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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.
(Score: 1, Informative) by Anonymous Coward on Saturday March 30 2019, @08:21PM (9 children)
My car has a bad sensor that keeps "randomly" activating my antilock breaks, which overrides my attempts to stop the car.
Also, the 737 MAX has about the expected accident rate for a plane with so few flights:
https://i.ibb.co/n138VFj/planecrash.png [i.ibb.co]
(Score: 1, Informative) by Anonymous Coward on Saturday March 30 2019, @10:02PM (2 children)
That's the breaks, sorry to hear that your antilock brakes are broken. [usage nut, sorry, can't help myself]
(Score: 0) by Anonymous Coward on Saturday March 30 2019, @10:19PM (1 child)
Thanks, for some reason I keep making that typo.
On the plus side I am no longer afraid to fly since driving a car with unreliable breaks is far more dangerous.
(Score: 1, Touché) by Anonymous Coward on Saturday March 30 2019, @10:35PM
I hope one day you can find a way to brake that habit.
(Score: 1, Informative) by Anonymous Coward on Sunday March 31 2019, @01:54AM
Airbus A320 had...issues... when it first came out with its software, too. Airbus philosophy then was "Otto Pilot Uber alles" - the autopilot would not disengage if pilot inputs contradicted the autopilot, whereas Boeing's systems then would. This did result in a few crashes early on. One incident in particular was recorded, where the plane was obviously struggling trying to figure out level flight, and crashed into a forest. At the time, there wasn't a way for the pilots to turn off that particular system... I think Airbus adjusted their thinking a little bit after a few crashes...
(Score: 2) by sgleysti on Sunday March 31 2019, @07:29AM (2 children)
I had the same problem on my car. It turned out to be a cracked reluctor ring; I had to replace the axel (half shaft?) for that wheel, since the ring itself could not be removed from the axel.
(Score: 2) by driverless on Sunday March 31 2019, @08:23AM (1 child)
I'm having a bit of trouble following that, could you explain it using a car analogy?
(Score: 1) by Sulla on Sunday March 31 2019, @03:29PM
Not a problem my man. You see the problem with a bad sensor causing ABS failure requiring the replacement of the half-shafts, if we were to use a car analogy, is like the sensor detecting window level failing so your have to replace the driver side door.
Ceterum censeo Sinae esse delendam
(Score: 2) by sonamchauhan on Sunday March 31 2019, @10:10AM
What a nonsensical post.
300 planes and 2 crashes with all passengers killed. Try telling that to your bus company or metro with a straight face.
(Score: 3, Informative) by RS3 on Monday April 01 2019, @04:44PM
Detailed explanation for those who don't know: ABS sensors are usually a (wire) coil around a permanent magnet which is located in close proximity to a reluctor ring (looks like a gear) which is around an axle or wheel hub. As the wheel rotates, the moving reluctor ring teeth create a varying magnetic field strength which induces an electric current in the coil. The coil is connected to the ABS electronic controller.
The symptom you described is usually steel dust particles stuck to the the magnet. They tend to form a magnetic short-circuit so that there is much less current induced in the coil, so the ABS system gets very little signal, so it thinks you have a wheel lockup and it kicks in. I suspect a lot of perfectly good ABS sensors get replaced for this reason.
One of my vehicles has a fairly audible ABS system, and every now and then it would randomly buzz for a second. I investigated, found the glob of iron dust, cleaned it out, and no more random ABS events. No new sensor needed. :)