Ethiopian airliner down in Africa
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Thank you Harry I appreciate that! In the back of my mind it seemed very unlikely that such an anomaly (radically changed airflow patterns secondary to larger engines mounted in forward positions) would slip through aerodynamic modelling and windtunnel testing etc unnoticed. It was naive for me to assume that the designers simply specified a big change in engine fitment without anticipating the consequences.
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I'm quite sure that if they were obvious, that the likes of Airbus etal. would have pointed them out to the regulators
This is the stuff that calls for "Special Condition" in the certification basis and unfortunately like all other parts of our risks in life is sometimes learned the hard way
Current and former engineers directly involved with the evaluations or familiar with the document shared details of Boeing’s “System Safety Analysis” of MCAS, which The Seattle Times confirmed.
The safety analysis:
The safety analysis:
- Understated the power of the new flight control system, which was designed to swivel the horizontal tail to push the nose of the plane down to avert a stall. When the planes later entered service, MCAS was capable of moving the tail more than four times farther than was stated in the initial safety analysis document.
- Failed to account for how the system could reset itself each time a pilot responded, thereby missing the potential impact of the system repeatedly pushing the airplane’s nose downward.
- Assessed a failure of the system as one level below “catastrophic.” But even that “hazardous” danger level should have precluded activation of the system based on input from a single sensor — and yet that’s how it was designed.
„In this atmosphere, the System Safety Analysis on MCAS, just one piece of the mountain of documents needed for certification, was delegated to Boeing.
[...]
„The higher limit meant that each time MCAS was triggered, it caused a much greater movement of the tail than was specified in that original safety analysis document.“
[...]
“None of the engineers were aware of a higher limit,” said a second current FAA engineer.
[...]
Peter Lemme, a former Boeing flight controls engineer who is now an avionics and satellite-communications consultant, said that because MCAS reset each time it was used, “it effectively has unlimited authority.”
If I was responsible for this, I'd be on my way leaving the country for good at this time.
Epic failure of certification and oversight.
[...]
„The higher limit meant that each time MCAS was triggered, it caused a much greater movement of the tail than was specified in that original safety analysis document.“
[...]
“None of the engineers were aware of a higher limit,” said a second current FAA engineer.
[...]
Peter Lemme, a former Boeing flight controls engineer who is now an avionics and satellite-communications consultant, said that because MCAS reset each time it was used, “it effectively has unlimited authority.”
If I was responsible for this, I'd be on my way leaving the country for good at this time.
Epic failure of certification and oversight.
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these are called lessons learned and belong to all the aircraft manufacturers.
I'm quite sure that if they were obvious, that the likes of Airbus etal. would have pointed them out to the regulators
This is the stuff that calls for "Special Condition" in the certification basis and unfortunately like all other parts of our risks in life is sometimes learned the hard way
I'm quite sure that if they were obvious, that the likes of Airbus etal. would have pointed them out to the regulators
This is the stuff that calls for "Special Condition" in the certification basis and unfortunately like all other parts of our risks in life is sometimes learned the hard way
Quote
The original Boeing document provided to the FAA included a description specifying a limit to how much the system could move the horizontal tail — a limit of 0.6 degrees, out of a physical maximum of just less than 5 degrees of nose-down movement. That limit was later increased after flight tests showed that a more powerful movement of the tail was required to avert a high-speed stall, when the plane is in danger of losing lift and spiraling down.The behavior of a plane in a high angle-of-attack stall is difficult to model in advance purely by analysis and so, as test pilots work through stall-recovery routines during flight tests on a new airplane, it’s not uncommon to tweak the control software to refine the jet’s performance.
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After reading the Seattle Times article I am left with a feeling that the Max has very undesirable stall characteristics, seen by the need to increase the MCAS limits from the intended and modest 0.6 degrees to the large 2.5 degrees.
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Interesting read from The Seattle Times article.
The original Boeing document provided to the FAA included a description specifying a limit to how much the system could move the horizontal tail — a limit of 0.6 degrees, out of a physical maximum of just less than 5 degrees of nose-down movement. That limit was later increased after flight tests showed that a more powerful movement of the tail was required to avert a high-speed stall, when the plane is in danger of losing lift and spiraling down.The behavior of a plane in a high angle-of-attack stall is difficult to model in advance purely by analysis and so, as test pilots work through stall-recovery routines during flight tests on a new airplane, it’s not uncommon to tweak the control software to refine the jet’s performance.
Quote
The original Boeing document provided to the FAA included a description specifying a limit to how much the system could move the horizontal tail — a limit of 0.6 degrees, out of a physical maximum of just less than 5 degrees of nose-down movement. That limit was later increased after flight tests showed that a more powerful movement of the tail was required to avert a high-speed stall, when the plane is in danger of losing lift and spiraling down.The behavior of a plane in a high angle-of-attack stall is difficult to model in advance purely by analysis and so, as test pilots work through stall-recovery routines during flight tests on a new airplane, it’s not uncommon to tweak the control software to refine the jet’s performance.
Quote
Or perhaps the key really is the reset. Does mcas reset with each trim input and takes the current position as the new neutral? If AoA vane is sending wrong data it's easy to see how this would result in a runaway trim.
This image shows the difference between a 737-800 (yellow) and MAX (magenta). Notice the bigger nacelles and same hstab size.
I thought 0.6 was a hard limit... e.g, we move this much and then it's up to the pilot. If it was 0.6 every 5 seconds it's still bad, but at least easier to manage.
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Browsing Google Patents, I stumbled across some interesting Boeing patent applications e.g. this one 6 years ago: PRIMARY FLIGHT DISPLAY PITCH AND POWER-BASED UNRELIABLE AIRSPEED SYMBOLOGY. (Download full PDF here in order to view Figs a little better ...).
In this one I was struck by their "Background" para [0013] which reads:
In this one I was struck by their "Background" para [0013] which reads:
QUOTE
The displayed symbology is not static and updates as the airplane weight, altitude, flap setting and thrust change. As a result, critical information is communicated in a format that is intuitive and in a form that the pilot needs, and is expediently usable by the pilot to maintain safe, stable flight conditions as a result of air data failures throughout the duration of the flight. This symbology is independent of the angle of attack (AOA) or the air data system.
UNQUOTE{my bold}
Is any of what's described yet designed into any production PFD?
The displayed symbology is not static and updates as the airplane weight, altitude, flap setting and thrust change. As a result, critical information is communicated in a format that is intuitive and in a form that the pilot needs, and is expediently usable by the pilot to maintain safe, stable flight conditions as a result of air data failures throughout the duration of the flight. This symbology is independent of the angle of attack (AOA) or the air data system.
UNQUOTE{my bold}
Is any of what's described yet designed into any production PFD?
On many of the accidents discussed here on PPRuNe, commentators are regularly criticised for "not waiting until the accident report is released".
I wonder why, in contrast, it seems accepted that Boeing can have a software fix done in weeks, way before any reports are produced, to get the aircraft back in the air.
I wonder why, in contrast, it seems accepted that Boeing can have a software fix done in weeks, way before any reports are produced, to get the aircraft back in the air.
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Is any of what's described yet designed into any production PFD?
There is more than one story like that . ..
Last edited by CONSO; 17th Mar 2019 at 16:18.
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Lion air's FDR show that the trim was moved to full of the available 7 notches (it's not clear how those translate to degrees). They would certainly still be alive if there as a limit. They kept it in air at ~ 3 notches. If max needs more to get out of stall, perhaps it does need a larger hstab/eleveator instead of a hacked together software?
Or perhaps the key really is the reset. Does mcas reset with each trim input and takes the current position as the new neutral? If AoA vane is sending wrong data it's easy to see how this would result in a runaway trim.
This image shows the difference between a 737-800 (yellow) and MAX (magenta). Notice the bigger nacelles and same hstab size.
I thought 0.6 was a hard limit... e.g, we move this much and then it's up to the pilot. If it was 0.6 every 5 seconds it's still bad, but at least easier to manage.
Or perhaps the key really is the reset. Does mcas reset with each trim input and takes the current position as the new neutral? If AoA vane is sending wrong data it's easy to see how this would result in a runaway trim.
This image shows the difference between a 737-800 (yellow) and MAX (magenta). Notice the bigger nacelles and same hstab size.
I thought 0.6 was a hard limit... e.g, we move this much and then it's up to the pilot. If it was 0.6 every 5 seconds it's still bad, but at least easier to manage.
March 17, 2019 12:15 p.m. ET https://www.wsj.com/articles/ethiopian-airlines-black-boxes-showed-clear-similarities-with-lion-air-crash-11552839318?mod=hp_lead_pos4 *
Analysis of Black Boxes of Crashed Ethiopian Airlines Flight Showed ‘Clear Similarities’ With Crashed Lion Air Flight —Ethiopian Transport Minister
*Data from ET302 Black Boxes Has Been Validated by Ethiopian, U.S. Investigators—Minister
*Investigators Were Able to Recover All Relevant Data from ET302 Black Boxes—Minister
*Preliminary Report on Crash to Be Released Within 30 Days—Minister
Analysis of Black Boxes of Crashed Ethiopian Airlines Flight Showed ‘Clear Similarities’ With Crashed Lion Air Flight —Ethiopian Transport Minister
*Data from ET302 Black Boxes Has Been Validated by Ethiopian, U.S. Investigators—Minister
*Investigators Were Able to Recover All Relevant Data from ET302 Black Boxes—Minister
*Preliminary Report on Crash to Be Released Within 30 Days—Minister
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Light aircraft pilot since the mid 70s... under what circumstances would a 737 variant require full UP trim or full DOWN trim? On the aircraft that I have flown, the trim spends all its time somewhere in the middle of the range. So again I ask, what purpose is there to having such extreme ranges of trim that it requires huge control forces to counter?
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If MCAS ran the stab full down it occurred through a number of cycles and over a significant period of time. Where were the pilots?
However, pilots and aviation experts say that what happened on the Lion Air flight doesn’t look like a standard stabilizer runaway, because that is defined as continuous uncommanded movement of the tail.On the accident flight, the tail movement wasn’t continuous; the pilots were able to counter the nose-down movement multiple times.In addition, the MCAS altered the control column response to the stabilizer movement. Pulling back on the column normally interrupts any stabilizer nose-down movement, but with MCAS operating that control column function was disabled. These differences certainly could have confused the Lion Air pilots as to what was going on.Since MCAS was supposed to activate only in extreme circumstances far outside the normal flight envelope, Boeing decided that 737 pilots needed no extra training on the system — and indeed that they didn’t even need to know about it. It was not mentioned in their flight manuals.
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Ethiopian safety board
I give full respect to the Ethiopian safety board investigating this crash.
but given that the two 737max crashes raise such massive questions about aircraft manufacturing,government and trans national oversight and trillion dollar industries as well national interests for the US aircraft msnufacturing industry vis a vis China snd Europe ,are tje Ethiopians a tiny bit out of their depth?
but given that the two 737max crashes raise such massive questions about aircraft manufacturing,government and trans national oversight and trillion dollar industries as well national interests for the US aircraft msnufacturing industry vis a vis China snd Europe ,are tje Ethiopians a tiny bit out of their depth?
