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package, the lifetime of the Sikorsky CH-34 airframes that were withdrawn from use with the military operators could be lengthed.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and purchased used S58s, like most of the Sikorsky H-34 Choctaw helicopters that were withdrawn from use 1972-74 in Germany.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.
Sikorsky S-58ET s/n 58-1539 was built in 1962 as a Sikorsky
HSS-1N for the US Navy and was prior delivery completed for the West
German Army as a H-34G-III Choctaw powered by a Wright R-1820-84B radial
air-cooled engine. The U.S. Government had agreed to the Mutual Defense
Aid Program (MDAP). It was under the terms of this program that 94
Sikorsky S-58 helicopters destined for the US Navy as Sikorsky HSS-1N were funded and
delivered to the Federal Republic of Germany as Sikorsky CH-34
helicopters. US Navy Bu150753 was one of the helicopters and was
delivered as a Sikorsky H-34G-III Choctaw to the Federal German Army
(Heeresflieger) and entered service as QA+481 with HFS-102. The Choctaw
served as QW+768 with HFSW (Heeresfliegerwaffenschule) and PY+342 with
HFB200. In 1967, the H-34G-III Choctaw was re-serialed as 8069. The
Sikorsky H-34G-III was able to carry up to 12 passengers and with its
range of 535 km the helicopter was very useful for the German Army. 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+69 was sold to Sikorsky and registered N82828. 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-BCLN with British Airways
Helicopters Ltd., Gatwick Airport. On 4 June 1980, ownership of S-58ET
G-BCLN changed, and the helicopter was registered with Aviation Trusting
International, Redhill, on 25 June 1980. After the helicopter was sold
to Lebanese Helicopters, registration G-BCLN was cancelled as exported
to Lebanon on 25 September 1980 and registered OD-AGK. After being
retired from service with Lebanese Helicopters, the S-58ET was
registered N42825 and N581SR in the USA. On 21 May 1998, the helicopter
was registered N902CH as a Sikorsky S-58JT with Construction Helicopters
in Howell, USA. Sikorsky S-58ET G-BCLN was photographed at the British
Airways Helicopters' base Beccles on 4 August 1979. British Airways
Helicopters operated in that years with several helicopters out of
Beccles Heliport, also known as Ellough Airfield. This former WW II
bomber airfield, was used as heliport for serving the oil and gas rigs
in the southern sector of the North Sea from 1965 to the 1990s.
Luchtvaart déjà vu
