Every aircraft around the world has a unique registration – similar to a licence plate – that consists of letters and/or numbers. The Fin Number is used by airlines to differentiate their fleet. Air Canada inscribes a three‑digit Fin Number on the vertical tail of the aircraft. (Some airlines use four digits.) The first number denotes the aircraft type, while the second and third indicate delivery date and aircraft model differences. Air Canada’s Boeing 767s start with a “6,” whereas the Airbus A330s use “9.” Visit aircanada.com for a list of 360 or so Fin Numbers.