MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
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Quite agree
In aviation we always wrestle with "safe enough". You could maybe build a crash proof environment but the cost would be astronomical and there would be no airlines making money.
Take the example of twin engined ETOPS jets. That is all based on "safe enough" and IFSD rates. Which by the way have been getting much higher recently.
Most pilots I know who have flown the 747 think her the queen of the skies because of the massive redundancy built into her. Lose an engine - carry on. Lose a hydraulic system - carry on and auto land CAT 111. Same with an engine out. Autoland still available - I seem to remember!!
Cheers
Yan
In aviation we always wrestle with "safe enough". You could maybe build a crash proof environment but the cost would be astronomical and there would be no airlines making money.
Take the example of twin engined ETOPS jets. That is all based on "safe enough" and IFSD rates. Which by the way have been getting much higher recently.
Most pilots I know who have flown the 747 think her the queen of the skies because of the massive redundancy built into her. Lose an engine - carry on. Lose a hydraulic system - carry on and auto land CAT 111. Same with an engine out. Autoland still available - I seem to remember!!
Cheers
Yan
The 747-400 can auto land with a loss of one hydraulic system but It was never certified or flight tested in this configuration for the type certificate.
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Change control is a major source of issues
A big part of the development process failure may be change management. The failures are still shocking but a little less so if a reasonable safety analysis had been conducted and then changes were made that invalidated that analysis but it was erroneously believed that the changes were not significant.
My expertise is in safety related electronics and software in the medical area and the FDA have research to show that changes to software is a major source of safety incidents.
Now I would say that my understanding of MCAS is that the fundamental flaw is not the software itself but the specification of the software and the sub-system design concept which is inadequate due to a failure to appreciate the severity of a failure of this sub-system. Howeve rthe ide a is teh same change management is a common cause of failures/high risk area in the development of safety related systems.
It still seems like a shocking failure of the development and certification/compliance processes.
My expertise is in safety related electronics and software in the medical area and the FDA have research to show that changes to software is a major source of safety incidents.
Now I would say that my understanding of MCAS is that the fundamental flaw is not the software itself but the specification of the software and the sub-system design concept which is inadequate due to a failure to appreciate the severity of a failure of this sub-system. Howeve rthe ide a is teh same change management is a common cause of failures/high risk area in the development of safety related systems.
It still seems like a shocking failure of the development and certification/compliance processes.
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Quote:. . .The possibility of a pitch-up tendency during approach to stall was identified for the flaps-up configuration prior to the implementation of MCAS.
Don't you think the bare-airframe testing that JATR recommended is essential and must largely determine the process of "fixing" the MAX? Who's going to want to fly the aircraft while there are unanswered stability questions?
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It isn't, those tests only identified the need for original (AOA + g) MCAS, the later requirement for MCAS activation on AOA alone, and at lower speeds, was only identified during actual flight tests, hence the late changes rushed through under pressure.
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So surely in that case the bare without MCAS test has already been done when they discovered that effect? And anyway, by now after several months of grounding, someone somewhere must have confirmed the MAX without MCAS enabled so the problem is known but does not have a simple solution.
Now I would say that my understanding of MCAS is that the fundamental flaw is not the software itself but the specification of the software and the sub-system design concept which is inadequate due to a failure to appreciate the severity of a failure of this sub-system. Howeve rthe ide a is teh same change management is a common cause of failures/high risk area in the development of safety related systems.
As I recall, the FHA was reviewed and determined the new function did not increase the hazard, so the SSA wasn't updated.
The new functionality was briefed to the FAA, but they didn't find it significant and instead focused on other changes in those briefings/discussions.
Keeping Danny in Sandwiches
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The time has come for a bit of clarity from the regulators who should withdraw any existing approval of the MAX and invite Boeing to submit the aircraft for certification as a new aircraft type; which it is.
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So surely in that case the bare without MCAS test has already been done when they discovered that effect? And anyway, by now after several months of grounding, someone somewhere must have confirmed the MAX without MCAS enabled so the problem is known but does not have a simple solution.
My take on it is that JATR didn't actually have the bare airframe test results to review, but they presume FAA has the data or can get it from Boeing. The purpose of the review is to ascertain whether MCAS is actually a stall-id system (which a stick pusher is, I think?) under the regs, which opens up another can of worms as to whether MCAS meets the regs. a for stall-id system.
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Stick pusher is anti stall not stall ID. A shaker would be stall ID. MCAS as implemented functions as anti stall system but all the Boeing folks here won't have that.
Boeing couldnt add the much needed stick pusher to the MAX and keep it same type as NG so MCAS is basically their work around for the stick pusher.
Boeing couldnt add the much needed stick pusher to the MAX and keep it same type as NG so MCAS is basically their work around for the stick pusher.
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Preach it !!
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I am not sure if this has been mentioned yet, but in this Nov 4 Reuters report, EASA thinks the Max will be certified first quarter 2020.
HELSINKI (Reuters) - Boeing’s (BA.N) grounded 737 MAX airliner is likely to return to service in Europe during the first quarter of 2020, the head of the European Union Aviation Safety Agency (EASA) said on Monday.
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Stick pusher is anti stall not stall ID. A shaker would be stall ID. MCAS as implemented functions as anti stall system but all the Boeing folks here won't have that.
Boeing couldnt add the much needed stick pusher to the MAX and keep it same type as NG so MCAS is basically their work around for the stick pusher.
Boeing couldnt add the much needed stick pusher to the MAX and keep it same type as NG so MCAS is basically their work around for the stick pusher.
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No need to play school teacher here. I'm going with the flow and most are referring to it as stall ID. Yes it's a type of warning. So warning and ID are one in the same as far as this thread is concerned. Hope this helps your confusion my friend.
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the certifying authorities today would require additional sim training for the Max If it came with a stick pusher new type or not.
it's a different type due simply to the flying characteristics. Check the data.
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The data? You need data from me to show you the effect the new LEAP engines have on the conventional NG frame? Ok......see all the above !
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... I am saying that the argument that they didn't use a stick pusher because that would have made it a separate type is not the real reason. The reason they didn't add a stick pusher is because the airplane is so aerodynamically messed up that it wouldn't be enough of a solution. But as far as I know, we have not been shown any data. ...
Only guessing as well, of course. As usual with most last minute changes under pressure, it is an exceptionally bad idea to abuse speed trim as a stick pusher.
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The control column override switch (and relay) was already there..all they had to do was tap into it...so that makes it even simpler, hardware-wise. Abuse-wise, too.
Last edited by Takwis; 4th Nov 2019 at 21:05.
A third possible reason could have been minimizing HW changes for a last minute, rushed band aid. MCAS is basically a software module running on the pre-existing FCC. HW consists only of two additional relays, one for "column cutout override" and one for "flaps up high trim motor speed", plus some cabling.
Only guessing as well, of course. As usual with most last minute changes under pressure, it is an exceptionally bad idea to abuse speed trim as a stick pusher.
Only guessing as well, of course. As usual with most last minute changes under pressure, it is an exceptionally bad idea to abuse speed trim as a stick pusher.
The last minute aspect (correction for issue discovered in flight test) was software only, adding the low Mach, higher authority operation.
Psychophysiological entity
Stick Push and Stick Nudge. Very different animals. Davis insisted upon the Push on T tailed rear-engined aircraft - the Nudge on the 707 etc., and as previously mentioned, the latter didn't require a new type rating.
Stability? I'm not sure we have a clear idea about the no-MCAS handling of the MAX. Not the absolute truth. Recent posts about marked unwanted rotation really shouts a kind of instability, though for the most of the last months it seemed that MCAS 'merely' countered a legally unacceptable lightening of stick forces while approaching the stall, and in very clearly defined configurations/speeds, balanced against long-established rules.
If indeed the bare aircraft - in any configuration - raced into an aerodynamically powered rotation into the stall, I too would be deeply concerned. But, for the last months, it has been strongly implied that MCAS only stops the lightening of control loads?
So the big question has to be, without MCAS, does the aircraft 'flop' nose-up in the late stages of stall entry?
OldnGrounded: . . . Don't you think the bare-airframe testing that JATR recommended is essential and must largely determine the process of "fixing" the MAX? Who's going to want to fly the aircraft while there are unanswered stability questions?
If indeed the bare aircraft - in any configuration - raced into an aerodynamically powered rotation into the stall, I too would be deeply concerned. But, for the last months, it has been strongly implied that MCAS only stops the lightening of control loads?
So the big question has to be, without MCAS, does the aircraft 'flop' nose-up in the late stages of stall entry?
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Recent posts about marked unwanted rotation really shouts a kind of instability, though for the most of the last months it seemed that MCAS 'merely' countered a legally unacceptable lightening of stick forces while approaching the stall . . . it has been strongly implied that MCAS only stops the lightening of control loads?
So the big question has to be, without MCAS, does the aircraft 'flop' nose-up in the late stages of stall entry?