Ethiopian airliner down in Africa
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MCAS is an add-on to an upgraded design.... Airbus on the other hand is designed in full around the centre of interest - FBW, hence Normal Law.
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Uh, they have nothing in common. Normal Law will ensure whatever you do with the stick, the airplane will remain inside the flight envelope. MCAS just trims the nose forward every 5s regardless of any other parameters.
Perhaps the bigger issue is the core design. Airbus, being FBW by design, has triple sensors. If one fails, the other 2 overrule the broken one. Boeing relies on 2 sensors, if one breaks all hell will broke loose.
Also, on a Bus, if things go south, the HAL will say "sorry, your plane", turn into degraded/direct law and let the pilot handle it (which does not always work, e.g. AF447). Mcas will fight the pilots and try to get its way unless it's manually shut down.
In short, mcas is probably going to be known as one of the biggest f***ups in modern aviation history (yeah, I'm jumping to conclusions fas here, but time will tell).
Perhaps the bigger issue is the core design. Airbus, being FBW by design, has triple sensors. If one fails, the other 2 overrule the broken one. Boeing relies on 2 sensors, if one breaks all hell will broke loose.
Also, on a Bus, if things go south, the HAL will say "sorry, your plane", turn into degraded/direct law and let the pilot handle it (which does not always work, e.g. AF447). Mcas will fight the pilots and try to get its way unless it's manually shut down.
In short, mcas is probably going to be known as one of the biggest f***ups in modern aviation history (yeah, I'm jumping to conclusions fas here, but time will tell).
Presumably they mean all 737 Max aircraft, not just the Max 8. Although Chinese airlines don't yet have any of the latter, Thai Lion Air operate the Max 9 into Guangzhou, Chengdu and Jinan.
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Uh, they have nothing in common. Normal Law will ensure whatever you do with the stick, the airplane will remain inside the flight envelope. MCAS just trims the nose forward every 5s regardless of any other parameters.
Perhaps the bigger issue is the core design. Airbus, being FBW by design, has triple sensors. If one fails, the other 2 overrule the broken one. Boeing relies on 2 sensors, if one breaks all hell will broke loose.
Also, on a Bus, if things go south, the HAL will say "sorry, your plane", turn into degraded/direct law and let the pilot handle it (which does not always work, e.g. AF447). Mcas will fight the pilots and try to get its way unless it's manually shut down.
In short, mcas is probably going to be known as one of the biggest f***ups in modern aviation history (yeah, I'm jumping to conclusions fas here, but time will tell).
Perhaps the bigger issue is the core design. Airbus, being FBW by design, has triple sensors. If one fails, the other 2 overrule the broken one. Boeing relies on 2 sensors, if one breaks all hell will broke loose.
Also, on a Bus, if things go south, the HAL will say "sorry, your plane", turn into degraded/direct law and let the pilot handle it (which does not always work, e.g. AF447). Mcas will fight the pilots and try to get its way unless it's manually shut down.
In short, mcas is probably going to be known as one of the biggest f***ups in modern aviation history (yeah, I'm jumping to conclusions fas here, but time will tell).
Last edited by zonak; 11th Mar 2019 at 08:28.
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Had an AOA vain failure on a 737-800 many years ago. Aircraft was in a cruise climb at around 6000 feet, A/P and AT engaged, when my PFD lit up with multiple warnings, low speed displays etc and we got the stick shaker. Its was CAVOK, the * pitch and power settings were clearly normal * for the phase of flight we were in and the F/Os instruments reflected this. Handed control to F/O, ran the checklists and told ATC we were coming back.
No real drama, but had it been a MAX with MCAS kicking in it may well have been more challenging ....
No real drama, but had it been a MAX with MCAS kicking in it may well have been more challenging ....
Last edited by Aldente; 11th Mar 2019 at 08:13.
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Originally Posted by BRE
MCAS sounds a lot like Airbus Normal Law, specifically pitch control and alpha protection. How does the Boeing implementation differ?
Very sad for this accident and for the lives lost, and my thinking goes to the professional fellows pilots involved: we, as professional pilots, know very well that we are paid for the increasing flight safety that our skills can provide to the system.
Happy landings.
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[QUOTE=ironbutt57;10413275]gotta love the interweb, where people don't get irony and jokes go over heads at mach .78.
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More pertinent here is flight with reduced static pitch stability. Basically, reducing static stability margin (flying with the CofG and centre of pressure closer together) means you need less downforce on the horizontal stab to counter the nose-down pitching moment. This means lower trim drag AND less lift required from the rest of the airframe to counteract the horizontal stab downforce. Less drag = less fuel burn = more efficient. Less induced drag from needing less lift to counter the horizontal stab = less fuel burn = more efficient.
The design challenge is to minimise cruise trim forces on the horizontal stab whilst maintaining JUST enough static stability margin. Works fine until you stick two new ruddy great big engines (with more wetted surface area) forward of the normal centre of pressure...
The design challenge is to minimise cruise trim forces on the horizontal stab whilst maintaining JUST enough static stability margin. Works fine until you stick two new ruddy great big engines (with more wetted surface area) forward of the normal centre of pressure...
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Not to mention the fact that the guys flying the Lion Air plane the day before (UK captain) had the same problem as the accident flight, hit the STAB TRIM CUTOUT switches and went on about their day. Even if this is MCAS, again, and even if it was the same for Lion Air, I still believe 100% that a US or European crew wouldn't have had any problem at all. A new captain and a 200-hour wonder is the absolute worst possible combination here... just saying.
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For those not in the know wrt B737 systems, the speed trim system (STS) is a speed stability augmentation system designed to improve flight characteristics during operations with a low gross weight, aft centre of gravity and high thrust when the autopilot is not engaged. The purpose of the STS is to return the airplane to a trimmed speed by commanding the stabiliser in a direction opposite the speed change. The STS monitors inputs of stabilizer position, thrust lever position, airspeed and vertical speed and then trims the stabiliser using the autopilot stabilizer trim. As the airplane speed increases or decreases from the trimmed speed, the stabilizer is commanded in the direction to return the airplane to the trimmed speed. This increases control column forces to force the airplane to return to the trimmed speed. As the airplane returns to the trimmed speed, the STS commanded stabilizer movement is removed. STS operates most frequently during takeoffs, climb and go-arounds.
So, STS is a bit like MCAS (albeit for slightly different regimes of flight) in that it operates automatically and moves the stabiliser.
Last edited by Old King Coal; 11th Mar 2019 at 08:15.
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How do you recognise a trim runaway?
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From what I understand one condition for the MCAS to work is manual flight. My question is, if the the MCAS starts to trim the nose down, can the AP be still engaged and save the situation?
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Are you kidding me? Are you flying a 737?
I think that all 737 pilots know this switch goes down instead of up to turn it off.
I think that all 737 pilots know this switch goes down instead of up to turn it off.
Silver
Last edited by silverstrata; 11th Mar 2019 at 08:35.
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hello,
pilots flying on the new boeing 737 Max come from the 737 Ng and are not used to correcting and monitoring what this MCAS system does§
It's not easy for them as they are supposed to fly on a safe plane
it's absurd to cut off the swith when the MCAS gets bogged down and will order the plane to nose down
Guys from Seattle should come to Toulouse, France to see how auto trim work
pilots flying on the new boeing 737 Max come from the 737 Ng and are not used to correcting and monitoring what this MCAS system does§
It's not easy for them as they are supposed to fly on a safe plane
it's absurd to cut off the swith when the MCAS gets bogged down and will order the plane to nose down
Guys from Seattle should come to Toulouse, France to see how auto trim work
Have you heard of high speed stall? Mach tuck?
And as someone mentioned, Coffin Corner.