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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 15th Mar 2019, 01:10
  #1401 (permalink)  
 
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AOA sensor reliability?

Anyone know if the AOA sensors on the MAX are any different from the NG? If not, are their reliability issues with the NG AOA sensors?

Otherwise, what chance is there for another AOA sensor triggering a MCAS event just now, when there are thousands of NGs making daily flights with no issues?

It just doesnít seem to make sense unless this is a new/different AOA sensor design, with a design flaw.

- GY
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Old 15th Mar 2019, 01:10
  #1402 (permalink)  
 
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IMO, the day Alan Mulally left Boeing was the beginning of the end of "Working Together." I'm not surprised at Boeing's current situation. Look at the KC-46's being delivered with trash, and tools left in them. It's like WTF is going on? Seems like a dire situation IMO.
I'll second that- years ago and even after I retired after /when working on 777 I had excellent communications with Alan - I'm probably only one of maybe 200 people who have personally been hugged by Alan after sending him an email on a weekend about a close friend known to Alan who was in the Hospital . Alan answered within an hour. My friend later passed and Alan attended his funeral. he always responded to direct emails and made sure that an answer was forthcoming. But that ran counter to the MDC gang in power. And as you infer- the rest is history !
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Old 15th Mar 2019, 01:14
  #1403 (permalink)  
 
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Originally Posted by GarageYears View Post
Anyone know if the AOA sensors on the MAX are any different from the NG? If not, are their reliability issues with the NG AOA sensors?

Otherwise, what chance is there for another AOA sensor triggering a MCAS event just now, when there are thousands of NGs making daily flights with no issues?

It just doesnít seem to make sense unless this is a new/different AOA sensor design, with a design flaw.

- GY


its not the sensor - its the fubar software and dependance on a single sensor which gets switched from side to side dependant on aircraft power cycles, but which can without any comparison or error checking drive a horizontal stabilizer !
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Old 15th Mar 2019, 01:22
  #1404 (permalink)  
 
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Originally Posted by JamesT73J View Post
That is interesting. Maybe a CoG problem, or misconfigured T/O trim?
Interesting choice of words. One item from the FAA grounding order that is missing from most conversations:
"On March 13,2019,the investigation of the ET302 crash developed new information from the wreckage concerning the aircraft 's configuration just after takeoff that,..."
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Old 15th Mar 2019, 01:29
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Salute!

Sorry, Garage, but MCAS doesn't care about altitude. With flaps up and AoA at a certain value or above and not in A/P it will activate unless we have been misinformed for 5 months. Not sure about main gear being up, but there has been a mention of "configuration" shortly after takeoff.
Gums sends...
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Old 15th Mar 2019, 01:32
  #1406 (permalink)  
 
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Originally Posted by CONSO View Post
its not the sensor - its the fubar software and dependance on a single sensor which gets switched from side to side dependant on aircraft power cycles, but which can without any comparison or error checking drive a horizontal stabilizer !
But the fubar software only does something if the AOA sensor is broken. My point is rather obvious. If there are thousands of the SAME sensors working perfectly, day in, day out, on NGs all over the world, itís very unlikely that two suddenly go wrong within a few months.

Either itís a different sensor, new with the MAX, or this could one of the universes rarest conincidences. Or the crash is unrelated.

- GY
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Old 15th Mar 2019, 01:39
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Originally Posted by gums View Post
Salute!

Sorry, Garage, but MCAS doesn't care about altitude. With flaps up and AoA at a certain value or above and not in A/P it will activate unless we have been misinformed for 5 months. Not sure about main gear being up, but there has been a mention of "configuration" shortly after takeoff.
Gums sends...
I rarely disagree with the smart folk, but there is DEFINITELY an altitude limit on MCAS engagement.

Pretty sure it is 1000 ft AGL, but Iím trying to find a definitive reference.

Respectfully, GY
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Old 15th Mar 2019, 01:44
  #1408 (permalink)  
 
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I've been a long time in read-only mode, felt it was time to contribute.

Originally Posted by silverstrata View Post
Interesting two graphs.
And of course the 21 second interval in vertical speed cycles, equates very nicely with 10 secs of MCAS trim input and 10 sects of manual trim resetting. Prima face evidence that MCAS was operating in this flight.
Silver
If I've read the second graph correctly, the 21 seconds is measured from 05:39:11Z to 05:39:32Z (per the FR24 data) - corresponding to 225 feet and 600 feet aal.

That seems rather low for the flaps to be fully retracted, for MCAS to kick in, and for 10 secs of manual trim to be completed.

It appears from the same data that ET302 had only just left the runway at 05:38:59Z or a few seconds earlier. From what we know about the system, is it really feasible that MCAS starts operating 12 seconds later?

Apologies if I've misunderstood something.
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Old 15th Mar 2019, 01:51
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Originally Posted by GarageYears View Post


But the fubar software only does something if the AOA sensor is broken. My point is rather obvious. If there are thousands of the SAME sensors working perfectly, day in, day out, on NGs all over the world, itís very unlikely that two suddenly go wrong within a few months.

Either itís a different sensor, new with the MAX, or this could one of the universes rarest conincidences. Or the crash is unrelated.

- GY
Bird strike or ramp rash or software error are three most obvious- the point is to alllow a SINGLE sensor to directly override pilot input and not be documented that it even exists is as close to criminal as one can imagine. MTBF makes no diff- And BA knows how to make a comparison for example 787

http://www.ata-divisions.org/S_TD/pd...ngtheB-787.pdf

see pages 40-41


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Old 15th Mar 2019, 01:58
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Originally Posted by JamesT73J View Post
That is interesting. Maybe a CoG problem, or misconfigured T/O trim?
What about the mentions of speed being far too high, even while they were climbing to a safer altitude?

That isn't a CoG or trim issue ... ??

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Old 15th Mar 2019, 02:01
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If there are any mx tech on here can you tell us if the Stab trim cut out switches are connected to the MCAS system ie will the switches in the cut out position actually stop the MCAS from trimming thanks
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Old 15th Mar 2019, 02:38
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Originally Posted by boeingboy737 View Post
If there are any mx tech on here can you tell us if the Stab trim cut out switches are connected to the MCAS system ie will the switches in the cut out position actually stop the MCAS from trimming thanks
The manual ones next to the trim wheel are. The ones at the column sensing a pull against the trim obviously aren‘t because the MCAS has to trim against a strong pull to maintain the desired positive stick force gradient.
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Old 15th Mar 2019, 02:40
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@ Boeing boy

Our resident engineer , FCeng84, and the wiring diagrams show that the switches cut off the electric trim motor. Trim wheel still works.
"bumping the trim switches on the yoke stops MCAS. then it starts again after 5 seconds if the AoA is still high. You can clearl;y see this on the 610 accident flight data and preceding flight.
So no dedicated MCAS power switches. It's all in the FCC boxes, thence wires to the trim motor.

Gums...

P.S. still can't find an altitude restriction or enabling condition.
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Old 15th Mar 2019, 02:44
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Originally Posted by GarageYears View Post


I rarely disagree with the smart folk, but there is DEFINITELY an altitude limit on MCAS engagement.

Pretty sure it is 1000 ft AGL, but Iím trying to find a definitive reference.

Respectfully, GY
i belive Lion Air was at 5000 feet when they had their issues. Doesnít make any sense to altitude limit the system as it would need access to digital terrain model to make decisions.
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Old 15th Mar 2019, 02:46
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Originally Posted by poldek77 View Post
Most probably not in this case but here it is:

Elevator Jam Landing Assist
This will give limited changes to the vertical flight path from the spoilers to assist the approach and landing if the normal elevator system jams. The control panel is located on the Aft Overhead Panel, even if it is switched on it will only be active when the flaps are 1 or greater. When in use, the spoilers rise to a preset position; they then extend or retract as the elevator column is pushed or pulled to increase or decrease the rate of descent.

(737 MAX - FBW Spoiler System)

Wild. The MAX has Direct Lift Control like the L-1011? To bad that's not used under normal circumstances.
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Old 15th Mar 2019, 02:52
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Training and implications

With regard to the many posts referencing the practice of various maneuvers and events during simulator training sessions:

Have a look at and thought about what is in those simulators.

Specifically, there was a fundamental shift over the last several years about where the software for the simulators comes from, and most specifically for the 787, 737 MAX and most recently the 777-X. One of the biggest differences between the current approach and the "classical" methods concerns the content of available malfunctions and fault scenarios to be trained. There was a very deliberate choice made to limit that content to only those events that are part of the QRH.

Since MCAS was never "advertised" to the flight crews, it almost certainly was not included in the list of "training events" for the MAX simulators. I *might* be wrong, but not based on the content I saw at several of the "working group" events up through about 2 years back.

Bear in mind that there is a huge difference between an engineering simulation and a crew training simulation. The latter type, especially for the MAX and other recent products, contains only what the provider decided that it should contain.

Take a guess as to who that provider is.
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Old 15th Mar 2019, 03:22
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[QUOTE=gums;10419051]@ Boeing boy

Our resident engineer , FCeng84, and the wiring diagrams show that the switches cut off the electric trim motor. Trim wheel still works.
"bumping the trim switches on the yoke stops MCAS. then it starts again after 5 seconds if the AoA is still high. You can clearl;y see this on the 610 accident flight data and preceding flight.
So no dedicated MCAS power switches. It's all in the FCC boxes, thence wires to the trim motor.

Gums...

P.S. still can't find an altitude restriction or enabling condition.[/QUOTE

This may help post 496 11 march 2019 ethopian airliner down thread (cannnot seem to post link )


[COLOR=start=#ffffff]Mar 2019, 21:55[/COLOR]
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[COLOR=right=#ffffff]) #496 (permalink) [/COLOR]




[COLOR=start=#ffffff]11th Mar 2019, 21:55[/COLOR]
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Old 15th Mar 2019, 03:23
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Originally Posted by boeingboy737 View Post
If there are any mx tech on here can you tell us if the Stab trim cut out switches are connected to the MCAS system ie will the switches in the cut out position actually stop the MCAS from trimming thanks
time for all new posters to RTFT. Ok not possible. Draw your own conclusions
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Old 15th Mar 2019, 03:38
  #1419 (permalink)  
 
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Something isn't quite making sense here....

IF that supposed ATC info is correct - that there seemed to be a sustained and abnormal acceleration - and this DOES seem to be borne out by the FR24 data, which seems to show increasing speed and increasing altitude then the aircraft flight path is NOT the same as Lion Air. Whatever various press releases seem to be claiming.

The Lion Air FDR data appears to show an aircraft exchanging kinetic and potential energy as it dives and accelerates, then climbs and slows , as it either is "MCASed" nose down or pulled back nose up alternately. The final DIVE is where the speed finally builds to by far the highest speed in the whole accident sequence.

ET doesn't do that. The FR24 data (unless there's something newer floating around) shows ground speed continuously increasing (albeit not at a constant rate) while the overall altitude trend is to climb - albeit with some instability. In other words, the ET aircraft seems to be gaining significant energy throughout the flight. No stab system malfunction can add total energy to the aircraft.

Dare I suggest something totally unrelated to MCAS, even though everyone has already jumped on that bandwagon (and grounded the aircraft). What about an uncontrolled high thrust event? Too much thrust, inability to reduce power from TO, something like that.
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Old 15th Mar 2019, 03:45
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What about an uncontrolled high thrust event? Too much thrust, inability to reduce power from TO, something like that.
if you find the link to the nasa anon reporting system for pilots, etc that apply to 737max- you will find one descriptioon of an uncommaned throttle change which I recall was the opposite ( throttle cut ) but my memory may be incorrect . .
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