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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 19th Mar 2019, 13:20
  #2061 (permalink)  
 
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Originally Posted by Nomad2 View Post
The single most powerful control surface on a transport jet is the THS.
Why Boeing would give control of it to a subsystem, like the MCAS is hard to understand.

No amount of hauling (or pushing) on the elevator is going to save you if the THS isn't where it should be.
Yup. that's where Ive been coming from too Nomad, for as long as I've been aware of MCAS
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Old 19th Mar 2019, 13:27
  #2062 (permalink)  
 
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Originally Posted by fizz57 View Post
I notice that in endlessly repeating your point of view you never mention the fact that the pilots were contending with unreliable airspeed and the distraction of a stick shaker. Care to illuminate us on why?
I have read the reports. There was nothing mentioned about unreliable airspeed. All 3 airspeed indicators appear to have matched. The press has said airspeed but they confuse it with AOA and the pilot report he made probably because of the stickshaker. As any pilot should know the stickshaker or stall warning is generated off the AOA probe. They had it because the AOA was damaged. Twice I have had the stick shaker activate at rotation because the AOA probe on the left side was damaged by jetways. Not a big deal. Cross check airspeed and flap/slat configuration and continue.
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Old 19th Mar 2019, 13:29
  #2063 (permalink)  
 
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Rated De, #2058,
Self-regulation is only as good as its oversight.
With drift, 'assumption precession', deviance in both design and regulation, culminate in lower safety standards.

A good time to look at other things. Trim? Electric pitch trim could suffer ‘jack stall’ if similar to previous 737; what if the changes to the max adds the risk of manual ‘jack stall’, the inability to apply sufficient force via the trim wheel with large offsets - tail arm, changed mechanics, alternative cable runs,…

Subtle language shifts …’, not forgetting misuse of language - culture, or ‘a dominant culture’?
https://www.dropbox.com/s/7425e8yykg...20%2B.pdf?dl=0
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Old 19th Mar 2019, 14:10
  #2064 (permalink)  
 
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Ian W, #2055, you, and others assume that the vane is the source of error; this may be based on the FDR readout, but without knowing the origin of the FDR value - vane, digital bus, output of a computation, there could be alternative sources for the error.

Thus consider alternatives for erroneous AoA, specific to the 737 Max - wiring, interaction, software.
Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

If a viable alternative is established or even if only likely (difficult to find a intermittent fault amongst the wreckage), then all Max aircraft will require inspection - if only we know what to look for.
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Old 19th Mar 2019, 14:20
  #2065 (permalink)  
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Originally Posted by Sailvi767 View Post


I have read the reports. There was nothing mentioned about unreliable airspeed. All 3 airspeed indicators appear to have matched. The press has said airspeed but they confuse it with AOA and the pilot report he made probably because of the stickshaker. As any pilot should know the stickshaker or stall warning is generated off the AOA probe. They had it because the AOA was damaged. Twice I have had the stick shaker activate at rotation because the AOA probe on the left side was damaged by jetways. Not a big deal. Cross check airspeed and flap/slat configuration and continue.
IAS disagree is a probable caution when you have an AOA disagree.

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Old 19th Mar 2019, 14:29
  #2066 (permalink)  
 
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Originally Posted by PEI_3721 View Post
Ian W, #2055, you, and others assume that the vane is the source of error; this may be based on the FDR readout, but without knowing the origin of the FDR value - vane, digital bus, output of a computation, there could be alternative sources for the error.

Thus consider alternatives for erroneous AoA, specific to the 737 Max - wiring, interaction, software.
Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

If a viable alternative is established or even if only likely (difficult to find a intermittent fault amongst the wreckage), then all Max aircraft will require inspection - if only we know what to look for.
Well true.
But it is obviously not happening in the worldwide fleet of NG and other 737 or failures would be too common to even think of using a single source of data.
So what in the chain of electronics from the vane to the ADIRUs and MCAS is different in the MAX - something has increased the AoA sensor failure rate.
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Old 19th Mar 2019, 14:48
  #2067 (permalink)  
 
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Originally Posted by Ian W View Post
For a safety system it makes no sense to have a 'single point of failure' this is a sine qua non of any safety related engineering. MCAS is obviously a safety system and (despite disparaging comments here) Boeing engineers will not have deliberately chosen to make it unreliable. So this begs a question.
First there are a LOT of 737's flying; from Wikipedia:

A large number of those 737 (if not all) will have the same AoA feeding similar ADIRU and will get an Unreliable Airspeed alert plus stick shaker if AoA disagree. Out of 50 or so Max 8 they have already had two errors only months apart. If that was the rate in the whole fleet there would be continual unreliable airspeed reports and no engineer in their right mind would hang a safety system onto a single AoA if they were that unreliable. From that one can only assume that AoA is normally very reliable to the extent that failures are very rare on previous 737 models.
So the question is - why are the AoA systems on 737Max8 failing at a rate higher than acceptable? Is this just a sad coincidence that when a safety related system is designed to use the AoA output - two failures arise in 6 months -or- is there something different about the Max that is leading to AoA problems?

Even 'ramp rash' could be affected by the different position of the engines when push crews and catering used to NG have to work with the Max.

Any thoughts?
There are at least two incidents involving B38M operated by SWA, and perhaps, one more related incident involving Sunwing Airlines.

=======================
Incidents 1 & 2:
Southwest Replaced Flight-Control Sensors of the Kind Implicated in Lion Air Crash
Investigators are examining how Boeing heeded earlier warnings about flight-control-sensor failures similar to the one implicated in 737 MAX crash

During the three weeks before Lion Air Flight 610 plunged into waters off Indonesia, Southwest Airlines Co. replaced two malfunctioning flight-control sensors of the same type that has been publicly implicated in the crash, according to a summary of Southwest maintenance records reviewed by The Wall Street Journal.

Both U.S. maintenance issues involved a Boeing Co. 737 MAX 8, the same model that crashed last month in Indonesia. The sensors measure whether the jetliner is angled above or below level flight. Those sensors, or related hardware, needed repairs in the Southwest instances, according to the summary document. The document also indicates Southwest pilots reported they couldn't engage automated throttle settings, similar to cruise control on a car.

A Southwest spokeswoman said the sensors didn't fail and were removed as a precautionary measure as part of a troubleshooting process. She said at least one was repaired...

[note: similarity to what had been reported anonymously on NASA's ASRS database.]


Incident 3 :
Sunwing 737 Max suffers spurious indication incident
Canadian investigators have disclosed that engineers replaced an air data computer on a Sunwing Airlines Boeing 737 Max 8 after the crew received spurious indications from the aircraft's instruments. Transportation Safety Board of Canada says the aircraft had been cruising at 35,000ft when the crew received "erroneous" indications on the captain's side. The first officer's instruments, and the standby indicators, were functioning normally and the first officer took control of the aircraft.

It descended to 25,000ft as a precaution, in order to clear instrument meteorological conditions, but "as it passed 28,000ft" the weather radar and TCAS both failed. The aircraft was some 50nm north-west of Washington DC at the time. The crew transmitted a "pan pan" urgency call. The safety board says a left-side inertial reference system fault light also illuminated. he flight continued to Toronto for a safe landing without further incident.

The Canadian TSB reported the left ADIRU was replaced before the plane returned to operation.
===================


Lion Air PK-LQP had various failures during its last four flights. The first flight DPS-MDC had Air Speed Indicator trouble. The second flight MDC-DPS had IAS problem persisted. AOA vane was replaced at DPS by the MX. The third flight, DPS - CGK, still had IAS problem but it also had additional problems: CAPT stick shaker, CAPT ALT AND STS trimming the opposite way [as the CAPT described it - actually it was the ghostly MCAS awakened from its slumber], but at least FO instruments were still reliable. The FO got the control and flied the AC manually and landed in CGK.

On the last fateful flight CGK-PGK, the problem got even worse, NONE of the instruments agreed, and of course MCAS compounded the crisis by faithfully following its mandated duty - executing a NOSE DOWN infinite loop.

I think problems which gotten worse over time seemed to point to a much deeper problem than just AOA vanes. Like what had happened to Sunwing, Lion Air PK-LQP problems might have been caused by the identical source: its left ADIRU.

Last edited by patplan; 19th Mar 2019 at 15:06. Reason: typo
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Old 19th Mar 2019, 14:48
  #2068 (permalink)  
 
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Originally Posted by Just This Once... View Post


Quite simply none of this is true in any sense.
Yet several crews were n the US have done exactly that as well as the previous Lion Air crew.
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Old 19th Mar 2019, 14:51
  #2069 (permalink)  
 
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HI Folks Its Yanrair here again. Just for info. I have flown the B737 several variants over twenty + years, and, have flown it in Manual Reversion with only a 24 v battery powering the plane. IT IS A MECHANICAL AIRCRAFT WITH COMPUTERISED OVERLAYS AND IT FLIES WITHOUT THEM. Actually very well.
The pilot is connected to the main controls directly with a wonderful thing called Fly By Wire - stainless steel wire 12mm thick! Not an amp or a volt in sight.
It is the only modern aircraft that can still do this. And that is one of its greatest strengths the in my view.
I flew many times as a certified flight tester on the 737 on behalf of XXX. Now, the point being missed here in hundreds of posts is that it is focusing on technical issues to do with MACS. And is becoming terribly geeky and academic about flight control laws and computers. It is nor focussing on the primary cause of why a crash was not avoided even given some technical issues. If you can fly a 737 with literally nothing working but a little 24 v battery - and the MAX is as far as I know no different, how come these two crashed? All you do on a 737, and not to be too technical - we used to say, if you utter the words 'what the f!!**! is it doing now?' ( ie Don't understand why plane is behaving the way it is and you don't like it) then turn off the autopilot, switch off the 'Jesus' switches (STAB TRIM) and fly manually straight and level until you have found out what is wrong.
OK, like Sully, I am a little older than some of the newer pilots, but perhaps this is where we should be looking? Not at a spurious input by a computer that could have been over-ridden. There is a massive attempt after every accident to muddy the waters so as to avoid legal issues and distribute the blame elsewhere. Which can be very sad if it doesn't get to the root cause.
In case you think that if it's not the plane, then it must be the pilots, that is not necessarily the case. A pilot is the end product of a massive training program and it is the quality of that training program that delivers the pilots.
Hope this helps to focus us a little more away from algorithms and more towards a possible cause - human factors.
Cheers - I enjoy this thread and am amazed at the in depth technical knowledge of many contributors.
It is just that most crashes, like the Everglades which was caused by poor airmanship and a faulty light bulb, are not that complicated.

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Old 19th Mar 2019, 14:52
  #2070 (permalink)  
 
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Originally Posted by Interflug View Post
So we stay at about 1 billion US $ for lost lives. Plus another 1-2 billion payments to customers for lost revenue due to the grounding.
Versus 600 billion US $ for Boeing's backlog for the 737 MAX?
I am in no way trying to defend Boeing here but pls don't mix up turnover and profit. The latter is somewhere between 6-10% of the former in real life and earned only over quite a number of years (bookkeeping tricks aside) where a lot can still happen.
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Old 19th Mar 2019, 15:17
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As noted in the numerous reports filed by pilots on very similar incidents, they simply turned off the autopilot.

The inherent difference here is the use and dependence on the AP.
As noted by one pilot, he usually doesnt engage it on until FL10, when he did, the ac began to squawk. Simply turning it off returned the ac to normal.

Perhaps this is why there are not as many incidents in more congested airspace, the ac is actually being flown. There are very few RNAV DEP.
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Old 19th Mar 2019, 15:21
  #2072 (permalink)  
 
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Originally Posted by patplan View Post
There are at least two incidents involving B38M operated by SWA, and perhaps, one more related incident involving Sunwing Airlines.

=======================
Incidents 1 & 2:
Southwest Replaced Flight-Control Sensors of the Kind Implicated in Lion Air Crash
Investigators are examining how Boeing heeded earlier warnings about flight-control-sensor failures similar to the one implicated in 737 MAX crash <<SNIP>>
Incident 3 :
Sunwing 737 Max suffers spurious indication incident
The crew transmitted a "pan pan" urgency call. The safety board says a left-side inertial reference system fault light also illuminated. he flight continued to Toronto for a safe landing without further incident.

The Canadian TSB reported the left ADIRU was replaced before the plane returned to operation.

<<SNIP>>
===================
I think problems which gotten worse over time seemed to point to a much deeper problem than just AOA vanes. Like what had happened to Sunwing, Lion Air PK-LQP problems might have been caused by the identical source: its left ADIRU.
That is what I was talking about.
From a very low 'improbable' level of failure there is suddenly a significant failure rate. Something has changed between the NG and the Max, and that something needs attention.
That is on top of ensuring that crews are up to speed in dealing with the subsequent failures and cacophony of warnings.
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Old 19th Mar 2019, 15:26
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Not surprisingly the EASA issued a statement today that the would not let the Max 8 fly again just because the FAA declares the software patch to be safe.
They will most probably look into the whole certification process. This could take a while and also mean that the final accident reports must be on the table before European Airspace is open for the Max again.
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Old 19th Mar 2019, 15:34
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Originally Posted by safetypee View Post
Rated De, #2058,
Self-regulation is only as good as its oversight.
With drift, 'assumption precession', deviance in both design and regulation, culminate in lower safety standards.

A good time to look at other things. Trim? Electric pitch trim could suffer ‘jack stall’ if similar to previous 737; what if the changes to the max adds the risk of manual ‘jack stall’, the inability to apply sufficient force via the trim wheel with large offsets - tail arm, changed mechanics, alternative cable runs,…

Subtle language shifts …’, not forgetting misuse of language - culture, or ‘a dominant culture’?
https://www.dropbox.com/s/7425e8yykg...20%2B.pdf?dl=0
And oversight is not as easy as it looks on paper. It gets reduced from technical examination to paper audits, turns engineers into clerks, and insulates the “overseers” from the technical details. Battles rage over the items to be retained by the FAA and can be beaten down by FAA management that is more sensitive to “customer” complaints.
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Old 19th Mar 2019, 15:39
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With that EASA statement following the Canadian one, Boeing would seem to have an even greater issue now. Who trusts the Boeing/FAA relationship? As this spins out, it looks like Boeing now have some VERY serious problems, not least of which will be finding parking space for the uncertified airframes as they roll of the production line, effectively ‘unfit for purpose’.

The loss of trust will take a long time to rebuild.
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Old 19th Mar 2019, 15:59
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Salute!
Gotta tellya, I am disappointed by several pilots here that are apparently clones of Chuck Yeager, Neil Armstrong or Jimmy Doolittle.
Yeah! The thing flies just like an old Stearman and you don't need a single electron because you have wires and pulleys and cables and...... NOT!!!
I throw the foul flag. This latest version is not the plane your grandfather flew 30 years ago. It is not the same plane your son flew 10 years ago. The "geeks" have put in stuff to "help" the "clueless yutes" that don't have the skill you have or because the plane behaves differently. And it does!!

Good grief, you'll have everyone saying we should kiss off two accidents that might have been prevented with knowledge of a kludge system and maybe a sim ride to show what could happen.

More later,

Gums rants...

Last edited by gums; 19th Mar 2019 at 17:33. Reason: typo
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Old 19th Mar 2019, 16:01
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Originally Posted by MPN11 View Post
It trims the horizontal stabiliser. Endlessly, unless stopped!
No, not endlessly, and that is a very important distinction. It does it in increments, and only starts a new increment when reset, e. g. by pilot electrical trim input.

This is so important because it is the qualitative difference separating it from "runaway trim".

And you can't stop MCAS in any normal normal sense. You can only temporarily inhibit it by using manual electric trim, or you can disable electric trim altogether, and that includes disabling the speed trim system, Mach trim and pilot-commanded electric trim. Only crank-and-pulley mechanical trim remains operational.

Bernd
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Old 19th Mar 2019, 16:18
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Originally Posted by bsieker View Post

No, not endlessly, and that is a very important distinction. It does it in increments, and only starts a new increment when reset, e. g. by pilot electrical trim input.

This is so important because it is the qualitative difference separating it from "runaway trim".


Bernd
Just because it is not running continuously doesn't mean it is not a runaway. How many times does it need to do something that you have not asked for to qualify?

If the lane keeping function on your car tried to pull you into the ditch 3 or 4 times would you just let it keep on doing that or would you see a pattern and turn it off?

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Old 19th Mar 2019, 16:23
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Originally Posted by flyingchanges View Post
Just because it is not running continuously doesn't mean it is not a runaway. How many times does it need to do something that you have not asked for to qualify?

If the lane keeping function on your car tried to pull you into the ditch 3 or 4 times would you just let it keep on doing that or would you see a pattern and turn it off?
STS always asserts unwanted trim input by design.

Is there any cockpit indication of what system(STS, Mach, MCAS) is actually commanding trim movement? If not, how does one reliably tell it is from MCAS?

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Old 19th Mar 2019, 16:31
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Two quick notes:

- Air Canada suspends Max 8 until July 1 at least and suspends new deliveries
https://www.cbc.ca/news/canada/nova-...ly-1-1.5062354

- BBC reports fix by end of March
https://www.bbc.com/news/business-47622721

TME

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