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They seem to have recognized that MCAS column cutout override robs the pilot of his natural countermeasure. Now they leave that override, and stick a SW band-aid on top. Arghhh...
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Originally Posted by spornrad
(Post 10624704)
They seem to have recognized that MCAS column cutout override robs the pilot of his natural countermeasure. Now they leave that override, and stick a SW band-aid on top. Arghhh...
Originally Posted by Peter H
(Post 10624686)
What a pity that a little of the MAX down-time wasn't spent testing/demonstrating the truth of that position. (Acceptable bare airframe aerodynamics.)
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"i am feeling the final decisions on acceptance will not be technically based."
This is the first leak from the regulatory community. I don't think it is a coincidence. I think it is a warning shot the bang from which could reverberate widely. So now we have 'straight from Steve' from the FAA, and 'straight to Steve' from TCCA: 'it's out there, and we aren't going to let you fudge it'. The more you read this email the cleverer it is: - - It is couched as prisoners friend (we all want it back in the air) - It pretty much says approval by Christmas is a pipe dream - It says the fix is still not stable, and not really a fix - It is a clear warning to the FAA - TCCA have not disowned him, but they have not backed him either: so now they have to get off the pot in public - He is effectively challenging Beoing to prove assertions the aerodynamic characteristics are benign - He is making it harder for foreign regulators to go weak at the knees I note he is a 30 year veteran. Likely reached the point where he does not need to fear for his future: or maybe he just works somehere a bit less toxic than the FAA. |
From the Canadian engineer's email:
...Not knowing the exact reasons for telling us that 12.1 as a fix is not effective (ref. F2.3 recent change to CAT), the fact is that it is another point that was just discovered... I read this as, the main mitigation measures supposed to defuse MCAS missfire (12.1) seem to be invalidated by a recent finding, that 12.1.B) leaves a misfire still as catastrophic event: 12.1 A) Activation by AOA B) Limit MCAS authority C) Inline Validity monitor, i.e. follow AOA values and accept only reasonable changes D) Delta disagree, i.e. compare both AOA values and detect a defective sensor Invoking Santa for help: Now (! meaning none?) of this helps get us to a level of confidence that having MCAS onboard was ever a good thing. The only way I see moving forward at this point ( and I say at this point because it's almost Christmas and we can always believe in miracles), is that MCAS has to go.... |
PeterH: What a pity that a little of the MAX down-time wasn't spent testing/demonstrating the truth of that position. (Acceptable bare airframe aerodynamics.)
OldnGrounded: Do we know that hasn't happened? We do know that JATR (and EASA?) have said that testing should be done. I was meaning that if B believed that the MAX had acceptable (or near acceptable) bare airframe aerodynamics they would have be wise to put convincing evidence into the public domain soon after the grounding. (I expect that the certifying authorities are forcing B to make some tests, and that B is keeping both the existence and results of these tests as confidential as they can.) However I'm certain that SLF3 has it right: The more you read this [TCCA] email the cleverer it is: [Among other things] He is effectively challenging Boeing to prove assertions the aerodynamic characteristics are benign |
Sounds EXACTLY like the Morton Thiokol engineer who stood up and said it is too cold to launch the Challenger! |
The basic Max did not meet the certification requirements; Max + MCAS similarly deficient.
Various MCAS modifications still not compliant. The recent TC text appears to suggest that the ‘lesser’ non-compliant option could be certificated, allowing an aircraft which does not meet requirements to operate. Not the best example of how to improve the public view of safety. Nor a good safety message for the industry, or for future certification. Other manufacturers have had to meet the certification requirements or agreed a dispensation before initial certification. Any dispensation for the Max after two accidents, after initial certification, just because a satisfactory solution is currently not available, would not bode well for future certification or international cooperation. |
Originally Posted by SLF3
(Post 10624750)
"i am feeling the final decisions on acceptance will not be technically based."
This is the first leak from the regulatory community. I don't think it is a coincidence. I think it is a warning shot the bang from which could reverberate widely. So now we have 'straight from Steve' from the FAA, and 'straight to Steve' from TCCA: 'it's out there, and we aren't going to let you fudge it'. The more you read this email the cleverer it is: - - It is couched as prisoners friend (we all want it back in the air) - It pretty much says approval by Christmas is a pipe dream - It says the fix is still not stable, and not really a fix - It is a clear warning to the FAA - TCCA have not disowned him, but they have not backed him either: so now they have to get off the pot in public - He is effectively challenging Beoing to prove assertions the aerodynamic characteristics are benign - He is making it harder for foreign regulators to go weak at the knees I note he is a 30 year veteran. Likely reached the point where he does not need to fear for his future: or maybe he just works somehere a bit less toxic than the FAA. |
Surely you cannot have an aircraft that is non compliant with regulatory requirements getting approval. That would leave the regulators in the dock as well as Boeing at every incident involving the MAX.
The job of Boeing is to produce a compliant aircraft; when it does so the regulators could and should approve it. Until that time the place for the Max is on the ground without passengers. |
Originally Posted by dufc
(Post 10624871)
I read the e-mail and quickly reached the conclusion that this was written to be leaked. He even indicates it is OK for his recipients to share it with others in their organisations making a leak of the email even more likely.
Imagine being one of the original recipients and wondering what life would be like if you didn't circulate this (including to press/public) and your agency signed on to MAX RTS, followed by . . . another crash. |
From what I've been reading (on here and elsewhere) it seems like there are patches on patches but nobody wants to take responsibility to say "to hell with it, lets start again"
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We've seen that MCAS misfire was classified as 'Major', if not hazardous etc...
With the new version, if AOAs disagree then MCAS is inhibited. How is MCAS inhibition classified ? Minor, Major ? Hazardous ? If Major or Hazardous, difficult to see how reading a tablet might suffice. If Minor only, why not dump the MCAS altogether, as proposed ? |
Originally Posted by sky9
(Post 10624873)
Surely you cannot have an aircraft that is non compliant with regulatory requirements getting approval. That would leave the regulators in the dock as well as Boeing at every incident involving the MAX.
The job of Boeing is to produce a compliant aircraft; when it does so the regulators could and should approve it. Until that time the place for the Max is on the ground without passengers. |
Passengers lives vs. document handling. Yeah, that’s a dilemma, all right. |
The many extensions made to the 737 culminated in unacceptable stick force at high alpha. The MCAS cure proved itself worse than the disease.
So yes, begin with removing MCAS and finish with restoring aerodynamics at least as good as on the NG. Most likely that will require a cowl location and sizing similar to the NG with an engine that fits. The MD marketing experts at B can figure out what discount would incentivise A to take the current MAX engines off B's hands. Perhaps a few original MAXes in drone configuration could be kept for the MBA crowd. There was a point when B could have taken over the now A220 program for a very good price. Instead their tariff lobbying put it into A's hands. |
Originally Posted by RatherBeFlying
(Post 10625095)
The many extensions made to the 737 culminated in unacceptable stick force at high alpha. The MCAS cure proved itself worse than the disease.
So yes, begin with removing MCAS and finish with restoring aerodynamics at least as good as on the NG. Most likely that will require a cowl location and sizing similar to the NG with an engine that fits. The MD marketing experts at B can figure out what discount would incentivise A to take the current MAX engines off B's hands. Perhaps a few original MAXes in drone configuration could be kept for the MBA crowd. There was a point when B could have taken over the now A220 program for a very good price. Instead their tariff lobbying put it into A's hands. |
Can you elaborate on the difference between “unacceptable stick force” and “non linear stick force which would be unacceptable for certification requirements”? I’m having a bit of trouble wrapping my head around that one. |
Originally Posted by sphealey
(Post 10625024)
Suppliers must have some assurance that when they file a document that is compliant with regulations and procedures that that document will be processed and approved or disapproved based on consistent criteria.
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Originally Posted by Takwis
(Post 10625108)
Can you elaborate on the difference between “unacceptable stick force” and “non linear stick force which would be unacceptable for certification requirements”? I’m having a bit of trouble wrapping my head around that one. |
Originally Posted by Takwis
(Post 10625108)
Can you elaborate on the difference between “unacceptable stick force” and “non linear stick force which would be unacceptable for certification requirements”? I’m having a bit of trouble wrapping my head around that one. |
unacceptable stick force gradient at high alpha. |
Can you elaborate on the difference between “unacceptable stick force” and “non linear stick force . . . |
Originally Posted by jimtx
(Post 10625104)
I envision two cases where the MAX's stick force non linearity might come into play. It might make a steep turn easier if you fly the attitude you want to put the performance where you want. It also might be a problem in a clean off autopilot windshear escape. Would have to see that in the airplane or simulator.
As far as what is and what isn't acceptable in force and gradient, AC25.7D covers the requirements, examples and suggested methods to ascertain § 25.173 Static longitudinal stability. Para C is of interest but so is A, B and D. For the amended MCAS, § 25.145 Longitudinal control may have been part of the compliance issue that led to the unfortunate turn of events in the repurposing of the MCAS from a high speed/manoeuver SAS to a low speed SAS system. The regs provide for an average stick force gradient to be met, but there is additionally a requirement on “local” reversals in the stick force versus airspeed relationship over the range of airspeeds tested. That is shown in the AC, in figure 7-1 (page 7-4) and 7-2 (page 7-5). Most times planes behave like darts, but they can get awkward, like the F-101 pitch up issue, the overbank of a BUFF, (where wing sweep and high bank angles with slip results in a lateral directional divergence, think Czar 52 @ Fairchild, limitations in the Dash-1 etc. [Your T-38 got a mention in PIO history for the condition you note, NASA/WPAFB put out a great doc on the subject, and an instrumented 38 gave impressive data]. https://cimg4.ibsrv.net/gimg/pprune....bfe3af18ba.png https://cimg9.ibsrv.net/gimg/pprune....5d218fb703.png REF: AC25.7D § 25.145: page 5-15 to 5-19 §§ 25.173 and 25.175 pages 7-1 through 7-5 |
Originally Posted by AerocatS2A
(Post 10625115)
If certification requirements were unnecessarily strict you could have a system that failed to meet certification requirements but were not actually a problem. That’s my reading of it anyway. |
Originally Posted by fdr
(Post 10625138)
The trigger mechanisms for the original MCAS had speed (mach) and aoa conditions. Those equate to conditions such as a wind up turn, which is quite a way from a wind shear avoidance and/or recovery case.
As far as what is and what isn't acceptable in force and gradient, AC25.7D covers the requirements, examples and suggested methods to ascertain § 25.173 Static longitudinal stability. Para C is of interest but so is A, B and D. For the amended MCAS, § 25.145 Longitudinal control may have been part of the compliance issue that led to the unfortunate turn of events in the repurposing of the MCAS from a high speed/manoeuver SAS to a low speed SAS system. The regs provide for an average stick force gradient to be met, but there is additionally a requirement on “local” reversals in the stick force versus airspeed relationship over the range of airspeeds tested. That is shown in the AC, in figure 7-1 (page 7-4) and 7-2 (page 7-5). Most times planes behave like darts, but they can get awkward, like the F-101 pitch up issue, the overbank of a BUFF, (where wing sweep and high bank angles with slip results in a lateral directional divergence, think Czar 52 @ Fairchild, limitations in the Dash-1 etc. [Your T-38 got a mention in PIO history for the condition you note, NASA/WPAFB put out a great doc on the subject, and an instrumented 38 gave impressive data]. https://cimg4.ibsrv.net/gimg/pprune....bfe3af18ba.png https://cimg9.ibsrv.net/gimg/pprune....5d218fb703.png REF: AC25.7D § 25.145: page 5-15 to 5-19 §§ 25.173 and 25.175 pages 7-1 through 7-5 |
The autopilot is a machine that will apply the required input to achieve the desired result. It doesn’t have expectations or past experience to fool it into doing the wrong thing. It doesn’t care if the “stick forces” change as it applies more elevator, it just does what needs to be done. |
Originally Posted by AerocatS2A
(Post 10625186)
The autopilot is a machine that will apply the required input to achieve the desired result. It doesn’t have expectations or past experience to fool it into doing the wrong thing. It doesn’t care if the “stick forces” change as it applies more elevator, it just does what needs to be done. |
Originally Posted by AerocatS2A
(Post 10625186)
The autopilot is a machine that will apply the required input to achieve the desired result. It doesn’t have expectations or past experience to fool it into doing the wrong thing. It doesn’t care if the “stick forces” change as it applies more elevator, it just does what needs to be done. |
Aircraft flight behavior has to follow the FARs not the other way around.
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For all the analysis, the expert and intelligent opinion on this thread alone, it’s clear the 737 has been designed right upto, and perhaps slightly over what the overriding aircraft type is capable of accepting. it isnt the only type that has gone up the edge of what is possible. But engineering fix over engineering fix in the name of progress and improvement is one thing, but time will tell whether the unfortunate incidents were sciences way of stepping in with the 737 and saying enough is enough, possibly decades after someone in Boeing should have made the ballsy decision. Posters mention “murky” in relation to the desperate teams over in the US trying in as cost effective way as they are able to navigate the MAX back into service, One thing that is extremely clear to me my close family my friends, mostly non aviation linked - is that the companies who end up with the MAX or unfortunately already own the MAX and can’t cost effectively rid it from their fleets without loss of face or substantial amounts of loss of finance, then its going to be extremely difficult to encourage joe public onto these jets. I’m speaking outside our sphere of understanding about the finer points of PoF and complex jet control systems. Basic general public level of understanding. A few “software updates” and supplemental sim training may satisfy the American regulators, and name changes may disguise the fact which aircraft the MAX actually is (I think it’s safe to say the media is in the starting blocks, ready for the exclusives with this particular part of the strategy) however, from a personal level, I know I shall check every airlines fleet list to ascertain who has these jets, and won’t be booking short haul flights with any company with these types. I am absolutely sure I won’t be alone with this strategy. There’s an old Latin saying somewhere that roughly translates to buyer beware that fits this scenario perfectly. I strongly suspect this this may be the much bigger problem than the reported “murky” dealings trying to get this jet back into service. It most likely will go back into service, possibly early next year. As stated, I won’t be getting on one, neither will many people I have spoken to recently either. I’ve personally not engaged in conversation other than to say make your own mind up. How Boeing fix this is going to make interesting viewing. The cost to buy these jets will now be bargain basement prices, so there will be the bait for airlines to buy them. But at what risk. Losing customers to competitors without MAX in their fleets, may be the biggest economic decision many airlines make in their lifetime. |
MAX test flights Someone is doing an awful lot of checking out over the last two days.
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Originally Posted by ktcanuck
(Post 10625426)
MAX test flights Someone is doing an awful lot of checking out over the last two days.
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Originally Posted by Three Lions
(Post 10625364)
For all the analysis, the expert and intelligent opinion on this thread alone, it’s clear the 737 has been designed right upto, and perhaps slightly over what the overriding aircraft type is capable of accepting. it isnt the only type that has gone up the edge of what is possible. But engineering fix over engineering fix in the name of progress and improvement is one thing, but time will tell whether the unfortunate incidents were sciences way of stepping in with the 737 and saying enough is enough, possibly decades after someone in Boeing should have made the ballsy decision. Posters mention “murky” in relation to the desperate teams over in the US trying in as cost effective way as they are able to navigate the MAX back into service, One thing that is extremely clear to me my close family my friends, mostly non aviation linked - is that the companies who end up with the MAX or unfortunately already own the MAX and can’t cost effectively rid it from their fleets without loss of face or substantial amounts of loss of finance, then its going to be extremely difficult to encourage joe public onto these jets. I’m speaking outside our sphere of understanding about the finer points of PoF and complex jet control systems. Basic general public level of understanding. A few “software updates” and supplemental sim training may satisfy the American regulators, and name changes may disguise the fact which aircraft the MAX actually is (I think it’s safe to say the media is in the starting blocks, ready for the exclusives with this particular part of the strategy) however, from a personal level, I know I shall check every airlines fleet list to ascertain who has these jets, and won’t be booking short haul flights with any company with these types. I am absolutely sure I won’t be alone with this strategy. There’s an old Latin saying somewhere that roughly translates to buyer beware that fits this scenario perfectly. I strongly suspect this this may be the much bigger problem than the reported “murky” dealings trying to get this jet back into service. It most likely will go back into service, possibly early next year. As stated, I won’t be getting on one, neither will many people I have spoken to recently either. I’ve personally not engaged in conversation other than to say make your own mind up. How Boeing fix this is going to make interesting viewing. The cost to buy these jets will now be bargain basement prices, so there will be the bait for airlines to buy them. But at what risk. Losing customers to competitors without MAX in their fleets, may be the biggest economic decision many airlines make in their lifetime. Of course, the whole saga will be replayed anyways in gory detail the next few times one crashes. |
The frequent fliers won't forget quickly. And it will be interesting to see how the American public react if the FAA so 'yes' and Europe, China, Australia and Canada say 'not proven'.
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Originally Posted by Fly Aiprt
(Post 10625332)
I'd say any test pilot will perform the tests he is asked to perform, but they don't have command of what becomes of their flight reports.
Gone are the Concorde days when test pilots were part of the development team... Now be it in the US or not, the issue will be how will they ensure that the test aircraft is 'MCAS-free'. On the other hand, what do those continuous test flights on Flight24 mean, whereas Boeing says their fixes have been ready for weeks now. Or does the leaked email really mean that new issues are still appearing day after day ? How will MCAS be disabled for the test, simplest would likely be a software load but that might raise questions of what else changed. Might also be possible by a HW/wire mod. Either one of course puts thing squarely in "test pilot" territory. Vefying MCAS free should be possible by taking it to conditions where it should kick in and verifying no trim action. The continuing flight may be collecting more data for simulator or exposing additional pilots to real aircraft response. |
Three Lions: For all the analysis, the expert and intelligent opinion on this thread alone, it’s clear the 737 has been designed right upto, and perhaps slightly over what the overriding aircraft type is capable of accepting. So it goes. |
why not fix a control force issue directly with a control force fix?
If Boeing's 737-MAX has a column control force issue, in a close to stall situation to abide by FAR's. Why did they did they take the scenic path to move the Stabilizer to fix it? Why didn't they just modify the Elevator Feel computer system to load up the control column correctly? That would be the most direct fix, and you wouldn't deal with a trim runaway issue if an AOA fails, just more force to deal with on the column suddenly. Pilots would notice the issue quickly, and instinctively fly the plane. You can control the force applied so as to not over power the pilots ability to fly the plane. You wouldn't have the danger of the plane getting far out of trim. That seems to me, to be the simple, direct, and safer fix. What am I missing?
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Originally Posted by GroundedDinosaur
(Post 10625565)
If Boeing's 737-MAX has a column control force issue, in a close to stall situation to abide by FAR's. Why did they did they take the scenic path to move the Stabilizer to fix it? Why didn't they just modify the Elevator Feel computer system to load up the control column correctly? That would be the most direct fix, and you wouldn't deal with a trim runaway issue if an AOA fails, just more force to deal with on the column suddenly. Pilots would notice the issue quickly, and instinctively fly the plane. You can control the force applied so as to not over power the pilots ability to fly the plane. You wouldn't have the danger of the plane getting far out of trim. That seems to me, to be the simple, direct, and safer fix. What am I missing?
Edit: See: https://www.pprune.org/tech-log/6202...l#post10442033 |
Originally Posted by GordonR_Cape
(Post 10625566)
AFAIK the B737 elevator feel computer is a hydraulic mechanism, not an electronic system. Reverse engineering it would create many more certification obstacles than it would solve. It would also be like adding FBW to an aircraft never designed for it. Oh wait, haven't we been down this road before...
And yet, moving the stabilizer just to correct a control column feel issue.... When one thinks the stick-nudger solution had already been implemented in some airplanes... |
RUNAWAY STAB.....
I never got more glass and push-button qualified than my last nine years on the 744, thus well out of date on any later stuff. However I did begin my 707 school with Boeing at Seattle.
A 'Runaway Stabiliser' had been briefly an issue with earlier versions, and it was always a priority memory item emergency drill practised on most recurrent training exercises. The first action made a lot of sense. It was for each pilot to lean over and physically grab the opposite trim wheel bloody quick. It certainly hurt a bit, but life might depend on this. Different aircraft, but is the strength required to halt the rotation not possible with the Max? Can't quite recall the 707 cut-off switches, but the follow up drill was Stab, Mach Trim, and Autopilot circuit breakers. Looks like the 737 Max has two Stab Trim cut off switches; 'Main Electric' and 'Autopilot'. Also would be surprised if sudden strong back pressure on the yoke wouldn't auto-brake in the forward runaway situation. That Idea was to allow time to get the handles out for manual re-wind prior to risk releasing the yoke again. There must be 737Max experienced pilots who can explain to those of us out of the loop why grabbing the wheel is not an obvious option? |
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