Britten-Norman Trislander
The Britten-Norman Trislander (more formally designated the BN-2A Mk III Trislander) is a three-engined piston-powered utility aircraft designed and produced by the British aircraft manufacturer Britten-Norman. The Trislander was designed in the late 1960s as an expanded derivative of the company's Islander, a twin-engined commercial aircraft that had proved to be a commercial success.
Source: Wikipedia — Britten-Norman Trislander (CC BY-SA 4.0)