Comment by jussij | Hacker News Reader

Comment by jussij | Hacker News Reader

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I don't the flight control was averaging the pilot inputs.

From this link: https://en.wikipedia.org/wiki/Air_France_Flight_447#Human_fa...

In April 2012 in The Daily Telegraph, British journalist Nick Ross published a comparison of Airbus and Boeing flight controls; unlike the control yoke used on Boeing flight decks, the Airbus side stick controls give little visual feedback and no sensory or tactile feedback to the second pilot.

Ross reasoned that this might in part explain why the pilot flying's fatal nose-up inputs were not countermanded by his two colleagues.

In a July 2012 CBS report, Sullenberger suggested the design of the Airbus cockpit might have been a factor in the accident. The flight controls are not mechanically linked between the two pilot seats, and Robert, the left-seat pilot who believed he had taken over control of the aircraft, was not aware that Bonin continued to hold the stick back, which overrode Robert's own control.

That suggest there was only ever one pilot flying and the way that pilot reacted to the situation had a big part to play in the final crash.

> That suggest there was only ever one pilot flying

"Pilot flying" is a human-factors title, not a software function-lock. It just indicates who has control responsibility at that moment but it is not enforced by technical means.

It is intended to eliminate ambiguity in crew functions; the PF can be a newbie copilot even if the commander of the aircraft is a 30-year-service Captain who would become the PNF at that point. Its all part of Crew Resource Management theory.

There should only be one PF in a cockpit at any one time, precisely to avoid the situation that arose with the Air France flight where the computer was receiving inputs from two pilots.

I was responding to the claim the flight control was averaging the two pilot inputs, because if that was the case then two pilots would have been flying the plane.

Might point was I doubt that this was in fact happening and there was only ever one pilot in charge.

> the Air France flight where the computer was receiving inputs from two pilots.

The link and quotes I posted suggest that was not happening.

The system was just ignoring the other pilot (and that was the designed fault) because it also failed to tell that other pilot he was being ignored.

>because it also failed to tell that other pilot he was being ignored.

It didn't fail to tell him. That's what the dual input alarm is for.

I will have to take your word on this dual input alarm as I have not read or seen any details on this alarm.

Now if that alarm was raised then that suggests both pilots were in error as they both seemed to have ignore that alarm.

However that was never the reason for my original reply.

All I was replying to was idea that the flight control was doing some sort of averaging of the two pilot inputs.

That to me just seems illogical as it would asume two pilots trying to fly the same plane and that scenario will never end well.

>Now if that alarm

The sounding of the alarm is in the transcripts in the accident report.

The Airbus does average the inputs if both pilots are making inputs at the same time.

> The Airbus does average the inputs if both pilots are making inputs at the same time.

Do you have a url/link/pdf that describes this behaviour?

https://safetyfirst.airbus.com/app/themes/mh_newsdesk/docume...

"When both sticks are moved simultaneously, the system adds the signals of both pilots algebraically."

Thanks for the link. It is a very interesting read.

In particular it also says this:

To avoid both signals being added by the system, a priority P/B is provided on each stick. By pressing this button, a pilot may cancel the inputs of the other pilot.

From this link: https://en.wikipedia.org/wiki/Air_France_Flight_447

As pilot flying, Bonin took control of the aircraft via the side stick priority button and said, "I have the controls."

Which again suggests at least in this case, Bonin was the only one flying the aircraft.

Yes, indeed, I have not found any reliable source for the claim that both pilots were making significant stick inputs simultaneously for any extended period of time.

You may be right about the averaging. From rereading the accident report, the Pilot Flying took back control of the plane after the Pilot Not Flying engaged his controls and tried to pitch down.

But, it’s the same basic idea. The PNF thought he’d gotten control of the plane, and didn’t understand why his input wasn’t having an effect. He didn’t get feedback from the stick telling him a different input was being honored. And neither pilot appears to have been fully aware that they were in a flight control mode where there was a risk of stalling. The PF especially never seemed to have made that connection, and the PNF took a fairly long time to call it out. As a result, the PF may not have been aware that he needed to actively keep the angle of attack inside the flight envelope.

So, PNF tries to pitch down, but isn’t aware the plane got put back into a mode where he isn’t in control. PF is pitching up, but isn’t aware the plane switched to a mode where this could lead to a stall. That’s the similarity I was getting at.

It’s weird to me how persistent this story is.

From the reported control traces, there was no prolonged period of dual input. There were 3 or so brief moments of dual control input (1 - 2 seconds), during which a warning was sounded. The pilots never spoke out loud about it, but we can infer that they heard the dual input warning and were aware when it happened because the sequence of events was the same each time; inputs from both joysticks received -> aural dual input warning -> input from one joystick stops.

Something about the idea of two pilots inadvertently fighting each other for control of the aircraft has definitely caught peoples’ imagination. But it didn’t happen.

100% correct.

The available evidence suggest this averaging thing never happened and certainly was not the cause of the crash.

What we have is situation of two pilots in close proximity to each other not communicating and the captain unfortunately caught in the toilet.

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