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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 23rd Mar 2019, 20:34
  #2421 (permalink)  
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Originally Posted by 73qanda View Post
FCeng84 or anyone more knowledgeable than me can you explain any relationship between the Feel diff press defect ( written up on the Lion Air aircraft) and the AOA vane?
My thoughts were that Feel Diff Press meant either a hyd system failure or the elevator pitot was in trouble.
Incorrect AoA data can cause the aircraft to "believe" it's in a stall situation, when it is not.

As a result it can increase the feel pressure to 4 times the normal pressure, to make it harder to pull the control column and bring the aircraft deeper into the stall.
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Old 23rd Mar 2019, 20:57
  #2422 (permalink)  
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Originally Posted by FCeng84 View Post
Hopefully Boeing will make the details of the MCAS modification clearer soon. MCAS in its original implementation would run again in the presence of AOA failed high following any amount of pilot pitch trim command. One can envision a modification to require that the pilot have run the trim back nose up at least a certain amount before allowing MCAS to go again. Or how about requiring that AOA drop low after having been high before allowing MCAS to go again. There are lots of things that could be done to provide additional interlocks. I am certain that we will learn that simply blipping trim with the revised logic will not trigger MCAS to reset to the point of running in another full increment of airplane nose down stabilizer motion.
From a programming point of view, having a system remember its previous state, and respond differently, creates all kinds of complexity. I would never want to go down that route, but can't see simple ways of avoiding the threat of multiple false MCAS activation, while still catering for repeated stalls.

Knowledge of the actual value of the trim stabiliser would be interesting, but I have not seen any mention of that as an input parameter.
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Old 23rd Mar 2019, 21:03
  #2423 (permalink)  
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The analysis by “Satcom Guru” is intriguing. He has found that the digital representation of AOA in the 737 is expressed as a 26 bit binary word, and if the 26th bit becomes incorrectly set (goes from binary zero to binary 1), it will correspond to an AOA of exactly 22 degrees, which is what the FDR on the Lion Air flight recorded for the left AOA sensor.

I strongly suspect that there was nothing wrong with the AOA sensor on LionAir - but rather some kind of intermittent hardware or software fault in the downstream conversion of the position data from analog to digital. If this also happened on Ethiopian, then the cause of this possible data corruption is going to have to be found and corrected on the Max in addition to any changes made to the MCAS system.
Hence my concern:- Because MCAS software was not produced to Level A, it is not assured to be at a high enough standard to allow it to directly control the stabilizer. The risk is that there could be a fault in the software that could cause an erroneous trim condition. The proposed patch may not have any effect on such a software fault.
If I were a betting man, I would put a few pounds on this suggestion. Failure of the AoA sensor seems to being clutched at like the proverbial man and a straw, but I've yet to see anything which confirms this. Let's hope Boeing are also pouring over the code with a very fine toothcomb.

Peter Lemme (Satcom Guru) has also commented on the AoA versus software issue.
The replacement of the identified "faulty AOA" sensor with another AOA sensor immediately before the Lion Air crash did not prevent the same "faulty AOA" sensor signal from reoccurring.

And why was the AOA faulty signal accompanied by similtaneous altitude, airspeed disagree indications along with PCU fault?

I agree that this all seems to be pointing at faulty sensor signal conditioning or processing in the air data computer software.

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Old 23rd Mar 2019, 22:18
  #2424 (permalink)  
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Here you go Blue Max

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Old 23rd Mar 2019, 22:34
  #2425 (permalink)  
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All these known issues with AoA sensors....from Boeing themselves Aero-12:

Stall warning devices have been mounted on the wing, but most modern commercial jet airplanes have movable leading edges that would interfere with such an installation. Most have the sensor located on the fuselage, far ahead of the wing, reducing the effect of changes in lift and configuration. Nearer to the nose of the airplane, the airflow is relatively clean and the boundary layer is thin, minimizing the required probe height.

Even at the nose, many factors can affect the relationship between the local AOA and true wing AOA (fig. 9). The angle of airflow around the nose is not the same as at the wing.

Also, the sensitivity to changes in AOA is greater, so a 1-deg change in true wing AOA causes a local flow change at the nose of 1.5 to 2 deg.

The trailing-edge flap position has an influence on a typical AOA sensor calibration, as has landing gear position (in particular, that of the nose landing gear doors).

Mach number affects the flow around the nose and therefore changes the sensor calibration.

Pitching the airplane can cause erroneous readings at the sensor. While the nose is pitching up (as in a turn), the local flow angle is reduced, causing the reading to be too low. Although the sensors are placed to minimize the effect of sideslip, it is not eliminated and can be quite significant at sideslip angles that may occur on short final approaches or with an engine out.

Even variations in the contour of the skin near the sensor can subtly affect the local flow angle. Many of these design challenges also affect pitot and static port installation and accuracy.

The sensor itself has potential for error. The combination of installation error, zero bias, and aerodynamic inaccuracy can total 0.5 deg or more. Contamination or damage can also affect the sensors accuracy.

For the most part, the effects discussed above can be compensated for and, depending on the airplane, many have been.

It should be noted, however, that each correction has its own inherent uncertainty and can also cause erroneous readings if the input data is incorrect.

Last edited by Smythe; 24th Mar 2019 at 02:42.
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Old 23rd Mar 2019, 22:58
  #2426 (permalink)  
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NYT article:Boeing Was ‘Go, Go, Go’ to Beat Airbus With the 737 Max

NYT article:Boeing Was ‘Go, Go, Go’ to Beat Airbus With the 737 Max

Boeing Was ‘Go, Go, Go’ to Beat Airbus With the 737 Max
By David Gelles, Natalie Kitroeff, Jack Nicas and Rebecca R. Ruiz

Boeing faced an unthinkable defection in the spring of 2011. American Airlines, an exclusive Boeing customer for more than a decade, was ready to place an order for hundreds of new, fuel-efficient jets from the world’s other major aircraft manufacturer, Airbus.

The chief executive of American called Boeing’s leader, W. James McNerney Jr., to say a deal was close. If Boeing wanted the business, it would need to move aggressively, the airline executive, Gerard Arpey, told Mr. McNerney.

To win over American, Boeing ditched the idea of developing a new passenger plane, which would take a decade. Instead, it decided to update its workhorse 737, promising the plane would be done in six years.

The 737 Max was born roughly three months later.

The competitive pressure to build the jet — which permeated the entire design and development — now threatens the reputation and profits of Boeing, after two deadly crashes of the 737 Max in less than five months. Prosecutors and regulators are investigating whether the effort to design, produce and certify the Max was rushed, leading Boeing to miss crucial safety risks and to underplay the need for pilot training.

While investigators are still trying to determine the cause of the crash in Ethiopia this month and one in Indonesia in October, they are focused on a newly installed piece of software designed to avoid stalls. The software was meant to compensate for bigger, more fuel-efficient engines and ensure the plane flew the same way as an earlier version.

Months behind Airbus, Boeing had to play catch-up. The pace of the work on the 737 Max was frenetic, according to current and former employees who spoke with The New York Times. Some spoke on the condition of anonymity because of the sensitivity of the matter.

Engineers were pushed to submit technical drawings and designs at roughly double the normal pace, former employees said. Facing tight deadlines and strict budgets, managers quickly pulled workers from other departments when someone left the Max project. Although the project had been hectic, current and former employees said they had finished it feeling confident in the safety of the plane.

The specter of Boeing’s chief rival was constant. Airbus had been delivering more jets than Boeing for several years. And losing the American account would have been gutting, costing the manufacturer billions in lost sales and potentially thousands of jobs.

“They weren’t going to stand by and let Airbus steal market share,” said Mike Renzelmann, an engineer who retired in 2016 from Boeing’s flight control team on the 737 Max.

The successful end of a 2014 test flight of the Airbus A320neo. When Airbus announced plans for the plane in 2010, a Boeing executive told employees that it posed no threat.

Dismissing a Rival

Boeing didn’t seem bothered at first by the A320neo, the fuel-efficient plane that Airbus announced in 2010.

At a meeting in January of the next year, James F. Albaugh, the chief executive of Boeing’s commercial airplanes division, told employees that Airbus would probably go over budget creating a plane that carriers didn’t really want, according to a recording of the meeting reviewed by The Times.

Mr. Albaugh boasted that carriers were already paying more for Boeing’s single-aisle jet than the Airbus version. He didn’t see the need to strike now — Boeing could wait until the end of the decade to produce a new plane from scratch, the executive said.
“I don’t think we need to get too spun up over the fact that they’re making some sales,” he said.

For decades, Airbus was barely on Boeing’s radar. A consortium started in 1970 by several European countries, it was slow to compete globally. Boeing, founded in 1916, dominated the passenger-jet market with its 737 midsize jet and the 747 jumbo jet.

Then came John Leahy, an American who rose through the ranks to become the chief Airbus salesman in 1994. Mr. Leahy was relentless. Once, the chief executive of an airline got sick just as a deal was about to close. Mr. Leahy traveled to the man’s house, and the executive signed the papers while wearing his bathrobe.

“Boeing thought we were a flash in the pan,” Mr. Leahy said in an interview. “But I thought there was no reason we couldn’t have 50 percent of the market.”

Mr. Leahy scored a major coup in 1999 when JetBlue decided to launch with a fleet composed entirely of Airbus A320s. In the years that followed, more low-cost carriers around the world, like easyJet, placed big orders, too.

Airbus had pulled ahead of Boeing by 2005. “Boeing has struggled with the development work needed to take the company into the 21st century,” Tim Clark, president of Emirates, the Dubai airline, said that year. Airbus, he said, “has been braver, more brazen.”

In 2008, Airbus delivered 483 airplanes, while Boeing delivered just 375. Three years later at the Paris Air Show, Airbus took orders for 730 aircraft, worth some $72.2 billion, with its new fuel-efficient version dominating.

“Boeing was just completely arrogant in dismissing the viability of the A320,” said Scott Hamilton, managing director of the Leeham Company, an aviation consulting firm.

As American considered placing its largest-ever aircraft order exclusively with Airbus in the spring of 2011, executives at the carrier initially didn’t believe Boeing thought that the threat was real, according to a person involved with the discussions, who spoke on the condition of anonymity.

Airbus had a team camped out in a suite at the Ritz-Carlton in Dallas, near American’s headquarters. Mr. Leahy traveled to Dallas and dined with the American chief, Mr. Arpey, at the Mansion on Turtle Creek, a five-star hotel. Boeing visited less frequently, according to several people involved in the sales process.

With American pondering which planes to buy, Boeing made a business decision. A former senior Boeing official said the company opted to build the Max because it would be far quicker, easier and cheaper than starting from scratch, and would provide almost as much fuel savings for airlines.

Eventually, American decided to make deals with both Boeing and Airbus, buying hundreds of jets from each. Mr. Arpey called Mr. McNerney again, this time reading from a script to carefully calibrate his words. First, he congratulated the Boeing chief on the deal, according to the person with knowledge of the discussions. Then he broke the news that American would also place an order with Airbus.

'Intense Pressure Cooker'

Inside Boeing, the race was on. Roughly six months after the project’s launch, engineers were already documenting the differences between the Max and its predecessor, meaning they already had preliminary designs for the Max — a fast turnaround, according to an engineer who worked on the project.

“The timeline was extremely compressed,” the engineer said. “It was go, go, go.”

One former designer on the team working on flight controls for the Max said the group had at times produced 16 technical drawings a week, double the normal rate. “They basically said, ‘We need something now,’” the designer said.

A technician who assembles wiring on the Max said that in the first months of development, rushed designers were delivering sloppy blueprints to him. He was told that the instructions for the wiring would be cleaned up later in the process, he said.

His internal assembly designs for the Max, he said, still include omissions today, like not specifying which tools to use to install a certain wire, a situation that could lead to a faulty connection. Normally such blueprints include intricate instructions.

Despite the intense atmosphere, current and former employees said, they felt during the project that Boeing’s internal quality checks ensured the aircraft was safe.

In a statement, Boeing said: “The Max program launched in 2011. It was offered to customers in September 2012. Firm configuration of the airplane was achieved in July 2013. The first completed 737 Max 8 rolled out of the Renton factory in November 2015.”

The company added, “A multiyear process could hardly be considered rushed.”

At the heart of Boeing’s push was a focus on creating a plane that was essentially the same as earlier 737 models, important for getting the jet certified quickly. It would also help limit the training that pilots would need, cutting down costs for airlines.

Rick Ludtke, an engineer who helped design the 737 Max cockpit and spent 19 years at Boeing, said the company had set a ground rule for engineers: Limit changes to hopefully avert a requirement that pilots spend time training in a flight simulator before flying the Max.

“Any designs we created could not drive any new training that required a simulator,” Mr. Ludtke said. “That was a first.”

When upgrading the cockpit with a digital display, he said, his team wanted to redesign the layout of information to give pilots more data that were easier to read. But that might have required new pilot training.

So instead, they simply recreated the decades-old gauges on the screen. “We just went from an analog presentation to a digital presentation,” Mr. Ludtke said. “There was so much opportunity to make big jumps, but the training differences held us back.”

“This program was a much more intense pressure cooker than I’ve ever been in,” he added. “The company was trying to avoid costs and trying to contain the level of change. They wanted the minimum change to simplify the training differences, minimum change to reduce costs, and to get it done quickly.”

Boeing said in a statement that the 2011 decision to build the Max had beaten out other options, including developing a new airplane.

“The decision had to offer the best value to customers, including operating economics as well as timing, which was clearly a strong factor,” the company said. “Safety is our highest priority as we design, build and support our airplanes.”

A Cascade of Changes

Months before Boeing’s announcement of the Max, the commercial airplanes executive, Mr. Albaugh, critiqued the decision by Airbus to refit the A320 with bigger engines, which could alter the aerodynamics and require big changes to the plane.

“It’s going to be a design change that will ripple through the airplane,” Mr. Albaugh said in the meeting with employees.

“I think they’ll find it more challenging than they think it will be,” he told them. “When they get done, they’ll have an airplane that might be as good as the Next Generation 737,” a plane that Boeing had launched in 1997.

But a main selling point of the new A320 was its fuel-efficient engines. To match Airbus, Boeing needed to mount the Max with its own larger and powerful new engines.

Just as Mr. Albaugh had predicted for Airbus, the decision created a cascade of changes. The bigger engines altered the aerodynamics of the plane, making it more likely to pitch up in some circumstances.

To offset that possibility, Boeing added the new software in the Max, known as MCAS, which would automatically push the nose down if it sensed the plane pointing up at a dangerous angle. The goal was to avoid a stall. Because the system was supposed to work in the background, Boeing believed it didn’t need to brief pilots on it, and regulators agreed. Pilots weren’t required to train in simulators.

The push for automation was a philosophical shift for Boeing, which for decades wanted to keep pilots in control of the planes as much as possible. Airbus, by comparison, tended to embrace technology, putting computers in control. Pilots who preferred the American manufacturer even had a saying: “If it’s not Boeing, I’m not going.”

The new software system is now a focus of investigators who are trying to determine what went wrong in the Ethiopian Airlines crash and the Lion Air tragedy in Indonesia. A leading theory in the Lion Air crash is that the system was receiving bad data from a faulty sensor, triggering an unrecoverable nose dive. All 737 Max jets around the world are grounded, and Boeing has given no estimate of when they might return to flight.

In Renton, Wash., where the 737 Max is produced in a 1.1-million-square-foot plant, the mere possibility that Boeing engineering contributed to the crashes has cast a pall over the factory. After the Lion Air crash, Boeing offered trauma counseling to engineers who had worked on the plane.

“People in my group are devastated by this,” said Mr. Renzelmann, the former Boeing technical engineer. “It’s a heavy burden.”

In a statement, Boeing’s chief executive, Dennis A. Muilenburg, said he had spent time in Renton recently and “saw firsthand the pride our people feel in their work and the pain we’re all experiencing in light of these tragedies.”

Boeing is working on an update to MCAS software. The company was meeting with carriers over the weekend to discuss the update, which is expected to roll out by April. It also intends to make a previously optional safety indicator in its cockpit standard in new Max jets.

The business is increasingly under pressure as airlines reconsider their orders and ask for compensation. But work in Renton is continuing apace.

Boeing now makes a record 52 Maxes a month, and aims to reach 57 by April. As fuselages and plane skeletons continued to chug into the factory by train this past week, crews worked around the clock to make thousands more.

A version of this article appears in print on March 24, 2019, on Page A1 of the New York edition with the headline: A Jet Born of a Frantic Race to Outdo a Rival.
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Old 23rd Mar 2019, 22:59
  #2427 (permalink)  
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@RUTUS, Since there are no other electrical connections in that diagram, the logical conclusion is that indeed on the NG any kind of automatic trim changes can be disabled by the AP cutout switch, and also by the column cutout switch connected in series with it.

I can't find a similar diagram for the MAX, but I remember reading that the cutout system has been redesigned. For example the two cutout switches have been renamed, from MAIN ELECT and AUTO PILOT, to PRI and B/U (primary and backup).

And, if I remember correctly, those two switches don't longer have independent functionality on the MAX, because they are connected together in series. If one of them gets stuck or fails shorted, the other can act a backup for it, so on the MAX both manual cutout switches would disable any kind of electric trim, manual or automatic.

I don't have further details about that, and I wouldn't want to speculate about exactly how it works on the MAX in combination with the column cutout switches, but this has been discussed previously in the Lion Air thread, you may try to look there for more details.
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Old 24th Mar 2019, 00:05
  #2428 (permalink)  
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Originally Posted by FlexibleResponse View Post
The replacement of the identified "faulty AOA" sensor with another AOA sensor immediately before the Lion Air crash did not prevent the same "faulty AOA" sensor signal from reoccurring.
And why was the AOA faulty signal accompanied by similtaneous altitude, airspeed disagree indications along with PCU fault?
There has been no mention of an AOA failure prior to its replacement on the evening prior to the crash. It was apparently replaced as trouble-shooting in response to repeated write-ups of Capt unreliable airspeed & altitude. This did not correct the unreliable airspeed & altitude, but rather introduced an additional failure on the last two flights.
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Old 24th Mar 2019, 00:23
  #2429 (permalink)  
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RUTUS. I fear that so much is being ripped out of this thread that the loss of continuity makes some posts meaningless.

I posted mentioning a previous link that stated that the rear (hidden) switch in each column had been removed from the MAX. If true, and it seems to be, it is a major change, inasmuch as a quick tug against a nose-down trim would not have remotely the same effect.

The changes to the two emergency cut out switches, mentioned again above, are extraordinarily misleading - if not covered in MAX conversion training.
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Old 24th Mar 2019, 00:54
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Originally Posted by Smythe View Post
What is unclear to me is why it is necessary for the AoA sensor to be a vane outside of the ac. It is assumed that airflow is horizontal, and the fuselage/wing combination is at an angle to horizontal. Why is the AoA sensor not internal like the IRU gyro?
Airflow is horizontal only in level flight ! not in climb or descent
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Old 24th Mar 2019, 00:54
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WSJ: Boeing Plans Fixes to Make 737 MAX Stall-Prevention Feature Easier for Pilots to

WSJ: Boeing Plans Fixes to Make 737 MAX Stall-Prevention Feature Easier for Pilots to Control
Subtitled: Federal Aviation Administration officials have tentatively approved sweeping software and pilot-training changes

Boeing Plans Fixes to Make 737 MAX Stall-Prevention Feature Easier for Pilots to Control

Federal Aviation Administration officials have tentatively approved sweeping software and pilot-training changes

By Andy Pasztor and Andrew Tangel

U.S. air-safety regulators have tentatively approved sweeping software and pilot-training changes for Boeing Co.’s BA -2.83% grounded 737 MAX jets, aimed at fixing problems with a suspect flight-control system, according to internal government documents and people familiar with the details.

The extensive revisions, these industry and government officials said, will make the automated stall-prevention feature, called MCAS, less aggressive and more controllable by pilots.

They also said the enhanced training, relying on self-guided interactive instruction on laptops, highlights information about when the system engages and how pilots can shut it off.

The changes amount to a reversal from major design and engineering principles Boeing relied on when it developed the stall-prevention system, which is suspected of causing the fatal dive that killed 189 people on board a Lion Air 737 MAX in Indonesia last October. A team of international crash investigators also is looking into whether a similar problem led to the crash of an Ethiopian Airlines plane less than five months later.

The Federal Aviation Administration has said it was working with Boeing to develop and install a revised MCAS system based on lessons learned from the Lion Air tragedy, but the extent of the changes goes beyond what some industry officials expected. An FAA spokesman declined to comment on specifics of the pending changes.

Accident investigators have said the Lion Air plane got erroneous information from one sensor that caused the stall-prevention system to misfire, repeatedly pushing the nose of the plane and ending at the maximum downward angle even though the pilots were resisting. Authorities have said they see clear similarities between that accident and the Ethiopian crash on March 10.

The modifications, officials said, create a gentler stall-prevention feature, redesigned so it won’t overpower other cockpit commands or misfire based on faulty readings from a single sensor. It is devised to automatically push the nose down only once—for no longer than 10 seconds—if the aircraft is in danger of stalling and losing lift.

The changes have been tentatively approved by FAA officials, the people familiar with the details said, subject to final ground-simulator checks and flight tests. They could be rolled out to airlines’ 737 MAX jets in the next few weeks.

A Boeing official said the new MAX software could still go through revisions, and the timing of formal approval from the FAA and foreign regulators remains fluid.

Even after the changes are fully implemented in the U.S., air-safety regulators in Canada and the EU are poised to conduct their own evaluation of the new software as well as how the FAA initially certified the plane to carry passengers. Those reviews could take months, according to safety experts.

Among other changes, the revised software would rely on two “angle of attack” sensors, rather than one, to measure the upward or downward angle of the wings and nose in flight. If two sensors send data differing by five degrees or more, MCAS wouldn’t activate at all, according to the officials briefed on the tentative changes.

The cockpit crew on the Lion Air flight struggled against MCAS—using manual nose-up commands some two dozen times—before losing control and plunging into the Java Sea at more than 500 miles an hour. The interim accident report revealed a constant 20-degree difference between signals from the sensor on the captain’s side and those from the co-pilot’s-side sensor.

On Saturday, Boeing said it has been “working diligently and in close cooperation with the FAA on the software update,” adding that the company is “taking a comprehensive and careful approach to design, develop and test the software that will ultimately lead to certification” by regulators.

During the investigations of the two crashes, Boeing and the FAA have faced criticism from pilot groups, airlines, politicians and airlines for alleged lapses in the original MCAS design—and for failing to adequately inform aviators.

About a dozen pilots from U.S. and international carriers are getting previews this weekend of the changes in the works, as well as related manuals and training, according to the Boeing official. "We want their feedback,” this official said. “It’s a dialogue.”

The group engaging in this weekend’s preview of the changes includes pilots from U.S. MAX operators: Southwest Airlines Co. , American Airlines Group Inc. and United Continental Holdings Inc., a person familiar with the matter said. On Wednesday, this person added, a larger group of more than 100 pilots from a broad cross section of MAX operators are due at Boeing’s 737 factory in Renton, Wash., for a similar session.

Investigators in the Lion Air crash said faulty data transmitted from a single sensor caused the MCAS system to assume the plane was in danger of stalling. The warnings began during takeoff and continued for much of the roughly 11-minute flight, apparently confusing the pilots and creating a cascade of related warning signals.

Under the new design, warning devices will alert crews if there is a problem with sensors before takeoff or in flight, people familiar with the redesign said.

They said automated commands to move a flight-control surface on the tail, called a horizontal stabilizer, can be counteracted by pilot commands.

The changes will be standard on all 737 MAX aircraft, for which Boeing has roughly 5,000 orders.

A draft FAA document spelling out the training revisions shows pilots now will be specifically informed about “MCAS activation thresholds,” “flight crew alerts” and how to turn off the system by flipping a single switch. Such details weren’t highlighted in earlier manuals or training materials circulated byBoeing.

FAA officials have determined the handing qualities of 737 MAX jets will be close enough to earlier 737 models that pilots won’t need additional training in ground-based simulators, which is expensive for airlines and disruptive to their schedules.
— Alison Sider and Robert Wall contributed to this article.

Write to Andy Pasztor at [email protected] and Andrew Tangel at [email protected]
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Old 24th Mar 2019, 01:55
  #2432 (permalink)  
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Originally Posted by jimjim1 View Post
I doubt very much it was a transmission/reception error on the BUS since that almost certainly has CRC error detection.
This is not correct. The error detection is a simple parity bit and so a bus error is not vanishingly unlikely.

ARINC 429 is pretty crude in the age of the interwebby
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Old 24th Mar 2019, 02:14
  #2433 (permalink)  
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Trim display and restricted sim availability

Two holes in the cheese:

​​​​Control surface position can be displayed on many ECAMs, along with flaps, spoilers, gear, etc. But where are trims shown besides on the wheel and knobs?

It may really help to show trim positions on the ECAM - and what is moving it when in motion: MAN, AP, STS, MCAS.

It might have helped the AF447 crew, especially if control stick/wheel disagree was displayed. But that would cost money and certification effort to develop.

A repeating theme in many posts is the expense, and consequential dearth, of sim sessions to explore the corners of the envelope. Crews are being trained to minimum standards because sims, and performance data in the corners of the envelope, cost money.

Now we see an imperative to develop new designs in a way that minimises, or even better eliminates, sim time.

The MBAs have succeeded at pinching carloads of pennies – but airframes are now outwitting the crews.
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Old 24th Mar 2019, 02:24
  #2434 (permalink)  
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Originally Posted by Loose rivets View Post
I posted mentioning a previous link that stated that the rear (hidden) switch in each column had been removed from the MAX. If true, and it seems to be, it is a major change, inasmuch as a quick tug against a nose-down trim would not have remotely the same effect.

The changes to the two emergency cut out switches, mentioned again above, are extraordinarily misleading - if not covered in MAX conversion training.
The switches are still there & work as always, but do not stop MCAS.
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Old 24th Mar 2019, 02:42
  #2435 (permalink)  
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Originally Posted by BobM2 View Post
The switches are still there & work as always, but do not stop MCAS.
... and they can‘t because that would make the MCAS useless. MCAS is there to change the stick force at high AoA values. To maintain a high AoA at decreasing speed (w/o retrimming) you will need to pull pretty hard. That is exactly the situation where the trim inhibit switches are activated. If they would stop the MCAS it would never be activated in the desired part of the flight envelope.
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Old 24th Mar 2019, 02:48
  #2436 (permalink)  
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After Go!Go!Go! and bad process in design and certification, the rush now is to create a quickfix and use lobbying to push the planes back into the air without an extensive check and recertification.

This may not be smart: the losses during an extensive safety recheck would be painful but bearable. The effect of another "incident" might push Boeing heavily into the red.

It may be useful to blame "foreign pilot" error for every crash, but in the end mostly every plane flown outside the US is flown by a "foreign pilot", and foreign certification authorities might be more eager than the FAA to pursue the issue of certification of the Max after design changes from the previous 737 types.

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Old 24th Mar 2019, 03:18
  #2437 (permalink)  
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Originally Posted by mosquito88 View Post
Perfectly put.
Reliance on a single sensor driving a system that was not known to the crew and that could take over command of the aircraft is sheer madness (not to mention extreme negligence).
the last word of your post will be the crux of the coming legal battle. If found Negligent, there is no shield for a professional engineer (licensed).
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Old 24th Mar 2019, 05:39
  #2438 (permalink)  
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Location: Melbourne, ɐıןɐɹʇsn∀
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A key modification to limiting stabilizer commands is a revision that allows only one trim application for each new trigger of the MCAS system. Under the original design, the MCAS trims the aircraft nose down by moving the horizontal stabilizer up at 0.27 deg./sec. for 9.2 sec., stops for 5 sec., then trims nose down again for 9.2 sec., and continues to do so until the trim reaches the stabilizer travel limit or the crew intervenes. Boeing says that, as before, the crew will retain the capability to override the flight control law using either electric or manual trim, or by following the existing runaway stabilizer procedure and using the cutout switches as reinforced in the Operations Manual Bulletin issued on Nov. 6, 2018.

The enhanced software was demonstrated for the FAA on March 12, the day after the Civil Aviation Administration of China announced the first in a wave of 737 MAX groundings around the world; the FAA followed suit on March 13. Aviation Week was told that the software upgrade certification load, dubbed P12.1, was flown on the first 737-7 developmental aircraft, 1E001.

The greater part of the 1-hr. 20-min. test flight was flown at medium altitude between 13,500 and 17,350 ft. in a racetrack pattern over southwest Washington state. According to data from the flight-tracking website Flightradar24, the crew performed a series of high AOA maneuvers to validate the performance of the revised MCAS. These included at least six conducted during initial ascent, followed by descents from 17,000 to around 14,250 ft., during which speed dropped from more than 330 kt. to less than 180 kt.

The aircraft was then flown to 17,350 ft. and 265 kt. before pitching steeply nose down and recovering at around 15,900 ft. and 295 kt. The maneuver was repeated at a slower speed, before a further test point was conducted during which the 737 descended steeply from around 15,550 ft. to 13,500 while speed increased from 180 kt. to almost 270 kt. Two further steep descents and recoveries were then performed before the aircraft leveled off and returned to Seattle for landing.
Those were great test flights at higher altitudes. I read into the figures some steep descents of maybe 2000 ft even when the pilots presumably knew what to expect. I wonder if Boeing test pilots would like to do a test flight at about 1000ft or even 3000ft above ground (like ET302 or JT610 accidents) in the jump seat while some line pilots, who have not been told what the exercise is, are in the hot seats? Or is the new MCAS disabled until more than say 5000ft above ground? Also for what parameters will the repetitive trimming be restricted. And what will the authority limits of the trim units be and whether different at different speeds and altitudes. If MCAS disables itself for erroneous sensor input, if its moved trim then will it re-trim to a "neutral" or expect the pilots to break out the handles on the trim wheels?

It will be interesting to see the full details of the new MCAS.

Last edited by LandIT; 24th Mar 2019 at 09:43.
LandIT is offline  
Old 24th Mar 2019, 05:56
  #2439 (permalink)  
Join Date: Oct 2017
Location: Vienna
Posts: 129
Originally Posted by deltafox44 View Post
Airflow is horizontal only in level flight ! not in climb or descent
If by horizontal you mean at AoA ~ 0 degrees, that is very, very incorrect
derjodel is offline  
Old 24th Mar 2019, 06:20
  #2440 (permalink)  
Join Date: Jul 2014
Location: Berkeley, Ca
Age: 32
Posts: 6
AoA vane question

Could someone familiar with the AoA vane and MCAS tell me what would happen if a bird strike jammed the vane in either an up or down condition?
Can the system detect a damaged sensor and if not, what would happen?
mosquito88 is offline  

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