The Savoia-Marchetti S.73 was an Italian three-engine airliner that flew in the 1930s and early 1940s. The aircraft entered service in March 1935 with a production run of 48 aircraft. Four were exported to Belgium for SABENA, while seven others were produced by SABCA. The main customer was the Italian airline Ala Littoria. Design and development The aircraft was developed in only four months, thanks to the use of the S.55 wing, combined with a much more conventional fuselage. Developed in parallel with a bomber version (the SM.81 Pipistrello) the prototype S.73 first flew on 4 June 1934 from Cameri, with Adriano Bacula as test pilot. The prototype had a four-blade wooden propeller on the central engine, and two-blade wooden propellers on each wing engine. Later all aircraft were fitted with three-blade metal propellers. The S.73 was a mixed-construction (a skeleton of steel covered by wood and fabric for the fuselage, wood for the three-spar wing) monoplane with a braced tailplane and fixed undercarriage. There were two generators, one in each side of the fuselage; the batteries were 24 V and were rated at 90 A. The pilot and co-pilot were seated side-by-side in an enclosed cockpit, with a compartment for a radio operator and a mechanic. A passenger compartment could house 18 passengers in two rows. It had eight metallic fuel tanks, all in the wings, with a total capacity of . The prototype had French Gnome-Rhône 9Kfr Mistral engines, but further aircraft had Piaggio Stella P.X, Wright R-1820, Walter Pegasus III MR2V, Alfa Romeo 125 or Alfa Romeo 126, driving ground adjustable, three-bladed, aluminium-steel propellers. It could be used from small airports, had reliable handling and was not too costly. With the Wright R-1820 engine the S.73 had cruise/max speeds of , range, and ceiling. With the AR.126 the S.73 had a maximum speed of , range, and ceiling. The SABCA license-produced aircraft had Gnome-Rhône 14K Mistral Major engines for a total of , comparable to the last models of S.79s or the CANT Z.1018. The S.73 had an unremarkable flight test programme with few modifications recommended by the Regia Aeronautica. It was easy to fly, rugged, and easy to operate on the ground, including the ability to fly from short airfields in treacherous terrain, in spite of being under-powered and the lack of leading edge slats. Its mixed construction and fixed landing gear were its main shortcomings,