Ethiopian airliner down in Africa
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Hans B
Working for the B Team lately
Never was a Nr Man as in memorizing a heap of Pitch Pwr.
But I love Whatever It takes , then BallPark !
Let me give it guess:
94 N1 to say 70% N1 ca 240kts F5, ehhh. 1 to 2 units ANU say 1.5 ( Trim CHANGE)
Pure guess
Never was a Nr Man as in memorizing a heap of Pitch Pwr.
But I love Whatever It takes , then BallPark !
Let me give it guess:
94 N1 to say 70% N1 ca 240kts F5, ehhh. 1 to 2 units ANU say 1.5 ( Trim CHANGE)
Pure guess
Last edited by BluSdUp; 5th Apr 2019 at 21:17. Reason: ( Trim Change) added for cleraty
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Not sure about jumping into this 3300+ post thread but here goes:
I'm concerned about the crew's actions both for the manual trim attempt, and with the electrical trim attempts just before they lose control. And I can't help but distrust the inexperienced First Officer more.
To summarize:
- they had the MCAS pitch control problems
- got the Cut-out switches to stop MCAS from trimming down any more
- they're flying OK, got some altitude banked, although still in crisis mode, still having to hold back pressure, deal with the one stick shaker, overspeed clackers after some point, and what not
- there's a discussion about the manual trim not working. We don't know the exact words used.
- Interpretation: Might have to do with high forces on the manual trim wheel, but it is also unclear whether the First Officer really doing what was expected. Was he just hitting the thumb trim switch, or trying to roll the trim wheel (without much experiences of the forces that might be involved) or did he actually have the fold-out handle open and still find he was unable to turn it?
- either way, they keep flying OK for another minute or so
- then there are the 2 very short electrical up trim attempts (as others have also commented on). I agree that the graphs show a small up trim effect. Hard to see on the graph but really does look like a little bit of nose up trim change. Barring any totally unexpected electrical issue, this is only possible with electric trim turned back on!
- very soon after, MCAS kicks in, trimming a bunch nose low, and the pilots lose control and nose over.
The preliminary report gives no indication that the pilots discussed turning electric trim back on. Nothing about, "Despite the AD saying to leave it off, you turn electric trim back on, I'll trim out these awful control forces, you turn it back off before this thing tries to pitch down again."
Did the Captain try turning it back on? Or was the First Officer fiddling around on his own? Trim gets turned back on with no consultation and but only 2 ineffective short trim activations are made. Were jackscrew forces so high that electric trim wasn't working well? Who knows, I'll leave that to the experts. But the electric trim attempts were two short blips, not like trying mashing that button down a full 5 seconds to see if they got some effect out of it.
That really messed them up, ineffective trim attempts without killing the electric trim system again afterwards.
I'm concerned about the crew's actions both for the manual trim attempt, and with the electrical trim attempts just before they lose control. And I can't help but distrust the inexperienced First Officer more.
To summarize:
- they had the MCAS pitch control problems
- got the Cut-out switches to stop MCAS from trimming down any more
- they're flying OK, got some altitude banked, although still in crisis mode, still having to hold back pressure, deal with the one stick shaker, overspeed clackers after some point, and what not
- there's a discussion about the manual trim not working. We don't know the exact words used.
- Interpretation: Might have to do with high forces on the manual trim wheel, but it is also unclear whether the First Officer really doing what was expected. Was he just hitting the thumb trim switch, or trying to roll the trim wheel (without much experiences of the forces that might be involved) or did he actually have the fold-out handle open and still find he was unable to turn it?
- either way, they keep flying OK for another minute or so
- then there are the 2 very short electrical up trim attempts (as others have also commented on). I agree that the graphs show a small up trim effect. Hard to see on the graph but really does look like a little bit of nose up trim change. Barring any totally unexpected electrical issue, this is only possible with electric trim turned back on!
- very soon after, MCAS kicks in, trimming a bunch nose low, and the pilots lose control and nose over.
The preliminary report gives no indication that the pilots discussed turning electric trim back on. Nothing about, "Despite the AD saying to leave it off, you turn electric trim back on, I'll trim out these awful control forces, you turn it back off before this thing tries to pitch down again."
Did the Captain try turning it back on? Or was the First Officer fiddling around on his own? Trim gets turned back on with no consultation and but only 2 ineffective short trim activations are made. Were jackscrew forces so high that electric trim wasn't working well? Who knows, I'll leave that to the experts. But the electric trim attempts were two short blips, not like trying mashing that button down a full 5 seconds to see if they got some effect out of it.
That really messed them up, ineffective trim attempts without killing the electric trim system again afterwards.
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Let me see:
1- All the update training for a pilot to fly a Max is 1 hour on an iPad, says the FAA, and Boeing.
2- A couple of max crashed.
3 - Older 737s seem safe in the hands of the same pilots.
The FAA and Boeing agree point 1 was not right.
Now the FAA and Boeing tell us that a fix will make point 1 right.
Should we believe them?
1- All the update training for a pilot to fly a Max is 1 hour on an iPad, says the FAA, and Boeing.
2- A couple of max crashed.
3 - Older 737s seem safe in the hands of the same pilots.
The FAA and Boeing agree point 1 was not right.
Now the FAA and Boeing tell us that a fix will make point 1 right.
Should we believe them?
Salute!
Getting into some good "what if" and "there I was" stuff, and some of it should be of interest to the Boeing folks in the design shop as well as some FAA folks. As Mawtha would say, "it's a good thing".
- I am willing to buiy most here a beer if the design folks and fault tree analysis folks ever considered activation of MCAS at 400 ot 500 ft ( depends on your procedures for flaps and such, but remember that in most of my jets I just raised gear when having a positive rate of climb, and then flaps a few seconds later; Viper was together, as flaperons went up and down with the gear handle)
The doggone thing (MCAS) seemed to be geared to a medium or high altitude turning maneuver at "holding" airspeed/AoA. Can't help but feel they never envisioned it cranking in over 2 degrees of trim at low altitude and low mach with stall warning going and stick shaking and warning lights illuninated.
- Why change the trim cutout switch wiring? You know. One for HAL and the other for me seemed to be the standard from day one. That configuration would please many of the Chuck Yeager folks on this forum, and I agree with them. At least I know what I have to play/work with. That aspect of the flght controls is not a consideration in the later model Airbus, Raptor or Stubby ( F-35) flight controls because you need electric power to the actuators 100% of the time! Duuuhhhh? We had a serious power supply design defect in the early Vipers, and it took two or three crashes to figure it out. After that, walla! And for you millenium yutes, our early FLCS computers were analog chips, not digital. They were very robust when volts and amps went into la la land because they failed gracefully. Later digital FLCS boxes had a more robust power supply configuration, because when those puppies go west. it is all or nothing!
In all fairness, in my leading edge flap failure adventure I used the only flight control switch besides for the deep stall direct mode doofer - the flap switch. It allowed me to lock the opposing flap to keep a more predictable (?) configuration, LOL.
- As with most pilots here, I feel badly the crew did not pull the power back as the 610 crew did. With all that was going on, I cut them a little slack. There are two good lessons to be learned, though. 1) Aero forces on the stab can give you a major headache if you are going fast with a trim problem, and 2) you should try to follow the same takeoff-to-climb sequence you did a thousand times. Remember to pull back power to climb or low altitude maneuvering power and pitch.
There many other lessons and design considerations to be had with these two crashes. I just hope the 737 pilots here are reading our whines and theories and war stories, then fold some scenarios into their personal procedures.
Gums sends...
Getting into some good "what if" and "there I was" stuff, and some of it should be of interest to the Boeing folks in the design shop as well as some FAA folks. As Mawtha would say, "it's a good thing".
- I am willing to buiy most here a beer if the design folks and fault tree analysis folks ever considered activation of MCAS at 400 ot 500 ft ( depends on your procedures for flaps and such, but remember that in most of my jets I just raised gear when having a positive rate of climb, and then flaps a few seconds later; Viper was together, as flaperons went up and down with the gear handle)
The doggone thing (MCAS) seemed to be geared to a medium or high altitude turning maneuver at "holding" airspeed/AoA. Can't help but feel they never envisioned it cranking in over 2 degrees of trim at low altitude and low mach with stall warning going and stick shaking and warning lights illuninated.
- Why change the trim cutout switch wiring? You know. One for HAL and the other for me seemed to be the standard from day one. That configuration would please many of the Chuck Yeager folks on this forum, and I agree with them. At least I know what I have to play/work with. That aspect of the flght controls is not a consideration in the later model Airbus, Raptor or Stubby ( F-35) flight controls because you need electric power to the actuators 100% of the time! Duuuhhhh? We had a serious power supply design defect in the early Vipers, and it took two or three crashes to figure it out. After that, walla! And for you millenium yutes, our early FLCS computers were analog chips, not digital. They were very robust when volts and amps went into la la land because they failed gracefully. Later digital FLCS boxes had a more robust power supply configuration, because when those puppies go west. it is all or nothing!
In all fairness, in my leading edge flap failure adventure I used the only flight control switch besides for the deep stall direct mode doofer - the flap switch. It allowed me to lock the opposing flap to keep a more predictable (?) configuration, LOL.
- As with most pilots here, I feel badly the crew did not pull the power back as the 610 crew did. With all that was going on, I cut them a little slack. There are two good lessons to be learned, though. 1) Aero forces on the stab can give you a major headache if you are going fast with a trim problem, and 2) you should try to follow the same takeoff-to-climb sequence you did a thousand times. Remember to pull back power to climb or low altitude maneuvering power and pitch.
There many other lessons and design considerations to be had with these two crashes. I just hope the 737 pilots here are reading our whines and theories and war stories, then fold some scenarios into their personal procedures.
Gums sends...
Last edited by gums; 5th Apr 2019 at 19:46. Reason: clarity
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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.
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.
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Any reduction in power would have created a significant AND moment. The longitudinal acceleration was positive throughout- right up until the final MCAS AND. (0.1g at end equivilant to 0-60mph/0-100kmh in 27seconds.) The actual acceleration provided by thrust would need to be calculated using both vertical (above 1g) and longitudinal (above 0g) acceleration data.
That thrust moment of the engines coupled with the aerodynamics of the engine cowling was in fact assisting them with pitch (and would do so with diminishing effect up until VH) The fact that it also masked the true trim when they initially cut it out is possibly the reason why they didn't attempt manual trim wheel as soon as cut outs were flicked.
That thrust moment of the engines coupled with the aerodynamics of the engine cowling was in fact assisting them with pitch (and would do so with diminishing effect up until VH) The fact that it also masked the true trim when they initially cut it out is possibly the reason why they didn't attempt manual trim wheel as soon as cut outs were flicked.
The engine cowling lift is only significant at high AOA (that's why MCAS only operates when it thinks the aircraft is at high AOA). The aircraft was actually flying with a low AOA. A reduced speed would have increased the elevator authority and reduced the load on the manual trim.
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At the speed they were traveling there should be no significant nose down pitch from reducing the power to a reasonable level.
The engine cowling lift is only significant at high AOA (that's why MCAS only operates when it thinks the aircraft is at high AOA). The aircraft was actually flying with a low AOA. A reduced speed would have increased the elevator authority and reduced the load on the manual trim.
The engine cowling lift is only significant at high AOA (that's why MCAS only operates when it thinks the aircraft is at high AOA). The aircraft was actually flying with a low AOA. A reduced speed would have increased the elevator authority and reduced the load on the manual trim.
A reduced speed by having a lower thrust setting to begin with, yes more controllable.
Reducing thrust from a higher thrust setting incurs a nose down moment. Basic stuff.
We're possibly getting confused between velocity and acceleration? Momentum around the CG?
If thrust were to be reduced for this flight it would have been best to do immediately after TO. But, in this case, immediately after takeoff was stick-shaker and airspeed warning- not the optimum time to reduce thrust when hundreds of feet AGL.
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I'm still struggling with the though that a grossly mis-trimmed stab on an NG cannot be recovered by either electric trim or by the strength of 1 or even 2 pilots cranking the wheels when the aircraft is at certain parts of the flight envelope.
As covered by others above, it seems bizarre to rely on having the airspace and time available to perform an acceleration or deceleration to a trimmable speed and/or perform a manoeuvre in the opposite sense to what you are trying to achieve in order to put the stab in a safe position.
Hopefully Boeing can enlighten us as to which parts of the performance envelop allow for PF solo cranking, PM dedicated cranking, both pilots cranking or just plain impossible to crank the wheel due to aerodynamic load. The NG is still flying and I am sure the AOCs would like to know, even if the FAA is asleep at the wheel at a benign 1G.
As covered by others above, it seems bizarre to rely on having the airspace and time available to perform an acceleration or deceleration to a trimmable speed and/or perform a manoeuvre in the opposite sense to what you are trying to achieve in order to put the stab in a safe position.
Hopefully Boeing can enlighten us as to which parts of the performance envelop allow for PF solo cranking, PM dedicated cranking, both pilots cranking or just plain impossible to crank the wheel due to aerodynamic load. The NG is still flying and I am sure the AOCs would like to know, even if the FAA is asleep at the wheel at a benign 1G.
Furthermore, the phenomenon of ‘elevator blowback’ may have played a role at the last, high speed phase of the flight. If that was the case, the elevators were blown back towards neutral, despite the combined hydraulic and muscle forces.
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I don't think you'll ever see the trim near full AND during normal ops.
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DO NOT CHANGE ANYTHING! ( For now)
I do appreciate the sensory overload that ensued after AP dropped out on Flap retraction.
This is why I am a strong believer in 3 things in an Emergency with control problems!
1 Fly the Aircraft ( Analyse)
2 Fly the Aircraft ( Doing nothing makes it worse? No, good!)
3 Fly the Aircraft ( Memory items IF it does not make it worse)
A terrible situation for this crew.
No blame
I just want to learn, and most important : Boeing has to learn or else,,,,,,,,
Respectfully
Cpt B
This is why I am a strong believer in 3 things in an Emergency with control problems!
1 Fly the Aircraft ( Analyse)
2 Fly the Aircraft ( Doing nothing makes it worse? No, good!)
3 Fly the Aircraft ( Memory items IF it does not make it worse)
A terrible situation for this crew.
No blame
I just want to learn, and most important : Boeing has to learn or else,,,,,,,,
Respectfully
Cpt B
I don’t fly the 737 Max, but after doing a bit of ‘what-if-ing’, I’ve come to the conclusion that if I were a Max pilot and had stick shaker on take-off, I would not fully retract the flaps. I would retract to Flaps 1. My experience on other Boeing’s (767 & 744) is that Flaps 1 provides the best manoeuvre margin to the stall and in the 737 Max would prevent MCAS doing it’s (evil) thing.
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Slightly off-topic.
Boeing is slowing production of 737 by one fifth, from 52 to 42 a month, effective in about ten days.
Boeing will slow 737 production by one-fifth; no layoffs planned
Boeing is slowing production of 737 by one fifth, from 52 to 42 a month, effective in about ten days.
Boeing will slow 737 production by one-fifth; no layoffs planned
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I don’t fly the 737 Max, but after doing a bit of ‘what-if-ing’, I’ve come to the conclusion that if I were a Max pilot and had stick shaker on take-off, I would not fully retract the flaps. I would retract to Flaps 1. My experience on other Boeing’s (767 & 744) is that Flaps 1 provides the best manoeuvre margin to the stall and in the 737 Max would prevent MCAS doing it’s (evil) thing.
Any electronic system on any aircraft should have a means of isolating the power to that system. Even if it is critical. Is the MCAS system so infailable that such a system does not have a CB tied into it to isolate it? I am not rated on 73s but know the basic stall identification and warning systems on other types. One they do not operate until the weight offs + time delay occur and there is simple methods to deactivate.. I smell a massive regulatory and manufacturer fail that should have been apparent with the Lion Air crash. Then again I am a techie, not a system designer.
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Manada
No no no
Me and my short sentences . It was a response to the Trim demand on pwr change in a previous post!
So spot on then , 94% TOGA at 5,6 trim
Then 73%
Trim I might have got wrong as it is not in my scan, but initially we trim AND after lift off and if You are right with 4 units we do not need a big ANU trim , once pwr is established, speed 210 to 240.
Having again read Hans B question , it is twofold
210 kts F5 hardly any change after INITIAL trim at say V2+ 20!
240 F-UP is a good 1 unit plus
Yeah , so lets say 4 to 5 units.
In short , SMALL changes for a safe speed with regards to stall and manual wheel trim, me thinks!
Idle on the other hand out of trim after 101% proved to be more of a problem for FlyDubay
Me and my short sentences . It was a response to the Trim demand on pwr change in a previous post!
So spot on then , 94% TOGA at 5,6 trim
Then 73%
Trim I might have got wrong as it is not in my scan, but initially we trim AND after lift off and if You are right with 4 units we do not need a big ANU trim , once pwr is established, speed 210 to 240.
Having again read Hans B question , it is twofold
210 kts F5 hardly any change after INITIAL trim at say V2+ 20!
240 F-UP is a good 1 unit plus
Yeah , so lets say 4 to 5 units.
In short , SMALL changes for a safe speed with regards to stall and manual wheel trim, me thinks!
Idle on the other hand out of trim after 101% proved to be more of a problem for FlyDubay
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I think it's still unclear whether they were both on the same page about elevator pitch, manual/electric pitch trim, and hand wheel pitch trim, but do stall concerns fit in with the above?
They spent a total of fifteen seconds working on pitch trim; first the FO, later, "together." It's not clear to me whether at any point they each freed up a hand to use on the hand wheels.
Last edited by fotoguzzi; 5th Apr 2019 at 21:32. Reason: typo; add timeframe info
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Simplicity, user friendliness and graceful degradation
Gums,
Like you I have absolutely zero experience in modern liners like the MAX or NEO. But when reading accident and incident reports, I get the feeling that beside the lack of proper and sufficient training, the modern liners are needlessly over complex, not user friendly, have poor and unintuitive man-machine interphase and when their systems degrade, they degrade very ungracefully. I know both Airbus and Boeing pilots who all tell me their machines are a joy to fly when all bells and whistles are working properly, but I don’t understand why the manufactures have chosen to go down the path of complexity, when I know from personal experience that an aircraft can be built in another way.
I know that most normal pilots are in love with their specific aircraft type, but going through the types I have flown in my career so far, the F-16 stands out above all other types in the way it is designed. For some reason it appears that when the F-16 was designed, Boyd, Hillaker and the rest of the so-called Fighter Mafia members actually understood what the pilots needed both when every system was working, but also when things went bad. They managed to build a very simple, user-friendly and from a technical point of view genius aircraft.
To begin with, the flight control system, the worlds first full FBW system in a combat aircraft, was very effective, robust, simple, reliable (when the first hiccups were dealt with) and best of all, so fantastically pilot friendly, that most pilots will feel that the aircraft becomes an extension of their body after half the take-off run on their first flight in the aircraft.
I don’t understand why it is not possible to build an airliner with such a clever flight control system? As you described, who needs dedicated flap levers? You only need flaps during take-off and landings, so why not integrate the flap function with the gear handle, as you need your gear to be down when taking off or landing. Flaps that can be manually selected down without the landing gear if a situation ever arises where it is needed (intercepting a cessna at 90 knots), and flaps that will retract by themself if an overspeed is about to happen. And by the way, the system changes the control gains from take-off/landing gains to cruise gains with the gear handle position. Automatic leading edge flaps that drop down on rotation to increase lift, and instantly go up to dump lift when touching down on landing. No need to arm them like spoilers and no need to stow them in case of rejected landing. A wing that changes shape (again by the use of leading edge flaps), so as to always have the optimal shape for the actual flight regime (with an envelope much wider than the typical airliner).
And in the very rare case where the system malfunctions, it degrades so gracefully that the pilot probably wont even notice any change in flying characteristics (like when the bus changes to direct law). Loose a control surface (loose like in it has fallen off), have a runaway elevator trim go full nose down, or even worse, have a LEF pointing straight up like in gums LEF incident, and still be able to counteract the roll, pitch or yaw with less then superhuman power, by just applying a bit more force then normal on the side stick.
And all this was designed in the mid 70’s. One would think that it would be possible to make an even better flight control system today. A system that would help the pilots instead of defeating them. Of course, complex systems are fine and work well if the operators are well trained, experienced pilots that understand the systems and all of their sub modes, but the average pilot today as I see him/her, is only trained to the minimum requirements, doesn’t get a lot of stick time, and doesn’t really understand the system 100%.
Aircraft engineers, is it not possible to keep it simple stupid anymore?
Like you I have absolutely zero experience in modern liners like the MAX or NEO. But when reading accident and incident reports, I get the feeling that beside the lack of proper and sufficient training, the modern liners are needlessly over complex, not user friendly, have poor and unintuitive man-machine interphase and when their systems degrade, they degrade very ungracefully. I know both Airbus and Boeing pilots who all tell me their machines are a joy to fly when all bells and whistles are working properly, but I don’t understand why the manufactures have chosen to go down the path of complexity, when I know from personal experience that an aircraft can be built in another way.
I know that most normal pilots are in love with their specific aircraft type, but going through the types I have flown in my career so far, the F-16 stands out above all other types in the way it is designed. For some reason it appears that when the F-16 was designed, Boyd, Hillaker and the rest of the so-called Fighter Mafia members actually understood what the pilots needed both when every system was working, but also when things went bad. They managed to build a very simple, user-friendly and from a technical point of view genius aircraft.
To begin with, the flight control system, the worlds first full FBW system in a combat aircraft, was very effective, robust, simple, reliable (when the first hiccups were dealt with) and best of all, so fantastically pilot friendly, that most pilots will feel that the aircraft becomes an extension of their body after half the take-off run on their first flight in the aircraft.
I don’t understand why it is not possible to build an airliner with such a clever flight control system? As you described, who needs dedicated flap levers? You only need flaps during take-off and landings, so why not integrate the flap function with the gear handle, as you need your gear to be down when taking off or landing. Flaps that can be manually selected down without the landing gear if a situation ever arises where it is needed (intercepting a cessna at 90 knots), and flaps that will retract by themself if an overspeed is about to happen. And by the way, the system changes the control gains from take-off/landing gains to cruise gains with the gear handle position. Automatic leading edge flaps that drop down on rotation to increase lift, and instantly go up to dump lift when touching down on landing. No need to arm them like spoilers and no need to stow them in case of rejected landing. A wing that changes shape (again by the use of leading edge flaps), so as to always have the optimal shape for the actual flight regime (with an envelope much wider than the typical airliner).
And in the very rare case where the system malfunctions, it degrades so gracefully that the pilot probably wont even notice any change in flying characteristics (like when the bus changes to direct law). Loose a control surface (loose like in it has fallen off), have a runaway elevator trim go full nose down, or even worse, have a LEF pointing straight up like in gums LEF incident, and still be able to counteract the roll, pitch or yaw with less then superhuman power, by just applying a bit more force then normal on the side stick.
And all this was designed in the mid 70’s. One would think that it would be possible to make an even better flight control system today. A system that would help the pilots instead of defeating them. Of course, complex systems are fine and work well if the operators are well trained, experienced pilots that understand the systems and all of their sub modes, but the average pilot today as I see him/her, is only trained to the minimum requirements, doesn’t get a lot of stick time, and doesn’t really understand the system 100%.
Aircraft engineers, is it not possible to keep it simple stupid anymore?
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I don’t fly the 737 Max, but after doing a bit of ‘what-if-ing’, I’ve come to the conclusion that if I were a Max pilot and had stick shaker on take-off, I would not fully retract the flaps. I would retract to Flaps 1. My experience on other Boeing’s (767 & 744) is that Flaps 1 provides the best manoeuvre margin to the stall and in the 737 Max would prevent MCAS doing it’s (evil) thing.
Now, I concluded that from the comfort of my armchair AFTER the Lion Air accident, so that if it happened to me, I would know what to do.
The Ethiopian crew obviously didn't, but neither did Boeing.
Mind you, I AM adopting a Boeing procedure here (the Airspeed Unreliable checklist) - It's just that I'm being choosey about which Boeing procedure to adopt and how, and using some additional system knowledge which we didn't have prior to the Lion Air report (i.e. flaps stops MCAS!).