no, not really. Each airline has its own system. CO uses straight numbers whenever possibe. ex N77303. The first 2 no's are not important, but the final three designate the aircraft, for CO, 3=737-300, and the ship no(03). Sometimes, numbers simply run out and have to be reused. AA's 767 registrations were once crried by their DC-7s. Today, AA's 757 fleet now numbers more than 100, so 601-699 are used, and then 181-184. The MD80 fleet covers the 200s,400s, and 500s!