MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
All DAL-A assures is that the software does what the software requirements say it should do, not that those requirements are themselves correct or complete. That's a SYSTEMS requirements issue not a software requirements issue - and indeed, can be thought of as applying to non-software aspects of design as well.
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I almost quit reading after "stall prevention" and managed to grit my teeth through "thrustline" but if he doesn't know that Brady is giving the correct reason for MCAS by now, absent any stunning new revelations from Boeing, it's hopeless. My question is what is the effin envelope and can the autopilot reach that envelope? Because either MCAS is there for human pitch feel linearity and the autopilot is not bothered by any non linear effect or MCAS is not active with the autopilot on because it would not be useable in the MCAS regime. Still, I wonder if the non linearity might be a minor one that would not affect humans if told about it or it's something that we couldn't compensate for. Again, once told to be careful at .9M in the T-38, I was careful. We hear many 737 pilot accounts of how this or that dash whatever model lands better than the other dash whatever model. Those handling differences do not bother the pilots.Nor did landing the 767-300 one day and landing the 757 the next bother me.
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https://theaircurrent.com/aviation-s...-design-issue/
Re-certification sliding into 2020, FAA reissues statement it will not be rushed, Ryanair specific high density model faces issue with overwing exit
Re-certification sliding into 2020, FAA reissues statement it will not be rushed, Ryanair specific high density model faces issue with overwing exit
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MCAS is a longitudinal stability enhancement. It is not for stall prevention (although indirectly it helps) or to make the MAX handle like the NG (although it does); it was introduced to counteract the non-linear lift generated by the LEAP-1B engine nacelles at high AoA and give a steady increase in stick force as the stall is approached as required by regulation.
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He quotes Brady in his article but expresses uncertainty about whether he is correct. Yes you have to wonder how that pencil whip actually performed in the windup turns.
75 trucks were tilted up, a stablising condition, 76 tilted down, just the opposite, could make a significant difference, guaranteed smooth touchdown every time on the 75, took what you got on the 76 !
Cant say it bothered me that much though !
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Originally Posted by Fly Aiprt 
I'll add that that trying to give an increase in stick force with a control slower than the stick-controlled elevator raises questions...
I'll add that that trying to give an increase in stick force with a control slower than the stick-controlled elevator raises questions...
Someday, some of the insiders will be ready to tell the whole story.
See the report of the 737 NG accident discussed in Flydubai crash at RVI final report out.
Re trim and assumptions about pilot previous experience, previous types and training, Boeing trim design philosophy.
If nothing else see the last page - the final footnote.
I hope that the FAA takes note; if not, then the other regulators; or failing that, operators and pilots.
Re trim and assumptions about pilot previous experience, previous types and training, Boeing trim design philosophy.
If nothing else see the last page - the final footnote.
I hope that the FAA takes note; if not, then the other regulators; or failing that, operators and pilots.
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There might be more to it than the official theory...
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1. Don't tell the pilots about the existence of MCAS
2. Expect the pilot to respond within seconds to an unintentional MCAS activation.
3. Expect the pilot to sit quietly through an intentional MCAS trim-down and the subsequent trim-up "reset" without touching the electric trim.
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I'm still having a lot of trouble getting my head around B's thought processes.
1. Don't tell the pilots about the existence of MCAS
2. Expect the pilot to respond within seconds to an unintentional MCAS activation.
3. Expect the pilot to sit quietly through an intentional MCAS trim-down and the subsequent trim-up "reset" without touching the electric trim.
1. Don't tell the pilots about the existence of MCAS
2. Expect the pilot to respond within seconds to an unintentional MCAS activation.
3. Expect the pilot to sit quietly through an intentional MCAS trim-down and the subsequent trim-up "reset" without touching the electric trim.
Possibly the assumption was that in an intentional MCAS trim-down the pilots would be otherwise occupied with impending stall, warnings, feel-shift etc. - this was proved correct...
Intentional but erroneous MCAS activation was never considered (if I understand JTAR correctly).
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FAA Takes Back Control Of Key Safety Step From Boeing
FAA Takes Back Control Of Key Safety Step From Boeing As Questions Linger On 737 MAX Fix
The Federal Aviation Administration is taking back the sole authority to issue airworthiness certificates for new 737 MAX aircraft for an indefinite period, marking a reversal in a program that had transferred responsibility to Boeing, even as questions linger on the re-launch of the troubled airplane.As Reuters has reported, the FAA issued a letter to Boeing on Tuesday notifying them of the decision. Citing the large number of 737 MAX planes that will need vetting that have piled up in storage as Boeing has continued production despite the global grounding of the plane, the FAA said it will “retain authority to issue airworthiness certificates and export certificates of airworthiness for all 737 MAX airplanes” for an indefinite period, until the Administration is satisfied that Boeing has “fully functional quality control and verification processes.”
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Beg to differ a bit. DAL A assurance is supposed provide convincing evidence that requirements are validated, and that they are traced to the code. The process for establishing software Design Assurance Level A is painfully extensive in time and resources. It is not an absolute guarantee of no software errors because testing to prove that is not possible. But the process, developed by manufacturers and regulators together has been in use for decades, though not without attempts to push back. Hopefully, energy to resist pushback at the rigor of DAL processes will be renewed as a result of the MAX debacle.
As you say, DAL-A is fundamentally a SOFTWARE assurance process not a systems design assurance process. For a holistic systems design process with rigour with regard to requirements, one has to look to something like ARP4754 instead. DAL-A starts with the assumption that the systems designer knows what he is doing, and makes sure the software does what he intends. DAl-A requirements validation will typically validate the software requirements against the systems requirements, but go no further into the design. ARP4754 more fundamentally questions the systems design and the assumptions therein.
True, the DAL-A process can sometimes highlight deficiencies in the higher level requirements - muddled thinking there may cause a muddle at the software level, and software design assurance will probably catch that, and if the breadcrumbs are followed (and the software folks will be motivated to do so, to prove it's not their fault!) then the problem may be found. But if the problem is not muddle but rather being wrong, but consistently so, then all DAL-A ultimately proves is that the SW does what it's supposed to.
A lot of what we sometimes lazily call a "software problem" is actually a systems design problem, and would have occurred whether the design were implemented in software, analogue electronics or even hardware. In other words, DAL-A is a necessary but not sufficient condition for correct design execution.
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Other than politics (which is obviously huge) I fail to see how the issuance of CofAs or similar has any relationship to design approval and TC issue. It's not even the same groups of people involved or responsible.
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See the report of the 737 NG accident discussed in Flydubai crash at RVI final report out.
Re trim and assumptions about pilot previous experience, previous types and training, Boeing trim design philosophy. [Emphasis Added]
If nothing else see the last page - the final footnote.
I hope that the FAA takes note; if not, then the other regulators; or failing that, operators and pilots.
Re trim and assumptions about pilot previous experience, previous types and training, Boeing trim design philosophy. [Emphasis Added]
If nothing else see the last page - the final footnote.
I hope that the FAA takes note; if not, then the other regulators; or failing that, operators and pilots.
A further consequence,
Europe demands approval of new Boeing 777X in snub to US regulators
According to the UK Daily Telegraph newspaper. Sorry, can't post the link.
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Here: https://www.telegraph.co.uk/business...max-airworthy/
No paywall here: The spotlight on Boeing and the FAA will only get hotter after the 737 Max crisis. Now global regulators are focusing on the plane-maker's newest jet.
Last edited by OldnGrounded; 27th Nov 2019 at 23:57.