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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 15th Mar 2019, 19:18
  #1521 (permalink)  
 
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How many turns does it take to go from max down to say a neutral position? Given they they were never that high from the ground , How long would it take them to trim from max down to something that would save the flight? What am trying to say is OK we have a trim problem disable trim motor via cut out switches.. Turn the manual trim wheel . Would they have the time to do this if the are only approximately 1000ft above ground?
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Old 15th Mar 2019, 19:21
  #1522 (permalink)  
 
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Originally Posted by YRP View Post
This is not for a fix from scratch. This is what they have been working on since the Lionair crash.
The question is whether it will satisfy the regulators (worldwide not just the FAA now) now that the second accident has happened.
The real question is not: Does it satisfy the regulators: FAA is effectively a Branch of Boeing. Whatever Boeing deems satisfying will be for them as well..
The real question is: Does it reliably prevent re-occurrence.
Another MCAS crash will definitely finish off the MAX and possibly the whole Boeing. I hope stupid short sighted Managers won't kill this legendary plane maker.
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Old 15th Mar 2019, 19:22
  #1523 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post
QNH around 1006 could make this happen if the reference is 1013 once airborne. What was the QNH in Addis when the accident happened?
See your logic ManaAdaSystem, but ADS-B was reporting "airborne" 1013 altitudes from much earlier in the take-off roll (first one at 93 kts GS with 80% of runway still ahead), and QNH was reportedly 1029. I'm not buying a sustained climb as early as deltafox44 either just yet. And claiming only 225ft achieved in 16 seconds from rotation - in a Cessna maybe? Doesn't ring true as any 737 number for me. I don't see anything close to continuous at that point other than the velocity. Everything else is just granular data and straight lines between points may not be helpful.

How did we get any intermediate 1013 baro report of 7075' anyway if runway elevation was 7625' and QNH 1029? Is there a big dip ?
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Old 15th Mar 2019, 19:30
  #1524 (permalink)  
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Originally Posted by joig View Post
How many turns does it take to go from max down to say a neutral position? Given they they were never that high from the ground , How long would it take them to trim from max down to something that would save the flight? What am trying to say is OK we have a trim problem disable trim motor via cut out switches.. Turn the manual trim wheel . Would they have the time to do this if the are only approximately 1000ft above ground?
I think it's approximately 60 turns from full nose down to 3 units which is about neutral.

Doesn't take that long to manually trim from neutral to full nose down or vice versa.


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Old 15th Mar 2019, 19:35
  #1525 (permalink)  
 
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Originally Posted by .Scott View Post
But Boeing is saying perhaps only 10 days...
https://www.cnbc.com/2019/03/15/boei...n-10-days.html

I'm a Software Engineer. Paint me incredulous.
the fix has been in development for 5 months and was due now anyway, they aren't starting from scratch.
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Old 15th Mar 2019, 19:37
  #1526 (permalink)  
 
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Originally Posted by joig View Post
If the trim is at max down and the pilot uses the Stab trim cut out switches does that mean that the aircraft is permanently trimmed down ? If this is the case can the pilots have any hope of recovery?
you can manually turn the trim wheel to trim the aircraft once the stab trim cutout switches have been used.
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Old 15th Mar 2019, 19:38
  #1527 (permalink)  
 
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Originally Posted by Luc Lion View Post
CORRECTION: Do you mean that what Boeing calls a "Elevator Feel Computer" is actually a mechanical computer ???

This is correct for the Elevator Feel Shift (EFS) module which simply increase by a factor 4 the system A pressure fed into the Elevator Feel & Centering Unit.
It is also true for the Elevator Feel & Centering Unit which transforms differential pressure into feel forces.
But the pressure normally fed into the Elevator Feel & Centering Unit is controlled by a computer unit, the Elevator Feel Computer, which uses airspeed and stab position inputs for computing how much hydraulic pressure it should transfer downstream.
I reckon that the AoA is NOT documented as an input data received by the Elevator Feel Computer ; AoA is only available to the EFS (in this area).

But an upgrade of the Elevator Feel Computer by adding AoA input and modifying its algorithms should not be more considerable than fixing the MCAS logic with dual AoA input.
The advantage of acting through the Elevator Feel System is obvious : no effect on the pilot pitch authority if the AoA probe goes mad in normal flight.
I cant answer for the specifics of the EFS computer other than that I am of the understanding that it is purely mechanical.

For sure there exists pure mechanical computers. Early fire control computers on various military ships during and after the WWII was purely mechanical. I have seen ducumentary about them and those computers was marvels of accurate mechanical engineering.

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Old 15th Mar 2019, 19:41
  #1528 (permalink)  
 
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Originally Posted by safetypee View Post
FCeng84, #1538,
Does that still apply if near or at jack stall; any difference between electric actuation and manual in this regard ?
I take it that your question relates to moving the stabilizer when the elevators are at large deflection thus generating high loads on the stabilizer jack screw. I did some looking to see if I could find any mention of how much force / torque is needed to turn the manual trim wheel but could not find any reference. All of the descriptions I have read speak to using this means of positioning the stabilizer when electric trim has been disabled, but do not mention how much force / torque is required.
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Old 15th Mar 2019, 19:53
  #1529 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
I think it's approximately 60 turns from full nose down to 3 units which is about neutral.

Doesn't take that long to manually trim from neutral to full nose down or vice versa.
Have you tried this in the air? A friend of mine had a trim failure in the air. He found manual trim so hard he though he had a jammed stabilizer and ended up with a FL15 landing at nearest suitable airport.

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Old 15th Mar 2019, 19:57
  #1530 (permalink)  
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fly nice :
How does one get to co-pilot a MAX with 200 hours? MPL? I will choose my airline accordingly.
MPLs are used in the whole Lufthansa group, DLH, City line ,Eurowings Austrian etc.. since the outset . i.e years ago.. Not the problem .
Anyway if F/O on that ET flight was a contributing factor , the CVR will tell us that., but frankly I doubt it.
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Old 15th Mar 2019, 19:58
  #1531 (permalink)  
 
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Originally Posted by Photonic View Post
I know the point was made earlier in the thread somewhere, but it's worth repeating that this has some similarity to the EC225's demise in the offshore oil industry.
Which like the 737 Max was a mid-1960s design stretched and tweaked and re-engined and only able to pass modern certification due to extensive grandfathering. Not a noble chapter in EASA history.
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Old 15th Mar 2019, 20:23
  #1532 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post


Have you tried this in the air? A friend of mine had a trim failure in the air. He found manual trim so hard he though he had a jammed stabilizer and ended up with a FL15 landing at nearest suitable airport.

I have used the Boeing manual trim system twice in the air. Itís a non event. You land at the flap setting specified in the QRH. Generally it is less than full to avoid large trim changes in the event of a go around.
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Old 15th Mar 2019, 20:27
  #1533 (permalink)  
 
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Originally Posted by TBC Retired View Post
It occurs to me that the usual scenario for a runaway stabilizer is that pilot has just commanded a trim change and a failure caused the stab to continue to the limit of its travel. Does that not give the pilot a clue that the problem he's experiencing might be connected to his action of changing the trim? He's been trained for that possibility and presumably has practiced the procedure of cutting the switches. Without knowledge of MCAS and the possibility that something external to the pilot might command the stabilizer to move, how in the world would he recognize what's happening and what to do?
The control column pressure, the spinning trim wheels rubbing his legs and the loud noise they make.
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Old 15th Mar 2019, 20:36
  #1534 (permalink)  
 
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Originally Posted by Ian W View Post
MCAS does not operate when in autopilot - it is intended solely for manual flying to ensure that the reduction in backpressure on the control column when in high AOA does not lead a pilot to inadvertently pull back into a stall. So the article you quote is not looking at the MCAS issue at all as the problem only occurred on engaging autopilot. It is probably looking at ASRS reports from crews that in some way mis-set the autopilot causing it to attempt to fly to where the crew had set it to fly. It is most definitely not MCAS..
I keep reading such explanations but to be clear, MCAS is always powered on. When and where it functions is defined by software alone. As such this is safety critical software and should meet the highest assurance levels. The designer did not wish for the aircraft to crash and may have set all the protection methods they could think of as a credible design goals. We have yet to learn if MCAS, as implemented, did respect the AP selection, flap configuration or anything else the designer had in mind.

MCAS being 'live' when it should not have been remains a plausible explanation. It ticks all the boxes for a latent failure - no direct indication to the crew, no failure modes displayed, no routine interaction with other systems, no BITE or similar and does not drive the stab at any point during a normal sortie. As long as it thinks the AoA is ok it does nothing.

Time will tell if functions like trim cutout, AP cutout, configuration cutout etc actually work. Given that the system seems to be blissfully unaware of the actual flight dynamics beyond simple unmonitored raw sensor data and will willingly fly the aircraft into the ground, I remain reluctant to accept the claimed operating envelope as gospel.

I guess I have spent too many years flight testing aircraft and my level of 'trust' has been swamped by 'verify'. As an aside, flight testing has become inconvenient in the last 15 years or so. We get more facetime and interaction these days post-crash - everyone is 'all ears' at that point. We need to get flight testing and training verified before an aircraft is released to the line. Kicking over aluminium at an accident site is just too late.
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Old 15th Mar 2019, 20:49
  #1535 (permalink)  
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Originally Posted by ManaAdaSystem View Post


Have you tried this in the air? A friend of mine had a trim failure in the air. He found manual trim so hard he though he had a jammed stabilizer and ended up with a FL15 landing at nearest suitable airport.

Yep, used to do engineering check flights. Part of that was manual reversion. It was a requirement to use manual trim because you had to count the number of turns.
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Old 15th Mar 2019, 20:51
  #1536 (permalink)  
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Originally Posted by Banana Joe View Post
I haven't followed the story continously, but it is my understanding that this is an option at the moment. Will be a standard fit with the next update.
Look back a few pages. With duff alpha you're likely to get up to 9 other warnings/indications not including the Southwest option.
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Old 15th Mar 2019, 20:51
  #1537 (permalink)  
 
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Originally Posted by canyonblue737 View Post
the fix has been in development for 5 months and was due now anyway, they aren't starting from scratch.
Which to me seems a huge issue. Before this second incident (assuming they're related) Boeing was downplaying the issue, basically trying to put lipstick on the pig. The second instance of this problem, in short order, shows that more is required than what was likely the lowest cost, most expedient fix Boeing could come up with. The assumption that Boeing made previously that pilots should be able to safely deal with another instance of this problem (hence justifying that grounding the fleet wasn't necessary, even after the second crash) proved to be sadly wrong and hence I conclude that the fix that Boeing had conceived before the second instance must also be flawed since it was based on their same myoptic attitude. To implement the 'fix' conceived of before this second incident within the next 10 days seems untenable. Unfortunately Boeing is motivated by $ to get any fix out there asap whether its a real fix or not. Today when news was leaked that the fix would be ready in 10 days (by Boeing?), the Boeing stock bumped 1.5%. If they had announced the fix would take another 5 months then likely the opposite would have happened or much worse. Hopefully, common sense will prevail and the required fix/action will be fully re-evaluated. I'm considering shorting Boeing stock but that would assume common sense will prevail.
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Old 15th Mar 2019, 20:58
  #1538 (permalink)  
 
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Guys, think people need to ease of the aircraft a little as if its got some huge design defect especially until we have some more facts, bear in mind many operators have been using this type for a fair while southwest nearly 3 years, with no such issues, also bear in mind that both operators here that have managed to "fly it into the ground" have very questionalble safety records as an operator.
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Old 15th Mar 2019, 21:03
  #1539 (permalink)  
 
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Originally Posted by Livesinafield View Post
southwest nearly 3 years, with no such issues
Those ASRS reports that have been widely circulated are anonymous. How do you know none of them were from SWA pilots?

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Old 15th Mar 2019, 21:18
  #1540 (permalink)  
 
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Originally Posted by Livesinafield View Post
Guys, think people need to ease of the aircraft a little as if its got some huge design defect especially until we have some more facts, bear in mind many operators have been using this type for a fair while southwest nearly 3 years, with no such issues, also bear in mind that both operators here that have managed to "fly it into the ground" have very questionalble safety records as an operator.
For the record, Southwestís first MAX revenue flight was October 1, 2017. Closer to 1.5 years than 3 years. Yes, Southwest has flown it a lot, and has a lot of data, but itís not three years of data.

Hoke

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