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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 10th Jul 2019, 17:29
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Originally Posted by infrequentflyer789
Aviation has a significant advantage in that it needs essentially zero infrastructure except at the ends, there is not a significant constraint there (excepting particular localities), if there was I submit that the A380 would not have been cancelled...
20Bn+ for LHR third runway vs. 2Bn to re-engine A380......
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Old 10th Jul 2019, 22:25
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Originally Posted by Peter H
From https://www.bloomberg.com/news/artic...-can-fly-again with my numbers
EASA’s checklist includes a number of issues that have been disclosed:
1 the potential difficulty pilots have in turning the jet’s manual trim wheel
2 the unreliability of the Max’s angle of attack sensors
3 inadequate training procedures
4 a software issue flagged just last week by the FAA pertaining to a lagging microprocessor
5 also listed a previously unreported concern: the autopilot failing to disengage in certain emergencies.

“Any of these could significantly affect the return to service, but we don’t know if they are actually going to become requirements or are they just
items for discussion,’’ said John Cox, a former 737 pilot who is president of the aviation consulting company Safety Operating Systems.
Good thing that items 1, 2, 4, and 5 are all nothingburgers according to 737 Driver/yoko and Boeing's PR cabal. Else it looks like the Max might be in serious trouble. Any speculation as to what would be necessary to redesign the manual trim system to fix the trim wheel issues?
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Old 10th Jul 2019, 23:03
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Nothing required for Manual Trim from what I have heard. System has been tested and works. Having used it in test flights it is not that hard to move and I understand the FAA and Boeing have retested it recently. Once outside the envelope it may be a different story but then you are outside the certified envelope for the aircraft.
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Old 10th Jul 2019, 23:22
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I believe the certification required a higher force to signal to the pilot the approach to the stall - enter MCAS.

Greetings, good sir. - I trust you and your good lady continue to enjoy retirement life.

The LSS concern is across the speed spectrum, where the pilot needs to feel more pull - the further below trim speed - or push - above trim speed - for the stability considerations to be acceptable. It's not really a relation to specific speed, stall or otherwise. Unfortunately, some aircraft, especially at lower speed/high alpha, and high thrust, can see the "up" lift force at the front of the engine installation cause a nose up pitch contribution which reduces the pilot's pull force requirement when the aircraft is below trim speed.

As I indicated previously, I am aware of one aircraft for which the effect, in the absence of the SAS's influence, is to reverse the force gradient with speed and the pilot ends up having to reduce the pull force/push the stick to avoid a further reduction in speed. While that is flyable, it is not a good situation, requiring some out of left field knowledge and a very high level of concentration by the pilot. In general, the TP will rise to the occasion, while the rest of us would tend to fall by the wayside ...

As I read the tea leaves, the usual SAS systems and MCAS are looking to address the same concern, albeit by slightly differing techniques.
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Old 10th Jul 2019, 23:39
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Originally Posted by coaldemon
Nothing required for Manual Trim from what I have heard. System has been tested and works. Having used it in test flights it is not that hard to move and I understand the FAA and Boeing have retested it recently. Once outside the envelope it may be a different story but then you are outside the certified envelope for the aircraft.
Multiple reports from reliable major international news outlets have reported that concerns about the effort required to trim using the manual wheels are on the EASA list.

Have you seen this video from Mentour Pilot?

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Old 11th Jul 2019, 01:55
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Salute!

Thanks JT and PJ
I continue to wonder how to certify a modern plane according to column/stick force as AoA increases, especially just before the stall AoA. I am looking for a plane in service besides some old Gooney Birds and floatplanes and critters of that ilk that have only cables, pushrods and such with absolutely no commands to the flight control surfaces from HAL or STS or anything but pure "manual" connections. Oh yeah, no "artificial feel".

Somehow the Airbus 320 and following are certified and those suckers have zero feel as the plane approaches a high AoA or low AoA or any damned AoA. The sticks provide no feedback to the pilot WRT control surface deflection or aero forces, nor any trim requirement if speed is changed, nor ........ "there must be fifty ways"

So my main question is why did FAA squawk about the column force? I have not seen a technical description of a commercial airliner built after 1950 that did not have some kinda "artificial feel" add-on to the ropes, levers, pulleys and tubes. Prolly 99% of every military "light" since 1950 had zero direct mechanical feedback from the control surfaces.

So how did the latest bus get certified, but the 737 had to add the MCAS?

My point from day one has been that MCAS was "sold" in order to compensate for poor basic aerodynamic characteristics that reduced the plane's pitch stability. So fix the aero and not implement a kludge hybrid system without informing all the pilots and maybe doing a better fault tree analysis of such syterm.

Gums still ponders....
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Old 11th Jul 2019, 02:26
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The sadly ironic thing is that the corner of envelope that MCAS was required for would have rarely been seen in airline ops. Airliners pretty much stick to the safe middle and not the outer edges, The MAX probably could have flown for years without one honest encourter with a high AOA situation in which MCAS wound have been needed..
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Old 11th Jul 2019, 03:00
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Originally Posted by john_tullamarine
I believe the certification required a higher force to signal to the pilot the approach to the stall - enter MCAS.

Greetings, good sir. - I trust you and your good lady continue to enjoy retirement life.

The LSS concern is across the speed spectrum, where the pilot needs to feel more pull - the further below trim speed - or push - above trim speed - for the stability considerations to be acceptable. It's not really a relation to specific speed, stall or otherwise. Unfortunately, some aircraft, especially at lower speed/high alpha, and high thrust, can see the "up" lift force at the front of the engine installation cause a nose up pitch contribution which reduces the pilot's pull force requirement when the aircraft is below trim speed.

As I indicated previously, I am aware of one aircraft for which the effect, in the absence of the SAS's influence, is to reverse the force gradient with speed and the pilot ends up having to reduce the pull force/push the stick to avoid a further reduction in speed. While that is flyable, it is not a good situation, requiring some out of left field knowledge and a very high level of concentration by the pilot. In general, the TP will rise to the occasion, while the rest of us would tend to fall by the wayside ...

As I read the tea leaves, the usual SAS systems and MCAS are looking to address the same concern, albeit by slightly differing techniques.
Hi JT, but it seems MCAS was to address a concern and 0.6 units was fine, but then later in the program another concern was encountered in flight testing. This required the supercharged MCAS of 2.5 units and faster to resolve.

There is very little information but it seems the first was for the stick feel certification issue, the other not mentioned as a stick feel issue but more a stability issue (possibly a stall issue).

The second has had very little commentary, but if true is possibly by far the greater issue to have and deal with.

From what I can work out the MAX has issues with high speed, high AoA in a turn having "correct feel" & low speed and high AoA - C of G and weights have effects as do G forces.

However a little flap or the autopilot fixes everything (all of the issues). I find this a little hard to fathom, but will agree the auto-pilot does not care for the stick forces getting light. At some stage the auto-pilot will just hand over the aircraft to the pilots in a flyable condition or not.

I spoke to my cousin that I think knows a bit about computers and software, if he knew about the Max he said yes he was following it (not on here). I asked him about the "fix" and what time frame he thought. The following is his reply.

"To be honest, I doubt it will be fixed, we'll just be told that it has been and something will be cobbled together. These problems are complex, and Boeing have sacked most of their senior knowledgeable engineers (the bit in that article about critical systems relying on only a single sensor input shows that design checking was absent from the process, leading to larger costs to fix such shortcomings). I spend a lot of my life fighting complexity creep in IT systems for primarily this reason (and why the stuff I write tries to follow Einstein's maxim of "as simple as possible, but no simpler").

The part in the original article about "No longer needing engineers because the software is mature" is typical management thought process, completely missing the point that this software is continually being changed for changing airframes.

I actually have a subconscious fear of riding elevators for this reason, knowing that the control systems are no longer written by seasoned professionals, but interns or otherwise."

My sister asked this - "Aside from stopping abruptly or I guess going really fast what issues are there to be worried about on an elevator that malfunctions?
I feel like I have limited thinking in this area if you have a subconscious fear. Are they likely to become rabid and eat us?"

His reply was this - "Or not stopping abruptly. The emergency brakes should be hardware interlocked, and independent of computer control, but cost cutting will end up with another https://en.wikipedia.org/wiki/Therac-25 on our hands. A lot of the software is not open to public scrutiny (locked up on the grounds of "proprietary"), so we have to trust people to write software with minimal bugs, but the pressure to market ensures that it's typically rushed. Boeing were initially denying that anything could be wrong with their software until the death of two plane-loads of people and mounting evidence forced them to admit their defects".
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Old 11th Jul 2019, 08:10
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Originally Posted by Bend alot
His reply was this - "Or not stopping abruptly. The emergency brakes should be hardware interlocked, and independent of computer control, but cost cutting will end up with another https://en.wikipedia.org/wiki/Therac-25 on our hands. A lot of the software is not open to public scrutiny (locked up on the grounds of "proprietary"), so we have to trust people to write software with minimal bugs, but the pressure to market ensures that it's typically rushed. Boeing were initially denying that anything could be wrong with their software until the death of two plane-loads of people and mounting evidence forced them to admit their defects".
A classic.
Here is another one frome the Aerospace industry - including deficient test planning and testing equipment:
ARIANE 5 Failure - Full Report

I just have some problem on the table to solve. Rootcause is some hipster big data internet of things component added to a decade old distributed control system breaking it from time to time. Love it.
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Old 11th Jul 2019, 08:28
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Certification requirements

Is the current CS 25 paragraph 671 valid for the B737, or are there grandfathering rights?
And how is paragraph 671 to be understood:
The aeroplane must be shown by analysis, test, or both, to be capable of continued safe flight and landing after any of the following failures or jamming in the flight control system and surfaces (including trim, lift, drag, and feel systems) within the normal flight envelope, without requiring exceptional piloting skill or strength.
A runaway of a flight control to an adverse position and jam must be accounted for if such runaway and subsequent jamming is not ‘extremely improbable’.
Is it required for the manual trim to be functional in the full flight envelope, after runaway to full ANU or AND?
Are other non FWB able to manually trim in the full envelope?
ManaAdaSystem was of the opinion that most aircraft could not be trimmed in this situation. MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
Does the B737 have the cut-out switches since a runaway is not ‘extremely improbable’, or is the switches an extra layer of safety?.
Some modern FBW aircraft does not have trim wheels, can they document that a runaway is ‘extremely improbable’?.
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Old 11th Jul 2019, 08:33
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Originally Posted by Water pilot
Yesterday afternoon I was stuck in traffic near Everett so I pulled off to the marina to wait it out. At exactly 4:30 PM, Isaw what I think was a 737 MAX not in livery (green primer or whatever) flying at a much more vertical attitude than I have seen any plane accomplish anywhere other than an airshow. It kept that attitude long enough for me to pull out my phone and get some video, although since it ended up flying over the top of my head the video does not do a good job of representing the angle of the plane relative to the ground.
So the good news to me is that at least Boeing is doing some real world testing. Tragically far too late, but real world and not some jumped up playstation. If there is interest and I can figure out how I will post the video but there is nothing really spectacular in it, perhaps an expert could spot something interesting. Basically the plane was flying level, pulled up in to a very steep (absurdly steep) flight angle, held for awhile, and leveled out. I got some of the steep angle and the overhead flight.
I would almost guess that they had pulled it into a stall (intentionally) but I am in no way qualified to judge that. Shortly after an unmarked white helicopter with video equipment flew past, may have been news for the traffic jam (although that is not news in Everett!) or perhaps Boeing recording the flight.
I was waiting to see if this interesting post generated any response but I don't think it has.
I just wonder if Boeing or someone else is asking the question, 'What actually does happen to this thing during take-off if the aerodynamic changes introduced by the new engines are allowed to run their course without any input from MCAS or anything else?'
But of course you'd think that question would have been asked, and answered, and the answer documented truthfully in the original flight test programme. Wouldn't you?
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Old 11th Jul 2019, 08:49
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Originally Posted by coaldemon
Nothing required for Manual Trim from what I have heard. System has been tested and works. Having used it in test flights it is not that hard to move and I understand the FAA and Boeing have retested it recently. Once outside the envelope it may be a different story but then you are outside the certified envelope for the aircraft.
The manual trim issue occurs when the aircraft is substantially out of trim, and electric trim is not available, but that is well within the envelope of the aircraft, as both JT and ET were for the most part of their foreshortened flights.

That is the problem...

It may be argued that this condition can only occur from a failure such as MCAS, however the A300 accidents, (RCTP, RJNN the old one) and the A320 splash (LFMP) along with USAir 320 events out of Reagan, A310 aerobatics at UUEE and LFPG, all of those were aircraft that ended up considerable out of trim without a failure of the trim system at all. For a similar case in say a B737NG, try getting the plane to Vref on an approach, going TOGA and failing the stab trim (simulating a failure or runaway resulting in cutout)... watch the fur fly. This is the easy fault, judicious use of bank will give a crew time to manage the problem. Nose down being that much out of trim is less likely before MCAS existed, but still will be challenging, and will take up some sky. The saving grace is just that the likelihood of the AND case is not as high as the ANU case, if and only if MCAS is removed from the equation.
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Old 11th Jul 2019, 09:22
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the first was for the stick feel certification issue, the other not mentioned as a stick feel issue but more a stability issue

I guess we all are interested and following the story in the hope of finding out more of the detail. Whatever that final story might be, it is untenable to posit that Boeing intended the system to function as it did in the two mishaps - clearly, the FMECA exercise didn't pick up some potential problems which it ought to have done. The folks involved, and the company, are going to have to wear some censure as a result.

However, in respect of your observation it needs to be kept in mind that LSS, basically, is stick feel as perceived by the pilot.

As to the detailed design considerations for MCAS, I don't think that sufficient information has been released yet into the public domain so, in my view, there remains much waiting for further details.
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Old 11th Jul 2019, 09:26
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If Boeing were testing MCAS in extreme takeoff modes I'm not sure they'd do it anywhere in sight of people, and certainly not at their home field! It would happen a long way away at a desert strip someplace where if something went wrong it would be easier to manage PR wise...

G
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Old 11th Jul 2019, 10:17
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Originally Posted by john_tullamarine
the first was for the stick feel certification issue, the other not mentioned as a stick feel issue but more a stability issue

I guess we all are interested and following the story in the hope of finding out more of the detail. Whatever that final story might be, it is untenable to posit that Boeing intended the system to function as it did in the two mishaps - clearly, the FMECA exercise didn't pick up some potential problems which it ought to have done. The folks involved, and the company, are going to have to wear some censure as a result.

However, in respect of your observation it needs to be kept in mind that LSS, basically, is stick feel as perceived by the pilot.

As to the detailed design considerations for MCAS, I don't think that sufficient information has been released yet into the public domain so, in my view, there remains much waiting for further details.
Just wanting the second MCAS "solution" put openly in view John - yes we need more details on that.

Lets hope the foreign regulators review and research this as part of the re-certification process.
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Old 11th Jul 2019, 12:57
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Just wanting the second MCAS "solution" put openly in view John - yes we need more details on that.

There is no "hiding" those concerns - plenty of references abound. I am sure that, at day's end, the company, the regulators, and so forth, will sort the problems out and the aircraft will go on to greater things. At this stage, though, some effort is required, whilst reading the tales, to sort the wheat from the chaff, methinks.

The only folks who can't win in this are those who were on the two mishap aircraft and their personal extended family and related networks.
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Old 11th Jul 2019, 13:26
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https://www.reuters.com/article/us-r...-idUSKCN1U52ME

Patience beeing lost slowly?
So who sees them back flying end of September?
And what will the SEC say?
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Old 11th Jul 2019, 14:05
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the problem with the training fix is that we're always training for the last accident. Im sure we are going to see a lot more stab training in our future just as Im sure that it will be a long time before we see another accident because of it. Used to be that there was always an unknown factor going into the box so you had to try to be prepared for anything just like there used to be a time when you could get more than one malfunction. Now it all goes by a preplanned syllabus that anyone can get a hold of so there are no surprises. I guess what Im saying is the surprise factor has been totally removed from training which as we know is not realistic. Nobody gets there real emergencies prebriefed. There is alot more to fixing the training than including McAS and runaway stab in the mix.
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Old 11th Jul 2019, 15:22
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Edit: I just found that this has been posted earlier in this thread - but here's another news site.
EASA gives requirements for return to flight.

The five requirements the European Aviation Safety Agency have listed so far are as follows:
  • Reduce the difficulty manually turning the trim wheel
  • Address the unreliability of Angle of Attack sensors
  • Address the training situation
  • Investigate software issues with a lagging microprocessor
The fifth one relates to difficulties in disengaging the autopilot under some conditions:

Investigations have concluded that pilots who encounter a stall scenario relating to the Manoeuvring Characteristics Augmentation System (MCAS) or similar flight control emergencies have difficulty disconnecting the autopilot.

Last edited by .Scott; 11th Jul 2019 at 20:52. Reason: Added Last quote - as requested by "Peter H".
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Old 11th Jul 2019, 22:27
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Boeing leader at Renton 737 MAX plant retires
https://www.seattletimes.com/busines...plant-retires/
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