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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 6th Apr 2019, 23:20
  #3481 (permalink)  
 
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Originally Posted by Takwis View Post
I think my first line of defense would be to leave the flaps at 1...or get them there. Completely agree on the instructions after the Lion Air crash.
As I said plenty of ideas on what should be in checklist and order of actions etc. I am sure that Boeing engineers/pilots would be able to provide the best one if given the mandate.

An interesting outcome of the inevitable legal discovery actions will be the internal Boeing discussions leading to the AD and revised checklist. How much pressure to "keep it in type" and similar.

Last edited by MurphyWasRight; 6th Apr 2019 at 23:22. Reason: typo
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Old 6th Apr 2019, 23:25
  #3482 (permalink)  
 
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Originally Posted by Capn Bloggs View Post
So we're test pilots too now? No mention anywhere by Boeing of keeping the speed down, these guys were probably totally focussed on the MCAS issue, not your bog-standard UAS/80%. Ask yourself: when did you last pull off a handful of thrust at 1000ft above ground, straight after takeoff with the stick shaker going? I would suggest that some pilots don't even touch the thrust levers after takeoff normally, let alone have it in their muscle memory to do it when all hell has just broken loose.


Any professional pilot would already have a very good visual concept of what happened here. Absolutely no need to watch someone dying, thanks.
that's the thing. What testing was done by Boeing to ensure this vital sequence of actions was debugged? The stick shaker was also present on other flights but was ignored by the AD. MCAS runaway was just the endgame of a series of events. That would have taken more time to fully test and document. It would have also been more complex, perhaps necessitating the grounding of the plane so that pilots could have more training. There was no time in that cockpit for the data of debate that are going on in the web.
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Old 6th Apr 2019, 23:36
  #3483 (permalink)  
 
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Originally Posted by Albino View Post
You need to go and read step 2 again. It wasn't completed, at any point after the MCAS AND.

What would disconnecting the autothrottle have achieved? Well you could set thrust to something more sensible and fly the aircraft.

You mean page 2 of the memo that gave specific operating instructions to crew? It even included a note (obvious to most with any common sense!) to put the aircraft in trim, then cut out the stabs.
Not so. Step 2 is "Autopilot (if engaged) disengage". A/P was no longer engaged. So forget Step 2. Even if you don't, it says "Control pitch with column and trim". The pitch has been controled, the trim was back at the limit of green band though a significative column force remained.

Never is said to use electric trim to full trim before cutout, nor any warning that manuel trim might be impossible at higher mistrim/speeds
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Old 6th Apr 2019, 23:43
  #3484 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
The takeoff ground speed, engine power, and pitch attitude in the climb, would probably all have been higher, to compensate for the lower air density (about 80% of sea level pressure). Not a pilot, but I can't think of any other differences, once they were airborne.
Less oxygen coming to the brain also. May be negligible, especially as they were used to this altitude, not higher than cabin altitude in flight.
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Old 7th Apr 2019, 00:13
  #3485 (permalink)  
 
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Originally Posted by wheelsright View Post
"as soon as MCAS starts trimming you can stop it with a reverse blip."

How do you know that?
I can't recall exactly but I have seen quite authoritative looking documents on t'interwebby that state it.

You can look for yourself at the LionAir preliminary report and notice the frequent truncated AND automatic trim pulses coincident with manual ANU trim pulses beginning. This was during the period when the captain was maintaining good trim on average for several minutes.

http://www.flightradar24.com/blog/wp...ary-Report.pdf

Edited to add:-
https://theaircurrent.com/aviation-s...ion-air-crash/

Has an image of what appears to be a Boeing document that includes the text "The nose down stabilizer trim movement can be stopped and reversed by the use of the electric stabilizer trim switches ... but may restart ...". See the Orange marked section below.



Last edited by jimjim1; 7th Apr 2019 at 00:51.
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Old 7th Apr 2019, 00:27
  #3486 (permalink)  
 
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Originally Posted by Ian W View Post
99.9% of PF would trim back to in trim if MCAS did operate incorrectly giving significant uncommanded nose down trim and after 2 or at worst 3 trim back would switch off Stab Trim.
99.9%, really ?

The pilots of the 2 last Lion Air flights did it. The Copilot in Lion Air crash and the Captain in ET302 did not. That's only 50% !

By the way, when speaking that an "average pilot" should be enough to succeed avoiding a crash, it implies that the crash probability is very near 50%, since by definition 49,99% of the pilots are higher than average and 49,99% under average
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Old 7th Apr 2019, 00:28
  #3487 (permalink)  
 
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Here's an explanation of the EASA position on the observation that the yoke trim switches on the MAX don't work throughout the entire speed envelope (with some highlighted text):

Explanatory Note to TCDS IM.A.120 – Boeing 737 Issue 10

EQUIVALENT SAFETY FINDING:
B-05/MAX: Longitudinal trim at Vmo
APPLICABILITY: Boeing B737-7/-8/-9 REQUIREMENTS: CS 25.161(a), CS 25.161(c)(3), CS 25.1301(a) and CS 25.1309(a) ADVISORY MATERIAL: N/A

STATEMENT OF ISSUE

The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation. Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts. In those cases, longitudinal trim is achieved by using the manual stabilizer trim wheel to position the stabilizer. The trim wheel can be used to trim the airplane throughout the entire flight envelope. In addition, the autopilot has the authority to trim the airplane in these conditions. The reference regulation and policy do not specify the method of trim, nor do they state that when multiple pilot trim control paths exist that they must each independently be able to trim the airplane throughout the flight envelope. Boeing did not initially consider this to be a compliance issue because trim could always be achieved, even during the conditions where use of the aisle stand trim switch was required. Subsequent to flight testing, the FAA-TAD expressed concern with compliance to the reference regulation based on an interpretation of the intent behind “trim”. The main issue being that longitudinal trim cannot be achieved throughout the flight envelope using thumb switch trim only.

EASA POSITION

Boeing set the thumb switch limits in order to increase the level of safety for out-of-trim dive characteristics (CS 25.255(a)(1)). The resulting thumb switch limits require an alternative trim method to meet CS 25.161 trim requirements in certain corners of the operational envelope.

The need to use the trim wheel is considered unusual, as it is only required for manual flight in those corners of the envelope.

The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope. Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches.

The trim systems on the 737Max provide an appropriate level of safety relative to longitudinal trim capability.


Page 15 of 114
From: https://www.easa.europa.eu/sites/def...20ISS%2010.pdf
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Old 7th Apr 2019, 00:32
  #3488 (permalink)  
 
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Originally Posted by deltafox44 View Post
Not so. Step 2 is "Autopilot (if engaged) disengage". A/P was no longer engaged. So forget Step 2. Even if you don't, it says "Control pitch with column and trim". The pitch has been controled, the trim was back at the limit of green band though a significative column force remained.

Never is said to use electric trim to full trim before cutout, nor any warning that manuel trim might be impossible at higher mistrim/speeds
The AD does in fact say to trim the forces out before using the cutout. https://theaircurrent.com/wp-content...AX-AD-1107.pdf
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Old 7th Apr 2019, 00:39
  #3489 (permalink)  
 
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Why didn’t Boeing incorporate an MCAS cutoff switch or circuit breaker? Rather than cut out an otherwise perfectly functioning stab trim, just isolate MCAS.
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Old 7th Apr 2019, 00:47
  #3490 (permalink)  
 
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Originally Posted by Just the fax maam View Post
Seems to me that once the stab due to MCAS or runaway trim reaches a certain point it is unrecoverable without the old roller coaster manouvre few have been trained on or practiced. And possibly not just the Max.
Please let's all forget the roller coaster theory. At 340 kt releasing aft column pressure would mean negative g's. So if you want to have the time to make the numbers of turns of the trim wheel you need to get trimmed again, you have the choice between an inverted loop or 180° roll before releasing pressure

At the end of the flight they got -2g with still both pilots applying full aft force !
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Old 7th Apr 2019, 01:02
  #3491 (permalink)  
 
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Originally Posted by locblue View Post
Why didn’t Boeing incorporate an MCAS cutoff switch or circuit breaker? Rather than cut out an otherwise perfectly functioning stab trim, just isolate MCAS.
Because MCAS exists purely in software. There is no separate wiring or mechanism that is specifically "MCAS" it's just the electric stab trim.
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Old 7th Apr 2019, 01:09
  #3492 (permalink)  
 
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Originally Posted by ams6110 View Post
Because MCAS exists purely in software. There is no separate wiring or mechanism that is specifically "MCAS" it's just the electric stab trim.
Perhaps therein lies the solution. I wouldn’t trust a “software update” from Boeing to well and truly fix this. They need to redesign MCAS such that it becomes a discrete and isolation-able input. Until, of course, the 737 is redesigned from scratch altogether.
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Old 7th Apr 2019, 01:15
  #3493 (permalink)  
 
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Why does Boeing not delete MCAS from their new B73 8/9s?. They have thousands flying around successfully without it.
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Old 7th Apr 2019, 01:17
  #3494 (permalink)  
 
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Originally Posted by Takwis View Post
"Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches."

Some decades ago...

Speaking of decades, what was the date on that document?
The Explanatory Note is an addendum to this EASA Type Certificate document dated December 17, 2018:

https://www.easa.europa.eu/sites/def...20rev%2017.pdf

According to a Reuters article the Note dates back to February 2016:

The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said.


https://mobile.reuters.com/article/amp/idUSKCN1RA0DP
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Old 7th Apr 2019, 01:35
  #3495 (permalink)  
 
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Originally Posted by Flt.Lt Zed View Post
Why does Boeing not delete MCAS from their new B73 8/9s?. They have thousands flying around successfully without it.
They needed it for certification.
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Old 7th Apr 2019, 02:00
  #3496 (permalink)  
 
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Originally Posted by deltafox44 View Post
Please let's all forget the roller coaster theory. At 340 kt releasing aft column pressure would mean negative g's. So if you want to have the time to make the numbers of turns of the trim wheel you need to get trimmed again, you have the choice between an inverted loop or 180° roll before releasing pressure
That's a very authoratative statement from someone who clearly hasn't even taken the trouble to find out what it actually involves!
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Old 7th Apr 2019, 02:08
  #3497 (permalink)  
 
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Originally Posted by AerocatS2A View Post

They needed it for certification.
Might a more comprehensive answer be that they needed it for certification without additional sim conversion training?

Is there any suggestion that an aircraft with those stall characteristics could not be certified at all? Doubtless someone here can advise.
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Old 7th Apr 2019, 02:21
  #3498 (permalink)  
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The gist is that it is required. You can't train around it.

By the way.
Meleagertoo #3509 There's no certification need or requirement to have manual trim operable at full deflection above VMO - how could there be?
A rather famous ‘Jet Upset’ comes to mind. The possibly supersonic 727 Mind you, it took the undercarriage to save the day, so I suppose the T tail wouldn't have worked anyway.
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Old 7th Apr 2019, 02:27
  #3499 (permalink)  
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A ghostly ring in the Aviation VOICE article comparing the sales of Airbus and Boeing. I read the link with an increasing sense of our blindness when we try to look into the future.
“Basic market forces are likely to reduce Airbus’s advantage eventually, but it is difficult to imagine a scenario that would cause a shift toward Boeing’s stated goal of a 50/50 balance.”
https://aviationvoice.com/airbus-a32...-201602121522/


abdunbar #3492 Super post. Ethiopian airliner down in Africa

My generation needed to be encouraged to embrace auto flight as it matured. We were spring loaded to dump it and manually fly if we got behind. As the years moved on we started to have new/younger pilots whose only experience was systems, auto flight and flight management computers that could handle all phases of flight except initial takeoff. We were encouraged to use these systems fully to reduce workload.
I recall being incensed on behalf of younger pilots about the policy of forbidding crews to hand fly. The main reason given was passenger comfort.


MemberBerry #3497

And having in mind that the current version of MCAS will re-activate in 5 seconds, it should also tell you to use the cutoff switches as soon as possible after you bring the trim to neutral, in under 5 seconds after your last electric trim use.
Can we safely assume that this five seconds starts upon resetting the Stab cut-out switches? The delay might only apply after thumb switch use.
.
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Old 7th Apr 2019, 02:52
  #3500 (permalink)  

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If any of the insightful contributors could fill my blanks:

How much of trim displacement in units is one spin of the manual wheel on the MAX/NG?

About the yoke elec trim thumb rocker switches
- do they control the actuators/motor directly in analogue, or only send signals to some sort of FCS logical subunit?
- what is the logic for simultaneous inputs L+/-R?

Is there an authoritative answer, whether or not will the MCAS routune re-activation (after the 5 sec denial period) override a live, running trim command from the elec thumb switches?
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