Boeing, and FAA oversight [Archive] - Page 2

Snyggapa

18th Feb 2020, 19:02

No.

I am a bit too lazy to look for the link to the wiring diagram, but I remember that the cut-off switches remove power from the whole system early in the diagram and undoubtedly before the wiring bundles carry the command to the tail section.

The hazard involved with the bundle is similar to the MCAS hazard : the pilots must cut-off the faulty command early if they want to save the day.

Not what the leak above suggests, which implies that I guess a permanent live for another part of the system runs in close proximity to the stab trim after the cutout switch - so if the two chafe and short, you get an uncontrolled runaway that you can't stop.

"In one instance, engineers found a hot power wire that was too close to two command wires running to the jet’s moveable horizontal tail, or stabilizer, one for commanding the tail to swivel to move the jet nose-up, the other to move it nose-down. The danger is a short that causes arcing of electricity from the hot wire to the command wire.

“If a hot short occurs between the power wire and either the up or down command wire, the stabilizer can go to the full nose-up or nose-down position,” the engineer said.

Furthermore, the electrical power in that wire could circumvent the cutoff switches in the cockpit that, in the event of such a stabilizer runaway, are used to kill electrical power to the tail. Theoretically, the pilots could be unable to shut it off."

Luc Lion

18th Feb 2020, 19:25

Thanks.
I stand corrected.

568

18th Feb 2020, 20:25

Yes, the reference has been cited multiple times. When it has, it's almost always in the context of someone claiming that MCAS isn't an anti-stall/stability-enhancement system -- because the MAX allegedly doesn't need one -- but is "only" to address the stick force requirement.

From now on, I think I'm going to save BDAttitude's post, just above, and paste it in as a response to repeated assertions that "it's not anti-stall."

OAG,

If you take a peek back at the locked thread on the ET accident, I mentioned that if MCAS was described as an "anti-stall" device, then the MAX would have to have a new type certificate as it differed from the previous 737 variants.

OldnGrounded

18th Feb 2020, 23:52

OAG,

If you take a peek back at the locked thread on the ET accident, I mentioned that if MCAS was described as an "anti-stall" device, then the MAX would have to have a new type certificate as it differed from the previous 737 variants.

Yup. I remember. Probably most here who were raised in the Anglophone world remember this, from Walter Scott's poem, "Marmion" (even if some of us didn't know the origin):

"Oh! What a tangled web we weave when first we practice to deceive"

568

19th Feb 2020, 00:03

Yup. I remember. Probably most here who were raised in the Anglophone world remember this, from Walter Scott's poem, "Marmion" (even if some of us didn't know the origin):

Know it well.

Just looking back at some posts in this thread and I was hoping that we keep the MCAS on a 'straight and level" and the main title thread as our diligent mods will want to keep the threads "on point".
The wiring bundle issue isn't going to go away as the regs have changed before the MAX was put into production.

Will be interesting to see what transpires.

BDAttitude

19th Feb 2020, 06:57

Given the data available from the NG fleet I could see a rewiring mandated for the next C or D-Check. It shouldn't be too much of a hassle, especially in the later case.
However delivering planes and issuing CoA to already manufactured but non-conforming planes ... that's a horse of different color, especially in today's regulatory atmosphere.
I guess we are seeing one of the risks in stockpiling not deliverable planes materializing. If only anybody had warned them.
They'd better save themselves a lot of time and money and start fixing them NOW.

fdr

19th Feb 2020, 11:21

Not what the leak above suggests, which implies that I guess a permanent live for another part of the system runs in close proximity to the stab trim after the cutout switch - so if the two chafe and short, you get an uncontrolled runaway that you can't stop.

"In one instance, engineers found a hot power wire that was too close to two command wires running to the jet’s moveable horizontal tail, or stabilizer, one for commanding the tail to swivel to move the jet nose-up, the other to move it nose-down. The danger is a short that causes arcing of electricity from the hot wire to the command wire.

“If a hot short occurs between the power wire and either the up or down command wire, the stabilizer can go to the full nose-up or nose-down position,” the engineer said.

Furthermore, the electrical power in that wire could circumvent the cutoff switches in the cockpit that, in the event of such a stabilizer runaway, are used to kill electrical power to the tail. Theoretically, the pilots could be unable to shut it off."

That's a fairly untidy situation. Applying opposite trim would have power to both sides of the trim motor, would be interesting to see how the logic circuits would work with that. TBC would be able to identify the potential power source for the offending wiring, and ascertain if they can be isolated safely without shedding power down to a dark plane. The plane can fly dark, not much fun and not great for pax experience, but it ain't necessarily over until the singing is done. (Take an iPad, Stratus S2, and an iridium go.... and Amex card, don't leave home without them)

[Off topic slightly, but FYI the following show what is available as information available from a completely independent system on an aircraft. That is 1090 ADSB IN info and a synthetic view of traffic, terrain, runway etc having spent 1/2 a million on "modern" systems, in the last couple of years, the only system that really impresses me is that below. No iPad, no fly IMHO. The iPad gives better information than TCAS II Ch 7.1 for my money. Add to the fact it uploads FPL to the APFD's, and we can modify the current path from the iPad, it's pretty neat. The SA enhancement is impressive in high terrain areas, better than the dual TAWS EGPWS/GPWS system for SA]

https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/1488x1984/1580647363952_dd6d07735417da8c7a3baecc87407a93a94707a8.jpeg

https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/img_0046_1cce840b0b2fc564c2bfff7485965638cdaf2ebc.png

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/img_0047_2_3253c90b44835bbf7a727fc8660f8cc9f0bb0838.png

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/img_0049_89ca7e7c62a66834d640566920b81d34aea11359.png

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/vqpr_paro_international_png_68c317f32fea074c18494efd75632a0d 31d4ee48.jpeg
https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/1500x2000/vqpr_paro_international_2_png_ba0d7eabfe6f5d5143062a943c439c 1ffac96554.jpeg

Twitter

19th Feb 2020, 11:52

Well, they’ll have plenty of time to change the wiring, while they dismantle the tanks and remove the FOD. In fact they have had plenty of time to put in some alternatives to MCAS, which were derided when proposed on pprune a year back - due to the unacceptable delay incurred...

OldnGrounded

19th Feb 2020, 14:49

Know it well.

Just looking back at some posts in this thread and I was hoping that we keep the MCAS on a 'straight and level" and the main title thread as our diligent mods will want to keep the threads "on point".
The wiring bundle issue isn't going to go away as the regs have changed before the MAX was put into production.

Will be interesting to see what transpires.

Oh, yeah, you're right about staying on-topic. I misunderstood your intent.

568

19th Feb 2020, 17:03

Oh, yeah, you're right about staying on-topic. I misunderstood your intent.

OAG,

No problem young Sir and I do enjoy your responses to posts.

568

19th Feb 2020, 17:07

BDAttitude

23rd Feb 2020, 15:28

OldnGrounded

23rd Feb 2020, 15:31

Spooky 2

23rd Feb 2020, 15:58

So, in an effort to not require sim training, they are talking about setting up ideal conditions for elevator jammed demo. Then, they are content to send pilots out on the MAX, knowing full well that if the holes in the cheese line up, and the not ideal conditions occur, the plane will likely crash.

Unbelievable.

I believe sim training is part of the corrective action needed to return the MAX to service.

Dave Therhino

23rd Feb 2020, 17:16

https://www.seattletimes.com/business/boeing-aerospace/delays-in-737-max-certification-flight-may-push-off-boeings-goal-to-win-approval-by-mid-summer/
More software glitches due to FCC architecture change.
Reading the tea leaves with regard to wiring bundles.
Preparing for further delay.

I suspect you are correct. Given the fact that the trim command wire separation issue is a potentially catastrophic single failure issue, given the FAA's past AD's on hot shorts within wire bundles indicate the FAA often doesn't accept arguments that such hot shorts are "extremely improbable," and finally because it's the stab trim system involved, I suspect the FAA will require not only the undelivered airplanes to be changed, but also the delivered airplanes. How much delay it causes would likely be driven by how long Boeing argues about fixing it.

DieselOx

24th Feb 2020, 05:04

I believe sim training is part of the corrective action needed to return the MAX to service.

Context. My comment was in relation to the released emails/ texts late last year, and about the conversations therein, years before. At the time of those conversations, they were still in the no sim required mode.

Interesting that B only agreed/suggested sim training just prior to or as those messages were released. Sounds like an admission that they should have from the get go.

OldnGrounded

24th Feb 2020, 22:02

Interesting that B only agreed/suggested sim training just prior to or as those messages were released. Sounds like an admission that they should have from the get go.

Yes, and think how much cheaper it would have been to require/provide the training and absorb the $1 million per aircraft penalty in the SWA contract, compared to what's been happening for the past year -- and isn't over yet.

Twitter

25th Feb 2020, 09:48

Yes, and think how much cheaper it would have been to require/provide the training and absorb the $1 million per aircraft penalty in the SWA contract, compared to what's been happening for the past year -- and isn't over yet.

On the other hand, in the light of what Boeing apparently had not considered in terms of single AoA input failure, I doubt whether the training at that time would have covered the accident scenario adequately. It for sure will now.

OldnGrounded

25th Feb 2020, 14:05

On the other hand, in the light of what Boeing apparently had not considered in terms of single AoA input failure, I doubt whether the training at that time would have covered the accident scenario adequately. It for sure will now.

I agree that training in the context of MCAS 1.0 would likely have been inadequate -- because the presence of that MCAS was a wholly-unacceptable risk all by itself. Still, training would have made it more likely that the issues with the system would be discovered before a couple of airplanes full of humans flew themselves into holes in the ground.

USMCProbe

26th Feb 2020, 05:26

The FAA lacks the depth of knowledge and experience to properly oversee Boeing's aircraft development, or the operations of a very complex major airline. They designate "Designees" among management at Boeing, airlines, and other suppliers etc to be their expert in the field. While this seems a bit in-bred (and it is), this basic relationship has taken a system with many fatal accidents a year, to zero fatal accidents most years, despite flying 10-100 times more flights per year. For the most part, it has functioned spectacularly well. We can thank our current level of aviation safety to this system.

But sometimes it appears, the system goes off the rails. Boeing has made some catastrophic engineering and production decisions over the last 10-15 years. Their FAA Designees have, at a minimum, lacked sufficient oversight and reporting to the FAA. More than likely, they have allowed the "in-breeding" to corrupt their decision making, and perhaps motivations.

The FAA, at the upper levels, have allowed this to pass. That might be a generous characterization, and the reality might be much worse. I really don't see anything going on in the public domain that makes me think they are fixing the system.

I think at this point they need outside assistance to investigate their institutional disfunction. They have been living in it for so long, it is their "normal".

I have a reasonable amount of time in the 737 classic and NG, and got my hours' worth of CBT time for the MAX, but never flew it. I thought the MAX was an abortion before I ever heard of MCAS, or knew of Boeings' problems with it.

I always wondered if they subjected the MAX to a full certification, circa 2017, if it would pass. Lots of things have changed in 50 years, including the physical ability, experience, and training of the pilots qualified to fly it.

DaveReidUK

26th Feb 2020, 06:21

I always wondered if they subjected the MAX to a full certification, circa 2017, if it would pass.

That was never an option.

BDAttitude

26th Feb 2020, 07:06

FAA playing tough with regard to the engine cowling issue (polished down conductive layer during rework, that is). I had already forgotten about that one.
https://www.seattletimes.com/business/boeing-aerospace/faa-directive-requires-boeing-to-inspect-and-fix-a-manufacturing-defect-on-all-737-maxs/

So we're having
- Elevator control forces
- Unable to recover from gross mistrim
- training requirements
- wire separation
- engine cowling
- FOD
- FCC Power on self test
- FCC elevator split indication
- MCAS MEL status

What did I forget?

Twitter

26th Feb 2020, 11:10

Pilot DAR

26th Feb 2020, 11:17

Transport Canada has said they are going to be much more involved;

https://www.cbc.ca/news/politics/boeing-737-max-recertification-flight-tests-1.5476130

Though national authorities generally credit each other's certification work in large part, Transport Canada is exercising the right to increase their involvement in this case. When Transport Canada involves itself in its own delegate's work, it's referred to as surveillance, which is part of the TC mandate for their service to the public. When they involve themselves in another authority's certification program, it's not surveillance, is an indication in a gap in confidence in that authority's certification process.

During this testing, the FAA and Boeing will know to present their very best certification process - which we would hope that the FAA and Boeing are doing all the time!

It would be interesting in this context to hear how EASA will involve itself in return to service certification testing.....

OldnGrounded

26th Feb 2020, 14:03

When they involve themselves in another authority's certification program, it's not surveillance, is an indication in a gap in confidence in that authority's certification process.

Is that gap in confidence exhibited in your informal contacts, DAR?

Takwis

26th Feb 2020, 14:54

The FAA lacks the depth of knowledge and experience to properly oversee Boeing's aircraft development...
So does Boeing, apparently.

I thought the MAX was an abortion before I ever heard of MCAS, or knew of Boeings' problems with it.

So did I. The name was a dead giveaway.

So we're having
- Elevator control forces
- Unable to recover from gross mistrim
- training requirements
- wire separation
- engine cowling (fit/conductive layer)
- FOD
- FCC Power on self test
- FCC elevator split indication
- MCAS MEL status

-Pickle Forkners

-Rudder cable vulnerability.
-Cowling disintegration from a thrown blade.

WillowRun 6-3

26th Feb 2020, 15:48

Inasmuch as there can be nothing "perfect" about the number three hundred forty-six (346) - that is, total fatalities - what replaces "perfect storm"? (Please remember, this is a "family" news....oh nvm).

I was going to hit the Amen button on USMCProbe's post but it seems to have automated away.

OldnGrounded

26th Feb 2020, 17:33

From the proposed AD on the fairing panels published yesterday:

The FAA proposes to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 737-8 and 737-9 airplanes. This proposed AD was prompted by a report that certain exterior fairing panels on the top of the engine nacelle and strut (the thumbnail fairing and mid strut fairing panels) may not have the quality of electrical bonding necessary to ensure adequate shielding of the underlying wiring from the electromagnetic effects of lightning strikes or high intensity radiated fields (HIRF), which could potentially lead to a dual engine power loss event from a critical lightning or HIRF exposure event.

This proposed AD would require a detailed inspection of the thumbnail fairing panels and mid strut fairing panels for excessive rework of the metallic (aluminum foil) inner surface layer, replacement of any excessively reworked panels, and modification of the thumbnail fairing assembly to ensure adequate bonding. The FAA is proposing this AD to address the unsafe condition on these products.

Full NPRM Here (https://s3.amazonaws.com/public-inspection.federalregister.gov/2020-03864.pdf)

ST Dog

26th Feb 2020, 17:57

I always wondered if they subjected the MAX to a full certification, circa 2017, if it would pass. Lots of things have changed in 50 years, including the physical ability, experience, and training of the pilots qualified to fly it.

No, but then the NG wouldn't have passed full cert when it was introduced never mind today.

Bend alot

26th Feb 2020, 19:33

SLF3

26th Feb 2020, 20:39

150k manhours (75 man years) to certify the A220 is an interesting number.

Does anyone know the equivalent FAA number for the Max?

BDAttitude

27th Feb 2020, 07:04

Pickle forks and CFM56-7B blade uncontained by cowling were NG only?

So we're having
- Elevator control forces
- Unable to recover from gross mistrim
- training requirements
- wire separation
- engine cowling (lightning strike protection)
- FOD
- FCC Power on self test
- FCC elevator split indication
- MCAS MEL status
- rudder cable vulnerability
- 90 seconds evacutaion (twin overwing exit)
- Pickle fornkners (NG)
- CFM56-7B cowling (NG)

DaveReidUK

27th Feb 2020, 07:37

Pickle forks and CFM56-7B blade uncontained by cowling were NG only?

The MAX hasn't suffered from the pickle fork problems, but that's almost certainly because they are all low-time aircraft, obviously.

BDAttitude

27th Feb 2020, 08:29

The MAX hasn't suffered from the pickle fork problems, but that's almost certainly because they are all low-time aircraft, obviously.
That's for sure. As I see, the AD only covers NG series. So the question would be, were there any changes - design wise or manufacturing practices - that would suggest the MAX would be less prone to these problems. Higher performance specs wouldn't help, I guess.

Twitter

27th Feb 2020, 11:41

That's for sure. As I see, the AD only covers NG series. So the question would be, were there any changes - design wise or manufacturing practices - that would suggest the MAX would be less prone to these problems. Higher performance specs wouldn't help, I guess.

NG Max comparison

Wing length?
Wing flex?
AUW?
Fuel outboard?

(Questions, not statements)

Ian W

27th Feb 2020, 12:44

NG Max comparison

Originally Posted by BDAttitude View Post (https://www.pprune.org/rumours-news/628714-boeing-faa-oversight-post10697058.html#post10697058)
That's for sure. As I see, the AD only covers NG series. So the question would be, were there any changes - design wise or manufacturing practices - that would suggest the MAX would be less prone to these problems. Higher performance specs wouldn't help, I guess.

Wing length?
Wing flex?
AUW?
Fuel outboard?

(Questions, not statements)

Aircraft wings designed for winglets as opposed to 'after market' accessory addition.

EDML

27th Feb 2020, 14:25

The MAX hasn't suffered from the pickle fork problems, but that's almost certainly because they are all low-time aircraft, obviously.

The MAX doesn't have the pickle fork problems because Boeing changed the manufacturer of the forks with or shortly before the MAX.

The new manufactures keeps the tight tolerances for the drilled holes so that the holes don't wear out and cause cracks.

fergusd

27th Feb 2020, 16:01

Seems it's not just FAA oversight that Boeing are playing fast and loose with . . .

https://web.archive.org/web/20200227113933/https://www.orlandosentinel.com/space/os-bz-boeing-safety-commercial-crew-20200226-bgvthodnjzgmlc36hsxcaopahu-story.html

Web archive link as I can't read the article from the UK directly.

MechEngr

27th Feb 2020, 16:49

The MAX doesn't have the pickle fork problems because Boeing changed the manufacturer of the forks with or shortly before the MAX.

The new manufactures keeps the tight tolerances for the drilled holes so that the holes don't wear out and cause cracks.

My understanding is the original process in question was to force each hole to expand after each hole is drilled so that when the force is removed the inside surface of the hole is left in compression. Being in compression offsets tension caused by loads carried through the fasteners and this offset delays the onset of fatigue cracking.This is independent of the hole diameter variation. Similar processes include shot-peening. The problem was changing from a good process which had a one-time use sleeve to protect the hole and transmit the force from an expansion plug to some other sleeve that was cheaper and either damaged the hole in some way or failed to produce the same deformation.

Drilled holes have all sorts of tiny defects that can lead to the initiation of fatigue cracks; holes can be reamed to removed those, but the holes are still susceptible to load induced fatigue.

This is why expansion rivets are so popular - they force the surrounding material into compression. But with bolts, that isn't available, so the holes need a secondary treatment.

kontrolor

1st Mar 2020, 20:48

apparently, the "new" way of how Boeing is conducting, or better said "conducting" tests is a real shame. Something needs to change in this company, or more people are going to die because their fixation on profit over safety of their product.

https://www.engadget.com/2020/02/29/boeing-starliner-failed-first-flight-report/

Zeffy

5th Mar 2020, 21:05

https://www.bloomberg.com/news/articles/2020-03-05/boeing-max-overhaul-sparks-u-s-canada-rift-over-pilot-guidance

Boeing Max Overhaul Sparks U.S.-Canada Rift Over Pilot Guidance
By Alan Levin and Julie Johnsson
March 5, 2020, 3:01 PM EST

Regulators’ disagreement on issue is raising tension on plane
Warning system for aerodynamic stall activated in two crashes

Canadian aviation regulators are at odds with their U.S. counterparts over guidance for pilots of the Boeing Co. 737 Max during an emergency, threatening to open a schism between nations critical to the plane’s return to service.

Canadian officials have insisted in contentious meetings that Max pilots should be instructed to disable a key warning system to avoid distraction during an emergency. Their counterparts at the U.S. Federal Aviation Administration argue that such a change would create additional risks, according to two people familiar with the discussions who asked not to be named because of their sensitivity.

While the disagreement doesn’t appear to threaten the grounded plane’s return to service in the U.S. and possibly other nations, it could slow the schedule in Canada, the people said. It also highlights continuing tension among global regulators sparked by two fatal crashes that rocked confidence in the FAA and now threaten a tradition of international cooperation in aviation.

Canada Minister of Transport Marc Garneau, speaking to reporters in Washington Thursday, said the country is in talks with other nations on the plane and may go its own way on some issues.

“If there are certain things that we will do differently from other countries, which is a possibility, that is not excluded,” Garneau said.

While each country around the world will make its own decision on allowing the Max jets to fly again, the FAA is the lead agency because the plane was certified in the U.S. The European Aviation Safety Agency, Canada and Brazil, all of which have major aircraft manufacturing industries, are also working with the FAA on the decision.

The dispute with Canada revolves around the so-called stick shaker, which causes the control column and yoke to vibrate aggressively and also causes a loud thumping noise. It is designed to get pilots’ attention when they are approaching a dangerous aerodynamic stall, which would cause a loss of lift and has been one of the biggest causes of airline accidents around the world.

As a result of malfunctioning sensors, the 737 Max’s stick shaker activated on the captain’s side of the planes in both fatal accidents -- on a Lion Air plane in October 2018 that went down in the Java Sea near Indonesia and an Ethiopian Airlines jet that crashed near Addis Ababa in March 2019.

The stick shaker appears to have added to the confusion in the cockpit in both cases.

Concerned about that, Canadian officials have said they believe pilots should be able to cut power to the stick shaker under circumstances similar to those in the accidents, three people familiar with the discussions said. Such cases would include when it was activated erroneously on only one side of the plane, said one of the people.

The change sought by the Canadians wouldn’t require a physical alteration to the plane but would add instructions for disabling the stick shaker to pilot procedures.

Garneau didn’t address the stick shaker issue directly at the Washington event, but said that Canada is concerned that pilots aren’t too distracted by emergencies similar to what occurred in the crashes.

“Crew workload in a very demanding environment physically is a factor that is essential to take into consideration because you have only so much time to respond,” he said.

Pilot Distraction
However, FAA officials have disagreed with the suggestion, according to people familiar with their position.

It would set a bad precedent to give pilots permission to cut power to such a critical warning system, one person said. Additionally, U.S. officials are also worried that attempting to reach the circuit breaker panel to switch it off during an emergency could cause dangerous distractions.

Amy Butcher, Garneau’s director of communication, said it would be premature to talk about specific recommendations the agency is making relative to the Max.

“We won’t hesitate to take any additional steps necessary to ensure all of our concerns have been addressed before approving a possible return to service of this aircraft,” she said.

The FAA didn’t comment directly on the issue when asked about it. “We haven’t made any official decisions and continue to have transparent discussions with all the regulators about a variety of issues,” the agency said in a statement.

A Boeing spokesman said, “We continue to work with the FAA to provide them the information they need to safely return the Max to service.” The planemaker says its estimate of a mid-year return to service is unchanged.

The updated Max software is designed to be simpler for pilots to handle if malfunctions such as those in the accidents occur. Instead of commanding a dive repeatedly, as planes did before the two crashes, the new system will only activate once and it will be easier to override. The company also is pouring resources into redesigning future cockpits to be more intuitive.

— With assistance by Peter Robison, and Kait Bolongaro

MechEngr

6th Mar 2020, 03:49

https://www.bloomberg.com/news/articles/2020-03-05/boeing-max-overhaul-sparks-u-s-canada-rift-over-pilot-guidance

I saw this suggestion on a video by a 737 pilot several months ago; I think he showed the breaker was over the shoulder of the left seat. I don't know if this disables both stick shakers, but if a system is lying it does little good to allow it to continue to lie. The first Lion Air flight went nearly 90 minutes with the shaker telling the crew of impending doom and they apparently did nothing specific about it. That suggests it either isn't a big deal or that the pilots ignored a critical warning.

airsound

6th Mar 2020, 10:54

Natalie Kitroeff and David Gelles (https://www.nytimes.com/by/david-gelles) at the New York Times have an interesting piece on the views of Boeing CEO David Calhoun.

https://www.nytimes.com/2020/03/05/business/boeing-david-calhoun.html?smid=nytcore-ios-share
In his eight weeks on the job, Boeing’s chief executive, David L. Calhoun, has come to one overriding conclusion: Things inside the aerospace giant were even worse than he had thought.

In a wide-ranging interview this week, Mr. Calhoun criticized his predecessor in blunt terms and said he was focused on transforming the internal culture of a company mired in crisis after two crashes killed 346 people.

To get Boeing back on track, Mr. Calhoun said, he is working to mend relationships with angry airlines, win back the confidence of international regulators and appease an anxious President Trump — all while moving as quickly as possible to get the grounded 737 Max back in the air.

“It’s more than I imagined it would be, honestly,” Mr. Calhoun said, describing the problems he is confronting. “And it speaks to the weaknesses of our leadership.”

Boeing’s previous chief executive, Dennis A. Muilenburg, was fired in December after presiding over a series of embarrassing setbacks that culminated in the shutdown of the 737 factory this year.

Mr. Calhoun ….. has been involved in this mess from the beginning. ….Mr. Calhoun has been on Boeing’s board since 2009, and was elevated to chairman late last year.

Before becoming the chief executive, he vigorously defended Mr. Muilenburg, saying in a CNBC appearance in November that Mr. Muilenburg “has done everything right” and should not resign. One month later, the board ousted Mr. Muilenburg and announced Mr. Calhoun as his replacement.
“Boards are invested in their C.E.O.s until they’re not,” Mr. Calhoun said.
“We had a backup plan,” he added. “I am the backup plan.”

Now that he’s in charge, Mr. Calhoun has become more willing to openly criticize Mr. Muilenburg. He said the former chief executive had turbocharged Boeing’s production rates before the supply chain was ready, a move that sent Boeing shares to an all-time high but compromised quality.
………
Mr. Muilenburg declined to comment.

airsound

BDAttitude

6th Mar 2020, 13:03

MechEngr

6th Mar 2020, 15:12

Zeffy

6th Mar 2020, 15:58

I saw this suggestion on a video by a 737 pilot several months ago; I think he showed the breaker was over the shoulder of the left seat. I don't know if this disables both stick shakers, but if a system is lying it does little good to allow it to continue to lie. The first Lion Air flight went nearly 90 minutes with the shaker telling the crew of impending doom and they apparently did nothing specific about it. That suggests it either isn't a big deal or that the pilots ignored a critical warning.

How about cancelling the stick-shaker via the same switch used to cancel the audible fire warning?
The cancel function might be made available only when the AOA disagree is active...?

kontrolor

6th Mar 2020, 22:02

https://transportation.house.gov/imo/media/doc/TI%20Preliminary%20Investigative%20Findings%20Boeing%20737%2 0MAX%20March%202020.pdf

preliminary Congressioanal report. Boeng should be cut in smaller companies and put under special scrutiny. FAA should get rid of all of its employees, who took active part in this shameful story.

turbidus

7th Mar 2020, 01:39

coupling the FCC's for "redundancy" is foolish. The 2 systems are independent for a reason.

Virtually nothing in an aircraft system is real time, but processed through filters and algorithms. There are many, many resolution errors that are adapted for in the programming.

It is not a surprise, when you couple them, that are multiple disagree warnings between the 2 systems.

Guess Boeing forgot why there are single channel vs dual operations.

MrBauer

7th Mar 2020, 01:47

It's easy to blame Muilenburg, since he isn't the biggest culprit on this max fiasco. Not absolving him, but (he was at least negligent) it just happened that all the Jenga collapsed under his watch.
For sure Calhoun didn't criticise Mcnerney, who is the real father of this Frankenmax 737 fiasco. Nor I think he would have the guts to do it, as it would be akin to taking responsibility for himself as a board member who greenlighted such a terrible idea instead of developing a new single aisle plane.

Big Pistons Forever

7th Mar 2020, 02:04

Reminds me of the old joke about the guy who is brought in to replace the fired CEO

Any advice he asks the departing guy

Yeah, I left you 2 letters. Open letter No 1 when you get into trouble and then letter No 2 if you are still in trouble

So pretty soon he decides it is time to open letter 1. Inside is a note that says, blame me for everything

So he does that and it works for awhile but things are still not getting better, so he opens letter No 2. It says

“write 2 letters”

Chris2303

7th Mar 2020, 03:15

Bend alot

7th Mar 2020, 06:33

Anybody know how much influence can be put upon Boeing and the FAA by this committee? Are their "recommendations" enforceable in law?

I believe they change the laws, I believe the chair was part of the committee that introduced ATPL pilots minimum hours for airlines to several thousand hours, up from several hundred hours.

But changing laws takes a long time.

safetypee

7th Mar 2020, 13:30

Congressional review approaching first anniversary of the Max grounding:- not a best wishes card …

Boeing: "… marred by technical design failures, lack of transparency with both regulators and customers, and efforts to obfuscate information about the operation of the aircraft.”

FAA: “grossly insufficient”,
“failed in its duty to identify key safety problems and to ensure that they were adequately addressed during the certification process."

In general: a “culture of concealment”, "jeopardized the safety of the flying public.”

also

“none of these expert reviews or investigations have come to the conclusion that our safety certification system is broken or in need of wholesale dismantlement.” i.e. not a congressional problem - really! Who oversees the overseers, provides funding, national commercial and political direction, etc. Accidents of organisation, from the top down.

Not the best foundation on which to improve Boeing - FAA oversight.

https://www-seattletimes-com.cdn.ampproject.org/c/s/www.seattletimes.com/business/boeing-aerospace/u-s-house-preliminary-report-faults-boeing-faa-over-737-max-crashes/?amp=1

Takwis

7th Mar 2020, 13:52

I saw this suggestion on a video by a 737 pilot several months ago; I think he showed the breaker was over the shoulder of the left seat. I don't know if this disables both stick shakers, but if a system is lying it does little good to allow it to continue to lie. The first Lion Air flight went nearly 90 minutes with the shaker telling the crew of impending doom and they apparently did nothing specific about it. That suggests it either isn't a big deal or that the pilots ignored a critical warning.
there are two circuit breakers, one behind each pilot, for their corresponding stick shakers. If I had one giving erroneous warning, I would not hesitate to pull it.

Rarife

7th Mar 2020, 20:49

MechEngr

7th Mar 2020, 21:15

Does anyone know what is this about? What sensors does HGS uses? I always though it just shows you known information.
Press Release – FAA Proposes $19.68 Million Civil Penalty Against The Boeing Co. (https://www.faa.gov/news/press_releases/news_story.cfm?newsId=24716)

It looks like BA installed a useful and fit-for-purpose, but not yet approved, Heads up guidance system that has since been approved for use in their aircraft. Cart before horse, apparently. I wonder what an investigation into the sales by Rockwell Collins of the devices might turn up. It's on BA to keep up with this, but certainly R-C would be cognizant of blow-back if a crash occurred due to some failure among nearly 800 installed not-yet-approved units.

The Rockwell Collins brochures make them seem like really nice additions, but I suppose the value is in what the pilot learns to do with them.

Pugilistic Animus

7th Mar 2020, 22:30

^^^^^ DLC could be Direct Lift Control. The Lockheed 1011 used this system (variable spoiler deployment) to control approach flight path without change of attitude.
Is the Old Boeing Push obsolete with DLC?

Loose rivets

7th Mar 2020, 23:24

I wonder how the Feds have got the nerve!! Finally they're prodded awake and then start making important noises to show they've come out of their toper.

568

8th Mar 2020, 00:23

It looks like BA installed a useful and fit-for-purpose, but not yet approved, Heads up guidance system that has since been approved for use in their aircraft. Cart before horse, apparently. I wonder what an investigation into the sales by Rockwell Collins of the devices might turn up. It's on BA to keep up with this, but certainly R-C would be cognizant of blow-back if a crash occurred due to some failure among nearly 800 installed not-yet-approved units.

The Rockwell Collins brochures make them seem like really nice additions, but I suppose the value is in what the pilot learns to do with them.

The 737NG had HGS (HUD) installed before 2015. The HGS/HUD was updated on later 737NG's to the best of my knowledge.
What the "pilot learns to do with them" (your quote) is taught in a separate simulator detail which includes a demonstration of a Cat 111 approach hand flown to minima.
The HGS/HUD displays a flare cue during the landing, amongst other details. The HUD also displays AOA, wind shear pitch commands, tail strike and a whole lot of other valuable features for the Captain only, as there is no HUD repeater on the FO's side.

esscee

8th Mar 2020, 09:37

Pugilistic Animus

8th Mar 2020, 13:39

From one 787 flight deck that I saw, it appears that it has dual HUD but perhaps that was just an option and not standard like dual tillers

568

8th Mar 2020, 16:27

From one 787 flight deck that I saw, it appears that it has dual HUD but perhaps that was just an option and not standard like dual tillers

I believe the 787 HUD on the FO side is standard fit.

568

8th Mar 2020, 16:38

So the HUD can be another distraction during operation then. After the Asiana B777 report which mentioned about the Autopilot controls being too complicated and suggested making future design simpler, appears too much technology baffles brains.

The HUD display does have a great deal of information to absorb.

Former military pilots transitioning to the left seat have no problems as they are somewhat familiar with the symbology on the display.

Having the ability to "over lay" the flight path angle (dashed line on HUD display;normally 3 degrees, but programable through the FMC HUD menu) near the runway threshold/touchdown zone aids SA on visual or instrument approaches.

Longtimer

8th Mar 2020, 21:08

An apparent rift between the FAA and aviation agencies in other countries involved in the recertification of the Boeing 737 MAX appears to center on cockpit distractions during an emergency.
The complete story can be viewed at: https://www.avweb.com/aviation-news/stick-shaker-disagreement-threatens-max-consensus/

So what do folks on this forum think, good idea to be able to be able to shut off a malfunctioning stick shaker or not? Seems to me that lightening the distraction load is a good idea.

2Planks

8th Mar 2020, 21:11

If it helps you to aviate, navigate, communicate more effectively then it seems to be a good idea.

RickNRoll

8th Mar 2020, 21:24

From that article

In both the Lion Air and Ethiopian Airlines crashes the stick shaker on the captain’s side remained activated by a faulty angle of attack sensor even as both pilots pulled with all their strength to try to arrest the uncommanded dive.

The idea that you would have to pull with all your strength to save a plane is so last century. Do all pilots on the MAX have to do body building.

RubberDogPoop

8th Mar 2020, 21:56

From that article

The idea that you would have to pull with all your strength to save a plane is so last century. Do all pilots on the MAX have to do body building.
Only the ones that skip the A/T Disengage step and insist on trying to relieve aerodynamic loads on the stab at 400kts indicated - try that in any other aeroplane and you'll have similar gym requirements...

8th Mar 2020, 22:20

aerodynamic loads on the stab at 400kts indicated - try that in any other aeroplane and you'll have similar gym requirements...

Not in FBW Airbus you won’t........side stick has identical resistance at 0 knots or 500 knots.

A4

MechEngr

8th Mar 2020, 23:04

From that article

The idea that you would have to pull with all your strength to save a plane is so last century. Do all pilots on the MAX have to do body building.

No. They only need to recall they have opposable thumbs able to push the trim buttons.This is the thing that seems forgotten when a false stick-shaker/stall warning is going off. This was demonstrated by 2 of 6 pilots in the three incidents with one pilot apparently abstaining when the first pilot continued to handle the situation in a reasonably safe fashion.

safetypee

8th Mar 2020, 23:21

Zeffy

8th Mar 2020, 23:26

https://www.wsj.com/articles/faa-poised-to-require-electrical-wiring-fixes-before-boeing-737-max-jets-can-fly-again-11583704341

FAA Poised to Require Electrical Wiring Fixes Before Boeing 737 MAX Jets Can Fly Again
Agency expected to mandate rerouting of certain wires to comply with longstanding safety regulations

By Andy Pasztor and Andrew Tangel
Updated March 8, 2020 6:48 pm ET

U.S. air-safety regulators are poised to order electrical wires relocated inside Boeing Co. BA 0.75% 737 MAX jets in the latest complication and potential delay for their return to commercial service, according to people briefed on the deliberations.

The preliminary decision, which hasn’t been reported before, covers all of the nearly 800 MAX airliners produced so far. The decision could be affected by further internal discussions and additional data the plane maker may submit to the regulator.

But in the past few weeks, these people said, Federal Aviation Administration managers and engineers have concluded that the potentially hazardous layout violates wiring-safety standards intended to prevent dangerous short-circuits.

Under extreme circumstances, wiring failures could cause flight-control systems to sharply point down an aircraft’s nose in a similar way to the automated maneuvers that brought down two MAX jets and claimed 346 lives.

The Chicago plane maker, according to people briefed on the details, has argued that the current wiring design meets FAA and international safety standards. Boeing also has told the FAA that because the risks are so remote—and such a relatively small number of similar short-circuits have occurred during the extensive history of the MAX’s predecessor model—no wiring redesign is necessary.

The emerging agency view, however, is based on longstanding regulations put in place following electrical fires and fuel-tank explosions on commercial jets over decades.

The FAA’s move caps several months of behind-the-scenes maneuvering between Boeing and the FAA that already has delayed crucial flights needed to vet fixes to MAX flight-control software and move forward with certifying the grounded jets as safe to carry passengers again.

Complications stemming from mandatory wiring changes could delay FAA directives ungrounding the beleaguered fleet for at least several weeks, some of the people said, potentially beyond the mid-June timeline previously projected by industry and government officials.

The wiring concerns also have turned into a test case of what Dave Calhoun, Boeing new chief executive, has touted as his more realistic and conciliatory approach toward FAA safety demands before allowing the MAX fleet back in the air.

The FAA said on Sunday that it continues to engage with Boeing on the wiring issue and the MAX will return to service only after the FAA is satisfied that all safety-related issues are addressed.

A Boeing spokesman said that discussions with the FAA continue, but regardless of the outcome the company’s estimate for a midyear return to service is unchanged.

If Boeing continues to press its case in the face of the FAA’s preliminary decision, one of the people briefed on the deliberations said, the likely upshot would be months of additional debate involving the FAA and foreign regulators in Europe, Canada and Brazil.

That is a major reason Boeing, which already has been devising ways to relocate certain wiring, ultimately is likely to accept the FAA’s position. And from a public perception standpoint, the people said, U.S. authorities are loath to break with demands from foreign regulators that wiring fixes must be completed before the fleet is allowed to resume operations.

Canadian regulators haven’t taken an official position yet on how Boeing should mitigate any risks associated with the wire bundles, said Nicholas Robinson, Transport Canada’s director general of civil aviation. But privately, according to people familiar with the details, Canada strongly supports relocating some wires.

“We’ve expressed our concerns to the FAA,” Mr. Robinson said in an interview at an aviation event in Washington, D.C., last week. “We’ll look at the FAA’s solution,” he added, “and then we’ll evaluate if that meets our needs.”

The planes have been grounded since March 2019, prompting a production shutdown, the biggest corporate crisis in Boeing’s history and severe disruptions to the global airline industry.

Industry and government safety experts have said the wiring issues should have been identified and resolved during the initial certification of the MAX. The stricter safety standards for wiring didn’t apply to earlier 737 models.

Among major questions that still need to be answered, according to these experts, is precisely how and when wiring will be redone on aircraft which operated before the grounding. Looking forward, Boeing has agreed to make wiring design changes once the assembly line revs up again.

The wiring debate follows a long string of setbacks and hurdles for Boeing regarding recertification of the 737 MAX, including a recent FAA directive proposing mandatory inspections and fixes to a metallic lining that serves as a shield against lightning strikes for engine-control wiring.

Before the FAA will authorize resumption of passenger operations, MAX jets also will be subjected to checks of fuel tanks for debris, along with verification of mandatory inspections, maintenance procedures and operational readiness flights. Unlike past FAA procedures, agency officials won’t delegate signoff authority to Boeing to ensure MAX jets are airworthy and ready for airline operations.

Write to Andy Pasztor at [email protected] and Andrew Tangel at [email protected]

MechEngr

8th Mar 2020, 23:36

This disagreement probably stems from the proposed MCAS modification.

With a dual system (pre mod) where each stick is independently associated with an AoA input, it should be possible to inhibit one side without loss of function.
In the initial situation the crew do not know if the stick-shake is valid or false, ie. which vane is inaccurate. After crosschecking airspeed for stall conditions it should be possible to identify and inhibit the faulty side, which should leave the unaffected side to provide any subsequent alert.
The crew can operate without distraction and still retain the stall alerting function.

However, if the MCAS modification 'cross-wires' the stick-shake functions as a result of having to use both FGCs and both AoA inputs for MCAS fault detection, then identification of a faulty stick-shake is more difficult, and inhibiting one side may also affect all stall alerting.
The debate then is to what degree is the shaker distracting vs the loss of stall alerting. It might be possible to retain one stick so that a subsequent valid stall would add shake the errant system so that the cumulative, change in alerting is recognisable.
A further complication in the Max is that AoA input to the ADC provides speed (and alt) corrections. There will be a difference in airspeed with erroneous AoA input or failure, but comparing with the standby ASI it should be possible to identify a faulty system. However, if by inhibiting one AoA this also affects both ADC (as per FGC hypothesis above) then both EFIS airspeed display will have an error. Thus the debate to inhibit AoA or not must additionally consider inaccurate speed together with with distraction.
The options are further complicated if shake can be inhibited independently of AoA, but if inhibited which system is the valid one ?
I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly. Earlier I wondered how the FGCs used the two inputs and was surprised to see they are bypassed to operate those alarms directly. Perhaps I misread it, but it makes a great deal of sense to push that function as early in the sensor chain as possible to decrease the number of links and the ability to fail.

I do agree that figuring out the desired failure handling is not easy. It has to be one that sorts false inputs from true inputs and tells the pilots what has gone wrong. Still it's been possible to shut down the remaining operating engine when the stress levels get too high, so it's clear that solving this general problem is not easy.

What is clear is that the outcome possible under the previous version will never happen again; that is, there won't be a chance that under an AoA disagree situation that an MCAS or, possibly, even STS correction to trim will be allowed. So now it's shifted to the more esoteric argument about how to automate proper handling of false information that looks exactly like true information. Anyone who comes to the certain solution for that problem will clean up in the stock market.

Lake1952

9th Mar 2020, 00:30

Not in FBW Airbus you won’t........side stick has identical resistance at 0 knots or 500 knots.

A4

Which is one of the reasons that I believe the original Canadian suggestion of simply getting rid of MCAS altogether and training for the non-linearity in the stick forces at some ends of the envelope was a proper approach to much of the problem.

Unless MCAS was needed for more than stick force linearity issues, of course...something we still don't know for sure.

568

9th Mar 2020, 02:25

I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly. Earlier I wondered how the FGCs used the two inputs and was surprised to see they are bypassed to operate those alarms directly. Perhaps I misread it, but it makes a great deal of sense to push that function as early in the sensor chain as possible to decrease the number of links and the ability to fail.

I do agree that figuring out the desired failure handling is not easy. It has to be one that sorts false inputs from true inputs and tells the pilots what has gone wrong. Still it's been possible to shut down the remaining operating engine when the stress levels get too high, so it's clear that solving this general problem is not easy.

What is clear is that the outcome possible under the previous version will never happen again; that is, there won't be a chance that under an AoA disagree situation that an MCAS or, possibly, even STS correction to trim will be allowed. So now it's shifted to the more esoteric argument about how to automate proper handling of false information that looks exactly like true information. Anyone who comes to the certain solution for that problem will clean up in the stock market.

Your quote "I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly".

Your information is incorrect:

Two independent, identical stall management yaw damper (SMYD) computers
determine when stall warning is required based upon:
• alpha vane angle of attack outputs
• ADIRU outputs
• anti–ice controls
• wing configurations
• air/ground sensing
• thrust
• FMC outputs.
The SMYD computers provide outputs for all stall warning to include stick shaker
and signals to the pitch limit indicator and airspeed displays and the GPWS
windshear detection and alert.
Two test switches are installed in the aft overhead panel. Pushing either of these
initiates a self–test of the respective stall warning channel. The No.1 activates the
Captain stick shaker, and the No. 2 activates the F/O stick shaker. Either stick
shaker vibrates both columns through column interconnects.

STALL WARNING TEST Switches
Push – on ground with AC power available: each test switch tests its respective
stall management yaw damper (SMYD) computer. No.1 SMYD computer shakes
Captain’s control column, No.2 SMYD computer shakes First Officer’s control
column. Vibrations can be felt on both columns

RubberDogPoop

9th Mar 2020, 04:14

Not in FBW Airbus you won’t........side stick has identical resistance at 0 knots or 500 knots.

A4

And unwinding the aerodynamic load on a stab using the manual trim wheel (such as a "trim runaway") at 400 knots has what to do with a non-FBW aircraft?
Whats it like in direct law in such a situation? Aerodynamic air loads skip the Airbus do they?

MechEngr

9th Mar 2020, 06:04

Your quote "I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly".

Your information is incorrect:

Two independent, identical stall management yaw damper (SMYD) computers
determine when stall warning is required based upon:
• alpha vane angle of attack outputs
• ADIRU outputs
• anti–ice controls
• wing configurations
• air/ground sensing
• thrust
• FMC outputs.
The SMYD computers provide outputs for all stall warning to include stick shaker
and signals to the pitch limit indicator and airspeed displays and the GPWS
windshear detection and alert.
Two test switches are installed in the aft overhead panel. Pushing either of these
initiates a self–test of the respective stall warning channel. The No.1 activates the
Captain stick shaker, and the No. 2 activates the F/O stick shaker. Either stick
shaker vibrates both columns through column interconnects.

STALL WARNING TEST Switches
Push – on ground with AC power available: each test switch tests its respective
stall management yaw damper (SMYD) computer. No.1 SMYD computer shakes
Captain’s control column, No.2 SMYD computer shakes First Officer’s control
column. Vibrations can be felt on both columns

Good. I was correct that it wasn't the FGCs, which was the main point, that the software BA is generating is not controlling the stall warnings.
Thanks for the correction, but it's the same outcome as far as STS and MCAS software is concerned.

MechEngr

9th Mar 2020, 06:08

And unwinding the aerodynamic load on a stab using the manual trim wheel (such as a "trim runaway") at 400 knots has what to do with a non-FBW aircraft?
Whats it like in direct law in such a situation? Aerodynamic air loads skip the Airbus do they?

I believe Airbus uses an electrohydraulic system to connect what look like fake trim wheels. I cannot tell if they are complete wheels or just an arc exposed above the console, but they provide no force feedback to the actual loads on the horizontal stabilizer and no way to put a full grip on them. It looked to me like their function could be handled with a paddle switch.

fizz57

9th Mar 2020, 07:19

I believe Airbus uses an electrohydraulic system to connect what look like fake trim wheels. I cannot tell if they are complete wheels or just an arc exposed above the console, but they provide no force feedback to the actual loads on the horizontal stabilizer and no way to put a full grip on them. It looked to me like their function could be handled with a paddle switch.

Wrong again :) On the A320-330-340 they are full wheels that are mechanically connected to the trim actuator and turn when the stab moves.
They are in fact a final backup for longitudinal control should all electrics fail. Still need hydraulics though, like the 747 and all later Boeings - the 737-o-saurus must be the only airliner of any size still flying with a direct mechanical connection to the THS. On the A350-380 they're gone completely and replaced by switches.

9th Mar 2020, 07:27

Airbus only goes into Direct Law when the gear goes down (apart from triple ADR Fault). In Alternate Law, longitudinal trim is still controlled by the FBW system - it remains very stable and easy to fly. More sensitive in role as it in now roll direct as opposed to roll rate.

The issue of pitch/thrust couple only occurs in direct law (gear down) as auto trim deals with this even in Alternate Law. There is Mechanical Back up “Law” which is a direct link between trim wheel to THS actuators (wheel NOT affected by aerodynamic load) but this is purely designed for used whilst you recover one of the 5 flight control computers (3 x SEC , 2 xELAC). I believe Airbus test pilots have landed the aircraft in mechanical back-up.

Anyway, my original post was purely to clarify that there is zero aerodynamic load effect in Airbus Side stick. What's the deal with 777/787 FBW control columns? Do they have artificial load feel?

A4

Typing at same time as Fizz57.....

safetypee

9th Mar 2020, 07:43

MechEng, 586,
Thanks for the clarification. A key aspect is the independence of each of the combined stall alerting (shaker) and stall ident (push) systems.

Prior to the mod, any one side could fail / be inhibited without loss of stall alerting / warning; - dual certification safety case.

The question post MCAS mod is if there is a situation where crew action (cbs), or reconfigured use of AoA (routing to SMYD), will result in the loss of both stall systems.

Thus the different opinions range between:-
- Continued flight with distracting alerts; stick shake and other alerting annunciation, and incorrect speed information, EFIS speed error and low speed awareness with differences between crews displays.
- Loss of all stall alerting with single AoA failure.

Either option could invalidate the previous safety case for stall protection. If so then Boeing could request an alleviation from the requirement - a reduced level of safety (stall alerting) after MCAS modification (AoA failure case) - debatable amongst regulators and not confidence promoting for the 737 Max.

Alternatively, that either or both Boeing and the FAA did not identify this weakness in their latest safety assessments; significantly embarrassing for reputations, even more so if Canada identified the issue because of previous grounding history.

Pilot DAR

9th Mar 2020, 11:43

“We’ve expressed our concerns to the FAA,” Mr. Robinson said in an interview at an aviation event in Washington, D.C., last week. “We’ll look at the FAA’s solution,” he added, “and then we’ll evaluate if that meets our needs.”

Yes, I am aware that Transport Canada will exercise their independence in re-evaluating the changed 737 MAX, rather than just accepting what the FAA and Boeing may present for acceptance. I'm also aware that Transport Canada's position was considered favourably by EASA and the Brazilian authority, who also were uneasy just accepting the FAA's certification.

MechEngr

9th Mar 2020, 13:04

Wrong again :) On the A320-330-340 they are full wheels that are mechanically connected to the trim actuator and turn when the stab moves.
They are in fact a final backup for longitudinal control should all electrics fail. Still need hydraulics though, like the 747 and all later Boeings - the 737-o-saurus must be the only airliner of any size still flying with a direct mechanical connection to the THS. On the A350-380 they're gone completely and replaced by switches.

Ok, but they are moving hydraulic valves via a cable and not moving the surface directly so there is no force feedback for the amount of trim discrepancy. That has to be a low-friction system, otherwise it will detect a problem and report as a jammed stabilizer.

Can the system decouple the THS actuator from the trim wheel input in the case the cable becomes jammed and not the stabilizer?

OldnGrounded

9th Mar 2020, 14:41

(Reuters) - Shares of Boeing Co <BA.N> dropped 12% on Monday after the planemaker's proposal to leave wiring bundles in place on the grounded 737 MAX failed to get the backing of U.S. aviation regulators, potentially delaying the plane's return to service.

Source (https://finance.yahoo.com/news/boeing-shares-plunge-faa-rejects-143002565.html)

568

9th Mar 2020, 15:39

Good. I was correct that it wasn't the FGCs, which was the main point, that the software BA is generating is not controlling the stall warnings.
Thanks for the correction, but it's the same outcome as far as STS and MCAS software is concerned.

No problem.
The new software update may prove to be unstable because of old memory architecture and data bus transfer.
I know there are folks on this forum with much more expertise on this subject than I could ever imagine.

cashash

9th Mar 2020, 15:45

Not sure what to think of this. If this is purely about safety and the wiring routing is deemed unsafe then its going to be just as unsafe in the 737NG as well as the 737Max, if that is the case then why are they not grounding the 737NG fleet.

Or is the FAA just overreacting after their recent failures in supervision on the 737Max program?

Mad (Flt) Scientist

9th Mar 2020, 15:53

cashash part of it may be overreaction (political) but there is also the issue that more than half of the grounded Maxs never entered airline service and may not have C of As. The continuing airworthiness requirements, in terms of safety assessments, are different for a newly built aircraft and an inservice aircraft - you can take time to fix an inservice issue (or never fix it at all, if deemed safe to take that route) but you have to fix many more such issues at CofA. (Both from a regulatory point of view and a commercial one - new customers don't like accepting aircraft with potential ADs etc hanging over them)

cashash

9th Mar 2020, 15:58

But as you pointed out - half the 737Max fleet already have CofA's and have been in service. If you are saying that he problem is so serious that those aircraft cannot fly because of it then by all logic that must also apply to all 737NG's. The only way I can see them getting around the issue of the 737NG fleet is to deem the 737Max a different type and so require certification under present day standards (which the wiring no longer meets).

However if they did decide that the 737Max was a completely new type and the present design did not meet todays standards then would Boeing have a financial claim for loses against the FAA, as the FAA have already approved the design albeit using their flawed approval process.

Ben_S

9th Mar 2020, 16:17

Swiss51

9th Mar 2020, 16:43

The wiring was compliant when the NG was certified wasn't it? It wasn't when the Max was certified. Thats the difference.It may be safe as is, but it doesn't meet the requirements, Boeing should have known this and not cut corners, but well, Boeing.
What exactly do you mean with "compliant"? To the standard of the 1960ties of the 2020ties? Maybe the FAA simply wants to get out of the excessive grandfathering of the 737 family. The requirements for wiring have undergone multiple changes in the past decades, and B was able to evade them throughout the whole lifetime of the 737 through the grandfathering and - in the most recent times - the delegated power of certification. Time to make some substantial corrections.

WHBM

9th Mar 2020, 18:49

Yes, I am aware that Transport Canada will exercise their independence in re-evaluating the changed 737 MAX, rather than just accepting what the FAA and Boeing may present for acceptance. I'm also aware that Transport Canada's position was considered favourably by EASA and the Brazilian authority, who also were uneasy just accepting the FAA's certification.
It will be interesting to see what the ramifications are of the aircraft not being certified everywhere. Just for the record, there were a range of European types which in the past were not certified by the FAA, either because they had an unacceptable feature or because they were not even offered. The Caravelle for example was unacceptable to the FAA for US registration until some substantial modifications were made, while the VC-10, the Super One-Eleven and the Trident were never offered. These all operated into the USA even though they had not been certified there. US airlines like Alaska will have a real issue if their Max could not enter Canadian airspace.

The key may be insurance. My personal insurers stipulate I am only covered on a multi-engined aircraft operating under an AOC. They only have to add "and certified by worldwide authorities" and that's a real issue - bearing in mind the insurers are already on the hook for the two accidents.

HighWind

9th Mar 2020, 19:05

The wiring was compliant when the NG was certified wasn't it? It wasn't when the Max was certified. Thats the difference.It may be safe as is, but it doesn't meet the requirements, Boeing should have known this and not cut corners, but well, Boeing.
I assume the wiring is for control of the trim.. And a wiring fault can result in two failure modes: Electrical trim not working, or Uncommanded trim runaway, maybe even preventing trim cut-out switches from working.
How is CFR25.671 to be affecting the certification of the MAX in light of the control forces in case of runaway, and the requirement of "without requiring exceptional piloting skill or strength" ?
If the hazard analysis of a fault in the electrical trim has changed from e.g. Minor to Hazardous, then this may also drive new requirements for probability of malfunction, fault detection, fault insulation, and redundancy in the manual trim.

turbidus

9th Mar 2020, 19:50

only the NG's made after the rule should be affected.

Fly Aiprt

9th Mar 2020, 20:03

Pushing either of these
initiates a self–test of the respective stall warning channel. The No.1 activates the
Captain stick shaker, and the No. 2 activates the F/O stick shaker. Either stick
shaker vibrates both columns through column interconnects.

STALL WARNING TEST Switches
Push – on ground with AC power available: each test switch tests its respective
stall management yaw damper (SMYD) computer. No.1 SMYD computer shakes
Captain’s control column, No.2 SMYD computer shakes First Officer’s control
column. Vibrations can be felt on both columns

Thanks 568 for this interesting information.
I emphasized some part of your response that ring a bell.
Last year when discussing the accidents I remember raising the issue of the difficulty of discerning whether one or both columns - and which one - was actively shaking in a stressful situation with lots of other alarms going off.
Can we conclude the mechanical interconnect might have rendered things difficult ?

lomapaseo

9th Mar 2020, 20:04

What were the terms of the original means of compliance for the max?

If some items were grandfathered (based on earlier model experience ) then that should still stand.

OTOH if that was simply swept under the rug and the FAA bought in on a pig-in-the-poke, then tough luck to Boeing and they should have to pay the piper :)

GlobalNav

9th Mar 2020, 20:38

What exactly do you mean with "compliant"? To the standard of the 1960ties of the 2020ties? Maybe the FAA simply wants to get out of the excessive grandfathering of the 737 family. The requirements for wiring have undergone multiple changes in the past decades, and B was able to evade them throughout the whole lifetime of the 737 through the grandfathering and - in the most recent times - the delegated power of certification. Time to make some substantial corrections.

The NG should have been compliant to the rules and the amendment levels negotiated, according to 21.101 the Changed Product Rule, and documented in the certification basis. It’s not just 1960’s vs 2000’s. Many rules have been amended over time since the original 737 certification. Generally, 21.101 requires that for the date of application, the certification basis is updated for all parts of the design that changed from the original. There are many nuances and exceptions, but that’s the gist of it. The new wiring rules may have been part of amendments that were issued after the NG certification, but prior to the application date of the MAX.

In my opinion, 21.101 itself as amended now is a practical mess, and is used with kid gloves with the applicant which find too many exceptions. 21.101 needs to be amended again, and simplified, in part to remove many provisions for exceptions and to shorten the life span of old regulation amendments. This would mean more new models, fewer derivatives, and more use of rules at the current amendment levels. Issuing this amendment would not get you on the Christmas card list of any OEM’s. But they had their chance to be “partners in safety” and opted to maximize share values instead.

Bend alot

9th Mar 2020, 20:49

cashash

9th Mar 2020, 21:01

The wiring was compliant when the NG was certified wasn't it? It wasn't when the Max was certified.

Well the Max was already certified, over 300 had been delivered and were in service. The fault lies with the FAA for allowing Boeing to call the 737max a variant of an existing type and not a completely new type if it now wants to make it built to all modern specifications. If the FAA are now saying they made a mistake and allowed an aircraft built to incorrect standards to enter service then I would have thought that would open them up to a rather large legal liability.

ST Dog

9th Mar 2020, 21:41

The new wiring rules may have been part of amendments that were issued after the NG certification, but prior to the application date of the MAX.

My understanding was the same bundles were used on the MAX as the NG. No changes. Since they didn't change the wiring there was no reason to treat it as a new part of the deign. The point of grandfathering is that unchanged items stay unchanged. So as far a Boeing was concerned it didn't need to be evaluated under new rules. There are 100s (1000s?) of places on the NG and the MAX that wouldn't have meet the changed rules at the time of certification but were allowed because is wasn't a new part of the design.

Now the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and wants to make that unchanged item meet the new standards.

ST Dog

9th Mar 2020, 21:46

It looks like BA installed a useful and fit-for-purpose, but not yet approved.

My understanding was that it was sensors used by the HGS, not the HGS as a whole.
The new (upgraded) sensors had not completed all the paperwork to allow installation on the 737.
All the testing was done, just not the paperwork exercise.

I haven't seen a good discussion about where that fell short. Did Collins say the new sensors were approved and someone just missed that it only for use with the HGS and not for the specific airframe? Did someone say that it was approved when it wasn't?

568

9th Mar 2020, 21:47

Thanks 568 for this interesting information.
I emphasized some part of your response that ring a bell.
Last year when discussing the accidents I remember raising the issue of the difficulty of discerning whether one or both columns - and which one - was actively shaking in a stressful situation with lots of other alarms going off.
Can we conclude the mechanical interconnect might have rendered things difficult ?

The MAX was built around the 737NG for certification purposes bar MCAS.
Having flown the NG (testing stalls) both pilots control columns will vibrate upon receipt of stall signals inputs from the hardware.

MAX should perform the same.

Twitter

9th Mar 2020, 21:50

My understanding was the same bundles were used on the MAX as the NG. No changes. Since they didn't change the wiring there was no reason to treat it as a new part of the deign. The point of grandfathering is that unchanged items stay unchanged. So as far a Boeing was concerned it didn't need to be evaluated under new rules. There are 100s (1000s?) of places on the NG and the MAX that wouldn't have meet the changed rules at the time of certification but were allowed because is wasn't a new part of the design.

No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.

Yes, but understandably - now they know what a nose down hardover after TO leads to.
To solve this conundrum they should check older NG aircraft for wiring condition and chafing to create a data bank, from which they may conclude how the Max will fare.
This will either give confidence in the Max wiring or cause NG wiring to be modded.

GlobalNav

9th Mar 2020, 22:35

My understanding was the same bundles were used on the MAX as the NG. No changes. Since they didn't change the wiring there was no reason to treat it as a new part of the deign. The point of grandfathering is that unchanged items stay unchanged. So as far a Boeing was concerned it didn't need to be evaluated under new rules. There are 100s (1000s?) of places on the NG and the MAX that wouldn't have meet the changed rules at the time of certification but were allowed because is wasn't a new part of the design.

No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.

There actually are cases where the new amendment is imposed regardless of product changes. I’m not a EE, but I think EWIS May have been a case of that.

MechEngr

9th Mar 2020, 22:46

The MAX was built around the 737NG for certification purposes bar MCAS.
Having flown the NG (testing stalls) both pilots control columns will vibrate upon receipt of stall signals inputs from the hardware.

MAX should perform the same.

I think the question was the case where one AoA sensor / SMYD was reporting a stall when the other was not.

ARealTimTuffy

9th Mar 2020, 23:44

My understanding was the same bundles were used on the MAX as the NG. No changes.......

No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.

Above you state that it is your understanding, then below you make a definitive statement.

I don’t think any of us know what small changes may or may not have been made to the trim system or related systems that would invoke the change product rule. There may have been some small changes made.

RickNRoll

10th Mar 2020, 00:33

My understanding was the same bundles were used on the MAX as the NG. No changes. Since they didn't change the wiring there was no reason to treat it as a new part of the deign. The point of grandfathering is that unchanged items stay unchanged. So as far a Boeing was concerned it didn't need to be evaluated under new rules. There are 100s (1000s?) of places on the NG and the MAX that wouldn't have meet the changed rules at the time of certification but were allowed because is wasn't a new part of the design.

No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.
The location of the engines has changed. There is more chance of damage in the case of an uncontained failure.

Dave Therhino

10th Mar 2020, 04:49

No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.

This is not a changed product rule issue. The stab trim system had several changes for the Max, including changes to the motor, the motor control, the pilots' control switches, and MCAS. These changes, even without MCAS, required the system to be re-examined for compliance with the system safety analysis regulation (25.1309(b)). That rule is unchanged since the time of the NG certification in 1997. When you change the system, the whole system - not just the part you changed - has to be re-examined and found compliant because the system safety analysis regulations are system-level requirements. The wiring deficiencies should have been caught by a competently performed failure modes and effects analysis, as would the effects of a failed high out of range AOA sensor. The EWIS requirements in 25.1707 introduced in 2007 are a red-herring in this case. While that rule is more prescriptive, 25.1309(b) effectively imposed the same requirement for adequate wire separation to prevent catastrophic events from wiring faults, and that requirement was identical for both the NG and Max programs.

Swiss51

10th Mar 2020, 05:50

The EWIS requirements in 25.1707 introduced in 2007 are a red-herring in this case. While that rule is more prescriptive, 25.1309(b) effectively imposed the same requirement for adequate wire separation to prevent catastrophic events from wiring faults, and that requirement was identical for both the NG and Max programs.
So, what you say is that - if the FAA is correctly trying to get back control over the certification, and the wiring is found to be changed based on the findings - the wiring in all NG's would need to be changed as well?

BDAttitude

10th Mar 2020, 09:02

So, what you say is that - if the FAA is correctly trying to get back control over the certification, and the wiring is found to be changed based on the findings - the wiring in all NG's would need to be changed as well?
See, the NG has been flying since mid of 90ies. If they had changed anything to the stab trim of the NG after 2007 they would have had to fulfill that requirement for the newly produced aircraft. I don't think they have though.

Dave Therhino

10th Mar 2020, 14:02

So, what you say is that - if the FAA is correctly trying to get back control over the certification, and the wiring is found to be changed based on the findings - the wiring in all NG's would need to be changed as well?

The system was changed for the Max, so the wiring should have been part of the new stab trim system safety analysis for the Max. It either wasn't examined or the issue was missed. At this point, because the design was already approved and the FAA did not revoke the type certificate, what's driving the FAA is apparently a determination that an unsafe condition exists warranting corrective action under 14 CFR part 39 (the part under which airworthiness directives are issued). To address the issue, Boeing has to propose a design change. That design change is required by 14 CFR part 21 to comply with the airworthiness requirements, including 25.1309 and 25.1707. A TC holder can't obtain approval of a non-compliant design change other than via an exemption. You can bet the FAA won't be issuing any exemptions from the system safety requirements for the stab trim system.

If the lack of wire separation and the consequences of that lack of separation are similar for the NG, you would normally expect a similar finding that an unsafe condition warranting AD action exists on those airplanes as well. However, at this point top FAA management is likely making the decisions rather than staff engineers following the normal processes, so it's hard to predict what the FAA will decide for the NG wiring. The normal FAA process would call for an AD if the wiring is found to have the potential for a single fault condition to be catastrophic. The Boeing lobbying will likely be based on a probability argument.

ST Dog

10th Mar 2020, 18:48

This is not a changed product rule issue. The stab trim system had several changes for the Max, including changes to the motor, the motor control, the pilots' control switches, and MCAS. These changes, even without MCAS, required the system to be re-examined for compliance with the system safety analysis regulation (25.1309(b)).

Your the first to say this isn't due to new wire separation rules that went into effect after the NG was certified.
All the other comments/reports have said it was related to changes in the rules that make the separation used on the NG no longer compliant.

Per Boeing the wiring in the areas of concern wasn't changed so it wasn't looked at.
They changed the "logic" in the console (signals/power passing through the switches and relays), but the same wires/signals eventually run out of the cabin to the tail. I'd have to go back and find both diagrams but I don't remember any new wires/signals compared to the NG.

Now whether the changes that were made would lead to a re-examination of the wire bundling/routing from cockpit to tail I'm not clear.
My inclination is that no, the wiring would not be looked at as they weren't changing it.
The new SSA would not have looked at the prior unchanged aspects for the unchanged portions.

And I'm still not clear where the possibility of a runaway that can't be stopped with the cockpit switches comes from.
If anything there are now 2 switches in series that cut the signal to the motor vs the old setup with parallel paths in the cockpit.
But either way there was just one signal going back to the tail.

I guess I need to find the wiring diagrams again and look at it again. This wasn't the focus at the time I last looked.

ST Dog

10th Mar 2020, 18:56

The location of the engines has changed. There is more chance of damage in the case of an uncontained failure.

That's a different issue. The uncontained engine failure issue is with the control cables, not electrical wiring.

I'm unconvinced the new engine/location is anymore likely to damage the cables. But I'm just a EE so may be missing something.
I'd love to see a comparative analysis, but alas I doubt sure will be made public.

MechEngr

10th Mar 2020, 19:35

Your the first to say this isn't due to new wire separation rules that went into effect after the NG was certified.
All the other comments/reports have said it was related to changes in the rules that make the separation used on the NG no longer compliant.

Per Boeing the wiring in the areas of concern wasn't changed so it wasn't looked at.
They changed the "logic" in the console (signals/power passing through the switches and relays), but the same wires/signals eventually run out of the cabin to the tail. I'd have to go back and find both diagrams but I don't remember any new wires/signals compared to the NG.

Now whether the changes that were made would lead to a re-examination of the wire bundling/routing from cockpit to tail I'm not clear.
My inclination is that no, the wiring would not be looked at as they weren't changing it.
The new SSA would not have looked at the prior unchanged aspects for the unchanged portions.

And I'm still not clear where the possibility of a runaway that can't be stopped with the cockpit switches comes from.
If anything there are now 2 switches in series that cut the signal to the motor vs the old setup with parallel paths in the cockpit.
But either way there was just one signal going back to the tail.

I guess I need to find the wiring diagrams again and look at it again. This wasn't the focus at the time I last looked.

If a power wire loses its insulation and a control wire loses its insulation and then something forces the conductors of the two wires together it is the same input as if a trim switch was used and happens downstream of the cutout switches, so it would not be stopped by opening the control wire enable switches on the console.

Eventually the way to handle this will be by avoiding simple on/off signals and require complex cryptographically signed handshakes between all control components. Recall the German plane that had the stick wired backwards? Easy-peasy. Put an accelerometer in the stick to compare it's movement to the control movement when the plane is on the ground. The aircraft company nearly killed everyone on the plane to save a couple of bucks in such a sensor.

A weak example of this communications protocol is used on cars for some functions with CANBus, where shorting power to a signal wire just disrupts every device on the network, so it's not a great drop-in solution for aviation. It does mean that a single wire can go to multiple devices to supply power and a single wire can carry comms, allowing a lamp holder to report to the car's computer that the lamp is not taking any current and is burned out; each component can self-test at startup and report the condition without having to have complicated test wiring on top of the function wiring. In aircraft the control could be over fiber-optic lines, avoiding short circuits, with a wireless option in case of major damage and local power for each actuator - nope, wait, that would be batteries and those are bad. Anyway, solving this sort of problem to 100% reliability is not easy.

ST Dog

10th Mar 2020, 20:49

If a power wire loses its insulation and a control wire loses its insulation and then something forces the conductors of the two wires together it is the same input as if a trim switch was used and happens downstream of the cutout switches, so it would not be stopped by opening the control wire enable switches on the console.

But the power for the trim motor is fed through a relay (R64 in the attachment on this post https://www.pprune.org/10445311-post194.html) and that relay is only engaged (passing power) when the stab trim breaker is closed and the cutout switched are in the NORM position.

Also the control signals (up, down, etc) are 28V DC while the motor power is 3 phase 115V AC.

fizz57

10th Mar 2020, 20:57

Recall the German plane that had the stick wired backwards? Easy-peasy. Put an accelerometer in the stick to compare it's movement to the control movement when the plane is on the ground.

Using a complex, failure-prone system to cure a simply-fixed and rare problem is generally not a good idea - ask Boeing.

The aircraft company nearly killed everyone on the plane to save a couple of bucks in such a sensor.

Quite apart from the fact that "an accelerometer in the stick" and its certification will cost a lot more than a few bucks (again, ask Boeing), anyone else notice the subliminal messaging going on here?

Swiss51

10th Mar 2020, 21:38

However, at this point top FAA management is likely making the decisions rather than staff engineers following the normal processes, so it's hard to predict what the FAA will decide for the NG wiring. .
So we can only hope that the FAA management still feels the scars from the nose rings that were put on them by B. If I understand you correctly the knowledgable engineers would require the change on the NT as well. And probably not only through an AD.

Big Pistons Forever

11th Mar 2020, 00:07

Addressing a problem identified by an AD does not necessarily mean physical changes have to be made. Many AD's stipulate an immediate condition and conformity inspection and then an enhanced inspection regime. Is it unreasonable to think that the stab trim wiring issue could be handled in this way ?

MechEngr

11th Mar 2020, 01:08

Using a complex, failure-prone system to cure a simply-fixed and rare problem is generally not a good idea - ask Boeing.

Quite apart from the fact that "an accelerometer in the stick" and its certification will cost a lot more than a few bucks (again, ask Boeing), anyone else notice the subliminal messaging going on here?

Honestly, I wasn't going for subtle.
The fact is that every accident or design problem can be fixed, in hindsight, if enough cash is thrown at it. But that certification would have looked cheap if the German-owned plane had augured into a kindergarten. So, figure in the additional costs and embrace the inexpensive new tech and the chance to clear off a ton of human-error potential problems. I am unsure what additional certification cost there would be that it doesn't already have to go through. It's already electronic; add a chip and look for qualitative changes. But, since no one died -this time- no certifying agency is forcing the planes to be grounded until a fix is made. And no one is adding a new requirement for new aircraft to meet.

As it is that stick would already be priced the same a typical used car. Maybe this adds the cost of new floor mats and a full tank of gas.

It's hardly "failure prone" This is what accelerometers do. It's all they do and they are very good at it. What happened with Boeing is they trusted that pilots would catch any trim problems, correct them, and then cut off the problem at the knees. I'm suggesting getting pilots out of the loop entirely - which is the Airbus philosophy. It seems to be working for them and they are entirely electronics and cross-checking.

Dave Therhino

11th Mar 2020, 01:47

But the power for the trim motor is fed through a relay (R64 in the attachment on this post https://www.pprune.org/10445311-post194.html) and that relay is only engaged (passing power) when the stab trim breaker is closed and the cutout switched are in the NORM position.

Also the control signals (up, down, etc) are 28V DC while the motor power is 3 phase 115V AC.

My understanding is that the wire isolation concern is with the potential for 28 VDC hot shorts to either the up or down control signal wires and the arm circuit wire (the circuit that closes the R64 motor power contactor relay). Those control and arm wires are routed together over much of their runs and are co-routed with numerous 28 VDC power wires. Hot shorts to the motor power wires themselves are not the issue.

Dave Therhino

11th Mar 2020, 02:13

So we can only hope that the FAA management still feels the scars from the nose rings that were put on them by B. If I understand you correctly the knowledgable engineers would require the change on the NT as well. And probably not only through an AD.

If you look at the FAA's TARAM handbook, which contains internal guidelines for determining whether an unsafe condition exists on transport airplanes, it has a discussion of the fail safe design expectation for transport airplanes in section 6.1. It says, "If you determine that the condition violates the fail-safe philosophy, you should consider the condition unsafe regardless of the calculated TARAM uncorrected fleet or individual risk values." Here's a link to that document. Section 6.1 is on page 33.

https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/4e5ae8707164674a862579510061f96b/$FILE/PS-ANM-25-05%20TARAM%20Handbook.pdf

If the same type of stab trim wiring fault vulnerability as has been described for the Max exists on the NG, the FAA's own guidelines would classify that as an unsafe condition requiring corrective action via design change and an AD. However, it also would be an expensive change. In such cases, the decisions are often made by the leaders rather than via the normal process for more routine AD decisions. There's nothing necessarily wrong with that - as long as they make good decisions.

Swiss51

11th Mar 2020, 13:17

There's nothing necessarily wrong with that - as long as they make good decisions.
I perfectly understand what you are saying. But I am also aware that the FAA has been very "weak" when it came to other safety aspects in the MAX certification by accepting explanations from B about the categorisation "risky" or "potentially fatal" (don't remember the exact wording, but you know what I mean). IIRC it was something around MCAS / AOA / single dependency. THAT makes me think hard and THAT makes me hope that the FAA Mgmt still feels the pain.

lomapaseo

11th Mar 2020, 13:24

If you look at the FAA's TARAM handbook, which contains internal guidelines for determining whether an unsafe condition exists on transport airplanes, it has a discussion of the fail safe design expectation for transport airplanes in section 6.1. It says, "If you determine that the condition violates the fail-safe philosophy, you should consider the condition unsafe regardless of the calculated TARAM uncorrected fleet or individual risk values." Here's a link to that document. Section 6.1 is on page 33.

https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/4e5ae8707164674a862579510061f96b/$FILE/PS-ANM-25-05%20TARAM%20Handbook.pdf

If the same type of stab trim wiring fault vulnerability as has been described for the Max exists on the NG, the FAA's own guidelines would classify that as an unsafe condition requiring corrective action via design change and an AD. However, it also would be an expensive change. In such cases, the decisions are often made by the leaders rather than via the normal process for more routine AD decisions. There's nothing necessarily wrong with that - as long as they make good decisions.

Vulnerability is not a failure condition.

if it were lots of military aircraft would never fly.

In my view currently flying aircraft come under "continued Airworthiness" standards which take into account in-service experience including maintenance

The issue at hand with the max is its original certification basis and whether the data used was valid..

ST Dog

11th Mar 2020, 15:07

My understanding is that the wire isolation concern is with the potential for 28 VDC hot shorts to either the up or down control signal wires and the arm circuit wire (the circuit that closes the R64 motor power contactor relay). Those control and arm wires are routed together over much of their runs and are co-routed with numerous 28 VDC power wires. Hot shorts to the motor power wires themselves are not the issue.

In that case the arm circuit and thus the cutout would stop the motor. Prior comments were saying that it couldn't be stopped by any reasonable crew action.
The post I replied to said "so it would not be stopped by opening the control wire enable switches on the console."
The cutout switches would do exactly what they are supposed to, disconnecting the power feed via the relay.

And other comments even implied that the trim breakers wouldn't stop the motor. Not sure where the breakers are, but I'll agree they may be difficult to reach quickly, but the cutouts are there specifically to stop runaway/unwanted uncommand movement.

The best I can tell it takes 2 signals to actual move the trim motor. The ARM signal form R1193 (MAIN TRIM ARM) enabled by the thumb switches (the upper set of contacts in the linked drawing) as well as the direction signals that pass through the limit switches.

So 2 control wires, 1 arm and 1 direction, would have to short to power. That just got a lot less likely.

Depending on where R850 (STAB TRIM INTERLOCK) is located on the NG, I might be more concerned about the NG wiring than the MAX.
(That diagram doesn't show how the NG FCC trim signals work)

Mad (Flt) Scientist

11th Mar 2020, 19:39

But as you pointed out - half the 737Max fleet already have CofA's and have been in service. If you are saying that he problem is so serious that those aircraft cannot fly because of it then by all logic that must also apply to all 737NG's. ....
What I was trying to say was that it may not be "unsafe" such as to require grounding or similar, but it may not be certifiable (enough) to issue a C of A to a new aircraft.

Bidule

12th Mar 2020, 06:17

Vulnerability is not a failure condition.

if it were lots of military aircraft would never fly.

The criteria for certification of military aircraft are not the same as for civilian air transport aircraft....

.

Bend alot

12th Mar 2020, 13:08

Adding to a sense of mounting anxiety, Boeing's new Chief Executive Officer Dave Calhoun was forced to apologize to senior staff after a rare attack on his predecessor and company leadership, which sources say provoked criticism from within the senior ranks of the company as well as the rank-and file.

Calhoun, who took over as CEO in January after serving about a decade on Boeing's board, told senior staff by email on Friday he was "both embarrassed and regretful" over his comments in a New York Times interview earlier in the week.

"It suggests I broke my promise to former CEO Dennis Muilenburg, the executive team and our people that I would have their back when it counted most," Calhoun said. "I want to reassure you that my promise remains intact."

https://au.yahoo.com/finance/news/boeing-shares-plunge-faa-rejects-143002565.html

CW247

14th Mar 2020, 14:34

How Boeing Lost Its Way. Found this video which looks at the whole Boeing fall from grace thing through the lens of corporate greed. Interesting bits about Boeing share buy back strategy, a tool used by companies to raise their own share price.

https://www.youtube.com/watch?v=EESYomdoeCs

Dave Therhino

14th Mar 2020, 17:02

Vulnerability is not a failure condition.

if it were lots of military aircraft would never fly.

In my view currently flying aircraft come under "continued Airworthiness" standards which take into account in-service experience including maintenance

The issue at hand with the max is its original certification basis and whether the data used was valid..

The FAA written policy and practice for decades in managing continued operational safety has been that a potential single failure (such as a wire bundle fault condition), unless that failure can be agreed to be effectively impossible, does not meet the fail safe standard intended to be applied to nearly all aspects of transport airplane systems design, and warrants corrective action. (There are a few specific exceptions to this standard due to practicality issues - turbine engine rotor failures for example.) I posted a link to the applicable policy above. The FAA has issued numerous airworthiness directives to address potentially catastrophic failure conditions resulting from a single failure even when that condition, or the initiating single failure, is not known to have already occurred in service. That was the basis for my comment on the stab wiring of both the Max and the NG.