Flight numbers are codes given to airplanes and helicopters that identify both the craft and its flightpath for passengers and airport personnel. Commercial air carriers are usually free to set their own flight numbers. While there are some conventions with respect to how numbers are chosen and used, airlines usually have the final say in how their flights are identified. Smaller, private flights, like charters, usually adopt the registration number of the craft as the flight number.
Most airlines operate many different flights each day to cities all over the world. Creating flight numbers is one of the easiest and most efficient ways of keeping them straight. A streamlined system of numeric codes helps passengers locate and identify flights, for one thing. It can also help airports and air traffic controllers quickly identify and communicate with pilots.
There are two parts to most flight numbers: an airline code and a numeric sequence. The airline code is universal and is recognized by all airports. Usually, the airline code is little more than the carrier’s initials, such as “BA” for “British Airways.” The numeric sequence is usually more random. It can be anywhere from one to four digits long, and represents the airline’s own flight classification system.
Airlines usually have the autonomy to assign their own flight numbers. There is always a risk with such an open system that two flights will arrive at the airport at nearly the same time, which is where airline codes come in. BA 175 is easily distinguishable from AF 175, for instance, and the overlap is only minimally confusing.
Numbers are rarely random, and there are a number of fairly regular patterns that are adopted across airlines. In most cases, airline flight numbers ascend in order throughout the day, with the lower numbers taking off in the morning hours. There is not usually any rhyme or reason to where the numbers start, though. Some airlines name their first flight “1,” but others may use starting points that are much higher, like “406” or “2201.”
Flights that immediately return or run in loops are often numbered sequentially. A flight from London to Paris might be 406 on the outbound, then 406 on the return from Paris to London. It is also common for airlines to use odd numbers for flights traveling north or west, but even numbers for flights heading south or east. This is mostly for the ease of air travel passengers and airline staff, and is not always followed. So long as they report their decisions to airport officials and any government airline regulators, airlines are usually free to use whatever numeric scheme they wish for choosing flight numbers.