[traceroute66]

> add a warning system in the case of dual input

The trouble is that those warnings should not be necessary.

It is drummed into the skulls of all pilots that there is only ever one person at the controls.

When you are a student pilot with an instructor in the other seat, the "I have control", "You have control" mantra is drummed into you.

When you progress onto professional multi-crew operations, this is further re-enforced through operational "Pilot Flying", "Pilot Not Flying" roles introduced during your MCC (Multi Crew Cooperation) training.

Also, from a purely practical perspective Boeing are yoke-based aircraft, not Airbus joysticks. So it should be pretty bloody obvious if dual control is going on.

[sokoloff]

> it should be pretty bloody obvious if dual control is going on.

Yet we have an example here where it wasn't obvious to a (presumably) fully competent crew who got to the point of missing an approach and declaring an emergency for a flight control anomaly that they couldn't diagnose as being the other human 4 feet away from them also being on the controls.

"Should be" obviously wasn't "is" in this case.

Edit to add: Also from the report:

  The following factors may have contributed to the simultaneous inputs on the controls:
  <snipped 5 other bullets> 
  • the conviction that simultaneous inputs on the controls would be quickly perceived by crews on this type of aeroplane.

[traceroute66]

> fully competent crew who got to the point of missing an approach and declaring an emergency

I think you need to re-read the PDF. My reading of it is that the missed-approach decision was made by the PF on the basis of the unstablised approach, and that it is what happened after that decision that is under investigation in this report. Undertaking MAP due to unstable approach is pretty standard stuff that occurs all day, every day.

The report states there were zero force inputs by PM prior to the missed-approach, which correlates with the other note in the report that the PM ghosted the controls in the period following the missed-approach and that is when the apparent reflex action occured.

[sokoloff]

My read is that the approach was not unstable (it met stabilized approach criteria at all significant checkpoints) at the moment when the PF (co-pilot) become spatially disoriented and began giving improper control inputs.

This disorientation of the PF was the triggering event, which caused him to call the go-around [prior to stabilized approach criteria being violated], the approach to be terminated, and required the PM (the captain) to make corrective [and conflicting] control inputs. These conflicting inputs were not accompanied by the normal exchange of controls communications.

You are correct that the missed approach procedure was initiated before the controls conflict between humans began (but after the co-pilot's disorientation made him suspect a flight controls problem). I was wrong on that point.

[seanmcdirmid]

Safety often comes via overwhelming redundancy and back up protections. The human should do X, but if they don't do X, another system will do Y to save the plane, and if that system fails, then another system will do Z...

Single points of failure should be avoided. Like in driving, things should work out if driver A or driver B does the right thing, or if the road is designed right, or if pedestrians are following reasonable rules, you just try to make all those things true, so if any of them are not, it isn't a disaster.

[MaxBarraclough]

This even has a catchy name: the Swiss cheese model.

https://en.wikipedia.org/wiki/Swiss_cheese_model

[declaredapple]

> The trouble is that those warnings should not be necessary.

Of course they shouldn't be, but it's a protection against scenerios such as miscommunication, being distracted and forgetting you handed them over, etc.

> mantra is drummed into you.

The real danger to well-trained behavior is emergencies and task-saturation. That's when you're most likely be distracted, act impulsively, etc.

Literally halve of all warnings can be covered by "The humans should have been paying attention and noticed it".