Sikorsky S-58t

Twin Rotorcraft

The Sikorsky S-58T represents one of aviation's most successful second-life stories — a comprehensive turbine conversion of the venerable piston-powered S-58 helicopter that first flew in 1954. Originally designed as a U.S. Navy anti-submarine warfare platform (designated HSS-1 Seawolf), the S-58 served military and civilian operators worldwide but was hampered by its thirsty Wright R-1820 radial engine. Beginning in the 1970s, multiple conversion programs replaced the original powerplant with twin Pratt & Whitney Canada PT6T-6 Twin-Pac turboshaft engines, dramatically improving performance, reliability, and operating economics. The "T" suffix denotes these turbine conversions, which typically boosted useful load by over 1,000 pounds, increased cruise speed to around 100 knots, and extended service ceilings while slashing maintenance demands. The transformation gave aging S-58 airframes decades of additional utility in roles ranging from firefighting and logging to offshore oil support and VIP transport. With a maximum gross weight of 13,000 pounds and never-exceed speed of 115 knots, the S-58T occupies a capable medium-lift niche — larger than light singles like the Bell 206 but more economical than modern turbine mediums. Though production of new airframes ended in the 1970s, converted S-58Ts remain in active service today, a testament to the soundness of Sikorsky's original design and the ingenuity of turbine retrofit engineering. SkyMeter has tracked 21 flights across 6 airframes and 4 operators, with MIDWEST TRUXTON INTERNATIONAL INC the largest observed operator.