The Koolhoven F.K.40 was a small airliner built in the Netherlands in 1928 for KLM. It was a conventional high-wing cantilever monoplane with enclosed seating for up to six passengers and powered by a single engine in the nose. The fuselage was of welded steel tube construction with a wooden wing skinned in plywood held in place by four bolts to facilitate removal. The cabin was spacious for an aircraft of its size, and was intended to be readily reconfigured for passengers, mail, or freight. Although up to six seats could be fitted, the only F.K.40 built flew with four.