In that specific plane, both control columns are physically connected. Moving one will move the other and controlling both will make you physically fight over t

In that specific plane, both control columns are physically connected. Moving one will move the other and controlling both will make you physically fight over the controls> There is a safety feature where if you put enough force on one control column, you can break this linkage. You then have independent control, but the left column will only control the left ailerons and the right column only the right aileron. I assume the second case happened on this flight, but I cannot be sure. There is no such switch or alarm because for Boeing planes, that's how they are built. The left column connects to the left wing, the right to the right, all via cables. In order for one column to control both, there have to be cables connecting them