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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 3rd Apr 2019, 18:15
  #2981 (permalink)  
 
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Salute!

Another solution that keeps the basic construction jigs and such in place for building more dinosaurs was proposed earlier here, but will still require certification, just not as much. Expensive, yes. But not as expensive as all the $$$ that will be paid out to the families and possibly airlines with useless airframes on the ramp.

Ditch all the STS, feel system, MCAS and such crapola. Go FBW and retain a few of those ropes, levers, pulleys, tubes and such that some here still prefer for a modern airliner. You wouldn't have to worry about control force versus AoA or "Q" or mach gradients, just ask the Airbus folks how they got by the FAR 25 requirements. And you knoiw what? I don't think the FBW version of the MAX would pass. The design is not as inherently as "nice" and gentle and forgiving as it should be.

The 'bus showed its inherent stability and pretty good aerodynamic characteristics on at least two crashes - the "showboat" public relations pass and AF447. Without all the "protections" and such, most pilots could fly the thing in the "direct mode" and get it back on the ground in one piece. After all, FBW primarily means replacing all those mechanical connections with a hydraulic source and an actuator commanded by an electrical signal. You do not even need a computer to have what the 'bus calls "direct law".

So I have a feeling this "fix" is gonna take a lot more time and $$$ before many carriers and countries are gonna buy in. I wish Boeing well, but I also wish Boeing would get back to the basics that made them one of the premier aircraft production empires in aviation history.
And just so you know, I never flew a single model of anything Boeing ever built. I flew McDonnell, Cessna, Lockheed, Convair/General Dynamics and Vought.military planes , and on the civilian side Luscombe, Piper, Aeronica and Taylorcraft.

Gums sends...
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Old 3rd Apr 2019, 18:45
  #2982 (permalink)  
 
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Not a very good lesson learned from lion.

I think the procedure should be:

If Trim is bad and you didn't put it there (memory item, but quite intuitive).

1. Bring it back to something reasonable with column switches.
2. Then cut it.

Maybe also including a suggestion to check that you actually are restoring trim in the direction you desire with a quick look at the trim wheel at step one, and go straight to 2 if you are not (different failure than what we are discussing).

If for some reason you need minute adjust afterwards, use the wheel.

Column switch vs mcas, column wins, it's faster and overrides mcas.

But,

Hand crank vs mcas, mcas wins. Hand crank too slow and perhaps underpowered. You may run out of usable sky or energy before you get it back.

I'm also in the group of those who would like to see an aero solution, although for some reason I would expect some lift added in the rear lateral fuselage at high aoa only, rather than modify the nacelles (I can't see in which way) or add a trailing lift device at the tip of the wings (big mess, and heavier due to shorter leverage)

Main advantage over software patch: it will actually help in real life.
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Old 3rd Apr 2019, 18:59
  #2983 (permalink)  
 
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One sensor, 10E-9 reliability, LoL!
(Referring to Post #3024 from RatherBeFlying).

Last edited by jpfle; 3rd Apr 2019 at 19:08. Reason: Added context.
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Old 3rd Apr 2019, 19:17
  #2984 (permalink)  
 
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MCAS authory vs column switch?

Originally Posted by ecto1 View Post
Column switch vs mcas, column wins.
I that dead sure? Have an authoritative source?
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Old 3rd Apr 2019, 19:28
  #2985 (permalink)  
 
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The problem is the instant you get airborne, you have the stick shaker AND IAS disagree. If you have the mental capacity to realise at this point that you aren't actually stalling (first instinct would be "oh sh!t, are my takeoff performance or flaps figures correct"), AoA probe failure wouldn't be my first thought.

Once you have had time and brainspace to process, "good, I'm actually still flying, no buffet, not stalling my speed & config are probably good", the next thought would be to notice IAS disagree, disconnect the autopilot (not engaged at this point) autothrottle blip blip off, lets climb at my initial performance tool target (if available ~15 +/- degrees). Now we are climbing away with a know thrust, known good pitch attitude, not stalling and that is going to get me toward a safe place (away from the hard stuff).

In all the confusion my buddy would probably be prompting me to turn off the flight directors too. At this point we have done the first part of the IAS disagree memory items, pitch and thrust to come.

This might make this sound somewhat logical, possibly easy, but believe me, that would be a REALLY bad day already and I might be between 400 to 1000' AGL before I can even begin to comprehend what MAY be wrong with my aircraft.

Boeing only gives guidance of 10 degrees nose up pitch and 80% thrust for this scenario. Would you really wanting do that with the stick shaker going off just after takeoff? It's going to climb like a dog and there are hills around and I have the SS going off, so I think I'm going to try to climb away for a while with some known good datums.

So, the problem is in this scenario disconnecting the autothrottle with the blip blip is actually going to leave you with takeoff, not climb thrust, not 80% N1 set. You may not revisit the thrust for some time because I still have the stick shaker. That is possibly a trap in all this. There is so much other stuff going on, that having takeoff thrust set is going to get you into the >230 knot realm real quick once you lower the nose to 10 degrees and forget to set the 80% N1 . Oh did I mention, that, at this point I may have to consider moving the stab trim switches to cutout too before retracting the flaps. Now I have to use the manual pitch trim wheel too as we accelerate.

I am actually now running TWO memory checklist simultaneously, the IAS disagree and Runaway Stabiliser. All because of a single sensor failure. Surely the certification basis for the aircraft is fundamentally flawed on this count alone.

Gums, the reason Boeing don't want to certify a new type is probably not so much the actual cost of the certification, rather the cost of type rating pilots. It was the operators who put the pressure on Boeing. Boeing knew if it was a new type they it would hand operators an opportunity to play the Airbus card against them, if you are going to have to put your pilots through a rating, does it matter if it is Boeing or Airbus?
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Old 3rd Apr 2019, 20:01
  #2986 (permalink)  
 
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Originally Posted by fgrieu View Post
I that dead sure? Have an authoritative source?
Control column cutout switches do not inhibit MCAS trimming (which makes sense if you think why the system was designed in the first place, but also no sense to a 737 pilot that doesn't expect the trimwheel to move AND when pulling up, pre-MCAS discovery).
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Old 3rd Apr 2019, 20:02
  #2987 (permalink)  
 
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CT:
It is a shame that the Mentour Pilot video has been disabled, I managed to watch it and it showed what happens when the IAS disagree and runaway trim checklist are followed in the (presumed) ET MCAS case. Overall fairly similar to your scenario.

The pilots in the sim calmly and methodically followed the checklists in what I would call a demonstrating or teaching mode, certainly not stressed or surprised.
Don't believer they even had a stick shaker going.

Even so they ended up in a state where manual trim inputs were physically close to impossible after electrical trim cutout due to the air speed.
My takeaway was that unless the pilot trimmed close to neutral before electrical tim cutout there was no way to manually trim.
Note that this should be possible (as shown in both lion air flights) since pilot trim cancels (for 5 seconds) MCAS trim actions.

One other observation from the video is that from the jumpseat camera point of view the trim wheel action is very obvious. I suspect it might be much less so for stressed pilots trying to make sense of the situation. This may be why the jumpseat pilot was able to save the penultimate Lion air flight.

Gums: If you are referring my post re making a full FBW 737, that was meant as a thought experiment on automation more than a practical suggestion, if for no other reason that it 737 FBW would certainly require more than a slideware conversion course.
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Old 3rd Apr 2019, 20:24
  #2988 (permalink)  
 
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Given the known the MCAS problem, and Boeing air directive, I would use flaps 1 for as long as possible to prevent MCAS from engaging if pilot sees IAS disagree. Once atleast 2500 agl retract flaps to see if MCAS engages. If yes, extend flaps immediately and return to airport. WSJ reported MCAS engaged in this flight at 450 agl which suggests plane already in clean configuration. Interesting to see what fdr shows for flap settings and retraction.
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Old 3rd Apr 2019, 20:47
  #2989 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
CT:
It is a shame that the Mentour Pilot video has been disabled, I managed to watch it and it showed what happens when the IAS disagree and runaway trim checklist are followed in the (presumed) ET MCAS case. Overall fairly similar to your scenario.

The pilots in the sim calmly and methodically followed the checklists in what I would call a demonstrating or teaching mode, certainly not stressed or surprised. Don't believer they even had a stick shaker going.

Even so they ended up in a state where manual trim inputs were physically close to impossible after electrical trim cutout due to the air speed.
My takeaway was that unless the pilot trimmed close to neutral before electrical tim cutout there was no way to manually trim.
Note that this should be possible (as shown in both lion air flights) since pilot trim cancels (for 5 seconds) MCAS trim actions.

One other observation from the video is that from the jumpseat camera point of view the trim wheel action is very obvious. I suspect it might be much less so for stressed pilots trying to make sense of the situation. This may be why the jumpseat pilot was able to save the penultimate Lion air flight.

Gums: If you are referring my post re making a full FBW 737, that was meant as a thought experiment on automation more than a practical suggestion, if for no other reason that it 737 FBW would certainly require more than a slideware conversion course.
I never got to see Mentour Pilot's latest video, but a previous one from 2 weeks ago on runaway stabiliser trim is still available. It shows a much 'tamer' scenario, with speed < 250kts, and positive pitch, but indicates that manual trim can be difficult. Worth watching a minute of footage (start at 18m35s), for those who can't visualise what actually happens in such a scenario:
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Old 3rd Apr 2019, 21:03
  #2990 (permalink)  
 
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Originally Posted by RatherBeFlying View Post
It appears that MCAS can in ten seconds move the stab whenever it's in the mood, but the pilots need considerably longer to bring back the stab with dozens of cranks of manual trim - provided that airload allows them to move the trim.


...... The software will have to get even fancier to satisfy 10E-9 reliability.

.
There is no such requirement applicable, besides you probably wouldn't believe it anyhow.

It's really a balance between the pilot and the design. If the pilot can't be relied on, then the design is not good enough
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Old 3rd Apr 2019, 21:20
  #2991 (permalink)  
 
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Originally Posted by jagema View Post
Control column cutout switches do not inhibit MCAS trimming (which makes sense if you think why the system was designed in the first place, but also no sense to a 737 pilot that doesn't expect the trimwheel to move AND when pulling up, pre-MCAS discovery).
The control column trim switches are not the "cutout" switches. I'm inclined to believe [Late edit: it turns out, wrongly] that central cutout switches have authority over MCAS, but control column trim switches do not, contrary to
Originally Posted by ecto1 View Post
Column switch vs mcas, column wins.
But again, do we have an authoritative answer, based on some circuit diagram, manual, first-hand knowledge?

Last edited by fgrieu; 4th Apr 2019 at 06:04.
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Old 3rd Apr 2019, 21:32
  #2992 (permalink)  
 
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An update from ABC News:

Sensor damaged by a foreign object on Ethiopian Airlines 737 MAX triggered fatal crash: Sources

The preliminary crash findings are expected to be released on Thursday.

By David Kerley and Jeffrey Cook Apr 3, 2019 5:04 PM

The Ethiopian Airlines Boeing 737 MAX, which crashed in March and killed 157 people, suffered a damaged angle-of-attack sensor upon takeoff from a bird or foreign object, triggering erroneous data and the activation an anti-stall system -- called MCAS -- sending the pitch of the plane downward and ultimately crashing into the ground, two aviation sources familiar with the investigation told ABC News.

As the jet was nose diving, the Boeing 737 MAX pilots did not try to electronically pull the nose of the plane up before following Boeing's emergency procedures of disengaging power to the horizontal stabilizer on the rear of the aircraft, according to the sources.

One source told ABC News that they manually attempted to bring the nose of the plane back up by using the trim wheel. Soon after, the pilots restored power to the horizontal stabilizer.

With power restored, the MCAS was re-engaged, the sources said, and the pilots were unable to regain control and the plane crashed.

The preliminary findings in the crash investigation are expected to be released by transportation officials in Ethiopia on Thursday morning.
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Old 3rd Apr 2019, 21:42
  #2993 (permalink)  
 
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I believe the basic problem is lift from the engine cowlings at high AoA in a turn with flaps up this I think pulls the CL in front of the C of G so the nose keeps pitching up.

I seem to remember Learjet had a problem with a T tail model that at high angel of attack could blank the tail so entering a deep stall, so required a stick shaker.

So to over come the problem they fitted under the rear fuselage what they called Delta Fins these at high AoA produced lift and pushed the nose down so no stick shaker or any other aid required. May be the fix the Max needs. Just a thought.
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Old 3rd Apr 2019, 22:09
  #2994 (permalink)  
 
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Originally Posted by fgrieu View Post
The control column trim switches are not the "cutout" switches. I'm inclined to believe that central cutout switches have authority over MCAS, but control column trim switches do not, contrary to

But again, do we have an authoritative answer, based on some circuit diagram, manual, first-hand knowledge?
Yes, we do. We are talking 3 sets of switches in series here: 1) thumb (normally open), 2) control column "extreme deflection" (normally closed) and 3)pedestal cutouts (normally closed).

What I meant is that if you electrically trim nose up with your thumb, MCAS stops trimming nose down right then, so you win. Plus, there is a 5 second delay between you releasing your thumb and MCAS trying to nosedive again. That's your timeframe to kill it with pedestal cutout switches.

I don't know where I learnt it first, but that fact is "authoritatively" shown on FDR from both lionair flights, to begin with. Also, reductio ad adsurdum: Otherwise no way the scenario is survivable for any amount of time with cutout switches to "normal". 60 seconds after first MCAS activation you are diving vertical, regardless of elevator position.

In fact, if you could hear it trim, (you cant because stick shaker) it would be quite trivial to discover that, as soon as you trim with your thumb switch, it stops. I'd bet the accidents would have not happened.

The only ongoing debate now* is (and as far as I know, there is no consensus yet but there will be soon) if you were slow with your thumb and got to a point in which you need a lot of pull to remain level, your control column "extreme deflection" trim cutout switches may inhibit your trim inputs and then (possibly) MCAS wins by lack of opposition. (because at that moment you will not recall yet another system working silently against you and release control column to regain the ability to trim).

Which, if comfirmed, is a frightening situation, because it only takes one panicking pilot pulling too hard to prevent both from trimming up and wining the fight against MCAS. Thats a good theory to explain what happened in the last seconds of the first crash.

*Edit: I'm quite convinced after examining again the schematics, that MCAS vs thumb trim switch battle is not affected by control column deflection switches.

Last edited by ecto1; 3rd Apr 2019 at 22:57.
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Old 3rd Apr 2019, 22:10
  #2995 (permalink)  
 
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Originally Posted by horizon flyer View Post
I believe the basic problem is lift from the engine cowlings at high AoA in a turn with flaps up this I think pulls the CL in front of the C of G so the nose keeps pitching up.

I seem to remember Learjet had a problem with a T tail model that at high angel of attack could blank the tail so entering a deep stall, so required a stick shaker.

So to over come the problem they fitted under the rear fuselage what they called Delta Fins these at high AoA produced lift and pushed the nose down so no stick shaker or any other aid required. May be the fix the Max needs. Just a thought.
Yes, that is also my impression.
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Old 3rd Apr 2019, 22:18
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Originally Posted by fgrieu View Post
I'm inclined to believe that central cutout switches have authority over MCAS, but control column trim switches do not
This is correct except that it's the control column cutout switches that do not have authority.

Originally Posted by ecto1
The only ongoing debate now is (and as far as I know, there is no consensus yet but there will be soon) if you were slow with your thumb and got to a point in which you need a lot of pull to remain level, your control column "extreme deflection" trim cutout switches may inhibit your trim inputs and then (possibly) MCAS wins by lack of opposition.
There is a forward and an aft control column cutout switch. Enough movement of the control column in either direction opens the circuit, creating a discontinuity and disallowing trim in the direction of column deflection (ie. You cannot trim up while pushing down) unless STAB TRIM OVRD switch is in OVRD. I guess you refer to the cutout switches installed in the column when speaking of "extreme deflection trim cutout switches". Schematic for clarity.

B737 Trim

edit: this is the schematic for the NG. The MAX introduced changed to the pedestal cutout switches, renamed PRI and B/U respectively.

Last edited by jagema; 3rd Apr 2019 at 22:48.
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Old 3rd Apr 2019, 22:20
  #2997 (permalink)  
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THS Airloads Mitigation Procedure

I am aware of the procedure but was never taught it on type training on the 737 conducted under FAA.

Simply, there is no manner by which such a heroic technique complied with the Type Certification requirements under Part 25. The rules do not permit the application of exceptional force, technique or skill, and any need to have 2 pilots apply force at the same time is grossly unacceptable, breaching the FAA’s own prohibition on control inputs by more than one pilot.

As the aircraft often flies with a seat unoccupied when nature calls, it would be incompatible to have a flight condition where both pilots must be able to have inputs onto controls at all times in flight.

The 737 is grandfathered to revisions of the rules in the 60’s but the basic rationales have not changed that much.

If the the plane has any condition that may necessitate rock n’ roll as a recovery, using both pilots, then I would imagine that it needs a type review and rectification of the underlying design deficiency.

How on on earth would it be acceptable to have a passenger transport with a known need for exceptional training outside of the training for CPL or ATPL/ATP, requiring both pilots simultaneous inputs on the flight controls, necessitating a ballistic flight path, where the pax are not required to be restrained at ALL times, I.e., whenever the flaps are retracted....

it it is not acceptable under the rules, and the plane has been known to have this characteristic for how long?

I’ve flown flown the 737 out way beyond VMO MMO Under controlled conditions, and while careful about tuck considerations, was not aware of a “jack stall” potential on the aircraft. That is troubling.

25.143 provides the general handling qualities requirements, including statements on skill, limit of force on elevator to 70 lbs short term, 2?hands, and 10 lbs long term.

25.255 covers mid trimmed cases, and potentially lets the OEM off the hook, but places the regulations in question. Recovery with a force of 120 lbs should be shown for a maximum runaway trim of 3 seconds of trim motion for the conditions of flight. MCAS action exceeds the 3 seconds, but the OEM is only required to show acceptable characteristics with 3 seconds of trim motion from in trim conditions, which is clearly inadequate to protect the aircraft operation.

Last edited by fdr; 3rd Apr 2019 at 23:12.
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Old 3rd Apr 2019, 22:28
  #2998 (permalink)  
 
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Originally Posted by RatherBeFlying View Post
It appears that MCAS can in ten seconds move the stab whenever it's in the mood, but the pilots need considerably longer to bring back the stab with dozens of cranks of manual trim - provided that airload allows them to move the trim.

Very much an unequal contest.

​​​​​​MCAS really shouldn't be putting in more trim than can be corrected by the crew in the interval before it reactivates.

But then, limiting MCAS authority might fail to achieve required stick force increase approaching stall. The software will have to get even fancier to satisfy 10E-9 reliability.

I'm with gums. Dump MCAS and fix the nacelle aerodynamics.
That's Design Assurance Level A. Does anyone here know what the DAL for this software actually is? As a previous poster said, it's no easy fix to make it so, if it's not DAL A.
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Old 3rd Apr 2019, 22:33
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Originally Posted by jagema View Post
This is correct
No it isn't. AFAIK

MCAS will operate regardless of the control column cutout switches.
It will not operate against the control column TRIM switches, or if the stab trim switches are cutout.
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Old 3rd Apr 2019, 22:38
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Originally Posted by Albino View Post
No it isn't. AFAIK

MCAS will operate regardless of the control column cutout switches.
It will not operate against the control column TRIM switches, or if the stab trim switches are cutout.
Precisely what I meant by "correct." We are saying the same thing. MCAS obeys all switches except for the aft and fwd motion of the column, essentially.

Edit: I thought I read control column cutout in my quoted post above. Corrected

Last edited by jagema; 3rd Apr 2019 at 22:49.
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