Twenty-four years have passed since that Tuesday, 11 September 2001 in the USA (it was 8:45am local time, 3:00pm in Italy), events that shocked the entire world and the sectors of transport by aircraft and safety- security. 

A series of four coordinated suicide attacks carried out against civilian and military targets of the United States of America by a group of terrorists belonging to the terrorist organization al Qaeda. The attacks caused the deaths of almost three thousand people (2,977 to be exact), plus 19 hijackers, and the wounding of over 6,000 ones. 

That morning four airliners, belonging to two of the largest US carriers (United and American), were hijacked by 19 terrorists belonging to al Qaeda. Two aircraft (flight AA 11 and UA 175) were flown into the North and South Towers of the World Trade Center (WTC), in the Lower Manhattan neighborhood of New York, respectively. Within one hour and 42 minutes both towers collapsed. The debris and fires then caused the partial or total collapse of all the other buildings in the WTC complex. 

A third airplane, flight AA77, was flown into the Pentagon, headquarters of the Department of Defense, in Arlington County, in the State of Virginia; the attack caused the collapse of the building's west facade. 

A fourth plane, flight UA93, was initially directed toward Washington but later crashed in a field near Shanksville, Pennsylvania, following a heroic revolt by the passengers on board.