thank you for your answer captplaystation,
would alerting the cabin crew help? (by shouting and being descriptive "fire - engine - right" - i know it is noisy during the roll, but hey i would try it anyway, people would spread the message fairly quickly towards the cc)
what would a pilot (sitting in a window seat as pax, and having the necessary knowledge of the type) do in a situation like Madrid? (witnessing a take-off with incorrect flaps setting)