obviously im not a pilot. But shouldn’t these planes have some kind of “oh ■■■■” button on the yoke to disconnect the autopilot in an emergency? Seems logical to an untrained eye, and it would appear most military aircraft have some sort of disconnect mechanism located on the main control.
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I would agree with that except that there is probably a LOT of commonality with regards to systems and engineering that shares DNA with the earlier models. I think the engines/airframe pairing was an aerodynamic or performance challenge and I doubt that there are a ton of similarly critical redesigns on the airframe or components within. I think the 737 is a proven and safe airframe…it was just this particular pairing of major components that really should have warranted more scrutiny. And at the cost of many lives, two airframes, and many (tens? hundreds?) of millions of dollars in lost revenue and compensation, that shortcut is going to turn out to be short-sighted. (Assuming again that what we all think is wrong, and is being reported, is what went wrong…)
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I hear you @HavlokUK and totally get it. It’s just that avoiding both the Max and Boeing is going to be a tough commitment for a typical traveler. But if it’s possible, I support it. (But please do make an exception for my airline 
) @Gunnyhighway, you are right that there should be one and, in fact, there is one. But, it does not disable trim. To disable trim you have 3 choices: press and hold the trim switch, grab the trim wheel for dear life, or lift the 2 guarded Stab Cutout Switches and switch them to Cutoff. There is a forth way which MCAS disables: Manually move the yoke in a direction opposite the electric trim motion.
Please allow me to get in the weeds here and make you guys even more informed than you already are. The 737 is not unique among jets in having two other “auto-trim” systems that were probably the inspiration for MCAS: Speed Trim and Mach Trim. Speed Trim begins just after takeoff and is there to create control forces to meet the FAA’s idea of stability. You can tell an experienced 737 pilot because he pre-empts the system by clicking a bit of trim when his intuition tells him that some Speed Trim is about to happen. Typically, and for reasons I never bothered to learn, Speed Trim often trims in the opposite direction than you want for smooth flight. But it is totally minor and easily ignored. Mach Trim helps reposition the yoke as the Center of Pressure changes at (IIRC) around M.75. The A320 trims for the dirt on approach at 50’. This system is calibrated so that the nose would be 2.5 degrees BELOW! the horizon (again IIRC) if the pilot did nothing. Sounds totally crazy right? But the intent is to force you to get the stick out of neutral and create a sense of adding back pressure for the flare. It works perfectly. The idiots who designed MCAS certainly must have thought that they were designing something as innocuous as these common and widely accepted little control tricks to create “feel” where none exists but where human factors designers felt should exist.
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Thanks for the detailed explanation of the system. Is the 5 or 10 second resumption of MCAS after pressing the trim disconnect on the yoke unique to the MAX? That is the part that most puzzles me…a system that reverts back to a protection mode when it has been explicitly commanded off (just not permanently with the two stab cutoff switches). I would think a logic of trim disconnect twice in X seconds should put the system into a standby mode. Is there a light or warning that MCAS has activated? And is it proper to call it a protection mode?
Yes, the Speed Trim I mentioned does the same thing. Totally, 100 percent innocuous in its case. It’s a completely ignorable system that’s been around for 50 years. But Speed Trim is really slow and just tiny little blips of trim applied mainly as a response to power changes (underslung engines cause a pitching moment). And it is Speed Trim, a system every pilot deals with, with some amusement everyday, that led me to believe early on that MCAS was a very big input and not the gentle little nudge that Boeing was claiming. Otherwise, even inexperienced pilots would be totally prepared to deal with it, known system or not.
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I would agree, every pilot knows about Speed and Mach trim in modern airliners, MCAS is a whole different beast and obviously the runaway is not easy to detect now that we know that the crew was scouring the manual and didn’t identify it in time.
Honestly, I’ve lost a lot of respect for Boeing and the FAA during this process and I haven’t seen them take the right actions given the circumstances.
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Some more info, including about the simulators which are still being built:
We were all flying the thing before the first simulator was built. I am still unsure if any US airline has access to a Max simulator even now. Anyway, without practicing the scenario that doomed the two flights, the simulator would be irrelevant.
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I agree, that’s probably not something to hold against them.
Ya, that’s what comes in later in the article from Ethiopian. CAE has only built a few, so they couldn’t even if they wanted to.
Definitely not something I hold against the pilots now given all the information coming forward. Hopefully CAE gets the sims built quickly, without any issues.
Holy heck what a story. So @smokinhole, if I understand it correctly, the thing that could have prevented those crashes would have been the pilots being aware of MCAS, its operation and how to disconnect it?! Sheeeeit, that stinks to high heaven man!
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You got it!
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Some info on the Flight Manual for the MAX’s - MCAS was only in the glossary.
BBC News - Ethiopian Airlines crash: ‘Pitch up, pitch up!’
According to this report, the pilots ‘repeatedly followed procedures recommended by Boeing but could not recover control of the aircraft’. It doesnt make it clear if this included disabling the electric trim.
BBC News - Ethiopian Airlines Boeing 737 pilots ‘could not stop nosedive’
A bit of a chilling read but I think it is appropriate to post here. I copied out some of the interesting events but there’s a lot more to go over.
At 05:40:27, the Captain advised the First-Officer to trim up with him.
At05:40:28 Manual electric trim in the ANU direction was recorded and the stabilizer reversed moving in the ANU direction and then the trim reached 2.3 units.At 05:40:35, the First-Officer called out“stab trim cut-out”two times. Captain agreed and First-Officer confirmed stab trim cut-out.
At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance of AND automatic trim command occurred without any corresponding motion of the stabilizer, which is consistent with the stabilizer trim cutout switches were in the ‘’cutout’’ position
At 05:40:44, the Captain called out three times “Pull-up”and the First-Officer acknowledged.
At 05:40:50, the Captain instructed the First Officer to advise ATC that they would like to maintain 14,000ftand they have flight control problem.
At 05:40:56, the First-Officer requested ATC to maintain 14,000 ft and reported that they are having flight control problem. ATC approved.
From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units.During this time,aft force was applied to the control columns which remained aft of neutral position. The left indicated airspeed increased from approximately 305 kt to approximately 340 kt (VMO). The right indicated airspeed was approximately 20-25 kt higher than the left. The data indicates that aft force was applied to both columns simultaneously several times throughout the remainder of the recording
At 05:41:20, the right overspeed clacker was recorded on CVR. It remained active until the end of the recording.
At 05:41:21, the selected altitude was changed from 32000ftto 14000ft.
At 05:41:30, the Captain requested the First-Officer to pitch up with him and the First-Officer acknowledged
.At 05:41:32, the left overspeed warning activated and was active intermittently until the end of the recording.
At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try.
At 05:41:54, the First-Officer replied that it is not working
At 05:42:10, the Captain asked and the First-Officer requested radar control a vector to return and ATC approved.
At 05:42:30, ATC instructed ET-302 to turn right heading 260 degrees and the First-Officer > acknowledged.
At 05:42:43, the selected heading was changed to 262 degrees.
At 05:42:51, the First-Officer mentioned Master Caution Anti-Ice.The Master Caution is recorded on DFDR
At 05:42:54, both pilots called out “left alpha vane”.
At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough.
At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units.
At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds.The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1.1 and 0.8units for the remainder of the recording.The left Indicated Airspeed increased, eventually reaching approximately 458 ktsand the right Indicated Airspeed reached 500 kts at the end of the recording. The last recorded pressure altitude was 5,419 ft on the left and 8,399 ft on the right.
I read about a theory of elevator blow back.
They get confusing information about high AoA and the aircraft pitches down.
They try to pitch up, but don’t reduce thrust.
They quickly enter a speed region where the down trim of the stabilizer overcomes the elevator, which can’t deflect into the airstream to counter the pitch down moment.
I suppose people much smarter then me have thought about that, but would that make sense with the LEAP engine, if they wouldn’t reduce thrust and disabled the MCAS system then in theory the engines should induce a strong pitch up momentum due to the forward location and thrust ratings, right?
Well, the thrust seems to have been high, during the event. Since the thrust line produces a pitch up, reducing thrust is counter intuitive, when you want to pitch up.
But thrust means speed, and speed will eventually push the elevator down and trim forces takes over.
That’s what I read, anyway.
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Less thrust would only have made the hole shallower.
I am totally at a loss after reading the above transcript. The two stab cutout switches each has a purpose. One removes electrical power from the trim motor used by the autopilot. The other removes electrical power from the motor that drives the pilot trim (yoke switches). That’s what I was taught. But that does not mesh with the transcript. Either my training was crap or that transcript is false. I’m 50/50 either way.