PPRuNe Forums

PPRuNe Forums (https://www.pprune.org/)
-   Rumours & News (https://www.pprune.org/rumours-news-13/)
-   -   Ethiopian airliner down in Africa (https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa.html)

jagema 4th Apr 2019 16:03

Preliminary report and FDR data are out.

It appears MCAS did in fact make several Stab Nose-down inputs.

Pilots trimmed back up and selected switches to CUTOUT. But the stab remained in a nose down angle. Crew seen pulling back on elevator continuously. They decide to re-energize the stab cutouts so as to trim nose up again (only slightly). It is then when MCAS goes "I've had enough" and adds another 2,5degs nose down. Airplane dives.


Semreh 4th Apr 2019 16:04


Originally Posted by 737mgm (Post 10438642)
Fair point, I should have written crews were overwhelmed instead of too easily overwhelmed. Nonetheless, despite all the stress and confusion that was surely occurring, the "only thing" that was happening is that the airplane was trimming nose down. According to Boeing this can be overriden with the electric trim switch and I have not seen any proof yet that this isn't the case. As I already wrote in an earlier post it is just very puzzling to me why a pilot would let his/her aircraft get to an extreme nose down state if it is possible to counter this with electric trimming. We obviously need more information to be able to understand what truly happened.

"Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts.
In those cases, longitudinal trim is achieved by using the manual stabilizer trim wheel to position the stabilizer. The trim wheel can be used to trim the airplane throughout the entire flight envelope.
In addition, the autopilot has the authority to trim the airplane in these conditions.
The reference regulation and policy do not specify the method of trim, nor do they state that when multiple pilot trim control paths exist that they must each independently be able to trim the airplane
throughout the flight envelope."
Reference: Explanatory Note to TCDS IM.A.120 - Boeing 737 Issue 10 page 15 [Ref 1]. My reading of this, and the preceding paragraph in the referenced document, plus an equivalent safety issue on the 747-8 / -8F [Ref 2], is that the aisle stand trim switches can be use throughout the flight envelope, but the yoke trim switches cannot.

Ref 1 - http://www.easa.europa.eu/sites/defa...20ISS%2010.pdf
Ref 2 - http://www.easa.europa.eu/sites/defa...ESF%20B-13.pdf

LaissezPasser 4th Apr 2019 16:09


"The crew performed all the procedures repeatedly provided by the manufacturer, but was not able to control the aircraft," said Ethiopian Transport Minister Dagmawit Moges, unveiling results of the preliminary probe into the crash.
Presumably Moges refers to "STAB TRIM CUT OUT switches (both) ... CUT OUT" on the Runaway Stabilizer Checklist.
Does the ET302 Preliminary FDR data support the assertion that the crew did this, and if so, when?

Airbubba 4th Apr 2019 16:11

Narrative of the flight from the preliminary report:


1 FACTUAL INFORMATION

1.1 HISTORY OF FLIGHT

On March 10, 2019, at about 05:44 UTC (All times listed is Universal Coordinated Time (UTC), as recorded on the FDR.), Ethiopian Airlines flight 302, a Boeing 737-8 (MAX), Ethiopian registration ET-AVJ, crashed near Ejere, Ethiopia, shortly after takeoff from Addis Ababa Bole International Airport (HAAB), Ethiopia. The flight was a regularly scheduled international passenger flight from Addis Ababa to Jomo Kenyatta International Airport (HKJK), Nairobi, Kenya. There were 157 passengers and crew on board. All were fatally injured, and the Aircraft was destroyed.

The following is based on the preliminary analysis of the DFDR, CVR and ATC communications. As the investigation continues, revisions and changes may occur before the final report is published.

At 05:37:34, ATC issued take off clearance to ET-302 and to contact radar on 119.7 MHz.

Takeoff roll began from runway 07R at a field elevation of 2333.5 m at approximately 05:38, with a flap setting of 5 degrees and a stabilizer setting of 5.6 units. The takeoff roll appeared normal, including normal values of left and right angle-of-attack (AOA). During takeoff roll, the engines stabilized at about 94% N1, which matched the N1 Reference recorded on the DFDR. From this point for most of the flight, the N1 Reference remained about 94% and the throttles did not move. The N1 target indicated non data pattern 220 seconds before the end of recording. According to the CVR data and the control column forces recorded in DFDR, captain was the pilot flying.

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 05:38:43 and about 50 ft radio altitude, the flight director roll mode changed to LNAV.

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 05:38:58 and about 400 ft radio altitude, the flight director pitch mode changed to VNAV SPEED and Captain called out “Command” (standard call out for autopilot engagement) and an autopilot warning is recorded.

At 05:39:00, Captain called out “Command”.

At 05:39:01 and about 630 ft radio altitude, a second autopilot warning is recorded.

At 05:39:06, the Captain advised the First-Officer to contact radar and First Officer reported SHALA 2A departure crossing 8400 ft and climbing FL 320.

Between liftoff and 1000 ft above ground level (AGL), the pitch trim position moved between 4.9 and 5.9 units in response to manual electric trim inputs. At 1000 ft AGL, the pitch trim position was at 5.6 units.

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.

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.

At 05:39:29, radar controller identified ET-302 and instructed to climb FL 340 and when able right turns direct to RUDOL and the First-Officer acknowledged.

At 05:39:42, Level Change mode was engaged. The selected altitude was 32000 ft. Shortly after the mode change, the selected airspeed was set to 238 kt.

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 05:39:50, the selected heading started to change from 072 to 197 degrees and at the same time the Captain asked the First-Officer to request to maintain runway heading.

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 05:40:05, the First-Officer reported to ATC that they were unable to maintain SHALA 1A and requested runway heading which was approved by ATC.

At 05:40:06, left and right flap position reached a recorded value of 0.019 degrees which remained until the end of the recording.

The column moved aft and a positive climb was re-established during the automatic AND motion.

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.

From 05:40:23 to 05:40:31, three Ground Proximity Warning System (GPWS) “DON’T SINK” alerts occurred.

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.

At 05:40:56, the First-Officer requested ATC to maintain 14,000 ft and reported that they are having flight control problem. ATC approved.

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 05:41:21, the selected altitude was changed from 32000 ft to 14000 ft.

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 05:42:10, the Captain asked and the First-Officer requested radar control a vector to return and ATC approved.

At 05:42:30, ATC instructed ET-302 to turn right heading 260 degrees and the First-Officer acknowledged.

At 05:42:43, the selected heading was changed to 262 degrees.

At 05:42:51, the First-Officer mentioned Master Caution Anti-Ice. The Master Caution is recorded on DFDR.

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.

GarageYears 4th Apr 2019 16:11

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

GordonR_Cape 4th Apr 2019 16:18


Originally Posted by GarageYears (Post 10438761)

Some very strange error messages, not just AOA offset:

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.
Edit: I thought it was not possible to engage the autopilot while there was AOA disagree, but it seems that it did happen for a short interval.

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?

DaveReidUK 4th Apr 2019 16:24

With apologies to the mods for the size:
https://cimg2.ibsrv.net/gimg/pprune....59d4ab09b9.jpg



sooty655 4th Apr 2019 16:25


Originally Posted by GarageYears (Post 10438808)
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

The left AOA also appears to correct itself (very briefly) at 05:43:25, and immediately go haywire again. Very strange.

Avionista 4th Apr 2019 16:25

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?

Organfreak 4th Apr 2019 16:27

I'm interested in this "bird (or other) strike." Where did that info come from? Is this a real event? How do we know that, CVR?

GarageYears 4th Apr 2019 16:36


Originally Posted by Avionista (Post 10438837)
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?

Those both occur while the AP was engaged, which is a 'disable' input for MCAS, hence I think we can assume those are STS.

-GY

moosepig 4th Apr 2019 16:40


Originally Posted by mryan75 (Post 10438854)
Link to the preliminary report please...

Post #3187.

T28B 4th Apr 2019 16:48

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.

bill fly 4th Apr 2019 16:48


Originally Posted by Airbubba (Post 10438807)
Narrative of the flight from the preliminary report:

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.

mryan75 4th Apr 2019 16:50

I owe the first officer, Ahmed Nur Mohammod, a true and heartfelt apology. He called the stab trim cutout and performed admirably. Two-hundred hours or not, he did his job well.

infrequentflyer789 4th Apr 2019 16:55


Originally Posted by GordonR_Cape (Post 10438822)
Some very strange error messages, not just AOA offset:

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:

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.
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?

Water pilot 4th Apr 2019 16:56


Originally Posted by sooty655 (Post 10438836)
The left AOA also appears to correct itself (very briefly) at 05:43:25, and immediately go haywire again. Very strange.

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?

LaissezPasser 4th Apr 2019 17:01


Originally Posted by GarageYears (Post 10438808)
Had they trimmed sufficiently and hit the cutouts, we'd not be have this exact discussion.

But they trimmed repeatedly and did hit the cutouts. From the preliminary report:


Originally Posted by Airbubba (Post 10438807)
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


GarageYears 4th Apr 2019 17:04


Originally Posted by LaissezPasser (Post 10438889)
But they trimmed repeatedly and did hit the cutouts. From the preliminary report:

I suggest you look at the FDR traces and then tell me what you think. I did...

- GY

GoodTimes 4th Apr 2019 17:05

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.


All times are GMT. The time now is 08:25.


Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.