 Having been slightly modified from the prototype, the three other aircraft were designated as M.F.9Bs (F.122, F.124 and F.126).At first the M.F.9s received an enthusiastic welcome in the RNNAS, but after a near-fatal spin accident due to a structural breakage in the engine in September 1926 confidence in the aircraft type began to wane.In July and August 1928 another series of four M.F.9Bs (F.128, F.130, F.132 and F.134) were delivered 
from the factory in Horten.