Comment by rogerrogerr
2 days ago
> That doesn't necessarily mean that either of the two pilots activated them
It does:
1. Those switches have physical interlocks and cannot be manipulated by any computer system.
2. The flight data recorder is measuring the position of the switches; they aren't inferring the position from some system state. There's a "position of this switch" channel.
The switches were physically moved in the cockpit, that's basically ground truth. The question now is who and why.
What is the path of the wires from the switch onward? Do they go into a digital input of the flight computer, or do they directly feed the fuel control valves?
https://simpleflying.com/boeing-787-technical-features-guide...
" Advanced electric controls
The 787 entered service with an improved fly-by-wire flight control system. Rather than mechanical processes, the systems convert flight deck crew inputs into electrical signals. Still, there were additional advancements with the type."
Can't find a definitive source right now, but everything is implying there are discrete lines - at least one for command signal to the FADECs, and a separate sense line to the DFDAU for packaging up and sending to the EAFR. That lines up with design philosophy on this stuff of sensing control input data as close to the source as you can get.
Thanks for looking. I worked for Boeing (satellites, not airplanes) for a good part of my career, and I was there when Dennis Muilenburg pushed through his cost saving measures. It was the same culture that created the problems with the 737-MAX. Experienced design engineers were replaced/outsourced and the culture of safety was sacrificed. One example here:
https://www.cnn.com/2019/04/30/politics/boeing-sensor-737-ma...
787 (Dreamliner) was pushing hard for weight reduction, and it would not surprise me at all if the switch output fed a digital computer input rather than routing directly to the fuel shutoff valves, but I don't have any direct knowledge of this.
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No, lacking other evidence (e.g. CVR recording) it doesn't mean they have been moved. The wiring in between the switches and the engine+FDR could've also developed an intermittent fault.
The fact that your car's engine stops doesn't mean you turned the ignition switch off. Anyone who has had to troubleshoot a car with intermitent electrical faults knows that.
We have other evidence - the crew noticed, and then moved them back to the Run position, and the engines responded as you’d expect.
The switches physically moved, and there is no motor to actuate them without physical intervention.