The Sikorsky S-58ET is a medium-weight multi-role utility twin pac coupled turbo shaft powered helicopter accommodating up to 16 passengers
and 2 crew. The Sikorsky S-58T is a development of the single piston-engined Sikorsky S-58 also known as the CH-34. On 30 January 1957, the
Sikorsky HSS-1F Seabat flew first. In fact was this the first tuboshaft-engined Sikorsky S-58. The Sikorsky HSS-1F was a flying testbed for
the General Electric T58 turboshaft engine. The airframe was modified to accept two GE Model XT58T engines. However the T58 turboshaft engine
gave the Sikorsky S-58 a significant power-to-weight advantage ratio, just a single turboshaft engined S-58 was converted at that time and
the Sikorsky S-58 in production remained piston-engined. However, the Sikorsky CH-34 was also built and developed under license in the
United Kingdom by Westland Aircraft from 1958. This company introduced Westland Wessex. The Westland Wessex was derived from the Sikorsky S-58,
a free-turbine supplanting the original piston engine. The Wessex prototype flew first on 20 June 1958 and the model entered service in 1961
with the Royal Navy. In 1970, Sikorsky announced it was developing a turboprop conversion package for the S58. With the turboprop coversion
package, the lifetime of the Sikorsky CH-34 airframes that were withdrawn from use with the military operators could be lengthed. Turbine
conversion with Pratt & Whitney PT6 Twin-Pac, comprising two PT6 engines and combining gearbox; improved performance includes greater
speed and lifting power, and better hot-and-high operation. The first S-58T conversion flew on 19 August 1970. The turboprop-engined S58T
was initially fitted with a Pratt & Whitney PT6T3 twinpack turboshaft. Later aircraft were fitted
with a Pratt & Whitney PT6T6 twinpack turboshaft. In April 1971, Sikorsky received FAA approval for the S-58T Twin Pac-powered turbine conversion
for S-58 airframes. Sikorsky set up a production line to convert customer S58s, offered kits for S58 operators to perform the conversion
and purchased used S58s, like most of the Sikorsky H-34 Choctaw helicopters that were withdrawn from use 1972-74 in Germany.
The converted H-34 helicopters were offered for sale as Sikorsky S-58T. One hundred and forty-six conversions, or conversion
kits, were produced until the rights were sold to California Helicopter International in 1981.
After the discovery of the natural gas below Slochteren in the
Netherlands the oil-companies started their hunt for natural gas below
the North Sea. In the early sixties World Wide Helicopters Inc. and Bristow
Helicopters settled down at Eelde airfield. World Wide operated two Sikorsky S-58 helicopters
and one Beech Twin Bonanza; Bristow operated two float equipped Westland WS.55 Whirlwinds 3 and
one Westland WS.51 Widgeon out of Eelde airfield. Bristow helicopters maintained their helicopters in one of the RLS hangars.
Sweat memories came back when their Sikorsky S-58ET G-BCTX was noted on 2 July 1977.
Sikorsky S-58ET c/n 58-1103 was built in 1959 for the Federal Republic of
Germany as a H-34G.II Choctaw powered by a Wright R-1820-84B radial air-cooled engine and registered by Sikorsky as N948.
Sikorsky H-34G-II Choctaw c/n 58-1103 was delivered to the Federal German Army (Heeresflieger)
and entered service as PB+207 with HFS-2. The H-34G.II Choctaw was able to carry up to 12 passengers
and with its range of 535 km the helicopter was very useful for the German Army. In service with the Heeresflieger
the Choctaw was re-serialed QA+473; PH+219 and PH+263. In 1967, the helicopter was re-serialed as 8038 and served with
HFS201 at that time. The Choctaws in service with the Federal German Army (Bundeswehr) were replaced between 1971 and 1973
by the Sikorsky CH-53G and withdrawn from use. The 80+38 was sold to Sikorsky and registered N82813. It was rebuilt
as a S-58ET powered by the Pratt & Whitney Aircraft of Canada PT6T-6
Twin Pac coupled turbo shaft. This conversion permitted the S-58ET to
carry up to 16 passengers at a maximum speed some 16 mph (26 km/h)
higher than the S-58s 122 mph (196 km/h) over slightly longer ranges,
with the additional safety of a twin-engine power plant. After the
conversion, the helicopter was registered G-BCTX with Bristow Helicopters Ltd., Redhill Aerodrome,
on 31 December 1974 and entered service with Bristow Helicopters as "Lyra". The S-58ET helicopters in service with
Bristow Helicopters were early 1979 replaced by Sikorsky S-76 and the G-BCTX was withdrawn from use. On 26 April 1979,
registration G-BCTX was cancelled as exported to South-Africa and registered ZS-HHZ. Sikorsky S-58ET ZS-HHZ was reported
as sold in Malaysia but was never recorded in Malaysia and the helicopter was broken up.