4 ms·

This other HN submission has some interesting hypotheticals on why the system might have been reactivated multiple times: https://news.ycombinator.com/item?id=

This other HN submission has some interesting hypotheticals on why the system might have been reactivated multiple times: https://news.ycombinator.com/item?id=19565056 https://news.ycombinator.com/item?id=19565056

acqq 8y ago
This analysis sounds very plausible (all emphasis marks mine): https://leehamnews.com/2019/04/03/et302-used-the-cut-out-switches-to-stop-mcas/ https://leehamnews.com/2019/04/03/et302-used-the-cut-out-swi... "the high speeds observed in ET302’s FlightRadar24 trace (Figure 1) were logical. It’s a consequence of following the Emergency checklist for “IAS disagree” (IAS is Indicated Airspeed, i.e. the dynamic air pressure experienced by the aircraft) after takeoff. The combination of the preceding checklist followed by an MCAS Trim Runaway checklist could create a situation where manual trimming after a Trim Cut-Out would be difficult to impossible and would require non-checklist actions." "At a miss-trimmed Stabilator, you either have to re-engage Electric trim or off-load the Stabilator jackscrew by stick forward, creating a nose-down bunt maneuver, followed by trim. Stick forward to trim was not an option for ET302, they were at 1,000ft above ground. According to The Wall Street Journal, the ET302 crew re-engaged electrical trim to save the situation, to get the nose up. It was their only chance. But too late. The aggressive MCAS kicked in and worsened the situation before they could counter it." The Airport elevation of Addis Ababa airport is 7625 feet AMSL. The highest point of the flight recorded by the flightradar24 is 8600 ft AMSL which gives the plane's altitude of around only 1000 ft at highest! The speeds relative to the ground recorded near the end were 380 kt, i.e. 640 ft/s. Obviously every second mattered, and at the above speeds, the plane was only a few seconds from crash away when the MCAS was pointing the nose down.
- js2 8y ago
  Weird, I guessed at something like that in a related article submitted earlier: https://news.ycombinator.com/item?id=19560596 https://news.ycombinator.com/item?id=19560596
  - cjbprime 8y ago
    Not quite the same -- the issue wouldn't be that they didn't crank enough, but that cranking was physically impossible due to the aerodynamic load on the stabilizer created by being at high speed with the elevator and stabilizer airflow opposing each other. You'd have to release the elevator in order to regain control of the stabilizer, and you can't do that without losing altitude that you don't have to give.
- cjbprime 8y ago
  I remember reading precisely this scenario theorized here on HN a few weeks ago: https://news.ycombinator.com/item?id=19383756 https://news.ycombinator.com/item?id=19383756
- inferiorhuman 8y ago
  Leeham worked with MentourPilot, a training captain for Ryanair, on this article. There was a video included, but it's since been taken down. If you've seen any of Mentour's videos they are fantastic and he is typically quite good about remaining objective and avoiding wild speculation.
- Gibbon1 8y ago
  > The combination of the preceding checklist followed by an MCAS Trim Runaway checklist could create a situation where manual trimming after a Trim Cut-Out would be difficult to impossible and would require non-checklist actions." This is a talk by Professor Nancy Leveson that describes exactly this type of problem. Dangerous interactions between systems. I posted this before when a lot of people were engaging in low grade racism by blaming the Indonesian and Ethiopian pilots competence and training. Seems very topical at this point tho. https://www.youtube.com/watch?v=WBktiCyPLo4 https://www.youtube.com/watch?v=WBktiCyPLo4
  - tempguy9999 8y ago
    I presume this is the same Nancy Leveson who wrote Safeware? If I could push one book on all engineers (and not just programmers as it goes over entire systems failures), let it be this, I recommend it to everyone. https://www.amazon.co.uk/Safeware-System-Safety-Computers-19/dp/0201119722/ https://www.amazon.co.uk/Safeware-System-Safety-Computers-19... I'll watch that link ASAP - thanks @Gibbon1!
- cjrp 8y ago
  > The highest point of the flight recorded by the flightradar24 is 8600 ft AMSL which gives the plane's altitude of around only 1000 ft at highest! Not to be pedantic, but altitude is the distance measured from MSL, height is measured from the ground. So their altitude was 8600ft, their height was ~1000ft.
- CaptainZapp 8y ago
  Thank you very much for the link. If true, and more and more seems to point into this direction, we can pretty much lay the arguments of the "badly educated and overworked third world pilots who are too dumb to work a checklist" to rest. I always found that reasoning rather bigoted and jingoistic. It seems more that Boeing was selling a death trap certified by their cronies at the FAA. What galls me most is the fact that they didn't ground that atrocity after the Lion Air crash, but used their energies to throw customers and pilots under the bus and developed a checklist, which, as it turns out, is actually counterproductive and does nothing to fix the inherent design problems of the plane. If anything, it serves the exact opposite. The second crash is mass murder for commercial reasons, period. If not legally then at the very minimum morally.

acqq 8y ago

This analysis sounds very plausible (all emphasis marks mine): https://leehamnews.com/2019/04/03/et302-used-the-cut-out-switches-to-stop-mcas/ https://leehamnews.com/2019/04/03/et302-used-the-cut-out-swi... "the high speeds observed in ET302’s FlightRadar24 trace (Figure 1) were logical. It’s a consequence of following the Emergency checklist for “IAS disagree” (IAS is Indicated Airspeed, i.e. the dynamic air pressure experienced by the aircraft) after takeoff. The combination of the preceding checklist followed by an MCAS Trim Runaway checklist could create a situation where manual trimming after a Trim Cut-Out would be difficult to impossible and would require non-checklist actions." "At a miss-trimmed Stabilator, you either have to re-engage Electric trim or off-load the Stabilator jackscrew by stick forward, creating a nose-down bunt maneuver, followed by trim. Stick forward to trim was not an option for ET302, they were at 1,000ft above ground. According to The Wall Street Journal, the ET302 crew re-engaged electrical trim to save the situation, to get the nose up. It was their only chance. But too late. The aggressive MCAS kicked in and worsened the situation before they could counter it." The Airport elevation of Addis Ababa airport is 7625 feet AMSL. The highest point of the flight recorded by the flightradar24 is 8600 ft AMSL which gives the plane's altitude of around only 1000 ft at highest! The speeds relative to the ground recorded near the end were 380 kt, i.e. 640 ft/s. Obviously every second mattered, and at the above speeds, the plane was only a few seconds from crash away when the MCAS was pointing the nose down.

js2 8y ago
Weird, I guessed at something like that in a related article submitted earlier: https://news.ycombinator.com/item?id=19560596 https://news.ycombinator.com/item?id=19560596
- cjbprime 8y ago
  Not quite the same -- the issue wouldn't be that they didn't crank enough, but that cranking was physically impossible due to the aerodynamic load on the stabilizer created by being at high speed with the elevator and stabilizer airflow opposing each other. You'd have to release the elevator in order to regain control of the stabilizer, and you can't do that without losing altitude that you don't have to give.
cjbprime 8y ago
I remember reading precisely this scenario theorized here on HN a few weeks ago: https://news.ycombinator.com/item?id=19383756 https://news.ycombinator.com/item?id=19383756
inferiorhuman 8y ago
Leeham worked with MentourPilot, a training captain for Ryanair, on this article. There was a video included, but it's since been taken down. If you've seen any of Mentour's videos they are fantastic and he is typically quite good about remaining objective and avoiding wild speculation.
Gibbon1 8y ago
> The combination of the preceding checklist followed by an MCAS Trim Runaway checklist could create a situation where manual trimming after a Trim Cut-Out would be difficult to impossible and would require non-checklist actions." This is a talk by Professor Nancy Leveson that describes exactly this type of problem. Dangerous interactions between systems. I posted this before when a lot of people were engaging in low grade racism by blaming the Indonesian and Ethiopian pilots competence and training. Seems very topical at this point tho. https://www.youtube.com/watch?v=WBktiCyPLo4 https://www.youtube.com/watch?v=WBktiCyPLo4
- tempguy9999 8y ago
  I presume this is the same Nancy Leveson who wrote Safeware? If I could push one book on all engineers (and not just programmers as it goes over entire systems failures), let it be this, I recommend it to everyone. https://www.amazon.co.uk/Safeware-System-Safety-Computers-19/dp/0201119722/ https://www.amazon.co.uk/Safeware-System-Safety-Computers-19... I'll watch that link ASAP - thanks @Gibbon1!
cjrp 8y ago
> The highest point of the flight recorded by the flightradar24 is 8600 ft AMSL which gives the plane's altitude of around only 1000 ft at highest! Not to be pedantic, but altitude is the distance measured from MSL, height is measured from the ground. So their altitude was 8600ft, their height was ~1000ft.
CaptainZapp 8y ago
Thank you very much for the link. If true, and more and more seems to point into this direction, we can pretty much lay the arguments of the "badly educated and overworked third world pilots who are too dumb to work a checklist" to rest. I always found that reasoning rather bigoted and jingoistic. It seems more that Boeing was selling a death trap certified by their cronies at the FAA. What galls me most is the fact that they didn't ground that atrocity after the Lion Air crash, but used their energies to throw customers and pilots under the bus and developed a checklist, which, as it turns out, is actually counterproductive and does nothing to fix the inherent design problems of the plane. If anything, it serves the exact opposite. The second crash is mass murder for commercial reasons, period. If not legally then at the very minimum morally.