The first of these was a 450 kW (600 hp) Lorraine 12Fd Courlis water-cooled W-12 engine, enclosed by a close fitting metal cowling which followed the contours of its three-cylinder banks.

[1] At the rear the empennage was conventional, with a cropped triangular tailplane mounted on top of the fuselage and braced from below on each side by an inverted V-strut, allowing its incidence to be varied in flight.

[1] The date of the first flight of the Potexz 50 is not known but it had already been tested by the end of June 1931 as it was selected, along with three other prototypes, to make a publicity tour of eastern Europe which began on 5 July.

[2] In October, still Courlis powered, it was at the government testing field at Villacoublay,[3] but in December it was back at the Potez base at Meaulte with an unspecified 480 kW (650 hp) Hispano-Suiza engine.

[4][5] By March another engine change had been made, this time to the Salmson 18AB, an eighteen-cylinder air-cooled radial[1][6] producing the same power as the Hispano.

Two Potez 50s were flying by the summer of 1932, one with an Hispano engine and the other with another radial, a supercharged, fourteen cylinder, 520 kW (700 hp) Gnome-Rhône Mistral Major.

[9] In March 1933 Lemoine set further French and world load carrying speed records, some at least in a Potez 505 14Kbrs powered variant.