There are two AOA sensors on the Max 8, each feeds into a flight control computer on its side of the aircraft. The plane uses one at a time, which alternates with each successive flight.

Not really related, but funny in a sad way:


In other news:

NAKED MAN ATTEMPTS TO BOARD FLIGHT AT MOSCOW AIRPORT, CLAIMS NUDITY MAKES HIM MORE 'AERODYNAMIC'

https://www.foxnews.com/travel/naked-man-attempts-to-board-flight-at-moscow-airport-claims-nudity-makes-him-more-aerodynamic

Should have told him to hop out on the wing and find out...

It looks like one of the AOA sensors was damaged shortly after takeoff, possibly by a bird strike or other FOD.

https://komonews.com/news/local/sensor-damage-on-ethiopian-airlines-737-max-abc-news-reports

A damaged angle-of-attack sensor may have erroneously triggered anti-stall MCAS software on board a doomed Ethiopian Airlines Boeing 737 Max jet.

ABC News reports the sensor was damaged on takeoff from a bird or foreign object sending the plane downward and eventually crashing into the ground. ABC cites two aviation sources close to the investigation.

It sounds like, with this information, they will be revisiting the Lion Air crash to determine if it may have suffered a similar fate. We do know, in their case, that they had recently performed some sort of service on the AOA sensors. It has been suspected that the service performed may have been substandard.

It's been reported that the Ethiopian pilots flipped the switches to disable MCAS... which sort of indicates that at least one of them recognized the problem and knew how to handle it...

...but then they flipped them back on.

I still can't wrap my mind around how Boeing allowed a non-redundant system on an airplane that had the ability to override a pilot's inputs.

The Air Force just stopped accepting the new tankers. The Air Force keeps finding tools and other debris in closed panels. Just completely unacceptable to get a new mega million dollar aircraft and part of a huge order, and have junk left behind by the workers. Not the publicity Boeing needs or wants. Well, maybe they do need it. Fire those production crews and hire some that want to do a good job, or move production to a plant that wants top quality production.

Why do they keep calling it anti-stall technology? From my understanding from both pilots and the manufacturer is that this is more like a force feedback controller, to make the efforts on the yoke feel the same as the earlier aircraft, especially at higher angles of attack. They still use a stick shaker/pusher when it gets close to a stall as well. One of the stories mentioned the MAX 7 has a version of MCAS as well.

jd, I wondered what else might be going on if they hit the cutoff switch and still could not control the aircraft and then decided to flip it back on. It sounds like they were trying to use the trim switches instead of the manual wheels in a couple of the more in depth reports. If that is the case, there may be some other training issues or a language barrier issue at hand here also.

Are those built in WA? They may have a very difficult time firing those employees if so.

The only reason to turn the switches back on would be so they could trim it electrically. At which point you'd think they'd turn it back off. I heard they turned it on and off 4 times but I haven't looked at the FDR traces yet to confirm that.

I read the same thing, four times. You would think they would leave it off and trim manually like you are supposed to do. A couple reports talked about the engines surging as well and a lot of disparity between instrumentation between the left and right seat. The instrumentation I can understand if the computer thinks they are at high (75* in one report) angle of attack since it would have unreliable data from a pitot tube at that angle but the pitch ladder doesn't make sense. Something really odd here. Hope it isn't bad software beyond the MCAS.

There is some indication that they were unable to trim manually, maybe from excessive aero forces. The prelim report can be seen here:

https://games-cdn.washingtonpost.com/notes/prod/default/documents/6375a995-4d9f-4543-bc1e-12666dfe2869/note/4cb6f748-a0c0-45c2-bf0b-f672ba3cfebe.pdf

It apparently all started with divergent AOA indications after rotation. One vane's data trace went to 75 degrees and stayed there.

Interesting to note the captain was 29 and the FO was 25. FO had a total of 361 hours.

It's clear they knew they had a trim issue and ran the checklist but they did some things that were not recommended. Maybe their decisions were correct, in light of factors that are unknown.

I wonder about the ability to trim the stabilizers in all corners of the flight envelope. I also wonder of they were both cranking on the trim wheels when they were trying to trim manually. It sounds like the Captain was flying and the FO cranking. Not strong enough? Impossible for anyone?

I've been following this guy with his 737 max updates

<iframe width="560" height="315" src="https://www.youtube.com/embed/HBqDcUqJ5_Q" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

I really don't understand why they didn't simply keep their thumb on the trim buttons until they had a normal stabilizer trim position. And, once they flipped the cutout switches back on, to use the trim switches after they failed to be able to adjust it manually, why the hell didn't they flip the switches back off after they finished their inputs? And why were the inputs so brief that they made almost no difference?

I realize that the left AOA indicator was indicating incorrectly, but the value was not credible so it should have been disregarded as erroneous. The FO should have tried to switch the AP on from his side, instead of the captain turning his on.

Then there's the whole issue of never retarding the throttles and getting up to and past the redline speed.

Things only really went south after the last electrical trim inputs, when thy left the cutout switches in the on position.

I’m not sure you can just disregard the AOA sensors. All that analog data from all the external sensors are fed into Seperate computers that convert the analog data into digital. Then those are fed into DADC’s. Dual air data computers. That get turned into usable data for the pilots. I can’t speak for the 737. But on the Airbus and other jets I’ve flown you always have the ability to turn off one side of the data. And use the other. I’ve never seen where you can just turn off say an AOA vane. But in reality. It’s difficult to know what is the right info. For example. If the f/o airspeed is reading 180 knots. And the Captain is showing 200. Who’s is right? Sure you can look at the standby. But say that’s at 190. Standby never seems to be accurate. Because of the location of the sensors.
Locking. And unlocking the brakes on the horizontal stab doesn’t sound like a good idea but maybe they were just trying to get the airplane so it an be flown in level flight.

Also the computer has full authority of the horizontal stab when trimming the airplane. The pilots only have a trim tab. Maybe the trim tab ran out of usefulness so they disconnected the stabilizer to try neutralize it, to get more trim control. You have to be Big John to fly a 737 straight and level with the horizontal stabilizer in the wrong position. Both feet on the dash with arms crossed behind the yoke. If it was me I’d probably disconnect the stabilizer brakes and try retrim.

I have to remind myself that maybe they didn't have AOA indicators on both sides of the cockpit. I think that was an option and they may not have ordered it. I think one is standard on the left side.

As I understand it, there are two AOA sensors, each which feeds eventually into the flight computer on their respective sides of the aircraft. As far as MCAS is concerned, only one computer is used per flight and it alternates with each cycle. I think that may have to change.

In any event, if the left sensor starts showing bad date right at rotation, I think any pilot could recognize that he's 15 degrees nose up, not 75.

Towards the end of the flight, they had to know the stabilizer position and when they turned the switches back on, I would have thought they would have kept their trim switches mashed continually, until the stabilizer had a lot more units showing and the column forces weren't so high that they were both pulling back as hard as they could. The two short inputs, that achieved almost no change in the stabilizer position or the aircraft's pitch, then leaving the switches on, I think doomed them.

It makes no sense to turn the electric trim back on. If the manual trim didn't work there was something else serious happening, or they were overwhelmed and confused. Another thing they could have and probably should have done after everyone reviewed Lion Air is run the flaps to 5* with the throttles back until it is stabilized. That would have taken MCAS out of the picture entirely.

I know, not there, speculation etc.

In Otto's video above, the (777 F.O.) pilot indicates that the aerodynamic forces can, at times, be so strong that it may become necessary to use the electric motor to change the trim setting - that the manual wheels would be too stubborn to turn. Perhaps, in the heat of the moment, they attempted to adjust the trim with power assist, so to speak, but lost track and left it energized. Speculation of course on my part...

Hence the flaps to 5* to use the electric trim.

They should have pulled the old Denzel and rolled inverted!