Sign in to follow this  
Maverick

Another 737 MAX down.

Recommended Posts

The things that I found interesting was that, assuming he is correct, I hadn't realized thrust line had changed that much. Also I also thought that some of his comments on Boeing's philosophy were interesting.

Share this post


Link to post
Share on other sites

Hi Greg;

The splash-screen seen here in the link to the video posted by Jaydee is a clear illustration of the change in the engine/cowling arrangement, (a "btw", IEEE is a technical/profession/engineering association of which the gentleman who wrote the article is a member.)

From the article:

Quote

With the 737 Max, the situation became critical. The engines on the original 737 had a fan diameter (that of the intake blades on the engine) of just 100 centimeters (40 inches); those planned for the 737 Max have 176 cm. That’s a centerline difference of well over 30 cm (a foot), and you couldn’t “ovalize” the intake enough to hang the new engines beneath the wing without scraping the ground.

The solution was to extend the engine up and well in front of the wing. However, doing so also meant that the centerline of the engine’s thrust changed. Now, when the pilots applied power to the engine, the aircraft would have a significant propensity to “pitch up,” or raise its nose.

The last statement about the raised thrust line being the cause of the pitch up does not make sense. A thrust line that is closer to the longitudinal centerline of the fuselage does not increase force, it reduces it, so the statement is wrong right away without examining the actual design. The higher thrust line is not the reason MCAS was required. It is stated that the increased area of the engine cowlings providing an increase in lift at higher AoA's. This lift came just at the point where the older Boeings would be providing a heavier control column feel to the pilots, which certification standards, (CFR 25.173, I have seen quoted, pasted below), required. On the MAX, as speed reduced and the stall AoA was approached, a certain, required "pull" on the control column was not evident, so Boeing used the MCAS solution to provide this additional pull, which was necessary if the single B737 "type" was to be retained. They just don't appear to have done an "FMEA" when designing/building the system. MCAS action is intermittent, and if the trim wheels are seen rotating right after takeoff, it's the same as STS, (Speed Trim System) operation which is designed to force the pilot to trim out the artificial-feel forces as speed increases. Since the late 60's, we've been trained to recognize a runaway stabilizer as a continuous event, not an intermitent one with "intervals" of operation, which do not raise awareness, signal danger or provide a hint of what's actually happening, particularly when the crew is trying to determine why the stick shaker is activated and the airspeeds appear unreliable.

Cheers as always, Greg!

 

Quote

14 CFR § 25.173 - Static longitudinal stability.

§ 25.173 Static longitudinal stability.

Under the conditions specified in § 25.175, the characteristics of the elevator control forces (including friction) must be as follows:

(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC/MFC, whichever is appropriate, or lower than the minimum speed for steady unstalled flight.

(b) The airspeed must return to within 10 percent of the original trim speed for the climb, approach, and landing conditions specified in § 25.175 (a), (c), and (d), and must return to within 7.5 percent of the original trim speed for the cruising condition specified in § 25.175(b), when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.

(c) The average gradient of the stable slope of the stick force versus speed curve may not be less than 1 pound for each 6 knots.

(d) Within the free return speed range specified in paragraph (b) of this section, it is permissible for the airplane, without control forces, to stabilize on speeds above or below the desired trim speeds if exceptional attention on the part of the pilot is not required to return to and maintain the desired trim speed and altitude.

[Amdt. 25-7, 30 FR 13117, Oct. 15, 1965]

 

Edited by Don Hudson

Share this post


Link to post
Share on other sites

Thanks Don

I sure admire how you have kept up with the technical aspects of our profession. I did kinda wonder about a soft ware designer,s acumen in all of this.

I sure wish we had stuck with, what I understand to be the original  plan, the Neo. I guess Boeing made an offer we couldn't refuse.

I'm heading over today to your neck of the woods to spend Easter with my son and his family including two new great grand-kids. I'm no longer a relative but an ancestor. 😎

Thanks again Don

Greg

Share this post


Link to post
Share on other sites

TWO great-grandbabies?! How wonderful for you, Greg! Please say hello to your son & family for us.

We have 3 GB's, 4, 2 & 4mo...we're often a hundred-and-an-eighth in coloring books, toys & 95-110db these days - 😉!

Yes, the Neo...never understood the switch to a 1966 cable-&-pulley bread-and-butter type. I hope it works out for Boeing, and all the airlines that trusted and bought the airplane, but truly, it's an organizational & design/engineering lesson that never should have needed learning.

Share this post


Link to post
Share on other sites

One other clue that the trim is running is sound. Unfortunately that would have been drowned out by the shaker. The sound of the trim spinning while hand flying and not manually (electric) trimming gets your attention.

Share this post


Link to post
Share on other sites

@Don Hudson

Thanks for your reply to my last post (a couple of pages back!). Yes, I agree with your interpretation of how the final AND occurred.

However, in respect of my comment, " manual trimming may be impossible ",  a Mentour Pilot video taken in a B738 Full Simulator has some points of interest - applicable to ET320.

The "roller coaster" method - to unload the HS and allow manual trimming, IF they'd known to use it, wouldn't get a look in due to terrain. Speed reduction may have, but it appears the crew didn't understand what they were dealing with.

Note:- these runaway stabilizer correction scenarios were migrated from the FCOM to the FCTM as of the 732.

The damming feature of the MCAS fitted to the MAX, is it is actually a system configuration control activated without cross reference to other ADIRU data, and hasn't the ability to detect a 'single point' air-data failure and remove itself from the control equation.

 

Share this post


Link to post
Share on other sites
On 4/20/2019 at 12:06 PM, Don Hudson said:

:

The last statement about the raised thrust line being the cause of the pitch up does not make sense. A thrust line that is closer to the longitudinal centerline of the fuselage does not increase force, it reduces it, so the statement is wrong right away without examining the actual design. The higher thrust line is not the reason MCAS was required. It is stated that the increased area of the engine cowlings providing an increase in lift at higher AoA's.

 

Yes, seemed like it could have been a good article based on the "claimed" expertise of the writer in both aviation and software design.  Unfortunately the error in assessing the effect of moving the thrust line casts doubt on the validity of anything else he wrote.  There is a possibility that the new engine could have been canted upward slightly which would have changed the thrust line but I have not seen anything about this while I have seen expert commentary on the effect of the larger cowls at higher AoAs so that's the likely impetus for the MCAS.

Share this post


Link to post
Share on other sites

My understanding is that in the flight regime MCAS is designed to operate in it is not so much a tendency for the airplane to pitch up but pitch control feel becoming lighter than desired when it should in fact feel heavier. MCAS AND trim designed to provide the proper "feel" to the pilot. A stability system more specifically than a stall prevention system. 

Share this post


Link to post
Share on other sites

Share this post


Link to post
Share on other sites

https://www.seattletimes.com/business/boeing-aerospace/faa-could-clear-boeing-max-to-fly-again-by-late-may-or-early-june/?utm_source=marketingcloud&utm_medium=email&utm_campaign=BNA_042619204614+BREAKING%3a+FAA+could+clear+737+MAX+to+fly+again+within+weeks_4_26_2019&utm_term=Active subscriber

 FAA could clear Boeing 737 MAX to fly again within weeks
April 26, 2019 at 1:17 pm Updated April 26, 2019 at 1:46 pm

Dominic Gates By Dominic Gates
Seattle Times aerospace reporter

The Federal Aviation Administration (FAA) could clear Boeing’s 737 MAX to fly again late next month or early June, according to a person familiar with the safety agency’s latest thinking.

If the FAA gives the green light that soon — much more quickly than many analysts have predicted —   airlines would still need weeks to get their planes ready and their pilots trained. But the timetable, which assumes no unforeseen developments, means U.S. carriers could have the MAX flying passengers again by early August.

That likely timeline was confirmed by a second person close to the discussions.

At a crucial meeting of the heads of civil-aviation authorities from around the world convened by the FAA on May 23, the U.S. regulatory agency is expected to outline its finalized safety analysis in an attempt to foster international consensus.

Unless some new issues are discovered, the FAA anticipates telling the assembled foreign regulators that it’s “in a position to clear the aircraft for service sometime in the near vicinity of that meeting,” potentially as early as a week later, said the person familiar with FAA’s latest thinking.

. . . .

 

Share this post


Link to post
Share on other sites

blues, I think most passengers don't know what airplane they're in. Safety announcments I've heard mention the type but many don't get the Emergency Card out and read it. I think fares have more impact than aircraft type.

  • Like 1

Share this post


Link to post
Share on other sites

I'm not so sure in this case Don. Everybody who I run into and knows that I flew ask me about the 737 Max. (Thanks to what you and others have posted on this forum I can fool them into thinking that I know what I'm talking about.) 😎

I don't know if there has ever been as much wide spread negativity about a specific aircraft before. I think it's going to take a while before the flying public forgets about this.

Share this post


Link to post
Share on other sites
13 hours ago, Don Hudson said:

blues, I think most passengers don't know what airplane they're in. Safety announcments I've heard mention the type but many don't get the Emergency Card out and read it. I think fares have more impact than aircraft type.

Perhaps but I think today’s social media and mass communication sources such as CNN brings immediate attention to just about anything which will now include what kind of plane passengers are boarding.  9-11 would not have affected the airline industry as it did in late 2001 if CNN and others had not repeatedly played those images of planes flying into the WTC towers. It didn’t help my last Canadian airline along with other poor business decisions  

In 1979 AA had a DC-10 crash departing ORD. Three engine mounting bolts not properly installed allowed one of the wing mounted engines to break away. No CNN or cell phones existed but the event still hurt future sales of the plane. Another crash due to a forward cargo door opening also didn’t help its reputation going forward. 

Boeing is planning to roll out a major PR event when this plane is ready to fly again. However Don I think you’re suggestion of air fare reductions will be the only real way to get passengers back into 737 Max seats.

Also in my opinion the NTSB is sitting on their release of the Atlas 767 crash. It must known that Boeing and the traveling public can’t handle anymore bad press. 

Edited by blues deville

Share this post


Link to post
Share on other sites

Can't help but wonder if airlines aren't busy scraping the word MAX off the side of their parked aircraft  :)

  • Thanks 1
  • Haha 1

Share this post


Link to post
Share on other sites

I remember riding in the back of a Westjet flight and the PA included something along the lines of; "Welcome onboard our newest 737 MAX"  Heavy emphasis on the "Max".  I'll bet that changes to "welcome onboard Westjet flight xxx" to avoid having a stampede of guests heading for the door.

Share this post


Link to post
Share on other sites

https://www.cnbc.com/2019/04/28/boeing-didnt-tell-southwest-that-safety-feature-on-737-max-was-turned-off-wsj.html?fbclid=IwAR0tRfkemSKdh0REYKsTbub-j98zasRJiIETiZDdvVWD_yrBOcBAMr3Jaag

 

Quote

Upon delivery (prior to the Lion Air event), the AOA Disagree lights were depicted to us by Boeing as operable on all MAX aircraft, regardless of the selection of optional AOA Indicators on the Primary Flight Display (PFD). The manual documentation presented by Boeing at Southwest’s MAX entry into service indicated the AOA Disagree Light functioned on the aircraft, similar to the Lights on our NG series. After the Lion Air event, Boeing notified us that the AOA Disagree Lights were inoperable without the optional AOA Indicators on the MAX aircraft. At that time, Southwest installed the AOA Indicators on the PFD, resulting in the activation of the AOA Disagree lights - both items now serve as an additional crosscheck on all MAX aircraft.

 

Share this post


Link to post
Share on other sites

Aviation Week: Max Disrupting NMA Plans

MAX Issues Are Disrupting Boeing’s NMA Plans

Guy Norris and Sean Broderick 

Boeing’s push to get the 737 MAX back in service and restore confidence in its cornerstone commercial program appears to be threatening its next major endeavor—the new clean-sheet design tapped to fill a gap between the 737 and 787. Efforts to restore the MAX are in full swing, but the undertaking is draining resources from the new midmarket airplane (NMA), pushing a possible launch further into the future.

Until the 737 MAX crisis struck in March, Boeing’s expected plan was to marshal its board of directors’ approval for official authority to offer (ATO) NMA to airlines by midyear 2019 and—assuming enough orders were placed—launch the program in 2020 in time for entry into service in 2025. The date is key for several reasons. Among the most critical: It is ideally timed to capitalize on the expected replacement window for in-service 757s and 767s.

Although the company remains committed to developing the new aircraft, Boeing is softening its line on timing for the NMA. A mid-2020s service-entry target is now “a potential opportunity,” Boeing CEO Dennis Muilenburg said during a first-quarter 2019 earnings call to analysts April 24. “We still have work to do before we get to an ATO decision,” he added. “We are still working on a pace to try and do that this year as we have previously announced, but I want to be very clear that when it comes to our application of resources, our top priority is the safe return to service of the 737 MAX.”

Discussions with potential customers have slowed as well. “It’s understandable that they’ve been distracted,” said Ed Bastian, CEO of possible NMA launch customer Delta Air Lines. “I expect them to be able to reengage in some conversations in the not-too-distant future”.

Although Boeing is depending on advances in automation and model-based systems engineering methods to shave almost two years off the traditional development cycle time for new aircraft, any further potential delays to the start of the NMA beyond late 2019 or early 2020 will almost certainly add pressure on an already compressed projected program schedule. In addition, the threat of delaying service entry into the second half of the 2020s will also likely cede potential sales to Airbus, which is expected to launch the A321XLR, aimed at areas of the same market space, sometime later this year. While these threats are significant, they pale in comparison to a prolonged MAX fleet grounding.

“Boeing maintained the opportunity for a 2025 entry into service and an authority to offer this year, but we did not pick up on a sense of urgency, given heightened focus on the 737 MAX, and we have a hard time seeing the board moving forward before the MAX is at least headed in the right direction,” JPMorgan analyst Seth Seifman says.
mail?url=https%3A%2F%2Fgallery.mailchimp
Boeing is focused on returning grounded 737 MAXs to service. Credit: Joe Walker
Indications from both Boeing and the FAA are that the effort to modify the MAX’s flight-control system—a must before the fleet is cleared to fly again—is entering its final stages. The FAA is targeting May 23 for a meeting of regulators to discuss finalized updates to Boeing’s 737 MAX flight control system, the agency confirms to Aviation Week.

While much remains up in the air, the gathering is expected to include regulators from around the world. Invitations are in the process of going out, and most are expected to attend. Among the key constituents likely to participate: representatives from state-of-design veterans Brazil, Canada, and Europe, emerging power China, which was the first to ground the MAX, and both Ethiopia and Indonesia, the two countries leading investigations into two fatal 737-8 accidents that triggered the upgrades and MAX fleet grounding.

“The FAA is inviting the directors-general of civil aviation authorities around the world to discuss the agency’s activities toward ensuring the safe return of Boeing 737 MAX to service,” the FAA says. “The meeting is intended to provide participants the FAA’s safety analysis that will inform its decision to return the 737 MAX fleet to service in the U.S. when the decision is made. Also, the FAA will provide safety experts to answer any questions participants have related to their respective decisions to return the fleet to service.”

The meeting, which will be limited to regulators, is part of an effort to build global consensus about removing the flight restrictions that were put in place. But the FAA is pressing forward with its own review of Boeing’s proposed fixes, and is prepared to base its decision on whether to approve the MAX’s return to service on its own analysis, not on concurrence from other regulators. This could mean that U.S. MAX operations could be authorized by early June, clearing the way for American Airlines, Southwest Airlines, and United Airlines to put the combined 72-aircraft MAX fleet back to work on domestic routes.

Using the meeting to spotlight the MAX changes hinges on the FAA approving Boeing’s updated maneuvering characteristics augmentation system (MCAS) software and related training. The FAA is preparing to conduct certification test flights of the proposed final software configuration—the follow-on to Boeing’s April 16 engineering demonstration flight. If the FAA signs off on the system’s performance, the next steps would include approving the complete software package, including documentation. The FAA has not received the final package.
mail?url=https%3A%2F%2Fgallery.mailchimp
Southwest Airlines has the largest fleet of 737 MAXs, at 34. Credit: Southwest Airlines
Training that accompanies the new configuration also must be approved. An FAA-organized Flight Standardization Board (FSB) has recommended a minimum standard of Level B computer-based training to explain the MCAS—which was added to the MAX’s speed trim system as a flight-stability function to make the new model handle like the 737 Next Generation—to pilots. But some airlines and regulators are expected to push for a minimum amount of simulator training. 

One possibility being floated: A compromise that mandates simulator training within a certain time frame for all MAX pilots, but not as a return-to-flight precursor. Such a move would allow airlines to work MCAS scenarios into planned simulator training sessions, minimizing training disruption and—more important to airline management—keeping costs down. Public comments on the FSB are due at the end of April, and are expected to be considered during production of a final training-standards document.

If approval of the modified MCAS’ functionality, underlying software and related training minima is in place before the May meeting, the FAA is not expected to wait long after the session to remove its MAX ban. The FAA issued its ban March 13—three days after the crash of Ethiopian Airlines Flight 302, the second 737-8 accident in five months, and after all non-U.S. MAX operations were prohibited by other regulators. The moves left all 370 in-service MAXs grounded until further notice.

The MCAS and how pilots responded to the system’s erroneous operation are at the center of each probe. Boeing determined the MCAS, which commands automatic stabilizer trim, needed modifications following the first accident, the Oct. 29, 2018 crash of Lion Air Flight 610.

Most airlines with MAXs have removed them from flight schedules until well into the summer, opting for predictable schedules that do not include MAXs over tentative ones that cancel flights as the grounding drags on. Meanwhile, Boeing is working to build a consensus among operators—some of which grounded the aircraft voluntarily. The key constituency being targeted: pilots.

“We think a key voice in all of this will be the pilots for our airlines,” Muilenburg said on the earnings call. “We’re working with our airline customers and those pilot voices to ensure that we can build on that going forward. To that end, we hosted multiple sessions around the world; more than 90% of our 50-plus MAX operators to date have had pilots in our simulator sessions with the new software. . . . I can tell you with those series of sessions that we’ve had around the world, the pilot feedback from the simulator sessions has been excellent.”

While most airlines and pilot groups continue to express general confidence in Boeing and the MAX, specific reactions to the updates have been more reserved. “United pilots have a seat at the table and will closely monitor these changes to ensure they fully and effectively mitigate all identified risks and meet the needs of our pilots to regain full confidence in the MAX,” the airline’s master executive council told its pilots following an April 12 meeting at the FAA to review the MCAS changes.

For Boeing, winning pilots over will mean convincing them that the company has learned from how the MCAS’ introduction was handled. While Boeing insists it did not hide the MCAS—the system was included in high-level technical briefings to operators, for instance—the flight-control law’s existence was not proactively communicated to pilots. Boeing expected it to operate in the background, and only if certain areas of the flight envelope were encountered. The MCAS was not explained in flight manuals, nor was it covered in MAX-specific training.

The sequence in each MAX accident exposed a failure mode that triggered the MCAS with one source of inaccurate data, pushing the aircraft’s nose down and forcing the crew to counter with nose-up inputs to keep it airborne. The sequences also suggested that all flight crews were not sufficiently prepared for a failure scenario linked to the system. Boeing did not proactively explain the MCAS nor highlight the existing emergency procedure to manage it—executing the stabilizer runaway checklist—until after the Lion Air accident.

“Boeing will, and should, continue to face scrutiny of the ill-designed MCAS and initial nondisclosure of the new flight-control logic,” Southwest Airlines Pilots Association President Jon Weaks said in a message to pilots following the April 12 FAA meeting.

Boeing says its software upgrades reduce the likelihood of an erroneous activation, while training and manual updates will shed more light on the MCAS.

“Both accidents were a chain of events. One link in that chain of events was the activation of the MCAS system with erroneous angle-of-attack data,” Muilenburg says. “We understand how to address that link. That’s our responsibility. We own that, and that’s what the software update does.”

Bigger-picture, Boeing is signaling that it is looking beyond the MAX’s return to service and preparing for the legal ramifications of the accidents and groundings. While admitting that the flight-control law software implicated in the accidents needed a redesign, Muilenburg has become increasingly defensive in response to suggestions that lapses in Boeing’s engineering or certification process for the MAX is to blame. “We understand our airplane . . . how the design was accomplished . . . how the certification was accomplished, and we remain fully confident in the product we put in the field,” Muilenburg says. “But there was no surprise, or gap or unknown here, or something that somehow slipped through the certification process. Quite the opposite.”

Share this post


Link to post
Share on other sites

All dressed up and no where to go/fly. Seattle Renton Field is close to standing room only.

AECA84E8-5A2B-4A92-936B-B47397F5DC51.jpeg

12DDA7EE-5410-4E52-B4F5-76B82D83F6DC.jpeg

Edited by blues deville

Share this post


Link to post
Share on other sites

A timely examination of a topic relevant to these two accidents:

https://www.researchgate.net/publication/332686552_The_Role_of_Alerting_System_Failures_in_Loss_of_Control_Accidents_CAST_SE-210_Output_2_Report_3_of_6/download

The Role of Alerting System Failures in Loss of Control Accidents
CAST SE-210 Output 2
Report 3 of 6
Randall J. Mumaw1, Loran A. Haworth1, and Michael S. Feary2
Executive Summary

This report is part of a series of reports that address flight deck design and evaluation, written as a response to loss of control accidents. In particular, this activity is directed at failures in airplane state awareness in which the pilot loses awareness of the airplane’s energy state or attitude and enters an upset condition. In a report by the Commercial Aviation Safety Team, an analysis of accidents and incidents related to loss of airplane state awareness determined that hazard alerting was not effective in producing the appropriate pilot response to a hazard (CAST, 2014). In the current report, we take a detailed look at 28 airplane state awareness accidents and incidents to determine how well the hazard alerting worked. We describe a five-step integrated alerting-to-recovery sequence that prescribes how hazard alerting should lead to effective flight crew actions for managing the hazard. Then, for each hazard in each of the 28 events, we determine if that sequence failed and, if so, how it failed. The results show that there was an alerting failure in every one of the 28 safety events, and that the most frequent failure (20/28) was tied to the flight crew not orienting to (not being aware of) the hazard. The discussion section summarizes findings and identifies alerting issues that are being addressed and issues that are not currently being addressed. We identify a few recent upgrades that have addressed certain alerting failures. Two of these upgrades address alerting design, but one response to the safety events is to upgrade training for approach to stall and stall recovery. We also describe issues that need additional attention: the need for improved alert integration for flight path management hazards, airplanes in the fleet that do not meet the current alerting regulations, a lack of innovation for addressing cases of channelized attention, and existing vulnerabilities in managing data validity.

Share this post


Link to post
Share on other sites

Look at what has turned up in the Wall Street Journal!

https://www.wsj.com/articles/boeings-own-test-pilots-lacked-key-details-of-737-max-flight-control-system-11556877600

Boeing’s Own Test Pilots Lacked Key Details of 737 MAX Flight-Control System
A culture of close collaboration between test pilots, engineering staff deteriorated in later stages of aircraft’s development

By Andrew Tangel and Andy Pasztor
May 3, 2019 6:00 a.m. ET

Boeing Co. limited the role of its own pilots in the final stages of developing the 737 MAX flight-control system implicated in two fatal crashes, departing from a longstanding practice of seeking their detailed input, people familiar with the matter said.

As a result, Boeing test pilots and senior pilots involved in the MAX’s development didn’t receive detailed briefings about how fast or steeply the automated system known as MCAS could push down a plane’s nose, these people said. Nor were they informed that the system relied on a single sensor—rather than two—to verify the accuracy of incoming data about the angle of a plane’s nose, they added.

Investigators have linked faulty sensor data to the flight-control system’s misfire, which led to crashes in Indonesia and Ethiopia that took 346 lives.

The extent of pilots’ lack of involvement hasn’t been previously reported and could bring fresh scrutiny from investigators and regulators already looking into Boeing’s design and engineering practices. It isn’t clear whether greater pilot participation would have altered the ultimate design of the flight-control system. But the scaling back of pilots’ involvement and their lack of detailed knowledge about the plane’s system add to the list of questions about engineering and design practices facing the Chicago-based aerospace giant.

A Boeing spokesman said test pilots and senior pilots didn’t have less of a role in the design, briefing and testing of the final version of MCAS when compared with their counterparts who worked on previous models featuring important new systems.

“Listening to pilots is an important aspect of our work,” the spokesman said. “Their experienced input is front and center in our mind when we develop airplanes. We share a common priority—safety—and we listen to them carefully.”

The MAX fleet has been grounded world-wide since the second crash in March, while Boeing and the Federal Aviation Administration complete a software fix to make MCAS less potent and have it rely on dual sensors. Chief Executive Dennis Muilenburg recently told investors Boeing would examine how it could improve the process of developing airplanes.

Boeing’s test pilots are an elite full-time crew, usually consisting of former military aviators, who try out systems on new aircraft before engineering specifics are locked in. Such test flights occur before the final version of the airplane is produced, cockpit procedures are set and the aircraft is delivered to customers.

Boeing’s management has long prided itself on close collaboration between test pilots and engineering staff. For decades, and particularly through the development of the first version of the wide-body 777 in the early 1990s, Boeing talked up how its roster of pilots and commercial aviators specifically recruited for feedback provided suggestions about the model’s cockpit design and function.

A senior Boeing executive said pilots have remained intimately involved in aircraft development. “The test pilots have to be fully aware of what those capabilities are, and how the airplane will respond in those situations because they are ultimately the judge and jury,” the senior Boeing executive said in a recent Wall Street Journal interview.

After Boeing decided to develop the MAX in 2011, executives overseeing the program welcomed and acted upon pilots’ suggestions, including adding larger cockpit displays, a senior pilot involved in the process said. Any suggestions that touched on safety got full attention, this pilot said.

But over time, an internal restructuring that began in 2009 introduced changes in that process, eventually reducing pilots’ clout, according to people familiar with pilots’ role in the process. Boeing had consolidated its testing and evaluation teams into a companywide group of pilots and labs to streamline operations as it kept a lid on costs. The teams had previously worked independently within Boeing’s commercial and defense divisions, which some pilots say had the effect of keeping aviators closer to engineering divisions on particular development programs.

About midway through the MAX’s development, the senior pilot recalls warning a Boeing executive about taking pilots out of the loop: “Something is going to get by, and it’s not going to be pretty.”

The senior Boeing executive said he hadn’t heard such concerns and defended the consolidated testing group. The restructuring added no additional cost pressure for testing, he said, and instead strengthened the group by making more resources available across the company.

The MCAS system was a new addition to Boeing’s 737 series, meant to kick in automatically and operate in the background to prevent a plane from stalling. A stall can occur when a plane is flying too slowly and its nose is too high to maintain lift. In the MAX, MCAS uses sensor data about the plane’s angle to push down its nose and keep it from stalling.

One former Boeing pilot who participated in some later-stage MAX test flights recalls hearing about MCAS in a general way, but wasn’t given further details. For instance, this pilot never learned about the system’s reliance on a single sensor transmitting data about the angle of a plane’s nose, or how far MCAS would be able to move a plane’s adjustable tail fin known as a “horizontal stabilizer,” which controls the up-and-down movement of a jet’s nose.

Test pilots did have the opportunity to try out the MAX and its automated system under various scenarios, but those didn’t include testing the full force of MCAS, some of these people said. Looking back, some pilots contend Boeing could have missed design flaws given their cohort’s at times limited involvement in the craft’s development.

In 2016, a year before the MAX began commercial service, some test pilots suggested adapting MCAS, initially designed to operate at high speeds, to also work when the plane was traveling at slower speeds, according to one of the people familiar with the matter. By then, test pilots had less say in how design revisions were implemented. They also weren’t told explicitly that in its final iteration, MCAS commands would be four times as powerful than in earlier versions, according to people familiar with the matter. That change was earlier reported by the Seattle Times.

In hindsight, test pilots “had no real input” into the ultimate MCAS design, one of the people said.

Senior Boeing pilots at times found themselves excluded from meetings involving engineers, prompting them to sometimes invite themselves or show up unannounced, according to this person. The senior Boeing executive said last week that current development programs aren’t characterized by such friction.

Share this post


Link to post
Share on other sites

https://aviationweek.com/commercial-aviation/update-boeing-did-not-fix-max-aoa-warning-issue-found-2017

UPDATE: Boeing Did Not Fix MAX AOA Warning Issue Found in 2017

May 6, 2019 Sean Broderick | Aviation Daily
 

WASHINGTON—New questions are being raised over the development and oversight of the Boeing 737 MAX after revelations the manufacturer knew about a mis-configured angle of attack disagree annunciator alert message on the aircraft in 2017 but did not fix it or tell operators about the problem until after last October’s crash of a 737 MAX 8—the first of two to strike the model in five months.

Boeing on May 5 clarified that within “several months” after MAX deliveries began in May 2017, it discovered that most of its 737 MAXs were being delivered without angle-of-attack (AOA) disagree alert message being activated as intended. It determined the issue was not a safety risk, however, and planned to address it as part of routine flight control software updates. The revelation adds more context to why the amber AOA Disagree alert messages, meant to tell pilots of a discrepancy between the aircraft’s two AOA sensors, have only been active on MAX aircraft equipped with a package of options.

“The Boeing design requirements for the 737 MAX included the AOA disagree alert as a standard, standalone feature, in keeping with Boeing’s fundamental design philosophy of retaining commonality with the 737NG,” Boeing said. “In 2017, within several months after beginning 737 MAX deliveries, engineers at Boeing identified that the 737 MAX display system software did not correctly meet the AOA disagree alert requirements. The software delivered to Boeing linked the AOA disagree alert to the AOA indicator, which is an optional feature on the MAX and the NG. Accordingly, the software activated the AOA disagree alert only if an airline opted for the AOA indicator.”

Boeing’s statement does not discuss whether the software was developed to its specifications, or whether the vendor introduced the error. Boeing’s statement does not name the vendor, but it is Collins Aerospace. Collins referred all questions to Boeing.

After it discovered the issue, Boeing said it followed its “standard process for determining the appropriate resolution of such issues,” including a review with “multiple company subject-matter experts.” The review “determined that the absence of the AOA disagree alert did not adversely impact airplane safety or operation,” Boeing said. “Accordingly, the review concluded, the existing functionality was acceptable until the alert and the indicator could be delinked in the next planned display system software update.”

Boeing’s senior management was not involved in the review, and neither Boeing’s senior leadership nor FAA were made aware of the issue until after the Oct. 29, 2018, crash of Lion Air Flight 610.

The AOA sensors provide key data to the MAX’s maneuvering characteristics augmentation system (MCAS) flight control law that is the focus of two fatal 737-8 accidents—Lion Air flight 610 and the Mar 10 crash of Ethiopian Airlines flight 302—in which all 346 people were killed and that have left the MAX fleet grounded.

In each accident, faulty data sent by one AOA sensor told the aircraft’s flight control computer that its nose was too high, causing MCAS to command horizontal stabilizer nose down trim. Preliminary reports on each accident suggest the pilots were not able to diagnose the failure quickly enough.

The original MCAS is programmed to command nose down trim if the AOA data shows the angle of attack is too high. Pilots can counter it in two ways: with electric trim input or via the manual trim wheel. Electric trim input resets MCAS, meaning faulty AOA data would trigger it again after a 5 sec. delay. In both accident sequences, the pilots countered with electric trim, setting up the MCAS’s cyclical activation.

Boeing’s safety analysis determined that crews would diagnose an unwanted MCAS activation as stabilizer runaway, and would follow the appropriate checklist, which includes de-powering the stabilizer trim motors by turning off the trim cutout switches, leaving the manual trim wheels as the only elevator trim inputs. The Ethiopian crew toggled off the cutout switches, but could not manually trim the aircraft at the relatively high indicated airspeed, so they turned on the trim cutout switches, which set the stage for MCAS to re-engage.

Neither Lion Air nor Ethiopian Airlines had the optional AOA disagree indicator package. The accident sequences would have triggered AOA disagree alerts, adding it to several that activated, including a stick-shaker stall warning.

Following the Lion Air accident, Boeing convened a “safety review board” (SRB) to revisit whether the AOA Disagree issue was a safety risk. “That SRB confirmed Boeing’s prior conclusion that it did not,” Boeing said. “Boeing shared this conclusion and the supporting SRB analysis with the FAA.”

Addressing reporters following a Boeing shareholder meeting Apr. 29, Boeing CEO Dennis Muilenburg downplayed the significance of the AOA Disagree alert’s role in delivering key information to pilots. “It’s not something that drives pilot action,” he said. “It’s not something that we designed in as a primary flight display in the flight deck of a commercial airplane. What pilots care about are things like altitude, airspeed, heading, pitch and roll. That’s what they fly. Those indicators are in the flight deck today. Airspeed and altitude in particular are the relevant items around these two [accidents].”

Even if the absence of the AOA Disagree lights is not linked to either accident, the issue adds more questions to the MAX’s development, and how much airlines knew about changes from the 737NG. MCAS was not on the NG, and most pilots didn’t know it existed until after the Lion Air accident.

Since just after the Lion Air accident, Boeing has described the AOA Disagree as an available option on the MAX, which was accurate. It was not until Apr. 29 that it explained the AOA Disagree’s status as an option was a mistake—it was supposed to be standard, as it is on the NG. Six days later, it acknowledged that it has known about this problem since mid-2017.

Boeing is updating MCAS, using both AOA sensors to prevent the system from acting on a single faulty sensor. The changes also will limit MCAS’s authority, in part by removing its ability to reset itself and potentially fire again based on faulty AOA data when the crew provides electric stabilizer trim input to counter it. 

In addition, Boeing will make both the AOA disagree alerts and AOA indicator standard on all MAXs, including offering free modifications for aircraft already delivered.

Note: This story has been updated from the original version published May 5. It includes additional details and clarifications on MCAS's operation and the AOA Disagree alert's intended function.

Edited by moeman

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this