Just before a fatal Air India crash in Ahmedabad, the pilot signaled 'MAYDAY' indicating a critical emergency. Pilots and air traffic controllers use various codes like 'PAN-PAN' for non-life-threatening situations and 'GPW S' for imminent ground collision warnings. Other crucial communications include 'NOTAM' for urgent updates, 'GO AROUND' for aborted landings, and 'V1/V2' speeds for takeoff decisions, ensuring flight safety.