The short-to-medium-range 727, which first flew in 1963, was the only Boeing-built trijet in its time. It was designed to operate out of small airports with shorter runways. The 131-passenger trijet also was the first Boeing commercial jetliner to use an auxiliary power unit (APU). The 727 also was built as a freighter and as a “quick change” version, which airlines could convert from a passenger transport to a freighter, or a combination of both, as they chose.