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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 6th Apr 2019, 01:10
  #3401 (permalink)  
 
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Originally Posted by deltafox44 View Post
Attempted level was FL320 !

With stall warning and attempting to clear the terrain, more speed means more potential energy, so I think overspeed was not on top of their priorities.

If Boeing NNC for trim runaway had included "reduce speed if manual trimming is too hard", perhaps they would have done it...
They set a lower alt in the window, so not trying to climb to F320
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Old 6th Apr 2019, 01:39
  #3402 (permalink)  
 
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Originally Posted by deltafox44 View Post
The nose up moment of the engines thrust may be important at lower speeds, but negligible at higher speeds, since the thrust is constant but any other aerodynamic moments vary as the square of speed.

What about the pitch of airbrakes ?
🧐

Thrust also varies as a square of speed?!

Acceleration is "metres per second squared"

I think I see where you may be trying to come from... thrust and drag are balancing out, increasing thrust will result in an ever decreasing change in velocity. (Or less acceleration)

But if you agree with this, you must also accept... in that state, a marginal reduction in thrust will result in an ever increasing change in velocity? (Or more deceleration)

My point is, doesn't matter where on the scale you want to pick, drag and thrust are always going to be proportional to eachother.

Last edited by positiverate20; 6th Apr 2019 at 02:18.
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Old 6th Apr 2019, 01:43
  #3403 (permalink)  
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Originally Posted by hans brinker View Post
Yeah, considering they switched the trim off, it sounds like they were aware of what was happening as far as trim. However they never reduced power and going 350kts with the flaps out is probably going to end bad too.
Don't know what you mean by "flaps out" hans brinker. If you mean the flaps were 'down', they were not. The flaps were up. If they were down, the MCAS would not have activated.
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Old 6th Apr 2019, 01:57
  #3404 (permalink)  
 
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>"Firing blanks"

That's not uncommon in avionics software. It simplifies code - and that, more often than not, makes it more reliable. Plus, the not-engaged FCC is then a hot spare, ready to engage without further logic.
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Old 6th Apr 2019, 02:11
  #3405 (permalink)  
 
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Originally Posted by deltafox44 View Post
Attempted level was FL320 !
From the narrative excerpted above:

At 05:41:21, the selected altitude was changed from 32000 ft to 14000 ft.
Addis airport elevation is 7657 feet.

Originally Posted by deltafox44 View Post
If Boeing NNC for trim runaway had included "reduce speed if manual trimming is too hard", perhaps they would have done it..
Or if it said 'don't forget to fly the plane!' Avoiding the overspeed by reducing power is pretty basic in my opinion.
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Old 6th Apr 2019, 02:11
  #3406 (permalink)  
 
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Originally Posted by AndyJS View Post
Does anyone else think that maybe the very fact that they're trying to solve this through a software update may be part of the problem?
Since the MCAS is just software (running in the FCCs) there is no other way.

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Old 6th Apr 2019, 02:12
  #3407 (permalink)  
 
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Originally Posted by TLB View Post
Don't know what you mean by "flaps out" hans brinker. If you mean the flaps were 'down', they were not. The flaps were up. If they were down, the MCAS would not have activated.
Yes, I should have said down, but was a direct reply to someone suggesting he would have left the flaps F1 in this situation, and seeing as we are up to 3000+ post already I would suggest you read before you post, so we don't get endless back and forth like this.
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Old 6th Apr 2019, 02:25
  #3408 (permalink)  
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I'm trying to read every post, so forgive if covered...

I'm not sure how microscopically detailed the data readouts are, but re the two blips of ANU which were not continued - Is it conceivable that PF was alarmed at the momentary high g due to excessive speed?

Over the last weeks I've not really been able to assess the captain's likely abilities during what must have been very demanding moments. Even gums has said he's not sure he'd have cottoned on to what was going on right away. I can well imagine the shaker, plus speed etc., causing the STS movements to blur with the intermittent MCAS rotations.

A recent poster mentioned a blip about every ten knots to counter the STS. That surprised me and shows the perfectly normal activity of the wheel in this phase.

As one who loved things going TU to make the day more interesting, I have to confess my 25 minutes with the stick-shaker going at 2000' in inky black chop really tested my ability to shut out what we quickly deemed to be a false warning. It was as though the warning was fighting to get past all reasoning. I recall my concentration giving an element of tunnel vision. I'm told it's a bog-standard human reaction but I doubt it would cut out the white patch of the wheel flashing by.
.
.

Last edited by Loose rivets; 6th Apr 2019 at 02:44.
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Old 6th Apr 2019, 03:26
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They are not “near together” the landing gear geometry is established by the sweep of the wings and the chord at fuselage join. The LG trunnions bearing is as close as physically practical to the intersection of the rear spar and MLG beam.

The b737 track is 5.7m. The A320 is 7.59m. So what? Astonishing? Since when has the B737 had a problem with scraped nacelles or crosswinds?

As has been explained by people with real B737 experience, the manual trim is very, very stiff to move when loaded at speed to the point that special technique is required - and that is assuming you even understand what the problem is in the first place - which they couldn’t since MCAS wasn’t on the training syllabus.

The MCAS put the aircraft into an almost (or totally) unrecoverable situation at low altitude and no BS about untrained inexperienced pilots is worth a pinch of rocking horse poo.

Try using any highly automated vehicle and see how YOU like it when something fails, even if you are on top of your game, the environment can get very confusing very fast. The B737 is supposed to be designed to be operated safely by the average commercial jet pilot and achieve the advertised performance when flown by said average pilot obeying the manufacturers instructions. Clearly Boeing has totally failed to do this in the latest variant of the 737 design.

As for the “new airplane” mob. It is difficult to understand how a redesign is going to make more than incremental changes to the basic B737 design. The design problem remains the same - which is why the A320 looks something like a 737. Fuselage cross section and engine position govern pretty much everything.


Last edited by Sunfish; 6th Apr 2019 at 03:38.
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Old 6th Apr 2019, 07:53
  #3410 (permalink)  
 
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Originally Posted by Gegenbeispiel View Post
Since the MCAS is just software (running in the FCCs) there is no other way.
My understanding is MCAS is only required for compliance of a regulation, and it can not be compliant due to lift from the engine cowlings during certain stages of flight without MCAS.

So the regulations could be looked at to see if still relevant, the engine cowlings could be modified or adjusted so lift is not happening in that stage of flight or the AOA interface be modified.

A software patch alone will not pass the pub test.
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Old 6th Apr 2019, 07:57
  #3411 (permalink)  
 
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Originally Posted by Bend alot View Post
My understanding is MCAS is only required for compliance of a regulation, and it can not be compliant due to lift from the engine cowlings during certain stages of flight without MCAS.

So the regulations could be looked at to see if still relevant, the engine cowlings could be modified or adjusted so lift is not happening in that stage of flight or the AOA interface be modified.

A software patch alone will not pass the pub test.
The trouble, for Boeing, with that is that it may well cause an increase in drag, as would rear fuselage strakes.
Maybe minor, maybe not so.
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Old 6th Apr 2019, 08:04
  #3412 (permalink)  
 
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Originally Posted by onsoutherntip
I am curious as to where the FDR data for the stabilizer trim is read from - yoke trim switches or the motor drive electronics? Most high power motor drives have feedback that detects if the power demand is exceeded. If this happens, power to the motor is disabled, in order to protect it. Therefore a situation could arise where even though the pilot is activating ANU trim, it results in just a short ANU motor movement, before the motor power limit is exceeded. So if the FDR records from the drive electronics, the trim ANU 'request' by the pilot, will be seen as just a 'blip' although the trim switch is still activated,

This would account for AND trim running the full period as motor power demand is not exceeded (low aerodynamic load), but ANU trim is fighting against high aerodynamic load, which activates the motor protection. Thoughts?
I have been thinking the same thing since the preliminary came out but with less Engineering knowledge than you hadn’t come to such a clear position.
I was just thinking “ I bet they were trimming nose up but the FDR only recorded what the screw jack did” without any systems knowledge to explain how that may be the case.
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Old 6th Apr 2019, 08:09
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Originally Posted by WingNut60 View Post
The trouble, for Boeing, with that is that it may well cause an increase in drag, as would rear fuselage strakes.
Maybe minor, maybe not so.
I think the problem for Boeing is they had a mechanical problem they tried to fix electronically, but badly and on the sly.
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Old 6th Apr 2019, 08:09
  #3414 (permalink)  
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Originally Posted by OldnGrounded View Post
I continue to find it disturbing and surprising that more than a few posts are focused on blaming, or at least strongly suspecting, crew error as a primary cause of the Ethiopian crash.

Surely, it should be clear, from all we have learned and discussed in the weeks since that accident, that the crew was faced with a situation that almost any crew would have found very difficult, if not impossible, to deal with successfully. If mistakes were made, they were made in an environment where not making mistakes was extremely unlikely and in which they would never have found themselves if the OEM and the regulatory authority had not made fundamental and extraordinary mistakes in designing and certifying the aircraft. And those entities weren't facing imminent sudden death when they screwed up.
I share exactly the same feelings, too many armchairs pilots ( and even non-pilots) here telling us what the crew should have done KNOWING THE FULL SITUATION IN ADVANCE.
Having myself unfortunately been through an accident , the first thing that comes to your mind is understanding what is happening and this takes a certain time to process . Your mind is rushing at 120% and things like FORDEC and DODAR are not the first things that come to your mind.., and hearing people telling me afterwards what I should have done was not helping at all. A bit of respect for the guys faced with horns , bells and Christmas trees thrown at you unexpectedly. A final remark to those advocating a reduction of power, come on after a stall warning (stick shaker) at less than 1000 Ft AGL ? , or course you will level off and keep the power ,I would argue in ANY airplane, but I am not flying 737s ...After that depends how your mind is prioritizing..

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Old 6th Apr 2019, 08:22
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A few contributors have suggested that they very quickly would have applied the Airspeed Unreliable memory items. ( flight directors off, 10 degrees NU and 80% thrust on the NG) . I think that the confusion when presented with a lot of information in a short space of time in a dynamic situation is often underestimated. It takes time to process information, and then more time to conclude its meaning and decide on a course of action. Salience is often key and I suspect that the stick shaker had it in spades. If the stick shaker did initially consume much of the Captains cognitive capability, then reducing thrust may not have been seen as a wise choice so close to the ground, with an inability to lower the nose much just after rotate the next pertinent step is to increase thrust if the stick shaker is valid.Confusion already in the first second or two is possible/probable.
Edited to add: ATC WATCHER I posted the above simultaneously as you posted with pretty much the same sentiment but without having read your post.
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Old 6th Apr 2019, 09:00
  #3416 (permalink)  
 
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It is not being wise after the fact to point out that this event was mis-handled as soon as the aircraft is airborne.
Liftoff is at 05:38:39
L/H stickshaker activates almost immediately. ( Birdstrike?)
Captains first attempt to engage autopilot is at about 400 ft AGL.
It doesn’t engage but after several attempts appears to have engaged till just after flap retraction at 05:39:45
MCAS cannot have been an issue till then, 1:06 after becoming airborne.
Engaging an autopilot with stickshaker active at 400 feet is a seriously bad idea.
It is not second guessing to say that at that point flying an attitude and thrust setting would have been the wisest option.
Startle factor is huge. I’ve been there. But that’s where you justify your pay check.
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Old 6th Apr 2019, 09:08
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Originally Posted by ATC Watcher View Post
KNOWING THE FULL SITUATION IN ADVANCE.
Were the crew unaware of the Lionair crash and the bulletin released by Boeing? How did this situation differ from that one in respect of MCAS activation?

It's an interesting point whether the stab readout is taken from what is commanded or the position of the jack. Considering the AND command is registered without stab movement I suspect it is demand, it's how the narrative reads as well.

Ethiopian have played a blinder IMO. By making their press release before the initial report media around the world are reporting that the crew repeatedly followed procedures, BBC are still highlighting this point. From the data released memory items for Airspeed Unreliable were not actioned, the aircraft was not controlled with pitch AND trim as per the Unscheduled Stab Trim memory items. Nobody has questioned the validity of this statement.

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Old 6th Apr 2019, 09:17
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I understand what you are saying GG and I agree that engaging A/P is not the way to go about solving problems like this, I also agree that an attitude and thrust setting is where you want to end up in this situation, however, between sensing the stick shaker, recognising it’s meaning, reassessing the airspeed, maybe glancing at the flap indicator, sensing that there are other warnings occurring and deciding not to lower the nose as per the memory items because it may be a false stick shaker, time will pass, how much time? As I said, I think some posters are underestimating how much time would pass before they reduced thrust that close to the ground.
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Old 6th Apr 2019, 09:26
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https://ecfr.io/Title-14/se14.3.121_1344

"§121.344 Digital flight data recorders for transport category airplanes.

(a) . . . The operational parameters required to be recorded by digital flight data recorders required by this section are as follows: . . .

. . . (19) Pitch trim surface position or parameters of paragraph (a)(82) of this section if currently recorded;

. . . (82) Cockpit trim control input position—pitch . . . "

So toss a coin. With help from Boeing and the carrier(s), the investigators should be able to determine the signal source.
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Old 6th Apr 2019, 09:27
  #3420 (permalink)  
 
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73,
I’ll predict that one of major findings in both of these accidents is that everybody forgot just to fly the aircraft.
The B737 is a very simple aircraft with lots of bells and whistles, most of which are nice to have, not must have.
An enthusiastic Boeing instructor once took me to 35,000 ft in the simulator at the end of a training session then reached up to the overhead panel and turned everything off.
The aircraft still flew.
Dont think they do much of that stuff anymore.
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