The BFW M.21 was a single-engined biplane trainer designed by Willy Messerschmitt for the German Ministry of Transport.

[1] During these negotiations, completed on 8 September 1927, the Ministry of Transport put pressure on Messerschmitt to produce military aircraft.

[2] The wings, which folded for transport had parallel chord, no sweep and very little stagger and there were ailerons on both planes.

The fuselage was square sided with triangular upper decking behind the open cockpits and it tapered to the rear, making the generous fin and rudder appear even more prominent.

[3] This example, civil registered as D-1566 flew until 1933 with DVS GmbH, the German sport flying association.