Savoia-Marchetti S.73

Savoia-Marchetti

Industry	Aerospace, Aviation
Founded	1920s (exact date not specified)
Headquarters	Italy
Products	Aircraft, including Savoia-Marchetti S.73 airliner

Template:Infobox aircraft

The Savoia-Marchetti S.73 was a tri-motor airliner developed in Italy during the 1930s and early 1940s. Production commenced with 48 units entering service in March 1935. Of these, four were sold to Belgium’s SABENA, while an additional seven were manufactured under license by SABCA. The primary operator was the Italian carrier Ala Littoria.

Design and development

The creation of this aircraft took merely four months, largely due to adapting the wing design from the S.55 combined with a more traditional fuselage structure. Developed concurrently with a bomber variant known as the SM.81 Pipistrello, the initial S.73 prototype conducted its maiden flight on 4 June 1934 at Cameri, piloted by test pilot Adriano Bacula.

Initially, the prototype featured a central engine equipped with a four-blade wooden propeller, while the wing-mounted engines each utilized two-blade wooden propellers. Subsequent production models were standardized with three-blade metal propellers.

The S.73 employed mixed construction techniques, combining a steel frame covered by wood and fabric for the fuselage, and a three-spar wooden wing design. It was a braced monoplane with a fixed undercarriage and tailplane supported by struts. Electrical power was supplied by two generators situated on either side of the fuselage, feeding 24-volt batteries rated at 90 amperes.

Crew seating included side-by-side positions for the pilot and co-pilot within an enclosed cockpit, along with space allocated for a radio operator and mechanic. Passenger accommodations allowed for up to 18 individuals arranged in two rows.

Fuel was stored in eight metallic tanks located within the wings, collectively holding approximately 3,950 L (1,040 US gal; 870 imp gal). While the prototype was powered by French Gnome-Rhône 9Kfr Mistral engines, later versions employed various powerplants including 522 kW (700 hp) Piaggio Stella P.X, 574 kW (770 hp) Wright R-1820, 544 kW (730 hp) Walter Pegasus III MR2V, as well as Alfa Romeo 125 or Alfa Romeo 126 engines, all driving ground-adjustable three-bladed aluminum-steel propellers.

Designed to operate from smaller aerodromes, the S.73 was noted for its dependable handling and economical operation. Equipped with the 574 kW (770 hp)Wright R-1820 engines, it achieved cruising speeds up to 270 kilometres per hour (170 mph), maximum speeds near 340 kilometres per hour (210 mph), a range of approximately 1,000 kilometres (620 mi), and service ceilings reaching 6,300 metres (20,700 ft). When powered by the 544 kW (730 hp) AR.126 engines, its top speed increased to about 345 kilometres per hour (214 mph), maintaining similar range but attaining a ceiling of around 7,000 metres (23,000 ft). The SABCA-built models utilized more powerful 671 kW (900 hp) Gnome-Rhône 14K Mistral Major engines totaling 2,013 kilowatts (2,699 hp), comparable to late-production Savoia-Marchetti SM.79 aircraft or the CANT Z.1018.

Flight testing of the S.73 was largely uneventful, resulting in minimal modifications as advised by the Regia Aeronautica. The aircraft was user-friendly in flight, robust in construction, and straightforward to handle on ground operations, including takeoffs and landings on short or difficult airfields despite being somewhat underpowered and lacking leading-edge slats. Its principal drawbacks were its mixed-material build and fixed landing gear, especially when contrasted with contemporary American and German designs featuring all-metal airframes and retractable undercarriages that offered superior performance. Nonetheless, the S.73 remained viable in commercial service for several years following its introduction.

Operational history

File:Sm 73.jpg

S.73 at Milan Linate airport

The Belgian carrier SABENA was the initial user of the S.73, acquiring five units powered by Gnome-Rhône 9Kfr Mistral Major engines directly from Savoia-Marchetti in 1935. These aircraft commenced operations on European routes during the summer of that year. In 1935, two of these planes were lost due to accidents. Subsequently, between 1936 and 1937, SABENA commissioned seven additional S.73s equipped with Gnome-Rhône 14K Mistral Major engines, produced under license by SABCA. This allowed the replacement of the Fokker F.VII on the Belgium-to-Congo route, a journey lasting four days without overnight flights and totaling approximately 44 hours of flight time.

Following SABENA, the Italian airline Ala Littoria became the next operator, receiving at least 21 S.73 aircraft powered by various engines such as the Piaggio Stella X, the Wright R-1820, and the Alfa Romeo 126 RC.10. These planes served routes within Europe as well as to Italy’s African colonies. In December 1935, an S.73 completed a trip from Italy to Asmara, carrying over 200,000 pieces of mail across a distance of 6,600 km (4,100 mi) over four days, returning to Rome by January 6, 1936. This operation established a commercial air route covering about 6,100 km (3,790 mi).Template:Fix/category Additional operators included Avio Linee Italiane, which utilized Alfa Romeo 126-powered models, and Československé Státní Aerolinie, which operated versions powered by the Walter Pegasus.

By the onset of World War II, the S.73 was considered outdated; nevertheless, some units were conscripted into military service with the Regia Aeronautica, conducting operations in Abyssinia and Spain.

In Eastern Africa, nine S.73s served as military transports. As British Commonwealth forces neared capturing Addis Ababa, the Duke of Aosta, who was the Viceroy of Italian East Africa, commanded an evacuation of the last three remaining S.73s. After several days of preparation, on April 3, 1941, these aircraft departed Addis Ababa with a total of 36 personnel aboard, aiming for a 2,500 km (1,600 mi) flight to Kufra in Libya that required extra fuel tanks installed inside their fuselages. All three planes were forced to make emergency landings in desert terrain but managed to refuel at Jeddah before continuing.

After enduring several challenging days—including sandstorms that clogged air filters—they resumed flight. The original plan included a stopover in Beirut; however, since Erwin Rommel had captured Benghazi, this city became their final destination. Two aircraft completed a flight lasting ten hours and covering approximately 4,500 km (2,800 mi), arriving at Benghazi after over a month of travel under harsh conditions that nearly incapacitated their occupants due to fuel fumes.

In May 1940, seven Belgian S.73s were relocated to the United Kingdom and incorporated into service with the Royal Air Force. Operated by SABENA crews, these aircraft transported ammunition to support the British Expeditionary Force in Northern France. On May 23, two were destroyed during a Luftwaffe attack at Merville. Following this loss, SABENA directed its remaining fleet—including five S.73s—to move into France in preparation for redeployment to the Belgian Congo. After Belgium’s surrender on May 28, these aircraft were assigned to French government use for transporting pilots between mainland France and French North Africa. Upon France’s capitulation on June 22, 1940, the Italian authorities seized SABENA’s fleet—including all S.73s—and incorporated them into Regia Aeronautica operations.

Within Italy, surviving S.73s equipped squadrons 605 and 606. By the time of the armistice in 1943, four S.73s remained operational: three were utilized by Allied forces while one served under the pro-Axis regime; all had been withdrawn from active service by war's end.

Accidents and incidents

7 November 1935

The SABENA-operated S.73P with registration OO-AGM sustained irreparable damage while taxiing at London-Croydon Airport.

10 December 1935

Main article: 1935 SABENA Savoia-Marchetti S.73 crash

The SABENA aircraft S.73 OO-AGN crashed near Tatsfield, Surrey, United Kingdom, resulting in the fatalities of all eleven individuals on board.

26 January 1937

The S.73P model OO-AGR, belonging to SABENA, crashed during its approach to Oran Es Sénia Airport (ORN/DAOO) in Algeria, causing the deaths of all twelve people aboard, including eight passengers and four crew members.

2 August 1937

An Ala Littoria S.73 registered I-SUSA crashed while approaching Wadi Halfa Airport (WHF/HSSW) in Sudan, with all nine occupants—six passengers and three crew—losing their lives.

30 April 1938

The Ala Littoria aircraft I-MEDA, an S.73, crashed on a flight from Tirana to Rome after colliding with mountainous terrain near Maranola, Italy. This accident claimed the lives of all nineteen individuals on board, comprising fourteen passengers and five crew.

13 August 1938

ČSA (Československé státní aerolinie) operated S.73 OK-BAG crashed on approach to Strasbourg, resulting in the deaths of all seventeen people aboard, including thirteen passengers and four crew members.

10 October 1938

The SABENA S.73P registered OO-AGT disintegrated mid-flight over Soest, Germany, while en route to Berlin. All twenty occupants—sixteen passengers and four crew—were killed.

17 October 1939

An Ala Littoria S.73 identified as I-IESI? crashed during a flight to Melilla Airport (MLN/GEML), with fifteen of the seventeen people on board perishing—ten passengers and five crew.

16 March 1940

The Avio Linee Italiane (ALI) S.73 I-SUTO crashed into Stromboli amid adverse weather conditions, resulting in the loss of all fourteen occupants, which included nine passengers and five crew members.

14 May 1940

To prevent capture by advancing German forces, the SABENA S.73P OO-AGP was destroyed while on the ground at Brussels-Haren Airport.

23 May 1940

While operating for No.271 Squadron RAF near Arques (likely Arques, Pas-de-Calais), the SABENA S.73P OO-AGS was shot down by German ground fire, resulting in one crew member's death.

23 May 1940

The SABENA S.73P OO-AGZ was destroyed on the ground at Merville aerodrome during transfer to No.24 Squadron RAF.

Civil operators

Template:BEL

• SABENA

Template:CZS

• ČSA

Template:Country data Kingdom of Italy

• Ala Littoria
• Avio Linee Italiane

Military operators

Template:BEL

• Belgian Air Force

Template:Country data Kingdom of Italy

• Regia Aeronautica
• Italian Co-Belligerent Air Force

Template:UK

• Royal Air Force
  • No. 24 Squadron RAF
  • No. 117 Squadron RAF

References

Bibliography

• Lembo, Daniele, SIAI 81 Pipistrello, Aerei nella Storia, n.33.