Regional airlines began by operating propeller-driven aircraft over short routes, sometimes on flights of less than 100 miles. In the early days of commercial aviation few aircraft had ranges greater than this, and airlines were often formed to serve the area in which they formed. That is, there was no strong distinction between a regional airline and any other airline. This changed with the introduction of long-range aircraft, which led to the development of the flag carrier airlines, such as British Overseas Airways Corporation and Trans-Canada Airlines. As the flag carriers grew in importance with increasing long-range passenger traffic, the smaller airlines found a niche flying passengers over short routes to the flag carrier's airport. This arrangement was eventually formalized, forming the regional airlines.