The new "Baby Bus" is the A318 which Airbus is using to pursue the top end of the RJ market and bottom end of the medium haul market. Launched by TWA but never operated by the carrier, the A318 has thus far been a slow seller but if history is indication, this program will be a resounding success. The A318 is very close in size and capacity to the 737-500 and 737-600. Frontier Airlines has become one of the latest operators of the type.