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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 7th Apr 2019, 00:02
  #3481 (permalink)  
 
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Originally Posted by locblue
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, 00:09
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Originally Posted by ams6110
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, 00:15
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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, 00:17
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Originally Posted by Takwis
"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, 00:35
  #3485 (permalink)  
 
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Originally Posted by Flt.Lt Zed
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, 01:00
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Originally Posted by deltafox44
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, 01:08
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Originally Posted by AerocatS2A

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, 01:21
  #3488 (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, 01:27
  #3489 (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, 01:52
  #3490 (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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Old 7th Apr 2019, 04:24
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Originally Posted by locblue
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 is not a powered device! It is software!
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Old 7th Apr 2019, 04:27
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A simple question from an engineer, why a designer should put a pilot in such situation, why the designer cannot prevent and design a solid system? And why if he is not able to do so the blame is on the operator? A wrong design is a wrong design, no matter how much you train the operators
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Old 7th Apr 2019, 05:22
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Originally Posted by Airbubba
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 (WHEEL) 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 (EACH FOR ITSELF OR SOME OR ALTOGETHER?).
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 (SAID IN 1ST SENTENCE ALREADY).
In addition, the autopilot has the authority to trim the airplane in these conditions.(OK, BUT WILL IT? WHAT DOES THIS MEAN?)
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. (THIS IS WERE THE DINNER WAS BOUGHT. WHEN THERE ARE MULTIPLE METHODS OF TRIM, EACH MAY JUST COVER A BIT OF THE ENVELOPE?? THAT'S RIDICULOUS)
Boeing did not initially consider this to be a compliance issue because trim could always be achieved, even during the conditions AS STATED ABOVE whereuse of the aisle stand trim switch (WHEEL) was is 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. (STH BEING "UNUSUAL" IS STRANGE FOR A CERTIFICATION COMMENT)

The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides (THEY MEAN "REQUIRES") 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 SHALL 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 (THEY MEAN "THUMB SWITCHES" !!!).

The trim systems on the 737Max provide an appropriate level of safety (SHOULD SAY: COMPLY WITH CS25....) relative to longitudinal trim capability.

Page 15 of 114
EASA aircraft certification document written by an intern.
Never challenged by his/her/its boss to explain what the writing means.
Four terms for the same subject (wheel), totally confusing
Confusing wheel and thumb switch in the most important sentence.
Aviation document quality.

Last edited by threemiles; 7th Apr 2019 at 05:58.
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Old 7th Apr 2019, 05:25
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Originally Posted by Flt.Lt Zed
Why does Boeing not delete MCAS from their new B73 8/9s?. They have thousands flying around successfully without it.
Originally Posted by AerocatS2A

They needed z for certification.

Originally Posted by meleagertoo
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.
It is not the stall charectoristics. The B737 MAX has pitch up tendencies which don’t meet FAA Static Longitudinal Stability certification standards. To meet the standard, MCAS was needed to reduce the pitch up tendency at high angles of attack.

Addtional sim training won’t exempt you from meeting the certification standard.



Sec. 25.173 Static longitudinal stability.

Under the conditions specified in Sec. 25.175, the characteristics of the elevator control forces (including friction) and the elevator control surface displacement must be as follows:

(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. In addition, if the elevator control forces are not dependent upon the hinge moments of the elevator control surface, it must also be shown that upward displacement of the elevator trailing edge is required to obtain and maintain speeds below the specified trim speed, and a downward displacement of the elevator trailing edge is required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC / MFC , whichever is appropriate, or lower than the minimum speed for steady, unstalled flight.

(b) The airspeed must return to within 10 percent of the original trim speed when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.

(c) The stable slope of the stick force versus speed curve may not be less than 0.5 pound for each three knots or exceed a value beyond which control of the airplane is difficult.





Last edited by Lost in Saigon; 7th Apr 2019 at 05:51.
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Old 7th Apr 2019, 05:43
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Originally Posted by Lost in Saigon

This must be shown at any speed that can be obtained
except
a) speeds higher than the landing gear (VLO) or wing flap (VFE) operating limit speeds or VFC / MFC , whichever is appropriate,
or
b) lower than the minimum speed for steady, unstalled flight.

I read it that this must be shown only for speeds between minimum for steady, unstalled flight and VLO/VFE. MCAS operates when flaps are retracted. The rubber word "appropriate" may be the secret.

Last edited by threemiles; 7th Apr 2019 at 06:13.
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Old 7th Apr 2019, 05:57
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Originally Posted by threemiles
I read it that this must be shown only for speeds between minimum for steady, unstalled flight and VLO/VFE.
Yes, that is true for condition (a).

I read it that condition (b) and condition (c) must also be met. (c) doesn’t mention a speed range so assume it is for all phases of flight.

Last edited by Lost in Saigon; 7th Apr 2019 at 06:08.
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Old 7th Apr 2019, 06:01
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Originally Posted by Lost in Saigon


Yes, that is true for condition (a).

I read it that condition (b) and condition (c) must also be met.
Not to be shown for b)
within the range specified in paragraph (a) of this section
Seems to be true for c), though
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Old 7th Apr 2019, 06:19
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Originally Posted by UnderDuress
Gear Up.
Stick Shaker, no problem as the aircraft is in trim, flaps, etc. are all just fine. A-Thl is still in HOLD.
Aviate and navigate.
Call out "AIRPSEED UNRELIABLE MEMORY ITEMS".
Do the MI's which takes 10-15 sec if you are fast or 159 sec if slow and forget them which is usual here.
10 Deg Pitch 80% N1 and simply fly runway heading climbing slowly with slow increasing IAS.
CP calls for the NNC 10.1 and skip Step 7 for now if you wish as that will take too long to open the page. Just keep the pitch and power set above. No terrain, CB's, windshear, TCAS risk, etc.
PM makes the PAN call, reaches and opens the NNC QRH.
Step 9 leads to 10.
Step 10, leads to Step 11 & the FO has Control.
Step 12 would have not worked or maybe just for a while. When the AP drops, manual flying on a beautiful sunny morning. Easy as VMC, two AC power sources, lots of fuel, flaps and slats and gear that will extend normally and crew well rested.
Step 13 switch from Alt 1 to 2.
Step 14 would have taken painfully long as CP's and FO's usually fumble their way thru there. Eventually open NNC page PI-QRH.10.1 & 10.2 and you are finished in maybe 150 to 300 secs.
All the while with F5 and you want to burn fuel anyways.
After Take Off Checklist.
Now all under control, adivse ATC, swing north or south, prepare for an over weight landing, PA to the Seatbelted Cabin Crew and Pax. Even a visual return is no issue as they all grew up flying locally around Addis but FMC still available for the RNAV 07R.
F40, AB3, Max Reverse and expect maybe a brake cooling issue. That is also hard for many to figure out here the Brake Cooling and since over Max Landing Weight you'd need the QRH again for the landing distance,
NNC finished and you will be on the ground in 10 - 20 mins safe after pressing TOGA.
Just like the sim, but the sim sessions at ET are dramatically different and produce this outcome, plus the commercial pressure GET TO NBO ITIS reared its head for sure.
Notes:
They would have kept F5, MCAS remains dormant and you live for another day.
So it comes down to following the standard published Boeing procedures.
That will be exactly how Boeing's massive legal team will argue it for the next many years of litigation.
BUT NO IT WAS A COMPLETE DIVERSION FROM THE SOP, FOM, FCTM, AND QRH and JEP EMERGENCY PROCEDURES.

So in doing what they did, you enter the realm of being a Test Pilot.
In the sim, would have been a Fail for the actual actions taken on March 5th.

Learn from it my Pilot Friends.
so you're blaming both sets of pilots? do you work for Boeing by any chance?

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Old 7th Apr 2019, 06:26
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Nope don't work for Boeing but flew the 38M.
Prove me wrong.
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Old 7th Apr 2019, 06:31
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Why isn’t there an “MCAS Active” warning or annunciator?
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