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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 27th Nov 2018, 22:14
  #1701 (permalink)  
 
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Digital world

I still wonder how the MCAS trim down logic was certified based on a single AOA input. Even if this has a reason that is buried somewhere between FAA and Boeing, there are plenty of other sensors/data available that could help the MCAS computer to determine it shall better not trim down, like pitch, roll, radio height, gps vertical rate, ground speed, you name it.

We build autonomously driving cars with amazing intelligence identifying objects and doing some kind of plausbile action. But we cannot program a simple logic for a commercial aircraft that carries 200 people that says: when pitch is normal AND there is no excessive bank AND at 5000 ft radio height AND at 300 kts ground speed, this MCAS system better does not push, but presents a caution about implausible sensor data? No, we can't, because of certification grandfather rights thinking. Just touch what's absolutely necessary.

This fits perfectly into the picture that an AOA disagree indicator is sold as an option, i.e. Boeing tries making money by upselling a safety feature, and the FAA grants them doing so.

​​​​A trim runaway is always a serious incident. Just saying, there is the pilot as a backup, he just needs to run the memory items and all is good, is too easy. This thinking is out of time. The age of analog heros is over, we live in a digital world. Hundreds of complex rules of ANDs and ORs and IFs on a digital flight deck are overwhelming human beings. The digital system must help itself, at least to some extent.
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Old 27th Nov 2018, 22:39
  #1702 (permalink)  
 
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Seattle Times Nov 27

Lion Air pilots struggled against Boeing’s 737 MAX flight-control system, black box data shows

[emphasis mine]

...The data shows that after this cycle repeated 21 times, the captain ceded control to the first officer and MCAS then pushed the nose down twice more, this time without a pilot response.
After a few more cycles of this struggle, with the horizontal tail now close to the limit of its movement, the captain resumed control and pulled back on the control column with high force.
It was too late. The plane dived into the sea at more than 500 miles per hour.
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Old 27th Nov 2018, 22:41
  #1703 (permalink)  
 
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Flaps

One other thought: MCAS is active with flaps up only. The pilots cycled the flaps after the first couple of MCAS trim downs for a reason. There was the perception that the trim downs started when flaps were up. So, they found out some kind of logic. If the system logic had been known to them (Flaps up, MCAS on - Flaps dn, MCAS off), i.e. if they had been informed or trained to understand the MCAS system, they most probably would have associated this logic with MCAS, then set flaps and return.
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Old 27th Nov 2018, 23:03
  #1704 (permalink)  
 
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Originally Posted by Derfred View Post
I don’t share your memory. I have not seen any reports from the 2 flights before.
I’m sure the investigators are looking at those flights, but so far, no leaks to my knowledge.
I have a recollection that at an early media conference investigators said for the sector into Denpassar the pilots had no airspeed data showing the whole flight.
We more or less know what happened after that flight landed.
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Old 27th Nov 2018, 23:14
  #1705 (permalink)  
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wiedhopf #1703

https://www.pprune.org/attachments/r..._knkt_data.pdf


Following a period of high fuel low there seems to be a varied median followed by a burst and later by a huge flow at time of final ascent. Given the new engine power and position, my guess is the pitch up would have been more than expected - just adding another stress factor to those last seconds.

The metered reduction of the flow trace after the peak is difficult to understand.
.
.

Last edited by Loose rivets; 27th Nov 2018 at 23:39.
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Old 28th Nov 2018, 00:31
  #1706 (permalink)  
 
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Re: number of previous flights with UAS:

It would be excellent if people would provide documented sources, rather than fallible memory and conjecture. This took all of 5 seconds to find on Google news.

https://www.theguardian.com/world/20...t-four-flights

The head of Indonesia’s National Transportation Safety Committee (KNKT) , Soerjanto Tjahjono, told reporters the Boeing 737 Max plane had suffered similar problems on its last four routes, according to information downloaded from its flight data recorder.

“When we opened the black box, yes indeed the technical problem was the airspeed or the speed of the plane,” Tjahjono said.

“Data from the black box showed that the two flights before Denpasar-Jakarta also experienced the same problem,” he said.

“In the black box there were four flights that experienced problems with the airspeed indicator.”
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Old 28th Nov 2018, 05:27
  #1707 (permalink)  
 
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Originally Posted by Rated De View Post
Would seem a little simplistic to let the manufacturer off the hook just yet.
But pulling back and or using electric trim did APPEAR to stop runaway - for 5 to 10 seconds - thus adding to the confusion...
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Old 28th Nov 2018, 05:39
  #1708 (permalink)  
 
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Originally Posted by CONSO View Post
But pulling back and or using electric trim did APPEAR to stop runaway - for 5 to 10 seconds - thus adding to the confusion...
Yes that appears the point.
Not knowing this system was embedded in the aircraft's architecture is one thing. Given the crew may have expected a possible airspeed disagree, it is plausible that they never knew what was at play.
It is very easy to sit there like that idiot Bryon Bailey did and blame a crew.
Imagine a crew working their darnedest to save an aircraft that did its level best to kill everybody, and never knowing what the problem was, nor the system causing it, for the manufacturer and the regulator deemed it not necessary to tell them.
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Old 28th Nov 2018, 06:39
  #1709 (permalink)  
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Originally Posted by Rated De View Post
Yes that appears the point.
Not knowing this system was embedded in the aircraft's architecture is one thing. Given the crew may have expected a possible airspeed disagree, it is plausible that they never knew what was at play.
It is very easy to sit there like that idiot Bryon Bailey did and blame a crew.
Imagine a crew working their darnedest to save an aircraft that did its level best to kill everybody, and never knowing what the problem was, nor the system causing it, for the manufacturer and the regulator deemed it not necessary to tell them.
Previous crew encountered same problem and dealt with it safely. Th accident crew had the benefit of that experience (from the write up). They also battled the trim for 6 minutes clearly understanding they had a trim runaway. Why they didn't hit the CUTOUT and why after six minutes they could no longer successfully counteract it, is unknown.

Although I read an article that said they swapped to copilot control immediately preceding the dive.
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Old 28th Nov 2018, 06:41
  #1710 (permalink)  
 
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Originally Posted by Loose rivets View Post
That would be a newspaper that probably got its data from hear. Possibly. Allegedly.
No. That was a direct quote from the head of Indonesia’s National Transportation Safety Committee, and was reported by numerous other news organizations. I’m sure you can find the press conferece taped online somewhere ass well.

I get the feeling the Airspeed indications were fine according to one log analysis.
Also, no. Look closer. There is a slight offset between the pilot and co-pilot’s computed airspeed. Refer to page 7 of the report, the traces labeled “COMPUTEDAIRSPEEEDLFDR” and “RFDR”

http://avherald.com/files/lionair_b3..._knkt_data.pdf

This is one of the expected and published effects of a bad AOA sensor on a 737. The ADIRU uses the angle of attack as one of the inputs to correct the raw indicated airspeed (as directly sensed at the pitot and static ports) for installation and position error, so that it can be used as computed airspeed and dislayed on the PFD.

The pilot and co-pilot’s air data systems and indications are independent. The computed airspeeds are monitored. If there is more than a certain difference beteen the pilot and co-pilot’s airspeed, and you will get the “IAS DISAGREE” message on the PFD. Which is what the head of the KNKT says occured on at least four different flights of this aircraft.
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Old 28th Nov 2018, 07:06
  #1711 (permalink)  
 
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Preliminary report is out.

http://knkt.dephub.go.id/knkt/ntsc_a...y%20Report.pdf

Some quick observations from the report:
From the report on side 12 it shows CC communicating "normally" with the tower just 19 seconds before end of recording/impact with sea. CC stated they could not determine speed nor altitude as all three instruments was indicating different values, this was 45 seconds before impact. Also at 56 seconds before impact the CC made a request due to weather, might they have been in non-visual conditions during the final dive? Truly horryfying reading.

Last edited by SteinarN; 28th Nov 2018 at 08:47.
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Old 28th Nov 2018, 07:08
  #1712 (permalink)  
 
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Originally Posted by gmx View Post
Previous crew encountered same problem and dealt with it safely. Th accident crew had the benefit of that experience (from the write up). They also battled the trim for 6 minutes clearly understanding they had a trim runaway. Why they didn't hit the CUTOUT and why after six minutes they could no longer successfully counteract it, is unknown.

Although I read an article that said they swapped to copilot control immediately preceding the dive.
There were only two pilots that knew precisely what they expected and what was ultimately encountered. Unfortunately, they cannot speak for themselves.
It is presumptuous to suggest they knew of, diagnosed correctly or indeed understood that the likely root cause of their predicament was the MCAS, which from all reports pilots did not know was there.

The pilot and co-pilot’s air data systems and indications are independent. The computed airspeeds are monitored. If there is more than a certain difference between the pilot and co-pilot’s airspeed, and you will get the “IAS DISAGREE” message on the PFD. Which is what the head of the KNKT says occured on at least four different flights of this aircraft.
No pilot (with few notable exceptions) will not fight to save the aircraft. These poor souls did the best they could do. They may well have expected an IASDISAGREE. They may have briefed for it, they may even have had the QRH at hand. No one knows definitively.
What is insidious is the Boeing statement, justifying the lack of information on the MCAS stating that (paraphrased) 'in normal operations the pilots would not know of its existence'.
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Old 28th Nov 2018, 07:16
  #1713 (permalink)  
 
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Boeing is going to cop a lot of flak over this event but the fact remains that
- The aircraft shouldnt have been dispatched in the first place , and probably wouldnt have been anywhere in the US , Europe or Australia etc.
- Disconnecting both stab. trim motors , as per the check-list , would have stopped the event cold.
-Subsequent Airspeed Disagree events etc. were resolvable by flying attitude and thrust and following the checklist.
Its an analogue aircraft,not fly by wire. Digital add-ons are nice to have,not must have.
Pilots are not backup.
Pilots are the first and last back-stop.
Disconnect and fly the the aircraft.
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Old 28th Nov 2018, 08:39
  #1714 (permalink)  
 
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The Preliminary Report (78 pages) linked to above is a very slow download this morning. And many press reports of it are - imho - based on the press releases accompanying it, not the text itself. So, here's the Synopsis section of the English version of the original document (p. vii), followed by the Safety Recommendations (p.27). [NB the translation to English is a tad odd - rushed? - in places]

SYNOPSIS
On 28 October 2018, a Boeing 737-8 (MAX) aircraft registered PK-LQP was being operated by PT. Lion Mentari Airlines (Lion Air) as a scheduled passenger flight from I Gusti Ngurah Rai International Airport (WADD), Denpasar to Jakarta as LNI043. During pre-flight check, the PIC discussed with the engineer of the maintenance actions that had been performed including replacement of the AoA sensor and had been tested accordingly.
The aircraft departed at 1420 UTC (2220 LT) at night time, the DFDR showed the stick shaker activated during the rotation and remained active throughout the flight. About 400 feet, the PIC noticed on the PFD the IAS DISAGREE warning appeared. The PIC handed over control to the SIC and cross checked the PFDs with the standby instrument and determined that the left PFD had the problem. The PIC noticed the aircraft was automatically trimming AND. The PIC moved the STAB TRIM switches to CUT OUT and the SIC continued the flight with manual trim without auto-pilot until the end of the flight.
The PIC declared “PAN PAN” to the Denpasar Approach controller due to instrument failure and requested to maintain runway heading. The PIC performed three Non-Normal Checklists and none contained the instruction “Plan to land at the nearest suitable airport”.
The remainder of the flight was uneventful and the aircraft landed Jakarta about 1556 UTC. After parking, the PIC informed the engineer about the aircraft problem and entered IAS and ALT Disagree and FEEL DIFF PRESS problem on the AFML.
The engineer performed flushing the left Pitot Air Data Module (ADM) and static ADM to rectify the IAS and ALT disagree followed by operation test on ground and found satisfied. The Feel Differential Pressure was rectified by performed cleaned electrical connector plug of elevator feel computer. The test on ground found the problem had been solved.
At 2320 UTC, (0620 on 29 October 2018 LT), the aircraft departed from Jakarta with intended destination of Pangkal Pinang. The DFDR recorded a difference between left and right AoA of about 20° and continued until the end of recording. During rotation the left control column stick shaker activated and continued for most of the flight.
During the flight the SIC asked the controller to confirm the altitude of the aircraft and later also asked the speed as shown on the controller radar display. The SIC reported experienced „flight control problem‟.
After the flaps retracted, the DFDR recorded automatic AND trim active followed by flight crew commanded ANU trim. The automatic AND trim stopped when the flaps extended. When the flaps retracted to 0, the automatic AND trim and flight crew commanded ANU trim began again and continued for the remainder of the flight. At 23:31:54 UTC, the DFDR stopped recording.
Until the publishing of this Preliminary Report, the CVR has not been recovered, the search for CVR is continuing. The investigation will perform several tests including the test of the AoA sensor and the aircraft simulator exercises in the Boeing engineering simulator. The investigation has received the QAR data for flight for analysis.
The investigation involved the NTSB of the United States of America as State of design and State of manufacturer, the TSIB of Singapore and the ATSB of Australia as State provide assistant that assigned accredited representatives according to ICAO Annex 13.

______________

4 SAFETY RECOMMENDATIONS
The KNKT acknowledges the safety actions taken by Lion Air and considered that the safety actions were relevant to improve safety, however there still safety issue remain to be considered. Therefore, the KNKT issued safety recommendations to address safety issues identified in this report.
4.1 Lion Air Lion AirLion Air
04.O-2018-35.1
Refer to the CASR Part 91.7 Civil Aircraft Airworthiness and the Operation Manual part A subchapter 1.4.2, the pilot in command shall discontinue the flight when un-airworthy mechanical, electrical, or structural conditions occur.
The flight from Denpasar to Jakarta experienced stick shaker activation during the takeoff rotation and remained active throughout the flight. This condition is considered as un-airworthy condition and the flight shall not be continued.
KNKT recommend ensuring the implementation of the Operation Manual part A subchapter 1.4.2 in order to improve the safety culture and to enable the pilot to make proper decision to continue the flight.
04.O-2018-35.2
According to the weight and balance sheet, on board the aircraft were two pilots, five flight attendants and 181 passengers consisted of 178 adult, one child and two infants. The voyage report showed that the number of flight attendant on board was six flight attendants. This indicated that the weight and balance sheet did not contain actual information.
KNKT recommend ensuring all the operation documents are properly filled and documented.

__________________END

Last edited by AGBagb; 28th Nov 2018 at 08:41. Reason: Missing link
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Old 28th Nov 2018, 08:44
  #1715 (permalink)  
 
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Originally Posted by George Glass View Post
Boeing is going to cop a lot of flak over this event but the fact remains that
- The aircraft shouldnt have been dispatched in the first place , and probably wouldnt have been anywhere in the US , Europe or Australia etc.
Possibly true, but largely irrelevant, because this could as well have happened on the first flight with the AoA problem.

- Disconnecting both stab. trim motors , as per the check-list , would have stopped the event cold.
There was no checklist for "unexpected MCAS trim", only for runaway trim, which in this case was not applicable, since the MCAS trim inputs could be stopped by pilot trim inputs. That is not runaway. Only Boeing's document and the subsequent EAD made the connection between this behaviour and the "runaway trim" checklist. Which is why using the wording "existing checklist" by Boeing is disingenuous. It's a weasel-word trying to imply that the pilots should have used the checklist, although it was not applicable before now.

Its an analogue aircraft,not fly by wire. Digital add-ons are nice to have,not must have.
That very much depends on how the "analogue" aircraft behaves without digital add-ons. It is likely that, because of the larger engine nacelles, it would have failed certification criteria for longitudinal static stability, so some system was required to restore that stability.

Pilots are the first and last back-stop.
Disconnect and fly the the aircraft.
We don't know if or when they could have diagnosed the problem, not being informed about MCAS at all. Criticising pilot action with our hindsight of what went on is not helpful. It is important to take the "inside view" and try to imagine what they knew, what they saw and heard and what they could have deduced from that in the available time, with a high workload. Which is usually not very much. Even recreating this in the simulator is very different because you already know what is going to happen.

Cheers,
Bernd
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Old 28th Nov 2018, 09:28
  #1716 (permalink)  
 
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Originally Posted by bsieker View Post
SNIP

There was no checklist for "unexpected MCAS trim", only for runaway trim, which in this case was not applicable, since the MCAS trim inputs could be stopped by pilot trim inputs. That is not runaway. Only Boeing's document and the subsequent EAD made the connection between this behaviour and the "runaway trim" checklist. Which is why using the wording "existing checklist" by Boeing is disingenuous. It's a weasel-word trying to imply that the pilots should have used the checklist, although it was not applicable before now.
SNIP

Cheers,
Bernd
From the Synopsis (quoted above) of today's Interim Report, about the previous flight:

The PIC noticed the aircraft was automatically trimming AND. The PIC moved the STAB TRIM switches to CUT OUT and the SIC continued the flight with manual trim without auto-pilot until the end of the flight.

Last edited by AGBagb; 28th Nov 2018 at 09:29. Reason: Layout
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Old 28th Nov 2018, 09:35
  #1717 (permalink)  
 
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'The register' has an article on the report, the comment section is interesting as well!
https://www.theregister.co.uk/2018/1...mcas_lion_air/
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Old 28th Nov 2018, 09:47
  #1718 (permalink)  
 
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Originally Posted by Rated De View Post
No pilot (with few notable exceptions) will not fight to save the aircraft. These poor souls did the best they could do. '.
A simple disconnect of the two electric trim switches would have saved the day. Those switches have been around since the first 737 rolled out of barn circa 1965. Common to 707 and 727.
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Old 28th Nov 2018, 10:02
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Indeed, that is what the previous crew did.
"The PIC moved the STAB TRIM switches to CUT OUT and the SIC continued the flight with manual trim without auto-pilot until the end of the flight. "
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Old 28th Nov 2018, 10:15
  #1720 (permalink)  
 
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Would it be fair to say that the previous crew worked an issue whilst not understanding the nature of the issue? In other words, they thought they had a trim runaway and flicked the stab trim switches. Luck rather than judgement?
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