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MCAS ALTITUDE V ATTITUDE ??

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MCAS ALTITUDE V ATTITUDE ??

Old 16th Mar 2019, 05:04
  #21 (permalink)  
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getting each pilot into a simulator and making sure they can recognise a trim fault, can hear the stall warning over their ipods, and can find the cutout switches and stop themselves from vertical parking would appear to not be asking too much at this point. If the crews are turning up to the aircraft and cannot ascertain what various messages mean on the PDF or ND, then there is a hint that all is not well with the preparatory training packages. The training doesn't need Level D, it needs guided instruction to ensure the guys have some confidence in their own operation.
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Old 16th Mar 2019, 05:35
  #22 (permalink)  
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Unhappy

Originally Posted by fdr View Post
getting each pilot into a simulator and making sure they can recognise a trim fault, can hear the stall warning over their ipods, and can find the cutout switches and stop themselves from vertical parking would appear to not be asking too much at this point. If the crews are turning up to the aircraft and cannot ascertain what various messages mean on the PDF or ND, then there is a hint that all is not well with the preparatory training packages. The training doesn't need Level D, it needs guided instruction to ensure the guys have some confidence in their own operation.
The quality of that report might well be summed up in the following quote from the article listed
would focus on the MAX's automatic stall-prevention system that was linked to the Lion Air crash in Indonesia
juxst wunnerful !

Thanks by the way for your post here from the other thread - perhaps some will try to see if the current ' system ' kludge would or did meet the requirements ? i dont think so !
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Old 16th Mar 2019, 07:11
  #23 (permalink)  
 
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Originally Posted by CONSO View Post
CURRENT - 833 PM SEATTLE TIME
BA plans to provide software fix within about 10 days and mandate installation. Then after a test flight- plane can be returned to service ! meanwhile the FAA and Boeing are going rounds as to type and kind and level of ' training ' on the ' new' software/system/ effects shall be required. !

The above is a paraphrase of the news release by a few ' sources'

https://www.thestreet.com/investing/...e-fix-14897876

I'm simply reporting- I'm sure within a few hours or less, more details will be available-

IMHO- while FAA may allow this in the U.S- I doubt anyone else will . but I'm just a poor SLF retired mechanical injun ear from BA and not an aeronautical whiz bang at all- Not even a microsoft simulator player .
A BBC report suggests that the FAA expects the B737 MAX to be grounded until at least May: https://www.bbc.com/news/business-47578555

As investigators work to determine the cause of the tragedies, the US regulator said the aircraft would be grounded until at least May.

Boeing has halted 737 Max deliveries and some airlines say they will demand compensation.

Some customers have signaled they could back away from orders.

But analysts say the long-term impact on the firm will depend the outcome of the investigation.
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Old 16th Mar 2019, 15:50
  #24 (permalink)  
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maybe worth taking a close look at

https://www.flightradar24.com/blog/w...ary-Report.pdf


especially pages 16 to 18 re maintenace log

page 23 to 26 plots
and additional info on pages 28 and on

now add in the possibility of a switch between FCC and ' active' AOA sensor -

Sort of like my brakes grabbed and pulled me to the right - OK we checked the front wheel brakes- PUT IN NEW PADS and all OK - but problem really was with right rear brake - so when you hit the ice . .

Which is the long way of saying DID MAINTENACE CHECK BOTH AOA SENSORS ??
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Old 16th Mar 2019, 16:14
  #25 (permalink)  
 
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Originally Posted by CONSO View Post
Which is the long way of saying DID MAINTENACE CHECK BOTH AOA SENSORS ??
Actually when looking at that maintenance writeup it looks like the AoA sensor was intermittent before maintenance in Denpasar. (But not necessarily wrong)
(The Captains AoA sensor was replaced as the captains airdata was intermittent)

After the maintenance in Denpasar the MCAS problem started showing up which suggests the problem originating with that maintenance action.
(Also in the FDR traces it is very clear it is that freshly replaced AoA sensor which is the problem on the last two flights of the aircraft)
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Old 16th Mar 2019, 19:53
  #26 (permalink)  
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AND NOW

https://www.inc.com/chris-matyszczyk...-disagree.html
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Old 16th Mar 2019, 19:55
  #27 (permalink)  
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(Also in the FDR traces it is very clear it is that freshly replaced AoA sensor which is the problem on the last two flights of the aircraft)

But since the ' active' AOA sensor changes from left to right, depending n power down and or WOW, and the default is ?? what sensor was checked/replaced ? Not clear from log

Last edited by CONSO; 16th Mar 2019 at 20:08.
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Old 16th Mar 2019, 20:37
  #28 (permalink)  
 
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Originally Posted by CONSO View Post
But since the ' active' AOA sensor changes from left to right, depending n power down and or WOW, and the default is ?? what sensor was checked/replaced ? Not clear from log
The FDR traces for the sensor data are separate, nothing switches.
Also the captains air data are always from the captains AoA sensor, those were intermittent.

Only thing that switches between flights is the FCC which is used for MCAS or something.
In this case after the maintenance in Denpasar, the left FCC (connected to captains AoA) was used for MCAS.
Then the following flight it was again the left FCC since the aircraft was powered down over night.

So yes it is quite clear which AoA sensor was replaced and on the following two flight provided wrong data.
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Old 16th Mar 2019, 20:43
  #29 (permalink)  
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FWIW



starts with a running jackscrew in ?? airplane
its about 2 min in before he identifies himself - and then starts to show a typical control diagram

And also this FWIW


But must go 16 min in to get to MCAS

Last edited by CONSO; 16th Mar 2019 at 20:57.
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Old 16th Mar 2019, 22:42
  #30 (permalink)  
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RE install of AOA sensor from previous thread in december

Maintenance Lapse Identified as Initial Problem Leading to Lion Air Crash


BUT that would also infer that the same error happened twice - wrong clocking or ??? Especially after the first earlier report ? About the swiss cheese lining up ?????

Last edited by CONSO; 16th Mar 2019 at 22:53. Reason: typos
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Old 16th Mar 2019, 23:36
  #31 (permalink)  
 
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Originally Posted by CONSO View Post
BUT that would also infer that the same error happened twice - wrong clocking or ??? Especially after the first earlier report ? About the swiss cheese lining up ?????
No after Denpasar-Jakarta they basically reset the computers and cleaned a couple of plugs.
(Not sure if flushing means flushing computers or flushing the actual pitot static system)

But they didn't touch the AoA sensor.

So they basically just didn't change anything as no one looked at the FDR or QAR.
For the IAS disagree they checked the pitot static system instead of checking the real source of the problem, the AoA sensor.
Of course the error description not mentioning the stick shaker can be considered lacking description of the problem.

The Lion Air incident basically shows lack of training and corner cutting everywhere.
That is one of the reasons Boeing wasn't as much under scrutiny i believe, a good part of the focus was on Lion Air.
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Old 16th Mar 2019, 23:37
  #32 (permalink)  
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And about what Boeing thinks the AOA sensor does ( dated approx year 2000 )

Aero 12 - Angle of Attack

he U.S. National Transportation Safety Board (NTSB) has recommended visual indication of AOA in commercial airplanes. This indication may take the form of a dedicated AOA indicator or other implementation, such as the PLI. A dedicated AOA indicator shown on the primary flight display (PFD) recently has been developed in cooperation with airline customers. The new indicator is offered as an option on the 737-600/-700/-800/-900, 767-400, and 777 at this time. During the development of the new indicator, discussions with airlines, the NTSB, and U.S. Federal Aviation Administration (FAA) pilots and engineers provided a unique opportunity to examine potential uses of AOA and the many existing uses that have evolved in recent decades along with advances in display and indication technology.
...
The indicator developed shows body AOA in degrees and is not normalized, which is related to the second objective above, that the indicator be useful when pitot or static data, and therefore Mach calculations, are unreliable because of blockage or a fault in the system. The pointer of a normalized indicator in this condition would behave erratically, making the indicator unusable. With the nonnormalized design, the position of the needle is a function only of sensed AOA. The red tick mark for stall warning may behave erratically in a pitot or static failure state, as may stick shaker, PLI, and speed tape amber and red bands. However, the AOA needle and digits will remain stable, and the indicator itself still will be useful as a backup for unreliable airspeed, provided the AOA vanes are undamaged.
I think the whole document is worth rreading now !!

Last edited by CONSO; 17th Mar 2019 at 00:32. Reason: add 2nd quote-
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Old 17th Mar 2019, 02:28
  #33 (permalink)  
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Seems to this SLF that a simple damped pendulum free to swing in the fore and aft direction ( eg a plumb bob ) and properly oriented to maybe 3 degrees body pitch with simple visual readout would make a simple ' AOA' sensor backup and could be part of a simple "inertial" standby system NOT dependant on anything else - sort of a needle , ball, ( and non alcohol ) system
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Old 17th Mar 2019, 09:54
  #34 (permalink)  
 
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Originally Posted by CONSO View Post
Seems to this SLF that a simple damped pendulum free to swing in the fore and aft direction ( eg a plumb bob ) and properly oriented to maybe 3 degrees body pitch with simple visual readout would make a simple ' AOA' sensor backup and could be part of a simple "inertial" standby system NOT dependant on anything else - sort of a needle , ball, ( and non alcohol ) system
(post deleted as there's no point in leaving it now that the mods have deleted all the subsequent discussion)

Last edited by DaveReidUK; 18th Mar 2019 at 18:14.
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Old 18th Mar 2019, 05:42
  #35 (permalink)  
 
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Apart from all this tech discussion (which is great) there are some other factors to consider. Namely politics.
No one at the FAA is gonna lift the grounding unless it is absolutely, positively, guaranted fixed so that any monkey could agree the problem is corrected. That includes the President of the US who made (so far as I know) first ever presidential grounding of an aircraft series. I don't see any bureaucrat in either the government or Boeing putting their reputation and company survival on the line until all possible questions have been satisfactorily answered. Oh and don't forget the lawsuits and congressional investigations which are just getting started.
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Old 18th Mar 2019, 11:25
  #36 (permalink)  
 
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Any one can explain why an erroneous AoA input can cause an IAS disagreement? Aren’t the inputs to the airspeed indicators just the static and pitot pressures?



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Old 18th Mar 2019, 11:57
  #37 (permalink)  
 
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Originally Posted by LNAV VNAV - View Post

Any one can explain why an erroneous AoA input can cause an IAS disagreement? Arenít the inputs to the airspeed indicators just the static and pitot pressures?



No the ASI is driven by the ADIRUs and they correct the inputs from the pitot and static ports using the AoA inputs. It is the ADIRU getting AoA disagree that alert to the airspeed being unreliable, I would have thought that the first check on unreliable airspeed in the Max would be set stab trim switches to CUTOUT that means manual trim but MCAS is now out of the loop.

I am surprised that after the Lion Air crash and the AD that any pilot on the Max would be unaware of the MCAS issue and have briefed accordingly before any flight about stab trim cutout if trimming became difficult - it is part of the standard runaway trip checklist. The fact that another crew had crashed and could have survived if they had switched stab trim to cutout should have concentrated minds.

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Old 18th Mar 2019, 12:08
  #38 (permalink)  
 
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Any one can explain why an erroneous AoA input can cause an IAS disagreement? Arenít the inputs to the airspeed indicators just the static and pitot pressures?
There are a couple of aspects to this I believe:
  1. The AOA is used as part of Static Source Error Correction (SSEC) calculations, basically to compensate the fact that the pitot tube isn't usually aligned exactly with the airstream.
  2. Since there is a relationship between AOA and IAS, the AOA can be used as a "cross check" to detect pitot/static problems (blocked ports, etc.) . So a malfunctioning AOA could erroneously show up as an IAS issue.
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Old 18th Mar 2019, 12:12
  #39 (permalink)  
 
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LNAV VNAV,

Much as above except I understood that the computation is in the ADC; thus AoA is used in the ADC for pressure error correction; if each AoA feeds it ‘own side’ ADC then the ADCs speed computations differ and alert the crew, similarly for Alt Disagree.

Also, if AoA is in error, so too the computation for low speed awareness (AoA to speed relationship) on the speed scale; this may / may not contribute to the ‘IAS disagree’ alert.

Ian W, the ADCs could be responsible for the AoA disagree (or fly guidance comp); however the alert is an optional installation, normally associated with the optional AoA dial display on EFIS. Which in this instance would be meaningless because there is no way to determine which AoA value is correct, whereas for IAS and ALT there is a third system to crosscheck.

Thus although the Lion maintenance electronic log flagged AoA amongst other problems, the crew’s report concentrated on the indications of unreliable airspeed and stick shake.
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Old 18th Mar 2019, 12:16
  #40 (permalink)  
 
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Thank you Ian. Do you by any chance have any reference to any manual that shows that the ADRs correct the pitot and static inputs using AoA data? I used to fly the NG and I don’t remember reading anything to this effect and there is nothing in the A320 manuals as far as I know. Unless this is just a Max thing.
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