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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 16th Oct 2019, 04:10
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Originally Posted by Tomaski
The degree of difficulty of using the manual trim is not so much a function of absolute trim position as it is how far from neutral trim the stab is - you don't have to hit the stops of the trim range to have a problem. I'm guessing that 2-3 units out of trim would be enough to create difficulty and 4+ units out would fall into the nearly impossible to move range (without something like the yo-yo maneuver to relieve pressure). It's really a matter of the total forces on the jackscrew/nut mechanism which, again, are a function of elevator (not stab) position, airspeed, and altitude. And again, manual trim can be safely used in all areas of the certified flight envelope as long as the stab is kept reasonably close to neutral trim (no forward or back pressure on the control column). Despite concerns to the contrary, I am not aware of any circumstances of aerodynamic loading that prevents the Main Electric Trim from being able to reposition the stab no matter how far out of trim it is. In the early months of the investigations there were some suggestions that the electric trim motor might have stalled in one or both of the MAX accidents, but none of the official investigating agencies have ever cited this as an issue. If this were an actual concern, it probably would have been included in the laundry list of deficiencies that needed to be corrected before the MAX can return to service.
Thanks for your detailed answer. I see your point about how far from neutral trim being the important number. I can’t remember from my ATPL theory how the pull force in an out of trim situation changes with speed, is it squared?
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Old 16th Oct 2019, 09:24
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Only a few more sleeps and many of the questions on this forum will be answered. Count on Indonesia’s KTNT publishing final accident report on JT610, or at least a comprehensive update, by end of October.
After loss of AirAsia QZ8501 in December 2014, KTNT met ICAO’s 12 month reporting deadline. See https://www.bea.aero/uploads/tx_elyd...XC-reduite.pdf.
KTNT will identify all “Contributing Factors” rather than a single cause. Some JT610 factors will be quite similar to QZ8501; e.g. defect reporting, maintenance, upset training and competencies, startle/CRM.
KTNT can lift other factors straight from Joint Authorities “Technical Review of Boeing 737 MAX Flight Control System”. The review has 51 pages of “Observations, Findings and Recommendations” about inadequacies of MAX certification. These are all issues that should have been resolved before aircraft was certificated; not after 347 died (I include the Indonesian diver who died during FDR recovery). Indeed the issues would have been resolved had each Authority independently validated Boeing/FAA Corp’s certification, as was normal before mutual recognition.
NTSB is contributing to JT610 investigation as “Accredited Representative for State of Manufacture & Design”. So KTNT is sure to reference NTSB’s recent Safety Recommendation Report “Assumptions Used in the Safety Assessment Process and the Effects of Multiple Alerts and Indications on Pilot Performance”.
Also, after battery fires on Boeing 787, NTSB was probably peeved that its Investigation Report 2014/AIR1401 on deficient ODA certification went unheeded. Hopefully NTSB gets KTNT to report forcefully on ODA certification of 737 MAX.
Boeing/FAA Corp. will read KTNT report before it’s released. PR will be primed.
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Old 16th Oct 2019, 11:08
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Originally Posted by hans brinker


Thanks for your detailed answer. I see your point about how far from neutral trim being the important number. I can’t remember from my ATPL theory how the pull force in an out of trim situation changes with speed, is it squared?
In general, force is proportional to speed squared, but there are a lot of moving parts, so to speak, that effect the total forces on the jackscrew. And while the forces on the jackscrew are actual, the pull forces that the pilot feels through the control column are artificially generated by the Elevator Feel System which is driven by a separate airspeed sensor on the tail.
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Old 16th Oct 2019, 19:03
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Originally Posted by discorules
Not sure if this has been previously covered, but China Southern's B737 MAX 8, B-1205, seems to have been doing quite a bit of flying over the last month. Does anyone know if these are evaluation flights?
My money would be on an A320 of CGH with a dodgy transponder.

I can't see any reason why a China Southern Max would be defying the grounding, particularly as it's shown on FR24 as operating a bunch of Air Guilin schedules.
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Old 16th Oct 2019, 20:27
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Salute!

Sorry, tiddles. Have to take issue with the single AoA aspect of the crashes, although MCAS use of a single sensor for a critical control surface was flat out unacceptable. Ditto for folks keep asserting that a third crewmember "saved" the previous Lion flight. Until we hear their testimony as to what happened, I remain a skeptic.

My view of the elephant
- Part of the elephant was the implementation.
- Another was not telling the operators.
- And finally, a certifiation process that scares the hell outta me.

The fundamental flaw was using a kludge trim system feature to meet 40 year-old certification requirements that apply to the cable/pulley/pushrod control system that provides control wheel feedback as AoA increases and you "should" have to pull harder to increase AoA. Airbus does not have to meet this requirement. How come?

The implementation of MCAS without explaining it to the pilots and maintenance folks and so forth was reprehensible. I may have handled the rogue MCAS after a rought few seconds or minutes before turning off the trim, but I most likely would haver turned off only one switch that disabled A/P inputs to the stab trim. You see? The switches didn't work like they used to for the last 30 years. The control column cutout switch was also disabled. Did they tell me about that too? I don't think so, because that was part of the kludge.

Did big B come clean with the FAA about how MCAS worked and changes to the basic implentation that was not as harsh or strong? How about fault tree analysis briefings?

Oh well. back to the cave.

Gums sends....
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Old 16th Oct 2019, 21:25
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Just out of interest, Mr Avro fitted an AoA indicator to the 1940s designed Shackleton, in service until the early 90s.

Yet Mr Boeing was quoting tens of thousands of dollars to fit similar to the NGs.

What price safety? With one of these indicating gibberish during the takeoff roll or post bird strike would the crew have had an extra clue as to what was wrong?

Unable to post photo but if you google Avro Shackleton Instrument Panel Photos it’s visible up on the coaming left hand side beside the ‘g’ meter, some pics clearer than others.
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Old 16th Oct 2019, 21:39
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Originally Posted by Grebe
Plot thickens- phony documents ???
File under general buffoonery. I heard this story third-hand a few months back but didn’t think it credible. I guess I was wrong. The Lion Air maintenance department certainly has not been distinguishing itself throughout this tragic episode.
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Old 16th Oct 2019, 23:25
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14:53 ETAir Canada Updates Schedule Through to February 14, 2020 in Response to Ongoing Grounding of Boeing 737 MAX Aircraft

MONTREAL, Oct. 16, 2019 /CNW Telbec/ - Air Canada said today that it has now removed the Boeing 737 Max from its flying schedule until February 14,...

Others will of course be doing the same.
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Old 17th Oct 2019, 00:44
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This illustrates the outstanding issue with aviation, due to the cert process, systems are hopelessly antiquated...a pitot tube, with all of its issues to measure winds...and AOA vane, with all of itas issues, to measure the angle of attack.

A pitot tube?? might as well stick your finger out the window...and gues ( I mean that is what all the algorithms have to do!)

Real world applications in the same areas use sonic OLD OLD technology...this is like using a cup anemometer to measure windspeed...OLD. Instantaneous winds with cups spinning in circles??? Really?

The required height of the measurement, 15m????? At what point on the runway is 15m of any use?

In the business we use sonics, both 2D and 3D for winds..

Using a cup anemometer, a pitot tube, or a mechanical AoA vane is laughable.

Time to evolve, or become a casualty of evolution...(as we are now seeing with the MAX)

Last edited by Smythe; 17th Oct 2019 at 00:55.
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Old 17th Oct 2019, 01:22
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Could always use one of these dohickies Smythe.


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Old 17th Oct 2019, 03:07
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Originally Posted by Smythe
This illustrates the outstanding issue with aviation, due to the cert process, systems are hopelessly antiquated...a pitot tube, with all of its issues to measure winds...and AOA vane, with all of itas issues, to measure the angle of attack.

A pitot tube?? might as well stick your finger out the window...and gues ( I mean that is what all the algorithms have to do!)

Real world applications in the same areas use sonic OLD OLD technology...this is like using a cup anemometer to measure windspeed...OLD. Instantaneous winds with cups spinning in circles??? Really?

The required height of the measurement, 15m????? At what point on the runway is 15m of any use?

In the business we use sonics, both 2D and 3D for winds..

Using a cup anemometer, a pitot tube, or a mechanical AoA vane is laughable.

Time to evolve, or become a casualty of evolution...(as we are now seeing with the MAX)
Pitot tube:
"It's a slender tube that has two holes on it. The front hole is placed in the airstream to measure what's called the stagnation pressure. The side hole measures the static pressure. By measuring the difference between these pressures, you get the dynamic pressure, which can be used to calculate airspeed".

Hope this helps.
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Old 17th Oct 2019, 03:31
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Originally Posted by Smythe
In the business we use sonics, both 2D and 3D for winds..
Using a cup anemometer, a pitot tube, or a mechanical AoA vane is laughable.
Time to evolve, or become a casualty of evolution...(as we are now seeing with the MAX)
A sonic sensor also comes with a lot of problems..
limited measuring range, sensitivity to rain,fog, ice, snow, nearby longwave transmitters operating at ultrasonic frequency, birds nesting, and insects.
The best solution is to have:
Self-dagnostic/fault-silent sensors (where possible) to prevent faults from propagating, some types of sonic can measure speed of sound in 2D/3D and compare.
, redundancy, diversity (Cup and sonic)
observer modeling e.g. deriving values from aero-mechanical loads, or GNSS/INS.
Sensor fusion to combine values.
All this is not going to fare well with purists wanting as little software as possible in aircraft.
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Old 17th Oct 2019, 08:25
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Originally Posted by Longtimer

14:53 ETAir Canada Updates Schedule Through to February 14, 2020 in Response to Ongoing Grounding of Boeing 737 MAX Aircraft

MONTREAL, Oct. 16, 2019 /CNW Telbec/ - Air Canada said today that it has now removed the Boeing 737 Max from its flying schedule until February 14,...

Others will of course be doing the same.
As observed many posts ago: allowing Ms Rosie Scenario to write your published predictions of an RTF date is a way to guarantee a steady stream of ANOTHER MAX DELAY headlines.
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Old 17th Oct 2019, 14:40
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Originally Posted by BARKINGMAD
Just out of interest, Mr Avro fitted an AoA indicator to the 1940s designed Shackleton, in service until the early 90s.

Yet Mr Boeing was quoting tens of thousands of dollars to fit similar to the NGs.

What price safety? With one of these indicating gibberish during the takeoff roll or post bird strike would the crew have had an extra clue as to what was wrong?

Unable to post photo but if you google Avro Shackleton Instrument Panel Photos it’s visible up on the coaming left hand side beside the ‘g’ meter, some pics clearer than others.
Ironically enough, my father' cousin Roy was killed in a Shackleton crash, when they were evaluating a stall-warning system.
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Old 17th Oct 2019, 14:43
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Another week went by and nothing happend! What the heck are they doing?
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Old 17th Oct 2019, 16:20
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Originally Posted by babemagnet
Another week went by and nothing happend! What the heck are they doing?
Keeping quiet and not making statements about every little thing that happens.

Have you ever reviewed certification artifacts like FHAs or SSAs?
It's a long, tedious process normally. With the higher scrutiny due to the publicity it's going to be longer than normal.
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Old 17th Oct 2019, 16:35
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Originally Posted by babemagnet
Another week went by and nothing happend! What the heck are they doing?
I'm pretty sure that a great many people are scrambling as fast as they can, while being as careful as possible, knowing that screwing this up would be catastrophic for Boeing, the FAA and US leadership in aviation. And I'd bet that they have thought they were "almost there" more than once over the past months, only to realize that there were more and bigger problems, and larger issues, than they previously understood.
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Old 17th Oct 2019, 17:12
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Southwest Airlines removes Boeing 737 Max from schedule until February 8th

PUBLISHED 4 HOURS AGOUPDATED 2 HOURS AGO
Leslie Josephs@LESLIEJOSEPHS

https://www.cnbc.com/2019/10/17/sout...-february.html
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Old 17th Oct 2019, 19:50
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leeham news has a link to aljazeers on 737 max all told quite good first and last 7m minutes are feel good - rest is very much to the point

leehamnews-------com-------2019/10/16/737-max-specialt repor------

Oh the games some play - for what reason unknown- but thou shalt not question . .
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Old 17th Oct 2019, 20:46
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Shackleton AoA Test Flight Crash

Nevillestyke, was that the Foolow, Derbyshire accident in 1956?

Regardless I’m sorry to hear you lost a relative in a ‘Shack’ accident, I hope my posting has not caused distress.
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