prebennorholm wrote:

Saintor wrote:

Sorry, absolutely nothing you wrote refuted what I wrote.

*Nothing*.

Again, it WORKED.

Yeah, it WORKED. It WORKED the way that it killed 132 on US 427 and almost killed 53 on Eastwind 517. That wouldn't have happened if UA 585 had been equipped with a modern FDR.

You are twisting the facts

I never said that the fix was found after the 2nd crash!!!

Once Boeing found the direct cause, it was communicated along the counter-measures to apply if a case would present again. 737 were updated over many years.

There was no more case so yes by all means, it worked. No more drama. Nicely done.

Today's paranoia is counterproductive. There is no sound reason the current context should have not been professionally managed like in the '90s.

PixelFlight wrote:

I have in my post #2965 2 weeks ago

No, that is where you haven't. Continuing to post this doesn't make your speculative theory any more plausible. In order for your speculation to be true, it means the FAA either knowingly disregarded or unknowingly didn't apply their own regulations in certifying the MAX. Instead of using your time to post it here, why aren't you alerting the FAA of their egregious error?

The far more plausible explanation is that you have misinterpreted the regulations, and you're using this misinterpretation as a debate tool.

sgrow787 wrote:

smartplane wrote:

https://www.flightglobal.com/news/articles/easa-advises-checks-for-parts-from-discredited-xtra-462677/

The article by David KAMINSKI-MORROW states that the closure of Xtra Aerospace repair shop does not imply the crash AOA sensor was miscalibrated. Yet David leaves in the (false) statement:

Xtra Aerospace's repair station certificate was revoked by the US FAA following the discovery that a crucial angle-of-attack sensor was improperly calibrated before it was fitted to the Lion Air Boeing 737 Max which crashed in October last year.

Again, there's no proof that the crash AOA sensor was "improperly calibrated", either by Xtra Aerospace, or by Lion Air maintenance. There is a statement in the final Lion Air report that incorrectly assesses the NTSB report as saying the left AOA sensor had an offset. The NTSB report only stated that the "signal" from the left AOA sensor had an offset. Because that signal has a path from the sensor, to the ADIRU, to the FCC, it's unknown the source of the offset (aka erroneous data, erroneous reading).

On the other hand, we know that the shop was calibrating sensors incorrectly. We also know it's the shop where JT610's sensor came from. So… that rather tilts the odds somewhat beyond a 50/50 chance.

Saintor wrote:

prebennorholm wrote:

Saintor wrote:

Sorry, absolutely nothing you wrote refuted what I wrote.

*Nothing*.

Again, it WORKED.

Yeah, it WORKED. It WORKED the way that it killed 132 on US 427 and almost killed 53 on Eastwind 517. That wouldn't have happened if UA 585 had been equipped with a modern FDR.

You are twisting the facts

I never said that the fix was found after the 2nd crash!!!

Once Boeing found the direct cause, it was communicated along the counter-measures to apply if a case would present again. 737 were updated over many years.

There was no more case so yes by all means, it worked. No more drama. Nicely done.

Today's paranoia is counterproductive. There is no sound reason the current context should have not been professionally managed like in the '90s.

So if you have a frame that is unsafe and leads to accidents, you happily fly it on and kill more crew and passengers until you find the fault, to not impinge on the producer of said airplane.

Happily this modus operandi, has somewhat changed today.

Is it the American way to keep crashing until the fault is found? In Europe frames have been grounded to find and rectify the fault before flying the frame again. It seems that the USA is also prepared to ground a foreign frame until the fault is found, see ATR.

aerolimani wrote:

On the other hand, we know that the shop was calibrating sensors incorrectly. We also know it's the shop where JT610's sensor came from. So… that rather tilts the odds somewhat beyond a 50/50 chance.

Please provide a source that shows "we know that the shop was calibrating sensors incorrectly". Yes, documentation of their capability list was lacking, which says nothing about calibrations. From the FAA's statement itself:

https://www.faa.gov/news/press_releases ... wsId=24314

According to the order, Xtra failed to comply with requirements to repair only aircraft parts on its list of parts acceptable to the FAA that it was capable of repairing. The company also failed to comply with procedures in its repair station manual for implementing a capability list in accordance with the Federal Aviation Regulations. Xtra is a repair station certificated under part 145 of the Federal Aviation Regulations.

MSPNWA wrote:

PixelFlight wrote:

I have in my post #2965 2 weeks ago

No, that is where you haven't. Continuing to post this doesn't make your speculative theory any more plausible. In order for your speculation to be true, it means the FAA either knowingly disregarded or unknowingly didn't apply their own regulations in certifying the MAX. Instead of using your time to post it here, why aren't you alerting the FAA of their egregious error?

The far more plausible explanation is that you have misinterpreted the regulations, and you're using this misinterpretation as a debate tool.

The facts that JT610 and ET302 didn't have effective longitudinal control to pitch up while the pilots definitively wanted to pitch up are absolutes hard facts that have cost a lot of lives, not a "speculative theory".
Sorry it #2965 was not enough for you. Now you have #3652 where I carefully made no interpretation of the regulation, so I can't misinterpreted the regulations. I expect ET302 final report to cover that subject.

sgrow787 wrote:

aerolimani wrote:

On the other hand, we know that the shop was calibrating sensors incorrectly. We also know it's the shop where JT610's sensor came from. So… that rather tilts the odds somewhat beyond a 50/50 chance.

Please provide a source that shows "we know that the shop was calibrating sensors incorrectly". Yes, documentation of their capability list was lacking, which says nothing about calibrations.

I've been saying since just after Lion Air that I'm open to the possibility the issue is in avionics or wiring. Indeed, the length of time fixing the problem does rather suggest they're delving deep into the system...

SomebodyInTLS wrote:

sgrow787 wrote:

aerolimani wrote:

On the other hand, we know that the shop was calibrating sensors incorrectly. We also know it's the shop where JT610's sensor came from. So… that rather tilts the odds somewhat beyond a 50/50 chance.

Please provide a source that shows "we know that the shop was calibrating sensors incorrectly". Yes, documentation of their capability list was lacking, which says nothing about calibrations.

I've been saying since just after Lion Air that I'm open to the possibility the issue is in avionics or wiring. Indeed, the length of time fixing the problem does rather suggest they're delving deep into the system...

I have read that it's odd to have two AOA vane failures so early in an airplane's lifespan. The FDR does seem to suggest that the vane was somehow knocked loose though.

I do have a hunch that there were more problems on the Ethiopian flight. Take a look at the initial take-off (before flaps were retracted, pre-MCAS commanding nose-down):



https://www.satcom.guru/2019/04/what-ha ... et302.html

Then there are also the reports of debris and smoke coming from the airplane as it flew overhead, and the mention of pitch and roll oscillations in the preliminary report.

aerolimani wrote:

kalvado wrote:

Baldr wrote:

If Boeing, on the other hand, had decided to just better the A320neo family -- i.e. more modern A320-type fuselage with a LD3-45 compatible lower hold, aluminium wings/fuselage structure and 787-derived systems (etc.) -- they could have had that aircraft in service by now.

Hindsight is always 20/20. Boeing ALMOST did what was planned. If MCAS was held to a little bit higher standard from beginning, things would be way better for Boeing. It is two crashes which resulted in very critical attitude towards MAX, and a very critical review of MAX. Rightly or not, if not for the crashes, MAX would continue to ride success wave of NG.
I am not willing to say that MCAS is a result of an oh-so-bad MAX aerodynamics. There are problems; but show me a complex $100M machine without any... It is the way Boeing deals with problems what bothers me...

It's questionable whether Boeing could have met their self-imposed launch schedule for the MAX, had they done MCAS properly. By "done properly," I mean that the hazard assessment would have been catastrophic, and required input redundancy. As I understand, achieving that is turning out to be a lot more difficult than initially assumed.

Boeing began work on the software shortly after the Lion Air crash, in November of 2018. It's December 2019 now. That's more than a year since they began work, and the plane is still not ready. I know that the bit-flip thing is also part of the situation, and that likely wouldn't have come up were it not for the crashes. The bit-flip issue appeared at the end of June, so still at least 8 months of delay. So, imagine Boeing telling its MAX customers that their aircraft are going to be delayed by 8, 12, 14 months… or even longer??? Who knows, exactly?

IMO, that would have been the best of all paths for Boeing, but that can only be realized with the benefit of hindsight. As a plane-lover, I would have loved to see an NSA, but I recognize that Boeing also needs to run a successful company in today's market environment. Truly though, I do wish that Boeing would become more of an innovator and less of a slave to Wall Street.

This is a great post - you summarize my thoughts exactly, and in slightly less overly-dramatic fashion than I likely would have.

It is very interesting how difficult it is has seemingly become to include redundant (and error-checking-capable) input sources. Of course now they need to go a few steps further, but given that the incredibly basic MCAS 1.0 was accepted by certification authorities around the world, they obviously could have gotten by with anything extra as well (at the time). Even if fault-checking between the two AoA's and selection or cut-out isn't possible with the other considerations now, without taxing the processors, it's certainly obvious that they could have at least added a very simple "check" to have the processors look at the two values and simply disable if they didn't match. Have it on the MEL and plane can't fly again till it's fixed. I don't think that would have added much of anything to the launch date of the aircraft.

The scary thing is that there are hundreds of engineers at Boeing, all of which are far smarter than I am. I know for a fact that likely every one of them on the MCAS project were thinking about items like this (and probably knew of the triple-redundant nature of similar control-actuating systems in other aircraft). That's NOT a "hindsight thing" either, there were a number of gigantic red flags that likely popped up along the way during MAX development (not to mention before MCAS... guessing engine location threw up some equally large flags!).

So again, I agree with everyone here that the only clear take-away is that management and oversight (on a number of levels) at Boeing is clearly at fault - there may be others, but this much we know for sure. It really doesn't matter if they thought it was "safe enough" and "pilots will figure it out" or "there's some stuff they can do to disable it" - NONE of that sounds like the Boeing philosophy or tradition of exceptional flying machines that got them where they are today (well, a couple years ago I should say).
They need to go back to their roots; innovation, quality, safety. Profits are important, but if time/cost have the potential to impact safety, there needs to be a management staff at Boeing that tells their shareholders to f'off - as a quality product will be worth it in the long term, and reflect what the company stands for. Of course, such an argument is much easier to make to the pencil-pushers after this whole debacle.

MSPNWA wrote:

Instead of using your time to post it here, why aren't you alerting the FAA of their egregious error?

The EASA did that already in there "Exchange of views" document of the "03 September 2019": https://www.europarl.europa.eu/cmsdata/186500/20190903_EASA_Ky-original.pdf
"EASA findings" Page 14
" Significant technical issues:"
" - Too high forces needed to move the manual trim wheel in case of a stabiliser runaway"
" Findings communicated to Boeing and FAA in July 2019"

estorilm wrote:

NONE of that sounds like the Boeing philosophy or tradition of exceptional flying machines that got them where they are today (well, a couple years ago I should say).

Rudder PCU hardovers, cargo doors opening in mid air, assembly using nonconforming parts, force fitting those parts, the DC-10... I’d say the 737 MAX is part of their tradition and philosophy. Minimize time and cost and hope it’s ok.

kalvado wrote:

Some more retirements at Boeing. There was a separate thread on that, but it is now gone.
Boeing Commercial Airplanes chief engineer John Hamilton is retiring, per multiple media reports: e.g. https://www.seattletimes.com/business/b ... s-retires/
Official biography is still on Boeing's site: https://www.boeing.com/company/bios/john-hamilton.page
It says "John Hamilton was named the chief engineer for Boeing Commercial Airplanes in March 2019. " I don't know if the timing is coincidence with ET crash; but I doubt retirement less than a year after promotion amidst of 737 crisis and after being grilled in front of Congress for MAX situation is actually planned - I suspect he was just fired.
I wonder if that is a sign MAX is actually worse off than we think...

TFA says:

“John had planned to retire last year, but we asked him to stay on to help us with the 737 MAX investigations and return to service efforts,”

This suggests he was brought in last year to help with the JT investigation and put in charge after ET.

There's no evidence that suggests he's being fired.

I can imagine the last year has been very stressful for him and he's more than ready to leave and enjoy his retirement.

PixelFlight wrote:

MSPNWA wrote:

Instead of using your time to post it here, why aren't you alerting the FAA of their egregious error?

The EASA did that already in there "Exchange of views" document of the "03 September 2019": https://www.europarl.europa.eu/cmsdata/186500/20190903_EASA_Ky-original.pdf
"EASA findings" Page 14
" Significant technical issues:"
" - Too high forces needed to move the manual trim wheel in case of a stabiliser runaway"
" Findings communicated to Boeing and FAA in July 2019"

Free gym membership for all MAX pilots? Sorry...couldn't resist.

Interesting that the replacement for Hamilton is Lynne Hopper, and a quick search showed this quote from her.

And Boeing is changing. When I joined Boeing in 1997 we were still thought of as an “airplane company.”

It might be better if Boeing was still an airplane company.

PixelFlight wrote:

The EASA did that already in there "Exchange of views" document of the "03 September 2019": https://www.europarl.europa.eu/cmsdata/186500/20190903_EASA_Ky-original.pdf
"EASA findings" Page 14
" Significant technical issues:"
" - Too high forces needed to move the manual trim wheel in case of a stabiliser runaway"
" Findings communicated to Boeing and FAA in July 2019"

1) The EASA is not the FAA. Don't move the goal posts.

2) Subsequent EASA communication appears to show that they have abandoned that stance as an issue worthy of correction.

Go tell the FAA. And while you're at it, remind the EASA too of the regulation the FAA missed.

Saintor wrote:

You are twisting the facts

I never said that the fix was found after the 2nd crash!!!

Once Boeing found the direct cause, it was communicated along the counter-measures to apply if a case would present again. 737 were updated over many years.

There was no more case so yes by all means, it worked. No more drama. Nicely done.

Today's paranoia is counterproductive. There is no sound reason the current context should have not been professionally managed like in the '90s.

Maybe it was because of this 90s-era Boeing's precedent of focusing on winning time instead of acting promtly and decisively that the MAX was stuck to the ground by regulators two decades later when they saw the same story arising again. Fool me once ...

767333ER wrote:

estorilm wrote:

NONE of that sounds like the Boeing philosophy or tradition of exceptional flying machines that got them where they are today (well, a couple years ago I should say).

Rudder PCU hardovers, cargo doors opening in mid air, assembly using nonconforming parts, force fitting those parts, the DC-10... I’d say the 737 MAX is part of their tradition and philosophy. Minimize time and cost and hope it’s ok.

I'm not a huge fan of Boeing, but this is a different situation - the PCU thing was a sub-contractor right? The cargo doors are an issue because they had some prior indicators and complaints (and failures) and din't really act - I'll give you that.

In the case of the MAX, you're giving a system which has the ability to manipulate flight controls a single data point (and no ability to decide if it's in fact good or bad data). Blows my mind to this very moment still.. but oh well.

MSPNWA wrote:

PixelFlight wrote:

MSPNWA wrote:

Instead of using your time to post it here, why aren't you alerting the FAA of their egregious error?

The EASA did that already in there "Exchange of views" document of the "03 September 2019": https://www.europarl.europa.eu/cmsdata/186500/20190903_EASA_Ky-original.pdf
"EASA findings" Page 14
" Significant technical issues:"
" - Too high forces needed to move the manual trim wheel in case of a stabiliser runaway"
" Findings communicated to Boeing and FAA in July 2019"

1) The EASA is not the FAA. Don't move the goal posts.
2) Subsequent EASA communication appears to show that they have abandoned that stance as an issue worthy of correction.
Go tell the FAA. And while you're at it, remind the EASA too of the regulation the FAA missed.

The EASA has already communicated the "Too high forces needed to move the manual trim wheel in case of a stabiliser runaway" to the FAA, so I don't have to.
You misinterpreted the EASA document.

mjoelnir wrote:

So if you have a frame that is unsafe and leads to accidents,

This is simply untrue. Hundreds of North American pilots did thousands of flight time on the 737 MAX. They have larger and more forward-mounted engines but it is all under control. The frames will come back unchanged.

The problem is that Boeing considered that some wild pilots abusing the engines would be able to create a sudden nose-up condition. So even if there weren't obliged to do so, they used an updated version of MCAS, but yes they did poorly. Despite their enormous mistakes, ET302 pilots should have been aware that retracting the flaps would prevent MCAS to be activated. It should have been explicitly stated by Boeing since the beginning, more of that even the mere existence of MCAS. They should have been also aware that manual trimming was impossible at 350-400 knots. Many mentions that it was a futile maneuver above the low-200s knots air speed. They lost a lot of time doing this.

sgrow787 wrote:

aerolimani wrote:

On the other hand, we know that the shop was calibrating sensors incorrectly. We also know it's the shop where JT610's sensor came from. So… that rather tilts the odds somewhat beyond a 50/50 chance.

Please provide a source that shows "we know that the shop was calibrating sensors incorrectly". Yes, documentation of their capability list was lacking, which says nothing about calibrations. From the FAA's statement itself:

https://www.faa.gov/news/press_releases ... wsId=24314

According to the order, Xtra failed to comply with requirements to repair only aircraft parts on its list of parts acceptable to the FAA that it was capable of repairing. The company also failed to comply with procedures in its repair station manual for implementing a capability list in accordance with the Federal Aviation Regulations. Xtra is a repair station certificated under part 145 of the Federal Aviation Regulations.

I retract. We don't know for sure that the shop was calibrating sensors incorrectly. However, given how badly things were being done at Xtra, and the specific deficiencies regarding the AOA sensor calibration, there's a very good chance that is what went wrong.

If you haven't already, you should read the sections in the JT610 report, starting on pages 89, 202, and 227. It's far more informative than the FAA press release. From the JT610 report, we know they were using different equipment to perform the calibration from what is actually specified. While they did get FAA permission to do use alternate equipment, there is a definite propensity for error introduced by the fact that Xtra's test equipment has capabilities which the originally specified equipment does not. This introduces the possibility for error, to set one of the machines incorrectly, and suddenly it is very easy to produce an incorrectly calibrated sensor; a mistake which would result in exactly the scenario that occurred on JT610.

More importantly, Xtra had no documentation of how to conduct the test using their nonstandard equipment; something supposedly required in the FAA authorization of alternate test equipment. While it is circumstantial, I think it's worthwhile to note that the FAA chose to shut down Xtra, and not simply fine them and monitor them for a while.

While things can go wrong anywhere along a signal path, the evidence is rather pointed at Xtra, and the sensor itself. If the JT maintenance crew had completed the test with viable documentation to prove the sensor was working, then we would have reason to strongly suspect something else. It appears that the FAA and Boeing also don't think it was something other than the sensor. I expect we would have heard by now, if something else was up. The hardware on a commercial aircraft is not some delicate lab equipment. It is specifically designed and tested to ensure its robustness. The same basic hardware has been flying around on thousands of NG's, and I think issues would have appeared by now, if they had the potential to cause a specific and sustained alteration of readings (or data) from the AOA sensor.

sgrow787 wrote:

Again, there's no proof that the crash AOA sensor was "improperly calibrated", either by Xtra Aerospace, or by Lion Air maintenance.

Also, you need to understand that that Lion Air had no part in calibration of the sensor. Calibration occurred exclusively at Xtra. JT maintenance was supposed to have confirmed that the sensor was functioning. However, the lack of evidence of any such test being done means it is possible that they didn't. Thus, an improperly calibrated sensor could easily have gone unnoticed.

Thanks for sending me down this rabbit hole. The rereading of the report sections has increased my feeling that the sensor was likely improperly calibrated from the start. I'm willing to agree with the report that the cause of the AOA reading incorrectly was most likely the sensor itself, as a result of probable improper sensor calibration by Xtra.

Let's also be clear that the report says most likely improperly calibrated. It's not imprecise, as you seem to indicate.

After Xtra Aerospace repair of the accident AOA sensor in November of 2017, the sensor was installed on the PK-LQP aircraft on left side position during the maintenance activity in Denpasar on 28 October 2018. On the subsequent flight, a 21° difference between left and right AOA sensors was recorded on the DFDR, commencing shortly after the takeoff roll was initiated (note it takes some airflow over the vane for the vanes to align with the airflow). This immediate 21° delta indicated that the AOA sensor was most likely improperly calibrated at Xtra Aerospace.
As noted, utilization of the Peak Model SRI-201B API by Xtra Aerospace for the test and calibration of the 0861FL1 AOA sensor should have required a written procedure to specify the proper position of the REL/ABS switch.

The lack of an API written procedure was not detected by the FAA’s FSDO. This indicates inadequacy of FAA oversight.

The report: http://knkt.dephub.go.id/knkt/ntsc_avia ... Report.pdf

Saintor wrote:

mjoelnir wrote:

So if you have a frame that is unsafe and leads to accidents,

This is simply untrue. Hundreds of North American pilots did thousands of flight time on the 737 MAX. They have larger and more forward-mounted engines but it is all under control. The frames will come back unchanged.

The problem is that Boeing considered that some wild pilots abusing the engines would be able to create a sudden nose-up condition. So even if there weren't obliged to do so, they used an updated version of MCAS, but yes they did poorly. Despite their enormous mistakes, ET302 pilots should have been aware that retracting the flaps would prevent MCAS to be activated. It should have been explicitly stated by Boeing since the beginning, more of that even the mere existence of MCAS. They should have been also aware that manual trimming was impossible at 350-400 knots. Many mentions that it was a futile maneuver above the low-200s knots air speed. They lost a lot of time doing this.

This is the most bizarre post I have seen on here.

How many of those flights flown by the wonder pilots in the USA had a dodgy AoA instrument?

StTim wrote:

Saintor wrote:

mjoelnir wrote:

So if you have a frame that is unsafe and leads to accidents,

This is simply untrue. Hundreds of North American pilots did thousands of flight time on the 737 MAX. They have larger and more forward-mounted engines but it is all under control. The frames will come back unchanged.

The problem is that Boeing considered that some wild pilots abusing the engines would be able to create a sudden nose-up condition. So even if there weren't obliged to do so, they used an updated version of MCAS, but yes they did poorly. Despite their enormous mistakes, ET302 pilots should have been aware that retracting the flaps would prevent MCAS to be activated. It should have been explicitly stated by Boeing since the beginning, more of that even the mere existence of MCAS. They should have been also aware that manual trimming was impossible at 350-400 knots. Many mentions that it was a futile maneuver above the low-200s knots air speed. They lost a lot of time doing this.

This is the most bizarre post I have seen on here.

How many of those flights flown by the wonder pilots in the USA had a dodgy AoA instrument?

As someone who has been critical of the pilots, especially ET, I agree with your post. I have not seen any reports of any other crew beyond Lion Air's two flights and the one ET flight that encountered an AoA sensor issue and resulting MCAS runaway on a MAX.

StTim wrote:

Saintor wrote:

mjoelnir wrote:

So if you have a frame that is unsafe and leads to accidents,

This is simply untrue. Hundreds of North American pilots did thousands of flight time on the 737 MAX. They have larger and more forward-mounted engines but it is all under control. The frames will come back unchanged.

The problem is that Boeing considered that some wild pilots abusing the engines would be able to create a sudden nose-up condition. So even if there weren't obliged to do so, they used an updated version of MCAS, but yes they did poorly. Despite their enormous mistakes, ET302 pilots should have been aware that retracting the flaps would prevent MCAS to be activated. It should have been explicitly stated by Boeing since the beginning, more of that even the mere existence of MCAS. They should have been also aware that manual trimming was impossible at 350-400 knots. Many mentions that it was a futile maneuver above the low-200s knots air speed. They lost a lot of time doing this.

This is the most bizarre post I have seen on here.

How many of those flights flown by the wonder pilots in the USA had a dodgy AoA instrument?

How that potentially bad AoA relates to a "bad frame"?

Saintor wrote:

mjoelnir wrote:

So if you have a frame that is unsafe and leads to accidents,

This is simply untrue. Hundreds of North American pilots did thousands of flight time on the 737 MAX. They have larger and more forward-mounted engines but it is all under control. The frames will come back unchanged.

The problem is that Boeing considered that some wild pilots abusing the engines would be able to create a sudden nose-up condition. So even if there weren't obliged to do so, they used an updated version of MCAS, but yes they did poorly. Despite their enormous mistakes, ET302 pilots should have been aware that retracting the flaps would prevent MCAS to be activated. It should have been explicitly stated by Boeing since the beginning, more of that even the mere existence of MCAS. They should have been also aware that manual trimming was impossible at 350-400 knots. Many mentions that it was a futile maneuver above the low-200s knots air speed. They lost a lot of time doing this.

This may be your opinion. Most of the regulators in the world look at the 737MAX as an unsafe frame that has to be fixed.

aerolimani wrote:

I retract. We don't know for sure that the shop was calibrating sensors incorrectly. However, given how badly things were being done at Xtra, and the specific deficiencies regarding the AOA sensor calibration, there's a very good chance that is what went wrong.

What specific deficiencies were identified? Any source for "how badly things were being done at Xtra"??

aerolimani wrote:

If you haven't already, you should read the sections in the JT610 report, starting on pages 89, 202, and 227.

My interpretation of page 89-91:

They were only able to show the possibility of an offset being inserted into the calibration procedure. They did not conclude that Xtra Aerospace actually did make that mistake, and make that mistake on the accident sensor.

They also state they witnessed a Xtra employee perform a calibration of identical AOA sensor, and concluded it was done satisfactorily (at least they don’t state any issues with what was done):

“An Xtra Aerospace technician performed tests 3.A through 3.E from the CMM Revision 8 Testing and Fault Isolation section. The tests performed were the Insulation Resistance test, Vane Friction test, Heater Current test, and Alignment Accuracy test. For this demonstration, the technician used a North Atlantic 8810A Angle Position Indicator (API) to measure the 0861FL1 resolver outputs. A Peak Electronics SRI-201B API (“Peak API”) in “relative” mode, is used to read the synchro connected to the vane zero/indexing test stand (Note the Peak API could also be used for measuring the AOA resolver outputs, but for this demonstration the North Atlantic 8810A was used). The CMM specifies that resolver angles should be measured using a North Atlantic Model 8810A Angle Position Indicator (API), but includes the note “Equivalent substitutes may be used.” The Peak SRI-201B is not listed in the CMM.”

Then they go into the Xtra maintenance history to determine what equipment was used during the time frame the crash AOA sensor was repaired by Xtra. They don’t state which of the equipment in the list was used during the crash sensor calibration, other than the Peak SRI-201B was on the list.

“Xtra Aerospace utilized several pieces of test equipment to complete repair and evaluations on the AOA sensor that were not specified in the CMM Revision 8. Xtra Aerospace instead utilized the following equipment in service at the time of repair of S/N 14488:
• Peak Electronics SRI-201B (Model 7724-00-2) (Peak API) (quantity 3); and
89
• North Atlantic 8810A (quantity 1).
“

Finally, the report states that, while the Peak SRI-201B is not listed in the CMM, the FAA Flight Standards District Office (FSDO) accepted its use based on Xtra’s engineering test equipment equivalency report.

The report states that they observed Xtra using the Peak API in relative mode for the vane indexing/zero fixture setup:

“A Peak Electronics SRI-201B API (“Peak API”) in “relative” mode, is used to read the synchro connected to the vane zero/indexing test stand (Note the Peak API could also be used for measuring the AOA resolver outputs, but for this demonstration the North Atlantic 8810A was used).
“

However, the 25 deg offset calibration scenario they demonstrated, used the Peak API for measuring resolver outputs in relative mode. But the FAA investigation stated they only observed the Peak API being used during the vane indexing/zero setup. So absolutely no impact on any of this IMO.

“The exemplar AOA unit was secured in the vane zero fixture, with both resolver gears disengaged from the main gear but positioned to 45°. The REL/ABS switch on the Peak API was positioned to ABS. Resolver 2 was then rotated until the display on the Peak API displayed 25° (Resolver 1 was not adjusted; its position remained at 45°). With the Peak API connected to Resolver 2, the REL/ABS switch was moved to the REL position at which time the Peak API display changed to indicate approximately 0°.
“

aerolimani wrote:

More importantly, Xtra had no documentation of how to conduct the test using their nonstandard equipment; something supposedly required in the FAA authorization of alternate test equipment. While it is circumstantial, I think it's worthwhile to note that the FAA chose to shut down Xtra, and not simply fine them and monitor them for a while.

The FAA and Boeing are motivated to find the AOA defective rather than a production issue with installing ADIRU assemblies on Max planes in Renton. Further, the FAA shutdown the repair shop a full year after the crashes, and just days before Boeing's CEO was to testify to Congress.

aerolimani wrote:

Let's also be clear that the report says most likely improperly calibrated. It's not imprecise, as you seem to indicate.

The KNKT needs to justify where and how they come to their conclusions. If they aren't 100% sure about something, they should at least state other possible scenarios like an issue with the ADIRU, for example.


My interpretation of page 202, 227

KNKT statement in section 2.6 is unfounded:

“The Xtra Aerospace utilized the Angle Position Indicator (API) Peak Model SRI- 201B (Model 7724-00-2) for test and calibration repair of the accident AOA sensor, part number 0861FL1 serial number 14488.
“

The investigation by the FAA described on page 89-91 only says that the Peak API was on the list of capable test equipment, of which an approved North Atlantic API was also listed as well.

The rest of KNKT statements in this section are only guesses and hypotheticals about what caused the 21 deg offset in the crash DFDR data, ending with:

“This immediate 21° delta indicated that the AOA sensor was most likely improperly calibrated at Xtra Aerospace.
“

Page 227 are KNKT’s recommendations for Xtra Aerospace operating manuals, based only on KNKT’s hypotheticals.

sgrow787 wrote:

aerolimani wrote:

I retract. We don't know for sure that the shop was calibrating sensors incorrectly. However, given how badly things were being done at Xtra, and the specific deficiencies regarding the AOA sensor calibration, there's a very good chance that is what went wrong.

What specific deficiencies were identified? Any source for "how badly things were being done at Xtra"??

The FAA shutting them down isn't enough for you? Oh, right. You think it's a convenient cover-up for ADIRU problems that the FAA and Boeing are trying to hide.

sgrow787 wrote:

aerolimani wrote:

If you haven't already, you should read the sections in the JT610 report, starting on pages 89, 202, and 227.

My interpretation of page 89-91:

They were only able to show the possibility of an offset being inserted into the calibration procedure. They did not conclude that Xtra Aerospace actually did make that mistake, and make that mistake on the accident sensor.

They also state they witnessed a Xtra employee perform a calibration of identical AOA sensor, and concluded it was done satisfactorily (at least they don’t state any issues with what was done):

“An Xtra Aerospace technician performed tests 3.A through 3.E from the CMM Revision 8 Testing and Fault Isolation section. The tests performed were the Insulation Resistance test, Vane Friction test, Heater Current test, and Alignment Accuracy test. For this demonstration, the technician used a North Atlantic 8810A Angle Position Indicator (API) to measure the 0861FL1 resolver outputs. A Peak Electronics SRI-201B API (“Peak API”) in “relative” mode, is used to read the synchro connected to the vane zero/indexing test stand (Note the Peak API could also be used for measuring the AOA resolver outputs, but for this demonstration the North Atlantic 8810A was used). The CMM specifies that resolver angles should be measured using a North Atlantic Model 8810A Angle Position Indicator (API), but includes the note “Equivalent substitutes may be used.” The Peak SRI-201B is not listed in the CMM.”

Then they go into the Xtra maintenance history to determine what equipment was used during the time frame the crash AOA sensor was repaired by Xtra. They don’t state which of the equipment in the list was used during the crash sensor calibration, other than the Peak SRI-201B was on the list.

“Xtra Aerospace utilized several pieces of test equipment to complete repair and evaluations on the AOA sensor that were not specified in the CMM Revision 8. Xtra Aerospace instead utilized the following equipment in service at the time of repair of S/N 14488:
• Peak Electronics SRI-201B (Model 7724-00-2) (Peak API) (quantity 3); and
89
• North Atlantic 8810A (quantity 1).
“

Finally, the report states that, while the Peak SRI-201B is not listed in the CMM, the FAA Flight Standards District Office (FSDO) accepted its use based on Xtra’s engineering test equipment equivalency report.

The report states that they observed Xtra using the Peak API in relative mode for the vane indexing/zero fixture setup:

“A Peak Electronics SRI-201B API (“Peak API”) in “relative” mode, is used to read the synchro connected to the vane zero/indexing test stand (Note the Peak API could also be used for measuring the AOA resolver outputs, but for this demonstration the North Atlantic 8810A was used).
“

However, the 25 deg offset calibration scenario they demonstrated, used the Peak API for measuring resolver outputs in relative mode. But the FAA investigation stated they only observed the Peak API being used during the vane indexing/zero setup. So absolutely no impact on any of this IMO.

“The exemplar AOA unit was secured in the vane zero fixture, with both resolver gears disengaged from the main gear but positioned to 45°. The REL/ABS switch on the Peak API was positioned to ABS. Resolver 2 was then rotated until the display on the Peak API displayed 25° (Resolver 1 was not adjusted; its position remained at 45°). With the Peak API connected to Resolver 2, the REL/ABS switch was moved to the REL position at which time the Peak API display changed to indicate approximately 0°.
“

aerolimani wrote:

More importantly, Xtra had no documentation of how to conduct the test using their nonstandard equipment; something supposedly required in the FAA authorization of alternate test equipment. While it is circumstantial, I think it's worthwhile to note that the FAA chose to shut down Xtra, and not simply fine them and monitor them for a while.

The FAA and Boeing are motivated to find the AOA defective rather than a production issue with installing ADIRU assemblies on Max planes in Renton. Further, the FAA shutdown the repair shop a full year after the crashes, and just days before Boeing's CEO was to testify to Congress.

aerolimani wrote:

Let's also be clear that the report says most likely improperly calibrated. It's not imprecise, as you seem to indicate.

The KNKT needs to justify where and how they come to their conclusions. If they aren't 100% sure about something, they should at least state other possible scenarios like an issue with the ADIRU, for example.


My interpretation of page 202, 227

KNKT statement in section 2.6 is unfounded:

“The Xtra Aerospace utilized the Angle Position Indicator (API) Peak Model SRI- 201B (Model 7724-00-2) for test and calibration repair of the accident AOA sensor, part number 0861FL1 serial number 14488.
“

The investigation by the FAA described on page 89-91 only says that the Peak API was on the list of capable test equipment, of which an approved North Atlantic API was also listed as well.

The rest of KNKT statements in this section are only guesses and hypotheticals about what caused the 21 deg offset in the crash DFDR data, ending with:

“This immediate 21° delta indicated that the AOA sensor was most likely improperly calibrated at Xtra Aerospace.
“

Page 227 are KNKT’s recommendations for Xtra Aerospace operating manuals, based only on KNKT’s hypotheticals.

Yeah… I get that you see a conspiracy here. It's an awful lot of people involved, though, for a conspiracy to hold up, and for nothing to leak. Don't you think?

Moving on… the report indicates that Xtra did keep records of the repair and calibration process of the specific part that was sold to Lion Air; serial number 14488. I think it's reasonable to assume that the records also indicate what test equipment was used. As far as I can tell, that is what the report is drawing its conclusion from. Can you prove that the Xtra records don't say what equipment was used? The report seems pretty confident about its information. Or, do you need to see scans of Xtra's documents?

Xtra Aerospace records reflect that repair activities of AOA sensor S/N 14488 included replacement of the AOA vane-slinger-shaft assembly (VSS). During VSS removal and replacement, it is highly unlikely that the resolvers retained their original position. During resolver calibration, utilization of the Peak API and selection of the REL/ABS switch in the REL position selection may have led to improper calibration because there was no written instruction for correct utilization of the Peak API in accordance with the CMM requirements. With the REL/ABS switch in the REL position for CMM return-to-service testing, the improper calibration would not be detected.

With all the other problems that have been dredged up, such as the bit-flip, fireproofing around the APU, and unprotected rudder cables, I'd be really surprised if it were possible for anything to be hidden. Can you even imagine how catastrophic it would be if Boeing and the FAA were found to be conspiring, and hiding another problem from the rest of the world's CAA's??? I really don't think they would even consider taking such a chance. I'm going to call it preposterous.

Unfortunately, we can guarantee the AOA sensor in question was destroyed upon impact. On the other hand, the chain of parts, where you are saying a fault might exist, is in every MAX built. If there's a problem, and a repair has to be made, how would Boeing hide that???

So… what's more likely here? The part was improperly calibrated at Xtra… or Boeing and the FAA are conspiring to hide a separate problem in the ADIRU?

aerolimani wrote:

sgrow787 wrote:

What specific deficiencies were identified? Any source for "how badly things were being done at Xtra"??

The FAA shutting them down isn't enough for you? Oh, right. You think it's a convenient cover-up for ADIRU problems that the FAA and Boeing are trying to hide.

You've gone over the edge already. Signs of a troll.

There are two main sources of sensor errors: (a) the sensor itself, or (b) the ADIRU. The wiring between the two and the FCC is another possibility if you want to add that as a third (c). Which of these would you rather ignore looking at if you were Boeing? Right. It doesn't take a conspiracy to avoid looking at something. It does take a mountain it seems to get Boeing and the FAA to take the certification process seriously, and in the case of quality issues in Boeing's manufacturing plants, to take employee concerns seriously.

When did you become so trusting of the FAA in all this?

aerolimani wrote:

With all the other problems that have been dredged up, such as the bit-flip, fireproofing around the APU, and unprotected rudder cables, I'd be really surprised if it were possible for anything to be hidden. Can you even imagine how catastrophic it would be if Boeing and the FAA were found to be conspiring, and hiding another problem from the rest of the world's CAA's??? I really don't think they would even consider taking such a chance. I'm going to call it preposterous.

There's a difference between knowing about a problem, addressing it after a crash has occurred, and taking responsibility for the source of the problem and being transparent about it.

Since the root cause of both crashes is a single-sensor design for a system concealed from pilots and airlines, and whose FMEA was concealed from the FAA, it doesn't really matter if mis-calibrated sensors wind up on future Max's. If Boeing has addressed the sensor redundancy issue, It shouldn't end up in a catastrophic event. But in terms of adding a slice of Swiss cheese to the model, yes a mis-calibrated sensor by a 3rd party is preferable over a Boeing production issue.

aerolimani wrote:

Unfortunately, we can guarantee the AOA sensor in question was destroyed upon impact. On the other hand, the chain of parts, where you are saying a fault might exist, is in every MAX built. If there's a problem, and a repair has to be made, how would Boeing hide that???

So… what's more likely here? The part was improperly calibrated at Xtra… or Boeing and the FAA are conspiring to hide a separate problem in the ADIRU?

If you can prove to me the impossibility that the 21 deg offset can be injected by a faulty ADIRU or improperly installed ADIRU, then I will more readily entertain the mis-calibration theory you seem readily willing to believe in. Until then, settle down, reign in your matter-of-fact belief that the sensor mis-calibration was at play in the Lion Air crash.

EDIT: Your disbelief about conspiracies shouldn't be used as a factor to put value on alternate theories. Currently the FBI and DOJ are investigating Boeing and the FAA for circumstances surrounding these crashes. That shouldn't be taken lightly by any means. But go ahead and think all this is just preposterous...

aerolimani wrote:

So… what's more likely here? The part was improperly calibrated at Xtra… or Boeing and the FAA are conspiring to hide a separate problem in the ADIRU?

It doesn't matter. Answer to your question has little relevance.

Dozens of thousands of planes have AoA sensors, and that has been the case for decades. Assuming Xtra is (was) a major sensor shop, a significant number of units have passed their shop. There will be statistics telling the story if their performance was inferior. Airline maintenance shops do not continue to buy sub standard spare part components from inferior shops. It is known if Xtra has sold inferior quality to their customers, only not known to us a.nutters. We know that Xtra procedures didn't pass FAA audit, and that's not good, but it doesn't indicate that a bad unit ever was released from Xtra.

What matters is that no airliner shall include a component which can fail, and for instance not be totally immune to bird strike, when failure can be potentially catastrophic. A 737MAX main wing spar cannot fail. An AoA sensor can. Therefore 737MAX must have effective redundancy like every other plane type has when sensing has influence on flight control.

sgrow787 wrote:

There are two main sources of sensor errors: (a) the sensor itself, or (b) the ADIRU. The wiring between the two and the FCC is another possibility if you want to add that as a third (c).
[...]
If you can prove to me the impossibility that the 21 deg offset can be injected by a faulty ADIRU or improperly installed ADIRU, then I will more readily entertain the mis-calibration theory you seem readily willing to believe in. Until then, settle down, reign in your matter-of-fact belief that the sensor mis-calibration was at play in the Lion Air crash.

Of course the ADIRU could have a problem, but how about the SMYD that provides the FDR values ?
From the JT610 final report:

"For each AOA sensor (left and right), one resolver is connected to the respective
Stall Management Yaw Damper (SMYD) computer and the second resolver is
connected the respective ADIRU."

"Both the SMYD and ADIRU monitor the resolver circuits within the AOA sensor."

"Each ADIRU receives AOA information from
one of the two resolvers contained within the associated AOA sensor (i.e. the Left
ADIRU uses left AOA vane and the Right ADIRU uses the right AOA vane).
Information from the other resolver contained within the AOA sensor, along with
data from other sources, is provided to the Stall Management Yaw Damper
computer (SMYD), which is used, along with data from other sources, for the
purpose of calculating and sending commands to the Stall Warning System (SWS)."

"Each AOA sensor has two resolvers within it, one of which is connected to the
associated ADIRU. The other resolver in each AOA sensor is connected to a stall
management yaw damper (SMYD) computer."

"The “Angle of Attack Failure” section of the SSA includes only AOA resolver
circuit failures (open circuit, high impedance, etc.) that can be detected by the
associated computer (ADIRU or SMYD)."

Figure 24: The FDR recorded IAS and ALT FLAG appeared since the flight from Tianjin
Show "AOA SYMD 1" and "AOA SYMD 2" where the 21° offset can be see near the end of the graph.
Others graphs in the report show "ANGLE OF ATTACK INDICATED LEFT" and "ANGLE OF ATTACK INDICATED RIGHT". I don't know if those values are from the ADIRU or the SMYD, but it's clear that the MCAS use the values from the ADIRU and his actions are in line with the left AoA value recorded from the SMYD. In addition the left Indicated Airspeed is computed by the ADIRU and his offset is in line with the left AoA value recorded from the SMYD. So it seem very hard to find a scenario where the problem could be the ADIRU alone: the SMYD would have measured the correct value and the stick shaker would not have been activated.

https://www.faa.gov/aircraft/draft_docs ... ound-2.pdf

MAX MMEL Rev 2 draft for public comment by Jan 4th 2020.

STAB OUT OF TRIM Light, SPEED TRIM FUNCTION, SPEED TRIM FAIL Light, CONTROL WHEEL TRIM SWITCH - All to be deleted from MMEL i.e. all must be available for despatch.

Only other changes seem to revolve around assuring that there is at minimum one means of display/annunciation of AUTOPILOT DISENGAGED available for despatch.

Ray

Similar changes proposed for Classic/NG MMEL.
https://www.faa.gov/aircraft/draft_docs ... _Draft.pdf

why are they still producing these aircraft? doesn't make any sense to me

they'll be stuck making modifications and clearing the deliveries backlog for years. and that is IF it ever flies again a

afgeneral wrote:

why are they still producing these aircraft? doesn't make any sense to me

they'll be stuck making modifications and clearing the deliveries backlog for years. and that is IF it ever flies again a

To the best of my knowledge the only modification will be uploading new software to the affected computers. Likely less than a 30 minute job from start to finish. It will take far more time to do the normal "bring out of storage" checks and services (est 100-200 hours per aircraft).

They are producing the aircraft because shutting down the line and restarting would be far more expensive than just parking aircraft and bringing them out of storage later. Contracts for parts are written with guarantees of minimum quantities for certain periods of time. Extremely expensive to stop production suddenly. Also, restarting shut down production lines is also costly as well and would have to be paid for again.

Most aircraft production slowly winds down over years with appropriate changes in the contracts so that by the end of the aircraft production run there are minimal - if any - cancellation charges.

The fact that the FAA released the DRAFT revised minimum equipment list for comment today tells me that the aircraft will fly again in commercial service... and not too far away as they obviously have accepted the key changes to be able to release these changes for comment.

My understanding is that Training Requirements are the next major thing to be determined.


Have a great day,

2175301 wrote:

They are producing the aircraft because shutting down the line and restarting would be far more expensive than just parking aircraft and bringing them out of storage later. Contracts for parts are written with guarantees of minimum quantities for certain periods of time. Extremely expensive to stop production suddenly. Also, restarting shut down production lines is also costly as well and would have to be paid for again.

I would add that they are producing the aircraft because their airline customers still want them, quite urgently. The airlines themselves have large investments in these aircraft via deposits, and have large investments in crew training and spares that are only applicable to 737 family members. Most of these operators are flying aging 737NG with CFM56 engines and are looking forward to 16% overall improvement in economy relative to NG and are not looking forward to spend money putting NGs through heavy checks and CFM56s through overhauls. FR has now closed two bases simply because they can't get their MAXes on a workable time line for them. WN has blamed Boeing for preventing them from taking advantage of growth opportunities. They want their MAXes, pronto!

If it was easy to switch to A320neo things would be different, but it is manifestly not easy to walk away from airplane contracts you've already signed, and there is no opportunity to get an A320neo for another 9 years or so if you do not have them on order already. Heck, look how difficult it was for QR to switch away from PW to CFM on their A320neo despite PW's quite visible flaws and inability to deliver fixes. They still had to take the PW and could only get CFM on their next tranche of orders.

XRAYretired wrote:

https://www.faa.gov/aircraft/draft_docs/media/afx/B-737_MAX_Rev_2_Draft_Round-2.pdf

MAX MMEL Rev 2 draft for public comment by Jan 4th 2020.

STAB OUT OF TRIM Light, SPEED TRIM FUNCTION, SPEED TRIM FAIL Light, CONTROL WHEEL TRIM SWITCH - All to be deleted from MMEL i.e. all must be available for despatch.

Only other changes seem to revolve around assuring that there is at minimum one means of display/annunciation of AUTOPILOT DISENGAGED available for despatch.

Ray

Similar changes proposed for Classic/NG MMEL.
https://www.faa.gov/aircraft/draft_docs ... _Draft.pdf

Bloomberg ( https://www.bloomberg.com/news/articles ... -s-737-max ) reports:

Because of revisions to the 737 Max’s flight computers -- which will be checking each other in Boeing’s proposed new design -- the FAA is changing requirements for how airlines operate if the computer or related functions aren’t working properly.

“This is a positive sign of the measured approach for ensuring the safe return to service of the 737 Max and the thorough approach by the FAA in this process,” Boeing spokesman Paul Bergman said in an email on Thursday night.

So it seems to also be requiring both FCCs and/or related hardware to be on the MMEL as well?

I wish the article was more detailed.

Revelation wrote:

XRAYretired wrote:

https://www.faa.gov/aircraft/draft_docs/media/afx/B-737_MAX_Rev_2_Draft_Round-2.pdf

MAX MMEL Rev 2 draft for public comment by Jan 4th 2020.

STAB OUT OF TRIM Light, SPEED TRIM FUNCTION, SPEED TRIM FAIL Light, CONTROL WHEEL TRIM SWITCH - All to be deleted from MMEL i.e. all must be available for despatch.

Only other changes seem to revolve around assuring that there is at minimum one means of display/annunciation of AUTOPILOT DISENGAGED available for despatch.

Ray

Similar changes proposed for Classic/NG MMEL.
https://www.faa.gov/aircraft/draft_docs ... _Draft.pdf

Bloomberg ( https://www.bloomberg.com/news/articles ... -s-737-max ) reports:

Because of revisions to the 737 Max’s flight computers -- which will be checking each other in Boeing’s proposed new design -- the FAA is changing requirements for how airlines operate if the computer or related functions aren’t working properly.

“This is a positive sign of the measured approach for ensuring the safe return to service of the 737 Max and the thorough approach by the FAA in this process,” Boeing spokesman Paul Bergman said in an email on Thursday night.

So it seems to also be requiring both FCCs and/or related hardware to be on the MMEL as well?

I wish the article was more detailed.

MMEL is by exception. If the equipment is required available it does not get listed. There are no changes related to FCC directly.

Ray

prebennorholm wrote:

aerolimani wrote:

So… what's more likely here? The part was improperly calibrated at Xtra… or Boeing and the FAA are conspiring to hide a separate problem in the ADIRU?

It doesn't matter. Answer to your question has little relevance.

Dozens of thousands of planes have AoA sensors, and that has been the case for decades. Assuming Xtra is (was) a major sensor shop, a significant number of units have passed their shop. There will be statistics telling the story if their performance was inferior. Airline maintenance shops do not continue to buy sub standard spare part components from inferior shops. It is known if Xtra has sold inferior quality to their customers, only not known to us a.nutters. We know that Xtra procedures didn't pass FAA audit, and that's not good, but it doesn't indicate that a bad unit ever was released from Xtra.

What matters is that no airliner shall include a component which can fail, and for instance not be totally immune to bird strike, when failure can be potentially catastrophic. A 737MAX main wing spar cannot fail. An AoA sensor can. Therefore 737MAX must have effective redundancy like every other plane type has when sensing has influence on flight control.

The statistics don't really inform us here. First of all, we don't have access to the stats in question.

As you point out, the MAX didn't have the necessary redundancy. All we needed was one bad sensor reading erroneously high, and a spurious MCAS event would happen. Just because we don't have evidence that other sensors from Xtra were faulty, that doesn't mean they didn't exist. Or, there is even the chance that this is the only time they sent out a miscalibrated sensor. Even if Xtra got it right 999 times out of 1000, the procedures are there to prevent that 1 in 1000 from happening. They weren't following correct procedures (and apparently lax FAA oversight is largely responsible for this), and so Xtra increased their chances of miscalibrating a sensor. In the JT610 report, you can read about exactly how Xtra could have produced a miscalibrated sensor. That mistake in the procedure was demonstrated twice; first at Xtra, and then again in Feb 2019 at Collins Aerospace, for the benefit of FAA and NTSB staff who missed the first demonstration.

PixelFlight wrote:

sgrow787 wrote:

There are two main sources of sensor errors: (a) the sensor itself, or (b) the ADIRU. The wiring between the two and the FCC is another possibility if you want to add that as a third (c).
[...]
If you can prove to me the impossibility that the 21 deg offset can be injected by a faulty ADIRU or improperly installed ADIRU, then I will more readily entertain the mis-calibration theory you seem readily willing to believe in. Until then, settle down, reign in your matter-of-fact belief that the sensor mis-calibration was at play in the Lion Air crash.

Of course the ADIRU could have a problem, but how about the SMYD that provides the FDR values ?
From the JT610 final report:

"For each AOA sensor (left and right), one resolver is connected to the respective
Stall Management Yaw Damper (SMYD) computer and the second resolver is
connected the respective ADIRU."

"Both the SMYD and ADIRU monitor the resolver circuits within the AOA sensor."

"Each ADIRU receives AOA information from
one of the two resolvers contained within the associated AOA sensor (i.e. the Left
ADIRU uses left AOA vane and the Right ADIRU uses the right AOA vane).
Information from the other resolver contained within the AOA sensor, along with
data from other sources, is provided to the Stall Management Yaw Damper
computer (SMYD), which is used, along with data from other sources, for the
purpose of calculating and sending commands to the Stall Warning System (SWS)."

"Each AOA sensor has two resolvers within it, one of which is connected to the
associated ADIRU. The other resolver in each AOA sensor is connected to a stall
management yaw damper (SMYD) computer."

"The “Angle of Attack Failure” section of the SSA includes only AOA resolver
circuit failures (open circuit, high impedance, etc.) that can be detected by the
associated computer (ADIRU or SMYD)."

Figure 24: The FDR recorded IAS and ALT FLAG appeared since the flight from Tianjin
Show "AOA SYMD 1" and "AOA SYMD 2" where the 21° offset can be see near the end of the graph.
Others graphs in the report show "ANGLE OF ATTACK INDICATED LEFT" and "ANGLE OF ATTACK INDICATED RIGHT". I don't know if those values are from the ADIRU or the SMYD, but it's clear that the MCAS use the values from the ADIRU and his actions are in line with the left AoA value recorded from the SMYD. In addition the left Indicated Airspeed is computed by the ADIRU and his offset is in line with the left AoA value recorded from the SMYD. So it seem very hard to find a scenario where the problem could be the ADIRU alone: the SMYD would have measured the correct value and the stick shaker would not have been activated.

So… long story short:
1) Two resolvers within the left AOA sensor are feeding separately their information to the the left ADIRU and the SMYD.
2) The evidence at hand indicates that the ADIRU and SMYD were both behaving as one would expect for a high AOA value.
3) Therefore, It seems much more likely that the source of the incorrect AOA information was the sensor itself. Otherwise, there would have to be a huge coincidence that both the ADIRU and the SMYD would be taking correct AOA information and then both screwing it up, similarly and simultaneously.

Is my reading correct, of what you wrote?

Revelation wrote:

So it seems to also be requiring both FCCs and/or related hardware to be on the MMEL as well?

I wish the article was more detailed.

The article says there is a 30 day time frame for public comment, do we want to speculate whether from the FAA point of view that no RTS until those submissions, review and updates if any are completed, in which case the RTS for the MAX is on a even greater moving time line?

par13del wrote:

The article says there is a 30 day time frame for public comment, do we want to speculate whether from the FAA point of view that no RTS until those submissions, review and updates if any are completed, in which case the RTS for the MAX is on a even greater moving time line?

I think FAA is doing what they said, working on their own time line. I'm sure Boeing would like this all to move along faster, but they are not in control of events. Overall Boeing should be thankful that no major show stopper that would extend the time line by months has emerged since the "bit flip" problem, nor any "smoking gun" that would totally undermine the program. Of course we never know if one is lurking in the shadows.

Bjorn Fehrm at Leeham has his final installment analysing the Lion Air JT610 crash posted. Key highlights:

The Lion Air accident was caused by an AoA sensor which was incorrectly calibrated.

In the Ethiopian Airlines case, it was with high probability a bird strike that ripped off the sensor, causing the sensor rotor to swing to over 70°.

AoA failures like these are not common. The report states Boeing statistics show a total of ~20 failures over the last 17 years. To have two such failures a short time after another precluded Boeing from have fielded at fixed MACS before the second AoA failure happened.

The Boeing 737 has a good safety record. The aircraft has no special vices and is void of dangerous modes like a deep stall or aileron or rudder reversal. The larger MAX engines called for a pitch augmentation to give the pilot a linear pitch feel all the way to stall.

The introduced augmentation to fix this had an unusually sloppy implementation. The uproar over how this could pass into a certified air transport aircraft was called for. But now the corrected augmentation is there. The enormous amount of work which has gone into the update has made MCAS one of the most analyzed and tested flight control augmentations ever. The updated MCAS is now safe, measured with any standards.

https://leehamnews.com/2019/12/06/bjorn ... sh-part-6/

aerolimani wrote:

So… long story short:
1) Two resolvers within the left AOA sensor are feeding separately their information to the the left ADIRU and the SMYD.
2) The evidence at hand indicates that the ADIRU and SMYD were both behaving as one would expect for a high AOA value.
3) Therefore, It seems much more likely that the source of the incorrect AOA information was the sensor itself. Otherwise, there would have to be a huge coincidence that both the ADIRU and the SMYD would be taking correct AOA information and then both screwing it up, similarly and simultaneously.

Is my reading correct, of what you wrote?

Yes !
At least until a new unexpected disruptive information will change the picture (unlikely in my opinion).

PixelFlight wrote:

Figure 24: The FDR recorded IAS and ALT FLAG appeared since the flight from Tianjin
Show "AOA SYMD 1" and "AOA SYMD 2" where the 21° offset can be see near the end of the graph.
Others graphs in the report show "ANGLE OF ATTACK INDICATED LEFT" and "ANGLE OF ATTACK INDICATED RIGHT". I don't know if those values are from the ADIRU or the SMYD, but it's clear that the MCAS use the values from the ADIRU and his actions are in line with the left AoA value recorded from the SMYD. In addition the left Indicated Airspeed is computed by the ADIRU and his offset is in line with the left AoA value recorded from the SMYD. So it seem very hard to find a scenario where the problem could be the ADIRU alone: the SMYD would have measured the correct value and the stick shaker would not have been activated.

Figure 24 looks to have Computed Airspeed and Baro Altitude invalid data for a majority of the previous flights (TSN-MDC-DPS, DPS-MDC-DPS) but not DPS-CGK. The top line in Figure 24 - ADR FAULT ADIRU - shows there was a ADIRU fault for those flights. There’s no report they replaced the ADIRU at Denpasar (DPS). And all I’ve heard reported is the left AOA (the one repaired by Xtra) was installed at Denpasar. The air pitot data module was cleaned, but only at Jakarta (CGK), so this doesn’t explain the clearing of the ADR ADIRU fault at Denpasar through Jakarta. Had they reported the ADIRU was replaced at Denpasar, then I would be compelled to accept a AOA miscalibration as the cause of the 21 deg offset.

EDIT: Note that Figure 25 only shows a single side plot of data (looks like the right side data, but not specific for some) yet the figure title is “Figure 25: The differences in speed indicator and altitude between left and right instruments recorded on the DFDR”. Brings the completeness and accuracy of the KNKT report into question.

EDIT2: If "ADR ADIRU Fault" and "AOA ADIRU Fault" plots (in Figure 24) are signals computed by the FCC based on erratic/erroneous AOA and ADR data received from the ADIRU, then I suppose we can assume these faults could be the result of a single bad AOA sensor (since bad AOA affects airspeed and altitude). Section 1.6.4.1 on page 37 of the report states the removed AOA sensor had an open circuit on Resolver 2.

PixelFlight wrote:

Figure 24: The FDR recorded IAS and ALT FLAG appeared since the flight from Tianjin
Show "AOA SYMD 1" and "AOA SYMD 2" where the 21° offset can be see near the end of the graph.
Others graphs in the report show "ANGLE OF ATTACK INDICATED LEFT" and "ANGLE OF ATTACK INDICATED RIGHT". I don't know if those values are from the ADIRU or the SMYD, but it's clear that the MCAS use the values from the ADIRU and his actions are in line with the left AoA value recorded from the SMYD. In addition the left Indicated Airspeed is computed by the ADIRU and his offset is in line with the left AoA value recorded from the SMYD. So it seem very hard to find a scenario where the problem could be the ADIRU alone: the SMYD would have measured the correct value and the stick shaker would not have been activated.

Also, since the "AOA SMYD 1/2" plot looks good (no offset) for the previous (pre Denpasar) flights, then one can conclude that Resolver2 is connected to the ADIRU, and Resolver1 to the SMYD.

Since the 25 deg offset calibration scenario tested by the FAA resulted in an offset seen on both resolver outputs (even though they induced the offset only in Resolver2, leaving Resolver1 = 45 deg), one would expect both the ADIRU and SMYD plots for AOA to have the same offset. So it appears this supports the mis-calibration theory. And unsupports the bad ADIRU theory, since it's virtually impossible to consider both ADIRU and SMYD would fail in the same way at the same time. I stand corrected. Where's the tallest bridge I can jump off of?

kalvado wrote:

Some more retirements at Boeing. There was a separate thread on that, but it is now gone.
Boeing Commercial Airplanes chief engineer John Hamilton is retiring, per multiple media reports: e.g. https://www.seattletimes.com/business/b ... s-retires/
Official biography is still on Boeing's site: https://www.boeing.com/company/bios/john-hamilton.page
It says "John Hamilton was named the chief engineer for Boeing Commercial Airplanes in March 2019. " I don't know if the timing is coincidence with ET crash; but I doubt retirement less than a year after promotion amidst of 737 crisis and after being grilled in front of Congress for MAX situation is actually planned - I suspect he was just fired.
I wonder if that is a sign MAX is actually worse off than we think...

That guy is in charge of max certification, and was on 737 program for a long time

9Patch wrote:

Bjorn Fehrm at Leeham has his final installment analysing the Lion Air JT610 crash posted. Key highlights:

The Lion Air accident was caused by an AoA sensor which was incorrectly calibrated.

In the Ethiopian Airlines case, it was with high probability a bird strike that ripped off the sensor, causing the sensor rotor to swing to over 70°.

AoA failures like these are not common. The report states Boeing statistics show a total of ~20 failures over the last 17 years. To have two such failures a short time after another precluded Boeing from have fielded at fixed MACS before the second AoA failure happened.

The Boeing 737 has a good safety record. The aircraft has no special vices and is void of dangerous modes like a deep stall or aileron or rudder reversal. The larger MAX engines called for a pitch augmentation to give the pilot a linear pitch feel all the way to stall.

The introduced augmentation to fix this had an unusually sloppy implementation. The uproar over how this could pass into a certified air transport aircraft was called for. But now the corrected augmentation is there. The enormous amount of work which has gone into the update has made MCAS one of the most analyzed and tested flight control augmentations ever. The updated MCAS is now safe, measured with any standards.

Not long ago, Björn postulated you'd have to pull 2Gs in order to stalll the aircraft. That was the exact same moment he lost all credibility.

https://leehamnews.com/2019/12/06/bjorn ... sh-part-6/[/quote]

B777LRF wrote:

9Patch wrote:

Bjorn Fehrm at Leeham has his final installment analysing the Lion Air JT610 crash posted. Key highlights:

Not long ago, Björn postulated you'd have to pull 2Gs in order to stalll the aircraft. That was the exact same moment he lost all credibility.

https://leehamnews.com/2019/12/06/bjorn ... sh-part-6/

The offending section of the article, part 2, is still up, with no corrections. I find this surprising and sad, coming from Leeham. https://leehamnews.com/2019/11/08/bjorn ... sh-part-2/

B777LRF wrote:

Not long ago, Björn postulated you'd have to pull 2Gs in order to stalll the aircraft. That was the exact same moment he lost all credibility.

You seem to be incorrectly recalling what he said. Please in the future verify statements you believe to be incorrect before citing them as a reason to doubt a person's credibility.

https://leehamnews.com/2019/11/08/bjorn ... sh-part-2/

In daily operation, a 737 MAX flies with an Angle of Attack below 7° to 8° and never passes 1.2 G in load factor (in fact it rarely passes 1.15 G, the load factor for a 30° bank turn).

MCAS is programmed to activate at almost double this AoA value and the pilot need to pull around 2G or more to get to where MCAS will be active.

He estimated it would take 2G's to cause MCAS to activate, not to stall. He does not explain how he arrived at that value, which is reasonable to question. I assume this is based on the speeds and AoA it activates at, but I'm unclear if he is stating that in reference to the design of MCAS as originally presented to the FAA, or based on changes that as I understand it were made to extend its operation to lower speeds.

sgrow787 wrote:

I stand corrected. Where's the tallest bridge I can jump off of?

Only if it's for a bungee jump to evacuate stress (usually very effective)