Sikorsky S-58t

Twin Rotorcraft

The Sikorsky S-58T represents a successful second life for one of the most versatile helicopters of the Cold War era. Originally designed in the early 1950s as the piston-powered S-58 for the U.S. Navy's anti-submarine warfare mission, thousands were built for military and civilian operators worldwide under designations including H-34 Choctaw and CH-34 Seahorse. By the late 1960s, however, the original Wright R-1820 radial engine was showing its age—underpowered, maintenance-intensive, and increasingly obsolete compared to emerging turbine technology. The S-58T conversion program, launched by California Helicopter International and later continued by others, replaced the thirsty piston engine with a modern Pratt & Whitney Canada PT6T-6 Twin-Pac turboshaft installation. The transformation was dramatic: the aircraft gained a 50-percent increase in useful load, significantly improved hot-and-high performance, reduced vibration, and far greater reliability. Maximum takeoff weight rose to 13,000 pounds, and the never-exceed speed remained a respectable 115 knots. The twin-turbine configuration also provided redundancy that the original single piston engine could not, making the S-58T particularly attractive for offshore oil support, logging, firefighting, and utility work in demanding environments. Though production of new S-58 airframes ended in 1970, the turbine conversions extended the type's operational relevance well into the 21st century. A handful remain active in specialized roles where their combination of cabin volume, external lift capacity, and rugged simplicity still proves valuable. SkyMeter has tracked 3 flights across 1 airframes and 1 operators, with HANGAR 58 LLC the largest observed operator.