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posted by chromas on Saturday March 30 2019, @08:12PM   Printer-friendly
from the press-X-to-not-dive dept.

Initial Findings Put Boeing's Software at Center of Ethiopian 737 Crash:

At a high-level briefing at the Federal Aviation Administration on March 28, officials revealed "black box" data from Ethiopian Airlines Flight 302 indicated that the Boeing 737 MAX's flight software had activated an anti-stall feature that pushed the nose of the plane down just moments after takeoff. The preliminary finding officially links Boeing's Maneuvering Characteristics Augmentation System (MCAS) to a second crash within a five-month period. The finding was based on data provided to FAA officials by Ethiopian investigators.

The MCAS was partly blamed for the crash of a Lion Air 737 MAX off Indonesia last October. The software, intended to adjust the aircraft's handling because of aerodynamic changes caused by the 737 MAX's larger turbofan engines and their proximity to the wing, was designed to take input from one of two angle-of-attack (AOA) sensors on the aircraft's nose to determine if the aircraft was in danger of stalling. Faulty sensor data caused the MCAS systems on both the Lion Air and Ethiopian Airlines flights to react as if the aircraft was entering a stall and to push the nose of the aircraft down to gain airspeed.

On March 27, acting FAA Administrator Daniel Ewell told the Senate Commerce, Science, and Transportation Committee's aviation subcommittee that there had been no flight tests of the 737 MAX prior to its certification to determine how pilots would react in the event of an MCAS malfunction. He said that a panel of pilots had reviewed the software in a simulator and determined no additional training was required for 737-rated pilots to fly the 737 MAX.

What follows is from memory from what I've gleaned from reading several news accounts over the past few weeks. I am not a pilot, so take this with the proverbial $unit of salt.

The design of the MAX version of the Boeing 737 used a larger diameter engine so as to improve fuel economy. Because the original 737 was designed to be low to the ground to facilitate boarding (no jetways back then), it required the engines to be mounted forward and higher than in previous models. This introduced a change in the flight dynamics. Adding throttle in certain conditions would cause the plane to "nose up". Because of the shear size of the engine nacelles, this further increased the lift of the nose (more surface exposed at an angle to the air flow). This would cause further lift and would exacerbate the situation. Boeing wanted pilots to be able to fly the MAX without undergoing expensive retraining. How can they make a different aircraft behave like its predecessor, the 737-NG? The solution Boeing came up with was MCAS which — in certain circumstances — was designed to push the plane's nose back down. So much authority was provided to this adjustment, and its repeated application in some cases, that it could lead to driving the plane downward in spite of the pilot's efforts to maintain level flight. Complicating matters, there was no mention of MCAS in any of Boeing's training materials: pilots were not even aware it was there.

It would be easy to "armchair quarterback" Boeing's decisions. The airline industry was transitioning from its hub-and-spoke system (which favored larger planes) to having a greater number of direct (no layover) flights which favored smaller aircraft. In the meantime Airbus had come out with a new model of more efficient aircraft which fit this flight profile. Boeing could have come up with a clean-slate design for a new aircraft, but that would require several years from design to construction to certification. They elected to modify the 737, instead. As long as it was sufficiently similar (I'm waving my hands around a bit here), it could be sold based on the certification of its earlier models. So, they decided to modify the 737... but not too much so as to avoid the time-consuming recertification process.

I've heard it said, "The longest distance between two points is a shortcut." It is sad that this shortcut appears to have been responsible for two flights crashing shortly after takeoff and killing nearly 350 people.


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  • (Score: 5, Interesting) by c0lo on Saturday March 30 2019, @11:48PM

    by c0lo (156) Subscriber Badge on Saturday March 30 2019, @11:48PM (#822538) Journal

    Seattle Times [seattletimes.com] - "Lack of redundancies on Boeing 737 MAX system baffles some involved in developing the jet":

    A faulty reading from an angle-of-attack sensor (AOA) — used to assess whether the plane is angled up so much that it is at risk of stalling — is now suspected in the October crash of a 737 MAX in Indonesia, with data suggesting that MCAS pushed the aircraft’s nose toward Earth to avoid a stall that wasn’t happening. Investigators have said another crash in Ethiopia this month has parallels to the first.

    Boeing has been working to rejigger its MAX software in recent months, and that includes a plan to have MCAS consider input from both of the plane’s angle-of-attack sensors, according to officials familiar with the new design.

    “Our proposed software update incorporates additional limits and safeguards to the system and reduces crew workload,” Boeing said in a statement.

    But one problem with two-point redundancies is that if one sensor goes haywire, the plane may not be able to automatically determine which of the two readings is correct, so Boeing has indicated that the MCAS safety system will not function when the sensors record substantial disagreement.

    Quartz [qz.com] - "The word “kludge” keeps coming up when pilots and engineers discuss Boeing’s 737 Max"

    A kludge, as Granholm notes, isn’t the work of amateurs—it’s a combination of complexity and “designasininity” that introduces errors in some unrelated, unexpected part.

    In the case of the 737 Max, it’s the combination of how two separate problems interacted—a plane whose design introduced aerodynamics issues and what now appears to have been a poorly designed anti-stall system—that seems to be drawing many to turn to Granholm’s term. The problems were compounded in many ways, including by the fact that pilots were not told of or trained for the Maneuvering Characteristics Augmentation System (MCAS) before the Lion Air crash, which killed all 189 on board.

    “Indeed, it seems the 737 MAX was a kludge to an existing design, and that MCAS was a kludge on top of that,” said a commenter on Hackaday.

    Indonesia’s preliminary report showed that the anti-stall system repeatedly pushed the plane’s nose down in response to erroneous data about the angle of the plane from a single sensor. As pilots desperately tried to redirect it, the system responded by again pushing the nose down. A previous method of counteracting this action had been disabled.

    Naked Capitalism [nakedcapitalism.com] - "Boeing Doubles Down on 737 Max, Rejects Need for Simulator Training"

    Reuters, which has a bias towards understatement, has an atypically pointed farming Boeing’s refusal to recommend pilot simulator training for the MCAS:

    Boeing Co said it will submit by the end of this week a training package that 737 MAX pilots are required to take before a worldwide ban can be lifted, proposing as it did before two deadly crashes that those pilots do not need time on flight simulators to safely operate the aircraft.

    In making that assessment, the world’s largest planemaker is doubling down on a strategy it promoted to American Airlines Group Inc and other customers years ago. Boeing told airlines their pilots could switch from the older 737NG to the new MAX without costly flight simulator training and without compromising on safety, three former Boeing employees said.

    Specifically, the Wall Street Journal reported that Southwest, which is the biggest buyer of the 737 Max, got Boeing to agree to a financial penalty if the new plane required additional simulator training.

    The company had promised Southwest Airlines Co. , the plane’s biggest customer, to keep pilot training to a minimum so the new jet could seamlessly slot into the carrier’s fleet of older 737s, according to regulators and industry officials.

    [Former Boeing engineer Mr. [Rick] Ludtke [who worked on 737 MAX cockpit features] recalled midlevel managers telling subordinates that Boeing had committed to pay the airline $1 million per plane if its design ended up requiring pilots to spend additional simulator time. “We had never, ever seen commitments like that before,” he said.

    Vox [vox.com] - "The emerging 737 MAX scandal, explained"

    As CBS Moneywatch’s Brett Snyder wrote back in December 2010, the basic problem was that you couldn’t slap the new generation of more efficient, larger-diameter engines onto the 737:

    One of the issues for Boeing is that it takes more work to put new engines on the 737 than on the A320. The 737 is lower to the ground than the A320, and the new engines have a larger diameter. So while both manufacturers would have to do work, the Boeing guys would have more work to do to jack the airplane up. That will cost more while reducing commonality with the current fleet. As we know from last week, reduced commonality means higher costs for the airlines as well.

    ..
    Boeing decided to put the too-big engines on anyway

    As late as February 2011, Boeing chair and CEO James McNerney was sticking to the plan to design a totally new aircraft.

    “We’re not done evaluating this whole situation yet,” he said on an analyst call, “but our current bias is to move to a newer airplane, an all-new airplane, at the end of the decade, beginning of the next decade. It’s our judgment that our customers will wait for us.”

    It’s not entirely clear what happened, but, reading between the lines, it seems that in talking to its customers Boeing reached the conclusion that airlines would not wait for them. Some critical mass of carriers (American Airlines seems to have been particularly influential) was credible enough in its threat to switch to Airbus equipment that Boeing decided it needed to offer 737 buyers a Boeing solution sooner rather than later.

    Committing to putting a new engine that didn’t fit on the plane was the corporate version of the Fyre Festival’s “let’s just do it and be legends, man” [complex.com] moment, and it not surprisingly wound up leading to a slew of engineering and regulatory problems.
    ...
    Recall, after all, that the whole point of the 737 MAX project was to be able to say that the new plane was the same as the old plane. From an engineering perspective, the preferred solution was to actually build a new plane. But for business reasons, Boeing didn’t want a “new plane” that would require a lengthy certification process and extensive (and expensive) new pilot training for its customers. The demand was for a plane that was simultaneously new and not new.

    --
    https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
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