The Sikorsky S-61N is a twin-engine medium utility helicopter with a sealed hull for amphibious operations
that can accommodate a basic crew of two and up to 26 passengers. The Sikorsky S-61N is based on the military
Sikorsky SH-3A/S61B Sea King series originally developed in the late 1950s for all-weather operations. The Sikorsky S-61B
prototype flew on 11 March 1959 and the type entered service with the U.S. Navy as the SH-3A Sea King in 1962.
The Sikorsky S-61N and its non-amphibious configurated variant Sikorsky S-61L are based on and essentially a commercial equivalent of
the militairy S-61B incorporating a number of changes, including a longer fuselage. The Sikorsky S-61L was flown for the first time on 6 December
1960 and received its FAA Type Approval on 2 November 1961. The S-61L entered production the same year. The Sikorsky S-61N with sealed hull and
stabilising SH-3's floats flew first on 7 August 1962. The S-61N version is optimized for overwater operations, particularly
oil rig support. The initial production S-61s were fitted with two 1250shp General Electric CT58-110-1 turboshafts. Both the S-61L and S-61N were
subsequently updated to Mk II standard with more powerful CT58-140 engines giving better hot and high performance and
other improvements and detail refinements. Production of the commercial Sikorsky S-61s ended in 1979.
On 30 March 1976, the 1976-built Sikorsky S-61N c/n 61765 was registered
G-BDOC in the UK with Bristow Helicopters Limited at Redhill Aerodrome.
The aircraft was christened 'Tolquhoun'. On 3 April 1985, the G-BDOC was
stationed at Sumburgh at the Shetland Islands and operated and maintained
on behalf of the UKMCA UK Maritime and Coastguard Agency on the HM
Coastguard services at MRCC Sumburgh as the primary SAR helicopter. On 1 October 2007, the SAR unit at Sumburgh moved from Bristow to CHC Scotia
and the G-BDOC departed Sumburgh for Aberdeen. After undergoing scheduled maintenance in Aberdeen,
Bristow Helicopters directed the aircraft to Den Helder in the Netherlands.
The G-BDOC "Coastguard OC" arrived at Den Helder-De Kooy on 22 October 2007.
At Den Helder Sikorsky S-61N MkII G-BDOC was used by Bristow in company
with Sikorsky S-61N MkII G-BIMU on their offshore SAR contract.
On 15 December 2009, the G-BDOC returned to the UK and was replaced on
the SAR contract by S-61N G-BPWB. Sikorsky G-BDOC was photographed during the Heldair Show Maritiem 2009 at Den
Helder Airport / Maritiem Vliegkamp De Kooy. Sikorsky S-61N MkII G-BDOC
was sold to Carson Helicopters in the USA and registration G-BDOC was
cancelled on 7 September 2010. The same day, the Sikorsky was registered N426GE with
Carson Helicopters Inc.