with autopilot engaged before flap retraction. The first MCAS activation was not immediately after flaps up, but only after the autopilot disengaged a few seconds later. A subtle difference perhaps?
Last edited by GordonR_Cape; 4th Apr 2019 at 17:23.
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However, you might add, at no point was thrust reduced from 94% N1, which allowed the airspeed to reach around 375kts.... which at the final ND trim was unrecoverable.
None of the crew trim inputs at any point were sufficient to counter the MCAS ND trim events, which is really where things went wrong. Had they trimmed sufficiently and hit the cutouts, we'd not be have this exact discussion.
Also, the AOA was not offset for the entire flight, it appears to an event that occured some8 seconds after takeoff. Bird strike maybe?
- GY
None of the crew trim inputs at any point were sufficient to counter the MCAS ND trim events, which is really where things went wrong. Had they trimmed sufficiently and hit the cutouts, we'd not be have this exact discussion.
Also, the AOA was not offset for the entire flight, it appears to an event that occured some8 seconds after takeoff. Bird strike maybe?
- GY
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Flaps UP at 05:39:45 but there appears to be two Automatic Trim Down commands prior to this which produced some Down Pitch Trim.
Is this STS, or MCAS operating when the flaps are down?
Is this STS, or MCAS operating when the flaps are down?
-GY
Administrator
I'll put it here again since the thread is moving at a nice clip:
Preliminary Report
Dear readers, please have a look at the Preliminary Report; it may answer some of your questions "up front." You'll probably have some questions that it does not answer.
Preliminary Report
Dear readers, please have a look at the Preliminary Report; it may answer some of your questions "up front." You'll probably have some questions that it does not answer.
Thanks for the tabulated data Bubba,
That puts it in pilot's perspective and makes terrible reading.
I hate to think what those poor fellows felt like.
Also opens up new questions which as usual we will guess at, until a reliable report emerges.
That puts it in pilot's perspective and makes terrible reading.
I hate to think what those poor fellows felt like.
Also opens up new questions which as usual we will guess at, until a reliable report emerges.
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And in the maint log too - and like Lion all were tested using BITE and found "ok".
I can't see that it is confirmed anywhere that they re-engaged electric trim
- FO called for stab trim cutout, and in the narrative it is after they trimmed up (anyone going to change their appraisal of him? edit: seems someone did, good)
- one period of MCAS AND has no effect (so cutouts worked)
- later two manual elec trim inputs seem to be ineffective, maybe they did turn back on but too short to see the effect?
- Another MCAS input and this time the stab goes down
Given the info we have, it seems that both "switches were re-activated" and "switches failed to stop MCAS" are plausible.
And then there is the AP - they got the AP to engage (left-side, despite dud AOA, WTF?) but it tripped out 33 secs later. The AP appears to have been trimming nose down too, and failing to climb, and then we have:
First impressions are that this ain't just a software fix, yes MCAS dumped them in the ground but even without that this was a brand new plane that was seriously sick.
All from one dud AOA sensor? - or something in the vicinity of the (left) ADIRU?
I can't see that it is confirmed anywhere that they re-engaged electric trim
- FO called for stab trim cutout, and in the narrative it is after they trimmed up (
- one period of MCAS AND has no effect (so cutouts worked)
- later two manual elec trim inputs seem to be ineffective, maybe they did turn back on but too short to see the effect?
- Another MCAS input and this time the stab goes down
Given the info we have, it seems that both "switches were re-activated" and "switches failed to stop MCAS" are plausible.
And then there is the AP - they got the AP to engage (left-side, despite dud AOA, WTF?) but it tripped out 33 secs later. The AP appears to have been trimming nose down too, and failing to climb, and then we have:
Six seconds after the autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes. These oscillations continued also after the autopilot was disengaged.
All from one dud AOA sensor? - or something in the vicinity of the (left) ADIRU?
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Wire chafe? Something got pinched or partially shorted (changing resistance) and briefly released? I have no idea how one would prove that given how little of the planes are left. A misrouted wiring harness on a new plane kind of fits the bill but there are a lot of other possibilities. Do they take detailed production photos?
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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 05:40:41, 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
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Why no mention of the fact that they reengaged the stab trim cutout switches at 5:43:11? Seems to me as though they reengaged the system, applied nose up trim via the electric trim switches and left the stab trim cutout switches engaged thus allowing MCAS to activate again once they stopped trimming.
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From the outside, after looking carefully at the Ethiopian crash flight recorder plot:
Systems should nowadays be able to detect faulty AOA sensor (or every other sensor) output automatically by checking whether it is congruent with the set of information available. Flight parameters are not independent of each other.
To be more specific, a correctly detected sudden increase in the AOA can have a limited number of causes:
a) very strong upward winds - very improbable, and if, only possible for a couple of seconds. Anyway, even then there has to be a corresponding spike in upward acceleration to be detected.
b) corresponding increase in longitudinal pitch
c) corresponding hefty decrease in airspeed
As none of those were present, a sensor failure should have been detected, the pilots informed and the sensor input to other systems blocked.
A similar reasoning can be set up for airspeed sensors.
If the pilots had consistently nullified the automatic downwards trim by manual upwards trim, they would have made it. So clearly they did not identify the chain of problems (wrong AOA, MCAS reacting) correctly. The stick shaker certainly didn't help here for a clear analysis.
Systems should nowadays be able to detect faulty AOA sensor (or every other sensor) output automatically by checking whether it is congruent with the set of information available. Flight parameters are not independent of each other.
To be more specific, a correctly detected sudden increase in the AOA can have a limited number of causes:
a) very strong upward winds - very improbable, and if, only possible for a couple of seconds. Anyway, even then there has to be a corresponding spike in upward acceleration to be detected.
b) corresponding increase in longitudinal pitch
c) corresponding hefty decrease in airspeed
As none of those were present, a sensor failure should have been detected, the pilots informed and the sensor input to other systems blocked.
A similar reasoning can be set up for airspeed sensors.
If the pilots had consistently nullified the automatic downwards trim by manual upwards trim, they would have made it. So clearly they did not identify the chain of problems (wrong AOA, MCAS reacting) correctly. The stick shaker certainly didn't help here for a clear analysis.
Last edited by dlen; 4th Apr 2019 at 17:24.
Originally Posted by Report, page 11 of 33, near bottom
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 05:41:54, the First-Officer replied that it is not working
(As I look at the Airspeed value, I keep thinking, will ask another question in a bit ...
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.
At 05:41:20, the right overspeed clacker was recorded on CVR. It remained active until the end of the recording.)
*As I read this, they had already put stab trim cut out.
At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and First- Officer 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
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I'm thinking wiring issue.