There is described a helicopter having a transmission for transmitting motion from a driving member to a driven member; the transmission has at least a first gear driven by the driving member, and a second gear meshing with the first gear and in turn driving the driven member; the first and second gear have teeth shaped so that the gears mesh with one another at at least two pairs of respective simultaneously meshing teeth; the teeth of at least one of the gears have a profile having an end portion relieved with respect to a starting theoretical involute; and the pattern of the distance between the points of the end portion and the starting involute along an axis of the tooth has at least a first and a second segment sloping with respect to each other.