From the all-metal GY.80 Horizon SOCATA developed an improved model that first flew in November 1967 with a lengthened fuselage, a redesigned cabin, a modified tail unit, a more powerful engine and revised landing gear. This last adopted main units that retracted inwards into the undersurfaces of the wings, while the nosewheel unit retracted to leave about one-quarter of the wheel exposed. Initially designated Super Horizon 2000 and then Provence, the type eventually became the ST.10 Diplomate by the time production deliveries began at the end of 1969. Despite the fact that it offered a usefully higher level of performance than the Horizon, the type failed to attract any real sales enthusiasm and SOCATA ended production in 1975 after delivery of only 56 examples.
ST.10 Diplomate
Type: four-seat sport and touring lightplane
Powerplant: 1 x Avco Lycoming IO-360-C1B, 149kW (200 hp)
Span: 9.70m (31ft 9.75in)
Length: 7.26m (23 ft 9.75 in)
Empty weight: 1594 lb / 723 kg
Max TO weight: 1220 kg (2,690 lb)
Max speed: 174 mph at sea level
Max cruise 75%: 143 kt / 165 mph / 265 kph
ROC: 1003 fpm / 306 m/min
Service ceiling: 16,400 ft / 5000 m
Operational range: 860 miles / 746 km / 1385 km
Baggage capacity: 154 lb / 70 kg
Cabin length: 7 ft 3.75 in / 2.25 m
Cabin width: 3 ft 8.75 in / 1.14 m
Cabin height: 4 ft 1.25 in / 1.25 m
All Aero 