Latécoère 631

Design and development

The origins of the Latécoère 631 can be traced back to 1936 and the issuing of a specification by the French Air Ministry that sought a new transatlantic airliner to be operated by the national flag carrier Air France; the prospective aircraft was to possess a range of 6,000 km (3,700 mi) as well as a capacity for up to 20 passengers and 500 kg of cargo. This high-profile specification quickly attracted the attention of various French aircraft manufacturers, including Lioré et Olivier and Potez-CAMS (which would submit their SE.200 Amphitrite and the Potez-CAMS 161 respectively); Latécoère was another firm that opted to produce a response. Designated as the Latécoère 631, it was both the largest and heaviest of the three flying boats designed to meet the specification. It featured all metal construction, an unorthodox V-tail arrangement, and stabilising floats that retracted into the nacelles of the outboard engines as to minimise drag, akin to the earlier Latécoère 611.

The Latécoère 631 was ordered in 1938, at which point it was intended for the flying boat to be powered by six Gnome-Rhône 18P radial engines, each capable of producing up to 1,650 hp (1,230 kW). During the following year, the first passenger flight across the Atlantic was flown by a competing flying boat, the Dixie Clipper; around this time, large flying boats were opening up long distance passenger and mail routes all over the world.

The outbreak of World War II would prove decisive to the future of the Latécoère 631; flying boats were turned to military purposes while developments made during the conflict substantially reshaped post-war air travel. Specifically, construction of the Latécoère 631 was temporarily halted shortly after the conflict broke out, but it was resumed shortly after the signing of the Franco-German Armistice in 1940. Final assembly of the first prototype was undertaken in a hangar at Marignane.

On 4 November 1942, the prototype, registered F-BAHG, performed its maiden flight. During its test flights, the flying boat reportedly exhibited favourable flight and seaworthiness characteristics in addition to the fulfilment of the specification's performance stipulations. One issue observed was an occasional vibration in the outermost portion of the wings. The prototype was subsequently confiscated by the Germans, and passed to the Luftwaffe, who allocated the codes 61+11 to it. The aircraft was flown to Lake Constance, where it was destroyed in an attack by two RAF Mosquito aircraft on 17 April 1944. One month later, France's provisional government, then based in Algiers, decided to pursue serial production of the Latécoère 631 once conditions were right to do so. Latécoère allegedly worked with the French Resistance to conceal components for a second aircraft from the German occupation forces.

Operational history

The second aircraft, F-BANT, first flew on 7 March 1945. It was powered by six Wright R-2600 Cyclone engines of 1,600 horsepower (1,200 kW) each. Four aircraft were purchased by Air France, and entered service on the Biscarrosse-Port-Étienne-Fort de France route in July 1947. The aircraft were withdrawn from service in August 1948 following the loss of F-BDRC. SEMAF operated two aircraft until 1950, when the survivor was withdrawn following the loss of F-WANU. The Société France Hydro operated one aircraft until it was lost on 10 September 1955. This was the last flying aircraft, with the remaining four survivors being scrapped. The Latécoère 631 had quickly become undesirable to operators, largely as a result of it being both unreliable and uneconomic to operate.