i'm not a pilot, know nothing about flying.
i'm curious to know if a large commercial airline has ever been successfully recovered from a deep stall such as occured in this case ?
either in test flights, real life or even on a sim ? is it actually possible and if so what altitude would be required?
i assume would require a change from tail down via wing down to nose down attitude, and that would be very tricky and unstable, risking spinning or going upside down and using up lots of altitude ?!