3 ms·

I’m the OP Dave BTW. Trevor copied a Facebook post I made a couple of days ago into those tweets. I don’t know all of the details about the EFS system but I’d

I’m the OP Dave BTW. Trevor copied a Facebook post I made a couple of days ago into those tweets. I don’t know all of the details about the EFS system but I’d be pretty sure it doesn’t use data from both sides for anything, because that would be against the brick wall isolation concept in the air data and flight control computers. You say that the MCAS is neither silent or subtle, but there is no light or master caution or anything, just the trim wheel turning and clicking. I’m not sure you’d notice it if you were wearing a headset and were being distracted by the stick shaker. The reason they died on activation #21 and not #1 is that the effects are cumulative. Every time it activates it dials in another 2.5 degrees of nose down trim. Eventually you can’t pull on the yoke hard enough to hold altitude. I agree that the jury is still out as to whether it’s a sensor issue per se or some sort of ADC or data transmission issue.

inferiorhuman 8y ago
The reason they died on activation #21 and not #1 is that the effects are cumulative. The stabilizer position was graphed on that preliminary report (see: pitch trim position). There was a slight trend towards nose down pitch, but no, at the time they lost control there's a sharp decrease in pitch that doesn't correlate with MCAS. If you look at the "trim manual" line you'll see that the pilot flying was continuing to input nose up pitch on the switches to no effect. Something changed and it wasn't simply that the pilot was overridden by MCAS. After 21 even MCAS continued to counter the pitch up inputs as the stabilizer continued to contribute additional nose down pitch. I agree that the jury is still out as to whether it’s a sensor issue per se or some sort of ADC or data transmission issue. To be clear I highly doubt the alpha vane was defective. It's a possibility, but look at that graph. The left "angle of attack indicated" mirrors the right one almost exactly except that there's a near constant twenty degree offset. If that's a sensor problem in two separate sensors I'll pull a Werner Herzog and eat my freaking shoe.
- engire 8y ago
  I totally agree here. Im an AME with Max Licence and i would have to say. Im quite sure this wasnt an AOA sensor. The FCC thats active with MCAS as its function (both have this Function) would have been looking at the right vane on one flight and then the left vane on the next flight, however on the last 3 legs the fault was the same. And trust me on this one. May have been different indications bbut all pointed at the same fault. I suspect the FCC or ADIRU was at fault or something it aircraft installation that was inducing the 20 degree difference between the 2.
inferiorhuman 8y ago
You say that the MCAS is neither silent or subtle, but there is no light or master caution or anything, just the trim wheel turning and clicking. I’m not sure you’d notice it if you were wearing a headset and were being distracted by the stick shaker. BTW the trim wheel has little stripes on it, moves quickly when being operated automatically, and is fairly noisy. It will get your attention. However, my suspicion is that pilots experienced on the NG will mistake the trim wheel doing counterintuitive things for normal STS operation (especially after takeoff). I don't know if the Cessna trim wheel(s) are any quieter or more subtle, but the Cessna certainly doesn't have all the band-aids that a 737 NG or MAX would. To this point here's a post from a 737 NG pilot[1]: As a long-time 737 driver I'll just chime-in a few points [...] (1) Just after takeoff there is a lot going on with trim, power, configuration changes, and as noted above, the darn speed trim is always moving that trim wheel in seemingly random directions to the point that experienced NG pilots would treat its movement as background noise and normal ops. Movement of the trim wheel in awkward amounts and directions would not immediately trigger a memory item response of disconnecting the servos. No way. (2) The pilots could very reasonably not have noticed the stab trim movement. Movement of the stab trim on the 737 is indicated by very loud clacking as the wheel rotates. On the -200 it was almost shockingly loud. On the NG, much less so. HOWEVER, the 737 cockpit is NOISY. It's one reason I am happy to not be flying it any more. The ergonomics are ridiculous. Especially at high speeds at low altitudes. With the wind noise, they may not have heard the trim wheel moving. The only other way to know it was moving would be yoke feel and to actually look at the trim setting on the center pedestal, which requires looking down and away from the windows and the instruments in a 'leans'-inducing head move. On the 717, for example, Ms. Douglas chimes in with an audible "Stablizer Motion" warning. There is no such indication on the 737. [...] Finally, runaway stab trim is a very, very rare occurence up until now. We trained it about once every other year in the sim because it is so rare. And when we did it was obvious. The nose was getting steadily heavier or steadily lighter with continuous movement of the trim wheel. That is a VERY different scenario than what these pilots faced. We also trained for jammed stabilizer, the remedy for which is overcoming it with force. The information they were faced with could very reasonably have been interpreted that way, too. 1: https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-102.html#post10423122 https://www.pprune.org/rumours-news/619272-ethiopian-airline...
autopilotsw 8y ago
I don't believe there is a brick wall design here since the FCC outputs are not compared so why would you isolate inputs. I believe it's just a bad design to use the single AOA input.

inferiorhuman 8y ago

The reason they died on activation #21 and not #1 is that the effects are cumulative. The stabilizer position was graphed on that preliminary report (see: pitch trim position). There was a slight trend towards nose down pitch, but no, at the time they lost control there's a sharp decrease in pitch that doesn't correlate with MCAS. If you look at the "trim manual" line you'll see that the pilot flying was continuing to input nose up pitch on the switches to no effect. Something changed and it wasn't simply that the pilot was overridden by MCAS. After 21 even MCAS continued to counter the pitch up inputs as the stabilizer continued to contribute additional nose down pitch. I agree that the jury is still out as to whether it’s a sensor issue per se or some sort of ADC or data transmission issue. To be clear I highly doubt the alpha vane was defective. It's a possibility, but look at that graph. The left "angle of attack indicated" mirrors the right one almost exactly except that there's a near constant twenty degree offset. If that's a sensor problem in two separate sensors I'll pull a Werner Herzog and eat my freaking shoe.

engire 8y ago
I totally agree here. Im an AME with Max Licence and i would have to say. Im quite sure this wasnt an AOA sensor. The FCC thats active with MCAS as its function (both have this Function) would have been looking at the right vane on one flight and then the left vane on the next flight, however on the last 3 legs the fault was the same. And trust me on this one. May have been different indications bbut all pointed at the same fault. I suspect the FCC or ADIRU was at fault or something it aircraft installation that was inducing the 20 degree difference between the 2.

inferiorhuman 8y ago

You say that the MCAS is neither silent or subtle, but there is no light or master caution or anything, just the trim wheel turning and clicking. I’m not sure you’d notice it if you were wearing a headset and were being distracted by the stick shaker. BTW the trim wheel has little stripes on it, moves quickly when being operated automatically, and is fairly noisy. It will get your attention. However, my suspicion is that pilots experienced on the NG will mistake the trim wheel doing counterintuitive things for normal STS operation (especially after takeoff). I don't know if the Cessna trim wheel(s) are any quieter or more subtle, but the Cessna certainly doesn't have all the band-aids that a 737 NG or MAX would. To this point here's a post from a 737 NG pilot[1]: As a long-time 737 driver I'll just chime-in a few points [...] (1) Just after takeoff there is a lot going on with trim, power, configuration changes, and as noted above, the darn speed trim is always moving that trim wheel in seemingly random directions to the point that experienced NG pilots would treat its movement as background noise and normal ops. Movement of the trim wheel in awkward amounts and directions would not immediately trigger a memory item response of disconnecting the servos. No way. (2) The pilots could very reasonably not have noticed the stab trim movement. Movement of the stab trim on the 737 is indicated by very loud clacking as the wheel rotates. On the -200 it was almost shockingly loud. On the NG, much less so. HOWEVER, the 737 cockpit is NOISY. It's one reason I am happy to not be flying it any more. The ergonomics are ridiculous. Especially at high speeds at low altitudes. With the wind noise, they may not have heard the trim wheel moving. The only other way to know it was moving would be yoke feel and to actually look at the trim setting on the center pedestal, which requires looking down and away from the windows and the instruments in a 'leans'-inducing head move. On the 717, for example, Ms. Douglas chimes in with an audible "Stablizer Motion" warning. There is no such indication on the 737. [...] Finally, runaway stab trim is a very, very rare occurence up until now. We trained it about once every other year in the sim because it is so rare. And when we did it was obvious. The nose was getting steadily heavier or steadily lighter with continuous movement of the trim wheel. That is a VERY different scenario than what these pilots faced. We also trained for jammed stabilizer, the remedy for which is overcoming it with force. The information they were faced with could very reasonably have been interpreted that way, too. 1: https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-102.html#post10423122 https://www.pprune.org/rumours-news/619272-ethiopian-airline...

autopilotsw 8y ago

I don't believe there is a brick wall design here since the FCC outputs are not compared so why would you isolate inputs. I believe it's just a bad design to use the single AOA input.