The Sikorsky S-61L and **S-61N ** are civil variants of the SH-3 Sea King military helicopter. They were developed and produced by the American helicopter manufacturer Sikorsky Aircraft. The commercial version of the Sea King was developed during the late 1950s. Two versions, the land-based S-61L and the amphibious S-61N, were created. The S-61L had an enlarged cabin and dispensed with some of the amphibious features, such as its float stabilizers, for greater payload capacity. It was considered attractive to utility operators, while the amphibious S-61N appealed to off-shore operators. The first models were delivered to customers during September 1961. By the turn of the century, they had become two of the most widely used airliner and oil rig support helicopters built. Airliners were a key customer for the S-61L. Los Angeles Airways, New York Airways, and Chicago Helicopter Airways were among the first operators. However, operations in this sector proved troublesome, with profits elusive and service often subject to noise complaints and accidents. S-61s also saw service in the search and rescue (SAR) sector in various countries. Third-party companies have often converted individual airframes by shortening the fuselage to bolster its lift capacity. Governmental organizations have procured the S-61: the United States Department of State was a prominent operator of the type into the twenty-first century.

Design and development

Background

In September 1957, Sikorsky was awarded a United States Navy development contract for an amphibious anti-submarine warfare (ASW) helicopter capable of both detecting and attacking submarines. On 11 March 1959, the XHSS-2 Sea King prototype made its maiden flight. Production deliveries of the HSS-2 (later designated SH-3A) commenced during September 1961. The initial production aircraft being powered by a pair of General Electric T58-GE-8B turboshaft engines, each capable of providing up to 930 kW. Sikorsky quickly decided to pursue development of a dedicated commercial model of the Sea King. In fact, two prime models were produced: the land-based S-61L and the amphibious S-61N. On 2 November 1961, the S-61L conducted its maiden flight; it was 4 ft longer than the HSS-2 to facilitate the carriage of a substantial payload of freight or passengers. Initial production S-61Ls were powered by two 1350 shp GE CT58-110 turboshafts, the civil version of the T58. The S-61L features a modified landing gear that eliminated the float stabilisers. On 7 August 1962, the S-61N performed its first flight. Being otherwise identical to the S-61L, this version is optimized for overwater operations, particularly oil rig support, by retaining the SH-3's floats. Both the S-61L and S-61N were subsequently updated to the Mk II standard, which was outfitted with more powerful CT58-140 engines that provided superior performance in hot and high conditions, along with incorporating measures to dampen vibration and various other refinements.

Further development

Additional civil models of the S-61 would soon be developed. The Payloader, a stripped-down version optimized for aerial crane work, was the third civil model of the S-61 produced. The Payloader features the fixed undercarriage of the S-61L, but with an empty weight almost 2000 lb less than the standard S-61N. Carson Helicopters was the first company to shorten a commercial S-61. The fuselage is shortened by 50 in to increase its single-engine performance and external payload. The improved lift performance lent itself to utility operations, particularly in the construction market. A unique version is the S-61 Shortsky, a conversion of S-61Ls and S-61Ns performed by Helipro International. VIH Logging was the launch customer for HeliPro's Shortsky, which performed its first flight during February 1996. One modification for the S-61 is the Carson Composite Main Rotor Blade. These blades replace the original Sikorsky metal blades, which are prone to fatigue, and permit a modified aircraft to carry an additional 2000 lb load, fly 15 kn faster and increase range 61 nmi. During the 2000s, the S-61T modernisation emerged. This model includes composite main rotor blades, a modular wiring harness, and (optionally) a glass cockpit; these changes reportedly boost the helicopter's lift capability as well as increase its speed. During June 2010, the United States Department of State signed a purchase agreement for up to 110 modernized S-61Ts, which will perform both passenger and cargo transport missions in support of its worldwide operations.

Operational history

The first civil operator to adopt the S-61 was Los Angeles Airways, which introduced the type to service on 11 March 1962. The company had reportedly bought them from Sikorsky at a unit price of $650,000 each. Sikorsky's foremost competitor for sales was Boeing Vertol with their Vertol 107 twin-rotor helicopter, which arrived on the market shortly after the S-61. While regarded as one of the most successful American scheduled helicopter airlines even by the 21st century, following several accidents involving its S-61s, including the crash of the prototype S-61 N300Y, Los Angeles Airways ceased operations in 1971. Even prior to the receipt of approval from the Federal Aviation Administration (FAA), the S-61 had been purchased by a number of airliners, including Los Angeles Airways, New York Airways, and Chicago Helicopter Airways. It was promoted as being the first U.S. helicopter designed specifically as a commercial airliner. The S-61 seated 25 passengers and had an estimated direct operating cost of 8¢ per seat mile. The operating costs of civil helicopter were considered to be crucial, even prior to the S-61's introduction, as airlines had typically been unable to achieve profitable helicopter routes and became dependent on government subsidies to operate, reportedly due to the limited capacity and high operating expense of the available helicopters. It was hoped that the S-61 would be able to noticeably improve on economics compared to its predecessors. New York Airways ordered an initial batch of ten S-61s to serve its helicopter routes. Perhaps most prominently, it started operated flights from a heliport on the 59-story Pan Am Building, and at one point planned to perform as many as 360 helicopter flights per day. Launched on 21 December 1965, the operation soon proved to be unprofitable, only carrying an average of only eight passengers, leading to the heliport's closure in 1968. While flights were resumed during February 1977, an accident three months later involving a S-61 helicopter that collapsed and flipped onto its side, killing five people, led to the heliport being closed indefinitely. Two years later, New York Airlines ended helicopter operations. From 1962 to 1966, Pakistan International Airlines (PIA) operated its Sikorsky S-61 helicopters for services within East Pakistan Helicopter Service (present day Bangladesh) using four S-61s. The helicopter route to Khulna reduced the 21-hour journey overland to 37 minutes by air. 20 towns and cities covered by the network, including Bogra, Sirajganj, Chittagong, Mongla, Kushtia, Barisal, Chandpur, Sandwip and Hatiya Upazila. The average price of a ticket was 25 rupees. It was the world's largest commercial helicopter network at the time. Between 1978 and 1986, a S-61 was used for an Airlink service between the London airports of Heathrow and Gatwick over a distance of 42 miles; it was operated jointly by British Caledonian Airways and British Airways Helicopters in partnership with the British Airports Authority (BAA). While the operation proved valuable prior to the opening of the M25 motorway, its noise led to it being a point of controversy, the route overflying several densely populated areas of London. Initially, the Civil Aviation Authority banned flights between 9.15pm and 6.30am to limit its impact, but the whole service came to an end after its licence to operate was revoked by the Transport Secretary on 6 February 1986. Numerous S-61s were also operated on other routes in Britain, often between the mainland and off-shore locations such as the Channel Islands, the Scilly Islands, and various oil rigs in the North Sea. The British operator Bristow Helicopters operated a number of S-61s; they were used to perform search and rescue (SAR) operations from civilian bases at Stornoway, Sumburgh, Lee-on-Solent, and Portland between 1983 and 2007. Between 1991 and 2013, the Irish Coast Guard operated its own S-61s for SAR operations. Various government organisations have also adopted the S-61. During the 2010s, the United States Department of State procured in excess of 100 S-61Ts in support of its worldwide operations. These rotorcraft have been operated in both Iraq and Afghanistan, amongst other locations.

Variants

Operators

Former operators

Notable accidents

1960s 1970s 1980s 1990s 2000s 2020s

Specifications (S-61N Mk II)

Citations