Aircraft have revolutionized the way we live. Billions of passengers take to the air every year and around the world airlines operate almost 80,000 flights daily. Before the revolution, flying was, as often as not, a personal struggle in which a lone pilot and his single-engine aircraft tan-gled with the elements, the limits of his own endurance and the uncertainties of technology. Many of the endeavors of the early aviation pioneers ended in heroic failure.