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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 4th Apr 2019, 19:37
  #3161 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
Except that trim did move slightly (as expected given short blips) and the FDR shows the switch activation directly, 2 short blips about 5s apart.
Yeah, from 2.1 to 2.3 units, I know.

It could very well be that the initial blip moved the trim slightly and then stopped, they released and try again but no avail. Each square in the FDR is 3 seconds, so the second "short" blip is 2s or so. Between the two, looks to me in the 3s area. (one full square) Let's say 2.5 to be safe.

The final AND input by MCAS was 5s and moved 1.3 units. The last pilot input ANU was 2.5s (combined) and moved 0.2 units. Something odd is there.

It is a theory, I could be mistaken. But it's plausible to my eyes.
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Old 4th Apr 2019, 19:38
  #3162 (permalink)  
 
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Originally Posted by GarageYears View Post
Later two very short pickle switch inputs NU were input indicating the crew re-engaged the electric trim, but they were very short and had a very small effect on trim.
I am struggling to see any effect, and I didn't see any other indication in the report that the crew re-engaged.

I suspect that cutout switch position is not directly recorded and has to be inferred, possibly this is where the rumours of disagreements and CVR reading problems originate from - maybe there are sounds or speech on the CVR that could indicate re-engagement but it isn't definite, or agreed. Any reference to the disputed sounds may then have been excised from the report.

5 seconds later MCAS, having been reset by the crew electric trim input, and now being active again, ran for less than 10 seconds and seems to have been interrupted by the Left AOA value changing.
This MCAS signal got through, which some will take as proving the switch position was changed, there is so much else going wrong not sure I would agree (that it is proven). Also, this still doesn't look right per the descriptions we've had:
- MCAS is supposed to have less authority at higher speed (maybe that's it, it is shorter input?)
- If AOA reduces then MCAS is apparently supposed to put the trim back up, if no pilot trim input - yet there isn't and it doesn't
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Old 4th Apr 2019, 19:39
  #3163 (permalink)  
 
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Re: The FDR plot

Note the call-out box which states "Automatic Trim Command With No Change In Pitch Trim". However, there is another downwards blip of automatic trim command shortly before the crash, which clearly causes more nose-down trim. This must be the result of the MCAS being re-enabled. For some reason, the CVR transcript does not say so, but the pilots must have re-enabled the Cutout Switch.
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Old 4th Apr 2019, 19:43
  #3164 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
Gets back to the question of why 2 short blips instead of continuous until collum force approaches neutral?
Could be a DFDR artefact. On another aircraft type I am more familiar with a continuous blip when the trim motor does not run just poles the DFDR data flag on and off again. This single pole will appear as a spike when graphed.

In the accident graph the 2 final electric trim blips do not appear to move the pitch trim, either due to cutout or aerodynamics overcoming the drive.
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Old 4th Apr 2019, 19:50
  #3165 (permalink)  
 
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Originally Posted by ecto1 View Post
Yeah, from 2.1 to 2.3 units, I know.

It could very well be that the initial blip moved the trim slightly and then stopped, they released and try again but no avail. Each square in the FDR is 3 seconds, so the second "short" blip is 2s or so. Between the two, looks to me in the 3s area. (one full square) Let's say 2.5 to be safe.

The final AND input by MCAS was 5s and moved 1.3 units. The last pilot input ANU was 2.5s (combined) and moved 0.2 units. Something odd is there.

It is a theory, I could be mistaken. But it's plausible to my eyes.
Unfortunately the plot has artificial slopes on binary events so without the raw data is hard to tell the actual length of short inputs so the total 'blip' could be significantly less than 2.5s.

Interesting idea that when they tried the electrical trim the system stalled so they tried again, hard to tell without raw data and CVR though.
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Old 4th Apr 2019, 19:51
  #3166 (permalink)  
 
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Originally Posted by infrequentflyer789 View Post
This MCAS signal got through, which some will take as proving the switch position was changed, there is so much else going wrong not sure I would agree (that it is proven). Also, this still doesn't look right per the descriptions we've had:
- MCAS is supposed to have less authority at higher speed (maybe that's it, it is shorter input?)
- If AOA reduces then MCAS is apparently supposed to put the trim back up, if no pilot trim input - yet there isn't and it doesn't
AFAIK MCAS uses the same rate of nose down trim of 0.27 units per second, it is the duration that varies, with a maximum of 9 seconds.
MCAS will 'unwind' the trim only when the AOA reduces below the 10 degree threshold, not when AOA reduces relative to its previous value.
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Old 4th Apr 2019, 19:52
  #3167 (permalink)  
 
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Originally Posted by Albino View Post
[ [Stab trim cutout switches.] Turned back on again contrary to advice (accept this is speculation at present) and the system was allowed to trim forward again.
Unless I misread the preliminary report, it appears that the "advice" that was followed was that of the FO, who advised that manual operation of the trim wheels was not possible. It's fairly easy to understand why the crew decided to flip those switches back on (if they did).
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Old 4th Apr 2019, 19:56
  #3168 (permalink)  
 
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Questions after reading the report

The preliminary report leaves me with several questions:

Shortly after Takeoff the Captain who was pilot flying had stick shaker on his side only. Why not transfer control to the first officer at this point or at least a little while later? That is actually what the Captain of the Lion Air flight previous to Lion Air 610 flight did. If you see that there is stick shaker on your side but not on the other wouldn't it make sense to rely on the FCC B side in this case? Why engage the autopilot on the A side that has the stick shaker? The captain tried to engage Autopilot A two times unsuccessfully at 400 Ft and 630 Ft. That would be another indication to either continue manually or at least try the other side. Finally he succeeded in turning the autopilot A on at 1000 Ft (for 33 seconds). Possibly Autopilot B would have worked since it seems like there was no false sensor indications on that side an MCAS would not have activated (speculation).

Based on the report the situation for ET302 was basically exactly the same as for Lion Air 610. Stick shaker right after Takeoff and then as the flaps were retracted MCAS started trimming the nose down.

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.

Knowing about the Lion Air Accident as the ET302 crew must have, were they expecting the nose down trim as they retracted the flaps? Based on their actions it seems like they did not even though the circumstances were the same. Would this not have been the point to carry out the runaway stab trim memory items?

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.

Instead the crew trimmed the aircraft nose up from 2.1 units back to 2.4 units. Why not trim back to the original 4.6 units before MCAS engaged so that it isn't necessary to increase back pressure on the column? Some people on this forum suggest the electric trim switch will not work sufficiently against MCAS. The preliminary report on Lion Air 610 shows otherwise as they countered MCAS up to 30 times.

By now we know that MCAS activates again 5 seconds after the electronic trim switches have been used. They were used by the crew but apparently only to offset the MCAS trim input to a small degree and now MCAS starts trimming the nose down again:

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.

This time the crew did trim against MCAS from 0.4 units back to 2.3 units therefore basically reversing the input from MCAS and showing that this is possible.

Now the First Officer suggested to set the stab trim cut out switches to cut out and MCAS was stopped.

Would it have been possible at this point to reduce the power and then trim the aircraft manually?
At the time the crew did try to trim the aircraft manually the aircraft was flying at the edge of it's envelope at 340 Knots according to the left side or outside of it already at 365 according to the right side. I am not surprised that at this point it was not possible to trim manually anymore.

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.

Since the crew said at 05:41:46 that electric trim did not work and now it was possible for them to trim electrically again it is likely that the stab trim switches were set back to their original position before being set to cut out. Aside from not reducing the power even when there was the overspeed warning, why did the crew not trim continuously as they did before in order really raise the nose? Also why did they then not set the stab trim switches back to cut out since it was to be expected that MCAS would engage again 5 seconds after release as it did before?

I am not judging the pilots or saying the same thing could not have happened to me. I am just asking myself these questions based on what I have read.

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Old 4th Apr 2019, 20:06
  #3169 (permalink)  
 
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Originally Posted by Takwis View Post
Here are the memory items for "Runaway Stabilizer":

I. Runaway Stabilizer
  1. CONTROL COLUMN - HOLD FIRMLY
  2. AUTOPILOT (if engaged) - DISENGAGE Do not re-engage the autopilot. Control airplane pitch attitude manually with control column and main electric trim as needed
    If the Runaway Continues
  3. STAB TRIM CUTOUT SWITCHES (both) - CUTOUT
  4. If the Runaway Continues
  5. STABILIZER TRIM WHEEL - GRASP and HOLD
Since the condition before step three says, "If the Runaway Continues", I would infer that at that point the aircraft is no longer in trim. Could you identify for me which subsequent step would put it back into trim?
It is looking very likely that moving the trim wheel with the trim set too far nose down is not physically possible, especially at high airspeed. As a last desperate measure, they tried something that wasn't in the checklist.
Step 2 - Control airplane pitch attitude manually with control column and main electric trim as needed.

Was this step done? 2 units is nowhere near in trim and significant control column input would've been needed. Full stabilizer authority was available to the pilots using the electric trim.

If runaway continues... I'd argue people are getting hooked up on semantics here. You can't put a long winded paragraph in covering every eventuality. The system is still not performing as expected so you cut out the stabs, ensuring step 2 is complete and the aircraft is in trim.

The bulletin Boeing sent to all operators and should have been read by all pilots was very clear on this point in 'Operating Instructions'.


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Old 4th Apr 2019, 20:06
  #3170 (permalink)  
 
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737mgm

That would be another indication to either continue manually or at least try the other side. Finally he succeeded in turning the autopilot A on at 1000 Ft (for 33 seconds). Possibly Autopilot B would have worked since it seems like there was no false sensor indications on that side an MCAS would not have activated (speculation).

Based on the report the situation for ET302 was basically exactly the same as for Lion Air 610. Stick shaker right after Takeoff and then as the flaps were retracted MCAS started trimming the nose down.
There is a subtle but perhaps crucial difference between the flights. With Lion Air 610 the autopilot was never engaged, and MCAS activated as soon as the flaps retracted. With ET302 the autopilot was engaged before flaps were retracted, and remained engaged for a few seconds longer, during which time MCAS was inhibited. The trigger for MCAS activation was autopilot disengage, not flaps retraction.

Cognitively this is a very different situation, and focusing on why the autopilot disengaged may have been a distraction from the MCAS activation. Conversely flaps retraction is a non-event cognitively, and more attention could have been given to MCAS activation. I do not know whether any of this is relevant, but it is perhaps important to see the whole sequence of events.
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Old 4th Apr 2019, 20:22
  #3171 (permalink)  
 
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Are pilots not used to using those thumb/pickle switches too much? Or perhaps trained to just blip/use sparingly?
It seems we’ve seen two crews (FO on Lion and now on ET) appear to just “blip” when more extended engagement might have been better?

Is there any reason they might be reluctant to go hard and extended on that thumb switch? I mean, if I saw it appear to counter that bad trim, I’d be jumping on it with both feet!

Just wondering why the apparently sparing use of the switch which had potential to correct trim....?
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Old 4th Apr 2019, 20:22
  #3172 (permalink)  
 
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Originally Posted by OldnGrounded View Post
Unless I misread the preliminary report, it appears that the "advice" that was followed was that of the FO, who advised that manual operation of the trim wheels was not possible. It's fairly easy to understand why the crew decided to flip those switches back on (if they did).
I don't disagree and I'd have probably done the same. Surely the moment they were back on though you'd be trimming hard?

From the narrative it sounds as if the Capt hasn't grasped what is happening and it's a suggestion from the FO to cut the switches out in the first place. So when they turn them back on is he 'in the loop'?
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Old 4th Apr 2019, 20:24
  #3173 (permalink)  
 
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Originally Posted by patplan View Post
That's the first time I've read about the nationality of the deadhead who'd hitchhiked Flight JT043... Care to show us your source?
There are multiple reports suggesting that the deadheading pilot was a Batik Air captain. I haven't seen any that mentioned their nationality, and I note that the poster who suggested it was a Brit hasn't come back with any confirmation of that.
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Old 4th Apr 2019, 20:25
  #3174 (permalink)  
 
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Originally Posted by Takwis View Post
How can the airplane be in trim AFTER a continued runaway? How do you know it is running away if it is not moving away from a trimmed condition?
In Mentour Pilot's video he demonstrates the process in the simulator. If (big IF) runaway trim is detected and stopped quickly enough, the aircraft is still flyable. AFAIK there is no specific term for that situation, in which it is not perfectly trimmed, and significant yoke forces are required to keep the nose level. It is also not so out of trim, that yoke forces cannot keep the nose level, and the aircraft goes into a dive. In/out are not absolutes,
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Old 4th Apr 2019, 20:36
  #3175 (permalink)  
 
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I surmise: killed by airspeed. By the time the cut-out switches were used it was already too late for nose up by any means.
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Old 4th Apr 2019, 20:42
  #3176 (permalink)  
 
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A couple things I drew from the report:

At no time did they reduce power. The airplane would be MUCH more sensitive to pitch commands as it neared VMO, hence much less controllable in the out-of-trim condition. IF the autothrottle was still engaged, they did NOT follow the non-normal procedure (Step 3) for Runaway trim.

At no time did they get the pitch trim back near an in-trim position. Granted, less nose-up trim would be needed at the high speed, but they continued to use aft column force in lieu of more trim.

It is unclear when/if they returned the Stab Trim Cutout switches to the Normal position at the 5:43:11 point. We may see that later IF there is a FDR trace for those switch positions. However, IF one or both of the Cutout switches were returned to normal, why was there NO yoke trim input after that? If I were to try that last-ditch move of re-engaging the stab trim, I would FIRST hold the yoke trim switches to the nose-up position...
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Old 4th Apr 2019, 20:54
  #3177 (permalink)  
 
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Seattle Times article

Ethiopian pilots fought the 737 MAX flight controls almost from take-off, preliminary report shows

Video at the link.

April 4, 2019 at 11:59 am Updated April 4, 2019 at 1:26 pm

https://www.seattletimes.com/busines...ight-controls/
By Dominic Gates
Seattle Times aerospace reporter

The preliminary investigation into the crash of Ethiopian Airlines Flight 302 last month reveals that pilots began fighting against the Boeing 737 MAX’s new automatic flight control system barely a minute after leaving the ground, after a sensor failed immediately on take-off.

Boeing Chief Executive Dennis Muilenburg issued a statement Thursday from the Renton 737 factory expressing “the immense gravity of these events across our company,” and acknowledging the role the new Maneuvering Characteristics Augmentation System, or MCAS, played in the crash.

He pointed to the software fix and associated pilot training Boeing is working on.

“As pilots have told us, erroneous activation of the MCAS function can add to what is already a high workload environment. It’s our responsibility to eliminate this risk,” Muilenburg said. “We own it and we know how to do it.”

The “black box” flight recorder data shows that after MCAS swiveled the plane’s horizontal tail to push the nose sharply down three times in succession, the pilots hit the cut-off switches stopping the automatic action and tried to adjust the tail manually, according to the report by the Accident Investigation Bureau of Ethiopia’s Transport Ministry.

In doing so, they were following instructions provided by Boeing last November, following the crash of Lion Air Flight 610, on how to deal with such an inadvertent triggering of the new flight control system.

Ahead of the release of the full report, Ethiopian Transport Minister Dagmawit Moges held a news conference in the capital, Addis Ababa, that was almost entirely focused on vindicating the actions of the pilots. “The crew performed all the procedures repeatedly provided by the manufacturer but was not able to control the aircraft,” she said.

The report says that while trying to follow Boeing’s directions, about three minutes into the flight, the two pilots found that the manual system for moving the horizontal tail — also known as the stabilizer — “was not working.” This meant they couldn’t move the large stabilizer wheel in the cockpit that is connected via cables to the tail.

Flight-control experts told The Seattle Times earlier this week that was probably because the forces on the tail of the plane moving at high speed made it next to physically impossible to move the stabilizer wheel as Boeing had recommended.

All the while, the control column “stick shaker” was vibrating the control column, and various messages were telling the pilots and that their airspeed, altitude and pitch readings were unreliable. Two minutes into the flight, losing altitude, an audible warning sounded that the plane was too close to the ground: “Don’t Sink!”

About four minutes into the flight, the pilots gave up on the manual stabilizer wheel and switched the electric power to the tail back on, then used the thumb switches on the control column to pitch the nose back up.

But just five seconds later, MCAS kicked in again and once more pushed the nose sharply down.

Just 35 seconds later, six minutes after take-off, the plane rolled over before plowing into the earth in a “high energy impact” at a speed of approximately 575 miles per hour.

This sequence of events was triggered by the failure of the left angle-of-attack sensor on the outside of the fuselage, just 44 seconds after take-off, the data shows.

There are two such sensors one, either side of the aircraft, that measure the angle between the wing and the airflow. Only one is used to trigger MCAS. The data shows that both sensors showed normal readings on the ground during the take-off roll but deviated immediately after lifting off and in less than a minute were divergent by 60 degrees.

Ethiopian Airlines issued a statement Thursday backing the Flight 302 pilots, saying that they “followed the Boeing recommended and FAA approved emergency procedures to handle the most difficult emergency situation created on the airplane.”

“Despite their hard work and full compliance with the emergency procedures … they could not recover the airplane from the persistence of nose diving,” the statement added.

Boeing CEO Muilenburg said while the Ethiopian and Lion Air “tragedies continue to weigh heavily on our hearts and minds,” Boeing remains “confident in the fundamental safety of the 737 MAX.”

“When the MAX returns to the skies with the software changes to the MCAS function, it will be among the safest airplanes ever to fly,” he said.
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Old 4th Apr 2019, 20:58
  #3178 (permalink)  
 
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Shit!

Just a few observations.
I have read a few hundred Accident reports and this one is one of the scariest!
Why did this Cpt select AP on, with stickshaker going?
Why did he retract flaps when he knew there was a 50/50 chance the MCAS would go off.
Why did he not set a reasonable pwr setting so as to not accelerate out of control?

Must have been confusing for him?

As for Boeing Max
It will never fly again without serious modifications!
Cpt B
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Old 4th Apr 2019, 20:59
  #3179 (permalink)  
 
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What caused the bogus airspeed readings in that scenario?
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Old 4th Apr 2019, 21:03
  #3180 (permalink)  
 
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Shortly after Takeoff the Captain who was pilot flying had stick shaker on his side only. Why not transfer control to the first officer at this point or at least a little while later?
As as been pointed out many times, the first officer was fairly inexperienced. So imagine that you are an experienced captain in a plane on takeoff that has a fault which you have never seen before. How quickly would you hand your life over to the greenhorn?
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